Science topic

Electric Impedance - Science topic

The resistance to the flow of either alternating or direct electrical current.
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Battery impedance is a combination of internal resistance and reactance where internal resistance + reactance, or (L+ C), equals impedance when using an ac stimulus. The internal resistance of a battery is made up of two components: electrical, or ohmic, resistance and ionic resistance.
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Hi Maam,
It plays an important role to know how the electrode-electrolyte responds toward the wide frequency range
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How to pick ideal AC and DC voltage for EIS measurements while testing supercapacitor? I understand that AC causes the perturbation for which I will be recorded by the potentiostat, but wha about the significance of DC?
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Dear Honest C Makamba,
it doesn't really matter, about "what is the DC potential chosen".
Choose 'any (ruling)', single, VDC-potential, but always inside the Vwindow.
A common cyclic voltammogram (CVL) reports about the V-limitations (Vwindow=Vhigh - Vlow) for your supercapacitor.
The EIS spectra (and the capacitance value) is, usually, the same[1], inside this Vwindow, for (common) supercapacitors.
1. Fundamental supercapacitors' function can be found from a CVL. However, there are two, main, different principles 'i-V:rectangular, for static capacitance' and 'i-V:curved, for pseudocapacitance' that might show two (super)capacitance values, but in two, different, spectral regimes.
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I am looking for the electrical resistivity of these polymers, does anyone know of any article that touches on this subject? Any help would be appreciated.
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Simão Sampaio its ok. I will try my best to find some extra information, dedicated to your issue. Best regards.
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What will be the equivalent electrical circuit of the following set of multiplied and divided impedances:
Z1 / (Z2 x Z3)
It is assumed that each of these impedances itself represents an element or electrical circuit.
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Thanks dears for your valuable answers
It seems from your answers that this kind of impedance combination is rather specific to the electrical engineering field. Am I right or are there applications in other scientific fields, especially in electrochemistry and electrochemical impedance spectroscopy (EIS)?
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Hello Everyone,
I am a hydrologist and want to model baseflow (i.e. surface-water groundwater interactions) via the development of a numerical groundwater model (GW model). One of the critical input parameters for the development of the GW model is the hydrogeology of the catchment in question.
Bore-well lithology datasets required for preparation of hydrogeology map or Fence Diagram is very limited (2 borewell logs only), Since, my study area lies in the headwater mountainous region. I am planning to do an electrical resistivity survey for mapping the hydro-geology of the basin in the catchment area of 102 Km2. I have a few questions, in planning Electrical survey in the basin-
1. What could be the optimum number of resistivity profiles required for appropriate representation of hydrogeology of the basin?
2. How to identify the most appropriate locations for Electrical resistivity profiling representative of the basin under consideration?
I request you all to give suggestions in this respect.
Thanking You.
Regards
Rajat
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In general, for this area of land, you must first try to drill at least 10 boreholes. This is so that you can have parametric soundings to calibrate and validate electrical soundings.
Now, and given that the number of drilling is very limited, it seems judicious to me to carry out a grid of 500 m and to carry out a sounding (SEV) with AB/2 of 1000 m in each point of the grid.
The solicited depth of the SEV depends on the increase in the depth of the aquifers (according to geological data). It is therefore necessary to increase the length of electrical soundings in the areas of increase in P and to add SEVs with AB/2 between 3000 and 5000 m (for example).
The establishment of the geo-electrical profiles can be distributed, according to the configuration of the ground, in the following way:
Total number of SEV Number of profile Number of SEV/profile
Zone 1 24 04 06
Zone 2 18 03 06
Zone 3 20 05 04
Best regards
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Can anyone suggest research where I can find thermoelectric properties of Chromal P (10% Nickel, 90% Chromium)?
Specifically I am looking for:
1. Thermal conductivity as a function of temperature
2. Electrical resistivity as a function of temperature
Temperature range of interest is 20C to 800 deg C (1100K)
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There is information for this Ni-Cr thermocouple alloy on the page:
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I have an EIS spectrum as illustrated in the images and I am trying to fit it by Randles equivalent circuit. My fit is not perfect but the question is which value should I use to calculate the conductivity of my solid electrolyte in the image? Usually, I was extrapolating the linear part of the curve down to X axis and take the value as resistance to calculate ionic conductivity according to the formula:
1/q=(1/R)*(l/S)
I recently read in this website that diameter of the semicircle can also be used to determine the resistance to calculate ionic conductivity. However, in my case both values are significantly different from each other. Therefore, I am looking for a more solid approach. How can I calculate ionic conductivity of my sample according to output of the Zfit? The value in the red marking is Warburg factor. Should I somehow convert it to resistance?
My sample is a lithium containing amorphous silicate thin film.
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the temperature and the DC-polarization(s) help to discriminate the (electronic vs ionic) conductivity character. How much your (EIS-)spectra change with the parameter of the DC-polarization, VDC , value(s) ?
Also say, please, what are
1) your (2 or 4?) electrodes (' materials ?),
and what is
2) the temperature and the DC-polarization(s), VDC (= ?) in this ('EIS curve.png') EIS study.
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Why the ohmic resistance value shown in the diagram is different from the value obtained by the equivalent circuit in the zView software? Is this difference related to the software settings?
R(diagram)=2.27
R(equivalent circuit)=2.109
Can this amount of difference be ignored?
Is there any way to get the exact values?
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Dear Fatemeh Yadollahi,
I see the main issue for the Ohmic resistance coming from the inductivity.
The attached image shows what happens if an inductivity is added to a circuit and how it affects the Ohmic resistance (a few further details in the article).
Best,
Dino
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Recently, I'd like to collect some formulas for some specific transmission line structures in PCB (single-ended stripline, single-ended microstrip line, etc)
I found that there is no formula related to the impedance of the microstrip line with solder mask (the region above the solder mask treated as the vacuum or the air)
Is there any suggestion to find that?
Thank your reading
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In this case case I would go for a numerical evaluation which is rather easy these days..even if there is a formula somewhere it will be an approximation and not straightforward to solve
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Metallic pipes are known to show low resistances compared to their surroundings(Vickery & Hobbs 2002). Does this imply we can effectively use ERT method to detect metallic pipes in the subsurface.
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It depends baisically on the resistivity contrast between the buried pipe and its surrounding...... The specific characterestics of the pipe itself determine if ERT is useful or no..... The combination of different geophysical methods with their good interpretations provides the optimum detection way.....
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I'm having problem with the correct determination of Rct(Resistance to charge transfer) and your value for a Randles Circuit with Waburg impedance. I just find methods with extrapolations. Can I calculate with some mathematical method?
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You can simulate the obtained EIS experimental points with Zview software using equivalent Randle circuit. The diameter of the semicircle gives the value of Rct.
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I have grown thin films (~100-500 nm) of PEDOT:PSS by electrodeposition on top of thin films of Au (~1 nm) and now I want to measure the impedance of the PEDOT:PSS thin film.
To accomplish this I am thinking of depositing another layer of Au (or another conducting metal) on top of the PEDOT:PSS for it to act as a capacitor and use 4 probe method to measure its impedance.
However I am apprehensive that by using a magnetron sputtering technique to deposit Au on top of the PEDOT:PSS thin film will alter its properties, rendering the impedance measurements not viable.
I can also do IBD deposition of Au, but I think this will be worse. I could also electrodeposit Au, however in doing that I needed to apply a negative potential which would reduce the deposited PEDOT:PSS rendering it non-conductive.
Opinions on how to deposit a conducting (can be very thin) layer on top of PEDOT:PSS without interfering with it ?
Thank you for your time.
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Dear Henrique Teixeira , I think magnetron sputtering of gold shouldn´t interfere or change your PEDOT:PSS film. Argon plasma is directed towards the gold target, and therefore implantation of argon on your PEDOT:PSS should be negligible and therefore it would mantain its electrical properties.
I wonder if your thin films of Au (just 1nm thick) could cause problems due to holes.
The combination of both PEDOT:PSS and gold sputtering has already been described in publications, for instance:
Thermal evaporation of gold is another option that shouldn´t damage or change the PEDOT:PSS layer:
Hope it helps.
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I want to measure electrical resistivity of a silicate glass in the melt state. The temperature is between 1000-1500C and the accuracy is not so important (5% error is acceptable). I found out that two wire method is a good way for measuring but I did not find enough information about the method. I have some questions like what is the surface area in this method? (I mean A in the formula p=R.A/L) or can I use DC current for measuring? and etc. If anyone can help, it will be appreciated.
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Hey Dr Soleimani,
How did you solve this problem?
Can you explain it to me in Details?
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Dear Researchers,
Grid impedance measurements/estimation techniques have been used to find the value of resistance and reactance of a three phase line. I would like to know the technical reason, why the values of R and X of a three phase lines cannot be accurately measured through R=V^2/P and X=V^2/Q considering the power factor unity just for simplicity. Technical reasons would be appreciated. Thank you.
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Hi Fahad,
If you apply voltage V across the terminals of a resistance R, then the power absorbed by the resistance is P given by P=V^2/R (This equation can be derived simply from Ohm's law.). To use the same equation in the context of line, the voltage V should be the voltage drop along the line (not the voltage measured at one point on the line), and P is the power loss along the line (not the total power flow along the line). Therefore, you cannot simply use the measured value (which are total power flow (P) and the voltage (V) at one point in the line V) in the above formula to calculate the resistance of the line.
I hope this helps!
Thank you.
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I made some impedance measurements under magnetic field to characterize magnetoelectric coupling on BTO-CFO composites. I can determine magnetoelectric coefficient by calculating dE/dH from obtained data.. i just don't know if such coefficient is enough reliable to report it in an article.
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The theorem states that the reactance of a passive, lossless two-terminal (one-port) network always strictly monotonically increases with frequency. Can this theorem be extended to two port circuit parameters like mutual impedance etc.?
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Let me first say that I am a beginner in electronics so I don't know about opamp.
I am using transimpedance amplifier for DISCLC measurement. The aim is to convert a small current signal into a measurable voltage signal to be read by an osciloscope without increasing the RC time constant of the device. 
A device is connected to inverting terminal of an opamp, the non inverting terminal is grounded and a feedback resistor is connected between output and inverting input. A square wave is fed into the device from a function generator. 
Since input impedance of opamp is very high (infinitely), the current through the device is equal to the current through the feedback resistor. The current does not flow into the opamp.
My question is, why does not the feedback resistor affect the RC time constant of the device since this is the only path for function generator circuit to be complete?
I want to know how does the suming point (inverting input) work exactly as the ground of function generator? How is the device charged to peak value of function generator skipping the Rf path?
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If you can make simple circuit analysis and knows the ideal operational amplifier characteristics. You can simply analyse the transimpedance amplifier very simply.
The ideal op amp has infinite differential gain, infinite input impedance and zero output impedance. So it does not draw currents in its inputs .
Grounding the positive input and injecting the current I in the negative input , it will continue in the feed back reassurance Rf. Since the positive input and negative input have almost the same potential then the negative input will be virtually zero. So, the output voltage V0 = - I Rf. This is the transimpedance amplifier relation The output voltage divided by the input current is equal to the the feedback resistance.
This is the simplest way to analyse and understand the operation of this circuit.
Best wishes
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Some people are using ohm.cm2 and others are using ohm/cm2 as the unit of impedance in their publications for EIS analysis. What is right one to use ?
thanks in advance
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The following analysis shows that the correct unit is the Ohm x cm^2.
Assume that we have two electrodes immersed in electrolyte where the immersed cross sectional area of the twp electrodes are equal of area A. assume that the spacing between the two electrodes is L and the resitivity of the electrolyte is roh, then accordingly one can expels the resistance between the two electrodes as
R= roh L/A,
Rearranging
R XA= roh/L
From this relation it is clear that
When A =1cm^2, then it will give the properties of the electrolyte roh and its path length L.
then the suitable unit is ohm.cm^2.
Best wishes
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Dear all:
How I can calculate the Impedance of a single white colour LEDs Strip? Does anyone know ?
I have a Strip of white light LEDs , at a Voltaje imput of 12V .
I'll appreciate any help :)
Regards !
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Dear Franklin,
welcome,
You measure the electrical impedance as you define it. Considering the impedance of LEDS connected in series they have by definition a large signal resistance and small signal impedance as the I-V characteristics of a single diode and a series connections of diodes is nonlinear.
The large signal resistance can be defined by R= V/I, this resistance decreases as the current in the strip increases.
To measure the ac small signal resistance one biases the strip into the DC operating point and measure its impedance as Z = dV/dI, where dV is the small signal voltage and dI is the resulting small signal current. Because of the capacitive behavior, the current dI leads the voltage dV by a phase angle phi.
Z will have an amplitude and phase or a resistive and capacitive reactance.
You can use the method developed in my paper given in the link to make the measurements: https://www.researchgate.net/publication/3062547_A_distributed_SPICE-model_of_a_solar_cell
You can use the method in this paper to measure the impedance of the led strip.
There is also a complete description of the impedance measurement in the paper at the link:
Best Wishes
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My department recently got a hold of an ECIS-Z machine for measuring cell monolayer impedance in real-time. I have been having issues getting the 96-well plate to properly align with the 96W array station. I always have between 2-6 wells fail the initial SETUP when the device is checking connectivity (occurs randomly). The department that loaned us the device did provide the 96-well plates and I noticed that they are 3 years old. My thinking is that the plates themselves are bad due to being so far out of date. I was wondering how difficult the procedure is with brand new plates when you initially insert them into the 96W array station. I have ordered some brand new plates so I hope I have better success once they arrive. Any advice or experience using the device is greatly appreciated.
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Chris Delavan To mount the 96well ECIS plate to the reading should not be difficult at all. All you need to do is to use one hand to firmly press the plate onto the reading while shifting the left latch to the right. Then continue to press your plate and shift the right latch to the left. You should feel that your plate sits firmly on the reader. I don't think that expired plates will give you issues with connectivity unless they were kept open and electrodes are corroded. What type of 96 well plate do you use? 20, 10 or 1 electrode?
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For large area SOFC testing I am using Scribner's test station. For the cell test I am using Ni-mesh and Ni wire as voltage send and current collector which is connected with the manifold using Ni-paste. So I found a large ohmic resistance (70~80%) of the cell compared to the total resistance while the polarization resistance is only 20~30%. So I doubt whether the position of the voltage send dose affect for high contact resistance. Please find the figure for the setup.
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Depending on the operating conditions, yes.
As Alexei V Ermakov suggests, reducing the ohmic drop caused by the electrolyte can help. Using a probe with a high surface area, or distributed to different points of the fuel cell is a good idea.
Jules
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I have a question about the precise calculation of carrier density by the use of mott-Schottky equation for nanostructured semiconductors. As one of the assumptions for Mott-Schottky equation is having a planar semiconductor, usually the calculated carrier density becomes too high for nanostructured photoanodes ( even higher than metals) used for photoelectrochemical water splitting. This is probably because the real surface area of the nanostructured is much larger than simply the geometrical surface area of adjacent semiconductor with electrolyte. Another point is that how can we consider a shape factor for capacitance in the mott-Schottky equation. I mean should we consider a shape factor when we have nanowire or nanoplate structure on the surface of a photoanode? Besides that, for this case is there any suggested method that can help us reach a close-to-reality calculation of carrier density in nanostructured photoanodes?
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Hi, I happened to consider about this question for a long time since my supervisor expected me to calculate the exact wideness of space charge layer, and I also found that M-S calculation is inproper for my nanowire arrays system, so I think there should be a geometric factor which included in the M-S calculation. Maybe you can try to use the Hall-effect equipment to test the carrier numbers.
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After changing a lithium ion (LFP) battery's SOC eg: 100 to 80 % and the cell is now made to rest to attain equilibrium. During this wait period, what all parameters change ? And it increases or decreases ?
So far, my finding were the charge transfer and double layer capacitance decreases during this wait time (through EIS spectra). Any other parameters change ? References will be useful.
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Thank you. Could you tell what other values changes during relaxation ? I means the model values which you know
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Hi , I'm trying to measure impedance of my PBS solution at 700 kHz with 100 mVpp within my 80*40 um microfluidic channel .the flow rate is 50 ul/min. I don't know why my 40 um width electrodes detach while testing.. the thickness of chrome layer is 10 um-30 um and Au layer is around 100 um. Chrome Au annealing at 450 deg c for 13 mins used in order to promote adhesion for some samples but the problem still remains. What is your idea?! what shall I do !?
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Maybe, HEPES with same conductivity would be helpful.
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I have a GNSS RF chip. I should connect the RF pin to an antenna connector with a 50 ohm microstrip transmission line.
I calculated the RF track width and printed the PCB
Now I want to measure the track impedance to verify calculation and design.
Is there any measurement device for that?
*The frequency of RF signal is about 1.5GHz.
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Denis:
My understanding of the 'exam question' that Farid Hosseinzadeh has set us is:
Given the PCB with GNSS chip installed, what piece of test equipment should be connected to the input connector of the PCB in order to find the characteristic impedance of the track connecting the input connector to the chip?
The picture I have in my head is that the track is in the order of a few cm in length and I am additionally assuming that no modification of the PCB to facilitate the measurement would be welcome.
From the assumption about track length I was then thinking along the lines of section 9.2 in Keysight Technologies, 'Time Domain Analysis Using a Network Analyzer' http://literature.cdn.keysight.com/litweb/pdf/5989-5723EN.pdf, which is saying that the TDR NWA should be operated with wide frequency span to resolve down to disconuity separations in the cm region.
If you could provide details of the measurement you thinking of, which answers the requirement as stated in this post, without using a wideband test pulse or a wide frequency span NWA test signal, I will happily be educated.
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In analyzing the electrical performance of multifunctional EDLCs, our group is using cyclic voltammetry testing to determine capacitance and attempting to glean information about the electrochemical activity of our system. In commercial EDLCs, CV plots are rectangular (often considered "ideal capactive behavior") and show stability at high voltages. Some say high ESR will cause the top-left and bottom-right corners to round, while low leakage resistance may skew the graph shape vertically. However with our EDLCs, we observe the "ideal" rectangular shape at low voltages (Picture 1), but when pushed past a specific voltage, a tail-shape deviation is seen in the top-right corner of the plot (Picture 2). We suspect this "tail" is an indication that our electrolyte is unstable past a certain voltage. What is the significance of this "tail"?
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I think this "tail" shape come from over potential window, which will cause polarization of electrolyte (accumulation of gases at the interface between electrode and electrolyte). so you must test your electrode below this value (decrease potential window less than this value).
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I have simulated a simple rectangular loop (10 mm X 2mm) in both CST and HFSS from 1MHz to 2GHz. Then I extracted Inductance using expression L= XL/(2*pi*Freq). I noticed that the inductance remains fairly constant till 10 MHz, then decreases till 322 MHz and again starts increasing. (Please see attached file). How to explain this behavior?
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Dear Rajas and colleagues,
I came late to this question but i find it very interesting. My question is do you simulate the loop while you inject an ac current in it and calculate the voltage across its terminal. Then V= I Z,
If you consider both electric and magnetic field resulting from the current in the loop then you have an LCR equivalent circuit. In order to interpret the simulation results one has to calculate Z magnitude as a function of frequency.
The second comment is whit is the dimensions pf metal wire and its material? How large is the simulation space and how the loop is contained in the space?
Best wishes
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Im doing a piezoelectric energy harvesters and intending to use a standard piezoelectric circuit with bridge rectifier and smoothing capacitor to charge a NI-MH battery, can it be done? I saw lots of article mentioned about impedance matching. Do i need to do a impedance matching with the piezo and the battery? how can this be done, by adding resistors?
Appreciate any kind of help. thank you!
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Dear Eris E Supeni,
if the current is, always, charging[1] the rechargeable battery, then you might ignore that, the value of the current is changing[2].
1. charging and the average value and RMS value of the current is, always, higher than the self discharge rate of the cell, in storage. Also, this project (or equivalent projects) might help towards prolonging the storage time of some rechargeable batteries.
2. It is always charging. It is not changing sign. This is why, we need a "good" (bridge) rectifier.
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Dear friends
I want to carry out impedance spectroscopy of my samples, if anybody knows the place for same kindly suggest me. Future, I want the data in term of Z' (real part of impedance) and Z'' (imaginary part of impedance) with frequency and temperature and the data file should be open and competible in Z-view software.
Please suggest me as soon as possible.
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Sir, I really not know about impedance spectroscopic analysis. But I am sure in NCL Dr. Gokhale will help you on that
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when we design any millimeter wave antenna for e.g at 1-2mm, what type of connectors are used?
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Hi Akhilesh,
Well, it all depends on your operating frequency. SMA is no good above 26.5 GHz, generally. When you said 1-2mm, I assumed you meant that was the wavelength (in free space), corresponding to about 150-300 GHz. If, instead, you mean that the antenna is 1-2mm in size, perhaps half a wavelength or smaller if used on a high-dielectric constant substrate, then it could be below 100 GHz.
Up to 110 GHz, you have the option of using 1mm coax -- but I can tell you from experience that the connectors, adapters, and cal kits for measurement are EXTREMELY expensive, and frankly don't perform very well. (I had to test a part once in 1mm coax where the performance of the part was far better than that of the test adapters, making the test practically meaningless). I wouldn't recommend it.
Really, for anything above 50 GHz, I would use waveguide. Waveguide to printed-circuit launchers can be made, but are typically custom. If you're geometry just wouldn't support a waveguide housing, then the best I can suggest is to test your antenna on a wafer probe station. Mm-wave wafer probes are readily available, but depending on what you want to measure (beam pattern, etc.) the geometry could be awkward.
Matt
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The eq used is - 
Cs=(i)/(m.dv/dt)
What is this "i'?
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Dear friend. i is the average current which can be calculated from CV curves. you can measure maximum peak current from anodic and cathodic parts of the CV. 
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Hi all,
I have been trying to use the NI USB-6008 for voltage measurements. I observe that just by connecting the card to the circuit I am observing some signals that should not be present. Even grounding as mentioned on the National instruments website did not help. What might be the issue? I am measuring voltage drop across a circuit with impedance in the range of 150 Kilo Ohms. (Pure Resistor circuit)
Any help will be much appreciated.
Thank you very much!
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Basically, the length and diameter of the wire connected to measure the signal matters a lot. So if the length is quite lengthy try to short it and measure it. Because I have also faced the same problem during measurement of my device.
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What could be inferred from changes in the imaginary component of impedance over time when running electrochemical impedance spectroscopy (EIS)? Thanks
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As the previous two responses stated: impedance that is capacitive is imaginary, but inductive impedance is also imaginary (-90 degrees vs +90 degrees out of phase).  Note also that some real phenomena like diffusion have both real and imaginary components (45 degree phase shift).
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1N=kg*m/s² vs. resistivity, electic power (s³), capacitance, permitivity (s^4)...
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dear Aparna, You are right! As it came to aberrations in physics, my motto is NOT: read your… manuals; remake them! That is the name of the game! But it will take time until they do recognize it. much time! 2-dimensional time :))
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plot against charge carrier density and the ratio of the Hall resistance (Rxx/Rxy) which is shown in the figure (attached below). any explanation and comments in your views will be highly appreciated  
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Fig 3 of the paper, conveys that with rise of temperature, Rxx decreases. Initially fast decrements up to about 100K then slow decrements. This effect is due to more no of free electrons with rise of temp and then towards saturation.
Rxy graph says that on Rxy temperature has fairly no effect. It remains fairly consant (Slightly rises up. This could be slight change in magnetic field over temperature which is assumed as constant).
You have taken ratio, where numerator (Rxx) reducing and Denominator (Rxy) is constant. Hence, ratio is decreasing (green line). Red line is no of free electron, which is increasing with temperature. 
You may say ratio is inversely proportional to temperature
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I have this new IVIUM Technologies Electrochemical Spectrometer and I´m trying to collect EIS data of a symmetrical ceramic cell from RT to 800 °C but all I get above 1 Hz is unreasonable impedance values (negative Z' and/or Z'' 2 o 3 orders of magnitude larger than the expected signal that should be a few ohms).
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Thank you Ioannis Samaras and Jerry Decker for your suggestions.
My runs are at high temperature, therefore humidity should not be a problem. I´m blowing air on the sample, though, so maybe I should check...
Noise seems to be related to some instability of the signal, because if I increase the excitation voltage amplitude I get cleaner spectra, but at lower voltages noise shows up. The problem with higher excitation voltages is that I get different spectra if I increase the voltage too much, probably due to 2nd order phenomena...
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I am characterizing some metal-oxide for charge storage. I was interested in seeing the impedance spectroscopy of my material. The EIS was performed with a sine wave of 5mV amplitude from 1Mhz- 0.01Hz. In the EIS spectra, there seems to be a tail kind of structure in the high-frequency region, rather than a semi-circle. I'm suspecting that this is a potentiostat problem as I tried changing different variables like the amplitude and the scan range without any luck. I was wondering if some can help me solve this issue. Thanks  
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I guess, Ionnis Samaras is absolutely right.
Your impedance magnitude is quite small for the high frequencies. You need a very good setup (potentiostat, wiring,...) to measure up to 1 MHz. Usually, you would expect inductive behaviour at high frequencies, but at very small magnitudes of the impedance and high frequencies, the results often go crazy as in your case.
Maybe you even do not need these very high frequencies for your analysis. Apart from the last, say 10 points, your impedance looks nice and converges nicely to the real axis for high frequencies. The capacitive branch is characteristic for energy storage systems.
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I have created a rectenna circuit.
I want to check the Input and output voltage to calculate effficiency
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I agree with Glen, also now we can find transistors that work for very high frequencies (> 10Ghz) for example:
- RF FET Transistor 10 GHz   "ATF-34143-TR1G"
and also
- "CPH6021" is a NPN Single RF Transistor, 12V, 100mA, fT=10GHz for High-Frequency Low-Noise Amplifier 
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I have manufactured some capacitors with silica as dielectric and I have measured them with an impedance analyzer, the Nyquists I was able to model them with the radle circuit. By plotting the normalized active and reactive powers for the complex power as a function of the frequency I have observed that they intersect at one point, even at one of the capacitors it crosses at two points. I have read in supercapacitor studies that the crossing of normalized powers is attributed to dielectric relaxation, but I do not completely understand what it means and why this happens with my capacitors in which I do not use any electrolyte.
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Thanks your reponds Michael. Then this is relates to the formation of space charge. I have read that the relaxation time is the time in which one moves from a resistive to a capacitive behavior. But if there is another time of relaxation. What physical or chemical meaning would there be two relaxation times?
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Hello,
I am running EIS to determine the impedance spectra of my sensor. The sensor consists of gold electrodes deposited on a porous paper membrane. And the electrodes are modifying with a thiol molecule.
I am then taking an EIS measurement in a phosphate buffered solution (attached), and would like to fit this data to an equivalent circuit. I have tried a simple RS circuit, I have tried a Randle's circuit, but the data does not fit very well.
I did some digging and found a paper (linked) with a circuit that fits my data well; however, I'm not sure I can use it to describe the processes that are occurring in MY system. Any advice on how to better fit my data? 
Thanks,
Hunter
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Dear Hunter Stevenson,
the EIS data for your "sensor" are measured[1] using with two or more electrical contacts ?
Also, note, please, the parametric value of the VDC(= ?) polarization[2].
1. Good EIS data are critical and beyond advices "on how to better fit my data". An advice: remeasure the high frequency part of EIS.
2. Also, start at the VDC (=OCV value, for i=0) polarization. Add 2 more VDC parametric values, as overvoltages  (about +-100mV).
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Hi, I wanna measure cell impedance. I've seen some equipment in the papers but I need a source that illustrated all detail of set-up.Could someone help me?
I appreciate any help that you will do
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You should use ferri-ferrocyanide electrolyte medium for the EIS measurement...you may use some other medium according to your requirements...but the selection of potential and medium is important in EIS measurement.
Please follow the following paper, it may be useful for you.
Best regards,
Piyush Kumar sonkar
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I am using four-probed method on Zive SP1 Potentiostat to obtain Nyquist plot for proton conductivity measurement of proton exchange membrane (SPEEK). However,  I could not get a proper Nyquist plot shown in literature, instead my impedance value is very random when the frequency is decreasing from 0.1 MHz to 100 mHz. May I know what is the  major problem?
When I manage to obtain a Nyquist plot, how can I fit into my equivalent circuit to obtain the bulk resistance?
Thank you
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I recommend you at first do the calibration and use the reference sample that you know exactly its results. and then check whether there is the same problem within the frequencies you mentioned or not. because some times the impedance instrument is not calibrated well, or sample holder is not clean, or wires have a problem,... If  impedance instrument is working well then your sample preparation may has a problem.
To fit your result you need software, usually each impedance spectrometer has a software. I use WinFit program for Novocontrol impedance spectroscope.
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I want to calculate the current density across IDT electrode, both electrodes are on the same surface of a solid material (a bulk ceramic disc). 
Imagine two parallel bar electrodes with length L, and separate with distance D. The material thickness is T. When a bias voltage, V, is applied between the electrodes, how to find the current density? How to find the effective area that current flows? 
Many thanks!
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This is a 3D problem and the current density J is a function of position with a maximum at the electrode positions and a minimum at the midpoint between the electrodes.  J(x, y, z) can be obtained by solution of the LaPlace equation in the volume of the disc.  
There are lots of ways to get approximate solutions.  If the disc can be thought of as having zero thickness with a given resistivity/square then the solutions have been worked out (see Van der Pauw in Wikipedia.).  If one needs just the current density at the midpoint between the electrodes, then one could assume a rectangular slab of length D, width L, and thickness T, with contacts covering the ends of the slab.  
At the electrodes, the current must all go through the electrodes and the current density will be approximately  J = I/LS, where I is the current and LS is the area of one of the electrodes.
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Dear all,
I have observed an interesting phenomenon during my experiment.
A conductive wire was used to connect a power supply's GND with the ground. The resistance of the wire measured by a multimeter (Agilent U1213A ) is 0.1 ohm when only one end is connected, this is normal.
However, when the two ends are connected, the measured resistance of the wire is 21.8 ohm. That's weird! I repeat the measurement again and again but doesn't change anything.
The wire is made of aluminum with diameter of about 2mm. The power supply is turned on during the measurement, and the voltage drop on the wire is 0.124V.
Could there be any explaination for it?
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Look at "active multimeters" in this page: http://meettechniek.info/passive/resistance.html 
You see that the multimeter measures the voltage over a wire, assumes a constant current that it imposes, and calculates the resistance from that (R=V/I, where V is measured and I is 'known'). 
When you connect the wire and current flows through the wire, a voltage drop over the wire will disturb the measurement , because the current I is not only what the multimeter imposes, but also the current that flows through the wire due to your setup. 
Conclusion: never measure resistance while your setup is powered!
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Dear friend; I have problem with Zview or other free software to fit equivalent circuit. Zview just pick up 15 point in my EIS text file. What should I do? I have tried other software such as Zsim or MEISP. All of them are Demo version and don't allow me to fit equivalent circuit on my data? Please suggest me a practical method. Thanks
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dear friend...first make dat file in origin then import it in Z view..it will work..keep all parameters in dat file..
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I have measured I-V characteristics of the pellet which is made of the powder sample (which is n-type) and connecting with copper wires on the both sides of the pellet with the help of silver paste which is stuck on the surface of the sample, it appears in non-linear nature which I have attached here. According to literature survey, this is Schottky type nature. But I don’t know why this type of non-linear nature comes in this I-V characteristics which bend in some position and after that, it is likewise expanding. What could be the possible explanations?
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First, the CdS powder grains likely have surface potential barriers so the pellet is somewhat like a polycrystalline CdS solid with grain boundaries.  If one could apply perfectly ohmic contacts  and measure it one would get non-linear I-V characteristics.  These would be symmetrical around the origin with shapes determined by the carrier density in the grains, the grain size, and the nature of inter-grain potential barriers. Qualitatively the shapes would be similar to the negative voltage branch of your curve. The current would be exponentially dependent on temperature.  Second, it is likely that the contacts are not ohmic and not the same. Silver point may react with the CdS if the temperature is elevated during fabrication forming Ag/x/S which is likely to be p-type making the contact more complex.  Doing a forward and reverse sweep is a good idea.  Also you might check for sensitivity to light.  You might read section 9.4, on electrical transport in polycrystalline thin films, and the first part of Ch. 10, on CdS/Cu2S solar cells, of my book "Fundamentals of Solar Cells." 
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Hello researchers please tell me regarding what the real impedance vs imaginary impedance nyquist plot of fet transistor tells.Actully I had plot the frequency analysis ( so called nyquist & bode plot) of a FET file attached but I am not able to understand that what it actually tells about my device.
 
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Share some experimental details.
The values obtained from the equivalent circuit are not matched with the Nyquist plot. Please check.
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Hi! I have experimental impedance spectra in format of .txt/.dat/.csv and I want to fit the specta and make an equivalent circuit by Zveiw. I've tried to open those .txt/.dat/.csv files in the Zveiw programme but data files opend incorrectly. Could anyone tell me how to solve this problem? 
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Hi,
Maybe there is a small change in your original data files you couldn't figure it out. Open a new empty Excell file. Add your file as data not a file. If you click data you will see options: access, web, text, others. When you click text (it is the best fot dat, txt or csv format), you will see a new window such as a kind of editor. If you click next, (2/3) you will see some line between your data lines. You can get moved lines , when you click mouse. If your data or text line is not correct, click the mouse on correct point. Please check next step (3/3) with advanced button for your file decimal system (dot or comma). Good luck.  
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I conducted a complex electrical impedance measurement for a water partially saturated rock.My complex electrical impedance data (Z' and Z'') between 500 ~10000 Hz can be well fitted by a Debye circuit. Through the fitting, I obtained the resistance R1 ,R2 and capacitance C.
For example,  R1= 112 ohm, R2=24 ohm, and C = 3.2e-6 F.
The capacitance is proportional to total permittivity (E)  or dielectric constant (Er) according to this relation     C = E*  k = E0*Er*k
Here k is the geometrical factor equaling 0.03 m,  E0 is the vacuum permeability (8.854e-12) and Er is the dielectric constant. Thus the dielectric constant D should be calculated as Er = C/E0/k. So I calculated the Er as 12047285.  This value is very huge compared to the common literature values.
If I am wrong, could anyone help me to point out where did I go wrong?
Thank you very much.
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Hello David,
Thanks for your response.
I have a very thin (few mm thick) rectangular pellet sample. I am measuring the capacitance using NF ZM2376 LCR meter with four probe measurement. How do I calculate correct A and d?
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How can  I find the equivalent circuit of EIS spectra? I have run some Nyquist plots but I could not find the equivalent circuit or any given procedure for find out this circuit...so How we should find out this?
And does it change when considering the EDLC type or Pseudocapacitor type?
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After getting the Nyquist plots, then follow these procedures
1. open the EC- lab software
2.open the Nyquist plot you wanted to get its equivalent circuit 
3.select the point graph
4.click analysis on the EC-Lab, and select electrochemical impedance spectroscopy, then Z fit.  
5. from there, you can see many types of equivalent circuit, you select one type and click calculate.
6. scroll down and select: method: "randomise and simplex" ; stop randomise iteration: "input the value like 60,000"; "stop fit on: input the value also.
8. if the select equivalent circuit is the correct one, then the standard deviation should be less one and x2 value should be 3*10-3
8. if the selected equivalent circuit does not fit with  your data, then standard deviation will not be close to one likewise the x2 value
9.then select another equivalent circuit and try again as before. 
8. the select equivalent circuit is the correct one, then the deviation should be less one and x2 value should 3*10-3
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IF I want to match the impedance of Archimedean spiral antenna with the components like R, L, C. The impedance of antenna is 180 ohms with plus minus 20 ohms reactance. Please suggest and help 
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If you use  a resistance then you need 69 ohms in parallel with the antenna (i.e. across the antenna terminals) but over 72% of the power will be lost in the 69 ohm resistor and less than 31% will get to the antenna.  It would be better to leave it unmatched which will reflect 32% of the power back to the generator, if the generator can stand it, and about 68% will go into the antenna.  If you feed it with co-ax then it will probably be unbalanced which will change the impedance and may mess up the radiation too.  A spiral antenna requires a balanced feed which is why a balun (or transformer) is needed if it is fed from co-ax.
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I am learning to calculate the maximum power of an energy harvester which is connected into a electrical circuit that consists of a resistance load. I always find the researchers measure the power output as a function of resistance. (ranging from kΩ to mΩ) 
Can somebody explain the mechanism of this phenomenon, that specific resistance leads to maximum power, to me?
Follow by this question, if that specific resistance is found to be extremely high, i.e. 500kΩ, does it waste the energy generated by the harvester? like generating heat instead of being used for meaningful purpose?
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As you increase the circuit resistance, electric energy is lost in the form of heat energy. Remember the Ohm's Law:
V = I x R
The Power (P) = I x V = V^2 / R
Hence, as R increases, the power (P) decreases
The specific resistance is measured in Ohms per unit length of the wire. Hence, if you use the specific resistance in P = V^2 / R, then P would be the maximum power.
Hope this helps answer your question.
Professor Yehia Khalil
Yale University
USA
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I am trying to maximize the generated energy form a certain power source (Irregular one), so I want to reach the maximum power transfer via defining an optimal load impedance. It happens that the optimal Load is not pure resistance (as the source itself has some reluctance/capacitance), is there a certain Power Electronic circuit such as Boost Converter that can be designed to "Emulate" that optimal LOAD.
Thanks
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Hello Mustafa,
In order to transfer the maximum amount of power from a power source you have to apply the “Maximum power transfer theorem”.
Please, suppose that your circuit has a power source with its internal impedance connected in series with the load impedance Rl+jXl.
The above mentioned theorem demonstrates that the maximum transferred power is obtained when:
-           Xl=-Xs
-           Rl=Rs.
This means that Zl=Zs* (i.e. the load impedance is the complex conjugate of the source impedance).
Finally, if the reactive part of Zl is constant, the maximum transferred power occurs when Rl=sqrt[Rs^2+(Xs+Xl)^2] which means that Rl is equal to the absolute value of the whole network impedence.
I hope this can help you!
 Regards,
Roberto
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Please refer to the picture attached alongside.
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@Xolani Thanks for replying. But There must be some reason to Literatures mentioning LG as the most severe fault at alternator terminals. Any idea why ?
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We use impedance network (DC side) in front of inverter and filters like [ L (or) LC (or) LCL ] after the inverter ( i.e AC side) which is connected to grid (or) local load. What is the difference between those two, in view of design and function?
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The dc side impedance networks provides the unique features which can help boost or buck the voltage as compared to VSI. The filters used on load side are to filter current ripples to make the output pure sine wave. Go through the articles on ZSI, you will get to know.
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I have already pelleted and sintered my cathode materials, and want to spread my solid electrolyte on it ,then measure impedance between them.
I tried to spread electrolyte on cathode pellet and pressed them into one pellet, but it always broke.
Another way is that I dissolved my electrolyte and some Naphthalene ,then loaded them on cathode pellet. But it seemed not work when I measured the impedance of the pellet.
My question is that if the ways I tried is not right ,or I need to modify something?
Thanks again‼!                             
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Dear Ioannis Samaras,
you mean like 4 probe resistance measurement?
measure cathode and electrolyte seperate and then maybe combine them into one pellet to measure again?
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Hello,
I want to find the junction thermal capacitance (J/K) based on the thermal impedance vs. time curve (we have this curve from the semiconductor specifications or IGBT module datasheet).
For instance, I attached a sample datasheet.
Thanks a lot,
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Hi Omid, the electrical analogy would be a constant current source loading a C parallel to an R. That would give Vc = R * I * (1 - exp(- t / (R * C))) or with temperature T = Rth * P * (1 - exp(- t / (Rth * Cth))). Since 1 - exp(-1) = 0.632, the pulse width at Rth = 0.632 * Rthmax should be equal to Rth * Cth. Division by Rth will result in Cth. In this case, Rth * Cth = approx. 40 ms. Cth = approx. 0.16 Ws/K. This is just an approximation, of course, based on modelling by lumped elements. Hope this helps.
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I want to measure impedance between two bare gold electrodes in a PDMS micro-channel. The results (please see the figure) were scanned one after another with a time interval of few seconds. However, no matter what solution I use (PBS or KCl or other solution), the scanned impedance always decrease as shown in the figure. Does anyone know what is the reason? How I can get very stable results?    
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Hi Pengfei,
Next time, please provide an image in format like png or jpg. The TIF file is so very large and takes long time to download.
To your question:
Almost all electrochemical systems show a transient behavior from the time you close cell switch and put it under potential control. So,in order to reduce the transient behavior, you must perform the EIS AFTER this effect has passed. So, close the cell switch and go to the potential where you want to do your EIS. Wait for 5 min or so. Now do the EIS, You should now expect to see the same curve if you repeat the EIS multiple times.
Observe that in you system 5min waiting might not be enough. I would suggest making an EIS each 30second for 20min with the first one starting directly after the closing of the cell switch. By doing so, you can study how the EIS values evolve by time. You will see that after a certain time, the spectra will not change any more. That time would be you optimized waiting time.
Good luck!
Gustav
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Not sure there are any practical advantages when you are pulsing a plasma just a few seconds, still there are proponents either way. I am interested in opinions from someone who has actually tried both methods
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In plasma ALD the plasma-on time can be quite small. As a result any variation during the formation period of the plasma can have a significant effect on the result.
In 'impedance matching' you tune the 'matchbox' to the vacuum condition to get highest voltage, and most reliable plasma strike. Here 'most reliable' means most consistent in terms of time. When the plasma strikes the load changes and the matchbox moves physical elements to get to a tune position. This takes some time. And, even with careful algorithms for control the transient between the two conditions may not always follow the same path. This means that there is a transient condition as the matchbox tunes (typically 2-20 seconds!) and that the transient can be different between multiple layers for the ALD process. PID settings that give fast, reliable tuning at one power/pressure setting may not be the right ones for different conditions.
Frequency tuning is quite similar, except instead of changing physical components in the matchbox (capacitors and inductors) the matchbox has fixed values and the generator senses the change in load (without/with plasma) and changes the generator output frequency to shift the matching position [w_resonance ~ 1/(L*C_plasma) ]. This frequency shifting can typically be done much faster than mechanical tuning. Furthermore, these generators are typically configured to operate in delivered-power mode, and don't complain if there is a modest amount of reflected power (they control on P_net=P_forward - P_reflected) which gets the system to a 'matched condition' faster than the mechanical tuning solution. As there is only a single knob (frequency) for tuning, the algorithm is typically stable, but you are dependent on the matchbox design being appropriate, and if there is an issue with an unstable transient this can be very hard to identify and correct for (you are dependent on getting support from the generator supplier.) In addition, as frequency-tuning only allows the matchbox to cover a single-arc across the Real/Imaginary tune-space, these matchboxes are typically designed with multiple 'taps', which are mechanical switches that can be changed (with the rf off, typically) to shift the tuning-arc. Operating the same chamber but with two different tap settings will likely give different strike-variation, and different tuning-times.
Personal opinion: for high-volume-manufacturing, frequency tuning - be careful with the matchbox engineering and the result will be the best for chamber-to-chamber matching/ cost/ maintenance/ etc.
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Hello,
I am trying to obtain the conductivity of a solid electrolyte by measuring EIS from a known area and thickness pellet.
I can not explain this weird values obtained on the impedance plots. Does anyone know what could it mean?
I would very much appreciate your help.
Thanks
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This is a set up problem. Do you have any dummy cell?
This will help you in knowing whether the connection are right enough.As per your instrument specification, I can see there are different current ranges . Try to change the current ranges if it is possible.
Regards,
Ritesh.
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How is Impedance Matching performed in Low Power and High Power Circuits? 
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impedance matching concept is based on that the load impedance should be the conjugate of the impedance of the source that is the general concept for low power excitation (small signal mode) for some cases the load changes depending upon the excitation (large signal mode). This is phenomena appears clearly on devices. For example the model for the GaAs MESFET device elements behaves linearly as the excitation nearly less than unity (1 Volt) as the excitation exceeds this limit  the capacitors of the model behaves nonlinear and the inter-modulation distortion appears.
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In a four probe method, if the area between the two probes is constant, then will the resistance change with the sample size?
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Since you are making your measurements on a thin film, the measured resistance will vary with the thickness up to the point where the thickness equals the distance between the two measurement pins.  If you would like to learn about the math behind the measurements, google "four pin Wenner method" to see how this is done in soils where the sample thickness is essentially infinite.
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what is the reason of opposite y coordinate direction?
why +y direction is not important on impedance plotting?
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Dear Alireza,
If I have well understood you are asking why we start from zero in the vertical axis of Nyquist plot. The reason is that before zero you can have a signal related to inductance at high frequency. Inductive behavior in the high frequency range is fairly easily explained by instrumental artifacts, or by the inductance of the electrode, or the inductance of the connecting wires. So you don’t know if it is a real inductance.
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In the derivation of Poole-Frenkel emission (Field assisted thermal emission),  the trap barrier is lowered  due to applied field and is given as
  • Delta U = sqrt((e^3/ pi*\epsilon)*E)
where E is applied field.
The derivation starts from the expression of the electrostatic potential energy due to coulombic trap as
  • V = e^2/(4*pi*epsilon*r)
From my understanding of electrostatics, the epsilon used in the potential energy expression is the low frequency permitivity (static permitivity). 
But the confusing part is all the papers I have read so far say that the permitivity appearing in Poole-Frenkel coefficient is high frequency component( some say electronic contribution). How can the permitivity introduced in electrostatic potential energy become high frequency part when it goes to Poole-Frenkel? 
Can anyone help me understand?
The importance of this is:  plotting Poole Frenkel emission of leakage current, the dielectric constant (permitivity) can be approximated. What do you compare it with? 
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In most materials dielectric permittivity is frequency dependent - static dielectric permittivity under near DC conditions is different to that at higher frequencies. There is an absorption coefficient for the material which equates to a loss of energy as the frequency increases.  This is well covered in the section of Kaye and Laby 'Tables of Physical and Chemical  Constants' dealing with the the various physical factors which affect a change in permittivity.  .      
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While studying piezoelectric transducer in frequency domain, it is found that electrical impedance has highest peak or value at fundamental frequency but decreases at higher harmonics. why it has a decreasing trend?
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Crystal resonator equivalent electrical circuits are  treated  as a series RLC with minimum impedance at  the  resonant frequency  (equivalent  to the mechanical element ) in parallel  with  a capacitance Cs,. This component is the crystal static  dielectric component   which  is independent of motion.   R  represents  any energy  loss element  which electrically would be  resistive  and mechanically  tends to express friction. The series  RLC  circuit characterizes  a minimum impedance (maximum, conductance) at  the resonant  frequency  and although this  reflects  the  mechanical element's natural frequency there are two other critical electri­cal  resonances to consider. .The first of the additional  resonances  lies very close to the primary dynamic resonance  but  is the point where the electrical resonance phase vanishes.  The  second  is characterized as an impedance which  rises  to  a
maximum at a frequency f, here too the phase vanishes. This tuned circuit  appears  from the mechanical series elements  acting  in parallel  with the crystals static capacitive component Cp.  Here Fr  = root(C'+Cp/LC'Cp)  and the impedance is a  maximum.  Above  and below  these   two  principle resonant states  the  impedance  is capacitive,  between  the two the impedance  is  inductive.  The 
difference  in frequency between the two series resonance  condi­tions  is  very small and the separation between the  series  and parallel  resonances  seldom exceeds 2%.  Although  the  parallel resonance is much utilised, the series resonance is preferred. In impedance analyzer microgravimetric analysis and crystal oscillo­metric microbalances the minimal value of R in the series  resonance mode reduces signal voltages and  favours the design of low impedance current derived feedback oscillators.  Both  resonances possess  a  very  sharp  resonant  characteristic  denoting   low resistive loss and a high quality factor Q ( = 1/R root L/C )
 
 
Piezoelectric  sensors are generally  plates or discs.  Operation
is  determined  by  plane of cut(i.e crystal  axis)   in  natural
piezoelectric materials, or by direction of electric polarization
in  synthetic materials such as PZT  piezoceramics.  Industrially
grown quartz has a higher purity than the natural mineral and  in
 
h2X/ Šthese  devices  the temperature coefficient is  lower.   Cleaving
along certain shear planes in the quartz confers improved temper­
ature  coefficients; at approximately 35 and 49 degrees from  the
principle optical axis  [the AT and BT 'cut'] temperature coeffi­
cients  are minimised. Values as low as 8 ppm / deg C are  usual.
Sensors can be classed  by axis ( plane of cut) or  dimensionally
(expander  or  shear i or in terms of wave  propagation  (surface
acoustic  wave  (SAW) or  shear wave(SH).  The  conventional  PZT
sensor   operates  as  an expander, the  whole  crystal  changing
dimensionally (expanding) with its plane of polarization.  Alter­
natively,  the crystal resonates lateral to the  electrode  plane
causing a shear displacement.  This shear mode resonance or Y cut
is usually categorised within  bulk acoustic wave (BAW)  devices.
 
 
We are aware that if the mass loading of a mechanically  resonat­
ing  system changes, so too will the frequency of  resonance.  We
have noted also that, as in the case for ARD,  in a piezoelectric
sensor, mechanical and electrical properties are mutually depend­
ent. Mass variations, therefore, effect the mechanically  depend­
ent  electrical  resonance. By  incorporating  the  piezoelectric
device  into an electronic amplifier and signal  generating  cir­
cuit,  it  is possible (but problematic) for mass changes  to  be
determined  by precision monitoring of changes in the current  at
the  series resonant  frequency. Changing load [mass] forces  the
current  maximum to appear at different frequencies as the  reso­
 
h2X/ Šnance  changes.   However, it is better to introduce  the  device
into a closed oscillatory circuit and allow the sensor to  deter­
mine frequency.
 
 
Unlike the  principle explained in the section dealing with  ARD,
the  oscillatory arrangement requires no separation  between  the
resonator  drive and detector. A piezoceramic resonator forms  an
electrode  connected two terminal device inserted  directly  into
the  amplifier  feedback path [ Figs. 12a & 12b]. With  no  other
dynamic component in the feedback circuit the frequency of oscil­
lation is dominated by the resonator. A very small mass  increase
will effect the base resonant frequency of the crystal, Sauerbrey
(1958) obtained the relationship; 
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Specifically, how much blood volume is relocated to abdomen, upper leg, and lower leg when assuming a seated position? 
In addition, what are the normal blood pressure and heart rate responses to passive sitting up from supine position?
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I've run an electrochemical impendance spectra for my chitosan-Fe3O4 composite and compared it with Fe3O4. As expected the charge transfer resistance (Rct) increased (from 200 ohms to 600 ohms) due to the nonconductive chitosan film in the composite. 
What I'm unsure is why the equivalent series resistance (ESR) is not increased in the sample but the it is the same and sometimes even slightly decreased for other samples.
I know that the ESR is attributed to the resistance of the electrolyte; the contact resistance between the electrolyte, current collector, and active material; and the intrinsic resistance of the active material itself. 
So the increased Rct in the composite means the electron transfer is obstructed due to decreased conductivity in the composite but the unchanged/slight lowered ESR could mean that the intrinsic resistance (or other factors) of the composite remains unchanged. Is that even possible?
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The system you describe: electronically conducting particles embedded in dielectric matrix, the whole system supported on a conducting material can be described using a transmission line model. The high frequency resistance shifts because of the relative values of the ionic and electronic conductivities through the system. Please check:
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According to the impedance criterion of Middlebrook, the stabilty of a system is determinded to the ratio of output impedance and input impedance.
I have a question that the stabilty of a system is determinded to the ratio of output impedance to input impedance or input impedance to output impedance?
Does anyone have his thesis which is published in 1976.
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Middlebrook Criterion The Middlebrook Criterion is a graphical method for determining if the input filter of a switching mode power supply will cause instability or degrade performance parameters of a duty-ratio (voltage) programmed dc-to-dc converter switching-mode power supply. As usually applied, the output impedance of the input filter is overlaid on the open-loop input impedance of the switching-mode power supply at the worse-case conditions of low-line and full-load and low-line with shorted output.
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I did scanning impedance experiment in wet-state and obtained a bode plot ( a  graph of a frequency response of the gel). I want to separate Z' and Z" to draw a Nyquist plot.
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If you have bode plot, say Impedance (Z) vs frequency and Phase angle (theta) vs frequency, then you can calculate:
Re(Z) = Z cos(theta)
Im (Z) = Z sin(theta)
Now just plot Im(Z) vs Re(Z). You will get Nyquist plot.  A common practice is to plot |im(Z)| vs Re (Z) in material characterization as the imaginary part because of capacitive contribution is negative.