[Show abstract][Hide abstract] ABSTRACT: We introduce a new 3-D flexible microelectrode array for high performance electrographic neural signal recording and stimulation. The microelectrode architecture maximizes the number of channels on each shank and minimizes its footprint. The electrode was implemented on flexible polyimide substrate using microfabrication and thin-film processing. The electrode has a planar layout and comprises multiple shanks. Each shank is three mm in length and carries six gold pads representing the neuro-interfacing channels. The channels are used in recording important precursors with potential clinical relevance and consequent electrical stimulation to perturb the clinical condition. The polyimide structure satisfied the mechanical characteristics required for the proper electrode implantation and operation. Pad post-processing technique was developed to improve the electrode electrical performance. The planar electrodes were used for creating 3-D "Waterloo Array" microelectrode with controlled gaps using custom designed stackers. Electrode characterization and benchmarking against commercial equivalents demonstrated the superiority of the Flex electrodes. The Flex and commercial electrodes were associated with low-power implantable responsive neuro-stimulation system. The electrodes performance in recording and stimulation application was quantified through in vitro and in vivo acute and chronic experiments on human brain slices and freely-moving rodents. The Flex electrodes exhibited remarkable drop in the electric impedance (100 times at 100 Hz), improved electrode-electrolyte interface noise (dropped by 4 times) and higher signal-to-noise ratio (3.3 times).
IEEE Transactions on Neural Systems and Rehabilitation Engineering 05/2014; 22(5). · 3.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A novel niobium-based superconducting RF microelectromechanical system (MEMS) varactor is presented, and its mechanical performance is characterized at both room and cryogenic temperatures. The device is amenable to integration with superconducting microelectronics (SME) technology. The RF performance of the varactor at cryogenic (4 K) temperatures indicates capacitance variations from 40 fF to 0.46 pF. Hence, the varactor is used to design a monolithically integrated tunable resonator, whose measured results at cryogenic temperature show a sweep of frequency from 2.62 to 2.54 GHz and a discrete shift from 2.54 to 1.95 GHz, when the biasing voltage varies from 0 to 58 V. Using the same fabrication process, a fixed niobium-based three-pole bandstop filter is designed with a center frequency of 2 GHz and a size of 5 mm × 0.85 mm. Tunable versions of the three-pole filter using semiconductor varactors and monolithically integrated MEMS varactors are also designed and characterized at 4 K. The results of the tunable bandstop filters are analyzed both theoretically and experimentally.
[Show abstract][Hide abstract] ABSTRACT: A niobium-based superconducting dc-contact RF microelectromechanical systems switch is introduced and is thoroughly analyzed. The switch is amenable to integration with superconducting microelectronics technology. A comparison of the switch's RF performance at room and cryogenic temperatures indicates a significant improvement in the insertion loss of the switch when niobium is superconducting. The mechanical characteristic of the switch at extremely low temperature (4 K) is also investigated. The switch exhibits an increase of 18% on the actuation voltage as the temperature changes from 293 K (room temperature) to 4 K. A niobium superconducting tunable resonator is designed and tested, employing the proposed switch as the tuning element in the form of a switched capacitor bank monolithically integrated with the resonator. The measured results at 4 K clearly indicate the discrete resonance frequency states of the resonator. A three-pole tunable bandstop filter is designed with a center frequency of 1.2 GHz and dimensions of only 5 mm $times$ 1.2 mm. The results demonstrate a tuning range of 12% while maintaining an excellent RF response of the filter.
IEEE Transactions on Microwave Theory and Techniques 01/2014; 62(7):1437-1447. · 2.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: High-Q tunable filters are in demand in both wireless and satellite applications. The need for tunability and configurability in wireless systems arises when deploying different systems that coexist geographically. Such deployments take place regularly when an operator has already installed a network and needs to add a new-generation network, for example, to add a long-term evolution (LTE) network to an existing third-generation (3G) network. The availability of tunable/reconfigurable hardware will also provide the network operator the means for efficiently managing hardware resources, while accommodating multistandards requirements and achieving network traffic/capacity optimization. Wireless systems can also benefit from tunable filter technologies in other areas; for example, installing wireless infrastructure equipment, such as a remote radio unit (RRU) on top of a 15-story high communication tower, is a very costly task. By using tunable filters, one installation can serve many years since if there is a need to change the frequency or bandwidth, it can be done through remote electronic tuning, rather than installing a new filter. Additionally, in urban areas, there is a very limited space for wireless service providers to install their base stations due to expensive real estate and/or maximum weight loading constrains on certain installation locations such as light poles or power lines. Therefore, once an installation site is acquired, it is natural for wireless service providers to use tunable filters to pack many functions, such as multistandards and multibands, into one site.
[Show abstract][Hide abstract] ABSTRACT: A novel reconfigurable millimeter-wave bandpass filter (BPF) capable of operating between 60 GHz and the E-band, with a good channel isolation, is presented. This fully integrated filter is designed with all reconfigurable elements embedded for compactness. A new method that increases fractional bandwidths is introduced. It uses inductively coupled invertersbut does not require tuning. New circuit models are provided for these inverters, reconfigurable resonators, and the reconfigurable bandstop stubs. The compact BPF achieved a footprint of only 4.75 mm $,times,$ 3.75 mm. Measurements for the filters show good agreement with the simulation results.
[Show abstract][Hide abstract] ABSTRACT: This paper proposes an electronically reconfigurable Doherty amplifier capable of efficiently amplifying multi-standard multi-band wireless signals centered at widely spaced frequencies. The paper outlines closed form equations for an effective design methodology of frequency agile Doherty amplifiers driven with multi-mode signals using a small number of electronically tunable devices. As a proof of concept, a reconfigurable Doherty prototype is designed and fabricated to operate at 1.9, 2.14, and 2.6 GHz meant to efficiently amplify signals with peak-to-average power ratio equal to 6, 9 and 12 dB. The measurement results obtained using continuous wave signals reveal drain efficiencies of about 67% and 42% at the peak power and 12 dB output back off power respectively for the three operating frequencies. In addition, the reconfigurable Doherty amplifier is successfully linearized when driven with 20 MHz wideband code-division multiple access and 20 MHz long term evolution signals, using a Volterra based digital predistrtion algorithm which exploits a pruned Volterra series.
Circuits and Systems I: Regular Papers, IEEE Transactions on 01/2014; 61(4):1229-1240. · 2.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a compact wireless headset for simultaneous multi-site neuromonitoring and neurostimulation in the rodent brain. The system comprises flexible-shaft microelectrodes, neural amplifiers, neurostimulators, a digital time-division multiplexer (TDM), a micro-controller and a ZigBee wireless transceiver. The system is built by parallelizing up to four 0.35 μm CMOS integrated circuits (each having 256 neural amplifiers and 64 neurostimulators) to provide a total maximum of 1024 neural amplifiers and 256 neurostimulators. Each bipolar neural amplifier features 54 dB-72 dB adjustable gain, 1 Hz-5 kHz adjustable bandwidth with an input-referred noise of 7.99 μVrms and dissipates 12.9 μW. Each current-mode bipolar neurostimulator generates programmable arbitrary-waveform biphasic current in the range of 20-250 μA and dissipates 2.6 μW in the stand-by mode. Reconfigurability is provided by stacking a set of dedicated mini-PCBs that share a common signaling bus within as small as 22×30×15 mm(3) volume. The system features flexible polyimide-based microelectrode array design that is not brittle and increases pad packing density. Pad nanotexturing by electrodeposition reduces the electrode-tissue interface impedance from an average of 2 MΩ to 30 kΩ at 100 Hz. The rodent headset and the microelectrode array have been experimentally validated in vivo in freely moving rats for two months. We demonstrate 92.8 percent seizure rate reduction by responsive neurostimulation in an acute epilepsy rat model.
IEEE Transactions on Biomedical Circuits and Systems 10/2013; · 2.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Intracortical microelectrodes play a prominent role in the operation of neural interfacing systems. They provide an interface for recording neural activities and modulating their behavior through electric stimulation. The performance of such systems is thus directly meliorated by advances in electrode technology. We present a new architecture for intracortical electrodes designed to increase the number of recording/stimulation channels for a given set of shank dimensions. The architecture was implemented on silicon using microfabrication process and fabricated 3 mm long electrode shanks with 6 relatively large (110 μm × 110 μm) pads in each shank for electrographic signal recording to detect important precursors with potential clinical relevance and electrical stimulation to correct neural behavior with low-power dissipation in an implantable device. Moreover, an electrode mechanical design was developed to increase its stiffness and reduce shank deflection to improve spatial accuracy during an electrode implantation. Furthermore, the pads were post-processed using pulsated low current electroplating and reduced their impedances by ~30 times compared to the traditionally fabricated pads. The paper also presents microfabrication process, electrodes characterization, comparison to the commercial equivalents, and in-vitro and in-vivo validations.
IEEE transactions on neural systems and rehabilitation engineering: a publication of the IEEE Engineering in Medicine and Biology Society 10/2013; · 2.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A novel high-temperature superconducting (HTS) microstrip K-band filter is designed, fabricated, and measured. The Chebyshev filter has five poles and is designed for the center frequency of 20.45 GHz with a percentage bandwidth of 2.5%. The proposed miniaturized resonator minimizes the unwanted coupling between nonadjacent resonators, which is typically pronounced at high frequencies. The layout is patterned on a 0.5-mm-thick MgO substrate. The dimension of the fabricated filter is 7.5 mm × 3 mm. The filter employs a via-less Coplanar Waveguide to microstrip transition and the layout is configured to allow ease of adjusting and tuning. The filter with via-less Coplanar Waveguide input/output pads is measured in an RF cryogenic probe station at 77 and 4 K to investigate variation of center frequency with operating temperatures. Simulation and measured results of the filter show a spurious-free response up to 35 GHz.
[Show abstract][Hide abstract] ABSTRACT: For implantable bioelectronic devices, the interface between the device and the biological environment requires significant attention as it dictates the device performance in vivo. Non-specific protein adsorption onto the device surface is the initial stage of many degradation mechanisms that will ultimately compromise the functionality of the device. In order to preserve the functionality of any implanted bioelectronics overtime, protein adsorption must be controlled. This review paper outlines two major approaches to minimize protein adsorption onto the surface of implantable electronics. The first approach is surface coating, which minimizes close proximity interactions between proteins and device surfaces by immobilizing electrically neutral hydrophilic polymers as surface coating. These coatings reduce protein fouling by steric repulsion and formation of a hydration layer which acts as both a physical and energetic barrier that minimize protein adsorption onto the device. Relevant performances of various conventional hydrophilic coatings are discussed. The second approach is surface patterning using arrays of hydrophobic nanostructures through photolithography techniques. By establishing a large slip length via super hydrophobic surfaces, the amount of proteins adsorbed to the surface of the device can be reduced. The last section discusses emerging surface coating techniques utilizing zwitterionic polymers where ultralow-biofouling surfaces have been demonstrated. These surface modification techniques may significantly improve the long-term functionality of implantable bioelectronics, thus allowing researchers to overcome challenges to diagnose and treat chronic neurological and cardiovascular diseases.
[Show abstract][Hide abstract] ABSTRACT: This paper proposes a frequency-agile Doherty amplifier capable of efficiently amplifying multiband wireless signals located at widely spaced frequencies. Starting with the study of the load modulation concept in the Doherty technique and the various frequency-dependent components involved in its realization, this paper suggests a simplified and effective design methodology for the development of frequency-agile and reconfigurable Doherty amplifiers using a small number of electronically tunable devices. As a proof of concept, a reconfigurable Doherty power amplifier (PA) prototype is designed and fabricated to operate at 1.9, 2.14, and 2.6 GHz. The measurement results obtained using a continuous-wave signal revealed drain efficiencies of approximately 70% and 60% at the peak power and 6 dB back-off power, respectively, for the three targeted operating frequencies. In addition, the reconfigurable Doherty amplifier was successfully linearized when driven with 20-MHz wavelength code-division multiple access and longterm evolution signals, using a Volterra-based digital predistrtion algorithm which exploits a pruned Volterra series.
IEEE Transactions on Microwave Theory and Techniques 04/2013; 61(4):1588-1598. · 2.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper proposes an electronically reconfigurable Doherty amplifier capable of efficiently amplifying wireless signals with significant time varying average power. This paper outlines closed-form equations used to design an effective Doherty amplifier that can be driven with signals of variable power levels using a small number of electronically tunable devices. As a proof of concept, a reconfigurable Doherty amplifier prototype was designed and fabricated that efficiently amplified signals centered at 2.6 GHz with output average power levels equal to 35, 30, and 25 dBm. The measurement results obtained using continuous wave signals revealed power-added efficiencies of greater than 66%, at input power level adjustments of 21 and 16 dBm, and more than 62% when the average input power level setting was adjusted to 11 dBm. In addition, the reconfigurable Doherty amplifier, driven with a 20-MHz long-term evolution signal, was successfully linearized using a pruned Volterra series based digital predistrtion algorithm.
IEEE Transactions on Microwave Theory and Techniques 01/2013; 61(12):4179-4187. · 2.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A dc contact and a capacitive contact niobium-based superconducting radio frequency (RF) microelectro-mechanical systems switches are presented for the first time. The switches are amenable to integration with superconducting-micro-electronics technology. A comparison of the RF performance of the switches at room and cryogenic temperatures indicate a significant improvement in the insertion loss of the switch when niobium is superconducting. A niobium-based dc contact single-port-double-throw switch is designed, fabricated, and tested. Two types of switched capacitor banks are also designed each implementing one of the two types of the introduced switches. The measured results of the capacitor bank with capacitive contact switches show variation of the capacitance value from 0.4 to 0.94 pF. The measured results of the capacitor bank with dc contact switches show variation of the capacitance value from 0.2 to 1 pF at 4 K.
[Show abstract][Hide abstract] ABSTRACT: A novel method for global post-fabrication tuning of microwave filters is presented. The method is based on designing and adding a compensating passive circuit in parallel with the detuned filter. This concept, which is demonstrated by experimental results, has several advantages over traditional techniques for filter tuning that use screws. It can be employed to filter structures that are not easily amenable to the use of tuning screws such as planar filters. Another important advantage of the proposed concept is that it can be employed without knowing details of the filter configuration. The compensating circuit that is added in parallel to the detuned filter, does not affect the individual elements of the filter. The experimental results obtained demonstrate the validity of this concept.
[Show abstract][Hide abstract] ABSTRACT: This paper presents a novel structure for tunable dielectric resonator (DR) filters using varactor tuning. The varactor is mounted outside the filter housing while interacting with the resonator through a PCB circuit board. The concept is analyzed both theoretically and experimentally. A prototype tunable DR filter employing this concept is designed, implemented and tested. The filter operates at 5 GHz with a bandwidth of 60 MHz demonstrating a tuning range of more than 300 MHz and a spurious free window larger than 1.0 GHz.
[Show abstract][Hide abstract] ABSTRACT: A novel CPW based phase shifter that relies on automatic collapse of capacitive switches is designed, fabricated and tested. The novel design of the phase shifter is due to a novel CPW topology and automatic collapse mechanical design that is designed to operate at several and gradual collapse voltages. The novelty of the CPW has been achieved through the corrugated grounds to create a slow wave transmission line. The resulted compact CPW will have an effective electrical length that is physically equivalent to a relatively longer conventional CPW. The automatic collapse of the designed capacitive switches comes through deferent lengths of the beams that are carrying those capacitive switches. The worst measured insertion loss and return loss are 1.7 dB and 13 dB, respectively, at 30 GHz with a phase shift of almost 106 degrees. The phase shifter is built on alumina substrate of gold material using UWMEMS process.
[Show abstract][Hide abstract] ABSTRACT: In this paper, several Giant Magneto Impedance (GMI) magnetic sensors have been designed, fabricated, post processed and tested to work in low field intensities (miliTesla range). The sensors are multilayer GMI sensors having CoSiB as GMI material surrounded with two thinner gold layers. The conventional thin film microfabrication process is employed to fabricate the sensors on a glass wafer. A post-processing thermal and magnetic treatment is suggested to magnetize GMI material and enhance performance of the sensors. The suggested post-processing step will decrease fabrication cost of GMI sensors and improve their performance effectively.
[Show abstract][Hide abstract] ABSTRACT: A thin film sensor for sensing magnetic fields bellow 10 Gausses is designed and fabricated based on a giant magneto-impedance (GMI) structure. Analytical equations describing GMI effect have been employed to design the sensor over the designated magnetic field and signal frequency. The GMI multilayer is comprised of an Au layer (200 nm) sandwiched between two Co73Si12B15 magnetic layers (400 nm). Various structures with different shapes and ratios have been studied to achieve the optimum performance. The sensors are fabricated on a glass wafer employing thin-film micro-fabrication processes. The paper also presents a new post-processing step to magnetize the GMI multilayer. The impedance of the GMI sensors as a function of external magnetic and excitation frequency is reported and discussed. The sensor has been utilized to change the state of an On/Off circuit in the presence/absence of magnetic field.
IEEE Transactions on Magnetics 01/2013; 49(7):3874-3877. · 1.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper proposes a monolithic GaN Doherty power amplifier (DPA) capable of efficiently amplifying communication signals located in multiple widely spaced wireless frequency bands. The proposed monolithic DPA incorporates a number of microelectromechanical systems switches which were used to mitigate the variation of the DPA circuit parameters within the operating frequency. A systematic design methodology was used to optimize the size and complexity of the frequency agile DPA thus locating the reconfigurability out of the combining network so that this latter can be kept off-chip. A monolithic DPA was designed and fabricated using the Canadian Photonics Fabrication Centre GaN500 monolithic microwave integrated circuit (MMIC) process (0.5 um gate length) which was operated at 1.7GHz, 2.14GHz and 2.6GHz. The preliminary measurement results demonstrated drain efficiency higher than 50% for power levels up to 6dB back-off from the peak output power.