Marcus Wolff

• Prof. Dr.-Ing.
• Professor (Full) at HAW Hamburg

This study compares the performance of a quartz tuning fork (QTF) with a highly sensitive ultrasound microphone in the context of acoustic measurements, applying the substitution calibration method. QTF sensors are increasingly used for high-precision tasks due to their sensitivity and stability, while microphones are still the standard in general...

Tunable diode laser spectroscopy (TDLS) is a measurement technique with high spectral resolution. It is based on tuning the emission wavelength of a semiconductor laser by altering its current and/or its temperature. However, adjusting the wavelength leads to a change in emission intensity. For applications that rely on modulated radiation, the cha...

Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) is a technique in which the sound wave is detected by a quartz tuning fork (QTF). It enables particularly high specificity with respect to the excitation frequency and is well known for an extraordinarily sensitive analysis of gaseous samples. We have developed the first photoacoustic (PA) cell for...

Photoacoustic spectroscopy (PAS) is well known for the detection of short-chain hydrocarbons, such as methane, ethane and propane, in the ppm (parts per million) or ppb (parts per billion) range. However, in the production process of natural gas and its combustion in gas-fired devices the composition, especially the concentrations of the main alkan...

The Mach–Zehnder intensity Modulator (MZM), named after Ludwig Mach and Ludwig Zehnder, is based on the corresponding interferometer. It splits light into two counter-rotating partial beams, which are later recombined with a controlled phase difference. The output of the MZM depends on the phase difference of the interferometer paths. This phase di...

The photoacoustic effect is an emerging technology that has sparked significant interest in the research field since an acoustic wave can be produced simply by the incidence of light on a material or tissue. This phenomenon has been extensively investigated, not only to perform photoacoustic imaging but also to develop highly miniaturized ultrasoun...

Can ordinary Micro-Electro-Mechanical-Systems (MEMS) microphones be used for near-ultrasonic applications? Manufacturers often provide little information about the signal-to-noise ratio (SNR) in the ultrasound (US) range and if they do, the data were determined manufacturer-specifically and are generally not comparable. Here, four different microph...

Can ordinary Micro-Electro-Mechanical-Systems (MEMS) microphones be used for near-ultrasonic applications? Manufacturers often provide little information about the signal-to-noise ratio (SNR) in the ultrasound (US) range and, if they do, the data are often determined in a manufacturer-specific manner and are generally not comparable. Here, four dif...

Photoacoustic spectroscopy (PAS) is typically used for the detection of trace gases. In this way, mixtures of short-chain hydrocarbons such as methane, ethane or propane can be analyzed with detection limits in the range of parts per million (ppm) or parts per billion (ppb) or even below. However, there are a number of applications where highly con...

Due to its extremely high detection sensitivity the concept of quartz-enhanced photoacoustic spectroscopy (QEPAS) became increasingly popular. QEPAS utilizes a quartz tuning fork as acoustic detector, thus, replacing the microphone. The high sensitivity of this approach is owed to the fact that the tuning fork represents an active band-pass flter a...

The spectral characteristic of interband cascade lasers (ICL) in continuous wave (cw) operation is well investigated. However, certain spectroscopic techniques require a modulation of the radiation. The most common way is here a variation of the operating current. In this case the spectral behavior deviates significantly from the cw operation. Howe...

For amplitude-modulated Photoacoustic Spectroscopy the optical power of the laser must vary periodically to excite the sample in a way that an acoustic signal develops. An electro-optic modulation can be achieved by a Mach-Zehnder Modulator (MZM), consisting of a Pockels Cell (PC) and a Mach-Zehnder Interferometer. However, MZMs often suffer from p...

We present a mathematical method which allows determination of the optimal spectral range for gas mixture analysis based on theoretical absorption spectra. The algorithm is particularly suited for tunable diode laser spectroscopy (TDLS) and represents a multi-step mathematical calculation which can easily be implemented in almost any programming la...

We present a mathematical method which allows determination of an optimal spectral range for gas mixture analysis based on theoretical absorption spectra. The resulting center wavelength is particularly suited for tunable diode laser spectroscopy (TDLS). The procedure contains several steps of numerical calculations which can easily be implemented...

Abstract The exact knowledge of the emission wavelength is one of the fundamental parameters in laser spectroscopy. Several spectroscopic techniques such as photoacoustics require a modulation of the radiation as a matter of principle. The determination of the momentary wavelength becomes extraordinarily difficult if a semiconductor laser emitting...

We describe two methods, based on Michelson interferometery, that enable the determination of the absolute wavelength of current-modulated semiconductor lasers. By non-linear regression of the instantaneous frequency of the interference signal, the rate of change of the wavelength of the radiation can be inferred. Alternatively, the absolute wavele...

Das Gebiet der Sensorik ist zurzeit einem auffälligen Wandel unterworfen. Viele neue Verfahren werden zur Marktreife geführt und verdrängen bis dato etablierte ältere Techniken. Neue Anforderungen, unter anderem durch die notwendige Automatisierungs- und Vernetzungstechnik im Zuge von "Industrie 4.0", beschleunigen diese Veränderungen zusätzlich. H...

Photoacoustic (PA) measurements with open resonators usually provide poor detection sensitivity due to signal leakage at the resonator opening. We have recently demonstrated three different approaches for modelling the photoacoustic signal of open resonators. In this work, one of the approaches is applied for the optimization of the geometry of the...

For mixtures of compounds with very similar spectral features, common for larger organic molecules, multivariate analysis (MVA) methods can be applied to determine the concentration of the individual components. We analyzed photoacoustic spectra of mixtures of different volatile organic compounds with and without different feature selection and fea...

Optical spectroscopy is based on the interaction between electromagnetic radiation and matter. As measured spectra of single substances are characteristic like a fingerprint, they can be used to identify atoms and molecules. Concentrations can be determined by the magnitudes of the individual features of the spectra. However, if the investigated sa...

Photoacoustic spectroscopy employs acoustic resonators for signal amplification. Resonators are usually closed, however, in some applications, open resonators are preferred. The opening deteriorates the photoacoustic signal hence reducing the sensitivity of the photoacoustic measurement. We present two new approaches for simulating the photoacousti...

We report, to our knowledge, the first optical detection scheme for short-chained hydrocarbon isotopologues. The sensor system is based on photoacoustic spectroscopy (PAS). Two continuous wave, thermoelectrically cooled, distributed feedback interband cascade lasers (DFB-ICLs) with emission wavelengths around 3.33 and 3.38 μm, respectively, served...

Photoacoustic (PA) spectroscopy has been demonstrated as an effective technique for non-invasive measurement of blood glucose concentration. The measurement is done by probing the interstitial fluid with an infrared laser source. The glucose level in the interstitial fluid, which is found 10 to 50 micrometers under the human skin, is related to the...

We report, to our knowledge, the first optical detection of the main isotopologues of short-chained hydrocarbons. The sensor system is based on photoacoustic (also known as optoacoustic) spectroscopy (PAS, OAS). This technique takes advantage of the fact that absorbed electromagnetic radiation is partially transferred into kinetic energy via inelas...

Photoacoustic spectroscopy has been demonstrated as an effective technique for non-invasive measurement of blood glucose concentration [1-3]. The measurement is done by probing the glucose molecules in the interstitial fluid with an infrared laser source. The interstitial fluid lies a few micrometers under the skin surface and the glucose concentra...

Photoacoustic Spectroscopy (PAS) is an extremely sensitive method for the detection of trace gases. It is based on the absorption of electromagnetic radiation and the non-radiating transfer of absorbed energy into heat. If the radiation is periodically modulated, expansion of the absorbing gas results in an acoustic wave with the modulation frequen...

In order to reduce the electric consumption for high intensity discharge lamps, the use of high frequencies electronic ballasts represents both a solution and many advantages such as the decrease in the congestion and low costs. However, high frequency operation is not regarded as perfectly reliable due to the appearance of acoustic resonances insi...

T-cell resonators have been used lately for non-invasive blood glucose measurements for photoacoustic spectroscopy on skin samples. A resonator has a significant role in determining the strength of the measured signal and the overall sensitivity of the sensor. Here we present results of the measurement of the photoacoustic signal of such a T-cell r...

We report, to our knowledge, the first optical detection of the main isotopologues of short-chained hydrocarbons. The sensor system is based on photoacoustic (also known as optoacoustic) spectroscopy (PAS, OAS). This technique takes advantage of the fact that absorbed electromagnetic radiation is partially transferred into kinetic energy via inelas...

The photoacoustic signal in a closed T-cell resonator is generated and measured using laser based photoacoustic spectroscopy. The signal is modelled using the amplitude mode expansion method, which is based on eigenmode expansion and introduction of losses in form of loss factors. The measurement reproduced almost all the calculated resonances from...

Photoacoustic sensors are well established in the detection of substances with small concentrations. Ordinarily, these sensors make use of closed acoustic resonators for signal enhancement. Due to special requirements for certain use cases, we need to consider an acoustic resonator with an opening. In the presentation, we give an account of the cha...

Photoacoustic spectroscopy (PAS) is an extremely sensitive method for the detection of trace gases. It is based on the absorption of electromagnetic radiation and the non-radiating transfer of the absorbed energy into heat. If the radiation is periodically modulated, expansion of the absorbing gas results in an acoustic wave with the modulation fre...

We report measurements of short-chained hydrocarbon isotopologues using two continuous wave (cw), thermoelectrically cooled (TEC), distributed feedback interband cascade lasers (DFB-ICLs) around 3.33 and 3.38 µm. The high resolution absorption spectra of ¹² CH 3 - ¹³ CH 3 , ¹³ CH 3 - ¹³ CH 3 and ¹² CH 3 - ¹² CH 2 - ¹³ CH 3 were recorded at room tem...

The photoacoustic signal in a closed T-cell resonator is generated and measured using laser based photoacoustic spectroscopy. The signal is modelled using the amplitude mode expansion method, which is based on eigenmode expansion and introduction of losses in form of loss factors. The measurement reproduced almost all the calculated resonances from...

We evaluate the spectral resolution and the detection thresholds achievable for a photoacoustic spectroscopy (PAS) system in the broadband infrared wavelength region 3270nm≲λ≲3530nm driven by a continuous wave optical parametric oscillator (OPO) with P¯≈1.26W. The absorption spectra, IPAS(λi), for diluted propane, ethane and methane test gases at l...

The photoacoustic (PA) effect consisting of the generation of an acoustic signal based on the absorption of light has already demonstrated its potential for various spectroscopic applications for both gaseous and solid samples. The signal produced during photoacoustic spectroscopy (PAS) measurement is, however, usually weak and needs to be amplifie...

The photoacoustic (PA) effect consisting of the generation of an acoustic signal based on the absorption of light has already demonstrated its potential for various spectroscopic applications for both gaseous and solid samples. The signal produced during photoacoustic spectroscopy (PAS) measurement is, however, usually weak and needs to be amplifie...

Photoacoustic spectroscopy allows the identification of specific molecules in gases. We evaluate the spectral resolution and detection limits for a PAS system in the broadband infrared wavelength region 3270 nm ≲ λ ≲ 3530 nm driven by a continuous wave optical parametric oscillator with P ≈ 1.26 W by measuring the absorption of diluted propane, eth...

Background: In 2016, a systematic literature review identified volatile organic compounds (VOCs) that could serve as lung cancer biomarkers for future breath tests. In order of priority, the six most relevant substances are 2-butanone, 1-propanol, isoprene, ethylbenzene, styrene and hexanal. A sensitive and selective detection of the six biomarkers...

We applied a multivariate analysis (MVA) to spectroscopic data of gas mixtures in the mid-IR in order to calculate the concentrations of the single components which exhibit strongly overlapping absorption spectra. This is a common challenge in broadband spectroscopy. Photoacoustic (PA) measurements of different volatile organic compounds (VOCs) in...

Das Gebiet der Sensorik ist zurzeit einem auffälligen Wandel unterworfen. Viele neue Verfahren werden zur Marktreife geführt und verdrängen bis dato etablierte ältere Techniken. Neue Anforderungen, unter anderem durch die notwendige Automatisierungs- und Vernetzungstechnik im Zuge von „Industrie 4.0“, beschleunigen diese Veränderungen zusätzlich. H...

Today’s driver hardware for High-intensity discharge (HID) lamps is bulky, expensive and not particularly energy-efficient. A downscaling of the devices seems possible by increasing the operation frequency from typically 400 Hz to some hundred kilohertz. However, efforts to design high-frequency lamp-driver systems were not successful, since the pe...

The processes inside the arc tube of high-intensity discharge lamps are investigated by finite element simulations. The behavior of the gas mixture inside the arc tube is governed by differential equations describing mass, energy and charge conservation as well as the Helmholtz equation for the acoustic pressure and the Reynolds equations for the f...

Multivariate analysis (MVA) was introduced in the early 20th century and first applied in psychology under the name of Multiple Factor Analysis (MFA). [...]

The multivariate analysis (MVA) was introduced in the early 20th century and first applied in psychology under the name of Multiple Factor Analysis (MFA). It is based on the principle component analysis (PCA) and can be of great use in other research fields as well. The MVA results in a reduction of unnecessary data, thereby reducing the error and...

Lung cancer is one of the leading causes of death worldwide [1]. The high mortality of this disease is the consequence of an often late discovery and a low survival rate at later stages [2]. A methodical general screening for lung cancer has not been established yet but could influence the dominance of this cancer type to the better. We have develo...

The measurement of short-chained hydrocarbon concentrations and their isotopic composition is essential to many applications from environmental research to natural gas exploration. For instance, the isotopic signature of methane (13CH4 : 12CH4) allows tracing the gas back to its ecological or anthropogenic source and can help constrain atmospheric...

Die Prozesse im Brenner von Halogen-Metalldampflampen werden mittels Finite-Element-Methode untersucht. Das Verhalten des Brennerinhalts wird durch insgesamt sieben gekoppelte Differenzialgleichungen beschrieben. Das Problem ist hochgradig nichtlinear. Eine direkte Lösung dieses Systems würde den Einsatz eines Hochleistungs-Computers erfordern. Es...

The processes inside the arc tube of high-intensity discharge lamps are inves- tigated by finite element simulations. The behavior of the gas mixture inside the arc tube is governed by differential equations describing mass, energy and charge conservation as well as the Helmholtz equation for the acoustic pressure and the Navier-Stokes equation for...

To the best of our knowledge, we present first-time measurements of the absorption cross sections of ¹³C ethane and propane isotopologues in the spectral region around 3000cm⁻¹. The spectra of ¹³C¹²CH6, ¹³C2H6 and ¹³C¹²C2H8 have been recorded at approximate room temperature and atmospheric pressure for concentrations between 0.325% and 0.750% in ni...

In order to reduce the electric consumption for high intensity discharge lamps, the use of high frequencies electronic ballasts represents both a solution and many advantages such as the decrease in the congestion and low costs. However, high frequency operation is not regarded as perfectly reliable due to the appearance of acoustic resonances insi...

With 1.6 million deaths per year, lung cancer is one of the leading causes of death worldwide. One reason for this high number is the absence of a preventive medical examination method. Many diagnoses occur in a late cancer stage with a low survival rate. An early detection could significantly decrease the mortality. In recent decades, certain subs...

The processes inside the arc tube of high-intensity discharge (HID) lamps are investigated by finite element simulations. The behavior of the gas mixture inside the arc tube is governed by coupled differential equations describing mass, energy and charge conservation as well as the Helmholtz equation for the acoustic pressure and the Navier-Stokes...

Das Gebiet der Sensorik ist zurzeit einem auffälligen Wandel unterworfen. Viele neue Verfahren werden zur Marktreife geführt und verdrängen bis dato etablierte ältere Techniken. Neue Anforderungen, unter anderem durch die Automatisierungstechnik im Zuge von „Industrie 4.0“, beschleunigen diese Veränderungen zusätzlich. Hier ist es schwierig den Übe...

The light flicker problem of high intensity discharge lamps is studied numerically and experimentally. It is shown that in some respects the systems behaves very similar to the forced Duffing oscillator with a softening spring. In particular, the jump phenomenon and hysteresis are observed in the simulations and in the experiments.

This review provides an overview of volatile organic compounds (VOCs) which are considered lung cancer biomarkers for diagnostic breath analysis. It includes results of scientific publications from 1985 to 2015. The identified VOCs are listed and ranked according to their occurrence of nomination. The applied detection and sampling methods are spec...

Absorption line positions for the ethane isotopologues 13C12CH6 and 13C2H6 have been determined in in the 3.2 – 3.6 µm spectral region from spectra recorded using an FTIR spectrometer (Newport MIR8025). Results are presented for approximately 1% of 13C-ethane (mixed with nitrogen 5.0) from spectra recorded at 0.5 cm-1 resolution at room temperature...

This review provides an overview of volatile organic compounds (VOCs), which are considered lung cancer biomarkers for diagnostic breath analysis. It includes results of scientific publications from 1985 to 2015. The identified VOCs are listed and ranked according to their occurrence of nomination. The applied detection and sampling methods are spe...

A new approach for continuous and non-invasive monitoring of the glucose concentration in human epidermis has been suggested recently. This method is based on photoacoustic (PA) analysis of human interstitial fluid. The measurement can be performed in vitro and in vivo and, therefore, may form the basis for a non-invasive monitoring of the blood su...

Operating high-intensity discharge lamps in the high frequency range (20-300 kHz) provides energy-saving and cost reduction potentials. However, commercially available lamp drivers do not make use of this operating strategy because light intensity fluctuations and even lamp destruction are possible. The reason for the fluctuating discharge arc are...

For energy efficiency and material cost reduction it is preferred to drive high-intensity discharge lamps at frequencies of approximately 300 kHz. However, operating lamps at these high frequencies bears the risk of stimulating acoustic resonances inside the arc tube, which can result in low frequency light flicker and even lamp destruction. The ac...

This paper describes a new photoacoustic spectrometer for the investigation of hydrocarbons based on a continuous wave optical-parametric oscillator (OPO). Two modulation methods for the generation of the photoacoustic signal are compared. In addition to the traditional modulation by a mechanical chopper a Mach-Zehnder modulator was set up for this...

Photoacoustic signal processing requires the extraction of a small alternating signal with known modulation frequency from a large interfering signal. For a long time lock-in amplification has been the method of choice for this task. It requires a reference with the modulation frequency of the signal and computes the signal usually by a dual phase...

For energy efficiency and particularly for cost reduction it is preferred to drive high-intensity discharge lamps at frequencies of approximately 300 kHz. However, operating lamps at these high frequencies bears the risk of stimulating acoustic resonances inside the arc tube, which can result in low frequency light flicker and even lamp destruction...

Approximately one fifth of the world production of electric power is consumed for illumination [1]. High-intensity discharge (HID) lamps represent a main part of the artificial light sources. They are used for street and shop lighting as well as automobile headlights and other applications. A superior color rendering index combined with a sun-like...

The measurement of short-chained hydrocarbon concentrations and their isotopic composition is essential to many applications from environmental research to natural gas exploration. For instance the isotopic signature of methane (13CH4 : 12CH4) allows tracing the outflow to its various ecological and anthropogenic sources and can help constrain atmo...

Photoacoustic signal processing requires the extraction of a small alternating signal with known modulation frequency from a large interfering signal. For a long time lock-in amplification has been the method of choice for this task. It requires a reference with the modulation frequency of the signal and computes the signal usually by a dual phase...

This presentation describes a new photoacoustic spectrometer for the investigation of hydrocarbons based on a continuous wave optical-parametric oscillator (OPO). Two modulation methods for the generation of the photoacoustic signal are compared. In addition to the traditional modulation by mechanical chopper a Mach-Zehnder modulator was set up for...

A stationary compressible three-dimensional (3D) model of photothermal processes inside an arc tube of a high-intensity discharge lamp is developed on the basis of the finite element method. It takes plasma, electrodes, and the tube wall into account and enables simulation of acoustic phenomena. The temperature profile of the discharge arc is used...

For the reasons of energy efficiency and mate-rial cost reduction one would prefer to drive high-intensity discharge lamps at frequencies of about 300 kHz. Operat-ing lamps at these high frequencies bears the risk of stim-ulating acoustic resonances inside the arc tube, which can result in low frequency light flicker and even lamp de-struction. The...

Introduction: High-intensity discharge (HID) lamps will in the foreseeable future be important light sources despite a growing market share of LEDs. Cost and energy efficient high frequency (300 kHz) operation is hampered by the excitation of acoustic resonances inside the arc tube which results in low frequency (10 Hz) light flicker. Our aim is to...

n photoacoustic spectroscopy that is adopted for gas sensing, microphones are usually used to detect the pressure variation inside the sample cell. The application of a new commercial inter-integrated circuit sound digital micro-electro-mechanical systems (MEMS) microphone that is enhanced with a filter and an analog-to-digital converter in a singl...

We presented a new optical gas detection scheme based on a photonic crystal laser. We showed emission and operation parameters of this radiation source as well as measured spectra of H2O at 1910 nm. The optical gas sensor based on the photonic crystal laser provides some considerable advantages over those based on traditional semiconductor lasers....

High-intensity discharge lamps frequently suffer emission disturbances due to the excitation of acoustic resonances. This paper presents experimentally determined light flicker frequencies and arc motion frequencies at different excitation frequencies and modulation depths. Light intensity fluctuation has been detected with a photodiode. Simultaneo...

This work presents experimentally determined light flicker frequencies and arc motion frequencies of high-intensity discharge (HID) lamps at different excitation frequencies and modulation depths. Light intensity fluctuation has been detected with a photodiode. Simultaneously, arc motion was recorded with a camera. The frequencies of both methods a...

High-intensity discharge (HID) lamps comprise a translucent vessel called arc tube, in which a plasma discharge arc between two electrodes is established. These lamps combine high lumen efficacies with excellent color qualities. Operating HID lamps at a high-frequency (20 – 300 kHz) would reduce cost and increase energy efficiency of the lamp-drive...

High-intensity discharge (HID) lamps are energy-efficient light sources with excellent color qualities. These HID lamps are operated on low frequency square wave drivers with a high-frequency ripple. A cost reduction and efficiency step can be made by operating these lamps on high-frequency electronic ballasts [1]. However, these tend to excite aco...

To the best of our knowledge, we present for the first time spectroscopic methane measurements using a laser diode at 3.3 μm operated in continuous mode at room temperature. The DFB-type laser emits a maximum optical output power of 1.5 mW with a spectral linewidth below 10 MHz. This novel kind of semiconductor laser allows precise photoacoustic me...

This paper presents a numerical model of high-pressure sodium (HPS) lamps, including acoustic streaming. The model is implemented in COMSOL and is based on the finite-element method using a 2-D axisymmetric geometry. Moreover, a revision concerning experimental acoustic resonance (AR) characterizations of HPS lamps will be also provided. The result...

In photoacoustic spectroscopy that is adopted for gas sensing, microphones are usually used to detect the pressure variation inside of the sample cell. We present the application of a new commercial I2S digital MEMS microphone that is enhanced with a filter and an analog-to-digital converter in a single package. The utilisation of the described MEM...

High-intensity discharge (HID) lamps comprise a gas encapsulated in a transparent container called arc tube. The imposed alternating electric current results in a plasma discharge arc between the electrodes. This intensive heat source leads to a buoyancy driven velocity field. Tuning the modulation frequency to an acoustic Eigenfrequency of the arc...

A new approach can be used for continuous and non-invasive monitoring of the glucose concentration in human epidermis [1]. The method is based on photoacoustic (PA) analysis of human interstitial fluid. The measurement can be performed in vitro and in vivo and, therefore, may form the basis for a non-invasive monitoring of the blood sugar level for...

The signal of photoacoustic sensors depends considerably on the shape of the sample cell. Taking advantage of acoustical resonances results in a signal boost and enables highly sensitive analyzers with low detection limits. A numerical optimization of the cell geometry has been performed with the objective being maximization of the photoacoustic si...

In Photoacoustic Spectroscopy that is adopted for gas sensing, standard condenser microphones are usually used to detect the pressure variation inside of the sample cell. We present the application of a new commercial I2S digital MEMS microphone that is enhanced with a filter and an analog to digital converter in a single package. The utilisation o...

To the best of our knowledge, we present for the first time spectroscopic methane measurements with a DFBtype laser diode at a wavelength of approximately3.3 μm. The laser diode can be operated near room temperature andemits a maximum of1.5 mW optical power with a spectral linewidth smaller than 10 MHz.This novel kind of semiconductor laser allowed...

The sensitivity of photoacoustic sensors strongly depends on the shape of the acoustical resonator. Up to now, mainly photoacoustic sensors consisting of a number of cylindrical parts have been investigated (cylinder cells, H cells, T cells etc.). In this paper, a numerical shape optimization of the resonator cell of photoacoustic sensors is descri...

We present first results of a research project that has the goal to develop an analyzer for volatile organic compounds (VOCs) with extraordinarily high detection sensitivity and detection selectivity. Due to its high potential concerning these two key parameters, optical spectroscopy is employed. The new detection scheme is based on photoacoustic s...

Intangible assets, such as intellectual property (IP), are increasingly finding their way into a company’s balance sheet. Studies prove that intangible assets have become as important as tangible ones and that companies that manage their intellectual property strategically well are considerably more successful in the entrepreneurial sense. It is re...

A considerable number of sensing applications concern the detection of volatile organic compounds (VOCs). These hydrocarbons play an important role in numerous industrial processes and particularly the concentration of hazardous and toxic species such as benzene, toluene or xylene (BTX) has to be sensitively measured and controlled. However, dete...

It is well known that the photoacoustic (PA) signal considerably depends on the shape of the sample cell and that modulating the radiation at an acoustical eigenfrequency of the cell significantly enhances the signal [1]. In order to further improve detection sensitivities of PA sensor system a numerical shape optimization of the resonator cell has...

A considerable number of environmental, industrial and medical sensing applications concern the detection of volatile organic compounds such as hydrocarbons [1, 2]. Hydrocarbons show their strongest absorption in the wavelength region between 3.2 and 3.6 µm with a maximum around 3.4 µm. These absorptions are result of the excitation of the symmetri...

High intensity discharge (HID) lamps operated at high frequencies suffer from arc instabilities caused by acoustic resonances. Arc instabilities result in light flickering, reduction of lamp lifetime and even lamp destruction. Therefore, HID-lamps are operated far below the optimal frequency range and bulky, hence power consuming and expensive, ele...

A finite element model including plasma simulation is used to calculate the amplitude of acoustic resonances in HID lamps in a 2D axisymmetric geometry. Simulation results are presented for different operation parameters and are compared with experimental data.

High detection sensitivity and spectral selectivity is important for gas analysers to identify the measured compound and to detect low concentrations. We investigated three different modulation methods – pulse gate modulation, pulse frequency modulation and chopper modulation – for a new pulsed quantum cascade laser based photoacoustic sensor. The...

The composition and concentration of exhaled volatile gases reflects the physical ability of a patient. Therefore, a breath analysis allows to recognize an infectious disease in an organ or even to identify a tumor. One of the most prominent breath tests is the 13C-urea-breath test, applied to ascertain the presence of the bacterium helicobacter py...

The composition and concentration of exhaled volatile gases reflects the physical ability of a patient. Therefore, a breath analysis allows to recognize an infectious disease in an organ or even to identify a tumor. One of the most prominent breath tests is the 13C-urea-breath test, applied to ascertain the presence of the bacterium helicobacter py...