Henry Bruhns - Academia.edu (original) (raw)

Papers by Henry Bruhns

Proceedings IMCS 2012, 2012

T-cell resonators have been used lately for non-invasive blood glucose measurements for photoacou... more 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 resonator. The signal is also modelled using the amplitude mode expansion method, which is based on eigenmode expansion and the introduction of losses in the form of loss factors. The measurement reproduced almost all the calculated resonances from the numerical models with fairly good agreement. The cause of the differences between the measured and the simulated resonances are explained. In addition, the amplitude mode expansion simulation model is established as a faster and computationally less demanding photoacoustic simulation alternative to the viscothermal model. The resonance frequencies from the two models differ by less than 1.8%. It is noted that the relative height of the amplitudes from the two models depends on the location of the antinodes within the different parts of the resonator. The amplitude mode expansion model provides a quick simulation tool for the optimization and design of macro resonators.

This paper describes a new photoacoustic spectrometer for the investigation of hydrocarbons based... more 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 wavelength range and used to shape the OPO beam. Spectra of three hydrocarbon test gases (methane, ethane and propane in nitrogen) were measured between 3200 nm and 3500 nm. The differences between the two modulation methods are explained and the advantages of the newly introduced Mach-Zehnder modulator are elaborated. In particular the frequency fluctuation and complexity of both methods are set in contrast with each other. The measured methane spectrum is compared against data from the HITRAN database. Copyright © 2015 IFSA Publishing, S. L.

arXiv: Instrumentation and Detectors, 2018

The photoacoustic signal in a closed T-cell resonator is generated and measured using laser based... more 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 the numerical models with fairly good agreement. The cause of the differences between the measured and the simulated resonances are explained. In addition, the amplitude mode expansion simulation model is established as a quicker and computationally less demanding photoacoustic simulation alternative to the viscothermal model. The resonance frequencies obtained from the two models deviate by less than 1.8%. It was noted that the relative height of the amplitudes of the two models depended on the location of the antinodes within the resonator.

Sensors, 2018

We evaluate the spectral resolution and the detection thresholds achievable for a photoacoustic s... more We evaluate the spectral resolution and the detection thresholds achievable for a photoacoustic spectroscopy (PAS) system in the broadband infrared wavelength region 3270 n m ≲ λ ≲ 3530 n m driven by a continuous wave optical parametric oscillator (OPO) with P ¯ ≈ 1.26 W . The absorption spectra, I PAS ( λ i ) , for diluted propane, ethane and methane test gases at low concentrations ( c ∼ 100 ppm ) were measured for ∼1350 discrete wavelengths λ i . The I PAS ( λ i ) spectra were then compared to the high resolution cross section data, σ FTIR , obtained by Fourier Transform Infrared Spectroscopy published in the HITRAN database. Deviations of 7.1(6)% for propane, 8.7(11)% for ethane and 15.0(14)% for methane with regard to the average uncertainty between I PAS ( λ i ) and the expected reference values based on σ FTIR were recorded. The characteristic absorption wavelengths λ res can be resolved with an average resolution of δ λ res ∼ 0.08 nm . Detection limits range between 7.1 ppb ...

Sensors, 2017

With 1.6 million deaths per year, lung cancer is one of the leading causes of death worldwide. On... more 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 substances in human breath have been linked to certain diseases. Different studies show that it is possible to distinguish between lung cancer patients and a healthy control group by analyzing the volatile organic compounds (VOCs) in their breath. We developed a sensor based on photoacoustic spectroscopy for six of the most relevant VOCs linked to lung cancer. As a radiation source, the sensor uses an optical-parametric oscillator (OPO) in a wavelength region from 3.2 µm to 3.5 µm. The limits of detection for a single substance range between 5 ppb and 142 ppb. We also measured high resolution absorption spectra of the biomarkers compared to the data currently available from the National Institute of Standards and Technology (NIST) database, which is the basis of any selective spectroscopic detection. Future lung cancer screening devices could be based on the further development of this sensor.

Proceedings IMCS 2012, May 21, 2012

SPIE Proceedings, 2011

We present first results of a research project that has the goal to develop an analyzer for volat... more 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 spectroscopy (PAS). PA detection utilizes the fact, that the

Optical Sensors - New Developments and Practical Applications, 2014

Sensors and Actuators B: Chemical, 2013

ABSTRACT To the best of our knowledge, we present for the first time spectroscopic methane measur... more ABSTRACT 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 measurements of characteristic methane absorption structures in the ν3 band. In addition, the setup enables a detection limit below 1 ppm.

International Journal of Thermophysics, 2014

In photoacoustic spectroscopy that is adopted for gas sensing, microphones are usually used to de... more In 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 single package is presented. The utilization of the described MEMS microphone together with an embedded microcontroller significantly reduces the required space and costs for the components needed to realize the signal detection path of the spectrometer. The measurement results of this signal detection path are compared with those of a conventional photoacoustic spectrometer that is equipped with a capacitive microphone, a microphone preamplifier, and a lock-in amplifier for signal processing. At the first stage of our study, the recorded 24 bit data streams of both microphones are evaluated. At a second stage, the digital output signals of the MEMS microphone are processed with the Goertzel algorithm. The results are compared with the digital output of a lock-in amplifier that is connected to the microphone preamplifier's output of the condenser microphone.