Photoacoustic spectroscopy

Gases can be detected very precisely and selectively by means of photoacoustic spectroscopy (PAS). Alexander Graham Bell already described the basic measurement principle in 1880: If a gas sample in a measuring cell is irradiated with a pulsed light source, specific gas molecules will absorb the light and the gas sample will heat up. According to kinetic gas theory, a local increase in temperature leads to an increase in pressure. Periodic modulation of the intensity of the incident light beam causes periodic pressure fluctuations whose frequency matches the modulation frequency of the light source. These acoustic waves, i.e. the photoacoustic signal, can be detected with sound transducers (e.g. commercial MEMS microphones). The signal amplitude correlates with the strength of the absorption and thus provides information about the gas concentration in the measuring cell.

© Fraunhofer IPM
Schematic view of a resonant photoacoustic chamber
© Fraunhofer IPM
Schematic view of a non-resonant photoacoustic chamber

Resonant and non-resonant measuring cells

The geometry of the measuring cell is essential for the sensitivity of the photoacoustic detector. The detector can either be operated resonantly or non-resonantly. In resonant operation, the modulation frequency of the light source matches the acoustic resonance frequency of the measuring cell. This significantly amplifies the photoacoustic signal and thus increases the detection sensitivity.

In non-resonant operation of a photoacoustic detector, the modulation frequency of the light source (typically a broadband IR emitter) is far below the acoustic resonance frequency of the measuring cell. Non-resonant systems can be operated at different frequencies and are more stable with regard to changing pressure and temperature during operation.

© Fraunhofer IPM
Resonant photoacoustic sensor with an LED as light source
© Fraunhofer IPM
Resonant photoacoustic sensor with a laser as light source

LED, laser or IR-emitter as light source

Depending on the target gas and application, different geometries of measuring cells and different light sources are selected. Cost-effective measurement systems that use rapidly modulatable LEDs as light sources, for example, can already determine target gas concentrations very sensitively (in the 1 ppm range). If lasers are used as light source, the selectivity and sensitivity of the measurement systems are improved, often reaching values in the low ppb range. 

Some examples:

For a compact SO2 measurement system used for emission measurement in the exhaust gas scrubber on ships, Fraunhofer IPM employs a resonant measurement cell with a UV LED as light source. Thus, the required high resolution of 1 ppm in the measuring range up to 50 ppm SO2 is achieved.

For a miniaturized photoacoustic CO2 sensor used for the detection of indoor air quality, a non-resonant measuring cell was combined with a broadband IR emitter and a MEMS microphone. This allows a particularly small sensor with a sensitivity of 50 ppm and a wide measuring range up to 5000 ppm CO2.

A laser-based PA module with a resonant measuring cell has been developed for detecting gas leaks, for example from gas pipes in the ground. The operation of the measuring cell is actively stabilized, and concentrations of methane (CH4) and ethane (C2H6) are achieved with a resolution of a few ppb in each case.

Applications »Photoacoustic spectroscopy«

Gases can be detected very accurately and selectively using photoacoustic spectroscopy (PAS). Possible applications range from harsh industrial environments to indoor air monitoring and medical applications. Fraunhofer IPM develops photoacoustic measurement systems that are particularly compact and energy-saving, depending on the application.

Refrigerant detection

Sensors for refrigerant detection can help monitor the strict regulations on the use of greenhouse gases. We develop cost-effective, precise, compact, and reliable refrigerant detectors.

 

Gas leak detection

We develop sensitive and convenient measurement technology for the quantitative leakage testing of gas infrastructure.

Sustainable agriculture

 

A wide variety of measurement data gathered in a digital ecosystem can make agriculture more efficient and climate-friendly.

Emission monitoring

 

Sensors that measure gas concentrations are used for the safety and protection of the environment – in everyday civil life as well as in industrial production.

Indoor air monitoring

 

We develop measuring systems for monitoring indoor air quality – in buildings as well as in vehicles.

Arterial blood gas test

Transcutaneous blood gas sensors monitor the respiratory function of intensive-care patients very exactly without the need for a breathing mask. 

Publications »Photoacoustic Spectroscopy«

Jahr
Year
Titel/Autor:in
Title/Author
Publikationstyp
Publication Type
2025 Optimizing Analog Front End Architectures for Enhanced SNR in Photoacoustic Imaging
Kindorf, Sebastian; Weber, Christian; Bierer, Benedikt; Wöllenstein, Jürgen
Konferenzbeitrag
Conference Paper
2025 Design of a Refrigerant Leak Sensor based on the Photoacoustic Dual-Chamber Detection Method
Yassine, Hassan; Weber, Christian; El-Safoury, Mahmoud; Brugger, Nicolas; Schmitt, Katrin; Wöllenstein, Jürgen
Konferenzbeitrag
Conference Paper
2024 Miniaturized Photoacoustic Sensors for the Detection of Trace Gases in Ambient Air
Weber, Christian
Dissertation
Doctoral Thesis
2024 Miniaturisierter CO2-Sensor mit wafer-gebondetem photoakustischen MEMS-Detektor
Gassner, Simon
Dissertation
Doctoral Thesis
2024 Photoakustische Detektion von BTEX-Komponenten im UV-Bereich
Hamburger, Miguel; Herbst, Johannes; Strahl, Thomas; Brunner, Raimund; Weber, Christian; Schmitt, Katrin; Wöllenstein, Jürgen; Kondziella, Ralph
Konferenzbeitrag
Conference Paper
2024 Miniaturized two-chamber photoacoustic CO2 sensor with a wafer-bonded MEMS (micro-electro-mechanical systems) detector
Gaßner, Simon; Essing, Simon; Tumpold, David; Schmitt, Katrin; Wöllenstein, Jürgen
Zeitschriftenaufsatz
Journal Article
2024 Improving the performance of artificial neural networks trained on synthetic data in gas spectroscopy - a study on two sensing approaches
Goldschmidt, Jens; Moser, Elisabeth; Nitzsche, Leonard; Bierl, Rudolf; Wöllenstein, Jürgen
Zeitschriftenaufsatz
Journal Article
2024 Towards a Miniaturized Photoacoustic Sensor for Transcutaneous CO2 Monitoring
El-Safoury, Mahmoud; Weber, Christian; Yassine, Hassan; Wöllenstein, Jürgen; Schmitt, Katrin
Zeitschriftenaufsatz
Journal Article
2024 Detection of SO2F2 Using a Photoacoustic Two-Chamber Approach
Yassine, Hassan; Weber, Christian; Eberhardt, Andre; El-Safoury, Mahmoud; Wöllenstein, Jürgen; Schmitt, Katrin
Zeitschriftenaufsatz
Journal Article
2023 How to Turn a MEMS Microphone Into a Photoacoustic Sensor: An Experimental Study
Strahl, Thomas; Steinebrunner, Jonas; Weber, Christian; Wöllenstein, Jürgen; Schmitt, Katrin
Konferenzbeitrag
Conference Paper
2023 Evaluation of Photoacoustic Detectors for Methyl Bromide Sensing
Yassine, Hassan; Weber, Christian; Wöllenstein, Jürgen; Schmitt, Katrin
Konferenzbeitrag
Conference Paper
2023 Photoacoustic methane detection inside a MEMS microphone
Strahl, Thomas; Steinebrunner, Jonas; Weber, Christian; Wöllenstein, Jürgen; Schmitt, Katrin
Zeitschriftenaufsatz
Journal Article
2023 Miniaturized SMD-Reflow-Capable Photoacoustic CO2-Sensor Using a Dual-Chamber Approach
Gaßner, Simon; Essing, Simon; Tumpold, David; Schmitt, Katrin; Wöllenstein, Jürgen
Konferenzbeitrag
Conference Paper
2023 Resonant photoacoustic cells for laser-based methane detection
Schmitt, Katrin; Sendelbach, Mara; Weber, Christian; Wöllenstein, Jürgen; Strahl, Thomas
Zeitschriftenaufsatz
Journal Article
2023 Towards a Miniaturized Photoacoustic Detector for the Infrared Spectroscopic Analysis of SO2F2 and Refrigerants
Yassine, Hassan; Weber, Christian; Brugger, Nicolas; Wöllenstein, Jürgen; Schmitt, Katrin
Zeitschriftenaufsatz
Journal Article
2023 Novel approach for efficient resonance tracking in photoacoustic gas sensor systems based on a light-induced wall signal
Weber, Christian; Kapp, Johannes; Wöllenstein, Jürgen; Schmitt, Katrin
Zeitschriftenaufsatz
Journal Article
2022 Verfahren und Sensor zum Bestimmen einer Konzentration eines Zielgases im Blut eines Lebewesens
Schmitt, Katrin; Weber, Christian; Wöllenstein, Jürgen; Yassine, Hassan
Patent
2022 Fluidmesszelle für einen photoakustischen Sensor
Weber, Christian; Kapp, Johannes; Schmitt, Katrin
Patent
2022 Gasmesszelle für einen photoakustischen Sensor und Verfahren zum Erfassen einer Eigenschaft eines Probengases
Weber, Christian; Kapp, Johannes; Schmitt, Katrin; Strahl, Thomas; Sendelbach, Mara
Patent
2022 LED-basierter, miniaturisierter photoakustischer CO2-Sensor zur Umgebungsluftüberwachung
Weber, Christian; Yassine, Hassan; Eberhardt, Andre; Schmitt, Katrin; Wöllenstein, Jürgen
Konferenzbeitrag
Conference Paper
2022 Miniaturisierter transkutaner Sensor für die Überwachung der CO2-Blutgaswerte
El-Safoury, Mahmoud; Weber, Christian; Yassine, Hassan; Wöllenstein, Jürgen; Schmitt, Katrin
Konferenzbeitrag
Conference Paper
2022 Resonante photoakustische Zellen zum laserbasierten Methannachweis
Schmitt, Katrin; Sendelbach, Mara; Strahl, Thomas; Weber, Christian; Wöllenstein, Jürgen
Konferenzbeitrag
Conference Paper
2022 Anodically Bonded Photoacoustic Transducer: An Approach towards Wafer-Level Optical Gas Sensors
Gassner, Simon; Schaller, Rainer; Eberl, Matthias; Koblinski, Carsten von; Essing, Simon; Ghaderi, Mohammadamir; Schmitt, Katrin; Wöllenstein, Jürgen
Zeitschriftenaufsatz
Journal Article
2021 On-Board Monitoring of SO2 Ship Emissions Using Resonant Photoacoustic Gas Detection in the UV Range
El-Safoury, Mahmoud; Dufner, Miguel; Weber, Christian; Schmitt, Katrin; Pernau, Hans-Fridtjof; Willing, Bert; Wöllenstein, Jürgen
Zeitschriftenaufsatz
Journal Article
2021 Comparison of laser-based photoacoustic and optical detection of methane
Strahl, Thomas; Herbst, Johannes; Maier, Eric; Rademacher, Sven; Weber, Christian; Pernau, Hans-Fridtjof; Lambrecht, Armin; Wöllenstein, Jürgen
Zeitschriftenaufsatz
Journal Article
2020 Gassensor-basiertes Analysesystem zur Bestimmung des Reinheitsgrades von Kältemitteln (CONTECT-R). Schlussbericht
El-Safoury, Mahmoud; Weber, Christian
Bericht
Report
2020 Smart Technologies for Indoor Environmental Quality Control
Ortiz Pérez, Alvaro
Dissertation
Doctoral Thesis
2020 The Optimization of a Photoacoustic Refrigerant Sensor System Using a Three-Chamber Concept
El-Safoury, Mahmoud; Weber, Christian; Wöllenstein, Jürgen; Kiesewetter, Olaf
Konferenzbeitrag
Conference Paper
2020 Miniaturized photoacoustic detection of organofluorine-based refrigerants
El-Safoury, Mahmoud; Weber, Christian; Kiesewetter, Olaf; Hespos, Yvonne; Eberhardt, André; Schmitt, Katrin; Wöllenstein, Jürgen
Zeitschriftenaufsatz
Journal Article
2020 Micro PA detector: Pushing the limits of mid IR photoacoustic spectroscopy integrated on silicon
Coutard, Jean-Guillaume; Berthelot, Audrey; Glière, Alain; Lhermet, Hélène; Scherer, Benjamin; Strahl, Thomas; Teulle, Alexandre; Verdot, Thierry
Konferenzbeitrag
Conference Paper
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