WO1996002820A1 - Detecteur de gaz photo-acoustique comportant un microphone infrasonore - Google Patents

Detecteur de gaz photo-acoustique comportant un microphone infrasonore Download PDF

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Publication number
WO1996002820A1
WO1996002820A1 PCT/CH1995/000138 CH9500138W WO9602820A1 WO 1996002820 A1 WO1996002820 A1 WO 1996002820A1 CH 9500138 W CH9500138 W CH 9500138W WO 9602820 A1 WO9602820 A1 WO 9602820A1
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WO
WIPO (PCT)
Prior art keywords
microphone
gas
membrane
photoacoustic
optical
Prior art date
Application number
PCT/CH1995/000138
Other languages
German (de)
English (en)
Inventor
Oscar Oehler
Philipp Bachmann
Urs Bögli
Original Assignee
Aritron Instrumente Ag
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Aritron Instrumente Ag filed Critical Aritron Instrumente Ag
Publication of WO1996002820A1 publication Critical patent/WO1996002820A1/fr

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Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/1702Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/1702Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
    • G01N2021/1704Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids in gases

Definitions

  • the invention is in the fields of acoustics and optics, in particular it relates to photoacoustic gas detection. It is a device for the selective detection of gases, wherein an optical infrasound microphone is used instead of a condenser microphone for measuring the acoustic signal.
  • the photoacoustic method for the selective detection of gases is well known. Attention is drawn to the work of D. Sourlier and O. Oehler (J. de Phys. Suppl. 10, 587 (1983)). The method allows the selective and very reliable detection of gases. Devices with high detection reliability meet a great need. The climate control in closed rooms, for example, can be used as applications.
  • the photoacoustic effect is based on the measurement of the pressure fluctuations that are generated in the gas collection cell when absorbing intensity-modulated infrared radiation.
  • Microphones are generally used to measure these pressure changes.
  • the charge A high voltage of 100 to 200 V is required. Apart from the provision of this high voltage, considerable effort is required to galvanically decouple it from the useful signal.
  • the so-called electret microphones are significantly more user-friendly.
  • These are condenser microphones that are provided with an electrically pre-polarized film, the so-called electret film. This film, like the microphone diaphragm itself, is subject to temperature and moisture influences, which can affect sound pressure measurement and thus photoacoustic detection.
  • the so-called optophones are known. With these microphones, the membrane position is not measured via a capacitance measurement, but via an optical distance measurement. In this context, it should be pointed to the work of S.M. Park and G.J. Diebold with the title "Interferometric microphone for optoacoustic spectroscopy" pointed out in Rev. Sei. Instruments, 58, 772 (1987).
  • the membrane is operated in acoustic resonance.
  • the deflection of the membrane is preferably measured using an optical position sensor. It is also intended to use a gas-permeable membrane as the microphone membrane, which before serving in its additional function as a gas exchange device for gas exchange of the gas detector with the environment.
  • optical microphones correspond to this
  • the optical measurement be carried out selectively, but after mechanical averaging over the entire membrane surface.
  • the membrane as a largely rigid unit converts the pressure signal into a mechanical movement. implementation and thus has a low fundamental resonance frequency.
  • This goal can be achieved by choosing the elastic properties and / or the mechanical inertia of the membrane surface.
  • this path is not feasible for microphones for use in audio technology, because in those applications a frequency response that is as constant as possible is required down to the 10 to 20 kHz range.
  • this means that the basic resonance frequency of the membrane must be very high, at least above the hearing range.
  • a favorable signal / noise ratio can be achieved if the microphone membrane is operated in acoustic resonance. In this case, a total movement of the membrane is guaranteed, on the other hand, the narrow resonance bandwidth means a reduction in noise.
  • An efficient transmission of the sound signal to the membrane vibration can be expected if it is not a higher vibration mode, but the basic resonance frequency of the membrane that is excited. Since the resonance frequency of the membrane depends on the temperature, the
  • the frequency of the photoacoustic signal and thus the modulation frequency of the light may have to track the resonance frequency of the microphone membrane.
  • the frequency tracking can even be dispensed with.
  • gas-permeable membranes have acoustic low-pass properties. This property is very important for carrying out a photoacoustic measurement, because on the one hand the photoacoustic cell must be sufficiently acoustically damned to ensure the build-up of a photoacoustic signal, and on the other hand disturbing external room sound must be kept away from the photoacoustic cell.
  • the acoustic damping of a gas-permeable membrane is sufficient even at a low frequency in the range from 10 to 20 Hz, so that a reliable photoacoustic measurement can be carried out in a photoacoustic gas detector closed with such a membrane.
  • the membrane allows a diffusion-controlled gas flow, so that gas exchange between the gas cuvette and its surroundings is ensured.
  • a gas-permeable membrane which is used as a microphone membrane, therefore has the double function of a device for detecting the photoacoustic pressure signal, ie a microphone membrane, and one
  • a condenser microphone should be less suitable for this purpose, since the required small spacing of the condenser plates, which extends over the entire membrane surface, impedes the gas flow and consequently an efficient gas exchange is not guaranteed.
  • a selective optical measurement of the condenser plates since the required small spacing of the condenser plates, which extends over the entire membrane surface, impedes the gas flow and consequently an efficient gas exchange is not guaranteed.
  • Microphone membrane position sufficient gas exchange.
  • the photoacoustic vibration movement of the membrane can have a favorable effect on the gas flow.
  • the usability of marketable components is favorable.
  • the availability of cheap, sophisticated microphones has had a very advantageous effect on the applicability of the photoacoustic effect.
  • FIG. 1 shows the structure of a photo-acoustic device corresponding to the prior art for measuring light-absorbing gases.
  • FIG 2 is an illustration of the inventive photoacoustic gas detection device with an optical infrasound microphone.
  • Figure 3 is an illustration of a photoacoustic device in which the microphone membrane is also the gas exchange device.
  • FIG.l shows the structure of a gas detection device based on photoacoustic principle, which largely corresponds to the prior art.
  • the optical filter 3 can optionally be dispensed with if the radiation is sufficiently monochromatic or if high gas selectivity is not required. Likewise, no mechanical light interrupter is required if the emitter 2 can be modulated via the current / voltage supply.
  • the intensity-modulated radiation from the light source 1 penetrates through a window 15 into the photoacoustic gas detector 5 and can produce pressure fluctuations there when the radiation is absorbed by the measurement gas, which fluctuations are measured with the microphone 6.
  • the microphone signal is evaluated by signal processing means 10.
  • the measuring gas is fed to the gas detector 5 by means of the gas supply device 9.
  • the use of an infrasound microphone 6, the membrane 7 of which has such elastic properties and / or mechanical inertia, is advantageous as a novelty, so that the resonance frequency of the microphone membrane 7 lies in the infrasound range.
  • FIG. 2 shows the representation of an example of the inventive gas sensor device. It is also based on the photoacoustic principle. Intensity-modulated and possibly monochromatized radiation from at least one light source 1, 1 'by means of optical filters 3, 3' penetrates through the windows 15, 15 'into the photoacoustic cell and acts on the measuring gas located there. The pressure signal occurring when the radiation is absorbed is recorded by at least one infrasound microphone 6. The same consists of at least one membrane 7, the position of which is determined with the aid of a position sensor 8. The same can, for example, according to the classic principle, the membrane system capacitively resp. measure inductively or optically.
  • the optical position sensor is composed of a light source 8 ′, in particular a laser diode, and an optical detector 8 ′′.
  • a position sensor 8 based on an interference measurement is provided, as is used for information acquisition from CD sound carriers.
  • the microphone membrane 7 has such elastic properties and such a high mechanical inertia that it meanders over the membrane surface. takes up the pressure signal. This means that the basic resonance frequency of the membrane is very low, preferably in the infrasound range.
  • the modulation frequency of the light source 1 and, if appropriate, the additional light source 1 ' is selected such that the microphone membrane 7 is excited to a resonance oscillation on account of the photoacoustic effect.
  • regulation of the modulation frequency of the light sources 1, 1 'with the aid of the control device 12, 12' is provided for maximum deflection of the microphone membrane.
  • the resonance mode does not have to be limited to an optical microphone; it is also useful with a condenser microphone. Because of the mechanical averaging, however, the microphone with an optical position sensor 8 is particularly well suited for the operation of the microphone membrane 7 in acoustic resonance.
  • the signal of the optical position sensor 8 is fed to a suitable signal processing device 10.
  • the gas detector 5 is provided with the measurement gas by means of a gas supply device 9, which, as shown in FIG. 2, consists of valves
  • the photoacoustic gas detection device in turn consists of a light source 1, the radiation of which, if necessary, passes through an optical filter 3 through the window 15 into the photoacoustic gas detector 5.
  • the photoacoustic signal is in turn detected by means of at least one microphone 6, 6 '.
  • At least one of these microphones is an infrasound microphone which consists of a microphone membrane 7 'and an optical position sensor 8.
  • the measuring gas is fed to the gas detector 5 through the gas-permeable microphone membrane 7 '.
  • such a membrane permits gas exchange with the surroundings, but, as has already been mentioned, is an efficient acoustic low-pass filter to ensure a sufficiently interference-free photoacoustic measurement covered, the gas flow through the membrane 7 'is only slightly impeded. If necessary, the radiation from the light source 8 'in the position sensor 8 is directed via a light guide 18 onto the microphone membrane, which may be gas-permeable (7'), and / or the reflected light is fed through a second light guide 18 'to the light detector 8 " .

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

L'invention concerne un procédé et un dispositif de détection photo-acoustique de gaz ou de constituants d'un mélange gazeux. Cette invention se caractérise en de que le détecteur photo-acoustique (5) est en connexion acoustique avec au moins un microphone infrasonore (6, 6'). La membrane (7, 7') du microphone peut être mise en résonance acoustique et son déplacement est détecté à l'aide d'un détecteur de position (8) composé d'une source lumineuse (8') et d'un détecteur de lumière (8'). Il est également prévu d'utiliser, comme membrane de microphone, une membrane perméable aux gaz (7'), de manière à ce qu'elle serve simultanément de détecteur de pression photo-acoustique et de dispositif échangeur de gaz (9).
PCT/CH1995/000138 1994-07-14 1995-06-20 Detecteur de gaz photo-acoustique comportant un microphone infrasonore WO1996002820A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH2245/94-9 1994-07-14
CH224594A CH686589A5 (de) 1994-07-14 1994-07-14 Photoakustischer Gasdetektor mit optischem Infraschallmikrophon.

Publications (1)

Publication Number Publication Date
WO1996002820A1 true WO1996002820A1 (fr) 1996-02-01

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WO (1) WO1996002820A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5933245A (en) * 1996-12-31 1999-08-03 Honeywell Inc. Photoacoustic device and process for multi-gas sensing
WO2014102486A1 (fr) * 2012-12-27 2014-07-03 Commissariat A L'energie Atomique Et Aux Energies Alternatives Microbaromètre à soufflet et à transducteur interférométrique
US8848191B2 (en) 2012-03-14 2014-09-30 Honeywell International Inc. Photoacoustic sensor with mirror
TWI735466B (zh) * 2015-09-29 2021-08-11 挪威商新泰夫提圖股份有限公司 雜波消除偵測器

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102008047658B3 (de) 2008-09-12 2010-01-28 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Gassensor und Verwendung eines Gassensors
DE102009029002B3 (de) 2009-08-28 2011-01-27 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Photoakustischer Sensor sowie Verfahren zu seiner Herstellung und Verwendung
DE102009045724B3 (de) 2009-10-15 2011-01-27 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Photoakustischer Gassensor sowie Verfahren zu seiner Herstellung und Verwendung

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1985003574A1 (fr) * 1984-02-07 1985-08-15 Oskar Oehler Installation pour la detection photo-acoustique de gaz
DE3817791A1 (de) * 1988-05-26 1989-12-07 Honeywell Elac Nautik Gmbh Vorrichtung zum selektiven gasnachweis und/oder zur selektiven gaskonzentrationsbestimmung
WO1989012375A1 (fr) * 1988-06-02 1989-12-14 Carvalho, Aparecido, Augusto De Microphone optique

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1985003574A1 (fr) * 1984-02-07 1985-08-15 Oskar Oehler Installation pour la detection photo-acoustique de gaz
DE3817791A1 (de) * 1988-05-26 1989-12-07 Honeywell Elac Nautik Gmbh Vorrichtung zum selektiven gasnachweis und/oder zur selektiven gaskonzentrationsbestimmung
WO1989012375A1 (fr) * 1988-06-02 1989-12-14 Carvalho, Aparecido, Augusto De Microphone optique

Non-Patent Citations (4)

* Cited by examiner, † Cited by third party
Title
A. DI LIETO ET AL.: "design of an optoacoustic cell for laser-stark spectroscopy", APPLIED PHYSICS B. PHOTOPHYSICS AND CHEMISTRY, vol. 27, 1982, HEIDELBERG DE, pages 1 - 3 *
G J PAPADOPOULOS ET AL.: "amplitude and phase study of the photoacoustic effect", BRITISH JOURNAL OF APPLIED PHYSICS, vol. 25, no. 4, 14 April 1992 (1992-04-14), LETCHWORTH GB, pages 722 - 726, XP000288742 *
J.H. CHU ET AL.: "michelson interferometric detection for optoacoustic spectroscopy", OPTICS COMMUNICATIONS, vol. 2319, no. 2-4, 1992, AMSTERDAM NL, pages 135 - 139 *
M. H. DE PAULA: "optical microphone for photoacoustic-spectroscopy", JOURNAL OF APPLIED PHYSICS, vol. 64, no. 7, 1988, pages 3722 - 3724 *

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5933245A (en) * 1996-12-31 1999-08-03 Honeywell Inc. Photoacoustic device and process for multi-gas sensing
US8848191B2 (en) 2012-03-14 2014-09-30 Honeywell International Inc. Photoacoustic sensor with mirror
WO2014102486A1 (fr) * 2012-12-27 2014-07-03 Commissariat A L'energie Atomique Et Aux Energies Alternatives Microbaromètre à soufflet et à transducteur interférométrique
FR3000545A1 (fr) * 2012-12-27 2014-07-04 Commissariat Energie Atomique Microbarometre a soufflet et a transducteur interferometrique
US9952109B2 (en) 2012-12-27 2018-04-24 Commissariat A L'energie Atomique Et Aux Energies Alternatives Microbarometer with a bellows and with an interferometric transducer
TWI735466B (zh) * 2015-09-29 2021-08-11 挪威商新泰夫提圖股份有限公司 雜波消除偵測器

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