EP1902303A1 - Detecteur photoacoustique en champ libre - Google Patents

Detecteur photoacoustique en champ libre

Info

Publication number
EP1902303A1
EP1902303A1 EP06754567A EP06754567A EP1902303A1 EP 1902303 A1 EP1902303 A1 EP 1902303A1 EP 06754567 A EP06754567 A EP 06754567A EP 06754567 A EP06754567 A EP 06754567A EP 1902303 A1 EP1902303 A1 EP 1902303A1
Authority
EP
European Patent Office
Prior art keywords
excitation light
acoustic
photoacoustic
detector according
photoacoustic detector
Prior art date
Legal status (The legal status 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 status listed.)
Ceased
Application number
EP06754567A
Other languages
German (de)
English (en)
Inventor
Klaus Breuer
Andrew H. Kung
Andras Miklos
Judit Angster
Klaus Sedlbauer
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Original Assignee
Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
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 Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV filed Critical Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Publication of EP1902303A1 publication Critical patent/EP1902303A1/fr
Ceased legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/1702—Systems 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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/1702—Systems 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
    • G01N2021/1704—Systems 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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/028—Material parameters
    • G01N2291/02809—Concentration of a compound, e.g. measured by a surface mass change

Definitions

  • the invention relates to a photoacoustic free-field detector. With such a photoacoustic detector should also be detected in a simple manner, a small amount of trace gases without expensive sampling.
  • Photoacoustic detection takes place in that excitation light is absorbed by absorbing substances. This causes a warming.
  • the heating leads to expansion, especially when gases are heated.
  • the heating of the gases can also be effected indirectly, for example by heated solid particles which heat the surrounding gas. If the heating and the resulting expansion take place sufficiently fast, sound is created that can be detected with an acoustic sensor, such as a microphone.
  • the detected sound is thus a measure of the absorbed energy, which depends on the intensity of the excitation light and the type and concentration of the absorbing substances.
  • photoacoustic detectors which are formed of closed cells with transparent windows. In such detectors, the actual photoacoustic detection takes place in an acoustic
  • Elements usually mirrors, are arranged outside the measuring cell, so that the excitation light has to pass through two windows each time it passes through.
  • the excitation light is weakened and there is only a small signal amplification.
  • the Absorption in the windows can also have the disadvantage that an unwanted photoacoustic background signal is generated by the absorption, which is superimposed on the measurement signal and thus reduces the measurement sensitivity.
  • the inlet and outlet are open to the gas but closed to the generated sound waves.
  • the outlets and inlets closed for sound waves only allow a difficult supply of the air to be examined. Therefore, so-called acoustically open photoacoustic detectors have been developed. In such photoacoustic detectors, however, the sound pressure caused by the absorption on the microphone is already so weakened that the measuring sensitivity is undesirably reduced.
  • JP 62 272 1 53 A is a photoacoustic
  • Measuring arrangement with an open cell known.
  • a measuring cell and a reference cell are present, which are pressed onto the surface of a sample. This creates airtight areas.
  • a fiber introduces modulated light to illuminate the sample. This creates pressure waves that reach a microphone. The position of the microphone is adjustable.
  • an open photoacoustic measuring cell for assessing the skin, in particular human skin, using a fiber optic cable and a microphone is known.
  • This measuring cell is characterized in that an open, non-resonant photoacoustic measuring chamber is provided.
  • the measuring cell is housed in addition to the microphone and the associated amplifier.
  • two brackets are provided for the displacement-free mounting of the measuring cell on a body part.
  • One embodiment of the microphone is an electret microphone.
  • a portable measuring cell for measuring the photosynthetic activity of photosynthetically active tissue is known.
  • the measuring cell is housed in a housing which is open at one end.
  • an acoustic sensor is arranged.
  • the housing is attached to or above the photosynthetic active probe.
  • Both a modulated and a continuously radiating light source are provided, with means being provided for conducting both the modulated light and the continuous light to the sample.
  • a radially or azimuthally non-resonant photoacoustic flow cell which operates without windows. This turns off the background signal of the window.
  • the cell is designed as a long tube.
  • the length of the cell is 34 x 10 3 cm divided by the modulation frequency of the light source and is made of conductive material.
  • a measuring chamber for photoacoustic sensors for the continuous measurement of radiation-absorbing substances, in particular of radiation-absorbing particles in gaseous samples is known. It is provided with at least one inlet and at least one outlet for the samples. It has a longitudinally flowed through by the sample
  • Pipe section in which a microphone is arranged. Furthermore, at least one aligned with the pipe section entrance and exit point for the laser beam is present. The entry and exit point are spaced by a respective chamber from the measuring tube.
  • two inlets are provided at the opposite ends of the pipe section and at least one outlet at a position midway between the inlets.
  • a photoacoustic measuring device for continuously determining the concentration of particles contained in a gas is known. It has two measuring cells, which are parallel to each other from the light of a laser be irradiated. The first measuring cell is fed gas without particles. In the optical path in front of each of the two measuring cells is a chopper. The first chopper is operated at a chopper frequency which corresponds to the resonant frequency of the first measuring cell, while the chopper frequency of the second chopper corresponds to the resonant frequency of the second measuring cell. With such a measuring device, for example, the particle content in exhaust gases, for. B. of vehicles.
  • Object of the present invention is now to provide an acoustically open photoacoustic free-field detector, in which a sufficient sound pressure at the acoustic sensor is present.
  • the object of the invention is also to provide a corresponding acoustic measuring method.
  • the solution to this problem is given in the independent claims. Advantageous developments can be found in subclaims.
  • a photoacoustic detector is provided with an acoustically open measuring range which is not completely enclosed by a housing. This is to be understood as meaning a measuring range in which the sound pressure generated by the absorption can escape at the relatively large inlets and outlets of the sample air.
  • This photoacoustic detector comprises means for introducing excitation light into the measurement area, so that the excitation light can be absorbed by the absorbents present in the measurement area to generate acoustic energy. Furthermore, at least one acoustic sensor is provided. The detector is characterized in that there are means for concentrating the acoustic energy. With these means, a local maximum of the sound pressure can be achieved at least one position. A local maximum of the sound pressure is to be understood as meaning a position at which the sound pressure is noticeably increased in comparison to the immediate environment. The at least one acoustic sensor is then arranged in the vicinity of the at least one position at which the local maximum of the generated sound pressure is present or can be generated. The concentration of the generated sound pressure makes it possible, even in an acoustically open measuring range with a sufficient
  • Sensitivity can be measured.
  • sample air is referred to above, since the main field of application is certainly the measurement of trace gases or particles in air or a gas mixture, it is conceivable to use a photoacoustic free field detector also for the measurement of liquids.
  • a photoacoustic free field detector also for the measurement of liquids.
  • the generation of a sufficiently high sound pressure is more difficult in liquids than in gases, but the photoacoustic measurement of absorbing substances in liquids is known and proven to be practicable.
  • a further increase in the photoacoustic signal obtained can be achieved if optically reflecting elements are arranged so that a multiple passage of the excitation light through the measuring range can take place. In this case, a higher energy is absorbed, which then leads to a corresponding higher sound production.
  • One way to concentrate the acoustic energy is to provide elements that influence the acoustic energy generated by the absorption of the excitation light such that at least one position with a local maximum of the sound pressure is achievable. Thus, the already generated sound is steered accordingly.
  • the concentration of the acoustic energy elements that allow such a distribution of the excitation light that the acoustic energy generated by the excitation light has a distribution such that a concentration of the acoustic energy can take place. Even so, at least one position with a local maximum of the sound pressure can be achieved.
  • the two methods ie concentrating the already generated sound and distributing the excitation light in such a way that the resulting sound due to the geometric arrangement itself tends to concentrate at certain positions, can be combined. Both variants allow a concentration of acoustic energy in an acoustically open measuring range.
  • acoustic mirrors are suitable. With these, the generated sound can be steered so that positions are achieved with a local maximum of the sound pressure.
  • optically reflective elements are suitable. Particularly suitable here are optical mirrors.
  • the photoacoustic detector so that the excitation light can be distributed in such a way that it is possible to generate acoustic energy in a circular and / or helical and / or polygonal subregion of the measuring region. With such a distribution of the excitation light, positions are formed at which a local maximum of the sound pressure occurs.
  • the present photoacoustic detector can also be operated with pulsed and / or modulated excitation light. It makes sense to tune the modulation frequency of the light pulses to a maximum sensitivity of the acoustic sensor.
  • diode lasers emitting infrared radiation can be modulated at a frequency of up to several hundred megahertz. Because of the limited diameter of the laser beams at these high frequencies, these can not be used in photoacoustics. The frequency range from 100 kHz to 500 kHz, however, is suitable for photoacoustic measurements. It is possible to modulate both the intensity and the wavelength of the excitation light.
  • Pulsed solid-state lasers that emit pulses with a duration of 10 to 50 ns are suitable for operating the detector with pulsed excitation light.
  • the temporal profile of the pulses is approximately Gaussian.
  • the absorption of the laser pulse by a gas leads to an acoustic pulse whose profile corresponds to the time change of the exciting light pulse.
  • a unipolar laser pulse thus produces a bipolar acoustic pulse of approximately the same duration.
  • Such bipolar acoustic pulses are caused throughout the irradiated area, as far as absorbing substances are present.
  • the total duration of the acoustic pulse outside the laser pulse is proportional to the time required for the acoustic pulse to travel through the laser pulse.
  • the duration of the acoustic pulse can be estimated at 3 ⁇ s.
  • the frequency spectrum of such an acoustic pulse is approximately Gaussian around a peak frequency of 300 kHz.
  • a suitable design of the condenser and / or electret microphone results when at a repetition frequency of the excitation light of 1 to 10khz can be measured at a harmonic.
  • a maximum sensitivity of the microphone can be achieved by tuning the repetition frequency of the excitation light.
  • an ultrasonic sensor as an acoustic sensor. It is quite conceivable not to use a broadband tuned ultrasonic sensor. For example, it lends itself to use an ultrasonic sensor, the on
  • Frequency values such as 40 kHz and / or 80 kHz and / or 120 kHz is tuned. Such ultrasonic sensors are available at low cost.
  • the described photoacoustic detector and a method in which absorbing substances are detected with the photoacoustic detector are well suited for monitoring indoor air quality, in particular for monitoring the air taken in indoor ventilation systems. This is due to the fact that photoacoustic detection can cover a broad measuring range for a wide variety of absorbing substances that can be irritating indoors. For aeration facilities, it is also necessary that a costly sampling is unnecessary, since a rapid adaptation of the ventilation to the detected pollutant concentrations is desired.
  • Figures 1 and 2 show an exemplary photoacoustic detector.
  • the exciting light beam 1 of a laser enters the measuring range. Due to the two optical mirrors 2, which have a diameter of about 50 mm, the light is reflected several times. The reflected light rays are in one plane (FIG. 3).
  • the first acoustic mirror 3 is a square-shaped flat mirror having a thickness of 8 mm and a side length of 100 mm. He has in the middle of a recess for the microphone 5.
  • the opposite second acoustic mirror 4 is cuboid with a side length of 100 mm. In the outer region of the second acoustic mirror 4 has a thickness of 30 mm.
  • the second acoustic mirror In an inner area having a diameter of 80 mm, the second acoustic mirror is concave toward the measuring area.
  • the microphone 5 is located on the axis of symmetry of the acoustic mirrors.
  • the microphone 5 has a distance of 25 mm from the second acoustic mirror 4.
  • FIG. 3 shows a structure in which the exciting light beam 1 passes through the measuring area several times. Each passage absorbs a certain amount of absorbent material. The reflection of the light beam 1 takes place at the mirrors 2, which are formed as optical mirrors.
  • FIG. 4 shows a detailed view of the second acoustic mirror 4. Thereafter, the maximum depression is 16 mm.
  • the radial distance from the center of the second acoustic mirror 4 is denoted by X; the depth of the depression with z.

Landscapes

  • 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 détecteur photoacoustique présentant une zone de mesure qui n'est pas entièrement enfermée dans un boîtier et qui est ouverte acoustiquement. Ce détecteur comprend des moyens pour introduire une lumière d'excitation dans la zone de mesure de sorte que cette lumière puisse être absorbée par des substances absorbantes se trouvant dans la zone de mesure pour produire une énergie acoustique. Le détecteur selon l'invention comprend par ailleurs au moins un capteur acoustique (5) et il se caractérise en ce qu'il présente des moyens (2, 3, 4) destinés à concentrer l'énergie acoustique pour obtenir au moins à un emplacement un maximum local de la pression acoustique, le ou les capteurs acoustiques (5) étant disposés à proximité du ou des emplacements auxquels le maximum local de la pression acoustique est atteint ou peut être produit. L'invention concerne en outre un procédé associé.
EP06754567A 2005-06-28 2006-06-26 Detecteur photoacoustique en champ libre Ceased EP1902303A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102005030151A DE102005030151B3 (de) 2005-06-28 2005-06-28 Photoakustischer Freifelddetektor
PCT/EP2006/006131 WO2007000297A1 (fr) 2005-06-28 2006-06-26 Detecteur photoacoustique en champ libre

Publications (1)

Publication Number Publication Date
EP1902303A1 true EP1902303A1 (fr) 2008-03-26

Family

ID=36851157

Family Applications (1)

Application Number Title Priority Date Filing Date
EP06754567A Ceased EP1902303A1 (fr) 2005-06-28 2006-06-26 Detecteur photoacoustique en champ libre

Country Status (5)

Country Link
US (1) US20090038375A1 (fr)
EP (1) EP1902303A1 (fr)
JP (1) JP5022363B2 (fr)
DE (1) DE102005030151B3 (fr)
WO (1) WO2007000297A1 (fr)

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DE102007014519A1 (de) * 2007-03-27 2008-10-02 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Photoakustischer Detektor zur Messung von Feinstaub
DE102007043951B4 (de) * 2007-09-14 2009-07-30 Protronic Innovative Steuerungselektronik Gmbh Vorrichtung zur Detektion von Molekülen in Gasen
JP5371268B2 (ja) * 2008-03-14 2013-12-18 三菱重工業株式会社 ガス濃度計測方法および装置
US9572497B2 (en) 2008-07-25 2017-02-21 Helmholtz Zentrum Munchen Deutsches Forschungszentrum Fur Gesundheit Und Umwelt (Gmbh) Quantitative multi-spectral opto-acoustic tomography (MSOT) of tissue biomarkers
US9271654B2 (en) 2009-06-29 2016-03-01 Helmholtz Zentrum Munchen Deutsches Forschungszentrum Fur Gesundheit Und Umwelt (Gmbh) Thermoacoustic imaging with quantitative extraction of absorption map
WO2011012274A1 (fr) 2009-07-27 2011-02-03 Helmholtz Zentrum München Deutsches Forschungszentrum Für Gesundheit Und Umwelt (Gmbh) Dispositif d’imagerie et procédé pour l’imagerie opto-acoustique de petits animaux
US8848191B2 (en) 2012-03-14 2014-09-30 Honeywell International Inc. Photoacoustic sensor with mirror
EP2742854B1 (fr) * 2012-12-11 2021-03-10 iThera Medical GmbH Dispositif portatif et procédé pour imagerie opto-acoustique tomographique d'un objet
EP2754388B1 (fr) 2013-01-15 2020-09-09 Helmholtz Zentrum München Deutsches Forschungszentrum für Gesundheit und Umwelt GmbH Système et procédé pour imagerie opto-acoustique à haut débit de meilleure qualité d'un objet
USD761346S1 (en) * 2014-11-20 2016-07-12 David Spampinato Temple sleeve
NO344002B1 (en) 2015-09-29 2019-08-12 Sintef Tto As Optical gas detector
DE102015117405A1 (de) * 2015-10-13 2017-04-13 Rbr Messtechnik Gmbh Vorrichtung und Verfahren zur Messung der Feinstaubemissionen aus Feuerungen
US10620165B2 (en) * 2016-12-29 2020-04-14 Infineon Technologies Ag Photoacoustic gas analyzer for determining species concentrations using intensity modulation
CN107014908B (zh) * 2017-06-14 2023-03-17 吉林大学 一种柔性超声相控阵换能器支架
GR1010249B (el) 2020-10-29 2022-06-16 Αριστοτελειο Πανεπιστημιο Θεσσαλονικης-Ειδικος Λογαριασμος Κονδυλιων Ερευνας, Διαταξη με αισθητηρα οπτικης απορροφησης με μεγαλη ευαισθησια και μεθοδος χρησης της για περιβαλλοντικες εφαρμογες

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Also Published As

Publication number Publication date
US20090038375A1 (en) 2009-02-12
JP2008544291A (ja) 2008-12-04
JP5022363B2 (ja) 2012-09-12
DE102005030151B3 (de) 2006-11-02
WO2007000297A1 (fr) 2007-01-04

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