EP0094413A1 - Detecteur de gaz a oscillateur a onde acoustique de surface - Google Patents

Detecteur de gaz a oscillateur a onde acoustique de surface

Info

Publication number
EP0094413A1
EP0094413A1 EP19820903532 EP82903532A EP0094413A1 EP 0094413 A1 EP0094413 A1 EP 0094413A1 EP 19820903532 EP19820903532 EP 19820903532 EP 82903532 A EP82903532 A EP 82903532A EP 0094413 A1 EP0094413 A1 EP 0094413A1
Authority
EP
European Patent Office
Prior art keywords
saw
gas
thin film
oscillator
gas 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.)
Withdrawn
Application number
EP19820903532
Other languages
German (de)
English (en)
Inventor
Donald L. Lee
John F. Vetelino
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.)
University of Maine System
Original Assignee
University of Maine System
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 University of Maine System filed Critical University of Maine System
Publication of EP0094413A1 publication Critical patent/EP0094413A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/022—Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices
    • 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
    • G01N2291/01—Indexing codes associated with the measuring variable
    • G01N2291/014—Resonance or resonant frequency
    • 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
    • G01N2291/025—Change of phase or condition
    • G01N2291/0256—Adsorption, desorption, surface mass change, e.g. on biosensors
    • 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
    • G01N2291/04—Wave modes and trajectories
    • G01N2291/042—Wave modes
    • G01N2291/0423—Surface waves, e.g. Rayleigh waves, Love waves
    • 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
    • G01N2291/04—Wave modes and trajectories
    • G01N2291/042—Wave modes
    • G01N2291/0426—Bulk waves, e.g. quartz crystal microbalance, torsional waves

Definitions

  • This invention relates to gas detectors and analyzers and more generally to detectors and analyzers of environ- mental-parameters which affect the properties of selectively sorptive and responsive thin films.
  • the invention is concerned with application of multi-channel surface acoustic wave (SAW), delay line oscillators, reson ⁇ ators and similar SAW devices as differential detectors and analyzers.
  • SAW surface acoustic wave
  • Such an oscillator generally comprises an . amplifier such as a microwave amplifier with a SAW delay line coupled in a feedback loop between the output and input.
  • the SAW delay line is generally provided by spaced apart interdigital transducers formed on a substrate, for example of quartz or LiNbO-, by photolithography or similar processes. Rayleigh waves are launched and detected by the interdigital trans ⁇ ducers and travel along the surface of the piezoelectric substrate material.
  • SAW delay line oscillators offer great advantages over conventional quartz and piezoelectric crystal bulk oscillators, because of their substantially greater stability and sensitivity.
  • the Kiewit U.S. Patent No. 4,107,626 assigned to Gould, Inc. describes the use of a surface acoustic wave device as a force sensor.
  • Two SAW delay lines are coupled as oscilla ⁇ tors in respective feedback circuits through respective amp ⁇ lifiers providing loop gain greater than one.
  • the oscilla ⁇ tors are arranged so that the SAW delay line portion of. one is along the compression surface of a beam while the SAW delay line portion of the other is along the tension part of the same beam.
  • compression of one surface portion and tension on the other respectively speeds and slows the SAW propagation rate thereby changing the resonant frequencies of the two oscill ⁇ ating circuits.
  • the frequency difference is measured by a mixer and counter for readout in digital form. The reading is proportional to the beam deflection and the force causing the deflection-
  • the Schwarz U.S. Patent 3,888,115 assigned to Texas Instruments describes another strain sensor using SAW de ⁇ vices.
  • a first SAW oscillator is applied to a first sub ⁇ strate forming a first leg which is to be stressed and mea ⁇ sured.
  • the second SAW oscillator is applied to a second substrate forming an unstressed reference leg.
  • the frequency difference between the signals derived from the stressed leg and reference leg is utilized as a measure of the strain applied to the first substrate.
  • the sample oscillator signal is changed in frequency by the amount of the component preferentially absorbed, and is passed through a mixer with the reference signal.
  • the resulting difference signal is appropriately converted for driving a recorder and for separating the sample peak from peaks of other constituents not preferen- tially absorbed.
  • Testerman et al U.S. Patent 3,144,762 also assigned to Phillips Petroleum describes a frequency difference anal ⁇ yzer in which two mechanical/pneumatic oscillators are provided at the output of a gas chroma ographic analyzer.
  • the two oscillators use the principle of oscillation of a jet stream by obstruction of the stream near the orifice.
  • the pulsation at the intersection of a feedback stream with the jet stream is a function of the concentration of a sampled constituent of the gas stream.
  • United States Patent 4,182,986 of Parker discloses the concept of using two coupled oscillators locked or synchron ⁇ ized in frequency as a detector for testing metal parts. Defects or variations in a tested metal part are used to vary the impedance in the resonant circuit of one of the oscillators. This variation in impedance produces a phase shift between the frequency locked signals of the two coupled oscillators. The detected phase shift provides a measure of the defect or other tested property of the solid metal.
  • This device uses transistor oscillators which are frequency locked or synchronized by coupling and exchange of energy between solid material that may introduce an impedance var ⁇ iation in a resonant circuit. Furthermore, the phase shift is used to provide a phase difference signal rather than a frequency difference signal. SAW devices are not utilized, nor are selective thin films.
  • a feature and advantage of the invention is that a very high sensitivity is achieved by the- synergistic interaction of the surface wave propagating along and con ⁇ fined to the SAW delay line channel/thin film interface.
  • a further object of the invention is to provide gas detectors applicable for detecting and measuring a wide range of gases, vapors and other substances of contemporary interest and concern while maintaining the high selectivity.
  • the invention offers the advantage of a wide range of appli ⁇ cability according to the selective characteristics of the thin film incorporated into the detector.
  • the present in ⁇ vention provides a first SAW oscillator having a first SAW propagation channel, a second SAW oscillator having a second SAW channel, and a thin film selectively sorptive of a gas or other substance to be detected formed on one of the first or second channels.
  • a difference detector is opera ⁇ tively coupled to the outputs of thw two SAW oscillators for generating a signal proportional to the difference in SAW propagation velocities in the first and second channels in response to selective sorption of gas or other substance
  • the difference detector responds to the difference in oscillation frequencies of the two SAW oscillators as a result.of the change in surface wave velocity in the channel containing the sorptive thin film.
  • two substantially identical surface acoustic wave delay lines or channels are fabricated side-by-side on a single piezo electric substrate.
  • a liquid or solid film selectively absorptive or adsorptive to a particular toxic or non-toxic gas is placed on the sub ⁇ strate between the pair of interdigital transducers of one of the delay lines.
  • Each delay line is connected in the feedback loop of a respective RF amplifier.to produce microwave oscillations in each loop of nearly equal frequency.
  • the surface acoustic wave properties, and in particular the velocity of propagation is retarded or other ⁇ wise changed resulting in a shift in the oscillation fre ⁇ quency of the SAW delay line or channel containing the film.
  • the outputs of the two oscillators are coupled together through a mixer and the difference, frequency is selected by a low pass filter. A signal is thereby obtained whose fre ⁇ quency is proportional to the quantity of sorbed gas. This signal may be converted to operate a recording device.
  • a small inexpensive, reliable and accurate gas detector is thereby provided.
  • the SAW delay lines or dual channel or dual path delay line may be formed on a piezo electric substrate of, for example, quartz or lithium niobate (LiNbO_) .
  • quartz or lithium niobate LiNbO_
  • a variety of organic or metallic materials may be used according to the gas or substance to be detected.
  • an organic triethonalamine film may be used for the detection of S0_.
  • sensitivity in detection of SO- to less than 70- parts per billion has been achieved.
  • the triethonalamine film may also be used for the detection of NO-,.
  • Triphenylamine films and films of ter ⁇ tiary amines may be used for detecting and measuring hydro ⁇ gen chloride (CHI) while ascorbic acid films or films of ascorbic acid with silver nitrate may be used for detecting ammonia (NH ) .
  • CHI hydro ⁇ gen chloride
  • NH ammonia
  • films of trans-chlorocarbonyl-bis (triphenyl-phosphine) are applicable, and alternatively, irridium films may be used.
  • metallic films are appropriate and provide films of greater stability than the organic compound films.
  • H_S hydrogen sulfide
  • silver or copper may be used as well as lead acetate or acetone extracts re ⁇ sulting from the burning of organochlorine compounds.
  • Gold film may be used for the detection of mercury, mercury com- pounds, and vapors.
  • Thin films of other compounds, elements and materials may also be used which are found to be select ⁇ ively sorptive of the gas or substance sought to be monitored by the SAW gas detector.
  • the selective film of desired sorptive characteristics is formed on one of the SAW delay lines or channels and the device is calibrated for substantial coin ⁇ cidence of resonant frequencies for the two oscillators.
  • the SAW gas oscillator is then placed in the test chamber or environment to be monitored for exposure of the thin film. After an exposure time factor.of, for example, one to three minutes or longer, a measurement is made of the frequency difference signal which shifts or increases in proportion to sorption of the targeted gas or substance and this is in turn a function of the concentration of the gas or substance in the monitored environment.
  • the SAW gas detector thin film system is reversible and after an exposure and measurement, the device is removed to the room air or outside air for desorption of the sorbed monitored gas or gases from the film.
  • the SAW gas detector is therefore reversible and reusable and is prepared for subsequent reuse by desorption in an uncontaminated atmosphere.
  • FIG. 1 is a schematic block diagram of the dual channel surface acoustic wave oscillator gas detector according to the present invention.
  • Fig. 2 is a graph of the difference frequency drift of the dual channel SAW oscillator with thin film formed on one of the SAW delay line channels indicating the stability of the film and hence stability of the oscillation frequency with time, prior to exposure.
  • Fig. 3 is a graph of the frequency shift of the thin film SAW oscillator channel from time of exposure of the thin film to target gas or gases in a test cell, for five different test runs, all shown in solid lines.
  • Fig. 4 is a graph comparing the sensitivity of response of the SAW gas detector according to the present invention indicated by the solid line with the response of a bulk wave conventional piezoelectric oscillator detector indicated by the dotted line. Data points for the SAW gas detector are shown by a circle along the solid line. Best Mode for Carrying Out the Invention
  • SAW socillator 11 includes a first SAW delay line 13 formed by spaced apart interdigital transducers 14 and 15 deposited on the piezoelectric substrate 16.
  • the piezoelectric sub ⁇ strate may be formed e.g. from quartz or lithium niobate.
  • a surface wave path or channel 17 couples the interdigital transducers 14 and 15 and in the case of the first SAW oscillator 11 does not include a thin film along the path or channel.
  • the second SAW oscillator 12 includes a second SAW delay line 18 composed of interdigital transducers 20 and 21 depo ⁇ sited on the common substrate 16.
  • a thin film 22 is deposited along the first surface wave path or channel 23, which film is select ⁇ ively absorptive or adsorptive of the gas sought to be moni ⁇ tored or detected by the cell.
  • the first SAW delay line 13 is coupled in feedback loop through amplifier 25 to form the first SAW oscillator 11.
  • SUBSTITUTE SHEET Amplifier 25 is adjusted to afford a gain of one, the oscillating condition for this feedback circuit.
  • the second SAW delay line 18 is coupled in a feedback loop through amplifier 26 to form the second SAW oscillator 12.
  • the amplifier 26 is also adjusted to provide a gain of one to establish the oscillating condition in the second feed ⁇ back circuit.
  • the difference frequency of the two oscil ⁇ lators is used as a baseline.
  • the surface acoustic wave portions and components of SAW oscillator gas detector 10 may be housed, for example, in a gas tight test cell 30 with sufficient capacity to admit a representative sample of the air or atmosphere to be moni ⁇ tored by the gas detector.
  • the gas type test cell may have a volume, for example, of 144 ml.
  • the SAW delay lines 13 and 18 may have dimensions to provide a surface wave path or channel having a length of approximately one centimeter.
  • the coincident frequency of oscillation of the SAW oscilla- tors 11 and 12 may be, for example, in the range of 100- 150 megahertz (mHz) .
  • the frequency shift of the resonant frequency of SAW oscillator 12 relative to SAW oscillator. 11 as a result of selective sorption of gas by thin film 22 in delay line channel 23 may be, for example, in the order of 100 kiloherz (kHz) up to, for example, 2 mega ⁇ hertz (mHz) .
  • the frequency difference between the two oscillators upon detection of the gas is no more than a few percent of the original resonant frequency of the oscillators.
  • the delay in the propagation of surface acoustic waves across channel 23 covered with thin film 22 as a result of absorption or adsorption of a targeted gas and change in the propagation velocity causes the shift in the resonant frequency of the SAW oscillator 12 relative to oscillator 11.
  • Output signals from SAW oscillators 11 and 12 are de ⁇ rived respectively through directional couplers 32 and 33. These output signals are coupled to the input of mixer 35 where the signals of shifted frequency are mixed. The sum and difference signals from the output of mixer 35 are fed
  • SUBSTITUTE SHEET ⁇ SHRE ⁇ to low pass filter 36 which passes the difference frequency signal to signal converter 38 which in turn converts the frequency signal to a voltage signal proportional to the frequency for driving the reocorder 40.
  • a dual channel SAW oscillator gas detector of the type illustrated in Fig. 1 was fabricated with delay lines formed on a lithium niobate substrate.
  • a triethonalamine film was coated on the channel 23 of delay line 18 for detecting the presence of sulphur dioxide (S0_) in a test cell.
  • S0_ sulphur dioxide
  • SAW oscillator gas detector of the present invention may be used in combination with a gas chromatograph column to achieve even greater selectivity.

Landscapes

  • Physics & Mathematics (AREA)
  • Acoustics & Sound (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)

Abstract

Un détecteur ou analyseur d'environnement (10) est formé en utilisant une paire d'oscillateurs à onde acoustique de surface (11), (12), possédant chacun un canal de propagation d'onde acoustique de surface (17, 23). Un film mince (22) absorbant sélectivement un gaz ou une autre substance devant être détéctée est formé sur l'un des canaux. Un détecteur de différence (35, 36, 38) est couplé de manière opérationnelle aux sorties des deux oscillateurs à onde acoustique de surface de manière à produire un signal proportionnel à la différence des vitesses de propagation de l'onde acoustique de surface du premier et du deuxième canaux en réponse à la sorption sélective d'un gaz ou d'une autre substance par le film mince. Le détecteur de différence répond à la différence des fréquences d'oscillation des deux oscillateurs à onde acoustique de surface en fonction de la variation de la vitesse de l'onde de surface dans le canal contenant le film mince absorbant.
EP19820903532 1981-10-13 1982-10-12 Detecteur de gaz a oscillateur a onde acoustique de surface Withdrawn EP0094413A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US31082481A 1981-10-13 1981-10-13
US310824 1981-10-13

Publications (1)

Publication Number Publication Date
EP0094413A1 true EP0094413A1 (fr) 1983-11-23

Family

ID=23204269

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19820903532 Withdrawn EP0094413A1 (fr) 1981-10-13 1982-10-12 Detecteur de gaz a oscillateur a onde acoustique de surface

Country Status (2)

Country Link
EP (1) EP0094413A1 (fr)
WO (1) WO1983001511A1 (fr)

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL8502705A (nl) * 1985-10-03 1987-05-04 Organisatie Voor Toegepast Nat Samengestelde drager, bestemd voor een toestel voor kwantitatieve bepaling van een in een gas of vloeistof aanwezig bestanddeel.
JPH04307351A (ja) * 1991-04-04 1992-10-29 Hitachi Ltd 冷蔵庫
GB2270564B (en) * 1992-09-11 1996-09-11 Marconi Gec Ltd A method of identifying analytes
US5885844A (en) * 1993-09-21 1999-03-23 Eev Limited Method of identifying analytes
DE9420199U1 (de) * 1994-12-07 1995-02-09 Siemens Ag Metallgekapselte Hochspannungsschaltanlage
GB9712299D0 (en) * 1997-06-12 1997-08-13 Univ Cambridge Tech Condensation point detection
JP2002539511A (ja) * 1999-03-05 2002-11-19 マルコニ アップライド テクノロジーズ リミテッド 火災検出装置
US7286942B1 (en) 2003-05-30 2007-10-23 United States Of America As Represented By The Secretary Of The Navy System and method of fluctuation enhanced gas-sensing using saw devices
CN103336053B (zh) * 2013-06-18 2015-11-04 电子科技大学 一种独用参比的声表面波气体传感器阵列
CN111189910B (zh) * 2020-01-10 2022-07-15 西安科技大学 一种基于延迟线型声表面波传感电路系统设计方法

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE631020A (fr) * 1961-05-15
US3431770A (en) * 1965-04-05 1969-03-11 Phillips Petroleum Co Analyzer for determining hydrogen-to-carbon ratio in a material
US4111036A (en) * 1974-07-29 1978-09-05 The Board Of Regents For Education Of The State Of Rhode Island Piezoelectric probe for detection and measurement of gaseous pollutants
US4055072A (en) * 1975-09-19 1977-10-25 Nasa Apparatus for measuring a sorbate dispersed in a fluid stream
US4312228A (en) * 1979-07-30 1982-01-26 Henry Wohltjen Methods of detection with surface acoustic wave and apparati therefor
US4361026A (en) * 1980-06-24 1982-11-30 Muller Richard S Method and apparatus for sensing fluids using surface acoustic waves

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8301511A1 *

Also Published As

Publication number Publication date
WO1983001511A1 (fr) 1983-04-28

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PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

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Inventor name: VETELINO, JOHN F.

Inventor name: LEE, DONALD L.