Abstract: A multiple-mode acoustic wave sensor apparatus includes an acoustic wave device comprising a piezoelectric substrate and at least one electrode on the substrate. When such sensor is used in a wireless configuration, a plurality of antennas can be configured on the substrate in association with the acoustic wave device, wherein each antenna among the plurality of antennas is responsive to varying interrogation signals transmitted wirelessly to the plurality of antennas in order to excite multiple frequency modes via at least one interdigital transducer on the substrate and thereby passively detect multiple and varying parameters of a sensed material utilizing the acoustic wave device.

Abstract: A method for manufacturing a flexural plate wave sensor includes the steps of depositing an etch-stop layer over a substrate, depositing a membrane layer over the etch stop layer, depositing a piezoelectric layer over the membrane layer, forming a transducer on the piezoelectric layer, etching a cavity through the substrate, the cavity having substantially parallel interior walls, and removing the portion of the etch stop layer between the cavity and the membrane layer to expose a portion of the membrane layer.

Abstract: A method for analyzing gas concentration using doubly resonant photoacoustic spectroscopy, and a doubly resonant photaoacoustic gas detector comprising: i) a continuous wave light beam whose wavelength coincides with an absorption wavelength of a gaseous analyte; ii) a closed path optical cavity having at least two reflective surfaces; iii) an acoustic resonator chamber contained within said optical cavity, and comprising an acoustic sensor for detecting sound waves generated by a gaseous analyte present within said chamber, the light beam passing sequentially into, through and out of said chamber, and being repeatedly reflected back and forth through said chamber, and being modulated at a frequency which is equal to or equal to one-half of an acoustic resonance frequency of said acoustic resonator chamber.

Abstract: A sensor for detecting hydrogen peroxide, comprising an element exhibiting piezoelectric properties having a metal-oxide-containing coating, the metal-oxide having a divalent or tetravalent state.

Abstract: A sensor and methods for making and using the same in which a mechanical resonator is employed, comprising a resonator portion for resonating in a fluid without the substantial generation of acoustic waves; and an electrical connection between the resonator portion for oscillating and a source of an input signal; wherein the portion for resonating, the electrical connection or both includes a base material and a performance-tuning material that is different from the base material.

Abstract: A gas concentration measurement instrument comprises: ultrasonic wave transmitting means for transmitting an ultrasonic wave according to an ultrasonic wave generation signal composed of a group of rectangular pulse waves; ultrasonic wave receiving means for converting the ultrasonic wave transmitted through the gas in the measurement region into an electric signal to use it as an ultrasonic wave reception signal; and gas concentration measuring means for measuring the signal output time when the ultrasonic wave generation signal is outputted, generating an envelope processing signal by subjecting the ultrasonic wave reception signal to an envelope extracting processing, measuring the threshold fall time when the envelope processing signal decreases below a predetermined threshold after exceeding the threshold, and measuring the difference between the threshold fall time and the signal output time as change in the gas concentration.

Abstract: A method of sensing the amount of a gas in a fluid flow includes operating an acoustic wave (AW) sensor at a first resonant frequency. The AW sensor includes a high temperature stable piezoelectric plate coupled to a first gas-absorbing layer. Also included is combining a fluid flow having a gas component with the first gas-absorbing layer at a temperature of at least about 500° C. At least one resonant frequency of the AW sensor is sensed. The amount of gas in the fluid flow is sensed by correlating the resonant frequency with the amount of gas absorbed in the first gas-absorbing layer. A sensor for sensing the amount of a gas in a fluid flow includes a first gas-absorbing layer, a high-temperature-stable piezoelectric plate coupled to the first gas-absorbing layer, and a controller coupled to the high-temperature-stable piezoelectric plate.

Abstract: A device for determining and/or monitoring at least one physical parameter of a medium, having at least one mechanically oscillatable unit and at least one drive-/receive unit. The drive-/receive unit excites the oscillatable unit to oscillate, or, it receives the oscillations of the oscillatable unit, as the case may be. The invention includes that in the drive-/receive unit at least one piezo-drive is provided, which has at least one exterior surface. The exterior surface is composed of at least two segments of different polarization, wherein the directions of polarization are directed essentially opposite to one another. The mechanically oscillatable unit is directly or indirectly connected with the exterior surface, so that the mechanically oscillatable unit is excited to a movement, or so that the movement of the mechanically oscillatable unit is received. The movement always has at least two different force components.

Abstract: An on-chip coil is provided in a micromachined device for magnetic actuation of a nanoelectromechanical microcantilever. The novel geometry involves a three dimensional solenoid or planar coil carrying high current that generates a large enough magnetic field in its close proximity to a permalloy thin film patch or columnar magnet disposed on the distal end of the piezoresistive microcantilever to effectively interacts with the magnetic thin film deposited on the microcantilever. The device comprises an effective actuators which can be integrated with biofunctionalized cantilever arrays in hybrid semiconductor-microfluidics devices for the analysis and detection of biological analytes.

Abstract: The disclosed sensor chip includes a substrate and a moving member coupled to the substrate and disposed for movement relative to the substrate. The moving member moves relative to the substrate in a first direction and in a second direction in response to movement of the substrate. The first direction is different than the second direction. The moving member includes a plurality of receptors. The receptors are configured for selectively binding to a first measurand.

Abstract: The disclosed apparatus and methods allow collection of concentrated samples of content in shipping packages without unsealing the package by forcing airflow via existing hidden gaps or, if necessary, creating one by a small incision. The air is injected into the hidden gaps by either probe or socket device to disturb and agitate contents inside the package, causing the contents to loosen and blending particulates on the surface into the air stream. Airborne particles are channeled into a detection device, where the particulates are concentrated. Display and warning apparatus receive and record the analysis results from the detection device. If the analysis finds that predetermined selection and sensitivity criteria for target hazard or contraband material are met, then the warning apparatus initiates the appropriate alert protocols.

Abstract: A microfabricated mass-sensitive chemical preconcentrator actively measures the mass of a sample on an acoustic microbalance during the collection process. The microbalance comprises a chemically sensitive interface for collecting the sample thereon and an acoustic-based physical transducer that provides an electrical output that is proportional to the mass of the collected sample. The acoustic microbalance preferably comprises a pivot plate resonator. A resistive heating element can be disposed on the chemically sensitive interface to rapidly heat and release the collected sample for further analysis. Therefore, the mass-sensitive chemical preconcentrator can optimize the sample collection time prior to release to enable the rapid and accurate analysis of analytes by a microanalytical system.

Abstract: The invention is concerned with a method and apparatus for real time analysis of gas mixtures, e g determination of air quality, including at least one resonator (1, 11), means for gas transportation to and from the resonator (1, 11), e g by diffusion or transit flow via openings (5) means for activation (2) and detection (3) of an acoustic signal within the resonator (1, 11), at least one means (7) for measurement of the temperature within the resonator (1, 11), and at least one means (4) for the determination of both the resonance frequency and the quality factor of the resonator (1,11) in real time. These entities are related to the average molecular mass and viscosity or thermal conductivity, respectively, of the gas mixture. The resonator (1, 11 may include a compliant element, e g a constricted volume (6) and an inertial element, e g ist opening (5) or may support standing acoustic waves, in which the sound wavelength is related to a physical dimension of the resonator (1, 11).

Abstract: An electronic signal relating to a sonic wave when an intended gas does not exist in air is synchronized and locked in a feedback circuit constituting a phase-locked loop (PLL). Then, an electronic signal relating to another sonic wave when the intended gas exist in the air is input into the feedback circuit to release the synchronization (lock) of the feedback circuit to measure as a given electronic signal the difference in phase of the sonic wave in the air between with and without the intended gas to be detected. The intended gas can be detected as the electronic signal due to the difference in phase of the sonic wave.

Abstract: A system for determining polarization of a gas comprises a container that contains the polarized gas. An oscillator circuit comprises an NMR coil that is positioned adjacent to the container. A pulse generator circuit is configured to generate an electrical pulse that may be transmitted to the optical cell through the NMR coil to excite the polarized gas responsive to a control processor. A Q-reduction circuit that is independent of the pulse generator circuit is configured to reduce oscillations in the oscillator circuit from the transmitted electrical pulse responsive to the control processor. A receive circuit is responsive to an electrical signal that is induced in the oscillator circuit due to the electromagnetic excitation of the polarized gas. The control processor is configured to determine the polarization of the gas based on the output signal of the receive circuit.

Abstract: A transducer-based sensor system, including a transducer array having a plurality of transducers, a selector coupled with the transducer array and an output processing subsystem. Defined between each transducer and the output processing subsystem is an output transmission path associated with the individual transducer. The selector is configured to apply control signals to the transducer array to cause the array to have at least one selected transducer and at least one unselected transducer. The system is configured so that, for a selected transducer, the output transmission path for that transducer is enabled, so as to permit output signals to be transmitted from the selected transducer to the output processing subsystem. The system is further configured to isolate any unselected transducers, by disabling the output transmission path for such transducers, to thereby prevent transmission of output signals to the output processing subsystem.

Abstract: In a sensor on the basis of surface wave components disposed in a housing with at least one surface wave component, a fluid channel and conductors for high frequency signals, the conductors are connected to coupling capacitors with capacitive coupling surface areas which are arranged opposite each other on the housing and the surface wave equipment and closely adjacent one another so that high frequency signals can be transmitted to, and from, the surface wave components.

Abstract: An ambient condition detector has a housing that carries a sensor of an airborne constituent such as a gas, and a condenser for minimizing an inflow of moisture into the sensor. A filter can be used to reduce fluid flow velocity prior to passing through or by the condenser.

Abstract: A gas sensor (10) including a measurement chamber (28) into which a gas GS is flown and a detection element main body (40) facing the measurement chamber (28). The detection element main body (40) includes an element case 42, and a protective film (48) is adhered to a bottom surface thereof. An acoustic matching plate (50) and a piezoelectric element (51) of a substantially columnar shape and a tube body (52) provided in a position surrounding the acoustic matching plate 50 and the piezoelectric element 51 are housed in the element case (42). A filler is then introduced into the element case (42), whereby the acoustic matching plate (50), the piezoelectric element (51), and the tube body (52) are sealed by a filled layer (99).

Abstract: A detecting-element assembly (40) is configured such that a piezoelectric element (51) is housed in a casing body portion (43) of a casing (42), and is attached to a housing portion (22) of a flow path formation member (20) via a flange portion (41). Therefore, the path between the piezoelectric element (51) and the position of attachment of the detecting-element assembly (40) is elongated, whereby ultrasonic waves which leak into the interior of the detecting-element assembly (40) from the piezoelectric element (51) become unlikely to reflectively return from a joint. Thus, the influence of, for example, noise stemming from reflected waves is reduced, thereby enhancing the accuracy of detection. An average clearance of 1 millimeter or more is provided along the outer circumferential surface of the casing body portion (43) of the detecting-element assembly (40), whereby a problem of collected foreign matter is unlikely to occur.

Abstract: A method and apparatus for measuring properties of a liquid composition includes a mechanical resonator, such as a cantilever, connected to a measurement circuit. The mechanical resonator can be covered with a coating to impart additional special detection propertied to the resonator, and multiple resonators can be attached together as a single sensor to obtain multiple frequency responses. The invention is particularly suitable for combinatorial chemistry applications, which require rapid analysis of chemical properties for screening. In one embodiment, the resonator is operated at a frequency of less than 1 MHz.

Abstract: The present invention provides a delay line SAW device fabricated on a lithium niobate substrate and coated with a bilayer of nanocrystalline or other nanomaterials such as nanoparticles or nanowires of palladiumn and metal free pthalocyanine which will respond to hydrogen gas in near real time, at low (room) temperature, without being affected by CO, O2, CH4 and other gases, in air ambient or controlled ambient, providing sensitivity to low ppm levels.

Abstract: A surface acoustic wave gas sensor for detecting predetermined substances includes a piezoelectric substrate, an input transducer and an output transducer which is formed on the piezoelectric substrate, and a sensitive film which is formed between the input transducer and the output transducer and detects at least one of acetone, benzene, dichloroethane, ethanol, and toluene. The sensitive film includes mercaptoundecanoic acid and CMP composed of cellulose nitrate, dibutyl phthalate, compound of benzene and ethanol, ethyl acetate. The surface acoustic wave gas sensor can quickly detect even small amounts of these substances.

Abstract: A plurality of quartz crystal resonators having different resonance frequencies are connected in parallel. A combined admittance of the resonators is measured. Equivalent circuit constants of all the resonators are obtained by a method of least squares from admittance characteristics. A change in the resonance frequency is measured and mass of a substance adsorbed to a piezoelectric transducer is calculated.

Abstract: A flexural plate wave sensor array includes a substrate, and a plurality of flexural plate wave sensors, each sensor including a cavity formed in the substrate, a thin film membrane layer spanning the cavity, a piezoelectric layer disposed on the thin film membrane layer, a transducer disposed on the piezoelectric layer and an absorptive coating disposed on said thin film membrane layer within the cavity. The cavity of each of the sensors includes interior walls which are substantially parallel to each other and to the interior walls of adjacent sensors.

Abstract: Disclosed are resonant gas sensors and methods for forming and using the disclosed sensors. The sensors include a resonator including a layer comprising adsorptive nanostructures, for example carbon nanotubes, activated carbon fibers, or adsorptive nanowires. The dielectric of the resonator is in electrical communication with the layer comprising adsorptive nanostructures such that the effective resonant frequency of the resonator depends on both the dielectric constant of the dielectric as well as the dielectric constant of the adsorptive layer. In some embodiments, the nanostructures can be degassed. The sensors can detect the presence of polar gases, non-polar gases, organic vapors, and mixtures of materials with both high sensitivity and high selectivity.

Abstract: A system and method for performing rupture event scanning and other sensing operations on a sample. The method includes providing a transducer with an immobilized binding partner material and a sample material disposed thereon. The sample material is applied to the immobilized binding partner material so that, if components in the sample material have sufficient affinity for the immobilized binding partner material, bonds will form between at least some of such components and the immobilized binding partner material. The method further includes accelerating the transducer to induce bond breakage, where such accelerating is performed by applying a drive signal to the transducer. The drive signal includes a waveform having multiple frequency components that are pre-selected based on expected resonance behavior of the transducer. The method may also include analyzing an output response of the transducer in response to application of the drive signal.

Abstract: A system and method for providing resonant movement about a first axis. A functional surface supported by a first pair of torsional hinges is driven into resonant oscillations about the first axis by inertially coupling energy through the first pair of torsional hinges. The resonant movement may be moved orthogonally on the target area by a gimbals portion of the functional surface pivoting about a second axis according to one embodiment. The resonant oscillation of the functional surface is monitored to detect changes in frequency due to mass changes of the functional surface.

Abstract: A method for measuring properties of a fluid that includes oscillating a tuning fork resonator in a fluid. The invention is particularly suitable for in-line monitoring of various physical and electrical properties of fluids flowing in a conduit.

Abstract: A molecular contamination monitor for monitoring molecular contamination on a surface of a subject surface susceptible to degradation by a molecular contaminant. The monitor includes a surface acoustic wave (SAW) device having a SAW measurement surface coated with a material that is equivalent to the subject material with respect to spontaneous contamination by a contaminant. In the preferred embodiment, the coating comprises the same material as the subject surface or a material that interacts chemically with the contaminant in an equivalent manner to the subject surface. Exemplary coatings include: photoresist, copper, silver, gold, platinum, titanium, tungsten, aluminum, nickel, metal oxides, stearic acid, silicon, gallium arsenide, gallium nitride, germanium, silicon germanium, silicon dioxide, silicon nitride, and glass. Exemplary coating methods include sputtering, CVD, ALD and misted deposition.

Abstract: In a mass-sensitive sensor consisting of an acoustic surface wave component on the basis of shear waves, the sensor includes a substrate with an active surface carrying two different layers, one which is a parylene layer of a thickness of between 0.2 and <1.6 ?m, which has been produced on the substrate by a vacuum-based deposition method and is capable of generating Love waves and the second layer forms a utilization layer, which interacts with an analyte disposed in a medium contacting the utilization layer.

Abstract: Hydrogen gas sensors employ an epitaxial layer of the thermodynamically stable form of aluminum nitride (AlN) as the “insulator” in an MIS structure having a thin metal gate electrode suitable for catalytic dissociate of hydrogen, such as palladium, on a semiconductor substrate. The AlN is deposited by a low temperature technique known as Plasma Source Molecular Beam Epitaxy (PSMBE). When silicon (Si) is used the semiconducting substrate, the electrical behavior of the device is that of a normal nonlinear MIS capacitor. When a silicon carbide (SiC) is used, the electrical behavior of the device is that of a rectifying diode. Preferred structures are Pd/AlN/Si and Pd/AlN/SiC wherein the SiC is preferably 6H—SiC.

Abstract: A chemical agent detector utilizing surface acoustic wave (SAW) sensors for detecting the presence of a multitude of chemical agents by sampling ambient air is provided. A pressure-differential manifold having an air intake port, an exhaust port, a valve and a pump is used to draw the ambient air into the manifold to be tested. A plurality of SAW sensors mounted on sensor driver boards which are in turn mounted on the manifold come into contact with the ambient air sample. Each SAW sensor is coated with a substance that has an affinity for detecting a particular chemical agent. Each SAW sensor driver board generates a continuous RF signal which emits a frequency shift if a particular chemical agent is detected. A power cycler module turns each sensor driver board on and off such that only one sensor driver board is powered-on at a given point in time.

Abstract: An apparatus for demonstrating, investigating and observing Brownian motion and temperature of a medium, such as gas or liquid, uses a small particle which is diamagnetically suspended in the medium. The tiny magnetized particle having a known mass is levitated using a diamagnetic technique, and the displacement of the particle over time is observable, which can be used to determine a temperature of the medium. Optionally, a second particle is suspended in a vacuum but mechanically connected to the same apparatus as the first enclosure with the first particle, thereby allowing observation and measurement of non-Brownian movement of the structure, and allowing more precise observation of Brownian movement effects on the first suspended particle.

Abstract: A method and apparatus for measuring properties of a liquid composition includes a mechanical resonator, such as a cantilever, connected to a measurement circuit. The mechanical resonator's response over the frequency range depends on various characteristics of the liquid being tested, such as the temperature, viscosity, and other physical properties. The invention is particularly suitable for combinatorial chemistry applications, which require rapid analysis of chemical properties for screening.

Abstract: A programmable device for analyzing mixtures of suspended vapors and air by pinging particles making up the vapors at their mechanical resonant frequencies and detecting the resultant rings.

Abstract: An apparatus and method for detecting gases, gasified agents or other analytes. The apparatus includes a solid body having a first surface area and a second surface area. A first, preferably polymeric, coating is superimposed on the first surface area of the solid body. A second, preferably polymeric, coating is superimposed on the second surface area of this solid body. The first coating and the second coating are different materials which adsorb different agents at different rates. A wave propagating transducer is positioned adjacent the solid body to propagate a first wavefront adjacent the first surface area of the solid body. This wave propagating transducer also propagates a second wavefront adjacent the second surface area of the solid body. These first and second wavefronts interfere to produce an interference pattern which is unique to the particular agent which is adsorbed by the first and second coatings.

Abstract: A method for manufacturing a flexural plate wave sensor includes the steps of depositing an etch-stop layer over a substrate, depositing a membrane layer over the etch stop layer, depositing a piezoelectric layer over the membrane layer, forming a first transducer on the piezoelectric layer and forming a second transducer on the piezoelectric layer, spaced from the first transducer. The method further includes the steps of etching a cavity through the substrate, the cavity having substantially parallel interior walls, removing the portion of the etch stop layer between the cavity and the membrane layer to expose a portion of the membrane layer, and depositing an absorptive coating on the exposed portion of the membrane layer.

Abstract: An acoustic wave sensor to detect an analyte, the sensor comprising a piezoelectric material including a wide bandgap semiconductor material grown using plasma source molecular beam epitaxy.

Abstract: A sensor for the measurement of carbon dioxide concentration within an air flow being input to a measuring cell (1) connected to at least one electroacoustic element (2, 3) for transmitting and receiving airborne acoustic waves within the measuring cell (1). The output signal of the sensor corresponds to the propagation velocity of these waves and an indirect measure of carbon dioxide concentration, with an automatic offset correction functionality for compensation of undesired offset variations of the signal, caused by temperature or humidity variations. Preferably, an accumulating function for minimizing the influence of the offset variations is included, which for humidity variations may consist of a material with high porosity and surface density of polar molecular groups. Temperature control of the inner sheath (4) is effected by a temperature sensor (11), a resistive heating element (12) in good thermal contact with the inner sheath (4), and a control circuit (13).

Abstract: A method for manufacturing a flexural plate wave sensor includes the steps of depositing an etch-stop layer over a substrate, depositing a membrane layer over the etch stop layer, depositing a piezoelectric layer over the membrane layer, forming a first transducer on the piezoelectric layer and forming a second transducer on the piezoelectric layer, spaced from the first transducer. The method further includes the steps of etching a cavity through the substrate, the cavity having substantially parallel interior walls, removing the portion of the etch stop layer between the cavity and the membrane layer to expose a portion of the membrane layer, and depositing an absorptive coating on the exposed portion of the membrane layer.

Abstract: A gas-concentration measuring apparatus for measuring the concentration variation of gas residing in a target region. The gas-concentration measuring apparatus comprises an ultrasound-transmitter adapted to transmit an ultrasound in response to an ultrasound-generating signal having a rate of voltage change equal to or greater than a slew rate of an operational amplifier, and further adapted to output the ultrasound-generating signal. An ultrasound-receiver adapted to receive the ultrasound wave passed through the gas residing in the target region, and further adapted to convert the received ultrasound into an electrical signal serving as a received ultrasound signal is provided. A gas-concentration determiner adapted to input the ultrasound-generating signal and the received ultrasound wave signal into the operational amplifier to generate an amplified transmitting-side chopping wave and an amplified receiving-side chopping wave is further provided.

Abstract: A sensor for measuring the speed of sound in a gas. The sensor has a helical coil, through which the gas flows before entering an inner chamber. Flow through the coil brings the gas into thermal equilibrium with the test chamber body. After the gas enters the chamber, a transducer produces an ultrasonic pulse, which is reflected from each of two faces of a target. The time difference between the two reflected signals is used to determine the speed of sound in the gas.

Abstract: A method for sensing a chemical analyte in a fluid stream comprises providing a microfabricated teeter-totter resonator that relies upon a Lorentz force to cause oscillation in a paddle, applying a static magnetic field substantially aligned in-plane with the paddle, energizing a current conductor line on a surface of the paddle with an alternating electrical current to generate the Lorentz force, exposing the resonator to the analyte, and detecting the response of the oscillatory motion of the paddle to the chemical analyte. Preferably, a chemically sensitive coating is disposed on at least one surface of the paddle to enhance the sorption of the analyte by the paddle. The concentration of the analyte in a fluid stream can be determined by measuring the change in the resonant frequency or phase of the teeter-totter resonator as the chemical analyte is added to or removed from the paddle.

Abstract: A microfabricated teeter-totter resonator comprises a frame, a paddle pivotably anchored to the frame by pivot arms that define an axis of rotation, a current conductor line on a surface of the paddle, means for applying a static magnetic field substantially perpendicular to the rotational axis and in the plane of the paddle, and means for energizing the current conductor line with an alternating current. A Lorentz force is generated by the interaction of the magnetic field with the current flowing in the conductor line, causing the paddle to oscillate about the axis of rotation. The teeter-totter resonator can be fabricated with micromachining techniques with materials used in the integrated circuits manufacturing industry. The microfabricated teeter-totter resonator has many varied applications, both as an actuation device and as a sensor.

Abstract: A device for measuring thickness and/or rate of thickness increase of a film comprises at least one piezoelectric element, and first and second electrodes in contact with the piezoelectric element. A method of measuring thickness and/or rate of thickness increase of a film comprises applying a voltage across a piezoelectric element from a first electrode to a second electrode, thereby causing the piezoelectric element to vibrate, and measuring the rate of vibration of the piezoelectric element. Heat may be applied to the piezoelectric element. The piezoelectric element may be formed of quartz crystal, e.g., IT-cut.

Abstract: The present invention provides means which can be used for maintaining the freshness of or controlling maturation of plants or perishables such as fruits, vegetables, and flowers and which is safe to the human body. According to the present invention, a method for maintaining the freshness of or conversely controlling the maturation of plants or perishables by controlling the concentration of ethylene gas by use of an ethylene gas adsorbent containing an alcohol extract solution of raw bamboo and a filter having held thereon the alcohol extract solution of raw bamboo. Also, according to the present invention, there is provided an ethylene gas sensor including a quartz crystal microbalance having coated thereon the alcohol extract solution of raw bamboo.

Abstract: A process to determine aerosol particles in gaseous samples, specifically in the exhaust of diesel motors, includes the at least indirect deposit of aerosol particles on a piezoelectric oscillating crystal and the determination of the oscillation parameters of the piezoelectrically stimulated oscillation of the crystal. In order to assure the required reproducibility reliably and independently of the type of aerosol particles, and thus to achieve a high quality of measurements, the piezoelectric crystal is charged to oscillation during less than half the period of deposit of aerosol particles.

Abstract: A sensor for monitoring gas content. The sensor comprises a housing defining at least two cavities and a resonating structure positioned in each of the cavities. Each of the resonating structures has a resonant frequency dependent upon a physical characteristic of a gas in its respective cavity. Means for exciting the resonating structures generates output signals therefrom, and means compares the output signals from each of the resonating structures and outputs a comparison signal indicative of a difference between the resonant frequencies of the two structures and the relative gas content of the at least two cavities.

Abstract: A surface acoustic wave gas sensor for detecting predetermined substances includes a piezoelectric substrate, an input transducer and an output transducer which is formed on the piezoelectric substrate, and a sensitive film which is formed between the input transducer and the output transducer and detects at least one of acetone, benzene, dichloroethane, ethanol, and toluene. The sensitive film includes mercaptoundecanoic acid and CMP composed of cellulose nitrate, dibutyl phthalate, compound of benzene and ethanol, ethyl acetate. The surface acoustic wave gas sensor can quickly detect even small amounts of these substances.