Showing papers on "Acoustic interferometer published in 1985"

Diffuse elastic waves at a free surface

Abstract: For a diffusely vibrating elastic body, the participation of the surface in the general disturbance is evaluated. It is shown that in the vicinity of a free surface a diffuse acoustic field may legitimately be regarded as a sum of incoherent isotropic and homogeneous independent plane waves incident upon the surface together with their respective outgoing reflected consequences. The work contributes to a conceptual basis for the study of acoustic emission signals on time scales large compared to acoustic travel times across the structure.

Surface acoustic wave device for sensing the presence of chemical agents

Abstract: A surface acoustic wave device is provided for sensing the presence of chemical agents by chemo-electronic means. The device includes a quartz substrate and means deposited on the substrate for propagating and receiving surface acoustic waves along the surface of the substrate. Regions are provided on the substrate containing etched tunnels, the walls of the etched tunnel being coated within with a chemical substance sensitive to the chemical agent to be detected. When surface acoustic waves are caused to pass over these regions, the reaction of the chemical agent to be detected with the chemical substance causes a change in the acoustic wave velocity.

Measurement of Humidity Using Surface Acoustic Waves

Abstract: Th i s paper d e s c r i b e s a t e c h n i q u e f o r measuri n g humid i ty wi th h igh s e n s i t i v i t y and wide dynamic range us ing s u r f a c e a c o u s t i c waves. A d e l a y l i n e s t a b i l i z e d SAW o s c i l l a t o r i s used , t h e d e l a y l i n e be ing coa ted wi th a t h i n f i l m o f a s u i t a b l e hygroscop ic m a t e r i a l . S o r p t i o n o f m o i s t u r e produces r a p i d changes i n t h e e l e c t r i c a l and mechanica l p r o p e r t i e s o f t h e f i l m . T h i s r e s u l t s i n a change i n t h e v e l o c i t y of t h e s u r f a c e acoust i c wave and hence i n t h e f r equency o f t h e SAW o s c i l l a t o r . With poly imide used a s t h e hygros c o p i c m a t e r i a l , t h e f r equency o f a 75 MHz o s c i l l a t o r f a b r i c a t e d on a 128" Y-X LiNbOj s u b s t r a t e i s found t o va ry by more than 150 kHz as t h e r e l a t i v e humid i ty i s v a r i e d f r o m n e a r 0% RH t o 100% RH. The c a l c u l a t e d d e t e c t i o n l i m i t (assuming o s c i l l a t o r sho r t t e rm s t a b i l i t y o f 1 p a r t i n 10') i s less than 1 .5 pp"v o f humid i ty , o r a co r re spond ing dew p o i n t of -72°C. S imul t aneous humid i ty and t empera tu re s e n s i n g h a s been demons t r a t e d u s i n g a d u a l d e l a y l i n e approach .

Surface acoustic waves velocity perturbation in LiNbO3 by proton exchange

Abstract: It is shown that the exchange of Li+ ions in LiNbO3 by protons leads to a large decrease of the (group) velocity of surface acoustic waves propagating in the x-direction on Y- and Z-cut samples. Changes up to about 20% were measured at a frequency of 180 MHz. This effect can be used to construct strip waveguides for surface acoustic waves.

SAW RF Spectrum Analyzer/Channelizer Using a Focusing, Phased Array Transducer

Abstract: The principle of Fourier t ransformation by wave diffraction has been demonstrated using surface acoustic waves. The input RF signal d rives a phased array of SAW interdigital transducers that act like a curved diffraction grating to focus and angularly disperse the generated acoustic waves with frequency. An array of output t ransducers partitions t he dispersed signal spectrum into contiguous narrow bands. The approach is novel and has a number of significant features. The device is passive, linear, and bidirectional, and preserves phase information. S idelobes and spurious signals can be suppressed by amplitude w eighting the input transducer elements and using mode selective output transducers. Several experimental devices has been constructed on LiNb03. These were evaluated electrically and with a scanning laser probe.

Compensation of acoustic wave devices

Abstract: Compensation for the effects of environmentally caused changes and aging on piezoelectric acoustic wave devices is electrically provided by the application of a signal, such as a DC bias voltage, to the finger elements of an interdigital transducer formed on the surface of the acoustic wave device. This produces very large field concentrations at the finger edges which act to magnify the electric field and accordingly the electroacoustic effect which alters the acoustic velocity of surface acoustic waves, shallow bulk acoustic waves and reflected bulk acoustic waves propagating in a piezoelectric substrate between input and output interdigital transducers.

Sound speed determination in V2O5 single crystals using laser‐generated acoustic waves

Abstract: The application of laser‐generated acoustic waves for the determination of sound velocities in solids is reported. As an example the longitudinal sound speed along the crystallographic b axis in vanadium oxide (V2O5) has been measured for the first time yielding a value of 3200 ms−1.

Surface acoustic waves

Abstract: The book describes surface acoustic waves in solids, one of the most interesting and important types of wave motion. Classification of the main currently known types of surface acoustic waves is given. Their physical properties, including the specifics of propagation, scattering, and interaction with electrons, are discussed. Much of attention is paid to surface waves in piezoelectric crystals, which play a particularly important role with regard to a variety of applications in signal processing devices. There are numerous examples illustrating various manifestations of surface acoustic waves in science and engineering.

Signal processing using surface acoustic waves

Abstract: Signal rug Using Surface Acoustic Waves, by William R. Shreve Compact, rug ged SAW correlation, that require no adjustment make real-time convolution, correlation, and dispersive filtering less difficult. Retrofitting for Signature Analysis Simplified, by Robert Rhodes-Burke Signature analysis is a great help in troubleshooting digital products designed to use it, but what about all the products that aren't? A Fast, by High-Quality Digital Display for Instrumentation Applications, by Kunio Hasebe, William R. Mason, and Thomas J. Zamborelli Why design a custom display when you can just plug one in? This one is easy for a microprocessor to talk to. Electronic instruments and systems usually have a display of some kind to present data to humans have a readily understandable form. More and more, such systems have microcomput ers inside, and while they may be fed continuously varying real-world quantities like voltages, speeds, and temperatures, the first thing they do with this analog data is convert it to binary numbers so that internally they can operate entirely digitally. This month's cover subject, the 1 345A Graphics Display Module, is a high-quality cathode ray tube display that's designed to be built based spectrum analyzers, network analyzers, and other electronic instruments based on microcomputers. The 1 345A is easy for a microcomputer to talk to, because it understands picture descriptions in a simple binary language. With it, an instrument designer can provide high-quality graphics and text while avoiding the time and expense required to design a custom display. Among the 1345A's contributions are its speed, line quality, resolution, number of brightness levels, and compactness †\" the entire module page 20. a little larger than the CRT. It tests itself, too. The design story begins on page 20. Complex digital systems, especially computers and microcomputer-based products, are particularly difficult to troubleshoot. If you connect an oscilloscope to any point in a digital circuit, you see a voltage switching rapidly between system, levels. Without specialized test equipment and detailed knowledge of the system, it isn't possible to tell whether that \"bit stream,\" as it's called, is correct. Yet it's impractical for every field service technician to have that developed Guided knowledge and equipment. Signature analysis was developed as a response to this problem. Guided by a test numbers the technician probes points in the system and observes four letters and/or numbers (a signature) displayed by a compact instrument (a signature analyzer). Comparing these signatures …

Neutron Diffraction from a LiNbO 3 Crystal with Excited Surface Acoustic Waves

Abstract: The rocking curves of neutron Bragg reflections from LiNbO3 crystals were measured with and without acoustic waves excited on their surfaces. Travelling waves and standing waves were excited on the LiNbO3 crystals, and symmetric Bragg-case diffractions of the (030) planes were used. Enhancement of the integrated intensity and increase in the peak height were observed. A qualitative interpretation based on the diffraction of distorted crystals is given.

Nonlinear sound waves from a uniformly moving point source.

Abstract: Nonlinear sound waves from a uniformly moving source with dimensions smaller than the wavelength of the emitted sound are investigated. They are described by spherical Burgers’ equations with parameters depending on the source velocity V and the direction angle θ from the source to the point of observation. It is seen that for certain V and θ values, both for V less than and greater than the sound velocity in the medium, shock waves occur, which do not occur in nonlinear waves from a fixed sound source.

Two‐material junction as a thermoelastic source of surface acoustic waves

Abstract: In the present work the junction of two thermoelastically different materials stuck together has been used as a thermoelastic transducer of surface acoustic waves. A simplified theoretical analysis gives a criterion of convenience for the pair of materials to be used. The experiments carried out proved the efficiency of such a source of surface acoustic waves.

Experimental investigation of the acoustooptic interaction in a waveguide interferometer

Abstract: An experimental investigation was made of the transfer characteristics and signal readout efficiency of devices utilizing surface acoustic waves. The investigation was carried out using a strip optical waveguide interferometer. A prototype of this interferometer was made from a YZ-cut lithium niobate substrate. Electrodes were used for electrooptic correction of ihe initial phase shift between the optical waves in the interferometer arms and an opposed-comb transducer was employed to excite acoustic waves. The results should be useful in the development of signal

Monitoring of Strain in Layered Media Using Clad Rod Acoustic Waveguides

Abstract: The propagation of ultrasonic interface waves along the boundary between the core and cladding materials of an all-glass cylindrical rod waveguide is discussed. Axi-symmetric torsional, axi-symmetric radial-longitudinal, and core-guided, shear modes typically propagate within such a clad rod if the velocity of plane shear waves in the cladding material exceeds that velocity in the material of the core. If instead the elastic constants of the core and cladding materials are reversed so the material with the slower shear wave speed is on the outside, no modes are supported within the core but an interface wave can exist on the core-cladding boundary. In this paper, the theory of such wave propagation is first reviewed. Experimental measurements of continuous interface wave velocity and attenuation are then compared with the analytical results. These measurements have been obtained for two glass-on-glass waveguides constructed by rod-and-tube techniques from glasses having markedly different elastic properties. The waves were observed using both pitch-catch ultrasonic and optical differential interferometric techniques. The resulting improved freedom from spurious responses obtained by this single mode acoustic operation is discussed.

Interferometric phase and frequency measurements of the propagation speed of acoustic waves

Abstract: It is shown that direct measurements of the phase and frequency of the electrical signal at the interferometer output yield an increase in the sensitivity and accuracy with which the propagation speed of acoustic waves in a medium can be determined.