Showing papers on "Acoustic interferometer published in 1975"

Surface Acoustic Wave Multielectrode Transducers

Abstract: In the basic SAW transducer, the fingers are connected alternately to the two bus-bars. Interesting responses can be ob- tained if there are more than two fingers per fundamental acoustic wavelength, and the fingers are connected to the bus-bars in various ways. Several of these structures are discussed qualitatively. The transmission spectra obtained from these various schemes are con- firmed experimentally. Quantitative calculations of admittance are also performed for several transducer structures. The measured data agree well with calculations.

Characteristics of Wedge Transducers for Acoustic Surface Waves

Abstract: Wedge transducers have long been used to excite and detect elastic surface waves, but there has beenno complete theoretical description of the phenomena that underly their operation. In this paper we show that the phenomena, when the wedge operates as a detector, are: 1) the excitation by the incident surface wave of a leaky wave propagating beneath the wedge; 2) the radiation of the leaky wave fields into the wedge; and 3) the detection of the nonuniform leaky-wave fields by the bulk wave transducer on the slant face of the wedge. By studying these phenomena, we have found the factors influencing the efficiency of the wedge transducer and have determined the conditons under which it may be made as high as 80% of the radiation e5ciency of the bulk-wave transducer. Because of reciprocity, the same efficiency is obtained when the wedge is used to excite surface waves. To obtain high efficiencies, it is necessary to control the perturbation of the surface wave due to the presence of the wedge; methods for achieving such control are described in a companion paper.

Method and apparatus for acoustic and optical scanning of an object

Abstract: A microscope for scanning an object with light and acoustic waves and producing both acoustic and optical images thereof. The microscope includes optical and acoustic lenses that focus both the light and acoustic waves on substantially the same point on the object. In one portion of the microscope the acoustic waves and light propagate coextensively through the same medium. The apparatus generates a simultaneous presentation of both acoustic and optical images formed by the microscope.

An interferometric investigation of laser−supported absorption waves

Abstract: Laser−supported detonation waves, other laser−supported absorption waves, and plumes of vaporized material were the subject of interferograms. Both instantaneous ruby laser interferometry and time−resolved argon laser interferometry were used to study these events. Qualitative behavior is seen in the interferograms which was not evident in photographic studies of these phenomena, such as the progress of radial shock waves and structure in the absorption zone. Abel inversion is used to obtain quantitative radial behavior of the change in the index of refraction. The differences between the laser−supported absorption waves ignited at the surfaces of several materials are discussed. Alumina specimens produced vapor plumes under these conditions whose temporal motion can be followed because of AlO absorption of the argon laser wavelength. The changes in the index of refraction were measured for similar events at the different wavelengths of the instantaneous and time−resolved interferometers and were used to ...

Wideband guided - Wave acoustooptic Bragg devices using multiple tilting surface acoustic waves

Abstract: waveslinch gives 90% of the response of an ideally flat mirror. To isolate the laser from the interferometer, and to provide means for varying the beam balance in the two legs, a polarizing beam splitter (PBS) with a quarter wave plate in each leg of the interferometer is used. The polarization angle of the incident beam is varied to change the beam balance. A second PBS is used to analyze the interference. By using both outputs from this second PBS, which has a 180” relative phase shift, the response is doubled and common mode noise is minimized. This system, with associated electronics and display circuitry, has been used to measure and display ultrasonic waves, and some examples are given. It is being used to measure ultrasonic transducer response, to measure and display the interaction between biologic tissue and ultrasound, and as an aid in the design of ultrasonic lenses. In this paper we want to stress the optical design of the system and discuss other applications in the measurement of small motions of mechanical objects.

Method and apparatus for acoustic scanning using waves scattered by an acoustic grating

Abstract: An acoustic scanning apparatus is described having an acoustic grating for scattering waves into a focused beam. Surface acoustic waves are generated by a chirp signal generator and are introduced along one surface of the scanning apparatus. These waves propagate along the surface, are scattered by the acoustic grating and are thereby converted into bulk acoustic waves. The bulk acoustic waves converge into a focused beam inwardly directed at an angle to the surface acoustic waves. The focused beam scans at substantially the same speed as the surface acoustic waves traveling along the surface of the apparatus. The acoustic grating can also be used to convert bulk waves to surface acoustic waves as either a variable chirp rate generator or a variable pulse compression filter.

Holographic Interferometry with Acoustic Waves

Abstract: Holographic interferometry has become one of the most important applications for holography. Except for a few preliminary experiments very little has been done to transfer the optical technology to acoustics. In this paper we report an extensive series of experiments demonstrating the practicality of acoustical holographic interferometry. Specifically, we have demonstrated double exposure single hologram interferometry, double exposure two-hologram interferometry, two-hologram aberration correction, two- frequency contouring and multiple-frequency contouring. Applications envisaged for this technique include large deformation analysis, periodic inspection of critical structures, imaging and mapping of low contrast objects such as the sea bottom, mapping of inaccessible inner surfaces of metal structures, and aberration free imaging through curved barriers. The results of these experiments will be shown and extrapolated to potential applications.

Surface wave convolver apparatus

Abstract: Apparatus for convolving acoustic surface waves without dispersion comprising a piezoelectric substrate having surface acoustic waves generated at opposite ends thereof and directed towards an interaction region formed from a semiconductor film deposited thereon. The film is deposited on the substrate at such an angle with respect to the direction of propagation of each of the two acoustic surface waves so that the dispersive components of the wave vectors associated with the surface acoustic waves refracted in the interaction region substantially cancel. Apparatus is also disclosed for substantially eliminating undesired wave reflections in a convolver operating in the degenerate mode wherein a conductive array of electrode fingers is disposed at an angle with respect to the direction of propagation of the acoustic surface waves such that the reflections therefrom are directed away from the paths traversed by said acoustic surface waves.

Observation and study of SAW by holographic technique

Abstract: A holographic technique for studying amplitude distribution of traveling, reflecting, and standing surface acoustic waves is described. The amplitude distribution can be directly displayed, and the phase velocity is accurately determined.

Transducers Applied to Measurements of Velocity Dispersion of Acoustic Surface Waves

Abstract: This talk concerns two new acoustic surface wave (SAW) transducer units developed and applied to the field of nondestructive testing. We confine ourselves here to tone burst transduction of Rayleigh waves (at MHz frequencies), although CW operation and (for example) Lamb and bulk waves are also possible. Disciplines Materials Science and Engineering | Structures and Materials This 6. transducers is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/cnde_yellowjackets_1975/48 TRANSDUCERS APPLIED TO MEASUREMENTS OF VELOCITY DISPERSION OF ACOUSTIC SURFACE WAVES * Harold M. Frost and Thomas L. Szabo Air Force Cambridge Research Laboratory (LZM) Hanscom Air Force Base, Massachusetts This talk concerns two new acoustic surface wave (SAW) transducer units developed and applied to the field of nondestructive testing. We confine ourselves here to tone burst transduction of Rayleigh waves (at MHz frequencies), although CW operation and (for example) Lamb and bulk waves are also possible. One of these new units is an array of three comb transducers and the other an electromagnetic transducer (EMT) of new design. Instead of printed circuit board or wire technology for the EMT, we used flat cable. A third transducer type the conventional wedge is included for comparison. We will show that the comb and electromagnetic transducers we've developed have significant advantages over the wedge. Directly below we describe our EMT ' s; later on in this talk we'll describe in detail the new comb design involving one transmitter transducer and two receivers. The transducer medly in Fig. 1 shows various wedge transducers on the top row. On the bottom row from left to right are the three-comb transducer unit, a flat cable EMT, and an EMT wound from wire. A closeup of a flat cable transducer as shown in Fig. 2 shows a commercially available flat cable section with ends soldered in a meander fashion. The conductor pattern so obtained is more uniform than typically realizable with wire, as seen by the photo in Fig. 3 for an early fabrication attempt. One thing that's easy to do is to have nonuniform wire spacing. We've operated the flat cable transducers in (Rayleigh wave) transmitter-receiver delay lines. The one shown in Fig. 2 is resonant about 1.15 MHz on Al. We've obtained two-way insertion losses of 90 dB while using magnetic fields of 5 kilogauss, a single winding of 15 conductor pairs, simple matching networks, and aluminum as a SAW substrate. Shown in Fig. 4 is a photo of a self-contained, compact electromagnetic transducer with commercially available flat cable conductors between flexible plastic backings. On aluminum the fundamental resonance is 2.2 MHz. The cable is mounted on·a permanent magnet with magnetic axis normal to the flat cable surface. There was a question earlier in this conference on whether electromagnetic transducers can replace conventional ones. I'm not going to answer that completely in the affirmative, but I can say that this transducer can be hand-held and moved over a test surface at will just as one can with a wedge transducer, while avoiding the serious problems of the wedge (to be described later.) The permanent magnet partially shown in Fig. 4 consists of a Co-Sm alloy with a maximum field of about 3 kilogauss. The field is normal to the SAW * Presently at: Food & Drug Administration, Bureau of Radiological Health, Division of Biological Effects (HFX-120), 5600 Fishers Lane, Rockville, Md. 20852

Correlation and convolution of bulk acoustic waves in nonpiezoelectric solids

Abstract: Nonlinear interactions between collinear bulk acoustic waves of orthogonal polarizations have been used to perform convolution and correlation in a nonpiezoelectric crystal. The analysis of the device operation and experimental results are reported.

The propagation of plane waves and higher order acoustic modes in multisectioned ducts

Abstract: A theoretical and experimental study of acoustic propagation in an anechoically terminated multisectioned duct was performed A unique source array consisting of two concentric rings of sources, providing phase and amplitude control in the radial as well as circumferential direction, was developed to generate plane waves and both spinning and non-spinning higher order modes Measurement of attenuation and radial mode shapes were taken with various finite length liners inserted between the hard wall sections of a duct with an anechoic termination A search technique was developed to find the complex eigenvalues for a liner under the assumption of a locally reacting boundary condition The experimental results were compared with a theoretical analysis which includes the modal transmission and reflection at the interface of each duct section, and this indicated that the local reaction boundary condition is valid for three liner configurations

Levitation of objects using acoustic energy

Abstract: Activated sound source establishes standing-wave pattern in gap between source and acoustic reflector. Solid or liquid material introduced in region will move to one of the low pressure areas produced at antinodes and remain suspended as long as acoustic signal is present.

Light beam deflector using surface acoustic wave - guided optical wave interaction

Abstract: The use of the acousto-optical interaction between guided optical waves and surface acoustic waves to make an efficient high resolution light deflector is discussed. Details of a device with a 150MHz bandwidth and 125 experimentally observed spots and using a novel acoustic transducer, are given.