Showing papers on "Acoustic interferometer published in 1979"

Acoustic microscopy with mechanical scanning—A review

Abstract: Acoustic waves in liquids are known to have wavelengths comparable to that of visible light if the frequency is in the gigahertz range. The phenomena of Brillouin scattering in liquids is based on such waves. In helium near 2 K acoustic waves with a wavelength of 2000 A were studied some ten years ago at UCLA. It follows from these observations that an imaging system based on acoustic radiation with a resolving power competitive with the optical microscope is within reach if an ideal lens free from aberrations could be found. Such a lens, which was so elusive at the beginning, is now a simple device and it is the basic component in the acoustic microscope that forms the basis for this review. In this article we will establish the characteristic properties of this new instrument. We will review some of the simple properties of acoustic waves and show how a single spherical surface formed at a solid liquid interface can serve as this ideal lens free from aberrations and capable of producing diffraction limited beams. When this is incorporated into a mechanical scanning system and excited with acoustic frequencies in the microwave range images can be recorded with acoustic wavelengths equal to the wavelength of visible light. We will present images that show the elastic properties of specimens selected from the fields of material science, integrated circuits, and cell biology. The information content in these images will often exceed that of the optical micrographs. In the reflection mode we illuminate the smooth surface of a crystalline material with a highly convergent acoustic beam. The reflected field is perturbed in a unique way that is determined by the elastic properties of the reflecting surface and it shows up in the phase of the reflected acoustic field. There is a distinct and characteristic response at the output when the spacing between the object and the lens is varied. This behavior in the acoustic ieflection microscope provides a rather simple and direct means for monitoring the elastic parameters of a solid surface. It is easy to distinguish between different materials, to determine the layer thickness, and to display variations in the elastic constants on a microscopic scale. These features lead us to believe there is a promising future for the field of acoustic microscopy.

Acoustic wave devices with temperature stabilization

Abstract: An acoustic wave device comprises a substrate carrying two or more acoustic components aligned in different directions and electrically connected together in parallel. The phase slope of the acoustic components are similar but their temperature coefficients of delay are different whereby their resultant frequency response is compensated over a useful temperature range. The acoustic components may be delay line employing surface waves or surface skimming bulk waves, or one or two port resonators using surface waves.

Scattering Analysis and Design of SAW Resonator Filters

Abstract: Simple approximate analytical expressions for the radiation resistance of meander tine and grating transducers for magnetoelastic surface wave transduction on YIG are developed. The standard simplifying assumptions of weak magnetoelastic coupling and the magnetostatic approximation are employed. In addition, the surface wave is heuristically modeled as a plane shear wave and the inhomogeneous elastic equation of motion is solved in the coupled mode approximation. The approximate expressions for the meander line radiation resistance compares well with a more exact numerical treatment done by other investigators. Manuscript received October 30, 1978; revised December 11,1978. This work was supported in part by the National Science Foundation under Grant ENG 75-18077. The author is with the Department of Electrical Engineering, University of Minnesota, Minneapolis, MN 55455. A

Liquid crystal cell for acoustical imaging

Abstract: The invention is related to an acousto-optical liquid crystal cell and the ways of using it in acoustical holography and imaging systems. The molecules of the liquid crystal layer can be reoriented in a direction perpendicular to the direction of an ultrasonic wave propagating in the medium. The cell has multi-layered walls providing high acoustical transparency for waves incident at various angles, such that multiple reflexions and parasitic effects in the liquid crystal are reduced. This results in a wide acoustic imaging field and high resolving power for details of an acoustic object. This cell makes possible the direct and real-time conversion of an acoustical hologram into a visible image representing at will the intensity on the phase variations of ultrasonic waves coming from the internal structures of a body.

Unusual Parametric Effects on Line Acoustic Waves

Abstract: Absrruct-Line acoustic wave (LAW) devices, in which waves are guided in a narrow region along an edge, permit one to achieve high local strains with relatively Little total power. One would expect to observe strong harmonic generation and parametric conversion, resulting from the fust-order elastic nonlinearity. However, first-order nonlinear effects are nulled out to a high degree by the symmetry properties of the LAW. Conventional pumping produces only small effects and second harmonic generation is weak. Pumping at one-half the usual frequency, however, interacts with the seconderder nonlinear elastic coefficient which is not subject to nulling and produces useful outputs which increase rapidly at higher frequencies. Experimental results obtained with a LiNb03 LAW device at 100 and 200 MHz are presented.

The Transmission of Acoustic Plane Waves at a Jet Exhaust

Abstract: An experimental study was conducted to determine the plane-wave acoustic transmission loss at the exit of an unflanged constant diameter circular duct with subsonic flow. This model geometry simulated the physical conditions at an engine exhaust in the simplest manner. Higher-order acoustic modes were not considered since at typical core-noise frequencies these modes are usually cut off and therefore decay before reaching the nozzle exit. The acoustic transmission coefficient was evaluated over a large range of jet Mach numbers and reduced frequencies. Results show that the plane-wave mode component of internal noise is transmitted at the duct exit interface with minimal attenuation at the high Mach numbers relevant to engine operating conditions.

Analysis of Finite-Width Interdigital Transducer Excitation Profiles

Abstract: Abstruct-In virtually all work on interdigital transducers, it is assumed that the excitation profiie across the width of the transducer is constant. This is a reasonable first approximation to make and in many cases provides acceptable predictions of experimental results Experimentally, the condition is approximated by keeping the interdigital transducer wide. However, as constraints on device size are applied to surface acoustic wave filters, the widths of interdigital transducers are being forced into a range where the transverse electrostatic end effects must be accounted for in describing device performance. As a step toward improved filter synthesis, the three-dimensional electrostatic field of a double electrode interdigital transducer has been found. Variations in the electrode charge distribution have been studied as a function of the distance between the electrode ends and the bonding pads and as a function of substrate anisotropy. Numerical results are provided for end gaps of fh, l h , 2h, and 3h on an isotropic substrate and for a $h end-gap transducer on (YZ) LiNbO,.

Investigation of transient acoustic waves in KDP electrooptic modulators

Abstract: Piezoelectrically generated acoustic transients in longitudinal KDP modulator crystals were investigated, using a photographic method developed for visualizing the acoustic waves. The method gives the possiblity of following the processes of acoustic wave propagation, the reflections of waves at the side faces of the crystal and the wave diffusion caused by crystal imperfections.

SAW Transduction on Silicon Substrates with PVF 2 Films

Abstract: PVF2 films have been used to excite longitudinal acoustic waves in various media. They have been applied extensively for transduction into water because of the good acoustic impedance match. The films have not been utilized for SAW transduction on nonpiezoelectric substrates because the films are weak in shear and have extremely large shear attenuation at room temperature. In the current study, the large losses are overcome by operating the acoustic delay lines at reduced temperatures. At lower temperatures, SAW propagation in PVF2 on (001)-oriented silicon is observed at frequencies in excess of 100 MHz. Untuned insertion losses of 60 dB were obtained with N = 20 interdigital transducers (15 wavelength aperture) and 48 wavelength propagation paths. Theoretical calculations are presented for the first four modes of the layered system.

Gasdynamic perturbations of the gas stream in pulseperiodic CO2 lasers. II. Acoustic waves

Abstract: The gas channel of a pulse-periodic CO2 laser is considered as an acoustic resonator. Experimental and theoretical investigations are carried out on acoustic waves in such a resonator and on how they limit the pulse-repetition frequency. The results of a numerical calculation are compared with the experimental data.

Three-dimensional acoustic Fabry-Perot interferometer of α-quartz as converter of acoustic modes

Abstract: A cube of α-quartz with polished flat and parallel sides was used as an acoustic three-dimensional Fabry-Perot interferometer. The sides of the cube are perpendicular to the crystallographic axesx, y, z of the quartz. By means of a transducer, transverse elastic waves were injected along thez-axis. Because of anisotropy, this produces a diffuse acoustic field in the cube. From this diffuse field, the interferometer selects pure longitudinal acoustic waves along thex andz axis, which were identified by means of the different velocities of propagation.

Investigation of piezoelectrically induced acoustic transients in KDP crystals

Abstract: Acoustic transients generated by high voltage pulses in longitudinal KDP modulator crystals were investigated. Photographic method has been developed to visualize the acoustic waves. The experiments directly demonstrate the piezoelectric acoustic wave generation, the acoustic wave propagation, the reflexion, diffusion and diffraction of acoustic waves and the interaction of acoustic waves with crystal imperfections. From the experimental results the velocity of shear waves and the related elastic constant can be evaluated.

Grating Acoustic Scanner Characteristics Measured by an Optical Probe

Abstract: The grating acoustic scanner (GAS) produces an electronically scanned and focused beam of acoustic longitudinal waves by coherent scattering of chirped Rayleigh waves from an array of parallel grooves fabricated on the surface of a substrate. A 100 MHz LiNbO, grating scanner with lcm field of view has been constructed and studied. By using a laser probe based on the acousto-optic Bragg effect, we have measured the focused beam profiles of the scanner. Lateral and depth resolution were approximately 100 pm and 375 pm respectively.

A monolithic SAW-CCD

Abstract: IN RECENT YEARS the charge-coupled device’ has been creating a great deal of interest for applications in memory, signal processing and imaging. The incentive for the interest lies in the simplicity in structure and high density. However, the CCD technology has a number of drawbacks which limit the density, the speed and the processing simplicity. For instance, in a typical CCD structure three or four phase clocks arc required to transfer the charges, multilevel metallization is required to effect the multiphase clocks, buried channel is required t o improve the speed, and for imagers, separate charge storage and transfer areas must be provided because of the masking of the clock busses. This paper will offer a study of a way to circumvent these problems by means of surface acoustic waves involving a monolithic device, whose operation will be described. In the SAW--CTD device, surfacc acoustic waves are used to create traveling longitudinal electric fields in the silicon and t o replace the multiphase clocks of CCD. The traveling electric fields create potential wells which will carry along charges that may be stored in the wells; Figure 1. The charges may be injected into the wells by light or using a PN junction as in a conventional CCD.

Interferometer matching to a plane wave

Abstract: The power coupled to an interferometer from an incom­ ing beam has been analyzed for the cases of infinite aperture and different beam waists and phase front curvatures and for a finite aperture. The transformation of the incoming beam is usually accomplished by means of systems of lenses. The purpose of this work is to calculate the power coupled from a plane wave limited by a pinhole into the modes of the interferometer. The radius of the pinhole that maximizes the power coupled to the fundamental mode is also calculated. Because the modes of an interferometer form a complete set, the field f(a) that results from limiting the plane wave by a pinhole of radius a can be expanded in terms of these modes; thus Now at z =0, the coupling from a Gaussian beam of beam waist w0 to a set of modes characterized by a beam waist w0 is z

Surface Acoustic Waves

Abstract: The physical properties of surface acoustic waves and their use for processing radar, television and radio signals have been discussed. A brief account of surface acoustic wave devices such as delay lines, filters, oscillators and convolvers is also presented.

A Statistical Model for Backscattering from a Randomly Fluctuating Surface

Abstract: An analysis is presented of the scattering of surface acoustic waves (SAW) by posts serving as spacers between a substrate supporting a Rayleigh wave and a (semiconductor) superstrate. The superstrate with Rayleigh velocity considerably larger than that of the substrate is modeled as a springlike load on the post. Radiation patterns for the power scattered into Rayleigh waves and bulk waves are Manuscript received June 8, 1978; revised August 18, 1978. This work was supported by the National Science Foundation under Grant The authors are with the Department of Electrical Engineering and Computer Science and the Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139. ENG77-24981. shown. Scattering of surface acoustic waves is studied as a function of the material parameters and the geometry of the post supports. Comparison with experiments is made. This study is relevant to the designing of efficient convolvers which minimize the scattering due t o the presence of a post-support structure. M