Showing papers on "Acoustic interferometer published in 1999"

Acoustic impedance measuring apparatus using ultrasonic waves

Abstract: An acoustic impedance measuring apparatus emits ultrasonic waves to a target measurement object and measures the acoustic impedance of the target measurement object by ultrasonic waves fed back from the target measurement object. This acoustic impedance measuring apparatus includes an ultrasonic transducer, pulse signal generator, signal separator, frequency converter, parameter extractor, and acoustic impedance calculator. The pulse signal generator generates a pulse signal to be applied to the ultrasonic transducer. The signal separator separates, from an output from the ultrasonic transducer, an immediate ultrasonic response signal resulting from ultrasonic waves reflected by the surface of the target measurement object. The frequency converter obtains the frequency characteristics of the immediate ultrasonic response signal. The parameter extractor extracts predetermined parameters from the frequency characteristics. The acoustic impedance calculator calculates the acoustic impedance of the target measurement object by using the parameters extracted by the parameter extractor.

Laser chamber with minimized acoustic and shock wave disturbances

Abstract: A laser chamber (100) had angled reflectors (116, 118) that reflect acoustic and shock waves away from the laser discharge area (103) to minimize acoustic and shock wave disturbances. The angled reflector may have different configurations to assist in the dissipation of the acoustic and shock waves. For example, the angled reflector (116, 118) may have a modulated reflective surface, such as having grooves or holes defined within the surface. Further, the angled reflector (116, 118) may have a reflective surface with acoustic and shock wave absorbing properties. The reflective surface with absorbent properties may be a felt metal or have multiple layered porous surfaces. In addition, the walls of the laser chamber (100) may be modulated to assist in the dissipation of the acoustic waves and shock waves through absorption, scattering, and by generating interference within the reflected waves. Multiple layered porous surfaces may be used along the walls to absorb and scatter incident waves. The walls of the laser chamber (100) may also be covered with an acoustic and shock wave absorbing material, such as felt metal. In other embodiments, the walls of the laser chamber (100) are modulated with grooves (132), such as triangular or rectangular horizontal grooves, which scatter incident waves and generate interference within reflected waves.

Fiber optic acoustic sensor array based on Sagnac interferometer

Abstract: A fiber optic acoustic sensor array is based upon a Sagnac interferometer rather than being based upon Mach-Zehnder interferometers as in known acoustic sensor arrays. The fiber optic acoustic sensor array is used to detect acoustic waves in water. By basing the sensor array on the Sagnac interferometer rather than on a Mach-Zehnder interferometer, the sensor array has a stable bias point, has reduced phase noise, has a larger dynamic range, and allows a broadband signal source to be used rather than requiring a more expensive narrowline laser. A large number of acoustic sensors can be multiplexed into the architecture of the Sagnac interferometer.

Signal processing of elastic surface waves for localizing buried land mines

Abstract: A system that uses elastic surface waves and electromagnetic waves has been developed to detect buried land mines. An algorithm based on local spatial frequency analysis is presented to illustrate the dispersive effect of the land mine on the acoustic waves and to estimate the wave velocity as a function of position and temporal frequency. In addition, an imaging algorithm is presented which calculates the reflected energy and generates a two-dimensional image that localizes the buried mines.

Asymmetric acoustic radiation in leaky SAW resonators on lithium tantalate

Abstract: We discuss an acoustic loss mechanism in leaky surface-acoustic wave resonators on 36°YX-cut lithium tantalate substrate. Our recent acoustic field scans performed with an optical Michelson interferometer revealed a spatially asymmetric acoustic field atop the busbars of a resonator, giving rise to acoustic beams which escape the resonator area and lead to undesired losses. Here, we link the phenomenon with the inherent crystalline anisotropy of the substrate crystal: the shape of the slowness curves and the asymmetry of the polarization for the leaky surface-acoustic waves propagating at an angle with respect to the crystal X-axis.

Acoustic touch position sensing system with large touch sensing surface

Abstract: A touch position sensing system including a transducer configured to transmit and modulate by pseudo random coding acoustic waves and to decode reflected waves generated by the acoustic waves by autocorrelating the pseudo random coding; a substrate configured to propagate the acoustic waves, including a touch surface having a first axis along a side of the perimeter of the substrate and a second axis which is perpendicular to the first axis and located along a second side of the perimeter; and, a first reflective array configured to reflect the acoustic waves transmitted by the transducer such that reflected waves are generated traveling parallel to the second axis, having a length substantially as long as the side of the perimeter corresponding to the first axis including partially reflective grating along the length and disposed lengthwise along the first axis of said substrate. Wherein, a touch to the touch surface attenuates the reflected waves such that said modulation by pseudo random coding of acoustic waves is varied, the transducer configured to detect the location of the touch based on variation in autocorrelation of the varied pseudo random coding included in the reflected waves.

Apparatus and method for measuring the thickness of a coating

Abstract: An apparatus and method for measuring the thickness of a coating adhered to a substrate. An electromagnetic acoustic transducer is used to induce surface waves into the coating. The surface waves have a selected frequency and a fixed wavelength. Interpolation is used to determine the frequency of surface waves that propagate through the coating with the least attenuation. The phase velocity of the surface waves having this frequency is then calculated. The phase velocity is compared to known phase velocity/thickness tables to determine the thickness of the coating.

Scanning phononic lattices with surface acoustic waves

Abstract: We examine the transmission and reflection of surface acoustic waves from a two-dimensional hexagonal lattice. Highly anisotropic signals are observed by continuously scanning the wavevector angle. Preliminary models of wave propagation through this phononic lattice predict the acoustic dispersion and a complete band gap; however, the experimental results indicate that more realistic modeling of surface acoustic waves in elastically modulated media is required.

Active impedance control within a cylindrical waveguide for generation of low-frequency, underwater plane traveling waves

Abstract: A cylindrical, water-filled acoustic waveguide with an active termination was used to generate constant-frequency, plane traveling waves. The waveguide was constructed of acrylic tubing with an underwater sound projector flanged to each end. One projector acted as the primary source and generated continuous harmonic waves. The active control system measured the transfer function between two hydrophones located inside the waveguide and used a pattern search algorithm to adjust the secondary source amplitude and phase in order to drive the measured transfer function to that for a plane traveling wave. The active control system was able to reduce the reflection coefficient to below 0.05 within the frequency range 12.5–400 Hz and adjust the acoustic pressure/particle velocity ratio to match that of a plane progressive wave.

Generation and observation of GHz ultrasonic waves on liquid surfaces and a liquid/liquid interface by transient reflecting grating method

Abstract: We optically generated and observed GHz ultrasonic waves on liquid surfaces and a liquid/liquid interface for the first time using the transient reflecting grating (TRG) method. Four kinds of samples were used for measurement of the surfaces; two types of black ink, an aqueous solution of crystal violet (CV aq solution) and ethanol aqueous solutions of CV. A cyclohexane/CV aq solution interface was used for measurement of the liquid/liquid interface. The 0.7 GHz and 0.6 GHz ultrasonic waves were generated on the liquid surfaces and the liquid/liquid interface, respectively. These ultrasonic waves resemble longitudinal acoustic waves partly localized at the surface, and they cause surface displacement. The amplitudes of TRG signals from surfaces of the CV mixed solvent solutions were found to be greatly affected by both the viscosity and surface tension. This result indicated the viscosity and interface tension must be considered as perturbations in the elastic theory. The strong dependence on interface te...

Therapy apparatus with a source of acoustic waves

Abstract: A therapy apparatus has a source with an acoustic axis for generating acoustic waves converging in a focus lying on the acoustic axis. The source has a light generator that emits a focused light beam of visible light with a substantially parallel beam path that substantially coincides with the acoustic axis of the source and makes it visible.

Surface waves over a convex impedance surface

Abstract: The existence of the surface wave in an upward refracting medium has been predicted by Raspet et al. [J. Acoust. Soc. Am. 89, 107–114 (1991)]. Making use of an acoustic analogy, one is able to study the surface waves above a convex cylinder and, hence, to simulate the propagation of sound over an impedance ground in an upward refracting medium. A suitable comblike surface may be used to facilitate the generation of surface waves above the convex ground. This paper describes laboratory experiments for the observation of surface waves over a convex impedance ground.

Sagnac effect in ring interferometers on “slow” waves

Abstract: We consider the Sagnac effect in ring interferometers on magnetostatic and surface acoustic waves. It is shown that the Sagnac effect for waves of arbitrary type (including both magnetostatic and surface acoustic waves) propagating in an arbitrary medium cannot be calculated using Galilean transformations but is explained within the framework of the special relativity and is related to the difference between the phase velocities rather than group velocities of counter-propagating waves in the rotating reference frame. We also show that the phase difference of counterpropagating waves due to the Sagnac effect depends on neither the phase velocity of the wave in a medium at rest nor the dispersion of the medium; it depends only on the wave frequency and the angular velocity of interferometer rotation. The minimum angular velocity that can be measured in the ring interferometers using magnetostatic and surface acoustic waves is estimated.

Acoustic treatment performance testing

Abstract: A method and system for acoustic treatment performance testing in a free-ld acoustic environment is provided. A sound source directs a gated acoustic pulse at an acoustic treatment. Acoustic pressures of the gated acoustic pulse and reflected energy from the acoustic treatment are measured from a location approximately in-line with the source and the acoustic treatment. This measurement location is at least one-half the wavelength of the frequency of interest away from the source and is at least a distance equal to (t*c/2) away from the acoustic treatment where t is equal to the duration of the gated acoustic pulse and c is equal to the speed of sound in the free-field acoustic environment. The acoustic pressures of the gated acoustic pulse and reflected energy are compared as an indication of performance of the acoustic treatment at a frequency of interest.

Extraordinary case of acoustic wave acceleration due to electrical shorting of piezoelectrics

Abstract: The regions of anomalous (decelerating) influence of piezoelectricity on the phase velocities of surface and bulk acoustic waves are numerically found near the orientations where the phase velocities of two acoustic modes coincide. Calculations of surface acoustic waves (SAWs) are performed for a potassium niobate crystal. An unusual, inverse in sign, velocity shift of Rayleigh-type SAWs caused by electrical shorting at the surface of the crystal is accompanied by a rise of the tranverse (shear-horizontal) displacement component. Nevertheless, the velocity shift is inverse in sign even in the case when this transverse component tends to zero. Bulk acoustic waves are studied in a semiconductor selenium crystal. The cone of angles confining the region of anomalous “piezoelectric softening” with increasing the conductivity of the crystal is determined.

X-ray standing waves effects for a multilayer mirror modulated by surface acoustic waves

Abstract: The x-ray standing wave technique has been used to characterize a multilayer mirror modulated by surface acoustic waves. Upon sinusoidal modulation of a multilayer by surface acoustic waves, fields of x-ray standing waves are found to form around the Bragg conditions and at the angular positions of the rocking curve diffraction satellites. It is shown that the angular position of the diffraction peaks in the rocking curve and the amplitude of x-ray standing waves are determined by the wavelength and the amplitude of the surface acoustic waves, respectively.

Surface and pseudo surface acoustic waves in langatate

Abstract: Langatate (LGT, La3Ga5.5Ta0.5O14) is a recent addition to new materials of the trigonal crystal class 32, which also include langasite, langanite, and gallium phosphate. These materials belong to the same crystal class as quartz and all have promising quartz-like characteristics with respect to temperature. They have higher electromechanical coupling coefficients that will lead to higher bandwidth devices for surface and bulk acoustic wave (SAW and BAW) applications. These materials present higher densities and permittivities than quartz, with resulting SAW phase velocities values which are 13 to 25% smaller than that of ST-X quartz. While such a reduction in the phase velocity may pose a problem for higher frequency applications, due to the increased difficulty in the actual device fabrication, repeatability, yield, and ultimately cost, it would extend the use of SAWs to lower frequencies. Pseudo surface acoustic waves (PSAWs) are a possible solution to the high frequency problem, since both the PSAW and the high velocity or HVPSAW have phase velocities which are 40 to 100% higher than that of the SAW. In the present work SAW contour plots of the phase velocity, the electromechanical coupling coefficient, and the power flow angle, are given showing the orientations in space where high coupling are obtained, with the corresponding power flow angles and phase velocity characteristics for these orientations. For the PSAW and HVPSAW modes, calculations are presented for these types of waves for some selected rotated cuts. The present study shows that propagation losses for the PSAWs of about 0.01 dB/wavelength, and phase velocities approximately 20% higher than the SAW, are observed along specific orientations planes for the PSAW, thus providing for higher frequency surface acoustic wave device applications.

Manipulation of acoustic waves using a functionally graded material and process for making the same

Abstract: A device for manipulation of acoustic waves is provided, comprising a functionally-graded material for interposing between a source of the acoustic waves and a target, which may be a detector of manipulated acoustic waves. The functionally-graded material has a gradient in acoustic wave velocity which is obtained by the generation of a gradient in at least one of the following properties: elastic modulus, Poisson's ratio, and density, that is perpendicular to a direction of propagation of the acoustic waves. The gradient is axial. Biaxial acoustic velocity gradients may be used for focusing/waveguiding (high-low-high) or dispersing (low-high-low), while monoaxial acoustic velocity gradients may be used for wave steering. Also in accordance with the present invention, a method of making the device is provided, comprising: (a) providing the source of acoustic waves; (b) providing the target for acoustic waves, e.g., detector of manipulated acoustic waves; (c) providing the functionally-graded material having a gradient in at least one material property; and (d) interposing the functionally-graded material between the source of acoustic waves and the target for acoustic waves such that the gradient is perpendicular to a direction of propagation of the acoustic waves. The functionally-graded material so provided can be used to manipulate, i.e., focus, disperse, steer, waveguide acoustic waves for applications such as, acoustoelectronics, acoustooptics, SONAR, ultrasonic imaging, non-destructive testing (NDT), etc.

Device and method for determination of physical parameters for a two-phase mix by propagation of an acoustic wave in the continuous phase of the two-phase mix

Abstract: A device measures the propagation time for an acoustic wave in a continuous phase of a two-phase mix (28) comprising the continuous phase and a dispersed phase forming droplets (40) in the continuous phase. The device comprises an electro-acoustic transducer (12) capable of emitting acoustic waves (30) and outputting a reception signal of reflected acoustic waves, a signal pulse generator capable of determining a propagation time starting from signals output by the transducer, and an acoustic lens for focusing acoustic waves and the frequency of the acoustic waves being adjusted to cause reflection of the waves on the droplets of the dispersed phase, essentially located within a focusing area.

Production of monochromatic radiation in an argon plasma by means of acoustic waves

Abstract: It is shown that monochromatic radiation (λ1=5888 A, λ2=5882 A, and λ3=4876 A) can be obtained in a gas-discharge plasma in argon with the use of acoustic waves.

Measurement of linear velocity using a resonant ring interferometer with a low-coherence light source

Abstract: It is demonstrated theoretically and experimentally that linear velocities of reflecting objects may be measured using a resonant ring interferometer with a low-frequency light source. The limiting sensitivity of this interferometer is estimated. It is shown that a resonant ring interferometer can be used to measure extremely low linear velocities corresponding to subhertz Doppler frequency shifts of light, which cannot be measured by conventional Doppler techniques based on direct measurements of the frequency difference between the initial and reflected waves.

Development of a scan system for Rayleigh, shear and longitudinal wave velocity mapping

Abstract: A high precision scanning acoustic microscope system to generate C-scan type velocity images of Rayleigh, surface skimming longitudinal (SSLW) and surface skimming shear waves (SSSW), has been developed. The acoustic microscope utilizes impulse excitation to separate in the time domain the direct reflected signal from the surface acoustic wave signals. Differences in the arrival times of these signals at two defocuses are used to compute the velocity and display a 2D x/y velocity in real time during the scan. A map of the Young's modulus of the material is generated using the velocity images. Examples of measurement on standard samples and Ti-6Al-4V alloys are presented.

Superhigh electromechanical coupling for acoustic plate waves in potassium niobate

Abstract: The characteristics of acoustic waves propagating in thin plates of single crystal potassium niobate are theoretically investigated. It is found that acoustic plate waves can provide extremely high values of electromechanical coupling. For example, values of Δv/v, the fractional velocity change produced by electrical shorting of the surface, as high as 0.5 can be obtained with the shear horizontal (SH0) wave. The influence of a thin conducting layer on the velocity and attenuation of plate waves is investigated. It is shown that variations in these parameters as high as 50% and 30 dB per wavelength can be achieved for change in layer sheet conductance from 10-7 to 10-5 S.

Investigation of the elastic parameters of hardened steel by laser-excited and detected acoustic waves

Abstract: Case hardened steel samples with different hardness are investigated by laser-excited and detected acoustic waves. The correlation between several temporal and spectral features of the acoustic waves and the microstructure of the samples is assessed.

Influence of a thin layer with arbitrary conductivity on the characteristics of acoustic waves in potassium niobate

Abstract: The influence of a thin layer of arbitrary conductivity on the characteristics of acoustic waves in potassium niobate is investigated theoretically. The conductivity of a thin layer on the surface of a potassium niobate crystal or plate is shown to have a significant influence on the damping and velocity not only of symmetric Lamb waves and quasi-shear-horizontal waves but also of Gulyaev-Bleustein waves. It is found that a relative change in velocity as large as 50% can be achieved for quasi-shear-horizontal waves by altering the surface conductivity. The results obtained reveal great prospects of using potassium niobate to create acoustoelectronic devices with controllable characteristics.

Laser generation and detection of surface acoustic waves using gas-coupled laser acoustic detection

Abstract: Laser generation and detection of ultrasound has the advantage of requiring no mechanical contact with the materials under investigation. We previously reported [1] laser-based measurements on Lamb waves in graphite/polymer composite laminates using a confocal Fabry-Perot interferometer for detection. Related work by other groups includes air-coupled detection of Lamb waves in similar composites using capacitive transducers [2,3] and interferometric detection of Lamb waves in paper [4]. Our earlier work has been extended using Gas-Coupled Laser Acoustic Detection (GCLAD), an economical alternative laser-based method which has the additional advantage that the detection laser beam is not reflected from the sample surface. GCLAD is thus particularly useful for materials with surfaces of poor optical quality. We demonstrate below that the combination of laser generation and GCLAD can be used to obtain well-resolved surface-acoustic waves (SAWs) in a variety of materials, including metals, paper, thin films, and composite pre-preg tape. We also show some preliminary SAW scans obtained with laser generation and GCLAD using metallic samples. Each pixel in the scans represents the strength of a SAW passing through a portion of the sample with an area of about 1 cm2. Scans of this type offer the possibility of economical testing of large sample areas, potentially on-line in a manufacturing environment.

Investigation of longitudinal leaky surface acoustic waves by scanning acoustic force microscopy

Abstract: We present first measurements on acoustic waves with quasi longitudinal polarization on quartz and lithium tantalate substrates as well as layered systems carried out by a scanning acoustic force microscope (SAFM). Acoustic phase velocities were measured for microscopic areas showing a good agreement with numerical calculations. The influence of the penetration depth of the high velocity pseudo SAWs (HVPSAW) on the SAFM signal formation is discussed.

Device and method for determining a propagation velocity of a sound wave in a diphasic mixture

Abstract: not available for EP1092149Abstract of corresponding document: US6560548A device measures the propagation time for an acoustic wave in a continuous phase of a two-phase mix (28) comprising the continuous phase and a dispersed phase forming droplets (40) in the continuous phase. The device comprises an electro-acoustic transducer (12) capable of emitting acoustic waves (30) and outputting a reception signal of reflected acoustic waves, a signal pulse generator capable of determining a propagation time starting from signals output by the transducer, and an acoustic lens for focusing acoustic waves and the frequency of the acoustic waves being adjusted to cause reflection of the waves on the droplets of the dispersed phase, essentially located within a focusing area.