Showing papers on "Acoustic interferometer published in 1980"

Prediction of nonlinear acoustic effects at biomedical frequencies and intensities

Abstract: Some fundamentals of nonlinear acoustics are reviewed to facilitate their consideration in biomedical ultrasound. The phenomena described include acoustic nonlinearity, finite amplitude distortion, shock formation, harmonic components, nonlinearly induced absorption, saturation, and the influence of these effects on ultrasonic beams. The simplified results of several theoretical derivations are presented and employed in illustrative calculations and plots. These maybe used to ascertain the importance of nonlinear effects in applications involving plane waves, spherically diverging waves, and spherically converging (focused) waves. A discussion of relevant experiments is given, along with some comments on possible consequences in diagnostic, surgical, and theraputic applications.

Method and apparatus for sensing fluids using surface acoustic waves

Abstract: This disclosure relates to a method and apparatus for sensing the presence of gases, vapors, and liquids using surface acoustic waves. At the present time the commercially available devices for measuring the presence of fluids, although fast reacting and generally quite accurate, are very expensive and bulky. Further, these devices do not lend themselves to advanced integrated signal processing and digital techniques. This disclosure describes a precise, fluid sensing unit that is small, easily integrated, and relatively inexpensive to fabricate. The apparatus includes a medium on which surface acoustic waves can be propagated, transmitting and receiving transducers, and a sensing member located across the path of the surface acoustic waves. The sensing member has a physical characteristic that varies the velocity and/or the attenuation of the waves when in the presence of the specific fluid being detected. The presence of the fluid is sensed by the apparatus by measuring the variation in the surface acoustic waves resulting from this interaction.

Gyroscopic Effect in Surface Acoustic Waves

Abstract: The effect of rotation on surface acoustic waves is derived theoretically in a perturbation treatment of the Coriolis force for an isotropic medium. The linear effect on the propagation velocity V in terms of (AV/V)/(R/w), where R and w are the rotation and SAN frequencies respectively, is found to depend only on the Poisson’s ratio of the nediun and varies between .27 and -.2. A dual-resonator gyroscope based on this effect will give a phase angle output equal to a maximum of 54% of the system attitude to be measured. The stability of the state-of-the-art commercial crystal oscillators implies a gyroscope resolution of 1/10 earth rotation rate.

ZnO Processing for Bulk- and Surface-Wave Devices

Abstract: Zinc-oxide thin-film transducers are used in a variety of microwave acoustic device applications for the generation and detection of bulk and surfaceacoustic waves. High coupling factor-low acoustic loss films are characterized by their dense, fine-grain, well-ordered crystallite structure, optical clarity and smooth surface texture. Sputtering the films using a compound ZnO target at moderate rates, with low reactive gas pressures on heated substrates, has produced films whose piezoelectric and acoustic properties approach those of single crystal zinc oxide. Several diagnostic techniques such as XRD, RED, SEM, TEM, optical, chemical and electrical havebeen used to characterize acoustic quality. This paper will discuss process conditions that lead to high quality film growth and diagnostic measures which best predict transducer performance.

Method and device for the measurement of the phase shift of the waves in a ring interferometer

Abstract: 1. A method of measuring the phase difference of electromagnetic waves circulating in opposite sense in a ring interferometer, comprising the step of generating an electromagnetic wave, separating this electromagnetic wave into two phase components which are fed into the end of the ring in order to generate the waves ciculating in opposite sense, modulating the phases of the two waves in periodical and reciprocal manner, recombining the two waves at the ends of the ring and detecting the recombined waves, characterized in that in the modulating step the phase of the two waves circulating in opposite sense are modulated at least at one end of the ring according to a function satisfying the relation PHI(t)=PHI(t+2 tau), wherein tau is the time necessary for each wave for passing through the optical way provided by the ring, and at that the step of detecting the phase difference between the two recombined waves is carried outs by measuring, at the frequency (1/2 tau) or at an entire multiple (k) of this frequency the optical power of the component of the recombined waves proportional to the sine of the phase difference between the waves.

Method and apparatus for acoustic scanning using bulk wave scattering of bulk waves by an acoustic grating

Abstract: Electronically focused and automatically scanning acoustic bulk waves are produced by scattering chirp acoustic bulk waves at grazing incidence from an acoustic grating. The same apparatus may be used in reverse to convert diverging acoustic bulk waves produced by a focused beam into chirp acoustic bulk waves. A pulse compression filter then converts the chirp waves into signals describing the source.

Piezoelectric single crystal and surface acoustic wave element employing the same

Abstract: A piezoelectric single crystal which has a composition represented by a general formula (Ba 2-x Sr x )TiSi 2 O 8 , the value x lying within a range of 0.25≦x≦1.2; and a surface acoustic wave element which is so constructed as to employ surface waves that propagate on a cut plane perpendicular to the Z-axis of the single crystal, or surface waves that propagate in a specified direction on a cut plane containing the X-axis of the single crystal. The piezoelectric single crystal and the surface acoustic wave element employing it have the merits that the electromechanical coupling factor of the surface acoustic waves is great and that the temperature coefficient of delay time of the surface acoustic waves is small.

Behavior of Bleustein-Gulyaev Waves in a Periodically Corrugated Piezoelectric Crystal

Abstract: The propagation characteristics of Bleustein-Gulyaev waves in a periodically corrugated piezoelectric crystal is investigated theoretically and numerically. The exact couple-mode equations governing the nature of Bleustein-Gulyaev wave interactions are derived with the aid of a singular perturbation procedure, and the interesting behavior of the filtering characteristics are shown numerically. It is found that the practically important characteristics such as wide stop-bandwidth and large wave-decay in the stopband can be achieved by choosing a value of the piezoelectric constant suitably, and/or coating the crystal surface with thin conducting material.

Acoustic phenomena in erosion of spark-gap electrodes

Abstract: Experiments have been conducted to show that acoustic waves generated in the electrode material may cause an order‐of‐magnitude increase in the rate of electrode erosion. This increase is due to the arrival of reflected acoustic waves at the electrode surface while arc ’’spots’’ are still molten.

Sound conversion phenomena at the free surface of liquid helium. I. Calculation of the coefficients of reflection, transmission, and transformation of sound waves incident on the liquid-vapor interface of helium

Abstract: On the basis of a set of boundary conditions describing quite generally mass and energy transport processes across the free surface of helium II, the acoustic coefficients of reflection, transmission, and transformation of first sound, second sound, and the sound wave propagating in the vapor are calculated in the case of perpendicular incidence of sound waves against the liquid-vapor phase boundary. Considering rigorously the influences of the Onsager surface coefficients, the isobaric thermal expansion coefficients, and the thermal conductivities of the liquid and the vapor, we derive sets of equations from which the acoustic coefficients are determined numerically. For estimations, simple explicit formulas of the acoustic coefficients are given. It is shown that the evaporation and energy transport processes occurring at the free surface of helium II due to the incidence of sound waves may be connected with appreciable energy dissipation. The surface absorption coefficients of first, second, and gas sound waves are deduced.

Display system for steady state waves

Abstract: A system for directly displaying steady state waves, such as sound waves, ultrasonic waves, electromagnetic waves, and the like, by instantaneously sampling the amplitude of the waves in a known phase relationship with some other portion of the wave train. The system includes a source of the waves, such as a speaker, and a transducer, such as a microphone, an electrical signal source being coupled to the wave signal source, and the transducer being connected to a sample and hold circuit whose output is applied to a light emitting diode (LED), or other display unit. The transducer is moved towards and away from the wave signal source in the path of the waves eminating from the wave signal source. In the following description the system will be described in conjunction with wound waves traveling in air, eminating from a speaker and transduced by a microphone. It will be evident as the description proceeds that the system may be used for displaying waves other than sound waves, such as ultrasonic waves; and/or for displaying waves traveling in a medium other than air.

Multimoding in SAW Convolver Waveguides

Abstract: Multimoding effects have been experimentally observed in thin-fdm aluminum waveguides on lithium niobate using a laser probe. When the waveguide is used as a convolver, these effects add dispersion and may adversely effect efficiency and minimum achievable time

Low-temperature ultrasonic velocity measurements in Na β-alumina

Abstract: The velocity of 1-GHz longitudinal acoustic waves has been measured in single-crystal Na $\ensuremath{\beta}$-alumina at low temperature. The temperature dependence is logarithmic in the range 0.1-5 K. This behavior, previously observed only in amorphous materials, is explained in terms of the two-level systems with a broad distribution of energy-level splittings. A value for the two-level-system acoustic-phonon coupling constant is deduced from the data.

An improved interferometer for ultrasonic attenuation or velocity measurements

Abstract: A method for increasing the sensitivity of ultrasonic interferometers through the use of phase (or amplitude) modulation and lock-in detection of the signal is described. The operation of such a modulated interferometer is analyzed and factors affecting performance are discussed. Experimental results are given which show that the system has good sensitivity for the detection of small ultrasonic velocity changes.

Strain‐induced phase noise in an acoustically sensitive fiber‐optic interferometer

Abstract: An acoustic interferometer subjected to random accelerations may experience strain‐induced phase noise which exceeds the photon shot‐noise limit. In order to minimize strain‐induced noise originating in the fiber leads to the interferometer, the leads may be closely juxtaposed so thal they experience the same strain. Experimental results using this technique are presented which show phase‐noise cancellalion of 40–60 dB. The observed residual phase noise is in close agreement with theoretical predictions and is shown to be dominated by terms arising from the nonlinearity of the optical indicatrix. Dependence of residual phase noise on lead length and on the static strain imbalance between the leads is discussed.

Electron Transport by Line Acoustic Waves in GaAs:Cr

Abstract: A new acoustoelectric current saturation effect is observed for the interaction of electrons with high power line acoustic and surface acoustic waves in Cr doped semi-insulating GaAs. Experimental results for acoustoelectric currents obtained by the transport of photo-generated electrons i ndicate that saturation of the l ocal e lectron velocity at the sound velocity occurs without significant free carrier bunching. The effect is observable because of the small free c arrier lifetime in semi-insulating GaAs. The experimental results are presented followed by a discussion of the proposed saturation model. The model is shown to agree quantitatively with the d ata and the e lectron conductivity mobility near the surface of a bulk sample of Cr:GaAs is estimated to be 566 cm2/V-sec on the basis of the d ata.

Suppression of Beam-Excited Electron Waves by an Externally Applied RF Signal

Abstract: Suppression of the beam-excited electron wave in a bounded system is investigated in connection with the beam distribution function. Wave suppression has two different processes depending on whether injected beams are reflected at the other end or not. In the absence of reflected beam electrons, deformation of the beam distribution function is observed in relation to the suppression of the electron wave. However, when beam electrons are reflected, the external wave suppresses the electron wave but distribution function shows no appreciable change. By using the method of partial simulation, interaction between two waves in the bounded system including nonlinear motions of beam electrons is studied numerically. Qualitative agreement between experimental and numerical results is obtained.

Low Frequency Imaging Technique for Acoustic and Elastic Waves

Abstract: Radar, active sonar, and ultrasonic pulse-echo nondestructive testing have the common goal of extracting as much information about the target as possible from backscattered signals.