Showing papers on "Acoustic interferometer published in 1993"

Accurate measurements of the sound velocity in pure water by combining a coherent phase-detection technique and a variable path-length interferometer

Abstract: An automated system for measuring the sound velocity in liquids has been developed by combining a coherent phase‐detection technique and a variable path‐length interferometer, in which a sample liquid is filled between an ultrasonic buffer and a moving reflector, and phase changes of a given echo of the ultrasonic pulse is measured by a phase‐sensitive detector (PSD) as a function of changes in the acoustic path length. For the accurate determination of the changes in the acoustic path length, the displacement of the moving reflector is measured by a Michelson interferometer that is illuminated by a frequency‐stabilized He–Ne laser. The sound velocity is determined from a direct comparison of the acoustic wavelength in the sample liquid with the optical wavelength of the laser. In order to check the performance of the apparatus, measurements were performed for distilled water in the temperature range 20–75 °C under atmospheric pressure with a carrier frequency of 16.5 MHz. The precision of the phase measurements by the PSD and systematic errors in the sound velocity measurement are evaluated. The total uncertainty of the sound velocity is estimated to be 0.001%. The results agree with reliable literature values within 0.003%.

Apparatus that generates acoustic signals at discrete multiple frequencies and that couples acoustic signals into a cladded-core acoustic waveguide

Abstract: Spherical annulus piezoelectric transducers 62, 64 and spherical disc piezoelectric transducer 66 form a spherical shell having a radius of curvature R with a focal point 70 near the end of cladded-core acoustic waveguide 72. Each transducer 62, 64, 66 generates a bulk acoustic wave of a unique frequency and transmits it to focal point 70 where it enters core 74 of cladded-core acoustic waveguide 72. Alternatively, a conical annulus piezoelectric transducers 92, 116 on a prism 90 generate bulk acoustic waves of multiple discrete frequencies and focus them through cladding 75 and into core 74 of cladded-core acoustic waveguide 72. Surface acoustic waves of multiple discrete frequencies can be generated by multiple sets of curvilinear interdigital conductors 132, 134 on a piezoelectric substrate 122. The shape of curvilinear interdigital conductors 132, 134 focuses the surface acoustic waves at focal point 70 located near the end of acoustic waveguide 72. The surface acoustic waves are converted into bulk/longitudinal waves by either curvilinear corrugations 142, 146 or by a coupling medium that causes the surface acoustic waves to become leaky longitudinal waves. Alternatively, the surface acoustic waves can be coupled to the core of the acoustic waveguide by converting them into either bulk/longitudinal waves or leaky longitudinal waves and guiding them through the cladding to the core. When the acoustic signals travel through the cladding to couple to the core, the acoustic waveguide can transmit optical signals.

Acoustic output device, and electronic apparatus using the acoustic output device

Abstract: Sound waves from a plate-shaped acoustic source, which generates fundamental waves (sound waves) having at least two frequencies, propagate through a propagating portion. The propagating portion consists of a medium in which a non-linear interaction is induced by the fundamental waves. A secondary sound wave having a frequency conforming to the difference between the two fundamental waves is generated by the medium. Fundamental wave components other than the secondary sound wave are absorbed by an acoustic absorber so that only the secondary sound wave is delivered as an output. The acoustic source, propagating portion and acoustic absorber are substantially transparent and stacked in three layers. This allows the resulting acoustic output device to be incorporated in the display unit of an electronic apparatus.

Development of interferometer for acoustic emission testing

Abstract: The characterization of the exact response of an acoustic emission sensor is of fundamental importance for the quantitative nondestructive evaluation of engineering components. To effectively determine an acoustic emission source, the influence of the sensor on the measured waveform must be determined. A heterodyne interferometer is developed and tested for the detection of acoustic emission signals. This optical device makes localized absolute measurements of out- of-plane surface velocities with very high fidelity. An important feature of this system is that a linear frequency modulation (FM) discriminator is used to de- modulate the carrier signal; as a result, the interferometer behaves as a Doppler- shift detector. A series of experiments was performed to test the response of commercially available, piezoelectric acoustic emission transducers in order to understand their potential influence on a measured acoustic emission waveform.

Deformation-sensitive cuts for surface acoustic waves in /spl alpha/-quartz

Abstract: The influence of external static forces on SAW (surface acoustic wave) velocity is computed for circular plates (membranes). The pressure sensitivity of the SAW velocity as a function of /spl alpha/-quartz crystal anisotropy is studied by sensitivity contour mapping from two independent variables: direction of SAW propagation and cut angles of /spl alpha/-quartz. Theoretical sensitivity values are compared with experimental ones for circular (membrane) plates, and good agreement is found. >

Polarizing optical interferometer having a dual use optical element

Abstract: A system for non-destructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading.

Sound velocity and ideal-gas specific heat of gaseous 1,1,1,2-tetrafluoroethane (R134a)

Abstract: A cylindrical, variable-path acoustic interferometer operating at 156.252kHz is developed for determining ideal-gas specific heats. Results of validation measurements with argon are very satisfactory, with the maximum deviation of the speed of sound equal to 3×10−4. The sound velocity of gaseous R134a has been measured at low temperatures and low pressures. The specific heat was then calculated from the results. The experimental results corrected for various dispersions for the sound velocity of gaseous R134a match well with an earlier publication, with a room mean square deviation of 2.56×10−4. A new relation for the ideal-gas specific heat as a function of temperature for R134a is obtained.

Acoustic output device, and electronic apparatus using said device

Abstract: Sound waves from a plate-shaped acoustic source (10), which generates fundamental waves (sound waves) having at least two frequencies, propagate through a propagating portion (2). The propagating portion (2) consists of a medium in which a non-linear interaction is induced by the fundamental waves. A secondary sound wave having a frequency conforming to the difference between the two fundamental waves is generated by the medium. Fundamental wave components other than the secondary sound wave are absorbed by an acoustic absorber (3) so that only the secondary sound wave is delivered as an output. The acoustic source (10), propagating portion (2) and acoustic absorber (3) are substantially transparent and stacked in three layers. This allows the resulting acoustic output device to be incorporated in the display unit of an electronic apparatus.

Furnace control apparatus using polarizing interferometer

Abstract: A system for non-destructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading.

Method for measuring axial force of rail

Abstract: PURPOSE: To directly evaluate the axial force of a rail and to measure local axial force distributions in the rail by fitting an ultrasonic transmitter and receiver to the web of the rail at a prescribed interval and finding the acoustic velocity from longitudinal waves reflected by the opposite surface of the web, and then, comparing the acoustic velocity with a reference value. CONSTITUTION: A transmitter 1 and receiver 2 are fitted to the web of a rail having a constant axial stress at angles of about 14.7° at an interval of about 1m with an ultrasonic wave propagating medium composed of water 3 in between. And, the acoustic velocity V of longitudinal waves is found by repeatedly transmitting pulse waves of, for example, about 0.25μsec in width at time intervals of about 1.2msec and only detecting the first waves with gate signals having a prescribed width when about 170μsec has elapsed after the transmission, and then, detecting the accurate propagating time of the longitudinal waves from the mean value of the detected first waves. The axial stress σof the rail can be found directly from the difference ΔV between the previously found reference value V 0 of the acoustic velocity (the acoustic velocity of longitudinal waves when the axial stress σ is zero) and the measured acoustic velocity V based on a formula ΔV/V 0 =Kσ (where, K is an acoustoelastic factor). COPYRIGHT: (C)1995,JPO

Method and apparatus for measuring surface movement of a solid object that is subjected to external vibrations

Abstract: A system for non-destructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading.

Time-delay Fizeau phase-conjugate interferometer.

Abstract: A time-delay Fizeau phase-conjugate interferometer is constructed by using a BaTiO3 crystal in a degenerate four-wave-mixing configuration. The slow response time of BaTiO3 is used to build a phase-conjugate mirror that functions as a holographic memory. An optical wave and its time-delayed version are stored inside the crystal sequentially while their phase-conjugate waves are generated simultaneously. Superposition of the two phase-conjugate waves produces an interferogram as a result of the relative phase change of the input waves. The simplicity and real-time operation of this technique lead to several advantages over the conventional holographic interferometry. The use of photorefractive crystal eliminates the darkroom process and reposition procedure. A higher accuracy can be achieved because the interfering waves are phase-conjugate waves. The principle of this technique is presented and the experimental results and its applications are discussed.

Dynamic localization of acoustic waves in superlattices.

Abstract: The absorption and change in velocity of acoustic wave interacting with electrons in a superlattice irradiated by an infrared laser field are investigated. Near the roots of the equation s 0 /4d=|J 0 (eFd/Ω)| (24 and d are the miniband width and period of the superlattice, F and Ω are amplitude and frequency of the laser field, and so is the sound velocity) a strong renormalization of sound velocity and intense absorption peaks are predicted. These phenomena have a straightforward relation with the dynamic localization of electrons and are called dynamic localization of acoustic waves

Elastic waves against a corrugated boundary

Abstract: A train of plane waves travels in an elastic semi-infinite medium bounded by a corrugated line having a sinusoidal shape. When the primary waves impinge against the surface, a new train of reflected waves is generated, and the question arises of determining the effect of roughnesses of the boundary on the shape and amplitude of the reflected waves.

Optical interferometric measurement of guided surface acoustic wave strains inside a solid

Abstract: The strain measurement of guided acoustic waves by optical interferometry is described. Unlike the traditional photoelastic technique, this method enables one to measure the phase shift rather than the change of the polarization state of the light. A comprehensive formalism based on the acoustically perturbed index ellipsoid of refraction and the Jones calculus is demonstrated. A relationship is obtained between the optical phase shift and the dilatational acoustic strains of guided waves. The strain fields of the Lamb waves s0 and a0 measured with the present method inside fused quartz, are in good agreement with the theoretical analysis

A 1.5 Ghz-band Saw Filter Using Flip-chip-bonding Technique

Abstract: We applied a stud-bump-bonding (SBB) technique which is a kind of flip-chip-bonding (FCB) technique to a l.5GHz-band surface acoustic wave (SAW) filter. The SAW filter mounted by the SBB technique showed almost the same frequency characteristics as that mounted by a conventional wire-bonding technique at 1.5GHz. Using the SBB technique, the area of the SAW filter became 115 comparing with conventional SAW filters mounted by the wire-bonding technique and the weight became less than 1/10 by the share of the package. The SBB technique has; a lot of potential to reduce the size and weight and to realize small and high performance modules even above GHz frequencies.

Detection of acoustic second harmonics using a laser interferometer

Abstract: Non-linear acoustic measurements can provide information on the microstructure or internal state of stress of materials and offer great potential for the nondestructive characterization of materials [1]. But non linear effects are difficult to measure, especially in industrial environments. For instance, changes in acoustic velocity with temperature or with applied stress are very small. The detection of acoustic harmonics [2], the interaction of multiple acoustic wavefronts [3], or of acoustic-radiation-induced static strain [4] requires sensitive transducers calibrated for absolute amplitude measurements to allow die determination of the third order elastic constants. Among these techniques, the detection of second harmonics offers potential for industrial applications because it requires no applied stress, no (slow) change in temperature and only one acoustic source.

Internal Diffraction of Acoustic Waves in Silicon

Abstract: Phonon focusing has been extensively studied using phonons with frequencies of several hundred GHz [1]. We have recently reported a related technique for studying anisotropies of acoustic flux at sub-GHz frequencies [2]. In these experiments using coherent waves, ultrasound is generated and detected by focused immersion transducers in a water bath. The transducers act as a point-source/point-receiver pair, one of which is scanned to produce an ultrasound image. We present here the experimental results for Si along with a model which accurately reproduces the observed images.

Impedance method for calculation of thermoelastic interaction of surface acoustic waves in solids

Abstract: A thermal impedance has been introduced for the solution of the problem of the thermoelastic interaction of surface acoustic waves (SAW) in solids. The analytic thermal impedance is obtained for isotropic solids from the weak thermoelastic coupling approximation. The value of thermal impedance obtained depends only on three parameters: the isothermal SAW velocity, the velocity for the case without dissipation of heat from the solid surface, and a thermal impedance without acoustic waves. The extended approach allows us to investigate and analyze the effect of different surface layers and continuous materials on the thermoelastic attenuation and velocity dispersion of the SAW. For example, an ideal heat conductive layer reduces the thermoelastic SAW attenuation to zero. By analogy with excitation of the SAW by means of a high frequency periodic electric field the problem of the excitation of the SAW by means of a thermal high frequency periodic perturbation (for example by means of a laser) may easily be solved with the help of the surface thermal impedance