Showing papers on "Acoustic interferometer published in 2006"

Measuring the free field acoustic impedance and absorption coefficient of sound absorbing materials with a combined particle velocity-pressure sensor

Abstract: Acoustic surface impedance of sound absorbing materials can be measured by several techniques such as the impedance tube for normal impedance or the Tamura method for normal and oblique surface impedance. In situ, the acoustic impedance is mostly measured by use of impulse methods or by applying two-microphone techniques. All these techniques are based on the determination of the sound pressure at specific locations. In this paper, the authors use a method which is based on the combined measurement of the instantaneous sound pressure and sound particle velocity. A brief description of the measurement technique and a detailed analysis of the influence of the calibration, the source type, the source height, the sound incidence angle, and the sample size are included.

Measurements of spatially growing dust acoustic waves in a dc glow discharge plasma

Abstract: In this paper, an experiment is performed on dust acoustic waves in a dc glow discharge plasma. Stereoscopic particle image velocimetry (stereo-PIV) techniques are used to make measurements of the dust acoustic waves. These stereo-PIV measurements reveal the spatial growth of the waves over three to six wavelengths before reaching a saturated level. Experimental measurements are shown to agree with a simple model for spatially varying waves.

Bleustein-Gulyaev-Shimizu surface acoustic waves in two-dimensional piezoelectric phononic crystals

Abstract: In this paper, we present a study on the existence of Bleustein-Gulyaev-Shimizu piezoelectric surface acoustic waves in a two-dimensional piezoelectric phononic crystal (zinc oxide, ZnO, and cadmium-sulfide, CdS) using the plane wave expansion method. In the configuration of ZnO(100)/CdS(100) phononic crystal, the calculated results show that this type of surface waves has higher acoustic wave velocities, high electromechanical coupling coefficients, and larger band gap width than those of the Rayleigh surface waves and pseudosurface waves. In addition, we find that the folded modes of the Bleustein-Gulyaev-Shimizu surface waves have higher coupling coefficients.

Bulk acoustic resonator and filter element

Abstract: A bulk acoustic resonator has an acoustic reflector portion formed on a substrate and including one or more low acoustic impedance layers and one or more high acoustic impedance layers having a higher acoustic impedance than the low acoustic impedance layer which are disposed in stacked relation and an acoustic resonator portion formed on the acoustic reflector portion and having a piezoelectric film At least one of the low acoustic impedance layers is made of silicon

Direct measurement of the dispersion relation of capillary waves by laser interferometry

Abstract: Surface waves on fluids with wavelengths in the millimeter range are known as capillary waves. Surface tension determines the propagation and dispersion of capillary waves while gravity plays a minor role. We describe a simple method for generating standing capillary waves of known frequency on water and introduce a novel noncontact technique based on laser interferometry to measure the wavelength of capillary waves with great precision. The data gives the dispersion relation of capillary waves and provides an accurate method for determining the surface tension of fluids.

4E-5 Measurement of Acoustical Parameters of Thin Films

Abstract: The workhorse of bulk acoustic wave (BAW) resonator design and analysis is the Mason model. This transmission line model takes as input parameters the thickness, (longitudinal) acoustic velocity and (longitudinal) acoustic impedance of the various layers constituting the resonator. Accurate knowledge of these parameters is essential for successful design and analysis of devices. In this paper we present a straightforward method for measuring these longitudinal wave parameters. Finally we will also make brief comments on how to evaluate the shear wave parameters

Investigation of liquid/solid interface waves with laser excitation and photoelastic effect detection

Abstract: Theoretical and experimental investigations on transparent liquid (water)∕solid (aluminum or steel) interface waves generated by laser pulse and detected with photoelastic effect are reported. When the detection beam of a laser interferometer is skimmed over the water∕solid interface and conjoined with the interface wave propagated in water, an extra optical phase shift is produced. The output signal from the interferometer is proportional to the acoustic pressure in water. The characteristic equation of the liquid∕solid interface wave is derived from elastic wave theory, and the transient response of acoustic pressure in water is simulated by means of inverse Laplace and Hankel transforms. The experimental results of acoustic velocity and wave form for all interface waves are in good agreement with theoretical predictions. They show that the optical detecting method based on photoelastic effect is very powerful for the research of liquid∕solid interface waves.

Optical generation and spatially distinct interferometric detection of ultrahigh frequency surface acoustic waves

Abstract: Generation and interferometric detection of 22GHz surface acoustic waves (SAWs) using two laterally separated absorption gratings on a Si substrate are presented. Optical phase sensitive detection of SAWs is demonstrated using a modified Sagnac interferometer. The reflection characteristics of the suboptical wavelength grating necessitate the use of only linear polarization. This is accomplished by employing a Faraday rotator to ensure path reversal of the reference and signal pulses. The enhanced sensitivity of the interferometer is exploited to measure the acoustic disturbance on an identical absorption grating at a distance of ∼4.5μm from the generation site.

Ultrasonic interferometric sensor for rheological changes of fluids

Abstract: An ultrasonic interferometric sensor has been introduced for the measurement of subtle changes in the physical properties of fluids such as density, viscosity, and bulk modulus Tone burst ultrasonic waves are generated using a single peizocrystal bonded in between two solid delay line media of slightly different lengths One side is in contact with a reference fluid (with known properties) and the other with a fluid whose properties are to be measured The ultrasonic waves reflect from the two solid-fluid boundaries and are received back by the peizocrystal where the interference effects are measured The longitudinal waves were used to measure the longitudinal impedance, while shear waves were used to measure the shear impedance Glycerin-water mixtures were used as the test material A simple plane wave model was shown to provide satisfactory comparison with experiments Various parameters that influence the measurement were studied

Component Operated by Guided Acoustic Waves

Abstract: A component working with guided acoustic waves includes a layer system configured to guide waves in a lateral plane. The layer system includes a piezoelectric layer, electrodes on the piezoelectric layer for exciting the wave, a dielectric layer with an acoustic impedance, and an adjustment layer with an acoustic impedance. A ratio of the acoustic impedance of the adjustment layer to the acoustic impedance of the dielectric layer is greater than 1.5.

Measurement of low-frequency ultrasonic wave in water using an acoustic fiber

Abstract: An acoustic fiber sensor for measurement of ultrasonic waves, which used the approximate Raman-Nath diffraction effect where light diffraction waves were generated in an optical fiber by strain due to the ultrasonic waves, was proposed and examined. In order to characterize the acoustic fiber sensor as a basic study, measurements of low-frequency ultrasonic waves in water were examined using a step index fiber operating as a detection sensor. The results showed that characteristics of detected signals agreed with the theoretical prediction based on Fraunhofer diffraction. This indicates that our proposed fiber sensor can be used for the detection of low-frequency ultrasonic waves as well as the transmission of light diffraction signals.

An acoustic reflector

Abstract: An acoustic reflector (10) suitable for use as a reflective target for navigational aids and for location and re-location applications. The acoustic reflector comprises a shell (12) arranged to surround a solid core (16) . The shell is adapted to transmit acoustic waves (18) incident thereon into the core (16) . Within the core the acoustic waves are focused before being reflected from an opposing side of the shell (20) to provide a reflected acoustic wave. A portion of the acoustic waves incident on the shell is coupled into the shell wall and guided within and around the circumference thereof (26) before being re-radiated and combining constructively with the reflected acoustic wave to provide an enhanced reflected acoustic wave.

Bulk conical and surface helical acoustic waves in transversely isotropic cylinders; application to the stiffness tensor measurement

Abstract: A point-source-point-receiver technique, based on laser generation and laser detection of acoustic waves, allows determination of mechanical properties of anisotropic cylinders. The anisotropic nature of the material and the geometry of the samples make the acoustic signature difficult to interpret. In addition to multiple surface waves, quasi-longitudinal and quasi-shear bulk waves are diffracted and acoustic rays are reflected with or without mode conversion at the cylinder surface. Moreover both bulk and surface diffracted waves have a dispersive behavior. To bypass the intricacies, wave fronts are synthesized with signals provided by scanning a straight line on the cylinder with the laser point source. Conical waves propagating in the volume and helical waves propagating along the surface are then numerically produced. The recovery of the stiffness-tensor components is based on the inversion of the bulk waves, phase velocities. The method is presented and applied to signals simulated or experimentally recorded for a composite material. The five independent stiffness coefficients of the hexagonal symmetry are thus measured with waveforms provided by a single scan along the cylinder surface. The method provides a unique mean for the noncontact measurement of elastic properties of cylindrical parts.

On the Propagation of Plane Acoustic Waves in a Duct With Flexible and Impedance Walls

Abstract: This Technical Memorandum (TM) discusses the harmonic and random plane acoustic waves propagating from inside a duct to its surroundings. Various duct surfaces are considered, such as rigid, flexible, and impedance. In addition, the effects of a mean flow are studied when the duct alone is considered. Results show a significant reduction in overall sound pressure levels downstream of the impedance wall for both mean flow and no mean flow cases and for a narrow duct. When a wider duct is used, the overall sound pressure level (OSPL) reduction downstream of the impedance wall is much smaller. In the far field, the directivity is such that the overall sound pressure level is reduced by about 5 decibels (dB) on the side of the impedance wall. When a flexible surface is used, the far field directivity becomes asymmetric with an increase in the OSPL on the side of the flexible surface of about 7 dB.

Generation of Ion-Acoustic and Magnetoacoustic Waves in an RF Helicon Discharge

Abstract: A study is made of the generation of ion-acoustic and magnetoacoustic waves in a discharge excited in an external magnetic field by an electromagnetic wave in the whistler frequency range (ωLH ≪ ω ≪ ωHe, where ωLH = \(\sqrt {\omega _{He} \omega _{Hi} } \) and ωHe and ωHi are the electron and ion gyrofrequencies, respectively). The excitation of acoustic waves is attributed to the decay of a high-frequency hybrid mode forming a plasma waveguide into low-frequency acoustic waves and new high-frequency waves that satisfy both the decay conditions and the waveguide dispersion relations. The excitation of acoustic waves is resonant in character because the conditions for the generation of waveguide modes and for the occurrence of the corresponding nonlinear wave processes should be satisfied simultaneously. An unexpected effect is the generation of magnetoacoustic waves by whistlers. A diagnostic technique is proposed that allows one to determine the thermal electron velocity by analyzing decay conditions and dispersion relations for waves in the discharge channel.

Acoustic wave propagation through the boundary between a liquid and the Heusler ferromagnetic alloy

Abstract: Incidence of an acoustic wave upon a plane boundary between a liquid and a ferromagnetic crystal is considered. The ferromagnet is the Ni2+x+yMn1−xGa1−y Heusler alloy with a shape memory, which is in the region of the premartensite or martensite phase transition in temperature. The directions of propagation and polarization and the amplitudes of the reflected and transmitted quasilongitudinal and quasitransverse waves in the (110) plane of the crystal are determined. Starting from a certain critical angle of incidence, a longitudinal wave in the crystal becomes inhomogeneous and gliding along the boundary with an accompanying surface oscillation. In the vicinity of the phase transition point, this wave may be radiated into the crystal bulk. Proceeding from the experimental data by Trivisonno for ultrasonic velocities and absorption in a Ni2MnGa crystal, numerical estimates are obtained for the aforementioned acoustic effects.

5J-2 A Method to Control the Electrical Impedance of Phased Array Elements

Abstract: A method that uses lateral coupling to generate the ultrasound waves was tested for reducing the electrical impedance of small phased array elements. Cylindrical, radially polled transducer elements were driven in their length mode. The electrical impedance could be controlled by the cylinder wall thickness while the operation frequency was determined by the length of the cylinder. Acoustic intensity (averaged over the cylinder diameter) over 10 W/cm2 was measured from these elements

P3K-4 Utilizing a Ray Technique to Calculate Multiple Reflections and Transmitted Waves from Layered Plates and Examine the Detection of Critical Disbonds, and Lamb Modes Generated

Abstract: This paper considers the problem of a single, or multilayer, isotropic plate and the problem of calculating the multiple reflections of acoustic waves within the plate, and the acoustic waves transmitted outside the plate (leaky waves). By using a ray method, and considering the paths traveled by the rays, it has been found that many of the multiple reflections will travel equivalent paths in space and time. Using superposition to combine the equivalent paths reduces the number of rays to track, and allows the process of calculations to be done in a time efficient manner. The use of the a ray model also gives initial results which are independent of properties of the incident acoustic waves. A separate set of calculations can be used expand the rays to a variety of more realistic acoustic waves, allowing a single result to be used for a variety of acoustic sources. The results from this model will be used to examine situations such as the detection of critical disbonds in plates, examination of the lamb modes which are generated, or examination of which situations produce the largest transmitted waves

The use of an ultrasonic interferometer for measurements in the critical region of light and heavy water

Abstract: An interferometer and a procedure for measuring the velocity and absorption coefficient of ultrasound in light and heavy water close to the critical point are developed.

Method for measuring the acoustic impedance of a liquid by means of an ultrasonic transducer

Abstract: The invention relates to a method for measuring the acoustic impedance of a liquid (2), especially for determining the density of a liquid (2). According to the invention, an ultrasonic transducer (1) is introduced into the liquid (2), at least one resonance frequency of the ultrasonic transducer (1) is measured in the liquid (2), and the acoustic impedance of the liquid (2) is determined from the measured resonance frequencies. The inventive method enables the acoustic impedance of a liquid to be precisely determined, and to determine the density of the liquid with high precision in conjunction with an ultrasonic transit-time measurement.

A Combined Method for Calculating the Field of a Point Source in a Waveguide (Plane-Layered Media)

Abstract: The two-dimensional problem of propagating the waves generated by a point source, in a depth plane-layered waveguide is investigated. The Dirichlet condition is given on the boundary of the waveguide and also two consistency conditions are defined on the interface between the fluid and the bottom. The velocity of acoustic waves is assumed to be dependent only on the depth of the waveguide. With the help of cumbersome transformations, the solution is represented as a sum of geometric-optical waves, normal waves, and a remainder. Sufficient conditions on the total amount of detached normal and geometric-optical waves are obtained. The remainder is expressed by a simple formula. Bivliography: 22 titles.

A pulse ultrasonic gauge for measuring velocities of surface acoustic waves

Abstract: A pulse broadband gauge designed for measurements of the velocities of surface acoustic waves is described. The gauge’s output signal is formed during mechanical translation of focused ultrasonic transducers relative to a specimen under study placed in an immersion liquid. A design of the device with line-focused lensless ultrasonic transducers for the frequency range 2–25 MHz is considered. The results of measurements of test samples are presented, and the algorithms for processing the output spatial-temporal signals for determining the frequency dependences of phase velocities of acoustic waves are described. Using a carbon steel sample as an example, it is shown that the random error component in acoustic-wave velocity measurements can be estimated as ±(2–8) and ±(1–3) m/s for longitudinal and lateral scanning modes, respectively.

Laser generation and detection of surface acoustic waves: used for breast cancer detection

Abstract: A non contact all-optical method for surface photoacoustic is described. The surface acoustic waves were excited employing a ArF excimer laser in the 10 µm thin polyimide film and detected with a Michelson interferometer using 633 nm HeNe laser due to an active stabilization for interferometer a surface displacement of 0.2 A. could be detected used for the purpose of discriminating between normal and maligned tissue. The acoustic waves propagate several millimeters in the sample differentiating maligned areas from normal breast tissue samples which having different acoustic impedance.

Modulation of cavity-polaritons by surface acoustic waves

Abstract: We modulate cavity-polaritons using surface acoustic waves. The corresponding formation of a mini-Brillouin zone and band folding of the polariton dispersion is demonstrated for the first time. Results are in good agreement with model calculations.

Active interferometer as an antenna for gravitational waves

Abstract: It is demonstrated that a gain medium in the cavity of the Michelson interferometer that serves as a detector of gravitational waves allows a sharp decrease in the output power of the external laser source.