Showing papers on "Acoustic interferometer published in 2003"

Spurious resonance free bulk acoustic wave resonators

Abstract: In this paper a device structure eliminating the spurious modes arising from lateral standing Lamb waves is presented. The operating principle behind the device is described with the use of a simple model. Experimental results of ZnO and AlN based resonators in SMR configuration are given. Laser interferometer measurements are presented that confirm applicability of the idea.

Acoustic nonlinearity parameter measurements in solids using the collinear mixing of elastic waves

Abstract: An alternative method for measuring the nonlinearity parameter β of longitudinal acoustic waves propagating in solids is presented. The method is based on the detection of the phase modulation resulting from the parametric interaction between a high frequency acoustic wave and a lower frequency acoustic pulse. Results are reported for various materials: fused quartz, duraluminum, titanium, and polystyrene.

Phase-sensitive absolute-amplitude measurements of surface waves using heterodyne interferometry

Abstract: Phase-sensitive absolute-amplitude measurements of surface waves using heterodyne interferometry. We describe a novel heterodyne interferometer for scanning surface-acoustic waves at high frequencies, up to 6 GHz. The heterodyne operation facilitates the measurement of the absolute amplitude of the surface waves without calibration. It simultaneously also enables measuring the phase. The amplitude and phase information allows a precise characterization of the surface acoustic waves. Moreover, the wave motion can be visualized in the form of animations to gain insight. The interferometer has been tested by measuring a 167 MHz SPUDT device and a 374 MHz fan-shaped SAW filter.

Theoretical verification of the backward displacement of waves reflected from an interface having superimposed periodicity

Abstract: Experiments are reported by Breazeale and Torbett [Appl. Phys. Lett. 29, 456 (1976)] that visualize ultrasonic backward beam displacement due to the excitation of surface waves by means of diffraction. The authors have simulated these experiments using the concept of inhomogeneous waves. Such waves have proven to be well suited in predicting beam displacements on plane interfaces. It is now found that inhomogeneous waves are even capable of predicting the experimentally observed displacement phenomena on periodic rough surfaces.

Apparatus for increasing the quality of sound from an acoustic source

Abstract: An apparatus for increasing the quality of sound from an acoustic source comprises in one embodiment a hollow enclosure, an acoustic source, an acoustic guide, a pair of acoustic inlet openings, a pair of acoustic exit openings, and pair of acoustic paths, wherein the acoustic inlet openings separate acoustic waves from the acoustic source and direct the acoustic waves the length of the acoustic paths to the acoustic exit openings in such a manner as to increase the quality of sound, and especially bass sound, from the acoustic source.

Zone-plate interferometry at 13 nm wavelength

Abstract: We report on interferometry using a two-zone-plate common-path interferometer operating at a wavelength of 13 nm. The interferometer was set up with a laser-driven high-harmonic source emitting radiation with the high degree of spatial and temporal coherence necessary for interferometry. The interferometer is suited for investigations of the coherence properties of the light source employed, as well as for simultaneous measurements of the real and imaginary part of the complex index of refraction in the 100 eV regime. This is demonstrated in a proof of principle experiment with a piece of Zr-foil as the phase-shifting and absorbing sample.

Stable Fabry-Perot interferometer

Abstract: A stable scanning or non-scanning Fabry-Perot interferometer and a method for stabilising the interferometer. The interferometer is composed of two plane mirrors arranged parallel to one another with a preselected optical distance between the optical surfaces of the mirrors. The interferometer radiates an output light signal in response to a light input signal applied parallel to the optical axis of the interferometer. The interferometer is stabilised by providing an arrangement for passing a plurality of reference light beams through the interferometer, the reference light beams being inclined at a preselected angle to the optical axis of the interferometer.

Focusing of electromagnetic waves by periodic arrays of dielectric cylinders

Abstract: By numerical simulations, we show that properly arranged two-dimensional periodic arrays, formed by dielectric cylinders embedded in parallel in a uniform medium, can indeed act as an optical lens to focus electromagneticwaves, in accordance with the recent conjecture in the literature. The numerical simulations are based on an exact multiple-scattering technique. The results suggest that the E-polarized waves are easier to be focused than the H-polarized waves. The robustness of the focusing against disorders is also studied. Comparison with the corresponding cases for acoustic waves is also discussed.

Real-time imaging of surface acoustic waves in thin films and microstructures on opaque substrates (invited)

Abstract: We present a real-time imaging technique for surface acoustic waves on samples with opaque substrates. We image the surface acoustic wave propagation on a silicon substrate coated with a gold film, and derive the dispersion relation for propagation in symmetry directions. In addition, we image surface acoustic waves at frequencies up to 2 GHz on a diamond substrate coated with a gold film, and on a microstructure deposited on a silicon substrate.

Creation of Acoustic Field in Linear or Partially Bent Holes by High-Intensity Aerial Convergent Ultrasonic Waves

Abstract: Using high-intensity convergent ultrasonic waves (frequency: 19.65 kHz; wavelength: 17.6 mm), a study was conducted on basic properties resulting from these acoustic waves entering linear holes with cross-sectional dimensions being less than 1/4 of the wavelength of the acoustic waves. The sound field formed inside the holes, whose length ranged from 2 to 60 mm, had the same characteristics as that formed when plane waves entered an acoustic tube with a closed end. In addition, even when the hole had a bent part of up to 90°, it was possible for the convergent acoustic waves to enter the hole. In this case, extremely high-intensity ultrasonic waves of approximately 174 dB were created at the bottom of the hole.

Multi-frequency and multi-mode GHz surface acoustic wave sensor

Abstract: We present a novel surface acoustic wave sensor, incorporating the advantages of multi-frequency and multi-mode operation in a single acoustic device structure. SAW sensors are commonly based on the change of the effective elastic constants or the mass loading of the device due to a different sensor environment. Usually, single acoustic modes at a fixed frequency are employed allowing for the detection of a certain chemical species, depending on the coating of the wave's propagation path. Analyzing multiple acoustic modes or multiple excitation frequencies that are each reacting differently on a particular load, allows for the multi-parameter analysis of gases and liquids. We present a sensor system that is based on floating electrode unidirectional transducers (FEUDTs) allowing for the excitation of a set of 48 equally spaced frequencies and at least two acoustic modes (depending on the material system) in a single transducer structure. FEUDTs allow for the efficient excitation of acoustic waves at GHz frequencies without the use of sophisticated nanofabrication techniques. Higher frequencies, on the other hand, are advantageous for the sensitivity of the device. We tested the basic operation of our sensor system by applying it to humidity sensing without a sensitive layer.

Methods of Measuring the Acoustic Characteristics of Sound-Absorbing Materials

Abstract: A comparison is made of methods of measuring the acoustic characteristics of sound-absorbing materials in an acoustic interferometer. The methods considered are the standing-wave, two-microphone, least-squares, three-points, and nonlinear regression ones. The advantages and shortcomings of each method are discussed. Experimental data are presented.

Pulse generating drive circuit for an electromagnetic source for generating acoustic waves

Abstract: A circuit for driving an electromagnetic source for generating acoustic waves has a dischargeable high-voltage capacitor with a diode or a diode module connected in parallel therewith.

Hybridization of acoustic waves in piezoelectric plates

Abstract: The conditions for hybridization of the zero-order and high-order acoustic waves propagating in a piezoelectric crystal plate have been studied. The dependence of the phase velocity of the hybrid waves on the parameter hf (h is the plate thickness and f is the wave frequency) is established for the potassium niobate and lithium niobate plates possessing various crystallographic orientations and conductivities. It is found that hybridization takes place when the conductivity of a thin surface layer exceeds a certain critical value, which can vary within broad limits depending on the plate material and orientation. The degree of dispersive repulsion of the coupled modes grows with increasing electromechanical coupling coefficient.

Phase Changes in Reflected Sound Waves

Abstract: Phase changes in waves are just varied enough and just unfamiliar enough to students to be confusing. The phase changes upon reflection of waves on a string and of sound waves are usually the first to be encountered by students, and can give a bridge to other such changes found, for example, in electromagnetic waves. Before digital oscilloscopes, phase changes in sound waves had to be taken on faith or tested indirectly. Now they are quite easy to show. This note describes an experiment that demonstrates phase changes of a reflected sound pulse in a long air-filled tube. The demonstration also gives an easy and straightforward measurement of the speed of sound, and shows that air temperature matters while pressure does not, as theory predicts.1

SAW device analysis using a combination of FEM/BEM calculations and scanning interferometer measurements

Abstract: Scanning laser interferometry has proven useful in the identification of novel acoustic loss phenomena. However, it remains challenging to provide a rigorous physical interpretation of the details of the optically measured acoustic field distribution. With the help of our powerful FEM/BEM finite transducer model, we can make a direct comparison between the measured and simulated acoustic field distributions. This enables us to search and correct for unwanted acoustic phenomena which can deteriorate the filter performance. Here we focus on the modeling of the stress at the interface between the electrodes and the substrate. We describe the FEM/BEM tool for finite transducers that we have developed and its validation with optical Michelson interferometer scans. We show how it is possible to evaluate and optimize the power-handling properties of a SAW device structure.

Field device for measuring acoustic impedance, especially for measuring the acoustic impedance of the vocal tract, has an acoustic excitation system and pressure and sound speed sensors

Abstract: Device for measuring the acoustic impedance in which in a small space an acoustic system is excited and a simultaneous measurement of pressure and sound speed made.

Acoustic properties of liquid measured by Rayleigh-SAW

Abstract: Damping and velocity of Rayleigh surface acoustic waves (SAW) were measured in liquid 4 He . A Rayleigh-SAW propagates along the substrate surface by emitting compressional waves into the liquid and thus the damping of the Rayleigh-SAW is determined by the acoustic impedance of the surrounding liquid 4 He . Temperature dependence agreed well with the reported values of the impedance and the superfluid transition in 4 He was clearly seen. We also set up a reflection plate 1.5 mm above the SAW device which reflected the emission waves. They were converted back into the SAW and used to measure the velocity and damping of ultrasound in liquid 4 He separately.

Scattering of plane acoustic waves at elastic particles with rough surfaces

Abstract: A comprehensive theoretical and numerical study of the influence of surface roughness of elastic particles in water on the scattering of ultrasonic waves has been carried out. For near spherical shape of the particles and with small rms-roughness heights, a perturbation method has been developed. In this method, the first-order perturbation contribution predicts the contribution to the incoherently scattered acoustic field due to surface roughness, and the second-order perturbation contribution predicts the change in the coherent field and will satisfy the requirement of energy conservation. The second-order perturbation contribution is evaluated by use of the form function concept, while the first-order perturbation to the total scattered acoustic field is evaluated by use of the scattering cross-section. As a function of the ka-value and for different rms-roughness heights a numerical study of the forward and backward scattering from rough, elastic particles has been carried out and a substantial roughness influence on the scattered field has been verified. Some experimental results from measurements of scattering from glass and cast iron spheres have given evidence to the numerical predictions.

Initial tests of a new X-ray Michelson interferometer

Abstract: A Michelson interferometer for X-rays of wavelength ∼1 A has been proposed to test the temporal coherence of FEL radiation. Such a device has been made at HASYLAB from a silicon single crystal. It is based on the BBB interferometer of Bonse and Hart. One of its mirrors can be pushed by a piezo to introduce the desired beam path difference. For the preliminary tests described in this paper, the crystal was also equipped with an LLL interferometer to check the quality of the crystal and of its preparation. The rotation of a phase-shifting object (a Plexiglas plate) in one of the LLL's beam paths has been found to produce a fringe pattern which can be shown to yield the phase-shifting material's index of refraction. The interferometer crystal's front section was held fixed with a compression spring. At the same time, the interferometer was bathed in viscous silicone oil to reduce vibrations.

Experimental Study of Sound Waves in Sandy Sediment

Abstract: : This dissertation describes experiments intended to help understand the physics of sound (compressional waves) propagating through sandy sediments (unconsolidated porous media). The theory (using a lumped parameter model) and measurements (using a reflection ratio technique) includes derivations and measurements of acoustic impedance, effective densities, wave speeds (phase velocities), effective pressures, mode shapes, pressure reflection coefficients, and material moduli. The results show the acoustic impedance divided by the phase velocity, rendering an "effective density," is less than the total density of the sediment (effective density 89% plus or minus 3% of total). The results also show the fluid in the sediment oscillates back-and-forth 2.2 plus or minus 0.4 times farther than the sand in the sediment (mode shape) during the passing of a sound wave. These facts suggest the existence of Biot waves (two compressional waves) in water- saturated sand.

Bellows for coupling a source acoustic waves to a subject to be treated

Abstract: A bellows for coupling a source of acoustic waves having an acoustic propagation medium, to a patient, has a geometrical modification in that region wherein the bellows can be seated against the patient for the introduction of acoustic waves into the patient . The geometrical modification in the propagation path of the acoustic waves generated by the source of acoustic waves shapes the acoustic waves in a designated (designed) manner. Additionally or alternatively, the bellows can have a section in the region that is formed of a different material than the rest of the bellows.

Acoustic Interferometer for Localized Rayleigh Wave Velocity Measurements

Abstract: Two instrumentation systems for measurement of Rayleigh surface wave (RSW) velocity are described The first system consists of a more conventional methodology using matched RF amplifiers and phase detector/mixer circuits In the second system, a lock‐in amplifier, operating at high frequency, replaces the matched RF amplifiers and phase detector/mixer circuit, therefore simplifying the instrumentation Both systems have been used to measure relative Rayleigh wave velocity using a cylindrically focused acoustic transducer consisting of three elements A high‐precision relative velocity measurement of Rayleigh surface waves is performed by exciting the central element and one of the outer elements with a tone burst signal and measuring the phase difference between the two received signals

Propagation-invariant waves in acoustic, optical, and radio-wave fields

Abstract: s of publications I–VIII I We consider periodically propagating pulses, devoid of diffractive spreading. They may feature arbitrary velocities of propagation but their spectral characteristics vary according to whether they are luminal, subluminal or superluminal. The wave modes introduced are closely related to the X waves and the focus wave modes, but they allow a frequency-dependent cone angle and they are not limited to the speed of light. II We introduce subsonic nondiffracting waves which — unlike the ordinary supersonic nondiffracting waves — evolve periodically under propagation. Such pulse-like waves have a subsonic uniformly propagating ‘core’, which is modulated by a supersonic plane wave. The subsonic core may also be considered an envelope for a truncated Bessel beam and subsonic nondiffracting waves may be used to describe signal propagation within Bessel beams. III A unified spectral and temporal representation is introduced for nondiffracting waves. We consider a set of elementary broadband X waves which spans the commonly considered nondiffracting wave solutions. These basis X waves have a simple spectral representation which leads to expressions in closed algebraic form or, alternatively, in terms of hypergeometric functions. The span of the X waves is also closed with respect to all spatial and temporal derivatives and, consequently, they can be used to compose different types of waves with complex spectral and spatial properties. The unified description of Bessel-based nondiffracting waves is further extended to include singular Neumann and Hankel waves, or Y waves. We also discuss connections between the different known nondiffracting wave solutions, and their relations to the present unified approach. IV Nondiffracting pulses are spatially and temporally localized wave fields that undergo no diffractive spreading under propagation through homogeneous media. We introduce an orthogonality condition for nondiffracting pulses and present an orthogonal set of X waves which possess temporal spectra of the form (polynomial in ω)×e−αω. The newly introduced Bessel-X pulses and X-wave transforms are discussed in the framework of orthogonal X-wave bases.

Surface Acoustic Waves And Guided Optical Waves In AlGaN Films

Abstract: AlxGa1-xN layers grown by MOCVD on sapphire substrates have been tested using the surface acoustic wave and guided optical wave techniques. Samples with molar fraction of Al up to 0.36 have been investigated. The parameters S11 of single surface acoustic wave transducers and S12 of two-port devices have been measured with the network analyzer. The values of the surface acoustic wave velocity and electromechanical coupling coefficient for the layer-substrate structure have been extracted and calculated using material parameters available from literature. The attenuation of guided optical waves along the propagation track in AlxGa1-xN layers has been measured using the CCD imaging technique. The attenuation dependence on the mode order and layer thickness has been studied. Our results show that the properties of AlxGa1-xN that determine surface acoustic wave and guided optical wave propagation are similar to the properties of GaN films within a relatively wide range of x up to x =0.36.