Showing papers on "Acoustic interferometer published in 2005"

In solid localization of finger impacts using acoustic time-reversal process

Abstract: Time reversal in acoustics is a very efficient solution to focus sound back to its source in a wide range of materials including reverberating media. It expresses the following properties: A wave still has the memory of its source location. The concept presented in this letter first consists in detecting the acoustic waves in solid objects generated by a slight finger knock. In a second step, the information related to the source location is extracted from a simulated time reversal experiment in the computer. Then, an action (turn on the light or a compact disk player, for example) is associated with each location. Thus, the whole system transforms solid objects into interactive interfaces. Compared to the existing acoustic techniques, it presents the great advantage of being simple and easily applicable to inhomogeneous objects whatever their shapes. The number of possible touch locations at the surface of objects is shown to be directly related to the mean wavelength of the detected acoustic wave.

Far-field imaging of acoustic waves by a two-dimensional sonic crystal

Abstract: The negative refraction behavior and imaging effect for acoustic waves in two-dimensional sonic crystals consisting of hexagonal arrays of steel cylinders in air are studied in this paper. The negative refraction and left-handed behaviors are demonstrated by the simulation of a Gaussian beam through a slab of the sonic crystal. Imaging effects by the sonic crystal slab with effective refraction index $n\ensuremath{ e}\ensuremath{-}1$ and $n=\ensuremath{-}1$ are investigated, respectively. Far-field images by two-dimensional sonic-crystal-based superlens for both cases are obtained by exact numerical simulations, which is in agreement with the physical analysis based on the wave-beam negative refraction law. Thus, extensive applications of such a phenomenon to acoustic devices are anticipated.

Generation of ultrahigh-frequency tunable acoustic waves

Abstract: We demonstrate versatile generation of ultrahigh-frequency, tunable acoustic waves. A novel retroreflection-based pulse shaper is used to generate optical pulse sequences whose frequency is tunable in the 2–2000 GHz range through movement of a single delay line. Multiple-cycle acoustic waves are detected interferometrically at the back of a 15 nm aluminum transducing film and the back of a film-sample-film assembly configured for narrowband acoustic spectroscopy.

Nearly backward reflection of elastic waves in an acousto-optic crystal of paratellurite

Abstract: Some features of the propagation and reflection of acoustic waves in the XY plane of a paratellurite crystal have been studied. It is established that the acoustic waves exhibit an unusual backward reflection from the side crystal facet in the case of glancing incidence onto the crystal-vacuum interface. The experimental results are in good agreement with theoretical predictions.

Experimental study of guiding and filtering of acoustic waves in a two dimensional ultrasonic crystal

Abstract: We present a combined experimental and theoretical study of the guiding, bending and filtering of acoustic waves in an ultrasonic crystal. The crystal consists of a two-dimensional periodical array of steel rods immersed in water, for wich a complete acoustic band gap extending from 240 to 325 kHz is found experimentally. Waveguides for acoustic waves are further created by removing a line defect, on which stubs can be added by removing rods from the side-walls of the waveguide. Full transmission is observed for a one-period-wide straight waveguide within the full-band-gap of the perfect phononic crystal, i.e. for a waveguide aperture smaller than one acoustic wavelength. Waveguiding over a wide frequency range is also obtained for a one-period-wide waveguide with two sharp 90° bends. Finite-difference time-domain computations are found to be in good agreement with the measurements in all experimental configurations.

Interferometric detection of acoustic waves at air-solid interface applications to non-destructive testing

Abstract: In this paper, some properties of acoustic waves at the air-solid interface are reviewed and laser-ultrasonics is used to optically excite and detect these waves. In comparison with the leaky Rayleigh wave, a large amplitude is observed for the acoustic disturbance which is composed of Scholte and lateral waves. However, it is apparent from theoretical results, taking source terms into account, that the normal displacement of these waves cannot be large in such an interface. Another explanation for the high-intensity fluctuation measured is the optical heterodyne detection of the refractive index variation induced in the fluid. This assumption is experimentally checked by probing the acoustic field parallel to the surface of the sample. The potentialities of these waves in non-destructive testing are also investigated. It is clearly shown that the transmitted, reflected, or diffracted acoustic fields provide useful information about the position or the size of structures intercepting the propagation path. Indeed, glass plate thickness or steel block position can be easily determined using a time of flight analysis. This suggests a lot of new applications in the sizing of structures where noncontact measurements on inaccessible parts would be necessary.

Convergence of sound waves radiated from aerial ultrasonic source using square transverse vibrating plate with several reflective boards

Abstract: An ultrasonic source using a metal square vibrating plate radiates extremely intense ultrasonic waves into the air. The plate experiences transverse vibration when a longitudinal vibration is applied to the central point of the plate. In the lattice mode, the nodal positions of the plate take the form of straight lines, creating a lattice-like pattern. The source radiates four directional sound waves in the far field. The aim of our study is to obtain high sound pressure by converging the sound waves radiating from a source of this shape in the near field. We studied the construction of an ultrasonic field converged by using several flat boards plus four parabolic reflective boards placed near the source. The results of the measurements of sound pressure and phase distributions show that these boards can create the convergence of sound waves.

Real Time Imaging of Surface Acoustic Waves on Crystals and Microstructures

Abstract: The use of acoustic pulses to image materials is well-known in echography or sonar applications. We are extending this field by generating point-excited sound pulses on solid surfaces with ultrashort laser pulses and imaging the resulting surface wave propagation in real time. To see the tiny vibrations of the surface, smaller in amplitude than the dimensions of a single atom, we use another set of laser pulses for scanned probing. The typical surface phonon wavelength is of the order of a few microns, corresponding to frequencies up to 1 GHz. With such a system we can watch coherent acoustic wave packets in two dimensions rippling across crystal surfaces and microscopic landscapes.

Spectrum of the seismic-electromagnetic and acoustic waves caused by seismic and volcano activity

Abstract: . Modeling of the spectrum of the seismo-electromagnetic and acoustic waves, caused by seismic and volcanic activity, has been done. This spectrum includes the Electromagnetic Emission (EME, due to fracturing piezoelectrics in rocks) and the Acoustic Emission (AE, caused by the excitation and the nonlinear passage of acoustic waves through the Earth's crust, the atmosphere, and the ionosphere). The investigated mechanism of the EME uses the model of fracturing and the crack motion. For its analysis, we consider a piezoelectric crystal under mechanical stresses, which cause the uniform crack motion, and, consequently, in the vicinity of the moving crack also cause non-stationary polarization currents. A possible spectrum of EME has been estimated. The underground fractures produce Very Low (VLF) and Extremely Low Frequency (ELF) acoustic waves, while the acoustic waves at higher frequencies present high losses and, on the Earth's surface, they are quite small and are not registered. The VLF acoustic wave is subject to nonlinearity under passage through the lithosphere that leads to the generation of higher harmonics and also frequency down-conversion, namely, increasing the ELF acoustic component on the Earth's surface. In turn, a nonlinear propagation of ELF acoustic wave in the atmosphere and the ionosphere leads to emerging the ultra low frequency (ULF) acousto-gravity waves in the ionosphere and possible local excitation of plasma waves.

Development of SAW thermocycler for small liquid droplets

Abstract: In this paper, we present a liquid-droplet-heating system using a surface acoustic wave (SAW) device. When liquid is placed on a Rayleigh-SAW-propagating surface, a longitudinal wave is radiated into the liquid. If the SAW amplitude increases, the liquid shows nonlinear dynamics, such as vibrating, streaming, small droplet flying, and atomizing. This phenomenon is well known as SAW streaming. The liquid temperature is measured during the longitudinal wave radiation and found to increase. First, the mechanism of liquid heating phenomenon is discussed. Second, the fundamental properties of the liquid temperature are measured by varying the applied voltage, duty factor, and liquid viscosity. The liquid temperature is found to be proportional to the duty factor and the square of the applied voltage. Therefore, the liquid temperature can be controlled by these applied signals. Also, by using highly viscous solutions, the liquid temperature is increased to more than 100 ˚C. Finally, the possibility of periodic temperature control is tested by varying the duty factor. The obtained results strongly suggest that an efficient thermal cycler is realized. A novel application of the SAW device is proposed on the basis of SAW streaming.

Microphone-free measurement of acoustic absorption coefficient of materials using a standing wave tube

Abstract: This paper reports a method for measuring the specific acoustic impedance or absorption coefficient of acoustic material using a standing wave tube without a microphone. The method was validated by tests conducted in a normal standing wave or impedance tube—a straight solid-wall tube with a speaker and a material specimen perpendicularly mounted at each end, respectively. Assuming that sound waves are planar in the tube, we derived the relationship between the impedance at the input and output ports of the loudspeaker as well as the same for the standing wave tube. Through these two relationships, the specific acoustic impedance of the material specimen is then expressed as a function of the input electrical impedance of the loudspeaker together with a few parameters characterizing the electro-acoustic system. With the resulted formula, probing the input voltage and current to the speaker alone allows quantitative evaluation of the specific acoustic impedance of the material specimen. Experimental results show that the method can correctly identify the absorption coefficient of acoustic materials in the lower frequency range. The results are less accurate in the higher frequency range due to the invalidity of the assumption of plane waves and the low signal-to-noise ratio. From the results, it is also observed that, due to the microphone-free feature, the reported method is suitable for in situ study of acoustical or vibrational conditions of the material or structural specimen at the end of a duct with geometry making microphone installation difficult or impossible.

Amplitude and phase measurement of surface acoustic waves within a saw filter having fan-shaped transducers and numerical simulations

Abstract: .� A new method of laser heterodyne interferometry is applied to the phase measurement of surface acoustic waves within a SAW filter having fan-shaped transducers on a 128Y-X LiNbO3 substrate. As a result, it is clarified that the standing waves inside the fan-shaped transducer move towards the open end of the fan, resulting in several diffraction beams. Furthermore, a simple numerical simulation concerning the wave propagation and electrical characteristics of a SAW filter

Intensity of reflected acoustic waves in acousto-optic crystal tellurium dioxide

Abstract: ΩPropagation and reflection of plane elastic waves in the acousto-optic crystal tellurium dioxide is examined in the presentation. The reflection of the waves from a free and flat boundary separating the paratellurite crystal and the vacuum is investigated in the (001) and the (110) planes of TeO2 in the case of glancing and inclined acoustic incidence on the boundary. The analysis shows that as much two elastic waves may be reflected from the crystal surface. Energy flow of one of the reflected waves propagates in a quasi-back direction with respect to the incident energy flow unusually reflected wave may be close to a unit in a wide variety of crystal cuts. Possible applications of the examined phenomena in acousto-optic devices are discussed in the presentation.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Loudspeaker device and method for outputting sound

Abstract: PROBLEM TO BE SOLVED: To obtain a sound image having an extent extensively over a wide range, by abutting a transmitter transmitting a displacement output from an actuator against an acoustic diaphragm, and exciting the acoustic diaphragm with vibration component in at least the face direction. SOLUTION: In a loudspeaker device, a driving rod 103a for the actuator 103 is abutted against the end face on the lower-end side of a pipe 102. The actuator 103 excites the pipe 102 by the vibration component in the direction (face direction) orthogonal to the end face on the lower-end side of the pipe 102 from the end face. The end face on the lower-end side of the pipe 102 is excited by longitudinal waves, and elastic waves (vibrations) are propagated gradually in the face direction on the pipe 102. The mode conversion of longitudinal waves, transverse waves, longitudinal waves and transverse waves is repeated, when the elastic waves are propagated on the pipe 102, and the mixed waves of longitudinal waves and transverse waves are obtained. Vibrations in the in-plane direction (direction vertical to a face) of the pipe 102 are excited by transverse waves, and sound waves are emitted. Large transverse waves are not generated at the excitation point of the pipe 102, and the sound waves from the excitation point will not be listened to as a sound that is very much larger than sound waves from other locations, thus obtaining the sound image having a sense of extent. COPYRIGHT: (C)2007,JPO&INPIT

Picosecond ultrasonics : an original tool for physical characterization of Bragg reflectors in bulk acoustic wave resonators

Abstract: Here, we present the application of the picosecond ultrasonic technique to the design and the characterization of Bragg reflectors used in the insulation of bulk acoustic wave resonators. We first show that picosecond ultrasonics is helpful for the design of Bragg reflectors through precise sound velocity measurements in thin films whose elastic properties may be much different. Secondly we apply the same technique to the complete reflector and show that it permits to check the matching of the thicknesses with λ/4 and provides a direct measurement of the reflector's central frequency.

Droplet ejector using surface acoustic waves

Abstract: The present study aims to investigate droplet ejection using Surface Acoustic Waves (SAW). The interests in droplet ejection microsystems have dramatically grown in recent years due to inkjet printhead demand (Drop-On-Demand). Among several actuating methods (thermal, piezoelectric, etc.), the thermally driven inkjet printhead is the most successful (low cost, easy fabrication and high printing quality). Almost all of the current ink jet printers eject ink droplets through nozzles, with a direction of ejection always perpendicular to the nozzle surface. Surface acoustic waves devices are widely used for frequency filtering and are mainly devoted to cellular phones and telecommunication handset. Nowadays, recently published works have demonstrated the interest of SAW for guiding and positioning small liquid droplet atop a flat surface. This paper describes a new way to eject droplets (water, ink, etc...) using SAW. The surface acoustic waves devices used to eject droplets are carried out on lithium niobate substrates (LiNbO3 cut Y+128°, X propagation). The Rayleigh waves are excited using classical inter-digital transducers (IDT). The design of IDT has been simulated with finite element analysis and boundary element methods. The computations on the design of the IDT have been compared with measurements. The vibration amplitude of the wave necessary to droplet ejection is measured using a heterodyne laser probe. The range of the droplets volume ejected is between 100nl and 1μl. The influence of the supply voltage on the ejection is described.

Silicon phononic crystal for surface acoustic waves

Abstract: The recent theoretical and experimental demonstra- tions of band gaps for surface acoustic waves have still enlarged the field of potential applications for phononic crystals. Direct excitation of this type of waves on the surface of a piezoelectric material, and their already extensive use in ultrasonics make them an interesting basis for phononic crystal based, acoustic signal processing devices. Thus is raised the issue of designing suitable structures for a given application. An ongoing study of the key parameters affecting the position and width of band gaps in phononic crystal is hence presented in this paper. In particular, closer interest is given to both the lattice structure and its filling fraction. Numerical examples are then given in the case of vacuum scatterers/solid matrix crystals. Eventually, a fabrication method of a silicon phononic crystal is presented, and characterization methods are proposed.

Displacement measuring interferometer system and method using tunable lasers

Abstract: A displacement measuring interferometer system and method for measuring the distance between two known points is disclosed. An interferometer is configured to provide a reference reflection of a reference point and a measurement reflection of a measurement point. A tunable laser is used to scan in wavelength into the interferometer to detect interferometer characteristics to measure the distance between the reference point and the measurement point from the interferometer characteristics. The invention describes a displacement measuring interferometer which uses a scanning tunable laser to accurately map out a fringe such that significant improvement in accuracy can be achieved by use of a tunable laser to scan the wavelengths and determine the fringe.

Simple acoustic multiplexer.

Abstract: Simple structures enabling the multiplexing of acoustic waves are presented Such structures are constructed out of two monomode acoustic wires and two masses bound together, and to the wires by springs We show analytically that these simple structures can transfer with selectivity and in one direction one acoustic wavelength from one wire to the other, leaving neighbor acoustic wavelengths unaffected We give closed-form relations enabling to obtain the values of the relevant physical parameters for this multiplexing phenomena to happen at a chosen wavelength Finally, we illustrate this general theory by an application

Channel drop process of elastic wave in a two dimensional phononic crystal

Abstract: We study theoretically the possibility of transferring acoustic waves of a given wavelength between two parallel guides created in a phononic crystal. The structure considered in this work is composed of a periodic array of steel cylinders in water that displays an absolute bandgap. Within this gap, a full transmission band exists for propagation inside a straight wave guide. We show that by choosing an appropriate coupling structure between two parallel wave guides, one can transfer a particular acoustic wavelength from one guide to the other. The coupling element is composed of two hollow cylinders interacting with four other hollow cylinders located at each side of the wave guides. We discuss how the demultiplexing phenomenon is affected by varying the inner radius of the hollow cylinders. Keywords-component; acoustic waves; phononic crystal; demultiplexer

Visualization of back reflected acoustic waves in paratellurite single crystals by means of acousto-optics

Abstract: This paper is devoted to experimental investigation of regular trends of acoustic waves propagation and glancing reflections in XY plane of TeO 2 single crystal. The unusual “backward” reflection of the acoustic waves from a side border of the crystal when the phase velocity of sound is directed along the border has been observed. All experimental results were in good agreement with the predictions of theory, related to the magnitudes of the phase and group velocities of ultrasound as well as to the acoustic energy walkoff angles in the crystal. Keywords: acoustic anisotropy, backward reflection, acousto-optical interaction geometry, quasicollinear filter, paratellurite INTRODUCTION It is known that acousto-optical devices have found wide application in Optics and Technology, e.g. in telecommunication systems, spectral image filtration, as well as in objects detection and recognition systems, structure visualization, etc 3 . The progress in modern Acousto-Optics stimulated the development of new types of the acousto-optical devices such as optimized acousto-optical tunable filters

Fabry-perot interferometer and infrared sensor apparatus using same

Abstract: PROBLEM TO BE SOLVED: To provide a Fabry-Perot interferometer for simultaneously transmitting an infrared wavelength having a characteristic for absorbing a gas whose concentration is sensed even if a plurality of components are contained in the gas whose concentration is sensed. SOLUTION: The Fabry-Perot interferometer comprises a first interferometer mirror 20 provided on and fixed to a substrate 10, and a second interferometer mirror 30 disposed and facing the first interferometer mirror 20 through a gap 60. At least one of the first and second interferometer mirrors 20, 30 is formed so as to have a step 50. A plurality of different gap lengths are set between the first and second interferometers 20, 30. COPYRIGHT: (C)2006,JPO&NCIPI

Anomalous resisto-acoustic effect for leaky surface acoustic waves

Abstract: First the existence of anomalous resisto-acoustic effect for weakly inhomogeneous surface acoustic waves in structure “piezoelectric crystal—thin conducting film” was experimentally confirmed. At that the experimental value of the positive change in velocity turned out to be significantly less than the theoretically expected value for the ideal state of the crystal surface. The investigation showed that this effect is extremely sensitive to real state of the waveguide surface, which is caused by mechanical and chemical processing of sample, and also by technology of film deposition and removing. Taking into account the real state of the surface led to good agreement of theoretical results with experimental data.

Observation of axial acoustic waves in multimode PMMA optical fibres and implications for a new class of optical fibre sensor

Abstract: Observations of axial acoustic waves in multimode polymethylmethacrylate (PMMA) optical fibres are reported. Rapid electrostriction was induced in a 1.25 m length of PMMA optical fibre using a pulsed transverse electric field of ~106 V m−1. By observing the effects of birefringence on a polarised laser beam, acoustic waves travelling with a speed of 1050 m s−1 were observed to travel between the fibre ends. Simple calculations indicate that these acoustic waves comprised shear waves, although propagation of surface waves could not be ruled out. The implications of these observations in terms of a new class of optical fibre sensors based on the propagation of axial acoustic waves are also discussed.

Interferometric identification of ion acoustic broadband waves in the auroral region: CLUSTER observations

Abstract: [1] We determine the phase velocity and k vector for parallel and oblique broadband extremely low frequency, ELF, waves on nightside auroral magnetic field lines at altitudes around 4.6 RE. We use internal burst mode data from the EFW electric field and wave instrument onboard the Cluster spacecraft to retrieve phase differences between the four probes of the instrument. The retrieved characteristic phase velocity is of the order of the ion acoustic speed and larger than the thermal velocity of the protons. The typical wavelength obtained from interferometry is around the proton gyro radius and always larger than the Debye length. We find that in regions with essentially no suprathermal electrons above a few tens of eV the observed broadband waves above the proton gyro frequency are consistent with upgoing ion acoustic and oblique ion acoustic waves.

Confinement of surface acoustic waves in AlN∕GaN∕γ‐LiAlO2 acoustic wells

Abstract: We numerically investigate the characteristics of surface acoustic waves (SAWs) in AlN∕GaN∕γ‐LiAlO2 heterostructures The markedly large sound velocity in AlN in comparison to that in GaN leads to an expulsion of SAWs from the top AlN layer and their resultant relocation to the middle GaN layer in the short-wavelength regime The SAW velocity in the limit of zero wavelength is given by a bulk sound velocity of GaN, owing to the capping by the AlN barrier layer The extra confinement of the SAW power in the acoustic well is advantageous in manipulating the operation of GaN-based devices by SAWs The threshold velocity for the appearance of guided Rayleigh-like modes is found to be smaller than the bulk transverse sound velocity in the substrate The present system exhibits furthermore unusual bowing behavior in the SAW dispersion

Propagation of acoustic waves though periodic structures containing phase nonregularities

Abstract: The analysis of peculiarities of BAW and SAW propagation through the system of two reflecting Bragg structures (mirrors) separated by a gap providing non regularity of the phase of acoustic waves - an acoustic analog of a Fabri- Perot resonator is given.

Waves, sound, and light

Abstract: Sound and light are waves that transfer energy from one place to another.

Nonlinear second sound waves in superfluid helium in a resonator

Abstract: We communicate the results of numerical studies of acoustic turbulence in a system of nonlinear second sound waves in superfluid He-II in a resonator. It is shown that at sufficiently high amplitude of the external driving force the power-like energy distribution over frequency is formed in the system of second sound waves. This distribution is attributed to formation of the acoustic turbulence regime in the system. The energy distribution inside this interval is close to Eω ~ ω−2 and it does not depend on the sign of the coefficient, i.e. the coherent structures (shock waves) do not contribute into statistical properties of the second sound distribution in the turbulent state.