Bulk Wave Excitation Research Articles

The dual mechanism underlying laser excitation of bulk and surface elastic waves in ablative regime

It is usually considered that plasma pressure impulse is the only mechanism corresponding to the laser excitation of bulk and elastic surface waves in an ablative regime. We report the first observation of a dual mechanism where the laser-induced shockwave impacts the target and generates secondary bulk and surface elastic waves some dozens of nanoseconds after the primary ones are generated by the plasma pressure impulse. We propose that the superimposing of the two wave groups can cause additional frequency components that should be considered in research and applications employing elastic waves generated by strong laser ablation.

Creeping motion characteristics due to bulk wave excitation in an elastic half-space

In this work, the contact problem between a preloaded rigid surface against a restrained elastic half-space is considered under wave excitation. The half-space is assumed to be bonded imperfectly to the rigid surface, and subjected to external tractions and bulk waves. Under incident bulk wave excitation at the contact, we study the creeping motion of the preloaded rigid surface. Two possible local regions at the interface are considered, namely slip region, and region of separation, which are described by the corresponding boundary conditions and inequalities at the interface. With these considerations, creeping motion characteristics and interface conditions are obtained analytically and discussed. The effects of interface imperfection, wave parameters, and preload tractions are studied numerically. The creeping motion is found to be affected significantly by nature of the imperfection. In addition, creep motion is also analyzed considering friction at the interface. These aspects have potential applications in ultrasonic devices for micro-positioning and micro-motion control.

Bulk wave excitation from the surface of a LiNbO3 crystal by a system of planar electrodes

Ultrasound generation using planar electrodes deposited on the surface of a lithium niobate crystal is investigated. The analysis is carried out in an acousto-optic device based on the XY cut of a lithium niobate crystal and in an acousto-optic cell designed as a prototype of a modulator of non-polarized radiation. The experimental investigation is conducted at different frequencies of the driving electrical signal. The generated acoustic field is visualized by the acousto-optic method at different polarizations of the incident optical beam in case of slow shear and longitudinal acoustic modes. A relation between diffraction efficiencies for ordinary and extraordinary polarized optical radiation is analyzed. The obtained experimental results on the diffraction efficiencies are compared to the theoretically predicted values. It is demonstrated that the polarization characteristics of the devices differ from the conventional characteristics by the dependence on the structure of the acoustic beam.

Measurements of Streams Agitated by Fluid Loaded SAW-devices Using a Volumetric 3-component Measurement Technique (V3V)

Utilizing surface acoustic waves (SAW) to induce tailored fluid motion via the acoustic streaming requires detailed knowledge about the acoustic bulk wave excitation. For the first time, the Defocus Digital Particle Image Velocimetry is used to measure the fluid motion originating from a fluid loaded SAW-device. With this flow measurement technique, the acoustic streaming-induced fluid motion can be observed volumetrically, which is attractive not only for application, but also for simulation in order to gain deeper insights regarding three-dimensional acoustic effects.

Theory of domain wall motion mediated magnetoelectric effects in a multiferroic composite

A model is discussed for magnetoelectric (ME) interactions originating from the motion of magnetic domain walls (DWs) in a multiferroic composite of orthoferrites $R{\mathrm{FeO}}_{3}$ $(R\text{FO}$) with magnetic stripe domains and a piezoelectric such as lead magnesium niobate-lead titanate (PMN-PT). The DWs in $R\text{FO}$ can be set in motion with an ac magnetic field up to a critical speed of 20 km/s, the highest for any magnetic system, leading to the excitation of bulk and shear magnetoacoustic waves. Thus, the ME coupling will arise from flexural deformation associated with DW motion (rather than the Joule magnetostriction mediated coupling under a static or quasistatic condition). A $c$ plane orthoferrite with a single N\'eel-type DW in the $bc$ plane and an ac magnetic field $H$ along the $c$ axis is assumed. The deflection in the bilayer due to DW motion is obtained when the DW velocity is a linear function $H$ and the resulting induced voltage across PMN-PT is estimated. It is shown that a combination of spatial and time harmonics of the bending deformation leads to (i) a linear ME coefficient defined by ${\ensuremath{\alpha}}_{E}=E/H$ and (ii) a quadratic ME coefficient ${\ensuremath{\alpha}}_{\mathrm{EQ}}=E/{H}^{2}$. The model is applied to yttrium orthoferrites (YFO) and a PMN-PT bilayer since YFO has one of the highest DW mobility amongst the orthoferrites. The coefficient ${\ensuremath{\alpha}}_{E}$ is dependent on the DW position, and it is maximum when the DW equilibrium position is at the center of the sample. In YFO/PMN-PT the estimated low-frequency ${\ensuremath{\alpha}}_{E}$ \ensuremath{\sim} 30 mV/cm Oe and resonance value is 1.5 V/(cm Oe). Since orthoferrites (and PMN-PT) are transparent in the visible region and have a large Faraday rotation, the DW dynamics and the ME coupling could be studied simultaneously. The theory discussed here is of interest for studies on ME coupling and for applications such as magnetically controlled electro-optic devices.

Reflecting Cell Model for SAW Structures

The study presents three-port reflecting cell model for analyzing SAW structures employing strong electrode reflections. Basic objective is to analytically approximate all the p-matrix elements for a SAW structure in terms of reflection, transduction, and transmission strengths. This model is an approximate one and it does not take into account the effects of bulk wave excitation, diffraction, and propagation loss etc for convenience. This 3port reflecting cell model has been used to show that it is possible to realize Infinite Impulse Response (IIR) filters on SAW devices, which can result in much smaller size as compared to very high order Finite Impulse Response (FIR) SAW filters for given specifications. Simulation results for this new 3-port reflecting cell model and IIR filter realization are presented for validation purpose.

Cherenkov radiation by an electron bunch that moves in a vacuum above a left-handed material

Cherenkov radiation by a nonrelativistic electron bunch that moves above an interface of a vacuum-left-handed material has been investigated theoretically. The electron density of the bunch is described by a Gauss distribution. Cherenkov radiation for the frequency range where the refractive index is negative is shown to lead to simultaneous excitation of both bulk and surface electromagnetic waves over one and the same frequency range. In this case the wave vector magnitude in the plane of the interface of surface electromagnetic waves is larger than the corresponding wave vector magnitude of bulk electromagnetic waves. The energy flows in a left-handed material have been calculated. The spectral density and the radiation pattern have been investigated.

Excitation of surface and leaky waves on a solid body-gas interface

We analyze excitation of bulk, leaky, and surface waves by a point time-harmonic forcing applied perpendicularly to a solid body – gas interface. The case where the sound speed in the gas is less than the Rayleigh-wave velocity on the solid surface is considered. Expressions for the radiation powers of longitudinal and transverse spherical waves in the solid body and of a Stoneley surface wave, averaged over their periods, are derived. Excitation of a spherical acoustic wave in the gas and a pseudo-Rayleigh leaky wave is analyzed. For the spatial region corresponding to zenith angles exceeding the arcsine of the ratio of the sound speed in the gas and the transverse-wave velocity in the solid body, where the leaky-wave energy is transformed into the acoustic wave, we derive formulas describing their summed radiated power.

Full-wave modeling of piezoelectric transducers for SAW acousto-optical interactions

In this paper we present an accurate and efficient numerical method for a rigorous full-wave analysis of interdigital transducers (IDT) for the excitation of surface acoustic waves on the piezoelectric substrate of acousto-optical devices. The problem is formulated in terms of an integral equation that is solved by the method of moments. The transducer input admittance and the power coupling factors to both surface and bulk waves are computed. Numerical results for some configurations of X-Y LiNbO3 IDT for acousto-optic applications are in very good agreement with measured data. It is pointed out that bulk wave excitation may be a serious limitation in the design of efficient, wide band transducers for acousto-optical devices.

Ultrasonic Properties of Lead Zirconate Titanate Thin Films in UHF-SHF Range

We describe the ultrasonic properties of lead zirconate titanate (PZT) thin films prepared by the sol-gel method. It is shown that the PZT thin film exhibits efficient transduction of bulk and surface acoustic waves in UHF-SHF range. A conversion loss of less than 4 dB is achieved for bulk wave excitation and detection at 1.7 GHz, where the electromechanical coupling factor k t reaches 30%. This indicates that the PZT thin film is promising for use in the development of large-bandwidth resonators and filters in modern communication systems as well as for high-frequency ultrasonic transducer applications.

Geometrical Aspects of the Diffraction of Critically Incident Bulk Waves and Gaussian Beams

This paper contains a study of some of the nonuniformities that can arise in the acoustic field radiated from a wavebearing boundary when it is insonified by either a bulk wave or a Gaussian beam. Particular attention is paid to cases of critical incidence for which the surface wave that can exist at the boundary is excited with maximum efficiency. By posing suitable diffraction problems local to the point of excitation of the surface wave, singular perturbation techniques are applied to establish the local structure of the total radiated field in this neighbourhood and these “inner” solutions are matched to “outer” solutions in which the various constituent waves can be unambiguously and independently identified. Doing so provides a geometrical methodology for predicting the region into which the radiation from the surface wave can penetrate. This is applied to the particular cases of bulk wave excitation of a supersonic “leaky” surface wave and of Gaussian beam insonification of a pure impedance plane. In the former case, the unusual spatial “cut-off” phenomenon is revealed and in the latter case, the lateral shifting of the geometrical axis of the recected beam is predicted. In all cases, the fine structure of the radiated fields are discussed and the many interesting diffraction effects generated by interferences between specularly reflected fields and surface wave radiation are ighlighted. Particular attention is paid to the geometrical aspects of these problems and it is shown how the solutions to the inner diffraction problems can be combined with ray theory to predict the various critical directions that arise in a natural and convenient way.

1 GHz low loss coupled resonator filter using surface skimming bulk waves and Bleustein-Gulyaev waves

A three-pole coupled resonator filter (CRF) based on the simultaneous excitation of surface skimming bulk waves (SSBW) and Bleustein-Gulyaev waves (BGW) with the same magnitude is described. This device operates at 1 GHz, has an insertion loss of 3–4 dB, a typical 1 dB bandwidth of 0.15% and can dissipate a power of more than 2W on a quartz substrate area of 3 mm2.

A model for evaluating the efficiency of an interdigital transducer for bulk wave excitation into liquid

An equivalent circuit model analysis of a liquid-loaded interdigital transducer is described. The electric loss related to the complex relative dielectric constant and the electroacoustic conversion efficiency are represented in the form of a function of the specific acoustic impedance (ρv) of the loaded liquid. The conversion efficiency for ultrasound into the liquid is estimated from only the acoustic impedance and the relaxation time of the substrate material, which are obtained relatively easily from the water measurement. The estimated theoretical efficiency is in good agreement with the experimental results for various liquids. These results also coincide with the results from the wave equation for the leaky surface acoustic wave propagation at the solid–liquid boundary.

New technique for excitation of bulk and surface spin waves in ferromagnets

A meander-line magnetic transducer is discussed in the context of bulk and surface spin-wave generation in ferromagnets. The magnetic field created by the transducer was calculated in closed analytic form for this model. The linear response of the ferromagnet to the inhomogenous surface disturbance of arbitrary ω and k was obtained as a self-consistent solution to the Bloch equation of motion and the Maxwell equations, subject to appropriate boundary condition. In particular, the energy flux through the boundary displays a sharp resonantlike absorption maximum concentrated at the frequency of the magnetostatic Damon–Eshbach (DE) surface mode; furthermore, the energy transfer spectrum is cut off abruptly below the threshold frequency of the bulk spin waves. The application of the meander line to the spin diffusion problem in NMR is also discussed.

The Excitation and Detection of Surface-Generated Bulk Waves

The Excitation and Detection of Surface-Generated Bulk Waves

The Excitation and Detection of Surface-Generated Bulk Waves

Absrruct-The performance of a conventional pair of surface acoustic wave interdigital transducers (IDT’s) used to generate bulk acoustic waves is analyzed. An IDT located on the upper surface of a thick, rotated Ycut quartz crystal acts as the acoustic equivalent of an array antenna, launchingacollimated beam into the crystal bulk. The beam is reflected off the crystal bottom and redirected towards the upper crystal surface where it is intercepted by a second receiving IDT. Closed-form expressions are derived for the important electrical and acoustical delay line characteristics and comparison is made with experimental measurements. The analyzed characteristics of the reflected bulk wave (RBW) delay line are significantly different from either the SAW or SSBWand include a) a frequency bandwidth directly proportional to transducer length, b) a center frequency determined not by finger-to-finger spacing but rather by the ratio of transducer separation to crystal thickness, c) a nonresonant radiation resistance, d) the capability to synthesize filter designs in which the frequency response is proportional to the correlation of the individual transducer finger weightings, and e) the capability to modify temperature stability by change of transducer separation and crystal thickness. ULK ACOUSTIC wave radiation generated by interdigital B transducers has historically been considered as spurious, often degrading or interfering with the performance of devices based upon surface acoustic wave (SAW) excitation. Within the last several years, however, there has been increased interest in utilizing the bulk waves generated by IDT’s for practical microwave applications. Such surface-generated bulk waves make use of the IDT as an acoustic equivalent of a phasedarray antenna, with the electrode fingers constituting the array elements. The phasing between these elements is controlled by the applied signal frequency thereby allowing the direction of the acoustic beam radiated into the bulk to be scanned.

A Green's Function Formulation for Analyzing Excitation of Surface-Skimming Bulk Waves

A Green's Function Formulation for Analyzing Excitation of Surface-Skimming Bulk Waves

Excitation and Detection of Surface Skimming Bulk Waves on Rotated Y-Cut Quartz

Excitation and Detection of Surface Skimming Bulk Waves on Rotated Y-Cut Quartz

Radiation Patterns of Bulk Modes from a Finite Interdigital Transducer on Y-Z LiNbO3

Radiation patterns of bulk acoustic modes from a finite in- terdigital transducer on Y-Z LiNb03 were found using moment method and then compared with the experimental results. The power density radiation patterns of shear and longitudinal bulk modes were computed as functionsof the radiation angle, the electrode metallization ratio, and the frequency. It was shown that a SAW transducer can be very effi- ciently used for shear bulk wave excitation. For instance, at the sec- ond harmonic of the Rayleigh wave the percentage power of the shear, longitudinal, and SAW is 67.2,26.4, and 6.4 percent, respectively. The bulk power density distribution versus radiation angle does not change in form with a change in the metallization ratio. The SAW power density increases with increasing values of the metallization ratio.

Efficient bulk wave excitation on ST quartz

Efficient excitation and detection of bulk waves on rotated 90° ST quartz are reported. Experimental results on three different transducer configurations are given and the possible applications are discussed.