Acoustic Microwaves Research Articles

Comparative between (LiNbO3) and (LiTaO3) in detecting acoustics microwaves using classification

Our work is mainly about detecting acoustics microwaves in the type of BAW (Bulk acoustic waves), where we compared between Lithium Niobate (LiNbO3) and Lithium Tantalate (LiTaO3) ,during the propagation of acoustic microwaves in a piezoelectric substrate. In this paper, We have used the classification by Probabilistic Neural Network (PNN) as a means of numerical analysis in which we classify all the values of the real part and the imaginary part of the coefficient attenuation with the acoustic velocity for conclude whichever is the best in utilization for generating bulk acoustic waves.This study will be very interesting in modeling and realization of acoustic microwaves devices (ultrasound) based on the propagation of acoustic microwaves.

A comparative study for two LiNbO3 cuts (Y-Z and Y-X) in detecting bulk acoustic microwaves using Probabilistic Neural Network

This work is mainly on the detection of the bulk acoustic waves (BAWs), where we have compared two Lithium Niobate cuts (Y-Z and Y-X), during the propagation of the acoustic microwaves in the piezoelectric LiNbO3-substrate. In this paper, we have used the classification by Probabilistic Neural Network (PNN) as a tool for numerical analysis in which we classify all the values of the real and imaginary parts of the attenuation coefficient for the propagation velocity. This analysis can allow us to demonstrate the best possibility in utilization for the BAW generation. This study will be very interesting in modeling and realization of acoustic wave devices (ultrasound) based on the propagation of acoustic microwaves.

Conditions for observation of the nonreciprocal effect in a collinear acoustooptic filter at various wavelenghts of light radiation

The features of the nonreciprocal effect observed during collinear acoustooptic interaction in a lithium niobate crystal are investigated theoretically and experimentally. It is shown that one of the main reasons that restrict the possibility of observation of the nonreciprocal effect in the crystal is damping of an acoustic wave. It is proved that, when an acoustooptic cell is illuminated with monochromatic light, the ultrasound damping increases the frequency band of the collinear acoustooptic interaction, a circumstance that affects the possibility of observation of the nonreciprocal effect in an acoustooptic experiment. The conclusion that the creation of acoustooptic filters having a high spectral resolution and operating at acoustic microwaves necessitates taking into account the nonreciprocal effect is drawn.

Identification of bulk microwaves and detection of Pseudo-singularities by wavelet technique in piezoelectric medium

In this paper, the analysis of pseudo-singularities (corresponding to rapid variations) which appear in some parameters during the propagation of acoustic microwaves in a piezoelectric substrate is considered. These pseudo-singularities have a major importance because they can inform of the presence of bulk waves. However, there is a problem for the detection of the waves when the pseudo-singularities exist but is unobservable with the classical methods. To solve this problem, it is proposed that a new technique of detection based on the famous wavelet transform. This transform insures the detection of pseudo-singularities because it has the property of being locally maximal around the points where the signal is singular (or pseudo-singular).

Pre-earthquake ULF electromagnetic perturbations as a result of inductive seismomagnetic phenomena during microfracturing

This paper proposes a generation mechanism of ULF electromagnetic noise observed several hours before some strong earthquakes. It is assumed that this effect results from the energization of crack formation and fracture process in a focal zone before the main shock. Electromagnetic noise is considered as a by-product of the summation of electromagnetic micro-fields appearing in the conductive medium ahead of acoustic micro-waves radiated by an ensemble of tensile cracks. These micro-fields and currents are generated due to the movement of conductive medium in the geomagnetic field. The electromagnetic perturbations depend on the direction diagram of radiation and the attenuation of acoustic waves emitted by opening cracks. We investigate two different zones and regimes of ULF magnetic field propagation. In the near zone we expect the prevailing diffusion regime, where the sign of components of electromagnetic fields is found to be the same for all the cracks independent of their space orientation. A similar coherent effect takes place at the far or acoustic zone. These surprising effects occur, because the effective magnetic moments of current systems generated by the cracks are always directed opposite to the vector of geomagnetic field; i.e. these moments are strongly paralleled. It was established that the coherent amplification of ULF signals generated by the cracks could appear if only their size exceeds several critical values. Such an effect might appear at the background of low seismic activity because the acoustic emission of cracks is incoherent. The averaging of the fields over the ensemble of opening cracks allowed us to relate the parameters of electromagnetic noise to porosity, volumetric strain, dilatational coefficient and average size of macro-cracks at the earthquake hypocenter. Our theory predicts magnetic and electric perturbations to be of the order of 1– 10 nT and 1– 10 μV/m , respectively, at the distance 10– 50 km from the epicenter. These values are very close to those observed prior to the occurrence of earthquakes at Loma Prieta and Spitak.

Interaction between light and acoustic microwaves excited by aperiodic multielement transducers. II

Aperiodic multielement piezoelectric transducers operating in the high-frequency part of the microwave range are studied theoretically. The efficiency of interaction between a plane light wave and the acoustic fields excited by the transducers with antiphase adjacent elements is calculated as a function of frequency. Structures where the pitch varies gradually or stepwise and the piezoelectric elements are wide-or narrow-band are analyzed.

Analysis of leaky and bulk acoustic microwaves by wavelet technique

An analysis of singularities which appear in some parameters during the propagation of acoustic (elastic) microwaves in a piezoelectric substrate is considered. These singularities have a major importance because they can inform us on the presence of pseudo-waves which are accompanied by some bulk and leaky waves. As classical methods of detection of singularities can be inefficient, a new method of detection is proposed here. It is based on the wavelet transform which can detect the singularities of a signal whatever its complexity. Copyright © 2000 John Wiley & Sons, Ltd.

Analysis of leaky and bulk acoustic microwaves by wavelet technique

An analysis of singularities which appear in some parameters during the propagation of acoustic (elastic) microwaves in a piezoelectric substrate is considered. These singularities have a major importance because they can inform us on the presence of pseudo-waves which are accompanied by some bulk and leaky waves. As classical methods of detection of singularities can be inefficient, a new method of detection is proposed here. It is based on the wavelet transform which can detect the singularities of a signal whatever its complexity. Copyright © 2000 John Wiley & Sons, Ltd.

Guided-Wave Theory of Light Diffraction by Acoustic Microwaves

Guided-Wave Theory of Light Diffraction by Acoustic Microwaves

Guided-Wave Theory of Light Diffraction by Acoustic Microwaves

The diffraction of a plane light wave incident obliquely upon an isotropic dielectric layer traversed longitudinally by an acoustic microwave is examined by means of a guided-wave approach. In addition to a considerable amount of physical insight, this approach provides a wide range of techniques that have already been developed extensively in the area of electromagnetic microwaves. As a consequence, available methods can be used to explain and express known aspects of the diffracted light in terms of simple guided-wave concepts which are applied herein to derive results that have not been available. It is shown that the difracted field within the dielectric layer, as well as in the exterior (air) medium, can be described by means of two alternative modal representations: 1) a description in terms of characteristic modes which progress independently of each other, and 2) a description in terms of coupled modes which interact with each other in the presence of the acoustic wave. While the two representations are equivalent, each has its own advantages and both are discussed in detail. It is also shown that these representations lead to equivalent networks that may be utilized to account for boundary conditions and for other features of the scattered field. In particular, diffraction phenomena in a Bragg regime are carefully investigated; qualitative and quantitative results are presented for situations wherein the orientation of the optic-acoustic interaction occurs at a Bragg angle of arbitrary order.

Parametric Traveling-Wave Acoustic Amplification in Ferromagnets

A theoretical evaluation is presented for the amplification of acoustic microwaves traveling in a ferromagnet by means of a parametric interaction with a spatially uniform pump magnetization and a spin-wave idler. In this interaction, the strong frequency dispersion of the idler wave suppresses the degenerative effect of the upper sideband frequency. Although the spin-wave boundary conditions would seem to require a standing-wave idler, the low group velocity, and resulting short decay length, permits traveling-wave operation. By means of a normal mode analysis including losses, expressions are found for the gain per unit length and the interaction bandwidth as a function of pump power. The ultimate interaction bandwidth is determined by the spin wave Q, but the usable bandwidth is reduced by the effect of acoustic mismatches. This amplifier, in common with the maser and laser, is bilateral and the usable gain is limited by regeneration. The range of usable gain is expressed in terms of the acoustic mismatches at the terminals. Nondegenerate operation is possible, permitting reduction of idler-wave thermal noise. Gain, bandwidth, and pump power, and their frequency dependence, are evaluated for a number of available materials. Performance limitations due to Suhl breakdown are also discussed.