Electroacoustic Echo Research Articles

Электроакустические свойства различных типов кварца в мелкодисперсном состоянии

An electroacoustic echo method for studying the high-frequency (HF) electrical and elastic properties of piezoelectric materials in a finely dispersed state is described. The characteristics and relaxation time of electroacoustic echo for natural and artificial quartz powders are determined. Natural one is represented by the following types: smoky quartz, citrine, amethyst, recrystallized, granular and columnar. It is shown that natural quartz (especially citrine), has a higher electromechanical coupling coefficient than artificial quartz. The amplitudes of HF electric field are determined, at which the saturation mode of the echo signals is observed.

Homogenized electromechanical coefficients and effective parameters of 1–3 piezocomposites for ultrasound imaging transducers

Analytical models can be useful tools to develop efficient transducers dedicated to a specific application field. This work proposes a homogenization technique for establishing the effective coefficients and parameters of 1-3 piezocomposite whose both phases are piezoelectrically active. Such piezocomposite materials may have homogenized electromechanical properties resulting from positive hybrid effect. A numerical simulation of the effective parameters resulting from a PZT-5A / PVDF-TrFE composition shows that, volume fraction influences significantly on the properties of the piezocomposite and consequently on its behaviour in service. As an end-user application for ultrasound imaging, those piezocomposite materials are effectively integrated in a piezocomposite transducer, coupled with a dedicated backing. The resulting characteristics in terms of impulse response and associated electroacoustic echo are compared and discussed for typical configurations. A method for the optimization of the design of such piezocomposite transducer is presented. Specific estimators based on the bandwidth flatness BWF and bandwidth amplitude product BWA are proposed as stable and smooth criteria for an optimization procedure.

Microscopic theory of the electro-acoustic echo in order-disorder antiferroelectrics

A microscopic theory of the electro-acoustic echo (EAE) is proposed for the case in which two pulses of a variable electric field act on an antiferroelectric. This theory augments the phenomenological theory proposed for the purpose of interpreting experiments on the main regularities of the electro-acoustic echo in order-disorder antiferroelectrics. The deuterization effect and “pre-polarization” effect are explained. The shape of the echo signal is derived analytically and it is shown that this shape depends on the time interval between pump pulses.

The past, present and future of audio signal processing

The article reviews, with technical depth, the history of research in audio and electroacoustics, including electroacoustic devices, noise control, echo cancellation, and psychoacoustics. It also reports on processes in signal processing technologies that are widely used in hearing aids, the consumer electronics area, and professional audio equipment. It provides an effective review of the history of signal processing.

Theory of the electroacoustic echo in single crystals of order-disorder ferroelectrics

The mechanism governing the shaping of the echo response in a monodomain order-disorder ferroelectric crystal to excitation by two pulses of a microwave electric field at the frequencies ω and 2ω [(ω, 2ω) echo] and at the frequency ω [(ω, ω) echo] is described in the framework of the pseudospin formalism (S=1/2). The parameters of the echo response are calculated, and the results obtained are in good qualitative agreement with experiment.

Microphones and feedback suppression in teleconferencing

The effect of room acoustics on microphone placement and selection for teleconferencing systems and current approaches to electroacoustic feedback and echo control in teleconferencing systems will be discussed.

Electroacoustic echoes and dielectric nonlinearity at the ferroelectric phase transitions

Abstract The temperature dependence of the dielectric nonlinearity at different bias electric fields has been measured in Cd2Nb2O7 crystal. The maximum of the dielectric nonlinearity as a function of the bias field has been found in three crystallographic phases in Cd2Nb2O7. The electroacoustic echo relaxation time T2 in this crystal shows different character of the exciting pulse amplitude dependence at the diffuse phase transition (PT) as compared with temperatures below this PT. The new type of the electroacoustic echo ω-2ω-2ω has been observed in SbSI crystal near the ferroelectric PT temperature. The data obtained have been discussed taking into account the influence of the domain structure and heterophase structure changes on the dielectric nonlinearity.

The Investigation of Successive Phase Transitions in Cadmium Pyroniobate Crystal

The dielectric properties, birefringence, domain structure, electrooptic and pyroelectric effects, specific heat and electroacoustic echo have been investigated in Cd2Nb2O7 at successive phase transitions. Physical properties in different phases have been discussed. The thermoactivated reorientations of polarization at the diffuse phase transition temperatures contribute not only to ε, electrooptic and pyroelectric effects, but also influence the electroacoustic echo relaxation time due to the spectral diffusion mechanism.

Continuum approach to electroacoustic echoes in piezoelectric powders

Based on an oriented continuum model, a continuum approach for powders made of piezoelectric grains proposed in a previous work is applied to the study of electroacoustic echoes in resonant piezoelectric powders. The nonlinear equations obtained through this approach govern the piezoelectric oscillations and microgyration motion of each grain, as well as the global behavior of the powder and lead to the echo formation. The evaluations of the dynamical echo at 2τ and the memory echo at T+τ are presented. A memory phenomenon lying in the reorientation of grains due to a ponderomotive couple inside the powder sample is placed in evidence. The global response of the sample consists in summing up all the elementary electric polarizations associated with the piezoelectric oscillations of grains. Then the echoes are caused not only by the nonlinear interaction effects between the deformation of grains and the electric field, but also by a refocalization of collective oscillations which, after a complete dephasing period, gives a coherent signal through the inversion of the phase evolution. This continuum approach presents definite advantages over previous ones. Typical numerical values of parameters involved in this phenomenon as well as physical interpretations are given.

New phenomena in ferroelectrics

Abstract Phonon electroacoustic echoes phenomenon in one of the recently observed echo-effects, the first of them being discovered by Hahn. It is described as a process of coherent recovery of the acoustic oscillations in certain time moments under the effect of the succession of r.f. electric field pulses. The application of the second pulse before the full relaxation of acoustic vibrations, generated by the first pulse, resulte in interaction and phase inversion of the oscillations, generated by both pulses, The phases of the oscillations, developine; in the time-inverted order, will coincide after the time interval τ, equal to the interval between the first and the second ref. pulses, and a two-pulse echo can be observed at time moment 2τ . At T + τ time moment a three pulse echo can be observed after application of the third pulse at t = T.

Problem of reversal of an acoustic wavefront and amplification of the reversed wave

A parametric phase-reversing amplifier of sound is described. Its operating principles and estimates of the parameters are given. An actual amplifier is described: its active medium is a liquid containing gas bubbles and it is pumped by an alternating electric field. The phenomenon of two-pulse electroacoustic echo is analyzed from the point of view of parametric reversal of acoustic wavefronts.

Wavevector reversed ultrasound as a new tool in investigations of phase transitions

Abstract Wavevector reversed ultrasound (electroacoustic echoes) has been developed into a new tool in ultrasonic investigations of phase transitions where sample inhomogeneity and nonparallelism often cause severe wave front distortion in conventional pulse reflection measurements. Echoes generated in Bi12GeO20 are used in an experimental study of the 185K structural transition in KMnF3 and are shown to overcome all interference effects otherwise present in reflection measurements.

Phonon electroacoustic echoes

Abstract A review of phonon electroacoustic echo investigations and applications to physical studies is presented. The storage mechanisms relating to both internal processes in the substance and the orientation of the powder particles are discussed.

Electroacoustic echoes and long-time storage in piezo- and ferroelectrics

Experimental and theoretical studies of two- and three-pulse electroacoustic echoes in powders have been carried out. Two-pulse-echo relaxation properties have been studied near ferroelectric phase transition. Electroacoustic-echo accumulation effect is different for two- and three-pulse echoes. Perspective of the electroacoustic echoes as a new tool of solid-state investigations is discussed.

On the mechanism of the long-time phase memory in piezoelectric powder

The long-time phase memory which manifests itself in the stimulated electroacoustic echo (SEAE) signals in piezoelectric powders and which is stored for weeks at room temperature is connected with the plastic deformations appearing under the action of the if fields of the exciting pulses.