E. Verona

Acoustic Lamb wave‐electric field nonlinear interaction in YZ LiNbO3 plates

The nonlinear electroacoustic effect has been investigated for acoustic Lamb wave propagation in a YZ LiNbO3 plate under a uniform bias electric field. A theoretical model is briefly outlined, which shows how the effect can be interpreted in terms of second and third order material constants. The strength of the nonlinear interaction has been experimentally evaluated through measurements of the change in phase velocity of Lamb modes produced by the bias field. The experiments were performed in the frequency range 8–33 MHz on most of the Lamb modes excited in a 1.25‐mm‐thick plate by an interdigital transducer with a periodicity λ=0.396 mm. The results evidence a strong dependence of the nonlinear effect on the order and symmetry of the analyzed modes.

Electroelastic effect in layer acoustic mode propagation along ZnO films on Si substrates

The influence of a bias electric field on the phase velocity of acoustic layer modes propagating along a ZnO overlay on a Si substrate is analyzed. Measurements of the fractional change in phase velocity as a function of the applied electric field were performed on both Rayleigh and Sezawa modes. The strength of the electroelastic effect has been experimentally determined for two samples obtained by different sputtering runs. An evident dependence of this parameter on the acoustic mode and on the quality of the sputtered film was observed. The maximum value of 15.8×10−6 μm/V was attained by the Sezawa wave in one of the specimens, while a weaker effect was observed in the other cases.

Lamb-wave electroacoustic voltage sensor

The effect of a bias electric field on the phase velocity of Lamb waves propagating in a piezoelectric plate has been investigated in order to develop an electroacoustic voltage sensor. Experiments were performed on YX and YZ LiNbO3 Lamb‐wave delay lines, used as the stabilizing element in the feedback loop of an oscillator, by measuring the fractional frequency change produced by a bias electric field normal to the plate surfaces. The results obtained have shown that Lamb‐wave sensors can exhibit a higher sensitivity and a better linearity than the corresponding Rayleigh‐wave devices.

Nonlinear electroacoustic interaction between a bias electric field and acoustic Lamb modes in LiNbO3 plates

The change in phase velocity produced by a bias electric field on Lamb acoustic waves propagating along yz‐ and zy‐LiNbO3 plates is analyzed here. This effect is interpreted theoretically in terms of the modifications produced by the bias field on the second‐order material constants, under the approximation of small‐amplitude acoustic waves superposed on a bias. According to this theory, these modifications are linked to the components of the bias field through combinations of second‐ and third‐order material constants. Measurements performed on several Lamb modes lead to the determination of the effective second‐order material constants in the presence of a bias field. The results obtained allow the evaluation of the electroelastic effect for acoustic propagation along any direction in the yz plane of the crystal, provided that the bias electric field lies in the same plane. In addition, these results give useful information on the nonlinear properties of the medium.

Second‐harmonic diffraction field in nonlinear propagation of transversely limited surface acoustic wave beams

The study of the Fresnel field of the second harmonic of a finite width surface acoustic wave, parametrically generated through the nonlinear interaction on a LiNbO3 substrate, is performed both theoretically and experimentally. Theoretically, a model has been developed which computes the acoustic field at each point as given by the sum of all the second‐harmonic plane wave fronts nonlinearly generated by the interaction of any two plane wave fronts present in the fundamental wave angular spectrum. Experimentally, a phase contrast optical probing technique has been used, which permits separating the contributions of the second‐harmonic field from that of the fundamental wave. Theoretical and experimental transversal amplitude profiles of the surface acoustic wave second‐harmonic field are presented, relative to the case of an acoustic beam launched from a 24‐wavelength‐wide transducer on the free surface of a LiNbO2 sample, at the fundamental frequency of 34.5 MHz.

Real time acousto-optical spectrum analyzer through unguided light-surface acoustic waves interaction

Abstract An acousto-optical spectrum analyzer is described, based on the linear relationship between frequency and angular deviation of an acousto-optical cell. A side-entry internal reflection geometry of interaction is used with surface acoustic waves propagating on a Y-Z LiNbO 3 sample. A CCD photodiode array is the detecting device, allowing 300 kHz resolution and 50 MHz bandwidth.

Interdigital transducer method of acoustic beam steering for bulk wave acousto‐optic Bragg cells

A LiNbO3 acousto‐optic Bragg cell is described, which uses an interdigital transducer deposited on the x surface of the crystal so as to excite longitudinal bulk acoustic waves along a direction almost normal to the surface itself. By a proper choice of the periodicity of the transducer electrodes, a frequency‐dependent steering of the acoustic beam can be obtained, which allows the Bragg conditions to be satisfied over a wide range of frequencies. Results are reported relative to a cell operating in the frequency range 1.4–2.1 GHz, with a diffraction efficiency of approximately 2% per watt of acoustic power.

Acousto-optics with Surface Acoustic Waves Devices and Applications

The diffraction of light by bulk and surface acoustic waves is briefly discussed, and the acousto-optical efficiency for the basic interaction geometries is analysed. Applications of light SAW interaction to acoustic field diagnosis, image scanning, signal processing, spectrum analysis, are reviewed as they were developed at the Institute of Acoustics ‘O. M. Corbino’.

Polarization interferometry in acousto‐optics

A simple polarization interferometry technique is introduced in acousto‐optics, which allows a polarization discrimination of the light scattered by acoustic waves, when no strain‐induced birefringence is produced by the acoustic perturbation. Results are presented, which are obtained through the use of a Savart plate in detecting light scattered by acoustic surface waves.

Time integrating acousto-optical correlator based on light polarization processing

Abstract A time integrating acousto-optical correlator has been realized, which exploits a polarization discrimination technique based on a shear wave acousto-optical cell and permits to process the signal directly on the image plane. A CCD photodetector array displays in time the time-integrated signal developed in space, thus furnishing the correct correlation integral. Preliminary results of autocorrelation functions are presented for single and double square pulses of 5 μs duration.