[Show abstract][Hide abstract] ABSTRACT: 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 LiNbO 3 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.
No preview · Article · Nov 1985 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: The nonlinear electroacoustic effect has been investigated for acoustic Lamb wave propagation in a YZ LiNbO 3 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.
No preview · Article · Feb 1985 · Applied Physics Letters
[Show abstract][Hide abstract] ABSTRACT: Thermal furnace and CO 2 laser annealing experiments on ZnO thin films are reported. Both the refractive index of the films and the effective refractive index of guided optical modes increase with thermal furnace annealing. However, the losses of guided modes increase, too. Laser annealing performed by scanning with a CO 2 laser beam does not affect refractive index but produces a marked decrease for guided mode losses.
No preview · Article · Dec 1984 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: Post-deposition annealing of sputtered ZnO thin films has been studied as performed with thermal furnace or CO2 laser. Similar results are obtained as far as refractive index changes are concerned.
No preview · Article · Feb 1984 · Materials Letters
[Show abstract][Hide abstract] ABSTRACT: The response of the SAW voltage sensor versus voltage is experimentally evaluated for YZ, YX LiNbO3 and (001) (110) Bi12 GeO20 substrates.In order to improve the symmetry of the response to polarity changes of the applied voltage satisfactory experiments were carried out with a differential technique.The use of the voltage sensor is then extended to the measurement of low frequency a.c. voltages, and the sensitivity to temperature is tested in the temperature range 20 – 50°C.Finally, a correction of the sensor response to temperature changes, as based on the use of the temperature-dependent zero bias frequency of the probe as an error signal, is described in d.c. and a.c. applications.
No preview · Article · Dec 1983 · Sensors and Actuators
[Show abstract][Hide abstract] ABSTRACT: 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 LiNbO 3 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 LiNbO 2 sample, at the fundamental frequency of 34.5 MHz.
No preview · Article · Jan 1983 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: A hydrogen sensitive detection technique utilizing a surface acoustic wave (SAW) delay line coated with a palladium thin film is presented. The hydrogen‐palladium interaction produces a change in the velocity of SAW propagating on the coated substrate, which is detected as phase shift at the output of the delay line. Presently, hydrogen concentrations as small as 50 ppm in a flowing H 2 +N 2 mixture have been detected.
[Show abstract][Hide abstract] ABSTRACT: Nonlinear interaction of collinear surface acoustic waves of different frequency generates wave beams at the sum and difference frequencies. The produced fields are here analyzed through the use of a theoretical model that considers the nonlinearly generated field at any given point to be obtained by the sum of all the possible contributions deriving from the interactions between the different plane wave components of the fundamental wave Fourier spectrum. Theoretical and experimental transversal profiles of the nonlinear field at sum and difference frequencies are given for surface acoustic waves propagating on a yz-LiNbO sample. The fundamental waves were emitted by two equally wide interdigital transducers with central frequencies f =60MHz, f =40MHz, respectively. 3
[Show abstract][Hide abstract] ABSTRACT: A new hydrogen sensor based on the velocity changes of surface acoustic waves (SAW) due to hydrogen absorption or desorption in a palladium thin film is described. A dual SAW delay-line is the key element of the device: one delay path is coated with the selective sorbant film, the other one is uncoated and is used as a reference in order to minimize the effects of both temperature and pressure variations.Response time, sensitivity and time stability of the device have been evaluated and first results are reported.
No preview · Article · Jan 1982 · Sensors and Actuators
[Show abstract][Hide abstract] ABSTRACT: A time integrating correlator has been developed in which the signal modulates the light source and the reference is fed into a shear acousto-optical cell. The use of a quarter wave plate in conjunction with the shear wave cell makes it possible to realize imaging conditions that provide a linear relationship between the output light intensity and the signal voltage applied to the cell. A CCD photodetector array displays in time the time-integrated signal developed in space, thus furnishing the correct correlation integral. Results of experiments in which single and double square pulses were used for reference and signal are presented.
No preview · Article · Dec 1981 · Optics Communications
[Show abstract][Hide abstract] ABSTRACT: A swept frequency spectrum analyzer is described, based on the filtering properties of a Bragg acousto-optical cell combined with a lens and a point photodetector. The detection of spectral components is performed by temporary shifting the whole spectrum by means of an external sweep oscillator. Design parameters and performances of the experimented analyzer are reported and briefly discussed.
No preview · Article · Sep 1981 · Optics Communications
[Show abstract][Hide abstract] ABSTRACT: An acoustooptical spectrum analyzer is described, based on the linear relationship between frequency and angular deviation of an acoustooptical cell. A side-entry internal reflection geometry of interaction is used with surface acoustic waves propagating on a Y-Z LiNbO3 sample. A CCD photodiode array is the detecting device, allowing 300 kHz resolution and 50 MHz bandwidth.
No preview · Article · Oct 1980 · Optics Communications
[Show abstract][Hide abstract] ABSTRACT: 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’.