Surface Acoustic Wave Measurements Research Articles

Ultrasonic experiments with lead zirconate titanate thin films fabricated by sol gel processing

Surface and bulk acoustic wave measurements with lead zirconate titanate (PZT) thin films fabricated by a sol gel processing technique are reported for the first time. The piezoelectricity of such films was achieved by poling. Good acoustic properties of these films are confirmed by the acoustic images and V(z) curves obtained by a scanning acoustic microscope.

Absolute calibration of interferometric systems for detection and measurement of surface acoustic waves

A calibration method for interferometric systems is shown to produce a minimum wave amplitude to which these systems may be calibrated in the measurement of harmonic surface acoustic waves. The calibration limit is ~3 orders of magnitude larger than the theoretical detection limit. The method proposed allows experimental determination of the detection limit of these systems. The calibration of a fiber-optic heterodyne interferometer is demonstrated, and the experimentally derived detection limit for the interferometer is shown to be 5.5 x 10(-15) m for unity detection bandwidth. This limit is obtained for a mirrored specimen with 0.14 mW of laser power incident on the optical detector.

LPE growth of ferroelectric tungsten bronze Sr 2KNb 5O 15 thin films

Ferroelectric tungsten bronze Sr 2KNb 5O 15 (SKN) thin films have been grown by liquid phase epitaxy on (100), (110) and (001) orientations of tungsten bronze Sr 0.6Ba 0.4Nb 2O 6 (SBN:60) substrates using vanadium-containing solvents. Single-crystal film growths of up to 25 μm thickness were achieved with very good film quality in all growth directions, due in part to the excellent lattice match with SBN:60. Surface acoustic wave (SAW) measurements show electro-mechanical coupling of up to 130 × 10 −4, comparable to values measured in other tungsten bronze ferroelectrics. The high dielectric constants available in these films also indicate potentially very large linear electro-optic effects which are roughly an order of magnitude greater than for LiNbO 3.

Thermodisplacement imaging of silicon membranes

Abstracts 65.70 - 42.60K - 81.70 Recently small-displacement measu- rement technique have made considerableprogress mainly as a result of the multipleapplications in gravitational waves’detec- tion [1], noncontact measurement of surface acoustic waves [2], nondestructive testing [3,4], photoacoustic spectroscospy and mi-croscopy [4,5], etc. A new application ofthis technique in the field of thermodis- placement imaging is presented in this pa-per. Thermoelastic waves excited by means of Joule heating in thin layers were used for visualizing the complex profiles of si-licon membranes used in the fabrication of sensors, actuators and frequency selectiveelements [6]. We used an one-arm phase-op- tical bridge [3] for measuring the thermo-eleastic displacements. The samples (which we worked on) were polished, 250 Rm thick (001)-cut Si plates. Thin membranes of 25 Rm with different geometrical shapes (Fig. Ib) were obtained through selective etch- ing. Narrow 330

Propagation of surface acoustic waves in magnetic bubble garnet films

Surface Acoustic Wave (SAW) delay lines have been fabricated on magnetic bubble garnet films. Interdigital transducers on a piezoelectric layer (zinc oxide film sputtered on top of the garnet film) have been used for acoustic wave generation and detection. Amplitude and phase delay variations of the SAW delayed signal were measured as a function of an externally applied dc magnetic field. The maximum change in the SAW propagation properties was observed when the applied field H was parallel to the SAW propagation vector k, and at field strengths of the same order as that required for FMR at the operating frequency. The results are explained qualitatively in terms of an approach which provides an explanation for the dependence of the SAW measurements on the orientation and magnitude of the applied field.

Surface acoustic wave measurements using an impulsive converging beam

A method for velocity and attenuation measurement of leaky surface acoustic wave on small areas of a solid surface was developed. This technique uses an impulsive converging beam generated with an acoustic lens. Reflected waves from a sample consisted of the axial wave and the leaky surface wave separated in time domain. From the time interval between these waves, the velocity of the leaky surface wave is determined using an expression derived along with ray optics. Because time interval measurements do not require any mechanical scanning, they can be done without special attention paid for mechanical precision of the scanning system, enabling rapid and simple measurement. Since the impulsive wave has a broad frequency spectrum, spectroscopic analysis of leaky surface wave is also possible. Frequency dependent attenuation measurement of leaky surface acoustic waves on heat treated steels and velocity dispersion measurement of leaky surface wave on titanium nitride film on tool steel are demonstrated.

An all fiber-optic sensor for surface acoustic wave measurements

A surface acoustic wave (SAW) sensor constructed from single-mode fiber-optic components is described. An analysis of reciprocal and nonreciprocal modes of operation of the sensor is presented. Results from measurements on a variety of SAW devices illustrate the use of the sensor. The amplitude sensitivity is 0.0003 A for an integration time of 0.1 s.

Surface Acoustic Wave Measurements of Surface Cracks in Ceramics

An investigation of scattering from surface cracks has been conducted. In particular, the change in the reflection coefficient of a Rayleigh wave incident on a surface indentation crack has been measured as the sample is stressed to fracture. The acoustic measurements have been correlated with the stable crack extension that precedes final failure. The crack extension behavior of as-indented specimens was found to differ appreciably from that of annealed specimens. Cracks in the annealed samples exhibited partial crack tip closure, but little stable extension, whereas cracks in the as-indented samples displayed both crack closure and irreversible crack growth. This behavior has been rationalized by invoking concepts based upon the residual stresses created by indentation.

Surface acoustic wave measurements of surface cracks in ceramics

An investigation of scattering from surface cracks has been conducted. In particular, the change in the reflection coefficient of a Rayleigh wave incident on a surface indentation crack has been measured as the sample is stressed to fracture. The acoustic measurements have been correlated with the stable crack extension that precedes final failure. The crack extension behavior of as-indented specimens was found to differ appreciably from that of annealed specimens. Cracks in the annealed samples exhibited partial crack tip closure, but little stable extension, whereas cracks in the as-indented samples displayed both crack closure and irreversible crack growth. This behavior has been rationalized by invoking concepts based upon the residual stresses created by indentation.

Phase sensitive laser probe for high-frequency surface acoustic wave measurements

Field measurements of surface acoustic waves can be performed by coherent light in several ways. A method is described where a laser beam is focused to a small spot on the surface to obtain phase and amplitude infomation. A modified knife-edge technique has been applied in combination with amplitude modulation of the laser beam and single-side-band modulation of the surface wave. The apparatus has proven to be a powerful and flexible analytical tool. It is able to retieve phase and amplitude information from a traveling wave, and a partially standing wave can be characterized in terms of phase and amplitude of its two haveling wave components. The apparatus has been used up to 450 MHz.