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A noncontact laser system has been designed that employs a pulsed photoacoustic source and an interferometric detector for the measurement of absolute velocity of surface waves. This can be achieved accurately at high temperatures without the need for thermal expansion corrections. Studies have been carried out on polycrystalline aluminum and single-crystal silicon and results have been presented for both at temperatures up to 800 °C. The angular dependence of surface wave velocities for propagation in the (001) plane of silicon has also been investigated, and has confirmed the system's 0.5% room temperature accuracy. [ABSTRACT FROM AUTHOR]

Miniaturized tuning forks, whose resonant frequencies are temperature dependent, have been manufactured from various materials using a precision milling machine under computer control. Two noncontact measurement systems that rely upon capacitive transducers as well as a pulsed ruby laser have allowed the generation and detection of fork vibrations at temperatures up to 900 °C. The usefulness of such a system for materials characterization will be demonstrated through the successful detection of the precipitation and dissociation of hydride platelets in a fork consisting of a Zr-Nb alloy. Also to be discussed are studies of single-crystal silicon tuning forks and the resultant program currently underway for the development of micromachined thermometers for corrosive and high-temperature environments. [ABSTRACT FROM AUTHOR]

Capacitive devices that are able to efficiently generate and detect ultrasonic fields in air have already been designed and manufactured. They consist of metallized insulating films resting upon rigid conducting backplates. In order to increase efficiency, the backplates must be roughened, providing a resonant air cushion behind the thin insulating films. Unfortunately, roughening by conventional mechanical means [D. W. Schindel and D. A. Hutchins, Proc. IEEE Symp. 1, 301-304 (1991)] will be shown to produce a transducer whose beam profile is highly nonuniform above several hundred kilohertz. Ways of overcoming this are being investigated, including the manufacture of backplates through irradiation of metals by high-intensity ultrasound and micromachining of silicon. The result of the characterization of such new transducers in terms of bandwidth, sensitivity and beam profiles will be given, along with a discussion of the versatility of air coupled transducers manufactured completely from integrated circuit processing techniques. [ABSTRACT FROM AUTHOR]