Acoustic microscope

RESEARCH AND DEVELOPMENT Acoustic microscope The concept of acoustic microscopy is not new but the means of constructing a working device are only now becoming available. Zenith have constructed an experimental microscope operating at 100 MHz with a resolution of the order 25/am. In operation a 100 MHz plane wave is launched through a specimen suspended in water. The transmitted sound strikes a plastics mirror causing a dynamic ripple pattern on the mirrored surface, which produces periodic angular deflexions of a scanned laser beam focused on the mirror. The modulated light-beam gives rise to an electrical signal in a photodiode which can then be converted either to a magnified picture of the sound field at the mirror, or an acoustic hologram on a television monitor. In the experimental arrangement the laser was focussed to a spot size of about 12/am and scanned an area of approximately 1 mm 2. The magnification from mirror to television screen was approximately 400. Initial tests have shown that the instrument has applications in biology, particularly in the study of in vivo mechanisms. Zenith Radio Corporation, 1900 North Austin Avenue, Chicago, Illinois 60639, USA

Mapping ultrasonic beam patterns A system for automatically plotting the sound-field patterns of ultrasonic transducers has been demonstrated by Mullard Research Laboratories to assist transducer manufacturers in detecting flaws prior to large scale production. In operation the sound pulses from the transducer are received by a miniature piezoelectric microphone (3mm diameter) which mechanically scans the area in front of the transducer in a zig-zag pattern. The pen of an x-y recorder traces this pattern, and the microphone signal is amplified and fed into a quantizer which is set to trip at five predetermined levels, each of which represents a certain sound intensity. The quantizer output is superimposed on one axis of the x-y recorder to produce the sound intensity contour patterns shown in Fig. 1. Mullard Limited, Mullard House, Torrington Place, London WC1 E7HD, UK

Fig.2 'Foolproof' ultrasonic seat belt. The engine will not start unless a sensor in the seat (C) is depressed by the weight of the driver who must buckle the belt properly across his body (B). Only then is the ultrasonic signal emitted from a small transmitter mounted on the belt (A) to a receiver on the A pillar to complete the electronic circuit

• Foolproof' ultrasonic seat belt A 'foolproof' ultrasonic car safety belt system which makes cheating and tampering impracticable by the introduction of an additional sequence in the ignition circuit could contribute to the reduction of fatalities in road accidents. The new system, developed jointly by Ford and Mullard, uses a piezoelectric transducer operating between 3 5 - 4 5 kHz in conjunction with discrete component circuitry. Fig.2 shows the seat belt sequence which must be followed before the ignition can be switched on. Ford Motor Company, Brentwood, Essex, UK

Light and ultrasound measure stress of strengthened glass A technique for investigating and measuring the properties of strengthened glass by a method using a combination of light and ultrasound has been announced by the Naval Research Laboratory.

Fig. 1 The ultrasonic beam patterns of two different transducers drawn by the automatic plotting system. The contour on the left is superior because the sound is concentrated into a narrower beam

U L T R A S O N I C S . M A R C H 1972

Until now there has been no known method of measuring stress on 'ion stuffed' surface strengthened glass. The new technique consists of inducing surface acoustic waves on glass samples and then scattering a laser beam from the small amplitude surface corrogations to measure the speed at which they travel down the surface. The resultant data is used to measure the strength of the glass sample and can be extended to study the strengthening mechanism itself. The Naval Research Laboratory, Washington DC, USA

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