V.N. Bindal

Acoustic power measurement of medical ultrasonic probes using a strain gauge technique.

A new method using a semiconductor strain guage is described for the measurement of the acoustic power output of ultrasonic medical therapy and other probe heads. The acoustic power output of the probe heads is found to be linearly related to the calibrated electrical output of the strain gauge transducer system, as expected theoretically. The instrument developed is inexpensive, portable and easy to operate for the routine measurement of ultrasonic output of the equipment in hospitals.

Acoustic levitation and its application in estimation of high power sound field

Abstract Acoustic levitation has been studied using airborne radiation from a high power magnetostrictive ferrite transducer of frequency 18 kHz. Spherical solid objects as well as liquid drops of varying weight and radii have been levitated under I G at the velocity antinodes of the standing waves formed with the help of a reflector. The dependence of the maximum weight of a spherical object that can be levitated on the sound pressure level and the radius of the obstacle has been studied. An attempt has been made to estimate the radiated high power sound intensity from the maximum weight of the spherical object that can be levitated.

Performance characteristics of ultrasonic NDT probes at high hydrostatic pressure for inspection of offshore installations

Abstract In the present work an attempt has been made to study the performance characteristics of commercially available contact-type NDT probes, at pressures up to 2.8 × 106 Pa (equivalent to 280 m depth). The parameters studied are pulse-echo sensitivity, its frequency response and the electrical impedance of a normal beam probe. Pulse-echo sensitivity is observed to decrease at high pressures to about 60% of its value at the normal pressure. The observed results have been explained in terms of the effect of the pressure on the backing material of the probe and hence the effect on the probe performance. From the frequency response of the pulse-echo sensitivity it is observed that the probe bandwidth decreases at high hydrostatic pressures.

INVESTIGATIONS ON EVALUATION OF TRANSDUCER PERFORMANCE AT HIGH ELECTRIC DRIVES

Investigations have been reported in the present work on evaluation of performance of transducers at frequencies of 300 KHz and 800 KHz at high electric drives. Methods which have been used for such assessment are study of admittance, motional loops and measurement of acoustic output as the frequency is varied around resonance using hydrophone and radiation pressure technique. It is felt that the parameters such as variation of conductance, shift in resonant frequency, extent of frequency asymmetry and variation in mechanical Quality factor can be fairly indicative of transducer performance at high drives. The study would be of help in sorting out methods for design evaluation of transducer particularly for oceanographic and medical applications.

A novel sonic weighing system for the blind

Abstract A novel system of weighing articles, which can be used by totally blind persons, is described. The weighing balance is based on the acoustic effects experienced by a membrane under tension and subjected to sonic radiations. The detection of the balance point for a given weight is provided by a sharp change in the sound level at a specific frequency, dependent upon the loading weight. Weighing operations, i.e. (i) weighing an unknown sample and (ii) weighing a material to a predetermined weight, are discussed. Subjective tests have been performed by various individuals, showing fairly consistent results, the greatest deviation being 3 per cent. The scope and socio-economic aspects of the device are also discussed.

Studies on evaluation of the strength of the adhesive-bonded joint using the ultrasonic resonance method

Abstract The authors have employed the ultrasonic resonance method to study the properties of an adhesive-bonded joint between two metallic sheets. The responses of the transducer swept in the vicinity of resonance, when coupled to the joint, show significant variation as the composition of the adhesive layer is varied. A correlation is found between the ultrasonic parameters measured at 290 kHz and the joint strength measured destructively. The method can be successfully used for comparative evaluation of the strength of the bonded joints.

An ultrasonic doppler system for the study of the law of freely falling bodies

Abstract A novel method is reported for the experimental verification of the law of motion of freely falling bodies using a simple and inexpensive ultrasonic air Doppler technique. The system employs a resonant-type piezoelectric transducer as a transmitter of ultrasound (frequency 32·8 kHz) and a wideband electrostatic transducer as a receiver. Its distinguishing feature is that instantaneous velocity is measured instead of time of fall. It has been shown that the values of instantaneous velocity of a falling steel ball measured experimentally and the values calculated from the relation V cal = (2gS) are in close agreement. The system is likely to be useful as a demonstration experiment in teaching institutions.

Study of motional admittance of piezoelectric transducers with different pressure release backings at hydrostatic pressure of 300 psi

Abstract Pressure release materials are used in underwater transducers to enable them to withstand high hydrostatic pressure and to decouple them from the housing. Although we have information on the type of pressure release materials for use at various depths, methods for their evaluation have not been reported. In this study, an attempt has been made to study the effect of various pressure release materials on the performance of piezoelectric transducers at hydrostatic pressure of 300 psi through motional admittance measurements.

A SELECTIVE AUDIO SIGNALLING SYSTEM

Studies on parametric generation in air are few and demonstration of the principle only. The paper reports a practical audio signalling system. Difference frequency tone of 4.1 kHz is produced by parametric interaction of two intense ultrasonic beams from two transducers resonating at 23.2 kHz and 19.1 kHz and having SPL of 143 dB and 131 dB at one foot (re. 0002 bar) respectively. The directivity pattern and the propagations characteristics of the resulting tone (4.1 kHz) are measured. The self contained system is capable of sending a coded signal in any desired direction which are audible with unaided ears at distances over 200 m in a narrow zone of semiangle 15° for selective communication.

A DIAPHRAGM TYPE STRAIN GAUGE ULTRASONIC POWER METER

Measurement of acoustic power output of ultrasonic sources is important for characterization work. A compact, portable and easy to operate ultrasonic power meter has been developed using radiation pressure method. Radiation pressure on the specially designed conical diaphragm, which forms a part of the top surface of an enclosed chamber, is balanced by the extra pressure pumped in the chamber and is monitored by the semiconductor strain gauge mounted on a spring under the diaphragm. Present method has all the inherent advantages of a null method and is suitable for measurement of acoustic power in the wide range of milliwatts to several watts.