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Linear motion from ultrasound
sent a little greater than a typical gravel particle, should be lower. Also a larger battery giving a longer operational life will be incorporated. The increased life will mean an increased chance of the pebble becoming buried, a situation still to be investigated. A multipebble system using different transmitted frequencies and a superheterodyne technique to identify a particular pebble may also be developed. In addition to the present requirements this transponder could be useful as a fixed marker on instruments or equipment in the sea. In such a case, size would not be limiting and large batteries could be incorporated.
Fig.2 Prototype pebble prior to assembly showing hemispherical transducers and circuit board
A. P. Dorey, A. S. Quinn (University of Southampton) and K. R. Dyer (NERC unit of Coastal Sedimentation, Taunton, Somerset). Acknowledgements
The circuit operates as follows. The incoming signal from the transducer is fed to a high-input impedance stage, using the FET VT2. VT1 acts as a limiting diode to prevent overload of the receiving circuit during the transmit phase. The signal then passes through five stages of amplification, one tuned and four untuned. The time constant of the circuit connected to the base of VT’5 was chosen to provide a dead space, so that the oscillator could not be triggered until approximately 25 ms after it is initially triggered. The Darlington pair, VT8 and VT9, are turned on by this amplified signal and provide a bias for the oscillator VT 10. The length of the oscillation burst is determined by the time constant of C8 and Rl 0.
The authors wish to acknowledge the help of R. B. Mitson of the Fisheries Laboratory, B. S. McCartney of the National Institute of Oceanography and A. Cuff for some of the early construction work on the pebble. The work was carried out as part of a National Environmental Research Council contract in conjunction with the Department of Oceanography at Southampton University. References 1 Mitson, R B., Storeton-West, T. J., A transponding acoustic fish-tag, 2
The transducers chosen for the first prototype (Fig.2) were two hemispherical Plessey transducers. This meant that as the sonar had an operating frequency of 47 kHz the transducers were operated off resonance. The hemispheres were separated by a 1 cm long tubular spacer which enabled the circuit board and battery supplies to be contained within the pebble. Only two devices in conventional (T092) packages are used with the loss of a little space, however, these can be replaced to give more room for extra battery capacity. Three Mallory cells type RM575H are used, which give a life of 300 hours if the device is not interrogated. The range of the sonar and its receiving sensitivity and resolution determined the design of the single transistor output-circuit, in particular its power output. To ensure that several pebbles can be operated together it must be arranged that if a pebble is within receiving range of another pebble the dead-time, determined by C8, must be greater than the acoustic transmission time between the pebbles. Thus with adjustment of the frequency and some associated loss of space, and an adjustment of the dead-time and output power to match the sonar, the Mitson fish-tag circuit has been adapted to this new function. Further developments A second form of pebble is being produced using similar electronics with a resonant cylindrical-hoop transducer. This should increase the acoustic efficiency and improve the polar radiation pattern of the pebble. As the transducer will occupy less space, the average density, which is at pre-
148
The Radio and Electronic Engineer Vol41 No 11 (November 1971) Haslett, R. W. G., Hannor, D., Some recent developments in sideways-looking sonars, Proc IERE Conf on Electronic Engineering in Oceanography
(1966)
Linear motion from ultrasound A piezoelectric transducer can be driven in such a way that its surface wave energy can be directly coupled to another surface to provide a linear motor without the use of electromagnetic or other drive elements. Research at Decca Radar has shown that a piezoelectric transducer in the form of a disc, driven at one of its resonant frequencies, has a resulting vibration mode in the plane of the disc, resembling the petals of a flower. If the periphery of the disc is placed in contact with a plane surface the snakelike motion of the periphery provides thrust in the axial direction. This can be utilized to move the surface relative to the disc or alternatively to move the disc along the surface. The transducer is a barium titanate disc 4 cm in diameter and 1 cm thick,driven by an oscillator at 70 kHz. The input power is of the order of 3 W. The disc propels itself in its axial direction at speeds of the order of 100 cm s-1 along an aluminium channel section. The technique is silent, employs no moving parts and requires no accurate machining. It appears feasible to make use of this technique in a number of linear transport applications, for example tape and chart recorders, drives and conveyor belts. Decca Radar Limited, Lyon Road, Walton on Thames, Surrey, UK
ULTRASONICS.
JULY 1972
Fig.2 Prototype pebble prior to assembly showing hemispherical transducers and circuit board
A. P. Dorey, A. S. Quinn (University of Southampton) and K. R. Dyer (NERC unit of Coastal Sedimentation, Taunton, Somerset). Acknowledgements
The circuit operates as follows. The incoming signal from the transducer is fed to a high-input impedance stage, using the FET VT2. VT1 acts as a limiting diode to prevent overload of the receiving circuit during the transmit phase. The signal then passes through five stages of amplification, one tuned and four untuned. The time constant of the circuit connected to the base of VT’5 was chosen to provide a dead space, so that the oscillator could not be triggered until approximately 25 ms after it is initially triggered. The Darlington pair, VT8 and VT9, are turned on by this amplified signal and provide a bias for the oscillator VT 10. The length of the oscillation burst is determined by the time constant of C8 and Rl 0.
The authors wish to acknowledge the help of R. B. Mitson of the Fisheries Laboratory, B. S. McCartney of the National Institute of Oceanography and A. Cuff for some of the early construction work on the pebble. The work was carried out as part of a National Environmental Research Council contract in conjunction with the Department of Oceanography at Southampton University. References 1 Mitson, R B., Storeton-West, T. J., A transponding acoustic fish-tag, 2
The transducers chosen for the first prototype (Fig.2) were two hemispherical Plessey transducers. This meant that as the sonar had an operating frequency of 47 kHz the transducers were operated off resonance. The hemispheres were separated by a 1 cm long tubular spacer which enabled the circuit board and battery supplies to be contained within the pebble. Only two devices in conventional (T092) packages are used with the loss of a little space, however, these can be replaced to give more room for extra battery capacity. Three Mallory cells type RM575H are used, which give a life of 300 hours if the device is not interrogated. The range of the sonar and its receiving sensitivity and resolution determined the design of the single transistor output-circuit, in particular its power output. To ensure that several pebbles can be operated together it must be arranged that if a pebble is within receiving range of another pebble the dead-time, determined by C8, must be greater than the acoustic transmission time between the pebbles. Thus with adjustment of the frequency and some associated loss of space, and an adjustment of the dead-time and output power to match the sonar, the Mitson fish-tag circuit has been adapted to this new function. Further developments A second form of pebble is being produced using similar electronics with a resonant cylindrical-hoop transducer. This should increase the acoustic efficiency and improve the polar radiation pattern of the pebble. As the transducer will occupy less space, the average density, which is at pre-
148
The Radio and Electronic Engineer Vol41 No 11 (November 1971) Haslett, R. W. G., Hannor, D., Some recent developments in sideways-looking sonars, Proc IERE Conf on Electronic Engineering in Oceanography
(1966)
Linear motion from ultrasound A piezoelectric transducer can be driven in such a way that its surface wave energy can be directly coupled to another surface to provide a linear motor without the use of electromagnetic or other drive elements. Research at Decca Radar has shown that a piezoelectric transducer in the form of a disc, driven at one of its resonant frequencies, has a resulting vibration mode in the plane of the disc, resembling the petals of a flower. If the periphery of the disc is placed in contact with a plane surface the snakelike motion of the periphery provides thrust in the axial direction. This can be utilized to move the surface relative to the disc or alternatively to move the disc along the surface. The transducer is a barium titanate disc 4 cm in diameter and 1 cm thick,driven by an oscillator at 70 kHz. The input power is of the order of 3 W. The disc propels itself in its axial direction at speeds of the order of 100 cm s-1 along an aluminium channel section. The technique is silent, employs no moving parts and requires no accurate machining. It appears feasible to make use of this technique in a number of linear transport applications, for example tape and chart recorders, drives and conveyor belts. Decca Radar Limited, Lyon Road, Walton on Thames, Surrey, UK
ULTRASONICS.
JULY 1972