The present invention relates in general to transducers, and more particularly to underwater sound acoustic piezoelectric projector transducers capable of radiating acoustic energy while in the presence of receiving hydrophones.
Underwater sonar systems use projectors to send acoustic waves out and often use closely packed hydrophones to detect the reflected signal from the target while the projectors are turned off. The presence of the projectors can reradiate and interfere with the reception from the hydrophones and make it difficult to locate the target. The projectors and hydrophones are typically piezoelectric designs and the projectors are turned off while the hydrophones receive the signal reflected from the target. However, unfortunately there are typically reflection like signals from the projector. If the projectors were transparent or acted as though they were transparent there would be no reflection from them. However, our analysis has shown that a major cause of receiving problems can be due to the reflected wave from the target exciting the resonance of the projector during this off cycle and that this parasitic (see J. L. Butler, A. L. Butler and V. Curtis, J. Acoust. Soc. 135, 2472-2477 (2014)) resonance radiation causes a distortion in the signal received by the hydrophone directly.
It is an object of the present invention to mitigate this effect by using a damped parasitic resonance technique as described herein.
Another object of the present invention is to provide a projector design having a simple means for electrically increasing the mechanical damping resistance of the turned-off projector, thus significantly lowering the level of the parasitic resonance that can be caused by the received reflected target signal.
To accomplish the foregoing and other objects, features and advantages of the invention therein provides an improved electro-mechanical projector transduction apparatus that is electrically driven by piezoelectric material along with a means for reducing the output of the parasitic resonance that would be activated by the wave reflected from the target. The means for accomplishing this reduction of the parasitic resonance from the received acoustic wave without affecting the transmitting response is presented here and can be seen to be a simple electrical solution to an otherwise difficult problem.
In accordance with the present invention there is provided an underwater acoustic electro-mechanical transduction apparatus comprising:
at least one hydrophone for detecting a reflected signal from a target;
a projector for generating an acoustic signal that is directed to the target;
said projector including a transducer structure that is selectively operable to generate the acoustic signal, and a drive circuit coupled to the projector; said drive circuit including a voltage drive source, two diodes and an electrical resistor to collectively provide a means for mechanically damping any mechanical resonance.
In accordance with other aspects of the present invention the two oppositely wired diodes are connected in parallel with the added electrical resistor and the two diodes and resistor are connected in series with the voltage drive source of the associated projector which is near the hydrophone or is disposed between a pair of hydrophones.
In accordance with the present invention there is provided an underwater sound electro-mechanical transduction apparatus that includes a projector and at least one hydrophone, the projector positioned adjacent to the at least one hydrophone while having a minimum effect on the performance of the at least one hydrophone during a receive mode of operation, the minimizing of the effect being accomplished by adding an electrical damping resistance to the projector along with an oppositely wired diode pair which is capable of converting the electrical resistance to mechanical damping resistance and which is then added to the mechanical losses in the projector causing a significant reduction in the projector resonance output which otherwise would interfere with the hydrophone reception of a signal from the target generated by the projector during a transmission mode.
Numerous other objects, features and advantages of the invention should now become apparent upon reading of the following detail description taken in conjunction with the accompanying drawings:
In accordance with the present invention the transducer appears transparent to the hydrophones so as not to significantly affect the receiving response of the hydrophones. It is recognized that the major interference of the hydrophone reception is due to the acoustic excitation of the projector operational resonance during the off time of the projector while the reflected signal is received by the hydrophones. Although there may be some effort to minimize the effect of the presence of the projector on the hydrophone by modifying the material of the projector, the present invention instead relates to modifying the electrical components of the projector to reduce the strength of the resonance and reradiation of the projector from the incoming reflected wave originally generated by the projector during the transmit mode of operation which occurs in the vicinity of the projector resonance. The invention uses two diodes D1, D2 and an electrical resistor Ro to provide a means for mechanically damping a mechanical resonance by electrical means.
In accordance with the present invention, there is now described embodiments for practicing the present invention. As shown in
We illustrate usage of transparent projectors for the common two cases of an omnidirectional and directional hydrophones shown in
The results show the receive response of the hydrophone (1) without projector (______), (2) with original projector turned off (______) and (3) the case with a modified projector circuit activated ( . . . . . . . . . ), in accordance with the present invention providing an electrical resistance means for damping the main resonance and reducing its effect on the hydrophone performance.
The following is a summary of important aspects of the present invention.
Having now described a limited number of embodiments of the present invention, it should now be apparent to those skilled in the art that numerous other embodiments and modifications thereof are contemplated as falling within the scope of the present invention, as defined by the appended claims.
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Entry |
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Butler, John L. et al., “Dipole Transducer Enhancement From a Passive Resonator,” J. Acoustic Society vol. 136, No. 5. Nov. 2014, pp. 2472-2477. |
Butler and Sherman, Transducers and Arrays for Underwater Sound, p. 265, Springer 2016. |