Drive system for acoustic devices

Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electrostrictive – magnetostrictive – or piezoelectric

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Details

381199, 381188, 381205, H04R 2500

Patent

active

054577527

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The invention relates to a mechanical drive system for use, inter alia, in acoustic devices. Current acoustic devices are able to operate as transmitters, i.e. as transducers for acoustic signals, and as receivers of acoustic signals. An acoustic device in which the invention may be used to great advantage is as a so-called Sonar, that is, a transmitter which sends out sound waves under water which, after reflection, can be monitored by hydrophones of various kinds.


BACKGROUND ART, THE PROBLEM

It is a well-known fact that low-frequency sound waves can travel longer distances through water than can high-frequency sound waves. For a long time there has also been a considerable need of powerful low-frequency sound transmitters which are capable of working under water, both from a military point of view and from the point of view of the offshore oil and gas industry. Transmitters of various designs and embodiments for these purposes and fields of use have been available on the market for quite a long time. A summary of such acoustic transmitters is given in an article in DEFENSE SYSTEM REVIEW, November 1984, pages 50-55, entitled "Sonar transducer design incorporates rare earth alloy".
Most acoustic transmitters which are used at present are based on either the piezoelectric effect or on magnetostriction. As is well-known, the piezoelectric effect means that a crystalline substance is subjected to a change in shape when an electric voltage is applied to its end surfaces and that a voltage is obtained when the substance is subjected to a physical deformation, respectively. Magnetostriction means that a magnetic material which is subjected to a change of the magnetic flux suffers a change in shape and that an externally caused change in length gives rise to a change in the magnetic flux, respectively. This means that a transmitter which utilizes these effects can also, in principle, be used as a receiver.
A variety of different embodiments of acoustic transmitters exist. In low-frequency applications it is common that they have a cylindrical shape with either a circular or elliptical cross section area.
The greatest problem with this type of transmitters is to achieve a sufficiently great amplitude of the oscillations. To this end, either a large transmitter area or a small transmitter area with great amplitude of oscillation would be required.
The introduction of the so-called giant magnetostrictive materials has improved the conditions for obtaining good acoustic transmitters. With such materials as driving elements, amplitude changes may be obtained which largely amount to 30 times the corresponding changes using piezoelectric materials. Transmitters which utilize these giant magnetostrictive materials have existed for several years. One property of transmitters which utilize giant magnetostrictive materials is that they must be mechanically prestressed. This can be done in different ways, for example as shown in U.S. Pat. No. 4,438,509 with the aid of prestressed wires.
A frequently occurring embodiment for the actual driving will be described in greater detail starting from a cylindrical transmitter with a near elliptical cross section. The cylindrical envelope surface consists of an elastic diaphragm or shell. Inside and parallel to the axis of the cylinder and making contact with the shell are two beams applying pressure to the shell. The cross sectional area of the beams is symmetrically mirror-inverted in relation to the minor axis of the elliptical shell and each beam is delimited by that part of the shell which faces the end of the major axis and a chord parallel to the minor axis. Between the beams and making contact with their plane-parallel sides there is arranged an electrically-controlled driving element in the form of a driving rod. The longitudinal axis of the driving rod coincides with the major axis of the elliptically-formed cross section and lies midway between the end surfaces of the transmitter. In those case where the magnetostrictive effect is utilized, the driving r

REFERENCES:
patent: 4438509 (1984-03-01), Butler et al.
patent: 4901293 (1990-02-01), Kuhn
patent: 4914412 (1990-04-01), Engdahl et al.
patent: 5101384 (1992-03-01), Tenghamn et al.
Greenlaw et al., "Sonar Transducer Design Incorporates Rare Earth Alloy" in Defense Systems Review, Nov. 1984, pp. 50-55.

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