Communications – electrical: acoustic wave systems and devices – Signal transducers – Underwater type
Reexamination Certificate
2002-01-25
2004-03-23
Pihulic, Daniel T. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Signal transducers
Underwater type
Reexamination Certificate
active
06711097
ABSTRACT:
FIELD OF THE INVENTION
The present invention refers to a driving device for hydroacoustic transmitters, including at least one actuating element, arranged to execute a reciprocating movement, wherein the movement of the actuating element includes an increase and a decrease of the distance between two ends thereof, and at least one spring member which is connected to the actuating element at said ends and which extends along a curved line between said ends.
Advantageously, the driving device can be employed to drive different types of acoustic apparatuses. Such apparatuses may work both as transmitters of acoustic signals and as receivers of acoustic signals. An acoustic apparatus, where the invention with great advantage may be of use is as a so-called sonar, i.e. a transmitter which sends sound waves under water, which waves after reflection can be monitored by hydrophones of different types.
However, the field of the invention may not only include acoustic apparatuses. The device may well be employed for other purposes than sound transmission. For instance, it can be employed for mechanical machining under water or for driving a hydraulic pump.
In the first place, however, the device is suitable for generation of low-frequent sound waves and is applicable on powerful low-frequent sound transmitters, which can work underwater.
The field of the invention also comprises applications of seismology and tomography. It refers to different arrangements, which in an active state are intended to be arranged completely below a liquid surface, for instance the water surface of a lake or a sea, in order to generate pressure waves in the water by moving quantities of water.
THE BACKGROUND OF THE INVENTION AND PRIOR ART
Most acoustic transmitters that are used nowadays are based either on the piezoelectrical effect or on magnetostriction. The piezoelectrical effect implies that a crystalline material presents a change of length when an electric voltage is applied to its end surfaces, and that an electric voltage ss obtained when the material is subjected to a physical deformation. Magnetostriction implies that a magnetic material, which is subjected to a change of the magnetic flux, presents a change of length and that an outer, onto the material forced change of length, causes a change of the magnetic flux. This implies that transmitters utilizing these effects also principally may be used as receivers.
Traditional driving devices for hydroacoustic transmitters can, on one hand, be of the type which is used for piston transmitters, and on the other hand of the type which is used for so-called flextensional transmitters. Driving devices for piston transmitters, normally include actuating elements which include piezoceramics or magnetostrictive materials. Normally, a clamp bolt is employed to pre-stress such piezoceramics or magnetostrictive materials and to adjust resonance frequencies for the transmitter. The piston which is driven by the driving device can be directly connected to said piezoceramics or magnetostrictive materials.
Also in driving devices for flextensional transmitters, the actuating element consists of piezoceramics or magnetostrictive materials. Here as well, a clamp bolt can be employed to pre-stress the piezoceramics or the magnetostrictive material and to adjust the resonance frequency for the transmitter. In the case of flex-tensional transmitters, the shell which is driven by the driving device and which is to act directly against a surrounding liquid is preferably connected to the actuating element at opposite end sections thereof. The shell can be in the form of a pre-stressing mechanism, whereby the need of a clamp bolt is eliminated.
When the shell is designed as described above and attached to opposite ends of the actuating element, the length oscillation of the actuating element will result in a corresponding change of the bulging of the shell. The described construction results in an amplification of the movement of the actuating element in the shell, so that a small movement of the actuating element results in a relatively large movement of at least some parts of the shell. When the shell is in direct contact with and surrounded by a liquid, its movements thus result in a displacement of the surrounding mass of liquid and a generation of hydroacoustic waves. The shell has double functions, one of which is to act as a spring member and in the best possible way amplify the movements of the actuating element, and the other to act as a displacement element against the surrounding liquid.
However, the shell presents a number of modes of oscillation, depending i.a. on its shape, deadweight and stiffness. The frequency characteristic of the shell, i.e. how it moves at different frequencies, can thus be influenced by the design of the shell. At certain frequencies, however, interferences between higher modes are obtained, which leads to the fact that the efficiency of the device at such frequencies is strongly reduced. Normally, the present transmitters have difficulties to generate high amplitudes below 100 Hz without said transmitters having to be large and complex due to the limited amplitude of the driving device.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a driving device which in particular is suitable for transmission of hydroacoustic waves and which efficiently utilizes the movements of an actuating element to accomplish a displacement of a mass and thereby a generation of hydroacoustic waves. A large displacement shall be accomplished by utilizing a relatively small movement of the actuating element. The device can be made relatively small and simple. Furthermore, it should allow large amplitudes and a good control of its frequency characteristic.
This object is achieved by means of a device of the initially defined kind, which is characterized in that it includes an element for displacement of a mass, which displacement element is connected to the spring member so that the movement of the latter is transmitted to the displacement element and generates a displacement thereof resulting in said mass displacement.
Thanks to the use of a separate displacement element, it is possible to work with further a mass and a stiffness, i.e. the mass and stiffness of the displacement element, to control the frequency characteristic of the device. The design of the displacement element, for instance its stiffness and shape, can be optimized with respect to the effective displacement of, for instance, a mass of liquid, while the stiffness of the spring member and the shape of the spring member can be optimized with respect to the desired pre-stress of the driving element and the maximum movement in the area where it is connected to the displacement element. Thus, the transmission ratio of the movement of the actuating element can be optimized.
According to a preferred embodiment, the displacement element is connected to the spring member in an area where the movement of the spring member occurs substantially perpendicularly to the reciprocating movement of the actuating element. Thereby, the largest possible displacement should be obtained thanks to an optimization of the transmission ratio change up of the movement of the actuating element.
According to a further preferred embodiment, the spring member, depending on the frequency of the movement of the actuating element, presents one or more modes of oscillation, the displacement element is connected to the spring member in an area where its bulge appears in the fundamental mode of the spring member. The spring member includes preferably a structure which provides a transmission ratio of the movement of the actuating element and can have the form of at least a part of an ellipse, whereby its bulging is influenced by the movement of the actuating element. The structure is preferably continuous and surrounds and encloses the actuating element.
According to a further preferred embodiment, the device includes at least one transmission element, via which the spring member is connected to the dis
Cetus Innovation AB
Harness & Dickey & Pierce P.L.C.
Pihulic Daniel T.
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