Communications – electrical: acoustic wave systems and devices – Signal transducers – Underwater type
Reexamination Certificate
1999-10-04
2001-10-02
Lobo, Ian J. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Signal transducers
Underwater type
C367S141000, C367S163000
Reexamination Certificate
active
06298012
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a doubly resonant push-pull class IV (dog bone) flextensional transducer having an improved operational bandwidth.
(2) Prior Art
Flextensional transducer devices are known in the prior art and have been used in a wide variety of applications. For example, U.S. Pat. No. 3,583,677 to Phillips describes an electro-mechanical transducer for secondary oil recovery. The transducer provides a dipole-type radiation field which extends along a single axis perpendicular to the axis of an oil well. This allows a surrounding casing to vibrate in a displacement mode rather than in a circumferential expansion mode to enable energy coupling to a surrounding oil-producing formation. The transducer includes two resonant beams forced to vibrate at an audio or sonic frequency by piezoelectric element stacks driven by an external electrical power source and transferring energy through additive shear waves to an external body. The transducer described in Phillips is a single frequency device operating in a shear bending mode.
U.S. Pat. No. 4,462,093 to Upton illustrates a transducer support system that couples the weight of the active portion of a transducer to the transducer's flanges without coupling the dynamic motion of the active portion of the transducer to the transducer's flanges. This support system is used in a flextensional transducer to produce a transducer with increased acoustic output and lower frequency.
U.S. Pat. No. 4,764,907 to Dahlstrom et al. illustrates an underwater transducer which includes a centrally located beam, a plurality of stacks of piezoelectric transducer elements extending from each side, and a rigid end beam at the opposite end of each stack. A plurality of bolts extending from one end beam to the other, on opposite sides of the stacks, are tightened to apply a desired amount of prestress on the ceramic stacks. Arcuate radiating elements are welded to opposite sides of each end beam, end cap members are fastened to the centrally located beam at each end of the transducer, and a jacket of elastomeric material is bonded to the edges of the end cap members to prevent ingress of fluid into the piezoelectric elements. Energizing of the piezoelectric elements causes expansion and contraction of the stacks, pushing the end beams in and out and causing bowing of the radiating elements to project sonar energy.
U.S. Pat. No. 5,291,461 to Boeglin et al. relates to an elastomer support for a sonar transducer which includes a ceramic stack electromechanical driver, a pair of rigid support members, and a pair of elastomer layers disposed between the ceramic stack electromechanical driver and the support members. The elastomer support provides effective mechanical stress reduction in the ceramic stack driver. The Boeglin et al. patent also describes a technique for removing excess heat from the ceramic stack components under high drive conditions.
U.S. Pat. No. 5,566,132 to Janus et al. relates to an acoustic transducer to which mechanical pre-stress is applied to the piezoceramic by spreading two plates symmetrically from the center with a bolt and nut arrangement. The acoustic transducer includes a housing and first and second stacks of transduction plates disposed within the housing. The first and second stacks are adapted to be held in compression between the housing opposed wall portions. A threaded stud extends from the first stack to the second stack. A nut is threadly engaged with the stud and adjacent one of the stacks. Movement of the nut on the stud operates to move the stacks toward the housing walls to compress the stacks, and operates to relax compressive force on the stacks to enable withdrawal of one of the stacks and replacement thereof.
Recently, polycrystalline and single crystal electrostrictive drive materials have been receiving considerable interest in research programs due to their significantly higher output power density potential. However, direct substitution of these new materials for those currently used is not possible without redesigning the transducer element's mechanical and/or electrical configuration. This is due to both elastic moduli differences and the fact that the new materials, unlike their PET counterparts, come unpolarized and require a D.C. bias for linear operation. One method of eliminating the need for D.C. bias for linear operation is operating the drive material in a push-pull mode whereby half-stack pairs are driven unidirectionally with alternating and opposing polarity.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a flextensional transducer device which produces multiple shell resonances for increased operational bandwidth.
It is a further object of the present invention to provide a flextensional transducer device as above which is lightweight and compact.
It is yet another object of the present invention to provide a flextensional transducer device as above which has utility in underwater applications.
The foregoing objects are attained by the flextensional transducer device of the present invention.
In accordance with the present invention, a flextensional transducer device comprises a multi-resonant shell and push-pull means for driving the shell so as to provide at least two tunable resonant modes, thereby increasing the operational bandwidth of the device. The push-pull drive means is formed by four rings of active drive material grouped to operate as two opposing push-pull pairs. The shell has a dog-bone configuration with two arcuately shaped interior web portions joined to the pairs of rings, end sections joined to the interior web portions, and a central concave section which functions as the primary radiating surface. Upon application of a desired current to the push-pull pairs, the interior web portions are caused to vibrate. These vibrations are transmitted to the end sections and the central concave section. By raising or lowering the bending stiffness of the interior web portions, the end sections, and the central concave section, one can selectively tune the modal resonance of the shell.
Other details of the flextensional transducer device of the present invention, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawing wherein like reference numerals depict like elements.
REFERENCES:
patent: 4384351 (1983-05-01), Pagliarini, Jr. et al.
patent: 4764907 (1988-08-01), Dahlstrom et al.
patent: 4972390 (1990-11-01), Pagliarini, Jr.
patent: 5515343 (1996-05-01), Boucher et al.
patent: 5757728 (1998-05-01), Tenghamn et al.
patent: 5926439 (1999-07-01), Piquette
Lall Prithvi C.
Lobo Ian J.
McGowan Michael J.
Oglo Michael F.
The United States of America as represented by the Secretary of
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