US 3755698 A
This disclosure is directed to a free-flooded ring type transducer in combination with a coaxial slow waveguide for transmitting or receiving signals which improves the performance by delaying the radiation from the inner surface by one-half wavelength so that the radiation from the inner and outer surfaces are in phase.
Claims available in
Description (OCR text may contain errors)
Trott Aug; 28, 1973 FREE-FLOODED RING TRANSDUCER WITH 3,302,163 1/1967 Andrews, Jr. 340/8 F1 SLOW WAVE GUIDE 2,922,140 1/1960 Levine et a1. 340/8 FT 3,325,779 6/1967 Supemaw..... 340/8 FT n n r: infield J- T tt. An andale, Va. 3,142,034 7/1964 Junger 340/8 0 Assisnee: The United states of America as 3,243,766 3/1966 Wa1ther 340/8 FT represented by the Secretary of the Navy, Washington, DC. Primary Examiner-.1. D. Miller Assistant Examiner-Mark O. Budd F  Apr 25 1972 AtI0rne v-R. S. Scrascra, Arthur L, Branmng et a1.  Appl. No.: 247,427
52 us. 01 310/8, 310/83, 310/90, [571 I ABSTRACT  l t Cl 310/26 340/8 3 2 4: I This disclosure is directed to a free-flooded ring type n r transducer in combination with a coaxial Slow wave  Field of Search 310/82, 8.3, 8,
310/9 1 9 4 34mm 8 Fr 8 C guide for transmitting or receiving stgnalswhich |mproves the performance by delaying the radiation from 5 6 R f C1 d the inner surface by one-half wavelength so that the ra- 1 e erences I e diation from the inner and outer surfaces are in phase.
UNITED STATES PATENTS 2,005,741 6/1935 Ha es 340/8 F1 2 Claims, 5 Drawing Figures PAIENTEDMJBZB ms 3; 755.698
SHEU 2 (IF 3 RELATIVE SOUND PRESSURE LEVEL (dB) (:1 0 0| 6 G I I I PATENIEB M18 28 $75 ObN ObN
FREE-FLOODED RING TRANSDUCER WITH SLOW WAVE GUIDE BACKGROUND OF THE INVENTION This invention is directed to a free-flooded ring type transducer and more particularly to an improved transducer.
Heretofore, free-flooded ring transducers in the form of magnetostrictive ring scrolls or piezoceramic rings have been used for deep submergence sonar. array applications. Such arrays are affected very little by hydrostatic pressure, they are usually omnidirectional in the plane of the ring and generally arrayed with more than one coaxial ring. In order to obtain unidirection radiation the ring array must be three-dimensional or mounted within a reflector.
It is well known that the acoustic radiation amplitude along the axis of the ring is quite low, relative to the radiation in the plane of the ring. This is due to phase cancellation of the external and internal ring radiation. At low frequencies, the ring transducer is equivalent to two rings, the outer surface and the inner surface operating in phase opposition. As the signal frequency increases, the radiation from the inner surface dominates due to the open-pipe resonance. Maximum efficiency occurs at the ring resonance and close coupling of the two resonant frequencies provides a transducer which operates over a fairly broad frequency range. An approximate mechanical circuit of a magnetostrictive ring has been set forth and explained in an article Application of a Slow Waveguide to a Free-Flooded Ring Transducer, by W. James Trott published in The Report of NRL Progress by the Naval Research Laboratory dated May 1971.
SUMMARY OF THE INVENTION This invention is directed to a rnagnctostrictive or piezoelectric ring type transducer which is coupled with an axially aligned slow waveguide. The slow waveguide is made to just fit inside of the inner diameter of the ring and yields maximum gain by delaying the radiation from the inner surface by one-half wavelength so that the radiation from the inner and outer surfaces will be in phase. As such, the structure provides a transducer which can be operated at great depths with a unidirectional directivity with an increase in source level (or directional gain). I
STATEMENT OF THE OBJECTS It is therefore an object of the present invention to provide a transducer structure which will operate at great depths with improved directional gain.
Another object is to provide a transducer structure by which the output radiation from the inner and outer surfaces are in phase for one direction along the axis of the ring.
Still another object is to provide a transducer which has an improved unidirectional response.
Other objects and advantages of the invention will become obvious to those skilled in the art upon reading the following description with a review of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates the transducer arrangement with portions cut away for illustrative purposes.
FIG. 2 illustrates relative source level curves for the free-flooded ring transducer with and without the slow waveguide.
FIGS. 3-5 illustrate comparative curves for the directional response at different signal frequencies for the transducer with and without the slow waveguide.
DETAILED DESCRIPTION Now referring to the drawings, there is shown by illustration in FIG. 1 a free-flooded ring transducer made in accordance with the teaching of the present invention. As shown, the transducer includes a free-flooded ring 11 of piezoceramic or magnetostrictive material such as Permendur which is a cobalt-iron alloy of very high magnetic saturation made by Allegheny Ludlum Steel Corporation. The ring has a coil of wire 12 wound thereon which connects with a conductor 13 through which a current is supplied from a suitable source. The entire structure is coated with a protective coating 14 of hysol epoxy or any suitable material to prevent harmful effects of sea water on the metallic elements and which will permit vibratory movement of the inner and outer surfaces of the ring element.
An elongated solid cylindrical element 15 made of silicone rubber having an outer diameter substantially equal to the inner diameter of the ring structure is secured in an axial relationship therewith. The elongated cylindrical element may be inserted flush with the back face of the ring, with the back end of the cylinder at the halfway point of the ring, or with the back face of the cylinder flush with the front face of the ring in a coaxial arrangement. It has been determined that the best re sults may be achieved with the front face of the ring flush with the back face of the silicone rubber cylinder as shown in FIG. 1.
The ring transducer is made of a 0.007 inch thick of 1.5 inch wide core wound about a mandrel into a scroll having an inside diameter of 5.63 inches with an outside diameter of 6. l 3 inches. A bonding agent was used between each layer to hold the scroll pennenently in shape. The ring was then wound with liner tape to insulate the ring from 210 turns of No. 19 wire wound tightly upon the tape and connected to an electrical lead. The resulting toroidally wound Permendur scroll core was polarized by briefly passing Ampers of DC through the windings. The wire wound core was then encapsulated in a clear HYSOL epoxy an orderless, tasteless, non-toxic, tough therrnosetting plastic that is highly resistant to chemicals and has a high dielectric strength a tradenarne of Houghton Laboratories Inc., Now HYSOL Corporation.
During encapsulation, a waxed wooden mold was fabricated to house the ring core while the HYSOL epoxy was pouredaround it. The mold was placed in an oven and baked at 60C for 4 hours which is sufficient for the epoxy to harden. The mold was then removed and the encapsulated transducer was cleaned and sanded. The final product has an inside diameter of 5.3 inches an outside diameter of 6.53 inches and a width of 1.90 inches.
The solid cylindrical silicone rubber has an outside diameter equal to the inner diameter of the finished transducer element with a length of 12% inches.
In operation the transducer assembly is placed in the water at the desired depth. A signal is applied to the coil thereby causing vibrational movement of themagnetostrictive ring to produce sound pressure waves within the water. The waveguide is operative to delay the wave output of the inner surface of the ring by onestrictive ring alone and the ring with the slow waveguide.
COMPARISON OF MEASURED PARAMETERS half wavelength. Thereby producing an output wave which is in phase with the wave produced by the outer surface. Thus, the transducer has unidirectional directivity with increased source level.
FIG. 2 illustrates relative source level curves of the ring alone and of the ring in combination with the waveguide for relative sound pressure level (dB) vs Frequency kHz.
Curve 1 shows the axial far-field sound pressure for the combination,
Curve 2 shows the radial far-field sound pressure in the plane for the ring for the combination,
Curve 3 is the back radiation of the combination,
Curve 4 shows the far-field axial sound pressure of the ring alone, and
Curve 5 shows the far-field radial sound pressure for the ring alone. The electrical current driving the ring is constant for these five curves. A significant improvement in source level is apparent by comparison of cures 1 and 5.
FIGS. 3, 4, and 5 illustrate a comparison of directional response for the free-flooded ring alone and the free-flooded ring in combination with the slow waveguide at 6kHz, 7kHz and 8kHz, respectively. The freeflooded ring alone is shown on the right side, and the combination on the left side. The dashed curves in FIG. 3 is a Sinl) directivity pattern at frequencies below the resonant frequencies which is seen to be substantially that of the 6kHz pattern which is above the open pipe resonance. In three dimensions the directivity is a figure of revolution about the 0 axis.
The following table illustrates a comparison of different measured parameters for the free-flooded magneto- Comparing the corresponding measurements at the respective frequencies, illustrates an increase in efficiency for each of the frequencies where the transducer included the slow waveguide. Further, one concludes that the application of a slow waveguide to a free flooded ring transducer yields a significant improvement in directivity and source level.
Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.
What is claimed and desired to be secured by Letters Patent of the United States is:
l. A free-flooded ring transducer which includes:
a transducer ring element,
means connected with said ring element for applying a signal source thereto to produce vibrational movement in said ring element, and
a slow waveguide operatively connected with said ring element in axial alignment therewith,
said slow waveguide is made of silicone rubber of cylindrical shape,
whereby sound pressure radiation from the inner surface of said ring is delayed by one-half wavelength so that the sound wave radiation from the inner and outer surfaces are in phase in one direction along the ring axis.
2. A free-flooded ring transducer as claimed in claim 1; wherein,
said slow waveguide has an outer diameter substantially equal to the inside diameter of said ring element and is coaxial therewith.