US3441904A - Electro-mechanical directional transducer - Google Patents

Description

April 9, 1969 5. L. WILSON 3,441,904

ELECTRO-MEGHANICAL DIRECTIONAL TRANSDUCER Filed Dec. 15, 1967 Sheet of s c, 0 c c 0 (3 0 7 7 H RI UU UU UU T R2 UU UU UU UU UU M 3 UU UU UU UU UU UU UU R4 UU UH UH UU UU UU UU 5 UU UH UU UU UU UH UU 6 UU UU UH UH UU R7 UU UU UU T Y; C; m -r--O E MG. 2

r i /F O INVENTOR L J Geoffrey L. Wilson AGENT A ril 29, 1969 e. L. WILSON ELECTRO-MECHANICAL DIRECTIONAL TRANSDUCER Filed Dec. 15, 1967 Sheet 8E2 wmwmmdmmww mfiwmo mwwwwm o o o o o o o m 3 $8 NiA w mwmmmwmmmw N. E N.

On me On an 2. SEEEE 1.52.2 w o w N N mm o mm M n Mm 0 we mm N. S mm mm 0 on 2 E M mm Mw o 8 mm Mm v m o 3 mm m o m mm Om mm Om Nv Om April 29, 1969 w sc 3,441,904

ELECTRO-MECHANI CAL D IRECT IONAL TRANSDUCER Filed Dec. 15, 1967 Sheet 3 of 5 FIG. 4 3-40 UJ RELATIVE AMPLITUDE-dB US. Cl. 340---9 2 Claims ABSTRACT OF THE DISCLOSURE An electro-mechanical directional transducer having an odd number of rows and columns of transducer vibratory elements. The central row and column have a common element at the geometric center of the transducer which eliminates the phase difference between the sum transducer output and the single central element output.

Background of the invention This invention generally relates to electromechanical transducers and more Particularly to underwater directional transducers.

In the past, electromechanical transducers have been employed for use in water at sonic and ultrasonic frequencies and have comprised a plurality of sensing electromechanical elements arranged in an even number of rows and columns to form a planar array. The electromechanical elements which have been shown to be most satisfactory have usually been composed of magneto strictive or ceramic materials, although other materials known to those skilled in the art have been used. One transducer in particular, comprised of generally U-shaped magnetostrictive units with readily removable windings, has met with great success in the underwater signalling field. This transducer is fully disclosed in US. Patent No. 3,082,401, issued to Bland et al.

In torpedo echo-ranging systems employing transducers of the Bland et al. type for example, quadrants are created to provide both azimuth and vertical steering control. A conventional way of doing this is by a comparison of sum and difference patterns from the transducer quadrants to give the necessary bearing information. This method is described more fully in Underwater Acoustics, V. M. Albers, chap. 11 (Pennsylvania State University Press, 1960).

Planar array transducers such as those described above have an even number of rows and columns of sensing elements disposed to have an equal number of elements in each quadrant, but having a decreasing number of windings on the elements going from the most central to the outermost. This is commonly known in the transducer art as amplitude shading, and reduces the level of the side lobes in the directivity pattern from the level that would be present from an unshaded array. In all such arrays there is a sudden reversal of the phase of the electrical signal at the transition from the main lobe to the adjacent side lobe, or between two adjacent side lobes. In some applications it is desirable to obtain a signal without such transitions as a phase reference. Such a signal would be obtained from the broad beam from a single element at the geometric center. A problem arises from this method, however, because there is no element at the geometric center. If one of the four elements nearest the center is used, there is an electrical phase difference between the sum output and the single element output for acoustic signals arriving other than along the transducers axis. In order to make this comparison, it was necessary therefore, to eliminate the effects of phase difference of output signals by demodula- 3,441,904 Patented Apr. 29, 1969 tion or some other means. In addition to these problems, it is desirable to develop a transducer having a reduced number of elements and windings without reducing the directional sensitivity of the transducer.

Summary of the invention An object of the invention is to provide an improved underwater transducer which provides the same degree of side lobe control of the sum and difference patterns as heretofore obtained and at the same time to provide an electrical reference signal free from undesirable phase reversals.

Another object of the present invention is to overcome the disadvantages and limitations of prior 'art directional transducers by providing a new and improved electromechanical directional transducer.

The above and other objects are attained by a unique arrangement of the vibratory sensing elements of a planar array transducer into an odd number of rows and columns whereby the center row and column share a single element at the geometric center of the transducer.

Brief description of the drawings The foregoing and other objects, and attendant advantages of the invention will be readily appreciated as the same become better understood by reference to the detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is an illustration of an electromechanical trans ducer depicting one embodiment of the invention;

FIG. 2 is a circuit diagram of the magnetostrictive element windings and signal outputs of the transducer of FIG. 1;

FIGS. 3a, 3b, 3c are an illustration of the winding strengths and relative positions of the magnetostrictive elements of the embodiment of FIG. 1;

FIG. 4 is a computed transducer output difference pattern for the embodiment of FIG. 1; and

FIG. 5 is a graphical difference pattern for a 7 x 7 transducer element array derived experimentally.

Description of the preferred embodiment of the invention Referring to FIG. 1, a transducer T is shown with an array of magnetostrictive elements M, such for example as a 7 x 7 array. The elements are distributed in 7 rows R to R and 7 columns C to C Rows R and R and columns C and C each have three elements. Rows R and R and columns C and C each contains five elements. The remaining center three rows and columns each have seven elements. All of the elements M are evenly distributed with equal spacing between elements. They are physically connected to the transducer housing H in the same manner described in the Bland et al. reference and require no additional refinements other than those discussed herein relating to the element positioning and shading arrangement.

A row of elements R and a column of elements C are positioned along the horizontal center and vertical center respectively of the transducer assembly. The center most element C R is at the geometric center of the transducer assembly providing a broad beam element signal output for comparison with a sum output.

The winding arrangement on the magnetostrictive elements is best shown in FIGS. 2 and 3. In FIG. 2, output lead A is conected to winding L which is series wound on each of the transducer elements in the same phase direction with the number of turns indicated in FIG. 3a. The output lead A connected in series with the common lead F provides a sum signal output in response to the magnetostrictive elements detecting acoustic signals.

Winding L is series wound on the elements with the number of turns shown in FIG. 3b. The underscored numbers indicate that the elements in the right half of the assembly are series wound in reverse phase from those in the left half. The elements at the vertical center receive no windings. Output lead B, series connected to winding L and common lead F, provides an azimuth difference output signal in response to detected acoustic signals.

Winding L is series Wound on the elements with the number of turns and the phase relationship depicted in FIG. 3c; the elements in the lower half of the transducer being wound in reverse phase to those in the upper half and the center horizontal row receiving no windings. A vertical difference output signal arises on output lead D when the magnetostrictive elements sense acoustic signals and induce electrical signals in winding L Winding L is a single element winding which in the embodiment described has 50 turns wound on center element C R This is best shown in FIG. 3a. With the centermost element C R having winding L series connected between output leads E and F, a single element broad beam signal is available for comparison with the sum signal. There is no electrical phase difference between the sum output and the signal element output for acoustic signals arriving at the transducer, so the two output signals may be compared directly. The azimuth difference, vertical difference and sum signals may be connected to conventional sum-difference comparison and control circuitry as desired.

FIGURES 4 and 5 illustrate computed and measured difference patterns for the 7 X 7 element planar array transducer for the embodiment described. The shading coefficients were chosen to give approximately a 40 db minor lobe suppression and the difference patern was measured at a frequency for which the element centerto-center spacing was .574 wavelength. It should be noted that the optimum sum and difference patterns from the 7 x 7 element array do not vary substantially from the conventional 8 x 8 array.

From the foregoing it should now be apparent that a new and improved underwater directional transducer has been developed which provides a phase reference signal from the center, is reduced in complexity by having fewer elements and windings, and maintains optimum sum and difference directivity patterns. It should be noted of course that the foregoing merely describes one preferred embodiment of the invention. Many other embodiments, features, and modifications are contemplated which do not depart from the spirit and scope of the invention.

The concept of having a single element at the center of at detecting array with an odd number of rows and columns of sensing elements may for example have applications in radar antenna systems. The number of rows and columns is not crucial provided the number is odd rather than even. Nine by nine element arrays or five by five element arrays are contemplated for example. Reference should be made to the appended claims, therefore, rather than the specification as indicating the scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A electromechanical transducer comprising a planar array vibratory unit assembly having a plurality of vibrating elements arranged in an odd number of rows and columns to form a planar signal sensing array, the center column of said vibratory elements lying in a line bisecting said array into right and left halves, the center row of said vibratory elements lying in a line bisecting said array into upper and lower halves, said bisecting lines intersecting at the geometric center of said array, at least one of said vibratory elements positioned at the geometric center of said array,

sum signal detecting means connected to elements in each of said halves and to the elements lying in said bisecting lines,

difference signal detecting means connected to elements in each of said halves, and

single elements detecting means connected to said central vibratory element.

2. The transducer of claim 1 wherein said vibratory elements are magnetostrictive elements and each of said detecting means include series connected windings on their respective elements.

References (Iited UNITED STATES PATENTS 2,323,030 6/ 1943 Gruetzrnacher 340-10 X 2,405,186 8/1946 Beniott 340-10 2,724,818 11/1955 Camp 340-9 2,921,288 1/1960 ONeill et al 340-9 X RODNEY D. BENNETT, JR., Primary Exan'ziner. BRIAN L. RIBANDO, Assistant Examiner.

US. Cl. X.R.

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