Physically damped noise canceling hydrophone

Abstract

A hydrophone is provided which includes at least four piezoelectric sensors mounted to a central section of syntactic acoustic dampening material as well as a layer of corprene between the piezoelectric sensors and the central section. Each of the piezoelectric sensors includes radially poled piezoelectric cylinders wired in series with inert polycarbonate endcaps and an isolator layer. The piezoelectric cylinders are assembled co-axially. The piezoelectric cylinders are then adhered to the central section and sandwich a layer of corprene. The corprene also adds noise dampening properties.

Claims

1. A hydrophone comprising: a cylindrical core with two end planes and at least four indents spaced ninety degrees apart between each said end plane with said core being syntactic acoustic dampening material; a layer of corprene adhered to each of said indents; and at least four cylindrical piezoelectric sensors; each of said sensors sized to position within each of said indents; wherein each said layer of corprene is affixed therebetween each of said sensors and said core.

2. The hydrophone in accordance with claim 1 wherein each of said sensors are assembled co-axially with radially poled piezoelectric cylinders wired in series, polycarbonate endcaps and an isolator layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Reference is made to the accompanying drawings in which is shown an illustrative embodiment of the invention, from which its novel features and advantages will be apparent, wherein corresponding reference characters indicate corresponding parts throughout the several views of the drawings and wherein:

(2) FIG. 1 depicts an expanded view of piezoelectric sensors and syntactic acoustic dampening material of the present invention;

(3) FIG. 2 is a graph depicting nominal free range voltage sensitivity across a frequency range in which the voltage sensitivity defines how much electrical output would be provided by certain incoming pressure waves;

(4) FIG. 3 depicts a single channel directivity pattern at a single frequency; and

(5) FIG. 4 depicts a single channel directivity pattern at another frequency and shows the backside noise cancelling capability of the design.

DETAILED DESCRIPTION OF THE INVENTION

(6) In the figures, FIG. 1 depicts a hydrophone 10 of the present invention. The hydrophone 10 includes cylindrical piezoelectric sensors 20 and a core of syntactic acoustic dampening material (SADM) 30. Each of the sensors 20 includes radially poled piezoelectric cylinders 22 wired in series, with inert polycarbonate endcaps 24 and an isolator layer 26. The piezoelectric cylinders 22 are assembled co-axially.

(7) The piezoelectric cylinders 22 are then adhered to the SADM 30 and sandwich a 3/32 inch thick layer of corprene 32 (a cork and rubber mixture). The corprene 32 also adds noise dampening properties.

(8) The layering of the SADM 30, the corprene 32 and the sensors 20 can also include contact adhesive 34. The contact adhesive 34 should be pliable when cured.

(9) FIG. 2 depicts nominal free field voltage sensitivity across a very wide frequency range. FIG. 3 and FIG. 4 each depict measured single channel directivity at a different frequency. As expected, the directivity increases with reducing beamwidth and frequency.

(10) Due to the arrangement of the sensors 20 at ninety degree separations around an approximately 2.75 inch diameter; sensors with one hundred and eighty degree separation can be used in conjunction to cancel additional acoustic noise when there is a need to focus the sensitivity into one hemisphere. This is accomplished by adding the received time series signals of the one hundred and eighty degree (ie: opposite) sensors but with a slight time delay that would account for the separation distance between the sensors, x, and the approximate sound speed of SADM (C.sub.SADM or X/C.sub.SADM.

(11) The resulting receive pattern is defined by Equation (1):
M.sub.e=(1+cos )/2,(1)

(12) where M.sub.e is the voltage sensitivity as a function of angle and defines the angle off the maximum response axis.

(13) This adds 4.8 dB to the receiver sensitivity and backside noise cancelling capabilities due to the increased directivity. Likewise, using all four sensors would increase the directivity to further add 8.8 dB to the receive sensitivity by weighting the sensor inputs as defined in Equation (2)
Me=(1+2 cos +cos 2)/4(2)

(14) The submitted design uses radially-poled piezoelectric cylinders with inert polycarbonate endcaps to provide the stated capabilities in a much smaller form factor (3-inch diameter). Prior art hydrophones use piezoelectric elements that operate in a different mode by using tonpilz elements that operate axially with a head mass, a tall mass and an active piezoelectric element in between and are arranged in a planar array.

(15) Furthermore, advantages of the hydrophone 10 of the present invention are simplicity, easily attainable materials and uncomplicated shapes that require minimal machining. Commercial hydrophones were considered; however, none would provide the adequate sensitivity and noise cancelling capabilities of the hydrophone 10 of the present invention.

(16) The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description only. It is not intended to be exhaustive or to limit the invention to the precise form disclosed; and obviously many modifications and variations are possible in light of the above teaching.

(17) It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.