Air-gap hydrophone
First Claim
1. Hydrophone apparatus for sensing vibrations in a fluid or fluid-like medium, comprisinga carrier plate positioned with a first side in contact with the medium and being subject to vibrational flexure upon being exposed to vibrations in the medium;
- vibration sensor means positioned on a second side of said carrier plate, which second side is not in contact with said medium, for sensing the vibrational flexure in the carrier plate and producing electrical signals indicative of the vibrations in the medium;
a chamber adjacent said second side of said carrier plate that is sealed from, and not in fluid communication with, said medium; and
,a low impedance Farraday cage surrounding said vibration sensor means.
1 Assignment
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Accused Products
Abstract
A hydrophone for the detection of sound or vibrational waves, comprising a piezo electric transducer within a Faraday cage such that it is in contact with and yet isolated from a deformable pressure transmitting medium that carries vibrations. The Faraday cage reduces noise interference. The deformable medium is usually a fluid and preferably a vegetable oil, but can also include a silastic compound couple. One side of the Faraday cage is a ground plane of a surface-mount printed circuit board. Components of an electronic circuit for conditioning the signal are mounted on the printed circuit board and include a buffer having an ultra-high impedance input and a very low impedance output. The circuit has a low power draw and is powered by a replaceable battery.
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Citations
27 Claims
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1. Hydrophone apparatus for sensing vibrations in a fluid or fluid-like medium, comprising
a carrier plate positioned with a first side in contact with the medium and being subject to vibrational flexure upon being exposed to vibrations in the medium; -
vibration sensor means positioned on a second side of said carrier plate, which second side is not in contact with said medium, for sensing the vibrational flexure in the carrier plate and producing electrical signals indicative of the vibrations in the medium; a chamber adjacent said second side of said carrier plate that is sealed from, and not in fluid communication with, said medium; and
,a low impedance Farraday cage surrounding said vibration sensor means. - View Dependent Claims (2, 3, 4)
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5. Hydrophone apparatus for sensing vibrations in a fluid or fluid-like medium, comprising
a carrier plate positioned with a first side in contact with the medium and being subject to vibrational flexure upon being exposed to vibrations in the medium; -
vibration sensor means positioned on a second side of said carrier plate, which second side is not in contact with said medium, for sensing the vibrational flexure in the carrier plate and producing electrical signals indicative of the vibrations in the medium; a chamber adjacent said second side of said carrier plate that is sealed from, and not in fluid communication with, said medium; a buffer circuit having an ultra-high input impedance and a very low output impedance, wherein said buffer circuit is a bipolar transistor assisted, modified source follower, with a first JFET for a first stage direct coupled to a second stage that utilizes a bipolar PNP transistor for lowering the output impedance, such that the reflected resistance through the base of the bipolar transistor is paralleled with the effective output resistance of the first JFET to produce a very low output resistance and a near unity voltage gain, and said bipolar assisted source follower further having constant current source means connected to the source of said first JFET and to the collector of said bipolar transistor for holding the current through the source resistor substantially constant in spite of externally induced spikes and fluctuations on the output signal from the buffer circuit. - View Dependent Claims (6, 7, 8, 9)
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10. Hydrophone apparatus, comprising:
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a cylindrical body enclosing a first compartment; vibration sensor means positioned at one end of said first compartment for sensing vibrations in a fluid and producing electrical signals that are indicative of the vibrations in the fluid, wherein said vibration sensor means includes a piezo electric element, one side of which is mounted on a conductive carrier plate, and conductive components substantially surrounding the remaining sides of said piezo electric element in close proximity thereto and in electrical contact with each other and with said carrier plate to form together with said carrier plate a wafer-shaped, low impedance Farraday cage around said piezo electric element; electric circuit means positioned in said first compartment for conditioning the signals produced by said vibration sensor means for transmission to a remote location; an elongated boot with flexible sidewalls enclosing a second compartment and attached to said cylindrical body around said vibration sensor means and extending outwardly therefrom such that said vibration sensor means is positioned at one end of said second compartment; and a coupling fluid filling said second compartment. - View Dependent Claims (11, 12, 13, 14, 15, 17, 18)
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16. In hydrophone apparatus having a high impedance piezo electric element for sensing vibrations in a fluid and producing a signal indicative of the vibrations, the improvement comprising:
a buffer circuit that has ultra-high input impedance on the order of about 1 M ohms and an output impedance on the order of about 400 ohms and constant current source means for preventing external EMF-induced spikes and interference on the output from being transformed into buffer-generated noise, wherein said buffer circuit is a bipolar transistor assisted, modified source follower with a first JFET for a first stage direct coupled to a second stage that has a bipolar PNP transistor for lowering the output impedance, such that the reflected resistance through the base of the bipolar transistor is paralleled with the effective output resistance of the first JFET to produce a very low output resistance and a near unity voltage gain, said constant current source means being connected to the source of said first JFET and to the collector of said bipolar transistor for holding the current through the source resistor substantially constant. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26, 27)
Specification