Ultra-broadband hydrophone

• US 5,694,375 A
• Filed: 03/22/1996
• Issued: 12/02/1997
• Est. Priority Date: 03/22/1996
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Woodall, Roger L.
• Primary Examiner(s): Pihulic, Daniel T.
• Application Number:
  US08/624,833
• Time in Patent Office: 620 Days
• Field of Search: 367/185, 367/174, 367/149, 367/142, 367/140, 367/186, 367/187, 310/337, 310/334
• US Class Current: 367/185
• CPC Class Codes: G01H 11/02 by magnetic means, e.g. reluctance
• CPC Class Codes: H04R 1/44 Special adaptations for subaqueous use, e.g. for hydrophone

Abstract

The present invention relates to an ultra-broadband hydrophone which has major electronic components and one mechanical component. The first electronic component comprises a flux-gate magnetometer for sensing changes in an ambient magnetic field and for creating an electrical signal representative of the ambient magnetic field. The second electronic component comprises an electrical circuit for demodulating the electrical signal and a low pass filter for smoothing the demodulated signal. The mechanical component is a magnetic diaphragm for receiving acoustic pressure waves and for causing changes in the ambient magnetic field in response to the received acoustic pressure waves. In a preferred embodiment, the hydrophone of the present invention also includes a sub-Hertz differential magnetic field winding for generating a differential magnetic field which nulls the ambient magnetic field about the flux-gate magnetometer.

Claims

1. An acoustic ultra-broadband hydrophone device which comprises:

first sensing means for sensing an incoming acoustic wave producing changes in ambient pressure, said first sensing means including a magnetic diaphragm producing vibrations in response to said changes in ambient pressure due to said incoming acoustic wave and causing changes in ambient magnetic field produced by said vibrations of said diaphragm to move synchronously with said changes in ambient pressure and producing corresponding changes in magnetic flux; and

second means for sensing said changes in magnetic flux and generating electrical signals representative of said changes in magnetic flux.

2. The hydrophone device of claim 1 wherein said magnetic diaphragm comprises a flexible light diaphragm impregnated with fine grain magnetic particles, said particles being aligned magnetically in the same direction as a response axis of said second sensing means.

3. The hydrophone device of claim 2 wherein said second sensing means comprises a flux-gate magnetometer.

4. The hydrophone device of claim 3 wherein said flux-gate magnetometer comprises:

two ferrite cores;

a saturation winding passing through said ferrite cores and being arranged orthogonal to said sensing winding;

a sensing winding wound about said ferrite cores and being arranged orthogonal to said saturation winding; and

whereby a high frequency bias current is passed through said saturation winding and changes in saturations are sensed by said sensing winding.

5. The hydrophone device of claim 4 wherein the electrical signal produced by said magnetometer is an AC signal that has an amplitude and phase relative to the ambient magnetic field'"'"'s strength and direction.

6. The hydrophone device of claim 2 further comprising:

means for generating an output signal;

said output signal generating means comprising means for demodulating said electrical signal generated by said second sensing means; and

said output signal generating means further comprising means for filtering said demodulated signal.

7. The hydrophone device of claim 6 wherein said filtering means smoothes the demodulated signal to a DC output signal which is a function of the magnitude and direction of the ambient magnetic field.

8. The hydrophone device of claim 6 further comprising means for generating a differential magnetic field for nulling the ambient. magnetic field at said second sensing means and increasing the sensitivity of said hydrophone device.

9. The hydrophone device of claim 8 wherein said differential magnetic field generating means comprises:

a sub-Hertz differential magnetic field winding;

a differential field driver; and

a sub-Hertz low pass filter for sensing the average voltage of said output signal and inputting the sensed average voltage to the differential field driver for generating said differential magnetic field.