Communications – electrical: acoustic wave systems and devices – Signal transducers – Receivers
Reexamination Certificate
1999-01-27
2001-01-09
Lobo, Ian J. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Signal transducers
Receivers
C367S171000, C367S173000, C367S188000, C367S131000, C181S122000
Reexamination Certificate
active
06172940
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to the measurement of underwater acoustic intensity, and more specifically to a novel apparatus having advantages over known underwater acoustic intensity probes.
Underwater acoustic intensity has been measured by various devices. For example, U.S. Pat. No. 4,982,375, dated Jan. 1, 1991 describes an acoustic intensity probe using multiple hydrophones and a fast Fourier transform analyzer. U.S. Pat. Nos. 3,274,539, dated Sep. 20, 1966 and 3,311,873, dated Mar. 28, 1967, describe devices which use a hydrophone and an accelerometer in combination. U.S. Pat. No. 5,392,258, dated Feb. 21, 1995, describes a device using a hydrophone and a geophone in combination. A similar device is described in T. B. Gabrielson et al., “A Simple Neutrally Buoyant Sensor for Direct Measurement of Particle Velocity and Intensity in Water,” J. Acoust. Soc. Am. 97, 2227-2237 (1994). Each of these devices uses at least one piezoelectric sensor, either in a hydrophone, or in an accelerometer.
A piezoelectric sensor is inherently a high impedance device. Because of its high impedance, the sensor, by itself, cannot deliver an output signal over a long distance without significant attenuation. Accordingly, it is usually necessary to locate a preamplifier in close proximity to the sensor, and to provide impedance matching networks at the input and output of the preamplifier, at the location of the sensor.
Another drawback of the intensity probe using hydrophone pressure sensors is that the pressure sensors are directly exposed to flow as the probe moves through a body of water (or as the body of water flows past the probe), and consequently subject to noise generation due to turbulent flow.
SUMMARY OF THE INVENTION
An important object of this invention is to provide an underwater acoustic intensity probe that can be used to transmit an output signal over a long distance, without the need for preamplification or other signal conditioning. Another object of the invention is to simplify underwater measurements at depths that exceed the maximum allowable length of signal cable connecting a piezoelectric sensor to its amplifier. Still another object of the invention is to reduce measurement errors associated with hydrodynamic noise due to flow over the body of the probe.
The invention takes advantage of the inherently low electrical impedance of a geophone. Because of the low impedance of the geophone, its output signal can be transmitted over relatively long distances without preamplification or other signal conditioning at the location of the geophone.
The term “geophone” as used herein refers to a passive analog transducer which senses mechanical motion by means of an inertial mass suspended in a rigid supporting structure, and in which the relative movement of the inertial mass and the supporting structure is converted to an electrical output by a coil movable in a magnetic field. The coil has a low electrical impedance, and the electrical output of the coil is a voltage that is proportional to the velocity of the coil relative to the magnetic field. In the geophone used in accordance with this invention, the inertial mass is mounted for linear movement along an axis, and thus the geophone is responsive to motion along that axis. When the geophone is immersed in water, its output provides a measure of acoustic particle velocity.
The discovery that two geophones can be used to measure underwater acoustic intensity arose from the observation that acoustic pressure can be inferred from the velocity gradient between two geophones disposed in spaced relationship to each other and mounted with their sensing axes in alignment. This is analogous to, but not readily apparent from, the known technique of determining acoustic particle velocity from the pressure gradient between two hydrophones. The low impedance electrical outputs of the two geophones can be connected through a long cable to a remote spectrum analyzer, without the need for intervening signal amplification at the location of the geophones.
The underwater acoustic intensity probe in accordance with the invention comprises a pair of passive geophones disposed in spaced relationship to each other and mounted so that the axes along which they are sensitive to velocity are aligned.
Preferably, the geophones are supported inside an acoustically transparent shell filled with liquid by mounts having sufficiently high radial stiffness to inhibit misalignment of the sensing axes, but relatively low axial stiffness so that acoustically induced axial movement of the geophones is substantially unrestricted. A foam structure encasing each geophone provides neutral buoyancy, and the geophones are magnetically shielded from each other. A cable, conducts electrical signals from the passive geophones directly to a spectrum analyzer at a remote location, and the spectrum analyzer is used to compute acoustic intensity from the velocity gradient between the two geophones as determined from the geophone output signals transmitted through the cable.
The two-geophone probe obviates preamplification, impedance matching and other signal conditioning, and consequently simplifies deep water acoustic measurements. The acoustically transparent, fluid-filled housing for the geophones reduces hydrodynamic noise resulting and permits more accurate measurements.
Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention, when considered in conjunction with the accompanying drawings.
REFERENCES:
patent: 3593258 (1971-07-01), Slavens
patent: 3720909 (1973-03-01), Sikora
patent: 3980985 (1976-09-01), Dale et al.
patent: 5084846 (1992-01-01), Smith, Jr.
patent: 5189642 (1993-02-01), Donoho et al.
Gabrielson Thomas B.
Lauchle Gerald C.
McConnell James A.
Billi Ron
Lobo Ian J.
The United States of America as represented by the Secretary of
LandOfFree
Two geophone underwater acoustic intensity probe does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Two geophone underwater acoustic intensity probe, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Two geophone underwater acoustic intensity probe will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2542918