Communications – electrical: acoustic wave systems and devices – Signal transducers – Receivers
Patent
1998-05-14
1999-09-07
Pihulic, Daniel T.
Communications, electrical: acoustic wave systems and devices
Signal transducers
Receivers
H04R 144
Patent
active
059497424
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a direction finding and ranging (DIFAR) transducer. The transducer is particularly suited to underwater applications including sonobuoys, but could also be used for seismic and air-borne sound applications.
DIFAR sensors, such as DIFAR hydrophones, have been used in sonobuoys for approximately twenty years. A known DIFAR hydrophone is described in U.S. Pat. No. 4,928,263. The hydrophone described therein comprises a hollow shell containing a mounting element from which an inertial mass is suspended by a relatively stiff suspension. The mounting element typically has a mass several times (often 10 or more) greater than that of the inertial mass. The inertial mass has four upwardly extending pins arranged in a cruciform fashion which engage piezoelectric elements which detect wobble of the inertial mass relative to the mounting element. During construction, screw threaded adjusters are used to adjust the force acting between the inertial mass and the piezoelectric elements. Once the screw threaded adjusters have been set, a canister is rigidly fastened to the underside of the mounting element so as to enclose the inertial mass and oil may be introduced into the canister. Furthermore, an `O` ring seal is provided between the inertial mass and the canister. This arrangement is then sealed within a waterproof housing. The known sonobuoy has a relatively complex construction.
Furthermore, a pressure wave impinging upon the surface of the sonobuoy is required to accelerate both the waterproof housing and the mounting element in order to induce relative motion of the mounting element and the inertial mass.
According to the present invention, there is provided a DIFAR sensor, comprising: an inertial mass; a sensing element comprising a wall portion enclosing a volume and upon which a surrounding medium exerts a pressure and which undergoes displacement in response to an acoustic pressure wave acting thereon; and sensors for sensing motion of the sensor element along two mutually orthogonal directions, in which the mass of the sensing element is less than the mass of the inertial mass.
Preferably, the mass of the inertial mass is more than ten times that of the sensing element.
Preferably, the DIFAR sensor is generally cylindrical and the wall portion is in the form of a hollow cylindrical wall coaxially mounted with the inertial mass.
The sensing element may include an integrally formed end cap, thereby effectively forming a sensing dome. Alternatively, the sensing a element may comprise an annular ring located between opposing sensor end portions which cooperate to form the inertial mass.
Advantageously, the sensing element is in floating contact with the inertial mass. The sensing element may be connected to the inertial mass by an elastomeric element which serves to urge the sensing element towards a predetermined rest position with respect to the inertial mass, but which also allows limited relative movement between the sensing element and the inertial mass. Advantageously, the elastomeric element forms a fluid-tight seal between the sensing element and the inertial mass.
Preferably, the sensing element carries radially inwardly facing projections which are arranged to cooperate with the sensors. The sensors may, for example, be strain gauges or displacement sensors. The projections may carry adjustors, such as screw threaded elements, whereby the force exerted on each sensor by the respective projection can be adjusted whilst the sensing element is at its rest position. Advantageously, the adjustors can be adjusted via access ports formed in the sensing element such that the adjustments can be made once the DIFAR sensor has been assembled. This has significant advantages compared with the manufacture of know DIFAR sensors, wherein such adjustments are made before the assembly of the sensor is completed.
Alternatively, the relative movement of the sensing element with respect to the inertial mass may be sensed in a non-contacting manner. Optical, electrical or magnetic non-conta
REFERENCES:
patent: 3739202 (1973-06-01), Cady
patent: 3803546 (1974-04-01), Leon
patent: 4326275 (1982-04-01), Butler
patent: 4928263 (1990-05-01), Armstrong et al.
Buckingham David Edwin James
Delany John Lionel
Pihulic Daniel T.
Ultra Electronics Limited
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