Communications – electrical: acoustic wave systems and devices – Distance or direction finding – With beam steering – scanning – or focussing
Reexamination Certificate
1999-01-28
2001-02-20
Lobo, Ian J. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Distance or direction finding
With beam steering, scanning, or focussing
C367S124000, C367S119000
Reexamination Certificate
active
06192006
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a device for and a method of determining the angle of incidence of a received signal by performing a vertical scanning operation using a generally cylindrical transducer, as well as to a scanning sonar employing such device and/or method.
Scanning sonars are widely used for detecting underwater objects. A scanning sonar employs a transducer having a generally cylindrical shape as shown in
FIG. 3
to detect underwater objects in all surrounding areas. Ultrasonic waves are radiated in all directions around the transducer and a vertically focused receiving beam, which is focused within a specified angle in a vertical plane to produce specific vertical directivity, is formed by summing signals reflected by the underwater objects and received by every vertical array, or column, of transducer elements with appropriate time delays inserted into the individual reflected signals. The receiving beam thus formed is rotated, as if a single column of transducer elements is mechanically rotated around the cylindrical shape, by switching the transducer elements from one vertical array to another around the transducer to scan the objects in all azimuthal directions. It is possible to control the downward-looking angle, or the tilt angle, of the receiving beam by varying the time delays applied to the individual transducer elements, whereby the scanning sonar can search out objects within a specific vertical sector area in all directions around the transducer.
In the conventional scanning sonar of the aforementioned construction, the receiving beam directed to a specific tilt angle is horizontally rotated around the transducer in each horizontal scanning cycle. Thus, if it is desired to detect vertically distributed objects, it is necessary to carry out successive horizontal scanning cycles while sequentially varying the tilt angle of the receiving beam in one scanning cycle after another.
Although the prior art discloses a transducer constructed in a spherical shape which can steer a receiving beam not only horizontally but also vertically, the spherically shaped transducer has such problems that it necessitates complex combinations of transducer elements for beam forming and its target detecting ability in horizontal scan mode, which is the most often used mode of operation, is inferior to that of the cylindrical transducer.
SUMMARY OF THE INVENTION
In view of the aforementioned problems of the prior art, it is an object of the invention to provide a device for and a method of determining the angles of incidence of a received signal that make it possible to vertically scan underwater objects using a transducer constructed of a plurality of transducer elements arranged in a cylindrical shape as well as a scanning sonar employing such device and/or method.
According to the invention, a device for determining the angle of incidence of an incident ultrasonic signal comprises an ultrasonic transducer constructed of a plurality of transducer elements which are arranged in multiple layers and columns forming as a whole a generally cylindrical shape, a horizontally focused beam former which sums signals received by the individual transducer elements of specific columns centered on a specified scan azimuth for each layer to generate horizontally focused beam signals which provide high horizontal directivity, a vertical scan signal former which forms a vertical scan signal by sequentially selecting and combining the horizontally focused beam signals from the uppermost layer to the lowermost layer, or from the lowermost layer to the uppermost layer, and an angle detector which detects the angle of incidence of the incident ultrasonic signal based on the amount of frequency shift of the vertical scan signal.
According to the invention, a method of determining the angle of incidence of an incident ultrasonic signal by using an ultrasonic transducer constructed of a plurality of transducer elements which are arranged in multiple layers and columns forming as a whole a generally cylindrical shape, the method comprising the steps of summing signals received by the individual transducer elements of specific columns centered on a specified scan azimuth for each layer to generate horizontally focused beam signals which provide high horizontal directivity, generating a vertical scan signal by sequentially selecting and combining the horizontally focused beam signals from the uppermost layer to the lowermost layer, or from the lowermost layer to the uppermost layer, and detecting the angle of incidence of the incident ultrasonic signal based on the amount of frequency shift of the vertical scan signal.
A scanning sonar of the invention comprises an ultrasonic transducer constructed of a plurality of transducer elements which are arranged in multiple layers and columns forming as a whole a generally cylindrical shape, a horizontally focused beam former which sums signals received by the individual transducer elements of specific columns centered on a specified scan azimuth for each layer to generate horizontally focused beam signals which provide high horizontal directivity, a vertical scan signal former which forms a vertical scan signal by sequentially selecting and combining the horizontally focused beam signals from the uppermost layer to the lowermost layer, or from the lowermost layer to the uppermost layer, and an angle detector which detects the angle of incidence of an incident ultrasonic signal based on the amount of frequency shift of the vertical scan signal, a vertically focused beam former which sums signals received by the individual transducer elements of each column to generate vertically focused beam signals which provide high vertical directivity, a horizontal scan signal former which forms a horizontal scan signal by sequentially selecting and combining the vertically focused beam signals derived from the individual columns around the transducer, and a signal generator which takes out a signal from a specified direction based on the amount of frequency shift of the horizontal scan signal, wherein the vertically focused beam former, the horizontal scan signal former and the signal generator are activated in horizontal scan mode, and the horizontally focused beam former, the vertical scan signal former and the angle detector are activated in vertical scan mode.
In one form of the invention, the angle detector and the signal generator of the aforementioned scanning sonar share a common correlator.
A principle applied to this invention is now briefly described with reference to
FIGS. 1A and 1B
. If a receiving transducer R is moving in a straight line with velocity v and a signal of frequency fs is incident on the receiving transducer R at the angle of incidence &agr; as shown in
FIG. 1A
, the apparent frequency f of the signal as it is received by the receiving transducer R differs from the actual frequency fs of the incident signal due to the Doppler effect. This can be expressed by
f
=(1+(
v/c
)sin &agr;)
fs
where c is the sound velocity. If the frequency fs of the incident signal is known, it is possible to calculate the angle of incidence &agr; by substituting the Doppler-shifted frequency f into the above equation.
While the receiving transducer R is physically moved in the example shown in
FIG. 1A
, a similar effect can be produced by using a phased array technique in which the incident signal is received by a transducer array whose individual elements are sequentially switched.
FIG. 1B
depicts an example of such phased array approach, in which a plurality of receiving transducer elements are arranged in a straight line at regular intervals d. Sequentially switching the transducer elements at a switching frequency s yields the same result as would be obtained by physically moving a single transducer element at a velocity v=d·s.
Based on the above principle, this invention provides means for vertical scanning (steering of an ultrasonic sounding beam in a specific vertical plane)
Fukuoka Itsuo
Hayashi Tatsuo
Iino Hiroshi
Ito Yasuo
Furuno Electric Company Limited
Lobo Ian J.
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