Communications – electrical: acoustic wave systems and devices – Echo systems – Distance or direction finding
Reexamination Certificate
2000-07-28
2002-09-03
Lobo, Ian J. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Echo systems
Distance or direction finding
C367S103000, C367S123000
Reexamination Certificate
active
06445646
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a signal processing method and a signal processing apparatus for use in such systems as communications equipment, sonar systems, ultrasonic diagnostic apparatus and ultrasonic flaw detectors. The invention also pertains to scanning sonars as well as to a sea bottom mapping sonar employing a crossed fan beam technique. A scanning sonar scans a wide range of directions by forming receiving beams in sequentially varying directions
The present invention will be explained hereinafter as embodied in a sea bottom mapping sonar which is a crossed fan beam type sonar system as a typical example of application of the invention.
A conventionally known crossed fan beam type bottom mapping sonar forms desired receiving beams by phasing echo signals individually received by 160 transducer elements by specific amounts and then combining the phased signals through an analog operation by using 160 mixers, for example.
Since the conventional bottom mapping sonar comprises a large number of transducer elements and receiving channels in its input stage, it has such problems that this sonar system inevitably becomes large-sized and its potential to achieve a high range resolution is more or less limited due to differences in the characteristics of analog circuits or their deterioration with the lapse of time.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a signal processing method and a signal processing apparatus applicable to such systems as communications equipment, sonar systems, ultrasonic diagnostic apparatus and ultrasonic flaw detectors whose circuit configuration is simplified by a time-division multiplexing technique.
Another object of the invention is to provide a crossed fan beam type bottom mapping or detecting sonar system using the signal processing method and the signal processing apparatus of the invention.
Another object of the invention is to provide a sonar system, in particular a scanning sonar, which scans a wide range of directions by forming receiving beams in sequentially varying directions using the signal processing method and the signal processing apparatus of the invention.
In one aspect of the invention, a signal processing method comprises the steps of receiving signals of a specific frequency f which is equal to 1/T where T is the period of the signals, sampling the signals at a specific first sampling time instant and at a sampling time instant (a+1/4)T after the first sampling time instant where a is 0 or an integer multiple of 0.5, and outputting data sampled at the sampling time instants as in-phase data and quadrature data of complex-valued sample data.
Preferably, the time interval of (a+1/4)T is smaller than half the recurrence interval of a point of the specific first sampling time instant.
In another aspect of the invention, a signal processing method comprises the steps of receiving signals of a specific frequency f which is equal to 1/T where T is the period of the signals, sampling the signals at a specific first sampling time instant, at a sampling time instant (n+1/4)T after the first sampling time instant, at a sampling time instant (n+1/2)T after the first sampling time instant and at a sampling time instant (n+3/4)T after the first sampling time instant to produce 0° sample data, 90° sample data, 180° sample data and 270° sample data respectively, where n is 0 or a positive integer, and outputting a value obtained by averaging the 0° sample data and the 180° sample data as in-phase data of complex-valued sample data and a value obtained by averaging the 90° sample data and the 270° sample data as quadrature data of the complex-valued sample data.
Preferably, the time interval of (n+1/4)T is smaller than one quarter of the recurrence interval of a point of the specific first sampling time instant.
In another aspect of the invention, a signal processing device comprises a plurality of signal input means, a plurality of multiplexers which multiplex signals entered from the signal input means into a smaller number of channels having output terminals than the number of the signal input means, wherein the multiplexers operate with synchronized switching timing, and a plurality of A/D converters respectively connected to the output terminals of the multiplexers which convert analog signals entered respectively and individually from the multiplexers into digital form, wherein the A/D converters operate with synchronized sampling timing.
In still another aspect of the invention, a signal processing device comprises a plurality of signal input means for inputting signals having a specific frequency, a plurality of multiplexers which multiplex the signals entered from the signal input means into a smaller number of channels having output terminals than the number of the signal input means, wherein the multiplexers operate with synchronized switching timing, a plurality of A/D converters respectively connected to the output terminals of the multiplexers which convert analog signals entered respectively and individually from the multiplexers into digital form, wherein the A/D converters operate with synchronized sampling timing, and a phase shifter which shifts the phases of individual sample data such that a specific phase relationship is established between the data sampled by the A/D converters.
In yet another aspect of the invention, a sonar system which emits an ultrasonic search pulse signal and receives echo signals by receiving beams formed successively and oriented in successively varying directions comprises a plurality of transducer elements for receiving echo signals of a specific frequency f which is equal to 1/T where T is the period of the echo signals, a plurality of multiplexers which multiplex signals entered from the transducer elements into a smaller number of channels than the number of the transducer elements, wherein the multiplexers operate with synchronized switching timing, a plurality of A/D converters which convert analog signals entered respectively and individually from the multiplexers into digital form, wherein the A/D converters operate with synchronized sampling timing and sample the analog signals at a specific first sampling time instant, at a sampling time instant (n+1/4)T after the first sampling time instant, at a sampling time instant (n+1/2)T after the first sampling time instant and at a sampling time instant (n+3/4)T after the first sampling time instant to produce 0° sample data, 90° sample data, 180° sample data and 270° sample data respectively, where n is 0 or a positive integer, outputting a value obtained by averaging the 0° sample data and the 180° sample data as in-phase data of complex-valued sample data and a value obtained by averaging the 90° sample data and the 270° sample data as quadrature data of the complex-valued sample data, a phase shifter shifts the phases of individual sample data such that a specific phase relationship is established between the complex-valued sample data derived from the individual transducer elements, and a matched filter for receiving the complex-valued sample data from the phase shifter and successively forming the receiving beams in different directions.
In yet another aspect of the invention, a sonar system which emits an ultrasonic search pulse signal and receives echo signals by receiving beams formed successively and oriented in successively varying directions comprises a plurality of transducer elements for receiving echo signals of a specific frequency, a plurality of multiplexers which multiplex signals entered from the transducer elements into a smaller number of channels than the number of the transducer elements, wherein the multiplexers operate with synchronized switching timing, a plurality of A/D converters which convert analog signals entered respectively and individually from the multiplexers into digital form, wherein the A/D converters operate with synchronized sampling timing and sample the analog signals for a plurality of w
Handa Minoru
Morimatsu Hideharu
Nishimori Yasushi
Watanabe Mitsuaki
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