GB2180935A

GB2180935A - Sonic range and bearing finder

Info

Publication number: GB2180935A
Application number: GB08523778A
Authority: GB
Inventors: Robert James Hodges; Francis Giles Overbury; Norman William Tester
Original assignee: STC PLC
Current assignee: STC PLC
Priority date: 1985-09-26
Filing date: 1985-09-26
Publication date: 1987-04-08

Abstract

A sonic range-finder uses as its responsive elements a ring of outwardly-facing microphones (a, b, c), which respond to sound from a target (1). If the range-finder is active it has a transmitter (2), which emits ultrasonic pulses at, for instance, one per half-second, in broadcast manner. The pulses reflected from the target are detected by two or more microphones and the relative responses indicate the range and direction of the target. If the range-finder is passive, operation is the same, except that it relies on sound from the target. The microphone array is a small (e.g. 60 cm in diameter) circular array of outwardly facing electret microphones stretched onto a printed circuit band and secured to a cylindrical member. <IMAGE>

Description

SPECIFICATION Sonic range finder This invention relates to sonic range-finders.

According to the invention there is provided a sonic range-finderwhich includes a numberofindi- vidual microphones arranged in a circle and responsive to incident sound from outside the circle, wherein sound which reaches the range-finderfrom a target is responded to by a plurality of said microphones, and wherein an assessment of the parameters ofthe responses ofthe microphones gives indications as to the distance of the targetfrom the range4inderand the direction ofthattarget.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which Figure 1, which is not to scale, shows a range-finding system based on a microphone phase detector array operating at ultrasonic frequencies, and Figure 2 shows schematically a cross-section and front view of two ofthe microphones ofthe array of Figure 1.

Figure lisa simplified representation of a phased etector array which uses microphones, usable to determine the range and position of a passing (orindeed stationary) target 1 .For ease of explanation it is assumed thatthe array is stationary. Two basic modes of operation are possible, active, in which case the array emits a signal which is reflected bythe target and detected, or passive, in which case the target generatesthe detected signal.

The array shown in the drawing is an active array, with a transmitter 2 at its centre. In the arrangement shown the transmitter emits a supersonic signal at intervals, e.g. every half-second. This signal as reflected bythetarget is detected by at leastthree microphonesa, b, c;these microphones, like all the microphones used, are directional and have polardiagrams similartothose indicated by broken lines. The relative phases or time delays of the signals reflected by the target are electronically processed to provide bearing and distance information. The times of emits sion ofthesignals from the transmitter 1 can be taken into account in the processing.

The transmitter produces an omni-directional signal, and the microphone array is scanned electronically to provide a 360" coverage.

A passive array, or an active array operating in the passive mode, relies on thetargetomitting a sonic, normallysuspersonic, signal, which must be ofsuf- ficient constancy in terms of frequency and phase during the detection and phase comparison time period to obtain the required accuracy.

A convenient microphone array, see Figure 2, uses electret microphones. The array, which as can be seen from Figure 1, is circular in its final form, isstret- ched around a circular body. It comprises a film 3 of electret material which has a metallisation 4 on one side. Th is forms a common electrical connection, and is clamped by a plastics strip 5 to a plastics printed circuit band 6. The strip 5 has holes such as 7, each ofwhich defines one of the microphones. The printed circuit board has circular metallic areas such as 8, each of which is roughened or patterned to form cavities into which the electret material may be def lected by incoming pressure waves.Each ofthese metallic areas forms the other contact of one of the microphones, and each has an etched track such as 9 in the printed circuit board to provide connection to the processing means. Protective films (not shown) are provided to protect the plastics strip from the effects of moisture.

It should be noted thatthe electret material hasto be stretched before clamping.

Polarisation ofthe diaphragm is effected after metallisation of the appropriate length of strip, which in a typical array is about two feet (60 cm) long, with dia phragms, i.e. individual microphones placed art a minimum pitch of about half an inch (1.25 cm).

Thewholestrip-likearraythus produced is, in the final assembly, secured to the cylindrical support member 10, which also supportsthesupersonic transmitter.

1. Asonic range-finderwhich includes a number of individual microphones arranged in a circle and responsiveto incident sound from outsidethe circle, wherein sound which reaches the range-finderfrom a target is responded to by a plurality of said microphones, and wherein an assessment of the parameters of the responses of the microphones gives indications as to the distance of the target from the range-finder and the direction ofthattarget.

2. A sonic range-finder as claimed in claim 1, in which the range-finder is passive, being responsive to sonic signals emitted from the targets.

3. Asonic range-finder as claimed in claim 1,in which the range-finder is active and is provided with its own transmitter located at the centre ofthe array, and in which the transmitter emits its signals omnidirectionally.

4. Asonic range-finder, which includes a number of individual microphones arranged in a circle and responsiveto incidentsupersonic sound from out- side the circle, and a supersonic transmitter located at the centre of the circle, which transmitter emits its signals omnidirectionallyand in pulsed form, wherein sound which reaches the range-finder after reflection from a target is responded to by a plurality of said microphones, and where as assessment of the parameters ofthe response of the microphones to the supersonic sound as reflected from a said target gives indications as to the distance of the target from the range-finder and the directions ofthat target.

5. A sonic range-finder as claimed in any one of the preceding claims, and in which the microphones are electret microphones.

6. A sonic range-finder as claimed in claim 5, in which the electret microphones are constructed as a unitary array which includes a strip of electret material metallised on one face to provide a common contactforall ofthemicrophones,aflexible printed circuit board adjacent the other face of the electret strip and having localised material regions each from the other side of a said microphone, each such region being roughened or patterned, and a plastics clam

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Sonic range finder This invention relates to sonic range-finders. According to the invention there is provided a sonic range-finderwhich includes a numberofindi- vidual microphones arranged in a circle and responsive to incident sound from outside the circle, wherein sound which reaches the range-finderfrom a target is responded to by a plurality of said microphones, and wherein an assessment of the parameters ofthe responses ofthe microphones gives indications as to the distance of the targetfrom the range4inderand the direction ofthattarget. An embodiment of the invention will now be described with reference to the accompanying drawings, in which Figure 1, which is not to scale, shows a range-finding system based on a microphone phase detector array operating at ultrasonic frequencies, and Figure 2 shows schematically a cross-section and front view of two ofthe microphones ofthe array of Figure 1. Figure lisa simplified representation of a phased etector array which uses microphones, usable to determine the range and position of a passing (orindeed stationary) target 1 .For ease of explanation it is assumed thatthe array is stationary. Two basic modes of operation are possible, active, in which case the array emits a signal which is reflected bythe target and detected, or passive, in which case the target generatesthe detected signal. The array shown in the drawing is an active array, with a transmitter 2 at its centre. In the arrangement shown the transmitter emits a supersonic signal at intervals, e.g. every half-second. This signal as reflected bythetarget is detected by at leastthree microphonesa, b, c;these microphones, like all the microphones used, are directional and have polardiagrams similartothose indicated by broken lines. The relative phases or time delays of the signals reflected by the target are electronically processed to provide bearing and distance information. The times of emits sion ofthesignals from the transmitter 1 can be taken into account in the processing. The transmitter produces an omni-directional signal, and the microphone array is scanned electronically to provide a 360" coverage. A passive array, or an active array operating in the passive mode, relies on thetargetomitting a sonic, normallysuspersonic, signal, which must be ofsuf- ficient constancy in terms of frequency and phase during the detection and phase comparison time period to obtain the required accuracy. A convenient microphone array, see Figure 2, uses electret microphones. The array, which as can be seen from Figure 1, is circular in its final form, isstret- ched around a circular body. It comprises a film 3 of electret material which has a metallisation 4 on one side. Th is forms a common electrical connection, and is clamped by a plastics strip 5 to a plastics printed circuit band 6. The strip 5 has holes such as 7, each ofwhich defines one of the microphones. The printed circuit board has circular metallic areas such as 8, each of which is roughened or patterned to form cavities into which the electret material may be def lected by incoming pressure waves.Each ofthese metallic areas forms the other contact of one of the microphones, and each has an etched track such as 9 in the printed circuit board to provide connection to the processing means. Protective films (not shown) are provided to protect the plastics strip from the effects of moisture. It should be noted thatthe electret material hasto be stretched before clamping. Polarisation ofthe diaphragm is effected after metallisation of the appropriate length of strip, which in a typical array is about two feet (60 cm) long, with dia phragms, i.e. individual microphones placed art a minimum pitch of about half an inch (1.25 cm). Thewholestrip-likearraythus produced is, in the final assembly, secured to the cylindrical support member 10, which also supportsthesupersonic transmitter. CLAIMS

6. A sonic range-finder as claimed in claim 5, in which the electret microphones are constructed as a unitary array which includes a strip of electret material metallised on one face to provide a common contactforall ofthemicrophones,aflexible printed circuit board adjacent the other face of the electret strip and having localised material regions each from the other side of a said microphone, each such region being roughened or patterned, and a plastics clam ping band overlaying the metallisation and having holesforeach said microphone.

7. A sonic range-finder as claimed in claim 6, in which the strip of electret material has a length ofthe order of 60 cms, with the microphones located at patches of about 12.5 mm.

8. Asonic range-finder, substantially as described with reference to the accompanying drawings.