GB2209602A

GB2209602A - Phased arrays of ultrasonic emitters used with a mobile receiver

Info

Publication number: GB2209602A
Application number: GB8721136A
Authority: GB
Inventors: Michael Owen
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-09-09
Filing date: 1987-09-09
Publication date: 1989-05-17
Also published as: GB8721136D0

Abstract

Points, loci and surfaces can be projected in space by sensing the cancellation of polyphasally displaced signals propagated in a sonic medium, emitted from known reference points. In one arrangement an array of four ultrasonic emitters are positioned, one emitter at each corner of an equilateral tetrahedron and each emitter emits signals 90 DEG out of phase from those of the next emitter. A point is then defined at the centre of the array where a hand-held sensor indicates a null output. The phased cancelling signals are derived from a common reference signal. In another arrangement a line is defined from a triangular array of three emitters, each emitting 120 DEG from the next and a plane may be defined by two emitters, 180 DEG out of phase.

Description

A PHASOR SUMMATION TECHNIOUE FOR IDENTIFYING SPATIAL PROJECTIONS This invention relates to the identification of spatial projections.

The measurement, for example, of a line or plane presents many problems. Traditionally a device such as a theodolite has been used. The conventional theodolite however requires two operators and is limited to the identification of a point along a proscribed line. The plotting of a plane requires a minimum of two settings.

This invention presents a technique which allows the definition of points, loci, and surfaces between an emitter device and a physically separated sensor device. The sensor device provides an output to indicate when positional correspondence with the point, locus or surface is achieved. The emitter device provides multiple sources of physically displaced 'cancellation' signals, typically ultra-sound. Although physically displaced, in order to generate these 'cancellation' signals, all sources are supplied with a common constant frequency 'reference' signal which will not interfere with the 'cancellation' signals, or a means cf deriving such at each source location from a common external stimulus. From the 'reference' signal each separate source derives a 'cancellation' signal, each having a common frequency but with possible variations in phase and amplitude.These signals may use a carrier to improve the propagation characteristics. The required phase displacements and amplitude differences for a given projection are a function of the physical separation of the sources. The criterion for detection of the spatial projection requires that the phasor sum of all the 'cancellation' signals produces a minimum.

The sensor device detects the derivative of the sum of the cancellation signal amplitudes with respect to spatial position by monitoring the signal strengths in the location of the projection under consideration.

specific embodiement of the invention will now be described by way of example. Three cases are described.

In common to each case, the velocity of sound is assumed to be 330 meters per second. fi carrier frequency of 40 kHz modulated by a constant frequency of 3.3 kHz is used for each of the sources within the emitter. For phasor calculation purposes therefore, a distance of 0.1 meters is equivalent to 360 degrees.

The sensor is a single ultra-sonic detector which feeds a demodulator coupled to a display via an amplification device. This is a hand held unit, which, by observation of the display whilst moving in the vicinity of interest, will indicate a minimum reading at the required location.

In the first case the emitter consists of four ultra-sonic sources, each placed at the apex of an equilateral tetrahedron.

Calculation requires that each source is phase displaced from the next by 90 degrees. R point is then defined at the geometric centre of the tetrahedron, which, by using the sensor, will indicate a resultant signal of zero.

In the second case the emitter consists of three ultra-sonic sources, each placed at the apex of an equilateral triangle.

Calculation requires that each source is phase displaced from the next by 120 degrees. n line is then defined which is perpendicuar to the plane of the triangle, and passes through its geometric centre. Use of the sensor will indicate a resultant signal of zero along this line.

In the third case the emitter consists of two ultra-sonic sources, each placed at the at known points in space. Calculation requires that each source is phase displaced from the next by 180 degrees. fi plane is then defined which is perpendicuar to the line joining the sources, and which is equidistant from them. Use of the sensor will indicate a resultant signal of zero along this plane.

Claims

CLAIM

n technique allowing the definition of points, loci, and surfaces between an emitter device and a physically separated sensor device. The sensor device provides an output to indicate when positional correspondence with the point, locus or surface is achieved. The emitter device provides multiple sources of physically displaced 'cancellation' signals, typically ultrasound. Although physically displaced, in order to generate these 'cancellation' signals, all sources are supplied with a common constant frequency 'reference' signal which will not interfere with the 'cancellation' signals, or a means of deriving such at each source location from a common external stimulus. From the 'reference' signal each separate source derives a 'cancellation' signal, each having a common frequency but with possible variations in phase and amplitude. These signals may use a carrier to improve the propagation characteristics. The required phase displacements and amplitude differences for a given projection are a function of the physical separation of the sources. The criterion for detection of the spatial projection requires that the phasor sum of all the 'cancellation' signals produces a minimum.

The sensor device detects the derivative of the sum of the 'cancellation' signal amplitudes with respect to spatial position by monitoring the signal strengths in the location of the projection under consideration.