Measuring and testing – Fluid pressure gauge – Vibration type
Patent
1996-11-18
1998-07-14
Chilcot, Richard
Measuring and testing
Fluid pressure gauge
Vibration type
73649, 73592, G01L 1100
Patent
active
057807450
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The technical scope of the present invention is that of acoustic pressure sensors sensitive to the amplitude and direction of the incident sound wave front.
BACKGROUND OF THE INVENTION
Conventional acoustic sensors, such as pressure or pressure gradient microphones, supply analogous voltage (scalar) whose strength is the result of the product of the contributions of each source of sound present in the detection area under consideration.
A microphone always comprises a mechanical-acoustic part which ensures the conversion of the acoustic energy into mechanical energy and an electromagnetic part which ensures the conversion of the mechanical energy into electrical energy.
According to the pass-range required and the operational environment (air, water), the technologies employed are very varied: dynamic microphone, capacitor microphone, of the electric type for example, carbon microphone, crystal microphone, stress gauge microphone, polyvinyldifluorate (crystal) microphone.
There are two distinct types of sensors: ambient pressure, and pressure wave at two points close together.
The direction of the source of sound is difficult to determine using a scalar sensor. To determine the direction, a mechanical scan is generally carried out with a directional microphone. The disadvantage of this mode of operation lies in the non-observation of certain phenomena since the sensor is only receptive in a single direction at any one time.
According to another process, a certain number of microphones are grouped together in a given geometric shape and the signals received are utilized by processes implementing phase shifts between signals. Understandably, the electronics required for this process are substantial.
SUMMARY OF THE INVENTION
The aim of the present invention is to supply an acoustic pressure gradient sensor both amplitudesensitive and direction-sensitive to external fields to which it is applied.
A further aim of the present invention is to propose a sensor providing information related to all the sources of sound in the surrounding space.
The subject of the invention is thus an acoustic pressure gradient sensor able to detect a sound signal, characterised in that it comprises: sensitivity to the pressure gradient, intended to transform the stresses into electrical impulses, and
According to one embodiment of the invention, the electromechanical means is formed of two printed circuits incorporating low noise amplifiers separated by beams marking out a triangular structure, each of which carries a gauge to measure the stresses, and the mechanical-acoustic means is formed of a sphere made of a relatively thin synthetic material, which has a diameter approximately ten times less than that of the wave length of the incident sound radiation.
The sensor comprises six beams marking out the triangular structure, producing six electric voltages containing the directional data of the source of sound.
Generally speaking, the sphere is for example bonded in a circular recess on one of the printed circuits, preferably the upper printed circuit, the centre of said recess matching the centre of gravity of the points of contact between the beams and the upper printed circuit, the electromechanical means being fastened for example on a metallic support by means of braces, the assembly being acoustically insulated by a sheet of synthetic foam. The stress gauges are for example formed of bars of silicon and the beams of ceramic with metallized ends.
A first advantage of the present invention lies in the fact that the sensor is omnidirectionally sensitive to pressure gradients.
Another advantage lies in the fact that a pressure wave reaching the sphere produces a distribution of the pressure field over the surface of the sphere such that the resultant force produces a vibration in the centre of gravity of the latter, characteristic of the direction of the incident wave.
BRIEF DESCRIPTION OF THE DRAWINGS
Other characteristics and advantages will become apparent from reading the additional descripti
REFERENCES:
patent: 3732535 (1973-05-01), Ehrlich
patent: 4368525 (1983-01-01), Obara et al.
patent: 4751848 (1988-06-01), Miyamoto
patent: 5231866 (1993-08-01), Peacock
patent: 5452264 (1995-09-01), Holroyd
Chilcot Richard
Giat Industries
Noori Max H.
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