GB2218298A - An ultra-sonic pulse-echo ranging device - Google Patents

Abstract

An ultra-sonic pulse-echo range-finding device which is activated when the reverse gear of a vehicle is engaged is intended to prevent accidents caused by the driver backing into things he cannot see. The assembly is made waterproof by enclosing the transducers used in a housing, the apertures in which are covered by a waterproof non-woven web material. The sensors, which are fitted to the rear of the vehicle are connected by cable to a control box. This may be mounted on the rear, near the transducer housings or inside the vehicle. On reversing the device will emit a series of sound pulses, the rate of repetition will increase as the vehicle approaches an object until at close range a continuous tone sounds from a loud speaker, which is usually situated in the cab. In this way the driver is alerted to the presence of any obstacles. <IMAGE>

Description

Improvements relating to the mounting of microphones and ultra-sonic transducers in wet environments.

I, Anthony David Hexes., + Digicom Communications, Unit 7 Highfields Science ParK, University Boulevard, Nottingham, England, a British Sub ject, do hereby declare the invention, for which I pray that a Patent may be granted to me, and the method by which it 15 t be performed, to be particularly described in and by the following statement : The invention relates to the use of microphones and ultra-sonic transducers in wet environments. Fulse-echo sonar systems using ultra-sonics are finding increasing application as vehicle reversing aids.The transducers used in such systems must continue to work in the rain and not be disabled by hose~pipe cleaning of the vehicle. Fully water-pr-oof transducers e > isti they have all their electrical components sealed within o metal can. Un+ortunately, these water-prcof transducers are consi derabl y less sensitive than their cheaper non-water-proof equivalents.

Non -water -proo+ transducers may be rendered water-proof using a tightly stretched plastic membrane. The amount of attenuation caused by such a membrane is a +junction of distance between the active elements of the transducer and the membrane. Even when optimally positioned the resultant sensitiXvity leaves much to be desired.

Clearly what is required is a material which is both transparent to sound and yet water-proo+.

Open pore +oam is transparent to sound; it is widely used for microphone wind shields. It is shower-proo+; ordinary rain droplets do not possess sufficient energy to penetrate provided the pore size is small; ie. of the order of l poresiinch. This ability to withstand rain is enhanced if the material is treated with one of the commonly available water repellent agents. However, even in its treated form the open pore +oam becomes water-logged when sprayed +rom a hose-pipe.

n alternative solution, and the one which forms the basis of this application, involves the use of a class of materials called nonwoven webs. Such material is used on the underside of vehicle mud flaps to reduce spray. One product made for this purpose is in fact called 'Spray Breaker'. Nonwoven webs are almost completely transparent to sound. Rain water is not retained because of the relatively large voids within the material. If a sheet of the material is supported vertically and sprayed by a horizontally mounted high pressure hose the water passes straight though. However the water simply runs down the back surface having lost all its horizontal momentum.Provided one leaves a suf f i ci ent gap and provided adequate drainage is allowed, standard non-water-proof ultra-sonic transducers, or indeed microphones, may be mounted behind such a sheet without any risk of there getting wet.

Figure 1, by way of an example only, shows the design of an ultra-sonic transducer housing which embodies these principles. In this example the transducers are mounted vertically at the focus of a parabolic reflector; water which enters the housing as a result of hose-pipe cleaning does not have enough momentum to climb up the parabola. The cavity is self-draining in that the water simply runs back out through the nonwoven web at the bottom of the parabola. 1 and 2 are transducers, one a transmitter and other a receiver. They are mounted in a closed pore material such as plastic, shaped so as to provide both the parabola (5) and a baffle between the two transducers (7) to reduce cross-talk. 4 is a thin (approximately 5 mm.) layer of nonwoven web.

Claims (3)

CLAIMS What I claim 1S:

1) A novel use of nonwoven web in a housing for standard non-water-proof microphones and/or elltra-sonic transducers thereby enabling their use in a wet environment without a degradation of their acousti c performance

2) An apparatus as claimed in 1) in which the space between the nonwoven web and the microphones or transducers is sufficiently large to enable adequate water drainage.

3) A microphone transducer mounting substantially as hereinbefore described with reference to and illustrated ln the accompanying drawing.