Communications: electrical – Audible indication – Piezoelectric
Patent
1997-10-06
2000-12-26
Hofsass, Jeffery A.
Communications: electrical
Audible indication
Piezoelectric
3403841, 3403881, 381190, 381191, 381202, G08B 310
Patent
active
061666246
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention concerns sound horns, especially for the equipment of motor vehicles and more particularly concerns a piezoelectric sound horn.
BACKGROUND OF THE INVENTION
Sound horns currently equipping motor vehicles make use of the vibration of a membrane under the effect of an electromagnetic system. However, these electromagnetic sound horns, which are used on a world-wide scale, do have the drawback of being heavy (about 250 g) and consume a large amount of electricity (between 4 and 8 amps under a serviceable voltage of 12 V).
The aim of the present invention is to mitigate the drawbacks mentioned above of electromagnetic sound horns and to this effect concerns the embodiment of a piezoelectric horn, that is a sound horn using the vibration of a piezoelectric membrane.
This effect known as the <<piezoelectric effect >> is already known by which electrical charges appearing on the faces of certain crystals (quartz in particular) when the latter are subjected to mechanical stresses. As these crystals are generally nonconducting, the charges appearing on their faces give rise to electric voltages, possibly extremely high, and these electric voltages are picked up by metallic electrodes on the faces of the crystals.
This piezoelectric effect is reversible. If an electric voltage is applied it, this results in this crystal being mechanically deformed.
The piezoelectric effect is characteristic of the order structures of the material (crystals), but mono-crystaline materials are rare and scarcely suitable in use. However, certain ceramics have a crystalline type structure lending themselves also to the use of piezoelectric effects in consideration of a prior orientation of the molecules constituting the ceramic material. This orientation is obtained by applying for several seconds a high electric polarization field on the ceramic material, thus provoking the alignment of the molecules inside the ceramic material. On removal of the electric polarization field, the molecular orientation exists and gives rise to a piezoelectric phenomenon identical to the one observed in the monocrystals.
The polarized ceramics are much more suitable in use than the crystals and in fact are obtained in the desired shape by means of sintering at a high temperature and baking at more than 1000.degree. C.
So as to produce sounds with the aid of a piezoelectric ceramic material, it has already been suggested to make use of a piezoelectric sound membrane formed of a thin metallic disk on which a piezoelectric ceramic disk is glued. A counter-electrode constituted by conductive ink is laid on the free surface of the ceramic disk and polarization is effected so that, when an alternative voltage is applied to the ceramic disk, the latter dilates or contracts diametrically. As these diameter modifications are set on one of its faces by the metallic membrane, everything is bent inward in the way of a bimetallic strip alternately in one direction and then in another, thus producing a vibration corresponding to the frequency of the excitation voltage.
So as to effectively use the piezoelectric membrane, the latter is mounted in a suitable support, this mounting device taking a significant part on the sound emission of the membrane in modifying the resonance frequencies of the membrane and more generally the frequency response of the device.
It is also known that this frequency response is likely to be modified by the use of flat non-circular metallic structures (especially rectangles) used instead of the thin metallic disk or in conjunction with the latter.
The piezoelectric membranes currently available on the market are solely used for low sound level applications. These applications mainly concern telephony, low level sound reproduction on portable devices, and also buzzers for industrial equipment and instrumentation, in particular motor vehicle buzzers (warning of neglecting to turn off the headlights, one door having remained open or an engine defect). The only applications with a sound
REFERENCES:
patent: 4767959 (1988-08-01), Sakakibara et al.
Nishiyama et al., "Piezoelectric Sound Component Used in Broad Range of Applications", JEE, Aug. 1988, Aug. 1990.
575 Nachrichtentechnik Elektronic 40 (1990) No. 12, Berlin.
Drucker William A.
Hofsass Jeffery A.
Mannava Ashok
Societe de Composants Electriques
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