Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-08-01
2004-08-17
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S365000
Reexamination Certificate
active
06777856
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to a piezoelectric crystal with transversal effect. Such piezoelectric crystals have changes or reactions in different planes to applied forces. Those changes generally occur transverse to the direction of the applied force.
Piezoelectric crystals are employed in various sensors for measuring forces, pressures, accelerations, strains and moments. For this purpose, crystals with transversal effect are cut into thin plates or rods, for example. For metrological uses, these thin plates are exposed typically to a pressure on the small end surfaces of the plate, causing an electrical charge to appear on the two large side surfaces. By placing an electrically conductive layer on the two side surfaces, which however have no electrical contact with each other, this charge is measured with an appropriate device in the sensor so that information about the pressure is obtained and may be transmitted further. Such sensors are well known.
What is crucial, however, is that the crystal is fitted vertically and centered on the axis of the sensor. Any slight tilt will result in a false measurement or fracture of the crystal under the influence of the forces occurring subsequently. A contact of the crystal to the edge of the sensor may lead to a short circuit or hysteresis.
Since the sensitivity of the crystal is proportional to the ratio of the charge pickup surface to the pressure surface, these conventional crystal plates are very thin. Hence the handling, especially the centering and aligning in the sensor, are very difficult and laborious.
Often the sensor is fitted with centering aids which hold the crystal in position. However the various materials of these centering aids do not tolerate very high temperatures. Consequently the application areas of the known sensors as a whole are limited to a lower maximum temperature.
The present invention provides for a piezoelectric crystal which can be fitted easily into a sensor without laborious centering and aligning, and without restriction to a lower temperature range. Furthermore, the crystal of the present invention can be manufactured in large quantities, at low cost and fully automatically.
The present invention, then, is a piezoelectric crystal with transversal effect that has at least one plate and at least one base at an angle to the at least one plate. The at least one base projects laterally beyond a thickness of the at least one plate on at least one side of the at least one plate. An embodiment of the present invention may have two such identical crystals.
The present invention also includes a sensor for detecting one or more of force, pressure, acceleration, moments and strain signals by using at least one of the piezoelectric crystals with transversal effect discussed above.
The present invention also includes a method for producing the piezoelectric crystals with transversal effect.
Other aspects, advantages and novel features of the present invention will become apparent from the following detail description of the invention when considered in conjunction with the accompanying drawings.
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Brechbühl Stefan
Sommer Roland
Barnes & Thornburg
Dougherty Thomas M.
Kistler Holding AG
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