A transducer assembly for a proximity sensor which com prises an elongated polymer piezoelectric film (16). The film is supported as an elongated series of arcuate segments which are curved in the same direction and have the same radius of curvature. Electrodes (18) on both sides of the piezoelectric film form opposed pairs, each pair being asso ciated with a respective arcuate segment. The electrodes are utilized for applying a varying electric field across the thickness of the film to cause an ultrasonic acoustic wave to be radiated from the film.
An ultrasonic tyre sensor is propased which determines the wheel load and the vertical deflection of the tyre. The sensor is mounted on the base of the wheel rim inside the tyre and measures continuously the distance to the opposite inner wall of the tyre providing a highly tional information, e.g. tyre temperature or tyre-road con-significant information about the status of the tyre. Additact parameters can he extracted from a more detailed evaluation of the sensor signal.To demonstrate the feasibility of this novel approach, measurements were performed at different tyre pressures and wheel loads with a small 400 kHz ulmsonic distance sensor on a tyre testbed. The results for the vertical deflection and spring stiffness are in good agreement with those obtained with traditional off-line methods. This proves, that the ultrasonic tyre sensor principle can be used for continuously measuring the vertical t y~ deflection during cruising.
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