Design of Bimorph Sensor Utilizing Piezoelectric Effect for Wide Range of Mass Measurement

This paper presents the design of sensor utilizing the piezoelectric effect to measure a wide range of mass. We aimed for a measurement range of 1g to 10kg. As a sensor structure for this, Piezoelectric vibrators are attached on both sides of a plate. First, when one of the vibrators is driven by the resonant frequency, it produces a primary mode vibration of the disk. Next, another piezoelectric vibrator follows the vibration so as to generate a voltage. For measurement, this sensor utilizes changes in vibration amplitude. When a weight is placed, the resonant frequency of the sensor changes. However, since the input frequency is kept constant, so the voltage amplitude decreases. In addition, in this study, the method of not placing a weight directly on the piezoelectric element has been shown to reduce the amount of decrease in vibration amplitude. This is done to increase the threshold of the mass where the voltage does not change because the output voltage and the mass have a non-linear relationship in order to extend the measurement range. Regarding the decrease in amplitude, previous studies have shown that the larger the contact area between the elastic body that deforms in response to force and the sensor, the smaller the vibration amplitude of the sensor. Therefore, in order to extend the measurement range, we proposed a method that does not directly apply a load to the piezoelectric element and a stack sensor that uses an elastic body. Specifically, the stack sensor has an elastic body arranged in a portion not on the piezoelectric element of the sensor, and the elastic body has a structure in which the contact area increases according to the weight in order to delay the saturation of the output voltage. As a result of constructing a stacked sensor by configuring these detection elements, the range of the stacked sensor was 1 g to 1kg.