A New Sensor for Static and Dynamic Force Measurement

In this work an innovative sensor for the measurement of forces is presented. The sensor is a thin film (1 mm thickness) based on a “sandwich” structure composed of two sensing elements glued together: one layer is a capacitive film and the other is a piezoelectric film. Both the layers are sensitive to compression loads, but they are suitable for working in different frequency ranges. In fact, while the capacitive element is capable of measuring from DC up to about 400 Hz, on the contrary the piezoelectric film works in the high frequency range. The output of both the sensors are acquired and then filtered and processed in such a way as to achieve a unique signal. This sensor was developed in order to synthesise in a small and cheap device the capability to measure forces in a wide range of frequencies. The sensor is very small and can be used in a variety of problems and applications, also in the field of modal analysis. In particular, the very reduced thickness allows to insert such sensor even in composite materials in order to characterise loads and excitations, on the surface or between different components of a more complex system or within the structure in order to obtain a smart structure. The paper describes the structure of the sensor and of the adopted signal processing strategies. The metrological characterisation procedure is discussed (in particular for normal forces) and an application is shown.