The Research On PVDF Dynamic Response And Design Of Keyboard Application

The PVDF film has the special characteristics of dielectric effect, piezoelectric effect and thermoelectric effect. Compared with the conventional piezoelectric material, the PVDF film has the advantages of wide frequency response, vast dynamic range, high sensitivity as electromechanical film, high intensity of mechanical strength, low acoustic impedance and so on. It can meet the demand of some special sensors and actuators. It also provides a range of sensor applications that have been successfully developed in recent years, for example, industrial control, instrumentation, underwater acoustic measurement, medical field, structural and system health monitoring.The PVDF film's basic principle and working mode were analyzed based on the piezoelectric effect and piezoelectric equations of piezoelectric material. This paper discussed the different piezoelectric equations when the PVDF film worked different working mode. the equivalent circuits of PVDF and the measurement circuit were introduced. By applying a sine wave stimulate signal on beam of uniform strength and recording the output waveform of PVDF sensor and stain gauge, the low frequency response of PVDF sensor was analyzed. it is concluded in that the PVDF sensor substantially overcame stain gauge in sensitivity, response time and noise level. The comparison between outputs of PVDF film and accelerometer was made and the high frequency response characteristic was acquired. The result of experiment showed that the PVDF film is typically high mechanical strength and impact resistance.The PVDF film was used as EMF to design a contactless keyboard according to its high frequency response. The structure of keyboard was comprised of a PCB base with molded recesses, single PVDF film and an electrode layer. Comparators were added to detect the status of pushbuttons. Experiments on a customized 4±2 keyboard was carried out, and the adjacent key interference as well as the interference between key-area and non-key-area were measured. The results proved the capability of the PVDF sensor for the lightweight and tiny keyboard. It can to some digree avoid the shortcomings existed in the traditional keyboard like short usage, reliability and complex structure.