Design and evaluation of a contactless piezoelectric keyboard using polyvinylidene fluoride as the active element

A contactless piezoelectric keyboard using biaxially stretched polyvinylidene fluoride as the active element is described. Pushbutton output is shown to correlate well with an average piezoelectric stress constant, d, which can be easily measured using a slightly modified visco-elastometer. This measurement can be used to characterize PVDF films and to predict the effect of metallization thickness on pushbutton output. The particular keyboard structure is shown to have a lifetime (at room temperature) of at least 15 million pushes. Keyboard output was measured over a −30°C to +60°C temperature range and these results are shown.