Semi-quantitative piezoelectric activity testing in polymer layers

A technique has been developed for measuring output voltages in piezopolymer layers such as polyvinylidene fluoride (PVDF). This technique can be used for comparing piezoelectric polymer layer responses and to investigate how changes in manufacture can affect the output voltage of the layers. The method can quickly measure the output voltages as response to pressure waves in a large number of samples and the result of each sample can be seen immediately. The test equipment consists of an ultrasound transmitter with a built in time delay layer with a metal contact under it and a Perspex layer with a metal contact placed below the transmitter. Both the delay layer and receiver have fixed sized metal contacts. The piezoelectric polymer layer to be tested is placed and clamped between the metal contacts on the delay layer on transmitter and the Perspex layer. An ultrasonic pulse wave from the transmitter deforms the clamped piezoelectric polymer sample with a time delay, which then produces a voltage pulse that can be measured by connecting an oscilloscope to the metal contacts. To ensure that the testing is reproducible for all the samples, the area of the metal layers are of fixed size and the tested sample is clamped between the metal layers with a fixed pressure as it is forced together with two contraction springs. A simple lever arrangement enables the sample to be clamped with great ease. The technique must be seen as semi-quantitative as the values of the output voltage would be different if the area of the metal contacts in the transducers were different. The same applies for the pressure caused by the springs to clamp the sample. These variables along with several others have not been optimised for the transducers to produce the highest output voltage, but this has been sacrificed to make the tester both easy and quick to use. As this measuring technique is reproducible for all the samples, it works very well for comparing layers. When developing ultrasonic layer fabrication techniques it is very useful to see if a given change improves the output voltage.