Mode of Operation of Piezoelectric Materials

Figure 11.3: Illustration of 33 and 31 mode of operations of piezoelectric material

Figure 11.3 illustrate two different modes in which piezoelectric material is generally used. Typically, piezoelectric material is used in 33 mode i.e. both the voltage and stress act in thickness direction. However, the material can also be operated in 31 mode, meaning that the voltage acts in the 3 direction (i.e. the material is poled in the thickness direction) and the mechanical stress / strain acts in direction 1. The most common type of 31 elements is bimorph in which two separate sheets are bonded together. As the element is subjected to bending, the top layer of the element is in tension and bottom layer is in compression or vice versa. If both the layers are poled in the same direction and electrodes are wired properly, the current produced by each layer will add. Bending elements with multiple layers can also be made with proper wiring for internal electrodes to improve the voltage to current ratio.