A piezoelectric transducer converts mechanical force into electrical output. This is made up of Quartz crystal which contains SiO2. Piezoelectric crystals are electrically neutral. The atoms inside the crystals in an unsymmetrical manner but their electric charges balanced

When the force is applied to stretch or bend it, an electric voltage is generated. If there is no stress, no charges are induced. When there is stress, positive charges are induced on one side and negative charges induced on the opposite side. Compression occurs in the crystal as the force is applied.