4.8.1 Piezoelectric effect Quartz crystal is a commonly used material a quartz crystal has a shape of hexahedral structure with three mutually perpendicular axes as its crystal axes The longitudinal axis Z-Z is known as optical aXIs The axis X-X going through the edge of the hexahedron and being perpendicular to the optical axis is called electrical axIs The axis Y-y perpendicular to both the axis x X and the axis Z-Z is called mechanical axis• Quartz crystal is a commonly used material. A quartz crystal has a shape of hexahedral structure with three mutually perpendicular axes as its crystal axes ➢ The longitudinal axis Z-Z is known as optical axis ➢The axis X-X going through the edge of the hexahedron and being perpendicular to the optical axis is called electrical axis ➢ The axis Y-Y perpendicular to both the axis X￾X and the axis Z-Z is called mechanical axis 4.8.1 Piezoelectric effect