Thermal bimetallic materials are composite materials firmly combined by two or more layers of alloys with different linear expansion coefficients. The alloy layer with a larger expansion coefficient is called the active layer, and the alloy layer with a smaller expansion coefficient is called the passive layer. An intermediate layer for regulating resistance can be added between the active and passive layers. When the environmental temperature changes, due to the different expansion coefficients of the active and passive layers, bending or rotation will occur.