a result of bending electrostatic charges form on the surfaces of the layers 2 and 3 with a magnitude directly proportional to the amount of tensile or compressive stress of the layers 2 and 3 the polarity of the electrostatic charges is dependent upon the direction of poling of the layers 2 and 3 and whether the stress is tensile or compressive taking these two factors into consideration the sensor 1 is adapted so that bending of the sensor 1 will produce electrostatic charges that cancel one another whereas temperature variation of the layers 2 and 3 results in a perceptible sensing voltage such charge cancellation is achieved by making the stiffness of the inner conductive layer 4 greater than the stiffness of the layers 2 and 3 combined with their respective conductive coatings 7 and 8 accordingly when the sensor 1 is bent the conductive layer 4 serves as a point of zero compression or tension and as indicated in the exaggerated view of fig3 the layer 3 is extended while the layer 2 is compressed however it should be understood that bending of the sensor 1 in the direction opposite to that shown will produce compression of the layer 3 and extension of the layer 2 due to the extension of the layer 3 positive and negative charges are respectively produced on the outer and inner surfaces thereof whereas compression of the layer 2 produces negative and positive charges on its outer and inner surfaces because of the conductive layer.