Metals which are widely used in many types of industries are usually subjected to fatigue and surface corrosion. There is a demand to detect the surface damage caused by fatigue and corrosion at an early stage to ensure the structural integrity. In this paper. a novel nonlinear ultrasonic technique based on the measure of third-order combined harmonic generation. https://www.lockdownsecuritycanada.shop/product-category/push-button-switch/