Detection of Metal Surface Cracks Based on Liquid Switch Controlled Spoof Surface Plasmon Polaritons

A spoof surface plasmon polaritons (SSPPs) sensor based on liquid switch control is proposed to detect metal surface cracks. The sensor consists of liquid switch controllers and power division structure. The liquid switch consists of a plastic pipe and syringe with water, which is fixed on the branch structure of SSPPs sensor. By filling the plastic pipe with water, the branch cannot transmit signal, which is called “ OFF” state. The branch retransmits signal by pumping water out of plastic pipe, which is called “ ON” state. By switching the “ ON” or “ OFF” state of sensor’s branches, it can control the transmission path of SSPPs sensor, that is, control the sensing area of SSPPs sensor. The detection method is based on the change of reflection coefficient of SSPPs sensor caused by cracks. By switching the states of branches in turn, it can detect whether there is a crack at each branch. The proposed sensor uses liquid switch instead of mechanical movement, which can realize rapid detection in the metallic materials with large surface area. The simulation and experimental results show that the SSPPs sensor can effectively detect metal surface crack with a width of 0.1mm.