A New Wireless Displacement Sensor Based on Reverse Design of Microwave and Millimeter-Wave Antenna Array

This paper introduces for the first time a new low-cost, nondestructive sensor to remotely monitor structural displacements (patent pending). The sensor consists of a two-element antenna array, operating at microwave or millimeter wave frequencies, remotely interrogated by a reader. The elements are stuck on the two sides of a crack to be monitored, no matter how large the crack is. The operating principle is based on the dependence of the array radiation characteristics on the element distance normalized to the wavelength. A combination of electromagnetic (EM) interferometry and Radio Frequency IDentification (RFID) technology allows the displacement of the antennas with respect to a reference configuration to be remotely determined. It is demonstrated that null measurements of the radiation pattern at microwave frequencies allow structural displacements to be predicted with uncertainties of the order of millimeters. The sensor accuracy is directly related to the wavelength of the radiated EM field.