Evolutionary Optimization of Antennas for Structural Health Monitoring

Monitoring and surveillance of buildings, especially in critical infrastructure is crucial to increase the lifetime of such structures. This is due to the fact, that concrete buildings, like bridges or road tunnels are prone to corrosion due to their exposure to the elements. For this task, wireless sensor nodes can be employed in structural health monitoring. In the last few years passive RFID sensors have been proposed to gather data from inside concrete structures. However, designing antennas which are operational inside concrete to transmit data from the sensor node to the outside world is extremely challenging, due to the fact that the performance of antennas is extremely depended on their surrounding material. In this work, the fully automatized design of an antenna for the UHF band in concrete with varying electrical properties is demonstrated. Using a novel multi-objective optimization method, the antennas are operational over a wide range of dielectric properties of the surrounding materials. In contrast to conventional approaches, no air spacers or boxes are needed around the antenna. The antenna parameters have been carefully obtained during the curing and drying process, in an outdoor like environment with 65% relative humidity. After 157 days of drying, a reflection coefficient of −13 dB and an antenna gain of −84 dB is achieved, at a water content of the concrete of 4.2% by mass.