This research investigates a passive wireless antenna sensor designed for strain and crack sensing. When the antenna experiences deformation, antenna shape changes, causing shift in electromagnetic resonance frequency of the antenna. A radio frequency identification (RFID) chip is adopted for antenna signal modulation, so that a wireless reader can easily distinguish backscattered sensor signal from unwanted environmental reflections. The RFID chip captures its operating power from interrogation electromagnetic wave emitted by the reader, which allows the antenna sensor to be passive (battery-free). This paper first reports the latest simulation results on radiation patterns, surface current density, and electromagnetic field distribution. The simulation results are followed with experimental results on the strain and crack sensing performance of the antenna sensor. Tensile tests show that the wireless antenna sensor can detect small strain changes lower than 20 με, and can perform well at large strains higher than 10,000 με. With a high-gain reader antenna, the wireless interrogation distance can be increased up to 2.1 m. Furthermore, an array of antenna sensors is capable of measuring strain distribution in close proximity. During emulated crack and fatigue crack 2 tests, the antenna sensor is able to detect the growth of a small crack.

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A tension/compression device is developed for applications as bracing elements in buildings. The device is designed to allow Nitinol forms, such as helical springs or Belleville washers, to be used in compression. The device allows both overall extension (tension) and compression while subjecting the Nitinol to an optimum deformation mode. It is possible, due to the versatility of the design, to adjust the force and stroke of the device without changing the overall configuration. This new device is subjected to a cyclic loading protocol that tests the Nitinol elementÕs ability to recover large deformations. The effect of different Nitinol configurations and a cyclic loading history are evaluated in the study. The results show that Nitinol helical springs produce good recentering and damping behavior while Nitinol Belleville washers show good potential to form the basis for a Nitinol damping device.

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