RFID threshold accelerometer

This paper presents the design, manufacture, and testing of a battery-free, wireless threshold accelerometer based on a fully compliant bistable mechanism (FCBM). The FCBM stores threshold acceleration measurements mechanically, eliminating the need for electrical power. The sensorpsilas state can be read wirelessly via a passive RFID tag. Because information can be stored in these tags for over 25 years, the sensor can be left unattended for long periods of time. The FCBM portion of the sensor is laser cut from a single sheet of plastic (Delrin) and integrated with an Atmel ATA5570 RFID chip. Both elements can be manufactured at low cost. The G-force needed to exceed the shock threshold can be varied by changing the mass of the FCBM. Multiple sensors were tested using three different methods. The first method was a centrifuge, providing a constant force input. The second method was a drop test that gave an impulse input to the sensor. The final method used a shaker table to provide a sinusoidal input. In each of these tests, it was found that the FCBM sensed the correct acceleration and retained its mechanical state. A number of prototype sensors were constructed with different masses resulting in threshold accelerations between 15 and 180 Gpsilas. The overall size of these sensors was approximately 28 mm x 26 mm. The RFID tags operate at 150 kHz and were read using a commercial off-the-shelf reader with a range of approximately 3 cm. Longer range readers are readily available at higher operating frequencies.