A coin size, 40mW, 20 grams sensor node for guided waves detection

In this work, a small footprint, low power, and light weight sensor node for guided wave detection on laminate composite and metallic structures is presented. This device is meant as a basic building block for smart structure passive sensor networks development. It draws power from a two-wires data-over-power (DoP) network communication interface, which is also used for half-duplex data handling at 200kbps. Each node is roughly 20x24mm, consumes less than 40mW, and weights less than 20 grams, making it attractive for aerospace systems where size, power and weight reduction are crucial. Elastic waves generated from impacts and propagating on the structure are recorded by an innovative, patent-pending, dual-element piezoelectric transducer and processed by an embedded low-voltage 8-bit PIC. A 1Mbit SPI serial SRAM is used for data storage while program instruction are stored in the PIC embedded 7 KB ash. A low-voltage, high-speed, half-duplex RS485 transceiver with an internal, programmable termination resistance is used to interface the PIC to the bus through a filtering mesh of passive components. This mesh also connects to a low-dropout voltage regulator, allowing it to draw power from the DoP bus without interfering with data transmission. A separate gateway device has also been developed: it is capable to simultaneously interface and feed the DoP bus by drawing power either from the USB or from an external power supply. A network counting up to 256 nodes can be implemented and interfaced to a PC for real-time impact detection applications.