Design and Evaluation of Low-Cost and Energy-Efficient Magneto-Inductive Sensor Nodes for Wireless Sensor Networks

A set of low-cost and energy-efficient sensor nodes are designed and implemented using magnetic induction (MI) communications for wireless sensor networks (WSN), which are especially suited for underwater and underground networks where the conventional mode of communication does not perform well. Hardware features of the sensor nodes include a three-dimensional MI coil antenna and its different configurations for transmit and receive operations, low-power circuits for sleep mode, several types of sensors, data storage, and best transmit/receive circuits selected to achieve the maximum communication range with low-power consumption. The material cost of a sensor node is less than \100 USD at the prototyping stage and can be drastically reduced at volume production. Software design utilizes low-power modes of microcontrollers and power supply circuits, state machine implementation of sleep, receive, sensing, and transmit modes, range estimation from received signal strength indicators (RSSIs), and medium access protocols, such as carrier sense multiple access (CSMA). Extensive lab and field tests conducted with the sensor nodes demonstrate promising performance in terms of low-power consumption, communication range, range estimation, and robustness against mismatching of coil orientations, and networking capabilities. The current consumption is as low as 60 \muA in sleep mode, 0.49 \text{m}A in receive mode, and 253 \text{m}A in transmit mode. The sensor node achieves a maximum of 40-m range with 1 kb/s data rate at 125 kHz carrier frequency.