Coherent Radiation from a Swarm of Wirelessly Powered and Synchronized Sensor Nodes

This paper presents a novel technique to synchronize a swarm of sensor nodes at the RF domain and produce coherent radiation from the sensor nodes to increase the amplitude of the reflected signal. A network is formed by an array of microchips that are wirelessly powered, and upon activation, radiate back an RF signal. The phase of the radiated signals from each microchip is synchronized using a wireless reference signal. This technique results in a coherent amplitude combing and power amplification. The microchips are fabricated in a 180-nm CMOS SOI technology. Each microchip occupies a total area of 3.9× 0.7 mm 2 that includes three on-chip dipole antennas that are used for power delivery, injection locking, and back RF reflection. Measurement results reveal that a reference signal in a frequency range of 7.72-7.79 GHz can successfully synchronize the reflected signals radiated from the microchips through a sub-harmonic injection locking scheme. A wireless reference signal of 7.733 GHz synchronizes an array of 2×2 microchips. The microchips are locked to half of the reference frequency and produce coherent radiation at 3.866 GHz. This scheme results in a power elevation of 12 dB on the reader side.