Increasing the range of wireless passive sensor nodes using multisines

Wireless Sensor Networks (WSNs) usually consist of battery-powered nodes. Therefore, once the batteries deplete, the networks collapse. Passive sensor nodes are immune to this kind of problem because they do not have batteries, but on the other hand, their range is significantly shorter. This paper shows that this range can be enhanced (in a noticeable manner) if the Radio Frequency (RF) source that powers the nodes is set up to radiate a multisine waveform instead of a pure sinusoid, considering the same average power. The passive sensor used to demonstrate the usefulness of combining multiple sinusoidal waveforms is based on a low-power 16-bit microcontroller, and includes circuits for bi-directional wireless binary communication (envelope detection for downlink, backscatter for uplink). The sensor also features a 50Ω antenna port and an interface for debugging and expansion composed of 26 pins. Considering a power source of 2Werp, the maximum range of the wireless sensor (together with a half-wave dipole antenna) is 5.3 meters.