Microwave tooth for sensor power supply in battery-free applications

A sensor power supply is proposed, comprising an antenna, rectifier and accumulator. For the rectifier, we modified the Greinacher´s rectifying circuit to achieve tunable input response for channel selection in the Digital TV (DTV) band and higher RF-to-DC conversion efficiency desired for DTV energy-harvesting given at least ™5 dBm power incidence. Channel selection is implemented by four input matching inductors and two static Single Pole Double Throw (SPDT) switches while higher efficiency is realized by the introduction of a grounding inductance, L_g. The measured efficiency exceeds 50% at -5 dBm input power, L_g = 56nH and 8.2kΩ optimum load resistance. The proposed sensor power supply was able to generate 1.5V DC, 24mA nominal current (P_DC ≥ 36mW) in 80 minutes. This power was enough to supply two different types of temperature sensors for demonstration purposes. Additionally, at 3V DC accumulated, it was possible to log temperature and altitude sensor data for 2 hours and radio transmit 748 bytes in 2 minutes.