Low-Power Density Wireless Powering for Battery-less Sensors

This paper presents an overview of far-field wireless powering for low-power wireless sensors. With expected RF power densities in the 20 to 200 mu W/cm(2) range, and desired small sensor overall size, low-power nondirective wireless powering is appropriate for sensors that transmit data at low duty cycles. The sensor platform is powered through an antenna which receives incident electromagnetic waves in the GHz frequency range, couples the energy to a rectifier circuit which charges a storage device (e. g. thin-film battery) through an efficient power management circuit, and the entire platform, is controlled through a low-power micro-controller. For low incident power density levels, co-design of the RF powering and the power management circuits is required for optimal performance. Results are presented with integrated antenna-rectifiers operating in the 2-GHz cellular band with over 50% efficiency for an incident power density of 75 mu W/cm(2).