Abstract: Detector circuitry (12) for controlling the operation of a power management module (14) of an energy-harvesting device (10), the detector circuitry comprising: an input (13) for receiving an electrical input representative of a level of harvestable power (Vin); and a trigger coupled to the input and operable to generate an activation signal for switching on the power management module via enabler input (15); wherein the trigger is configured to generate the activation signal upon detecting at least a threshold level of harvestable power, and not to generate the activation signal upon detecting less than the threshold level of harvestable power.

Abstract: The present invention provides an apparatus comprising an RF energy harvester and an RF energy meter. The RF energy harvester comprises an antenna, a rectifier, an energy storage module and light output module. The antenna is arranged to receive an RF signal. The rectifier is arranged to generate a DC voltage from the received RF signal. The energy storage module is arranged to store the DC voltage. The light output module is arranged to output light pulses using the stored energy. The RF energy meter comprises a light detection module, a control module and an output module. The light detection module is arranged to detect light pulses output by the light output module of the RF energy harvester. The control module is arranged to count the number of light pulses detected by the light detection module. The output module is arranged to provide an output indicative of an amount of energy harvested by the RF energy harvester based on the counted number of light pulses.