Increasing numbers of electronic devices implies increasing amounts of consumed electrical power and a greater need to conserve power in electronic devices. For that reason, Faycel Fezai, a hardware engineer with Thales Air Systems, France, and co-researchers from various locations throughout France, propose an efficient RF-based energy-transfer system and RF-to-dc conversion circuit and switch with the ability to “wake up” commercial and industrial electronic devices as needed. The technology employs an integrated emitter and receiver working in the industrial-scientific-medical (ISM) frequency range from 2.40 to 2.48 GHz.
The researchers set an energy-consumption limit at 1 mW for electronic devices. They based their system solution on antennas with easily tuned radiation efficiency and a receiver without a direct power supply that has a rectifying circuit optimized for low RF power levels. In addition, the solution is coupled to a self-maintained switch. The system’s intent is to be able to wake up an electronic device from a distance of 5 m by means of some form of remote-control device.
The emitter is based on a commercial transceiver from Texas Instruments used with a lithium-polymer (LiPo) battery. The transceiver’s output is connected to a commercial power amplifier with 29-dB gain and then to an antenna.
Although the amplifier normally exhibits power consumption of 600 mA, the RF emissions for the transceiver system are based on a 10% duty cycle consisting of a 20-ms burst repeated three times during a 200-ms period. The researchers note that this particular amplifier and duty cycle were chosen for the benefits of gain, energy consumption, and cost in a commercial marketplace, with an expected operating lifetime of two years.
A parasitic-element antenna was developed for the transceiver using the same commercial printed-circuit-board (PCB) material as the transceiver circuitry. Adding surface-mount-technology (SMT) components to the PCB tuned the antenna pattern; then, commercial computer-aided-engineering (CAE) software programs, such as MATLAB from MathWorks and CST Microwave Studio from Computer Simulation Technology, were used to design and optimize the antenna. The compact antenna aided the wake-up circuit’s effectiveness by means of a maximum gain of 5.75 dBi across a 200-MHz bandwidth from 2.4 to 2.6 GHz in the main radiated direction of interest (0°).
See “Reducing Electronic Device Standby Power Using a Remote Wake-Up System,” IEEE Antennas & Propagation Magazine, Vol. 58, No. 5, October, 2016, p. 66.