The Need

Conventional rectifying circuit designs convert alternating-current (AC) signals into direct-current (DC) signals via the used of diodes. Low-barrier Schottky diodes are used in low AC power cases such as with ambient radio frequency (RF) signals. Ideally, each diode is only turned on during the positive AC cycle and shut off during negative cycle regardless of different circuit schemes such as half-wave rectifier, full-wave rectifier, voltage multiplier, etc. The AC-to-DC conversion bandwidth and efficiency are related to AC power level, diode characteristics, and load impedance. The diode characteristics also depend on frequency, input power level, and output current. That is why most existing rectifying circuit designs can only operate at a reasonable efficiency within a single narrow bandwidth. As a driver for wearable technology and distributed sensor networks, efficient wireless power generation would enable considerable growth in these markets and pave the way for the next generation of mobile devices.

The Technology

The Ohio State University researchers, led by Dr. Chi-Chih Chen, have developed a rectifying circuit design that includes a novel harmonic harvesting loop for harvesting unrectified AC powers contained in the harmonic signals at the output of conventional rectifying circuit designs. As a result, this novel rectifying circuit design can achieve wider bandwidth and higher rectifying efficiency. Researchers have demonstrated that an efficiency improvement of over 25% is observed when a single harmonic harvester is added at the output of a conventional rectifier. This design can be used for harvesting power form ambient RF signals of mobile phones and wireless networks from 825 and 2500 MHz. Additional power harvesting technologies are currently being implemented by the team to promote the adoption of wireless charging.

Commercial Applications

• Efficient energy harvesting from radio frequency (RF) signals at higher frequencies used for GSM or Wi-Fi from 700 MHz to 2500 MHz.
• Improving rectifying efficiency at low RF input power level as in the case of most ambient RF signals.
• Harvesting RF energy contained in the harmonics produced by the non-linear property of rectifying diodes.

Benefits/Advantages

• Improved rectifying efficiency and extended upper frequency limit of conventional rectifying circuits.
• Efficient energy harvesting from radio frequency (RF) signals at higher frequencies.
• Reduced waste of un-rectified energy in harmonics produced by diode’s non-linear I-V property and rectifying process.