Establishing basic formulas for squeezing wireless energy from radio frequency systems

Sep 25, 2013
Figure 1. Wireless energy harvesting scheme, which equivalently comes down to the closed circuit shown in Fig. 2.

Radio-frequency (RF) wave rectifier circuits play an invaluable role in extracting the appropriate DC voltage and current in wireless energy applications, such as mobile power supplies and environmental energy harvesting.

To squeeze the maximum power from an RF source, circuit designers have to repeat a process of rectifier topology implementation and element parameter optimization for each system. This approach necessitates extensive and computing resources.

Here, Takashi Ohira at Toyohashi Tech. describes the establishment of a set of mathematical formulas that can characterize RF diode rectifiers.

Figure 1 shows a simple example of energy harvesting scheme. Electromagnetic energy arrives at the antenna, is rectified by the diode, smoothed by the capacitor, and output as DC voltage to the load. The designer's primary task is to make the circuit well matched to the load resistance so that the arriving RF is not reflected by the diode but fully converted into DC voltage. This problem is mathematically equivalent to that presented by Takashi Ohira in Fig. 2. Adapting Kirchhoff's laws for the diode's nonlinear switching states, imposing the cyclostationary conditions upon the voltage waveform, and taking the current continuity property into account, Takashi Ohira successfully obtained a type of transcendental equation in terms of the diode's flow angle. By solving this equation, Takashi Ohira finally derived expressions for the DC output voltage and current.

The resultant formulas for DC output power show that the source-to-load resistance ratio crucially dominates the circuit behavior. Takashi Ohira consequently derived the optimum source-to-load matching conditions for rectifiers in single-diode half wave, bridged-diode full wave, double-diode double voltage, and double-diode double current operations.

Figure 2. Simple and basic problem that looks easy but involves the essence of RF-to-DC power conversion.

The formulas deduced in this work open up a clear vista for circuit designers in RF power electronics. This approach is much more elegant and insightful than exploring the solution by repeating nonlinear time-domain or harmonic-balance simulations. The theory will pave the way to wireless power transfer for running electric vehicles, air-to-air recharging for electric planes, and even underwater feed stations for motor-driven submarine vessels.

Explore further: Renesas announces SRAM using leading-edge 16 nm FinFET for automotive information systems

More information: Ohira, T. Power efficiency and optimum load formulas on RF rectifiers featuring flow-angle equations, IEICE Electronics Express, vol. 10, issue 11, pp.1-9, June 2013. DOI: 10.1587/elex.10.20130230

add to favorites email to friend print save as pdf

Related Stories

Japanese scientists explore electric roads for EVs

Sep 20, 2011

(PhysOrg.com) -- Masahiro Hanazawa of Toyota Central R&D Labs and Takashi Ohira from Toyohashi University are working on a solution for avoiding battery recharge headaches in powering electric cars. They are ...

Silicon carbide solutions to solar challenges revealed

Sep 11, 2012

STMicroelectronics is revealing innovations in silicon carbide devices at Solar Power International (SPI) 2012 that enable systems producers to build ultra-efficient electronics for converting raw solar energy ...

Recommended for you

US seeks China's help after cyberattack

1 hour ago

The United States is asking China for help as it weighs potential responses to a cyberattack against Sony Pictures Entertainment that the U.S. has blamed on North Korea.

Why the Sony hack isn't big news in Japan

18 hours ago

Japan's biggest newspaper, Yomiuri Shimbun, featured a story about Sony Corp. on its website Friday. It wasn't about hacking. It was about the company's struggling tablet business.

Off-world manufacturing is a go with space printer

22 hours ago

On Friday, the BBC reported on a NASA email exchange with a space station which involved astronauts on the International Space Station using their 3-D printer to make a wrench from instructions sent up in ...

Cadillac CT6 will get streaming video mirror

23 hours ago

Cadillac said Thursday it will add high resolution streaming video to the function of a rearview mirror, so that the driver's vision and safety can be enhanced. The technology will debut on the 2016 Cadillac ...

Sony faces 4th ex-employee lawsuit over hack

23 hours ago

A former director of technology for Sony Pictures Entertainment has sued the company over the data breach that resulted in the online posting of his private financial and personal information.

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

vacuum-mechanics
1 / 5 (3) Sep 25, 2013
Figure 1 shows a simple example of energy harvesting scheme. Electromagnetic energy arrives at the antenna, is rectified by the diode, smoothed by the capacitor, and output as DC voltage to the load. The designer's primary task is to make the circuit well matched to the load resistance so that the arriving RF energy is not reflected by the diode but fully converted into DC voltage.


By the way, it is interesting to note that in actual case when the antenna radiates RF energy it has to overcome what which called as 'radiation resistance'(which is matched to the load resistance), but the challenge problem is – what this radiation resistance due to? It seems that no one could answer the question in the conventional way; maybe this unconventional view could solve the problem…
http://www.vacuum...21〈=en

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.