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: X-ray detector on plastic delivers medical imaging performance

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

Simplicity is key to co-operative robots

5 hours ago

A way of making hundreds—or even thousands—of tiny robots cluster to carry out tasks without using any memory or processing power has been developed by engineers at the University of Sheffield, UK.

Freight train industry to miss safety deadline

6 hours ago

The U.S. freight railroad industry says only one-fifth of its track will be equipped with mandatory safety technology to prevent most collisions and derailments by the deadline set by Congress.

IBM posts lower 1Q earnings amid hardware slump

7 hours ago

IBM's first-quarter earnings fell and revenue came in below Wall Street's expectations amid an ongoing decline in its hardware business, one that was exasperated by weaker demand in China and emerging markets.

Microsoft CEO is driving data-culture mindset

8 hours ago

(Phys.org) —Microsoft's future strategy: is all about leveraging data, from different sources, coming together using one cohesive Microsoft architecture. Microsoft CEO Satya Nadella on Tuesday, both in ...

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

More news stories

Simplicity is key to co-operative robots

A way of making hundreds—or even thousands—of tiny robots cluster to carry out tasks without using any memory or processing power has been developed by engineers at the University of Sheffield, UK.

Microsoft CEO is driving data-culture mindset

(Phys.org) —Microsoft's future strategy: is all about leveraging data, from different sources, coming together using one cohesive Microsoft architecture. Microsoft CEO Satya Nadella on Tuesday, both in ...

Floating nuclear plants could ride out tsunamis

When an earthquake and tsunami struck the Fukushima Daiichi nuclear plant complex in 2011, neither the quake nor the inundation caused the ensuing contamination. Rather, it was the aftereffects—specifically, ...

Patent talk: Google sharpens contact lens vision

(Phys.org) —A report from Patent Bolt brings us one step closer to what Google may have in mind in developing smart contact lenses. According to the discussion Google is interested in the concept of contact ...