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Japan researchers proposing novel method for powering on-road EVs

Masahiro Hanazawa at Toyota Central R&D Labs and Takashi Ohira at Toyohashi University of Technology (Toyohashi Tech) are proposing a novel solution for powering EVs capable of running unlimited distances without being hampered by battery limitations. Their basic concept stems from electric railways, where each car of the train is powered from an overhead wire.

To avoid the use of dangerous contacting devices such as pantographs for on-road transportation, the duo propose up-converting the energy from power lines into radio frequency (RF) using high-speed inverters implanted along tracks in the road. The RF voltage is applied to a balanced metal track embedded under the surface of the road. The EV picks up the RF voltage via electrical capacitance between the metal and a steel belt installed inside of the tires of the EV.

The researchers conducted feasibility experiments to test their ideas, and to explore the RF frequencies where such power transfer is effective and practical. In the experiments, the researchers put small metal plates on the floor and inside a tire, and positioned another metal plate above the tire. Finally, they measured the electrical impedance between the two plates. This set-up should be equivalent to double the impedance between a plate and a steel belt.

A schematic of the proposed power transfer system for a running automobile. This system transmits electric power thorough a capacitor composed of a steel belt and a metal plate attached to the road, and the power feed in differential mode. Notably, the leakage electromagnetic field is small, and the infrastructure can be set up at low cost compared with coils. Click to enlarge.   The proposed model and measurement model. As a the measurement model a metallic board were arranged above and below the tire, and the complex impedance was measured. Pieces of styrene foam of different thickness were placed between the upper surface of the tire and metallic plate. The measurement frequency was from 10 kHz to 10 MHz. Click to enlarge.

Experimental results showed the impedance to depend linearly on the RF frequency. Then the researchers designed and implemented a 50 ohm reactance circuit to match this, where 50 ohm is the standard impedance for RF transmission lines. This experimental set-up enabled a high transmission efficiency with sub 1 dB loss.

Although these were low power experiments, they demonstrate the feasibility of energy transfer from the road to a running automobile, the researchers said. If this energy transfer could be increased to tens of kW on express ways, then in the future it may be possible to take EV from a house to the nearest interchange with a small battery and then cruise on the expressway via this feeder system.


  • Masahiro Hanazawa and Takashi Ohira, “Power Transfer for a Running Automobile”, IEEE MTT-S International Microwave Workshop Series on Innovative Wireless Power Transmission, IMWS-IWPT2011, pp.77-80, Kyoto, May 2011.



Wireless e-energy transfer to moving e-vehicles is the final answer to eliminate range anxiety and extend e-range without limits.

An International Standard will have to be set up to ensure that all highway capable BEVs are compatible.

An excellent long term project.


Dunno. Seems like a LOT of trouble here. RF? Imagine the interference with cell and other consumer spectra. Impedance changes with insulation & resistance. So, it rains...

And what if you get out of your car with your new titanium, stainless artificial hip or knee??

Finally, why when discussing units of RF are we measuring in units of sound?


A system operating in the range of kHz up to 10 MHz isn't going to interfere with cellular systems at 900 MHz and up.

what if you get out of your car with your new titanium, stainless artificial hip or knee??
Same thing as if you stand by an AM radio station's transmitter: nothing.
why when discussing units of RF are we measuring in units of sound?
The units are decibels (dB) of attenuation, not dBa. A dB is a dB in whatever medium; it's a factor of the tenth root of 10.


Ohhh, yes. This is MUCH simpler than stringing a wire overhead.
Except where you have to tear up the entire roadway infrastructure to place the RF-spewing metal strips under the road.
And where you have to retool the entire tire design to accept the RF-accepting steel belt inside the tire without interfering with balance, design wear, and the other steel belt which reinforces the tire's durability.
Oh, and exactly how do you then send the received RF-feeding electricity into the car's electrical systems from a wheel spinning at 2000 rpms or more?
Of course, more research (and grant money) is needed...


What if you pull off in the breakdown lane? That powered too? What about a wicked wreck? That gouges the asphalt like a rolled over tanker in SALT? ZzzzzzzTTT!!!

Or... how 'bout using the incremental improvement in battery storage for EVs?


Ah, Reel$$ shows what he's really afraid of: electrification that suddenly removes the monopoly of oil companies on transport energy. I almost hate to mention that a car with a TRACTION BATTERY, almost however small, can get itself to the breakdown lane and back under its own power.

That same battery can power a vehicle past damaged parts of the power cable. Funny how that works.

SV's objections are clever but reflect ignorance of electrodynamics. Unless the steel belt of a tire is an active or patterned element (not just a roughly continuous conductor), the details of its construction probably don't matter very much. As for the power cable itself, any asphalt road could probably be trenched, en-cabled and patched at the rate of several miles per day. Concrete would take longer.

My own leanings are toward steel rails and conductive power transmission, but this scheme is brilliant and may have most of the advantages (still won't have as high efficiency and lacks the feature of slashing pavement damage by off-loading weight to steel). A buried cable can be followed by a self-steering vehicle, so the self-driving, road-powered car is just as feasible with this idea.

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