The following diagram shows power transmission efficiency with regard to position displacement between coupled elements (electrodes in capacitive coupling and coils in electromagnetic induction).
When position displacement between coupled elements (dz/D) is 1, the overlapping area between electrodes (in capacitive coupling) or coils (in electromagnetic induction) on the power transmitting and receiving sides is almost totally eliminated and displacement becomes significant (an electrode is displaced by as much as its own width).
In capacitive coupling, the decrease in power transmission efficiency is only 20% or so. If the position displacement is smaller, the decrease in power transmission efficiency remains at around 10%.
For this reason, capacitive coupling provides horizontal position freedom with an easy-to-use charging system for end customers. This means, for example, that a mobile phone does not have to be placed in an exact position on a charging pad to charge.
Comparison of position displacement efficiency in electromagnetic induction and capacitive coupling (DC input – DC output)
This position freedom can be further improved by switching multiple electrodes during power transmission.
With this approach, only electrodes located near the equipment are in operation providing high-efficiency charging everywhere on the charging pad.
This system does not cause noise problems, and has very little effect on the human body or equipment.
Charge is possible everywhere on the charging pad.
Since, capacitive coupling is only required to provide the desired capacity between power transmitting and receiving electrodes, electrodes can be any shape. (Electrodes do not have to be square. They can be triangular or circular as well.)
Also there are very few limitations in terms of electrode materials and thickness, since only a few mA of current flow through electrodes.
We can flexibly accommodate customer requests for electrode shape, size and material to suit equipment requirements.
Examples of electrode placement
Mounting in low-profile equipment
Since less than a few mA of current flow through electrodes in capacitive coupling, as mentioned above, hardly any Joule heat (determined from current and resistance values) is emitted.
This means the temperature in the wireless power transmission area does not rise, which protects battery from heat even when the unit is placed nearby.
Metal objects other than the equipment to be charged do not result in heat generation either.
Wireless Power Transmission Modules
