Wireless Power Charging

Probably the best-known example of wireless transfer of energy is Nikola Tesla’s demonstration during the world fair 1893 in Chicago. He was able to light an electric bulb wirelessly using electric fields with high frequency. With the construction of the Wardenclyffe Tower (300kW) on Long Island, Tesla enhanced his vision of wireless charging based on magnetic induction. Unfortunately due to several reasons this project had no success.

Why is wireless transfer of energy gaining importance right now?

This topic has seen an enormous boost due to the massive changes in the behavior of smart phone users in the last 2-3 years. Huge displays, fast processors, high amount of data, social networks, mail and chat and also a vast amount of applications lead to high energy consumption which requires charging a device every day.


What are the user’s advantages?

Wireless charging solves several problems and offers unprecedented opportunities

  • Charging at public places (restaurants, airports, cinemas, …)
  • No compatibility issues with connectors
  • No cable jumble
  • Convenient way of charging; also in cars
  • Safety; no exposed contacts (explosion control, toys)
  • No mechanical attrition and higher reliability in rough environments (moisture, dirt)


What are the conditions to successfully spread the technology?

The main factor of success for wireless charging is creating and maintaining a technical standard. This is the only way to ensure, that the user will be able to charge his device safe, reliable and manufacturer-independent for all available charging spots.


What are the main areas for applications for wireless transfer of energy?

A. Battery-powered devices

Consumer terminals <20W are currently driving the technology. In the future, devices with higher performance levels will be charged wireless in a comfortable way.

B. Direct power supply of capsuled devices

Kitchen appliances such as water boilers, mixers, and coffee brewers can be powered with wireless electricity.

In the industrial sector for example pumps inside a tank are operated without drilling a hole for wires.

What are the different technologies existing for wireless charging?

Currently there are 3 different approaches for standardized solutions based on electromagnetic technology.

A. Close coupled - Wireless Power Consortium (WPC since 2008)

  • Transferring energy over a short distance with inductive coupling (mm range)
  • Transmitter (Tx) and receiver (Rx) coils are inductive coupled coils
  • In the small area between transmitter and receiver coil the magnetic field is fixed
  • Every receiver needs its own transmitter
  • Different power classes (5W, 20W, higher is being planned to 2,5kW)
  • Frequency range 100 – 205 kHz
  • Form of coils: wound on ferrites or printed on circuit boards
  • At the moment the most established solution at the market.
  • 170 licensed devices with 15 Mio. pieces worldwide


B. Loosely coupled (magnetic resonance) - Alliance for Wireless Power (A4WP since 2012)

  • Charging concept of magnetic response
  • Greater distance in z-direction (50mm), exact positioning of receiver not necessary
  • Transmitter is able to supply multiple receivers at the same time
  • Planned power classes for smart phones and tablets, currently till 22W
  • Frequency range: energy 6,78 MHz (ISM), data 2,4 GHz (Bluetooth)
  • No compatibility with A. or C.


C. Power Matters Alliance (PMA) - Powermat

  • Technically similar to A.
  • No compatibility with A. or B.

D. Capacitive Murata

  • Basically this solution separates a plate capacitor, a plate in the transmitter and another one in the receiver.
  • For an efficient charging the voltage between the plates has to be in the kV range.
  • Therefor big transformers in transmitters and receivers are needed.
  • A transmitter is able to supply multiple receivers at the same time.
  • Currently a solution with an output of 10W.
  • Advantages of this solution are less self-heating and an EMC neutral behavior.
  • Disadvantage: safety aspect of generating high-voltages for transfer.


Market Segments

High-volume communication technology (smart phones) is driving the market. The key advantage is that the technical solutions will be price-optimized and available in higher volumes on the market.

That implies higher approval for other applications (medicine, industry, safety, …) to use the technology – adapted to own demands.

Which market segments can offer wireless transfer of energy?

Generally speaking - Wireless charging can provide a solution for a wide range of applications in various industrial sectors. Battery-powered devices are only one possibility. Especially in areas with rough or explosion-prone environmental conditions or sterile applications, wireless transfer of energy provides more safety, easier use and better reliability.

Medical Technology

In the area of medical applications wireless transfer of energy is made for applications that are hermetically encapsulated, easy to clean or easy to sterilize. The technique’s advantage is that the contacts cannot get damaged by aggressive cleansers or disinfectants in contrast to traditional contacts made of metal. Hardly reachable spots do not exist.

Another area is implants (e.g. hearing aid) which have to be powered by energy.

Industrial applications

Wireless charging provides enormous advantages especially for industrial applications.

Areas in which devices are exposed to filthy or aggressive fluids gain more reliability and safety with wireless transfer. High mechanical load of wires can be avoided. In a wet or dusty environment devices can be encapsulated completely (no exposed contacts). This increases the reliability and durability. The range lasts from battery-powered tools to power supply of e.g. pumps or bigger machinery. Coil solutions or power classes which exceed today’s standards will be certainly needed in the future.

In security related applications wireless transfer of energy can solve the problem of sparking. The risks of unwanted electric charge in a wet environment can be avoided.

The wide range of electrically operated toys has to be taken seriously. Missing contacts, battery compartments and wires increase safety for children.

Accidental or prohibited opening of devices can be avoided by fully encapsulating the device.

Furniture / office restaurant establishments 

a) Output up to 20W

Charging smart phones and tablets wireless offered at public places. Furniture in offices, hotels, restaurants, airports,… will be equipped with wireless charging.

b) Output up to 2,5kW

There are further options in the power class <20W for the integration of output to 2,5kW in the kitchen area. Devices like toasters, coffee brewers, mixers, rice cookers and intelligent pots and pans can be powered without chords.

The WPC develops specifications for this market at the moment. First products are expected in 2014.

Applications in motor vehicles

The possibility for passengers charging their devices in motor vehicles is about to increase speed. Toyota is already offering a version with a Qi charger right off the factory (Avalon).

Especially the use of consumer devices in cars leads to a higher need for energy in this area. Energy is used for Bluetooth connection to the speakerphone in addition to the standard use. The navigation feature of smart phones is often used while driving which consumes more power.

On the other side a trip in the car is an ideal possibility to use the time for charging a smart phone. That is why wireless charging is a convenient solution in this case.

Accessory for customer devices

Next to the original equipment provided by manufacturers - smart phones and tablets offer various opportunities for third-party suppliers to offer charging stations


Würth Elektronik product portfolio