Wireless Power Transmission

Wireless Power Transmission

The wireless power transmission (WPT) refers to the efficient transmission of electric power from one point to other without use of wires or any other...

The wireless power transmission (WPT) refers to the efficient transmission of electric power from one point to other without use of wires or any other material


his technology can be used where conventional wires are unaffordable, inconvenient, expensive, hazardous, unwanted or impossible. It can also be used for applications where either an instantaneous amount or a continuous delivery of energy is needed. This is the future technology which will be adopted  by the world eventually.

In 1899, Nikola Tesla performed experiments in the field of pulsed wireless energy transfer. Tesla’s Magnifying Transmitter, an early type of Tesla Coil that measured 16 meters in diameter, was able to transmit tens of thousands of watts without wires.

Wireless power techniques mainly fall into two categories, non-radiative and radiative. In near field or non-radiative techniques, power is transferred by magnetic fields using inductive coupling between coils of wire, or by electric fields using capacitive coupling between metal electrodes. Inductive coupling is the most widely used wireless technology; its applications include charging handheld devices like phones and electric toothbrushes, RFID tags, and chargers for implantable medical devices like artificial cardiac pacemakers, or electric vehicles.

In far-field or radiative techniques, also called power beaming, power is transferred by beams of electromagnetic radiation, likemicrowaves or laser beams. These techniques can transport energy longer distances butmust be aimed at the receiver. Proposed applications for this type are solar power satellites, and wireless powered drone aircraft.

Long distance transmission

Electricity is needed to be transformed into a suitable energy form for its transportation. For wireless transmission, this has to be a form that can travel through air. Microwave frequencies hold this ability. The microwave spectrum is defined as electromagnetic energy ranging from approximately 1 GHz to 1000 GHz in frequency.


Components of microwave based wireless power transmission system:

A complete microwave transmission system consists of three essential parts:

  1. Electrical power to microwave power conversion
  2. Absorption antenna that captures the waves
  3. Re-conversion to electrical power


The components include a microwave source, a transmitting antenna and a receiving antenna. The microwave source consists of an electron tubes or solid-state devices with electronics to control power output. The slotted waveguide antenna, parabolic dish and micro-strip patch are the most popular types.

Using a powerful focused beam in the microwave or laser range long distances can be covered. There are two methods of wireless power transmission for bridging application. First is the direct method, from transmitting array to rectenna (A rectenna is a rectifying antenna—a special type of antenna that is used for converting electromagnetic energy into direct current (DC) electricity). A line of sight is needed and is therefore limited to short (< 40 km) distances. Above 40 kilometers, huge structures are needed to compensate for the curvature of the earth.

The second method is via a relay reflector between the transmitter and rectenna. This reflector needs to be at an altitude that is visible for both transmitter and rectenna.

The Primary components of wireless power transmission are microwave generator, transmitting antenna and Receiving antenna (Rectenna).


Microwave Generator

The microwave transmitting devices are classified as Microwave Vacuum Tubes (magnetron, klystron, Travelling Wave Tube (TWT), and Microwave Power Module (MPM)) and Semiconductor Microwave transmitters (GaAs MESFET, GaNpHEMT, SiC MESFET, AlGaN/GaN HFET, and InGaAS). The microwave transmission often uses 2.45GHz or 5.8GHz of ISM band. The other choices of frequencies are 8.5 GHz, 10GHz and 35GHz. The highest efficiency over 90% is achieved at 2.45 GHz among all the frequencies.


Transmitting antenna

The slotted wave guide antenna, microstrip patch antenna, and parabolic dish antenna are the most popular type of transmitting antenna. The slotted waveguide antenna is
ideal for power transmission because of its high aperture efficiency (> 95%) and high power handling capability (Refer Pic. 1 & 2).


The rectenna is a passive element consists of antenna, rectifying circuit with a low pass filter between the antenna and rectifying diode. The antenna used in rectenna may be dipole, Yagi –Uda, microstrip or parabolic dish antenna. The patch dipole antenna achieved the highest efficiency among the all.

The performance of various printed rectenna is shown below:

Schottky barrier diodes (GaAs-W, Si, and GaAs) are usually used in the rectifying circuit due to the faster reverse recovery time and much lower forward voltage drop and good RF characteristics.



Wireless Power Transmission system would completely eliminate the existing high-tension power transmission line cables, towers and sub stations between the generating station and consumers and facilitates the interconnection of electrical generation plants on a global scale. It has more freedom of choice of both receiver and transmitters. The cost of transmission and distribution become less and the cost of electrical energy for the consumer also would be reduced. The power could be transmitted to the places where the wired transmission is not possible. Loss of transmission is negligible level in theWireless Power Transmission; therefore, the efficiency of this method is very much higher than the wired transmission. Power is available at the rectenna as long as theWPT is operating. The power failure due to short circuit and fault on cables would never exist in the transmission and power theft would be not possible at all. However, the current capital cost for practical implementation of WPT seems to be very high.

Manoj J. Semwal,

Sterling AndWilsonPvt. Ltd.