Wireless power transfer

The technology of wireless power transmission can eliminate the use of the wires and batteries, thereby increasing the mobility, convenience, and safety of an electronic device for all users.

[19][20][21] An important issue associated with all wireless power systems is limiting the exposure of people and other living beings to potentially injurious electromagnetic fields.

Michael Faraday described in 1831 with his law of induction the electromotive force driving a current in a conductor loop by a time-varying magnetic flux.

Transmission of electrical energy without wires was observed by many inventors and experimenters,[24][25][26] but lack of a coherent theory attributed these phenomena vaguely to electromagnetic induction.

[29] During the same period two schemes of wireless signaling were put forward by William Henry Ward (1871) and Mahlon Loomis (1872) that were based on the erroneous belief that there was an electrified atmospheric stratum accessible at low altitude.

[35][39] Tesla failed to make a commercial product out of his findings[40] but his resonant inductive coupling method is now widely used in electronics and is currently being applied to short-range wireless power systems.

Early on he seemed to borrow from the ideas of Mahlon Loomis,[42][43] proposing a system composed of balloons to suspend transmitting and receiving electrodes in the air above 30,000 feet (9,100 m) in altitude, where he thought the pressure would allow him to send high voltages (millions of volts) long distances.

Tesla thought this would allow alternating current to be received with a similar capacitive antenna tuned to resonance with it at any point on Earth with very little power loss.

[48][49][50] His observations also led him to believe a high voltage used in a coil at an elevation of a few hundred feet would "break the air stratum down", eliminating the need for miles of cable hanging on balloons to create his atmospheric return circuit.

[53][54] In 1901, at Shoreham, New York he attempted to construct a large high-voltage wireless power station, now called Wardenclyffe Tower, but by 1904 investment dried up and the facility was never completed.

[28][55][56] The development of microwave technology during World War II, such as the klystron and magnetron tubes and parabolic antennas,[55] made radiative (far-field) methods practical for the first time, and the first long-distance wireless power transmission was achieved in the 1960s by William C.

[78] Another application area is "transcutaneous" recharging of biomedical prosthetic devices implanted in the human body, such as cardiac pacemakers, to avoid having wires passing through the skin.

[citation needed] In the United States, the Federal Communications Commission (FCC) provided its first certification for a wireless transmission charging system in December 2017.

[78] An environmental and economic benefit of wirelessly powering small devices such as clocks, radios, music players and remote controls is that it could drastically reduce the 6 billion batteries disposed of each year, a large source of toxic waste and groundwater contamination.

[72] A study for the Swedish military found that 85 kHz systems for dynamic wireless power transfer for vehicles can cause electromagnetic interference at a radius of up to 300 kilometers.

For EWPT devices having identical resonant frequencies, the magnitude of power transfer is entirely dependent on critical coupling coefficient, denoted by

The dimensions of the components may be dictated by the distance from transmitter to receiver, the wavelength and the Rayleigh criterion or diffraction limit, used in standard radio frequency antenna design, which also applies to lasers.

Microwave power beaming can be more efficient[clarification needed] than lasers, and is less prone to atmospheric attenuation caused by dust or aerosols such as fog.

Here, the power levels are calculated by combining the parameters together, and adding in the gains and losses due to the antenna characteristics and the transparency and dispersion of the medium through which the radiation passes.

[113][114] Power beaming by microwaves has the difficulty that, for most space applications, the required aperture sizes are very large due to diffraction limiting antenna directionality.

While it did not prove to be particularly useful for power transmission, this beam antenna has been widely adopted throughout the broadcasting and wireless telecommunications industries due to its excellent performance characteristics.

Experiments in the tens of kilowatts have been performed at the Goldstone Deep Space Communications Complex in California in 1975[118][119][55] and more recently (1997) at Grand Bassin on Reunion Island.

[121] A change to 24 GHz has been suggested as microwave emitters similar to LEDs have been made with very high quantum efficiencies using negative resistance, i.e., Gunn or IMPATT diodes, and this would be viable for short range links.

[126] In 2021 the FCC granted a license to an over-the-air (OTA) wireless charging system that combines near-field and far-field methods by using a frequency of about 900 MHz.

[130] Advantages compared to other wireless methods are:[131] Drawbacks include: Laser "powerbeaming" technology was explored in military weapons[133][134][135] and aerospace[136][137] applications.

Scientists from the Chinese Academy of Sciences have developed a proof-of-concept of utilizing a dual-wavelength laser to wirelessly charge portable devices or UAVs.

[162] Although the efficiency of conversion is usually low and the power gathered often minuscule (milliwatts or microwatts),[162] it can be adequate to run or recharge small micropower wireless devices such as remote sensors, which are proliferating in many fields.

[169] The first passive RFID (Radio Frequency Identification) technologies were invented by Mario Cardullo[170] (1973) and Koelle et al.[171] (1975) and by the 1990s were being used in proximity cards and contactless smartcards.

[174] In 2011, Dr. Christopher A. Tucker and Professor Kevin Warwick of the University of Reading, recreated Tesla's 1900 patent 0,645,576 in miniature and demonstrated power transmission over 4 meters (13 ft) with a coil diameter of 10 centimetres (3.9 in) at a resonant frequency of 27.50 MHz, with an effective efficiency of 60%.

[177] At NASA's Jet Propulsion Laboratory, he and Robert Dickinson transmitted 30 kW DC output power across 1.5 km with 2.38 GHz microwaves from a 26 m dish to a 7.3 x 3.5 m rectenna array.