Wireless power transfer

Inductive charging pad for a smartphone as an example of near-field wireless transfer. When the phone is set on the pad, a coil in the pad creates a magnetic field which induces a current in another coil, in the phone, charging its battery.
Generic block diagram of a wireless power system
Generic block diagram of an inductive wireless power system
An artist's depiction of a solar satellite that could send energy by microwaves to a space vessel or planetary surface.
A laser beam centered on a panel of photovoltaic cells provides enough power to a lightweight model airplane for it to fly.
Tesla demonstrating wireless transmission by "electrostatic induction" during an 1891 lecture at Columbia College. The two metal sheets are connected to a Tesla coil oscillator, which applies high-voltage radio frequency alternating current. An oscillating electric field between the sheets ionizes the low-pressure gas in the two long Geissler tubes in his hands, causing them to glow in a manner similar to neon tubes.

Transmission of electrical energy without wires as a physical link.

- Wireless power transfer

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Space-based solar power

Concept of collecting solar power in outer space by solar power satellites (SPS) and distributing it to Earth.

SERT Integrated Symmetrical Concentrator SPS concept.NASA
A laser pilot beam guides the microwave power transmission to a rectenna
Artist's concept of a solar power satellite in place. Shown is the assembly of a microwave transmission antenna. The solar power satellite was to be located in a geosynchronous orbit, 35786 km above the Earth's surface. NASA 1976
Artist's concept of a solar disk on top of a LEO to GEO electrically powered space tug.
Comparison of laser and microwave power transmission. NASA diagram
A Lunar base with a mass driver (the long structure that goes toward the horizon). NASA conceptual illustration
An artist's conception of a "self-growing" robotic lunar factory.
Microwave reflectors on the moon and teleoperated robotic paving rover and crane.
"Crawler" traverses Lunar surface, smoothing, melting a top layer of regolith, then depositing elements of silicon PV cells directly on surface
Sketch of the Lunar Crawler to be used for fabrication of lunar solar cells on the surface of the Moon.
Shown here is an array of solar collectors that convert power into microwave beams directed toward Earth.
A solar power satellite built from a mined asteroid.

Since wires extending from Earth's surface to an orbiting satellite are not feasible with current technology, SBSP designs generally include the wireless power transmission with its concomitant conversion inefficiencies, as well as land use concerns for the necessary antenna stations to receive the energy at Earth's surface.

Inductive charging

A wirelessly powered model lorry at the Grand Maket Rossiya museum.
The primary coil in the charger induces a current in the secondary coil in the device being charged.
Wireless charging pad used to charge devices with the Qi standard.
Samsung Galaxy Note 10 smartphones have "Wireless PowerShare" technology
iPhone X being charged by a wireless charger.
200kW Charging-Pad for Buses, 2020 Bombardier Transportation.

Inductive charging (also known as wireless charging or cordless charging) is a type of wireless power transfer.

Inductance

Tendency of an electrical conductor to oppose a change in the electric current flowing through it.

T equivalent circuit of mutually coupled inductors
π equivalent circuit of coupled inductors

Stongly-coupled self-resonant coils can be used for wireless power transfer between devices in the mid range distances (up to two metres).

Induction cooking

Performed using direct induction heating of cooking vessels, rather than relying on indirect radiation, convection, or thermal conduction.

Top view of an induction cooktop
An induction cooking surface boiling water through several layers of newsprint. The paper is undamaged since heat is produced only in the bottom of the pot.
Inside view of an induction cooker: the large copper coil forms the magnetic field, a cooling fan is visible below it, and power supply and line filter surround the coil. In the centre of the coil is a temperature sensor, covered in white thermal grease
Side view of an induction stove
Cookware may carry a symbol that identifies it as compatible with an induction cooktop.
Household foil is much thinner than the skin depth in aluminum at the frequencies used by an induction cooker. Here the foil has melted where it was exposed to the air after steam formed under it. Cooking surface manufacturers prohibit the use of aluminum foil in contact with an induction cooking surface.
An early induction cooker patent from 1909 illustrates the principle. The coil of wire S induces a magnetic field in the magnetic core M. The magnetic field passes through the bottom of the pot A, inducing eddy currents within it. Unlike this concept, a modern cooking surface uses electronically generated high-frequency current.

The resulting oscillating magnetic field wirelessly induces an electrical current in the vessel.

Inductive coupling

In electrical engineering, two conductors are said to be inductively coupled or magnetically coupled when they are configured in a way such that change in current through one wire induces a voltage across the ends of the other wire through electromagnetic induction.

k is the coupling coefficient, Le1 and Le2 is the leakage inductance, M1 (M2) is the mutual inductance
Example of inductive coupling, 1910. The bottom coil is connected to AC power. The alternating magnetic field through the top coil induces current in it which lights the lamp.

Wireless power transfer

Microwave

Form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively.

A telecommunications tower with a variety of dish antennas for microwave relay links on Frazier Peak, Ventura County, California. The apertures of the dishes are covered by plastic sheets (radomes) to keep out moisture.
The atmospheric attenuation of microwaves and far infrared radiation in dry air with a precipitable water vapor level of 0.001 mm. The downward spikes in the graph correspond to frequencies at which microwaves are absorbed more strongly. This graph includes a range of frequencies from 0 to 1 THz; the microwaves are the subset in the range between 0.3 and 300 gigahertz.
Waveguide is used to carry microwaves. Example of waveguides and a diplexer in an air traffic control radar
Disassembled radar speed gun. The grey assembly attached to the end of the copper-colored horn antenna is the Gunn diode which generates the microwaves.
A satellite dish on a residence, which receives satellite television over a Ku band 12–14 GHz microwave beam from a direct broadcast communications satellite in a geostationary orbit 35,700 kilometres (22,000 miles) above the Earth
The parabolic antenna (lower curved surface) of an ASR-9 airport surveillance radar which radiates a narrow vertical fan-shaped beam of 2.7–2.9 GHz (S band) microwaves to locate aircraft in the airspace surrounding an airport.
Small microwave oven on a kitchen counter
Microwaves are widely used for heating in industrial processes. A microwave tunnel oven for softening plastic rods prior to extrusion.
Absorption wavemeter for measuring in the Ku band.
1.2 GHz microwave spark transmitter (left) and coherer receiver (right) used by Guglielmo Marconi during his 1895 experiments had a range of 6.5 km
ku band microstrip circuit used in satellite television dish.
Heinrich Hertz's 450 MHz spark transmitter, 1888, consisting of 23 cm dipole and spark gap at focus of parabolic reflector
Jagadish Chandra Bose in 1894 was the first person to produce millimeter waves; his spark oscillator (in box, right) generated 60 GHz (5 mm) waves using 3 mm metal ball resonators.
Microwave spectroscopy experiment by John Ambrose Fleming in 1897 showing refraction of 1.4 GHz microwaves by paraffin prism, duplicating earlier experiments by Bose and Righi.
Augusto Righi's 12 GHz spark oscillator and receiver, 1895
Antennas of 1931 experimental 1.7 GHz microwave relay link across the English Channel.
Experimental 700 MHz transmitter 1932 at Westinghouse labs transmits voice over a mile.
Southworth (at left) demonstrating waveguide at IRE meeting in 1938, showing 1.5 GHz microwaves passing through the 7.5 m flexible metal hose registering on a diode detector.
The first modern horn antenna in 1938 with inventor Wilmer L. Barrow
thumb|Randall and Boot's prototype cavity magnetron tube at the University of Birmingham, 1940. In use the tube was installed between the poles of an electromagnet
First commercial klystron tube, by General Electric, 1940, sectioned to show internal construction
British Mk. VIII, the first microwave air intercept radar, in nose of British fighter. Microwave radar, powered by the new magnetron tube, significantly shortened World War II.
Mobile US Army microwave relay station 1945 demonstrating relay systems using frequencies from 100 MHz to 4.9 GHz which could transmit up to 8 phone calls on a beam.

Microwaves can be used to transmit power over long distances, and post-World War 2 research was done to examine possibilities.

Nikola Tesla

Serbian-American inventor, electrical engineer, mechanical engineer, and futurist best known for his contributions to the design of the modern alternating current (AC) electricity supply system.

Portrait by Napoleon Sarony, 1890s
Rebuilt, Tesla's house (parish hall) in Smiljan, now in Croatia, region of Lika, where he was born, and the rebuilt church, where his father served. During the Yugoslav Wars, several of the buildings were severely damaged by fire. They were restored and reopened in 2006.
Tesla's baptismal record, 28 June 1856
Tesla's father, Milutin, was an Orthodox priest in the village of Smiljan.
Tesla aged 23, c. 1879
Edison Machine Works on Goerck Street, New York. Tesla found the change from cosmopolitan Europe to working at this shop, located amongst the tenements on Manhattan's lower east side, a "painful surprise".
Drawing from, illustrating the principle of Tesla's alternating current induction motor
Tesla's AC dynamo-electric machine (AC electric generator) in an 1888
Mark Twain in Tesla's South Fifth Avenue laboratory, 1894
Tesla demonstrating wireless lighting by "electrostatic induction" during an 1891 lecture at Columbia College via two long Geissler tubes (similar to neon tubes) in his hands
X-ray Tesla took of his hand
In 1898, Tesla demonstrated a radio-controlled boat which he hoped to sell as a guided torpedo to navies around the world.
Tesla sitting in front of a spiral coil used in his wireless power experiments at his East Houston St. laboratory
Tesla's Colorado Springs laboratory
A multiple exposure picture of Tesla sitting next to his "magnifying transmitter" generating millions of volts. The 7 m long arcs were not part of the normal operation, but only produced for effect by rapidly cycling the power switch.
Tesla's Wardenclyffe plant on Long Island in 1904. From this facility, Tesla hoped to demonstrate wireless transmission of electrical energy across the Atlantic.
Tesla's bladeless turbine design
Second banquet meeting of the Institute of Radio Engineers, 23 April 1915. Tesla is seen standing in the center.
Tesla on Time magazine commemorating his 75th birthday
Newspaper representation of the thought camera Tesla described at his 1933 birthday party
Room 3327 of the Hotel New Yorker, where Tesla died
Gilded urn with Tesla's ashes, in his favorite geometric object, a sphere (Nikola Tesla Museum, Belgrade)
Tesla c. 1896
Tesla c. undefined 1885
Nikola Tesla Museum in Belgrade, Serbia
Belgrade Nikola Tesla Airport was named after the scientist in 2006.
This Nikola Tesla statue in Zagreb, Croatia was made by Ivan Meštrović in 1954. It was located at the Ruđer Bošković Institute before it was moved to the Tesla street in the city center in 2006.
Nikola Tesla Corner in New York City
Nikola Tesla statue in Niagara Falls, Ontario

From the 1890s through 1906, Tesla spent a great deal of his time and fortune on a series of projects trying to develop the transmission of electrical power without wires.

Tesla coil

Electrical resonant transformer circuit designed by inventor Nikola Tesla in 1891.

Tesla coil at Questacon, the National Science and Technology center in Canberra, Australia
Homemade Tesla coil in operation, showing brush discharges from the toroid. The high electric field causes the air around the high voltage terminal to ionize and conduct electricity, allowing electricity to leak into the air in colorful corona discharges, brush discharges and streamer arcs. Tesla coils are used for entertainment at science museums and public events, and for special effects in movies and television
Large coil producing 3.5 meter (10 foot) streamer arcs, indicating a potential of millions of volts
Solid state DRSSTC Tesla coil with pointed wire attached to toroid to produce brush discharge
Electric discharge showing the lightning-like plasma filaments from a 'Tesla coil'
Tesla coil (discharge)
Tesla coil in terrarium (I)
A small, later-type Tesla coil in operation: The output is giving 43 cm sparks. The diameter of the secondary is 8 cm. The power source is a 10 000 V, 60 Hz current-limited supply
Electrum sculpture, the world's largest Tesla coil. Builder Eric Orr is visible sitting inside the hollow spherical high voltage electrode

Tesla used these circuits to conduct innovative experiments in electrical lighting, phosphorescence, X-ray generation, high frequency alternating current phenomena, electrotherapy, and the transmission of electrical energy without wires.

ISM radio band

The ISM radio bands are portions of the radio spectrum reserved internationally for industrial, scientific and medical (ISM) purposes, excluding applications in telecommunications.

Comparison of frequency band designations

Long-distance wireless power systems have been proposed and experimented with which would use high-power transmitters and rectennas, in lieu of overhead transmission lines and underground cables, to send power to remote locations.

Coupling (electronics)

Transfer of electrical energy from one circuit to another, or between parts of a circuit.

Modern surface-mount electronic components on a printed circuit board, with a large integrated circuit at the top.

Atmospheric plasma channel coupling