A rectenna (''rec''tifying ant''enna'') is a special type of receiving antenna that is used for converting

electromagnetic In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of a ...

energy into

direct current Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or eve ...

(DC)

electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as describ ...

. They are used in wireless power transmission systems that transmit power by

radio waves Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz ( GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (s ...

. A simple rectenna element consists of a

dipole antenna In radio and telecommunications a dipole antenna or doublet is the simplest and most widely used class of antenna. The dipole is any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole w ...

with an RF diode connected across the dipole elements. The diode rectifies the AC induced in the antenna by the microwaves, to produce DC power, which powers a load connected across the diode.

Schottky diode The Schottky diode (named after the German physicist Walter H. Schottky), also known as Schottky barrier diode or hot-carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal. It has a low forward voltag ...

s are usually used because they have the lowest voltage drop and highest speed and therefore have the lowest power losses due to conduction and switching. Large rectennas consist of an array of many power receiving elements such as dipole antennas. Meshed1GHzPrintedRectenna

Power beaming applications

The invention of the rectenna in the 1960s made long distance wireless power transmission feasible. The rectenna was invented in 1964 and patented in 1969 by US electrical engineer William C. Brown, who demonstrated it with a model helicopter powered by microwaves transmitted from the ground, received by an attached rectenna. Since the 1970s, one of the major motivations for rectenna research has been to develop a receiving antenna for proposed

solar power satellite Space-based solar power (SBSP, SSP) is the concept of collecting solar power in outer space by solar power satellites (SPS) and distributing it to Earth. Its advantages include a higher collection of energy due to the lack of reflection and a ...

s, which would harvest energy from sunlight in space with

solar cell A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. A proposed military application is to power

drone Drone most commonly refers to: * Drone (bee), a male bee, from an unfertilized egg * Unmanned aerial vehicle * Unmanned surface vehicle, watercraft * Unmanned underwater vehicle or underwater drone Drone, drones or The Drones may also refer to: ...

reconnaissance aircraft with microwaves beamed from the ground, allowing them to stay aloft for long periods. Millimeter wave textile rectenna

In recent years, interest has turned to using rectennas as power sources for small wireless microelectronic devices. The largest current use of rectennas is in

RFID Radio-frequency identification (RFID) uses electromagnetic fields to automatically identify and track tags attached to objects. An RFID system consists of a tiny radio transponder, a radio receiver and transmitter. When triggered by an electroma ...

tags,

proximity card A proximity card or prox card also known as a key card or keycard is a contactless smart card which can be read without inserting it into a reader device, as required by earlier magnetic stripe cards such as credit cards and contact type sma ...

s and

contactless smart card A contactless smart card is a contactless credential whose dimensions are credit-card size. Its embedded integrated circuits can store (and sometimes process) data and communicate with a terminal via NFC. Commonplace uses include transit ticke ...

s, which contain an integrated circuit ( IC) which is powered by a small rectenna element. When the device is brought near an electronic reader unit, radio waves from the reader are received by the rectenna, powering up the IC, which transmits its data back to the reader.

Radio frequency rectennas

The simplest

crystal radio A crystal radio receiver, also called a crystal set, is a simple radio receiver, popular in the early days of radio. It uses only the power of the received radio signal to produce sound, needing no external power. It is named for its most impo ...

receiver, employing an antenna and a demodulating diode (

rectifier A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation (converting DC to AC) is performed by an inve ...

), is actually a rectenna, although it discards the

DC component DC, D.C., D/C, Dc, or dc may refer to: Places * Washington, D.C. (District of Columbia), the capital and the federal territory of the United States * Bogotá, Distrito Capital, the capital city of Colombia * Dubai City, as distinct from t ...

before sending the signal to the headphones. People living near strong radio

transmitter In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to ...

s would occasionally discover that with a long receiving antenna, they could get enough electric power to light a light bulb. However, this example uses only one antenna having a limited capture area. A rectenna array uses multiple antennas spread over a wide area to capture more energy. Researchers are experimenting with the use of rectennas to power sensors in remote areas and distributed networks of sensors, especially for

IoT The Internet of things (IoT) describes physical objects (or groups of such objects) with sensors, processing ability, software and other technologies that connect and exchange data with other devices and systems over the Internet or other com ...

applications. RF rectennas are used for several forms of

wireless power transfer Wireless power transfer (WPT), wireless power transmission, wireless energy transmission (WET), or electromagnetic power transfer is the transmission of electrical energy without wires as a physical link. In a wireless power transmission system, ...

. In the microwave range, experimental devices have reached a power conversion efficiency of 85–90%. The record conversion efficiency for a rectenna is 90.6% for 2.45 GHz,McSpadden, J. O., Fan, L., and Kai Chang, "Design and Experiments of a High-Conversion-Efficiency 5.8-GHz Rectenna," ''IEEE Trans. Microwave Theory and Technique'', Vol. 46, No. 12, December 1998, pp. 2053–2060. https://ieeexplore.ieee.org/document/739282 with lower efficiency of about 82% achieved at 5.82 GHz.

Optical rectennas

In principle, similar devices, scaled down to the proportions used in

nanotechnology Nanotechnology, also shortened to nanotech, is the use of matter on an atomic, molecular, and supramolecular scale for industrial purposes. The earliest, widespread description of nanotechnology referred to the particular technological goal o ...

, can be used to convert

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...

directly into electricity. This type of device is called an '' optical rectenna'' (or "nantenna"). Theoretically, high efficiencies can be maintained as the device shrinks, but to date efficiency has been limited, and so far there has not been convincing evidence that rectification has been achieved at optical frequencies. The

University of Missouri The University of Missouri (Mizzou, MU, or Missouri) is a public land-grant research university in Columbia, Missouri. It is Missouri's largest university and the flagship of the four-campus University of Missouri System. MU was founded ...

previously reported on work to develop low-cost, high-efficiency optical-frequency rectennas. Other prototype devices were investigated in a collaboration between the

University of Connecticut The University of Connecticut (UConn) is a public land-grant research university in Storrs, Connecticut, a village in the town of Mansfield. The primary 4,400-acre (17.8 km2) campus is in Storrs, approximately a half hour's drive from H ...

and

Penn State Altoona Penn State Altoona is a Pennsylvania State University Commonwealth campuses, commonwealth campus of Pennsylvania State University, The Pennsylvania State University located in Logan Township, Blair County, Pennsylvania, Logan Township, Pennsylvan ...

using a grant from the

National Science Foundation The National Science Foundation (NSF) is an independent agency of the United States government that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National ...

. With the use of

atomic layer deposition Atomic layer deposition (ALD) is a thin-film deposition technique based on the sequential use of a gas-phase chemical process; it is a subclass of chemical vapour deposition. The majority of ALD reactions use two chemicals called precursors (a ...

it has been suggested that conversion efficiencies of solar energy to electricity higher than 70% could eventually be achieved. The creation of successful optical rectenna technology has two major complicating factors: # Fabricating an antenna small enough to couple optical wavelengths. # Creating an ultra-fast diode capable of rectifying the high frequency oscillations, at frequency of ~500 THz. Below are a few examples of potential paths to creating diodes that would be fast enough to rectify optical and near-optical radiation.

Geometric diodes

A promising path towards creating these ultrafast diodes has been in the form of "

geometric diode Geometric diodes, also known as morphological diodes, use the shape of their structure and ballistic / quasi- ballistic electron transport to create diode behavior. Geometric diodes differ from all other forms of diodes because they do not rely on ...

s". Graphene geometric diodes have been reported to rectify

terahertz radiation Terahertz radiation – also known as submillimeter radiation, terahertz waves, tremendously high frequency (THF), T-rays, T-waves, T-light, T-lux or THz – consists of electromagnetic waves within the ITU-designated band of fre ...

. In April 2020, geometric diodes were reported in

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...

nanowires A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre (10−9 metres). More generally, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less ...

. The wires were shown experimentally to rectify up to 40 GHz, but that was instrument limited, and theoretically may be able to rectify signals in the THz region as well.

References

External links