Otis Singleton
Antennas, also known as aerials, are metal rods or dishes that catch radio waves and convert them into electrical signals for devices such as radios, televisions, and telephones. Transmitters, a type of antenna, perform the opposite function, converting electrical signals into radio waves that can travel vast distances. Radio waves are a type of electromagnetic wave, which are created by the exchange of energy between electric and magnetic waves at a fixed frequency. This frequency is determined by the energy source and cannot be changed as the waves travel through space. In radio communication, an amplifier strengthens a weak signal using energy from another source. Transmitters that can produce higher-frequency microwaves are required for efficient transmission.
| Characteristics | Values |
|---|---|
| Wireless power transfer | Wireless energy transmission or WET |
| Wireless power transmission system | An electrically powered transmitter device generates a time-varying electromagnetic field that transmits power across space to a receiver device |
| Wireless power techniques | Near and far field |
| Near-field or non-radiative techniques | Power is transferred over short distances by magnetic fields using inductive coupling between coils of wire, or by electric |
| Far-field methods | High-directivity antennas or well-collimated laser light produce a beam of energy that can be made to match the shape of the receiving area |
| Radio communication | At the receiver, an amplifier intensifies a weak signal using energy from another source |
| Radio waves | Travel at the speed of light, taking your radio program with them |
| Radio waves | Can speed around the Earth's curvature in what's known as a ground wave |
| Radio waves | Shoot up to the sky, bounce off the ionosphere (an electrically charged part of Earth's upper atmosphere), and come back down to the ground again |
| Radio waves | During the daytime, waves shooting off to the sky are absorbed by lower layers of the ionosphere |
| Radio waves | At night, higher layers of the ionosphere catch the radio waves and fling them back to Earth |
| Digital signals | An abstraction that humans use to describe and understand things by omitting information that is not of interest |
| Digital signals | Do not exist in reality |
| Digital signals | Must be converted first into something that exists outside of abstraction, like an analog signal which represents the information to be transmitted |
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What You'll Learn
Radio waves and how they are transmitted and received
Radio waves are a type of electromagnetic radiation with the lowest frequencies and longest wavelengths in the electromagnetic spectrum. They typically have frequencies below 300 gigahertz (GHz) and wavelengths greater than 1 millimeter. Radio waves are generated by charged particles undergoing acceleration, such as time-varying electric currents.
Radio waves are transmitted and received through antennas, also known as aerials. An antenna acts as a receiver by catching radio waves and turning them into electrical signals that feed into devices like radios, televisions, or telephones. When radio waves strike the receiving antenna, they push the electrons in the metal back and forth, creating tiny oscillating currents that are detected by the receiver.
A transmitter is a different type of antenna that performs the opposite function of a receiver. It turns electrical signals into radio waves, allowing them to travel vast distances. In radio communication, the transmitter generates higher-frequency microwaves, which can be focused in narrow beams toward a receiver.
The development of microwave technology, such as klystron and magnetron tubes, and parabolic antennas, has made long-distance wireless power transmission possible. Radio waves can be bent or reflected back to Earth by the ionosphere, enabling global radio transmission. Additionally, the ground wave, a form of electromagnetic wave that closely follows the Earth's surface, particularly over water, further facilitates long-distance communication.
Radio waves are used for wireless transmission of sound messages, information, and communication, as well as for maritime and aircraft navigation. They play a crucial role in modern telecommunication, allowing simultaneous transmission of signals from multiple transmitters without interference.
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How antennas work
Antennas are metal rods or dishes that transmit or receive radio waves. They are critical for establishing and maintaining a reliable radio connection. Transmitters are a type of antenna that turns electrical signals into radio waves so they can travel long distances. Receivers, another type of antenna, do the opposite job of a transmitter: they catch radio waves and turn them into electrical signals that feed into devices like radios, televisions, or telephones.
Radio waves are a combination of a magnetic field at a right angle to an electric field. Both fields oscillate at a specific frequency and travel together in a direction perpendicular to both fields. These electromagnetic fields move at the speed of light through free space. The voltage across the antenna elements and the current through them create the electric and magnetic waves, respectively.
The radiation pattern of an ideal isotropic antenna, which radiates equally in all directions, would look like a sphere when represented by a three-dimensional graph or polar plot. Many nondirectional antennas, such as monopoles and dipoles, emit equal power in all horizontal directions, with the power dropping off at higher and lower angles. This is called an omnidirectional pattern. The radiation of many antennas shows a pattern of maxima or "lobes" at various angles, separated by "nulls", angles where the radiation falls to zero. This is because the radio waves emitted by different parts of the antenna typically interfere, causing maxima at angles where the radio waves arrive in phase and zero radiation at other angles where the waves arrive out of phase.
The height of an antenna affects the distance over which it can transmit a signal. For example, arrays of vertical towers are used to achieve directionality at low frequencies and will occupy large areas of land. For non-directional portable use, a short vertical antenna or small loop antenna works well.
Wireless power transfer (WPT) is the transmission of electrical energy without wires as a physical link. In a wireless power transmission system, a transmitter device generates a time-varying electromagnetic field that transmits power across space to a receiver device, which extracts the power from the field and supplies it to an electrical load. Wireless power techniques mainly fall into two categories: near and far field. In near-field or non-radiative techniques, power is transferred over short distances by magnetic fields using inductive coupling between coils of wire, or by electric fields. In far-field methods, longer ranges are achieved, often multiple kilometers. High-directivity antennas or well-collimated laser light produce a beam of energy that can be made to match the shape of the receiving area.
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Wireless power transfer
The basic principle behind WPT is electromagnetic induction, where induction coils produce an electromagnetic field that transmits power across space. The transmitter device, connected to a power source, generates a time-varying electromagnetic field. The receiver device, which can be a coil on a portable device, then extracts power from this field and converts it into electrical power, supplying it to an electrical load. This process is also known as inductive coupling or resonant inductive coupling.
WPT can be categorized into near-field (non-radiative) and far-field (radiative) techniques. In near-field techniques, power is transferred over short distances using magnetic fields and inductive coupling between coils. This method is commonly used for charging handheld devices such as phones and electric toothbrushes. Far-field techniques, also called power beaming, use electromagnetic radiation like microwaves or laser beams to transfer power over longer distances. However, these techniques require the transmitter to be aimed at the receiver.
The efficiency of WPT is a critical parameter, as the goal is to ensure sufficient energy reception by the receiver. This efficiency is influenced by the distance between the transmitter and receiver, with wireless power technologies potentially limited by distance. Additionally, WPT systems must consider the potential exposure of people and living beings to electromagnetic fields, ensuring their safety.
WPT has been an area of interest since the late 1890s, with Nikola Tesla's experiments in wireless power transmission. Today, companies like PowerbyProxi are leading innovators in the wireless power field, offering solutions for efficient power transfer in various applications, including industrial and consumer electronics. The Wireless Power Consortium (WPC) has also standardized Qi charging, which supports both inductive and resonant charging technologies. As technology progresses, WPT is expected to play a significant role in shaping the future of electronic devices and systems.
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The role of electromagnetic waves
Electromagnetic waves are crucial in transmitting electrical signals wirelessly, enabling communication and power transfer without the need for physical connections. These waves are formed by the exchange of energy between electric and magnetic waves at a fixed frequency, determined by the energy source.
In the context of wireless communication, electromagnetic waves are utilised to transmit information. Antennas, also known as aerials, act as receivers by capturing radio waves and converting them into electrical signals for devices like radios, televisions, and telephones. Transmitters, on the other hand, transform electrical signals into radio waves, allowing them to travel vast distances. This bidirectional functionality of antennas is fundamental to modern telecommunication systems.
The process of transmitting electrical signals wirelessly involves several key steps. Firstly, microphones convert sound into electrical energy, which is then amplified and transformed into radio waves by transmitters. These radio waves, travelling at the speed of light, carry the encoded information. Upon reaching the receiver, the radio waves are converted back into electrical signals, which are then interpreted by electronic components and transformed into a format that we can understand, such as sound or images.
The development of microwave technology during World War II played a pivotal role in advancing wireless power transmission. Researchers like William C. Brown and Peter Glaser made significant contributions to this field. Brown's invention of the rectenna in 1964 enabled the efficient conversion of microwaves to DC power, paving the way for wireless-powered aircraft. Glaser's concept, introduced in 1968, proposed harnessing solar energy and transmitting it as microwaves to rectennas for conversion into electrical energy.
Wireless power transfer offers notable advantages, including enhanced mobility, convenience, and safety for electronic devices. It eliminates the need for interconnecting wires and batteries, making it particularly useful in situations where wired connections are impractical, hazardous, or impossible. This technology has broad applications, from powering devices to providing wireless lighting, heat, and motive power.
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The history of wireless signalling
In the 17th and 18th centuries, experiments were conducted, and in 1807, French mathematician Jean Baptiste Joseph Fourier discovered Fourier's theorem. In 1820, Danish physicist Hans Christian Orsted discovered the electromagnetic field caused by electric current. In 1831, British scientist Michael Faraday discovered electromagnetic induction and predicted the existence of electromagnetic waves. In 1837, the US House of Representatives passed a resolution to investigate the feasibility of a semaphore system, which had been experimented with in France and the Netherlands in the 1830s.
In 1864, James Clerk Maxwell proved the existence of electromagnetic waves, and Heinrich Hertz sent and received wireless waves in 1888. In 1866, American dentist Dr. Mahlon Loomis patented and demonstrated a wireless transmission system over a 22km distance. In 1882, American physicist Amos Emerson Dolbear patented a wireless transmission system using an induction coil, microphone, telephone receiver, and battery.
The first wireless telegraph system was invented by Italian engineer Guglielmo Marconi in 1894 or 1896. He sent Morse radio signals over a mile and later across the Atlantic Ocean. Marconi demonstrated a radio transmission to a tugboat over an 18-mile path across the English Channel in 1897. He sent the first international wireless message from England to France in 1899. Marconi's work earned him the 1909 Nobel Prize in Physics, shared with Karl Ferdinand Braun, for their contributions to wireless telegraphy.
The first mobile telephone call from handheld equipment was made in 1973 by Martin Cooper, a researcher at Motorola. This marked a technological revolution, and today, with over 6.6 billion mobile cellular subscriptions worldwide, wireless phones are a ubiquitous part of everyday life.
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Frequently asked questions
A signal is the process and result of transmitting data through media by embedding some variation. In electronics and telecommunications, a signal is a time-varying voltage, current, or electromagnetic wave that carries information.
An electrical signal is a type of analog signal that uses the voltage, current, or frequency of the signal to convey information. For example, a microphone converts an acoustic signal to a voltage waveform.
An airborne electrical signal is transmitted through the air as radio waves. Radio waves are a type of electromagnetic radiation that travels at the speed of light.
Airborne electrical signals are transmitted by a transmitter, which converts electrical signals into radio waves. These radio waves can then be received by an antenna, which converts the radio waves back into electrical signals that can be understood by devices such as radios or televisions.
The theory of radio was first developed by Scottish physicist James Clerk Maxwell in 1864. In 1888, Heinrich Hertz proved the existence of radio waves, and in 1894, English physicist Oliver Lodge demonstrated how radio waves could be used for signalling. The first long-distance wireless power transmission was achieved in the 1960s by William C. Brown.
