Otis Singleton
Radio waves are produced when an electric field rapidly changes, creating an alternating current. This alternating current generates a magnetic field that expands quickly and then collapses when the current decreases or stops. The collapse of this magnetic field creates a radio signal. Researchers have developed devices that can convert radio waves into electricity, such as rectennas, which are receiving antennas that convert energy from electromagnetic waves into electricity. These devices have the potential to power portable electronics and medical devices, as well as harvest energy from radio waves to power smart cities and vehicles.
| Characteristics | Values |
|---|---|
| How electricity turns into radio waves | When an electric field changes, it creates a disturbance in the space around it, which moves outward at the speed of light, creating a wave. This wave is a radio wave. |
| Radio waves | Produced when the electric field rapidly changes; there must be an alternating current. |
| Electric field | Spreads out into space. When changed, the distant parts do not change instantly. |
| Magnetic field | Created perpendicular to the current. When the current decreases, stops, or reverses, the magnetic field starts to collapse, and the remaining field is a radio signal. |
| Rectennas | Receiving antennas that convert energy from electromagnetic waves into electricity. |
| Applications | Medical devices, powering ultra-low-powered devices, powering implants, cellphones, and other portable devices |
| Materials | Graphene combined with boron nitride, molybdenum disulfide (MoS2) |
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What You'll Learn
Electric circuits and radio waves
Radio waves are a type of electromagnetic wave, and they are all around us. These waves are produced by fluctuating electric fields, which create a disturbance in the field that spreads out into space, much like a ripple in a pond. Electric circuits create these disturbances, and the radio waves propagate in a pattern depending on the number of times the circuit is turned on and off.
The process of converting electricity into radio waves involves the use of an electrical circuit with diodes to generate an electric field. This field can then steer the radio waves through the device as a direct current (DC). The diode allows for the conversion of signals at higher frequencies by reducing parasitic capacitance. This is achieved through the use of a material like molybdenum disulfide (MoS2), which behaves as a switch, changing from a semiconductor to a metallic structure.
Radio waves can also be converted back into electricity through the use of rectennas, which are receiving antennas that can convert the energy from electromagnetic waves into electricity. This technology has been used in RFID cards and could potentially power medical implants and other portable devices.
Researchers at the University of Central Florida have developed a prototype system that can harness the electrical potential of radio frequency electromagnetic waves to power ultra-low-powered devices without batteries. This technology uses piezoelectric materials, which generate an electrical charge through mechanical stress on solid objects.
Additionally, graphene, a carbon material with unique quantum mechanical properties, has been combined with boron nitride to create a device that can convert terahertz waves into a direct current.
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Magnetic fields and radio signals
Radio waves are a type of electromagnetic radiation, which also includes microwaves, gamma rays, and visible light. They are generated by accelerating charged particles and can be naturally emitted, as seen in radiation from the Sun, or artificially generated for various applications.
Electromagnetic waves are composed of electric and magnetic fields, which obey the properties of superposition. These fields can have components in the same or opposite directions, resulting in constructive or destructive interference, respectively. James Clerk Maxwell's equations revealed the wave-like nature of these fields and their symmetry.
In certain circumstances, magnetic fields can weakly influence the propagation of radio waves. This is because magnetic fields contain energy and contribute to the mass-energy tensor in General Relativity. As a result, they produce a very small gravitational effect that can bend the path of electromagnetic radiation, including radio waves. However, the effect is minuscule, and it is generally accepted that magnetic fields do not interact with radio waves.
It is important to distinguish between the effects of magnetic fields and the influence of matter and metals, which can affect the propagation of radio waves. For example, electrical wires create a magnetic field perpendicular to their length, depending on the current running through them. However, the impact of this magnetic field on radio waves is negligible unless the wire acts as a correctly matched antenna.
Radio waves have found applications in wireless energy transmission and data transmission. For instance, rectennas, or receiving antennas, can convert energy from radio waves into electricity, powering devices such as RFID cards and medical implants.
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Converting radio waves into electricity
Radio waves can be converted into electricity using a rectifier, which is a device that converts alternating current (AC) to direct current (DC). This process involves using an electrical circuit with diodes to generate an electric field that can steer radio waves through the device as a DC current. This technology is known as a rectenna, a blend of the words "rectifying" and "antenna". Rectennas are receiving antennas that can convert energy from electromagnetic waves into electricity.
The process of converting radio waves into electricity typically involves the following steps:
- The AC signal from the radio waves is converted to DC using a diode, which is a device that allows current to flow in only one direction.
- The anode of a small-signal diode is connected to the antenna wire, while the cathode is connected to one terminal of a galvanometer.
- The ground wire is then touched to the other terminal of the galvanometer, causing the needle to jump, indicating the presence of DC.
It is important to note that radio waves yield very small amounts of power, so the use of an antenna to investigate electricity is generally safe. However, it is recommended to use insulated wire and avoid conducting experiments near electrical outlets, power lines, or during thunderstorms.
Researchers have developed innovative ways to utilise this technology. For example, a stretchable wideband dipole antenna system can wirelessly transmit data collected from health-monitoring sensors. Additionally, rectennas have been proposed to power implantable medical devices, allowing them to transmit patient health data wirelessly. This technology could also be used to power smartwatches and other portable devices, such as cellphones and implants.
Another approach to converting radio waves into electricity involves the use of graphene combined with boron nitride. This design takes advantage of the quantum mechanical behaviour of graphene. By combining it with boron nitride, the electrons in graphene are directed towards a common direction. Incoming terahertz waves then shuttle the electrons through the material as a direct current.
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Radio wave power transfer
Radio waves are a type of electromagnetic wave that can be converted into electricity. This process involves using a receiving antenna called a rectenna, which combines the words rectifying and antenna. Rectennas convert the energy from electromagnetic waves, including radio waves, into electricity.
A novel device developed by researchers at Carnegie Mellon University can charge electronics using the energy from radio-frequency waves, such as Wi-Fi signals. This technology could be used to power implants, cellphones, and other portable devices, offering an advantage over lithium-ion batteries, which have limited capacity and safety concerns.
The process of converting electricity into radio waves involves creating an electric field that spreads out into space. By fluctuating the electric field, a wave is created. This wave travels at the speed of light and can be used to transmit information or power.
Additionally, at MIT, researchers have been working on a design that takes advantage of the quantum mechanical behavior of graphene. By combining graphene with boron nitride, the electrons in graphene are directed toward a common direction. Incoming terahertz waves then shuttle these electrons, creating a direct current that can be used as an energy source.
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Radio waves and medical devices
Radio waves are a type of electromagnetic radiation, characterised by their wavelength and frequency. Radio waves are generated by the movement of electrical charges in an antenna.
Radio waves have been used in medical applications for over 125 years. Radiofrequency (RF) energy is used in diathermy, a treatment that uses RF-induced heat as a form of physical therapy and in surgical procedures. Diathermy can be used to destroy neoplasms, warts, and infected tissues, and to cauterise blood vessels to prevent excessive bleeding. The technique is particularly valuable in neurosurgery and surgery of the eye.
RF energy is also used in hyperthermy treatment for cancer, electrosurgery scalpels, and radiofrequency ablation. Magnetic resonance imaging (MRI) uses radio frequency waves to generate images of the human body. Radio frequencies are also used in aesthetic treatments, such as skin tightening, fat reduction, and promoting healing.
Pulsed electromagnetic field therapy (PEMF) is a medical treatment that uses electromagnetic radiation of different frequencies, including RF, to purportedly help heal bone tissue. This method was explored in a NASA study. RF electromagnetic waves have also been used to power optogenetic microneedles injected into mice.
In addition, radio waves in the form of Wi-Fi, Bluetooth, and cellular signals can be used to transmit patients' health data from implantable medical devices. This technology could provide an advantage over current lithium-ion battery technologies, which can be dangerous and have limited capacity.
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Frequently asked questions
Radio waves are produced when an electric field rapidly changes, creating an alternating current.
An electric field is created by a magnetic field, which is produced when a current flows. When the current decreases, stops, or reverses, the magnetic field starts to collapse, and the remaining magnetic field becomes a radio signal.
Radio waves are used for wireless energy transmission, Wi-Fi signals, Bluetooth, and cellular signals.
Yes, rectennas are receiving antennas that can convert energy from radio waves into electricity.
Radio waves can be used to power ultra-low-powered devices without the need for batteries or sensors, and they can also be used to transmit data and power wirelessly.
