Umair Gaines
Scientists have been exploring ways to convert radio waves into electricity, with the aim of powering electronic devices such as implants, cellphones, and other portable devices. This process involves the use of rectifiers or antennas to convert electromagnetic waves from their oscillating current to direct current. The concept, known as Electromagnetic energy harvesting from ambient radiation sources, has led to the development of rectennas, which are receiving antennas that can convert energy from electromagnetic waves into electricity. This technology has the potential to power low-energy devices and sensors in urban environments, as well as medical devices, by harvesting Wi-Fi, Bluetooth, and cellular signals that are constantly around us.
| Characteristics | Values |
|---|---|
| Process | Converting electricity into radio waves |
| Devices | Rectennas, rectifiers, antennas |
| Materials | Graphene, boron nitride, MoS2, piezoelectric materials |
| Use Cases | Wireless energy transmission, RFID cards, Wi-Fi signals, medical devices, charging electronics, smart cities, IoT |
| Challenges | Signal transmission, power requirements, frequency range, efficiency, scalability |
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What You'll Learn
- Using rectennas to convert radio waves into electricity
- How antennas turn radio waves into electricity?
- The use of piezoelectric materials to generate electricity from radio waves
- The conversion of electromagnetic waves into direct current
- The use of graphene to convert terahertz waves into direct current
Using rectennas to convert radio waves into electricity
Wireless energy transmission was made possible in the 1960s with the invention of the rectenna, a portmanteau of the words "rectifying" and "antenna". Rectennas are receiving antennas that convert energy from electromagnetic waves into electricity.
Rectennas can wirelessly harvest electromagnetic radiation in the Wi-Fi (2.4 GHz and 5.9 GHz), global satellite positioning (1.58 GHz and 1.22 GHz), cellular communications fourth-generation (4G) (1.7 GHz and 1.9 GHz), and Bluetooth (2.4 GHz) bands. They then convert the energy from these electromagnetic waves into alternating current (AC). The AC electricity is then sent to the rectifier, which converts it to direct current (DC) electricity.
In a paper published in the journal Nature, Dr. Xu Zhang and co-authors from Carnegie Mellon University describe a novel device that can charge electronics using the energy from radio-frequency waves, including Wi-Fi signals. The authors describe their design as a building block that can be integrated into and provide power for the fast-evolving world of flexible electronic systems. The MoS2 sheets for the rectifiers can be produced inexpensively, enabling the researchers' vision of a "smart-skin" application: a distributed network of sensors covering and providing information about our buildings and infrastructure.
Another potential application for this technology is in medical devices. Co-author Jesús Grajal from the Technical University of Madrid says that they could allow implantable medical devices to transmit patients' health data, as radio waves in the form of Wi-Fi, Bluetooth, and cellular signals are constantly surrounding us. This presents an advantage over current lithium-ion battery technologies, which can be fatal if they leak and have far more limited capacity due to space and chemical issues.
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How antennas turn radio waves into electricity
Radio waves can be converted into electricity with the help of antennas. This process of converting radio waves into electricity is known as "Electromagnetic energy harvesting from ambient radiation sources".
Receiving antennas can wirelessly harvest electromagnetic radiation in the Wi-Fi (2.4 GHz and 5.9 GHz), global satellite positioning (1.58 GHz and 1.22 GHz), the cellular communications fourth-generation (4G) (1.7 GHz and 1.9 GHz), and Bluetooth (2.4 GHz) bands. This energy from electromagnetic waves is converted into alternating current (AC) electricity. The AC electricity is then sent to the rectifier, which converts it to direct current (DC) electricity.
The authors of this process describe their design as a building block that can be integrated and provide power for the fast-evolving world of flexible electronic systems. The MoS2 sheets for the rectifiers can be produced inexpensively, enabling the researchers' vision of a "smart-skin" application: a distributed network of sensors covering and providing information about our buildings and infrastructure.
In a recent development, researchers have designed a new metasurface-based antenna that takes us a step forward in the quest to practically harvest energy from radio waves. The metamaterial used to make the antenna exhibits perfect absorption of radio waves and was designed to work with low intensities. Lab tests of the device showed that it can harvest 100 microwatts of power from radio waves with an intensity of just 0.4 microwatts per square centimetre, approximately the level of intensity of the radio waves 100 metres from a cell phone tower.
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The use of piezoelectric materials to generate electricity from radio waves
Radio waves are a type of electromagnetic wave, and electromagnetic waves can be converted into electricity. One way to do this is through the use of receiving antennas, or rectennas, which convert energy from electromagnetic waves into electricity.
Piezoelectric materials can also be used to generate electricity from radio waves. The piezoelectric effect is a reversible process where certain crystalline materials with no inversion symmetry exhibit an electromechanical interaction between their mechanical and electrical states. This means that when the structure of these materials is deformed, they generate piezoelectricity, and conversely, when an external electric field is applied, their static dimension changes.
Piezoelectric materials such as quartz crystals have been used to generate electricity from the impact of cars driving over them on highways and from people dancing on a floor made of piezoelectric materials. The amount of electricity generated from these methods is small, but enough to power a light with 60 people dancing.
Another application of piezoelectric materials is in the detection and generation of sonar waves, as well as in power monitoring for medical treatment, sonochemistry, and industrial processing. Piezoelectric transducers are also used in electronic drum pads and to detect muscle movements in medical acceleromyography.
The global energy crisis and environmental pollution caused by non-renewable energy sources have prompted researchers to explore alternative energy technologies that can harvest energy from the ambient environment. Piezoelectric energy harvesting is one such technology that has received interest from the scientific community due to its high electromechanical coupling factor and piezoelectric coefficient. Recent advancements in micro and nanoscale materials and manufacturing processes have made piezoelectric generators more flexible, stretchable, and easily integrable for diverse applications.
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The conversion of electromagnetic waves into direct current
Electromagnetic waves can be converted into electricity through a process called "Electromagnetic energy harvesting from ambient radiation sources". This process involves the use of antennas or rectennas (a blend of the words rectifying and antenna) to convert energy from electromagnetic waves into electricity. Rectennas are receiving antennas that can harvest electromagnetic radiation in the Wi-Fi (2.4 GHz and 5.9 GHz), global satellite positioning (1.58 GHz and 1.22 GHz), cellular communications (1.7 GHz and 1.9 GHz), and Bluetooth (2.4 GHz) bands. The harvested energy is in the form of alternating current (AC) electricity, which is then sent to a rectifier that converts it into direct current (DC) electricity.
In the context of converting electromagnetic waves into DC electricity, the rectifier plays a crucial role. A rectifier is a device that converts alternating current (AC) to direct current (DC). In the case of electromagnetic wave conversion, the rectifier receives the AC electricity generated by the antenna or rectenna and converts it into DC electricity. This process enables the utilization of electromagnetic wave energy for various applications, such as powering wireless sensors, implantable medical devices, and other electronic systems.
The design of efficient rectifiers is essential for maximizing the conversion of electromagnetic waves into DC electricity. Researchers have developed flexible rectifiers using MoS2 sheets, which can create Schottky diodes (a junction of semiconductor and metal). These Schottky diodes can convert signals at higher frequencies due to the reduction in parasitic capacitance, allowing for the capture of high-frequency Wi-Fi band radio waves. This technology has the potential to power a wide range of electronic devices and systems.
Additionally, there are other methods for converting electromagnetic waves into electricity, such as using piezoelectric sensors for energy harvesting or electromagnetic energy harvesters that capture energy from low-frequency vibrations. These methods can be explored for specific applications, such as wireless transmission systems or structural health monitoring systems, where battery power may be limited. Overall, the conversion of electromagnetic waves into direct current opens up opportunities for innovative solutions in energy harvesting and wireless power transmission.
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The use of graphene to convert terahertz waves into direct current
Converting electricity into radio waves involves the use of antennas, which can turn electrical power into radio waves and vice versa. This process, known as electromagnetic energy harvesting from ambient radiation sources, allows energy from electromagnetic waves to be converted into electricity.
Researchers at MIT have been working on developing a graphene-based device that can convert ambient terahertz waves into a direct current. Terahertz waves, also known as T-rays, are electromagnetic waves with frequencies between microwaves and infrared light. They are emitted by any device that sends out a Wi-Fi signal and are also produced by objects that register a temperature, including human bodies and inanimate objects.
The MIT team's design takes advantage of the quantum mechanical behaviour of graphene. By combining graphene with boron nitride, another material with a honeycomb lattice structure, the forces between graphene's electrons are altered. This results in a phenomenon called "skew scattering," where clouds of electrons skew their motion in one direction. Incoming terahertz waves then shuttle these electrons to flow through the material as a direct current.
To ensure the electrons move in a single direction without scattering, the graphene must be free of impurities. The researchers have published their findings and are collaborating with experimentalists to turn their design into a physical device. The successful conversion of terahertz waves into direct current could provide an alternative energy source, potentially powering devices such as cellphones.
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Frequently asked questions
Some devices that can convert electricity into radio waves include rectennas, rectifiers, and antennas.
An antenna that is matched to the frequency of the radio wave can convert electricity into radio waves. The antenna transmits the radio waves, which spread out spherically.
Rectennas are receiving antennas that convert energy from electromagnetic waves into electricity. They were invented in the 1960s and are a blend of the words "rectifying" and "antenna". Rectennas convert electromagnetic waves into alternating current (AC) electricity, which is then sent to a rectifier that converts it into direct current (DC) electricity.
Rectifiers are devices that convert electromagnetic waves from their oscillating (alternating) current to direct current. They use an electrical circuit with diodes to generate an electric field that can steer radio waves through the device as a direct current.
