Our eyes are tuned only to a narrow band of possible wavelengths of electromagnetic radiation, about 390-700 nanometers. If you would like to see the world on different wavelengths, you would know that in an urban area you illuminated even in the dark — everywhere infrared radiation, microwaves and radio waves. Part of this electromagnetic radiation to the environment is emitted by objects that scatter everywhere their electrons, and part transfers radio signals and Wi-Fi signals that are the basis of our communication systems. All this radiation also carries energy.
What if we could harness the energy of electromagnetic waves?
Researchers from the Massachusetts Institute of technology presented a study that appeared in the journal Nature, where it is described as embarked on the practical implementation of this goal. They developed the first fully flexible device that can convert energy from Wi-Fi signals into usable direct current electricity.
Any device that can convert AC signals (AC) to direct current (DC), called rectennas: rectifying antenna (rectifying antenna). The antenna picks up electromagnetic radiation, transforming it into alternating current. It then passes through the diode, which converts it to direct current for use in electrical circuits.
For the first time rectenna was proposed in the 1960-ies and even used to demonstrate a model helicopter powered by microwaves, 1964 inventor William brown. At this stage, futurists have dreamed of wireless power transmission over long distances and even use recten to collect solar energy on satellites and transmission to Earth.
Today, new technologies in the nanoscale enable many new things. In 2015 researchers from the Georgia Institute of Technology collected the first optical rectenna, able to cope with high frequencies in the visible spectrum from carbon nanotubes.
While these new optical rectenna have have a low efficiency, about 0.1%, and therefore can not compete with the growing efficiency of photovoltaic solar panels. But the theoretical limit for solar cells based on rectan probably higher than the limit Shockley-Kusser for solar cells, and can reach 100% when illuminated by radiation of a certain frequency. This enables efficient wireless energy transfer.
The new part of the device MIT, takes advantage of the flexible radio frequency antenna which can capture wavelengths associated with the Wi-Fi signals and convert them to alternating current. Then, instead of the traditional diode to convert this to DC, the new device uses “two-dimensional” semiconductor thickness of only a few atoms, creating a voltage that can be used to power wearable devices, sensors, medical devices or electronics large area.
New rectenna consist of such “two-dimensional” (2D) materials — molybdenum disulfide (MoS2), which is only three atoms thick. One of its remarkable properties is the reduction of parasitic capacitance — the tendency of materials in electrical circuits to act as capacitors that hold a certain amount of charge. In electronics, the DC’s may limit the speed of signal converters and the ability of devices to respond to high frequency. New rectenna of molybdenum disulfide have a parasitic capacitance an order of magnitude below those that have been developed to date that allows the device to capture signals up to 10 GHz, including in the range of a typical Wi-Fi devices.
In such a system, there would be fewer problems associated with batteries: its life cycle would be much longer the electrical device is charged from ambient radiation would not be necessary to dispose of components, as in the case with batteries.
“What if we could develop electronic systems that wrap around the bridge or which will cover the whole trunk, the walls of our office, and provide electronic intelligence to everything that surrounds us? How will you provide energy for all this electronics?”, asks co-author Tomas Palacios, a Professor of electrical engineering and computer science at the Massachusetts Institute of technology. “We invented a new way to power electronic systems of the future.”
The use of 2D materials allows you to cheaply produce a flexible electronics that will potentially allow us to place it on a large area for collection of radiation. Flexible devices could equip a Museum or a road surface, and it would be much cheaper than using rectenna of traditional silicon semiconductors or gallium arsenide.
Is it possible to charge the phone from Wi-Fi signals?
Unfortunately, this option seems highly unlikely, although for many years the topic of “free energy” fooling people again and again. The problem is the energy density of signals. The maximum power that can be used by the access point Wi-Fi without a special license for broadcasting, typically 100 milliwatts (mW). These 100 mW radiated in all directions, spreading over a surface area of a sphere the center of which is the access point.
Even if your mobile phone has gathered all this power with 100 percent efficiency for charging the battery of the iPhone still it would take days, and the small size of device and distance from access point would severely limit the amount of energy that he could gather from these signals. New device from MIT can capture about 40 milliwatts of energy when exposed to a typical density Wi-Fi at 150 milliwatts: this is not enough to power the iPhone, but for simple display or remote wireless sensor.
For this reason, much more likely that wireless charging for larger gadgets will rely on an induction charging device, which can power the device at a distance of one meter, if between the wireless charger and charging facility nothing.
However, the ambient RF energy can be used to power certain types of devices, you think, was a Soviet radios? And the coming “Internet of things” definitely will use these models supply. It remains only to create sensors with low power consumption.
Co-author with jesús Grajal from the Technical University of Madrid, sees a potential application in implantable medical devices: a pill that the patient can swallow, give health information back to the computer for diagnostics. “Ideally I would not want to use a battery to power such systems, because if they miss lithium, the patient could die,” says Grahl. “It is much better to collect energy from the environment to nourish these little laboratories inside the body and transmit data to external computers.”
The current efficiency of the device is about 30-40% compared to 50-60% for traditional rectan. Along with concepts such as piezoelectricity (the materials that generate electricity by physical compression or stretching), electricity generated by the bacteria and heat to the environment, “wireless” electricity could become one of the power sources for microelectronics of the future.
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