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Ultra-compact Nano antennas made of Nano Materials have applications from wearables to airplanes, spacecraft and military

An antenna is a device used to propagate, receive, and/or transmit electromagnetic waves which can have information embedded within them. The antenna creates an electromagnetic wave that carries the original embedded sound information through the atmosphere/space around it. An antenna at a different location, receives the electromagnetic wave, sending it to circuitry (your radio) that then translates it to an electronic signal and then back to a sound wave.

 

Radio waves are used for wireless transmissions (such as from cell phone towers to the cell phone and wireless internet connections). The radio wave is created by an accelerated charge. This can be done using an alternating current circuit, which forces the electrons in the electrically conducting antenna (a transmitter or receiver) to move back and forth along the antenna. As they move back and forth they speed up and slow down and create an electromagnetic wave. One of the important requirements of an antenna is that the antenna’s length be related to the wavelength of the electromagnetic wave that it is trying to transmit or receive.

 

The shrinking of mobiles and other communication devices is demanding miniaturization of the antenna as much as possible while preserving the efficiency. “We identified ultra-compact antennas as the critical last step in true device miniaturization. Researchers had successfully shrunk most electronic components, but the true miniaturization of antennas was still a missing piece,” said Howe.

 

The miniaturization is also needed because it will enable to integrate multiple antennas in a device to support MIMO schemes. Multiple transmit and multiple receive (MIMO) antennas has emerged as one of the most significant technical breakthroughs in next generation wireless communications. MIMO is the use of multiple antennas at both the transmitter and receiver to improve communication performance.

 

In the future, networks of nano-devices will be a key component of almost every field of our society, with applications in biomedicine, environmental protection, entertainment, and homeland security, and beyond. In order to enable nano-devices to communicate with each other, many fundamental challenges need to be addressed. Electromagnetic (EM) communication in the Terahertz (THz) band (0.1–10 THz) enabled by graphene-based plasmonic nano-transceivers and nano-antennas has been suggested as one of the possible approaches for communication among these devices.

 

The development of ultra-compact antennas has great significance to military as it leads to miniaturization of military and commercial communication systems. The miniaturization of military electronics is of significant benefit to the warfighter, not only in terms of device size, but in transportability, space requirements, weight, and many factors,” said Dr. Brandon Howe, a materials scientist with the AFRL. “It can allow us to fit more into a given space, whether that be in a field pack or on an aerial platform. It gives us greater capability in a smaller space.

 

Vast amounts of data zip across the Internet each day in the form of light waves conveyed by optical fibers. But our computers still rely on electrical signals traveling through metal wires, which have much lower bandwidth. Optical interconnects that could guide light through the labyrinth of a circuit board would increase computing speed and save power, but so far they haven’t made it out of the lab. Now researchers are devising new techniques that may may enable engineers to build nanoscale antennae that turn light into a different sort of wave that can move through metal; the result could be data transmission speeds that are orders of magnitude higher than today’s.

 

Nano means one billionth. A nanoantenna is an antenna that is very, very small, and It is used to gain understanding about what is happening on an atomic scale. An image of a gold nanoantenna created by the Paul Alivisatos group at Lawrence Berkley National Laboratory, along with researchers at the University of Stuttgart in Germany, is shown below. Above the gold nanoantenna is a palladium nanoparticle. The purpose of their research is to figure out a way to measure interactions on the atomic scale so that an extremely sensitive gas sensor – one that might be able to detect a single particle – may be created. The optical properties of palladium are altered when hydrogen atoms are nearby and this should be detectable, but the effect is so small that it is hard to measure. Measuring the presence of hydrogen gas with more commonly used techniques can be dangerous because hydrogen is very explosive.

 

Alivisatos-SEM-Figure

Hydrogen can be absorbed into palladium. The hydrogen atoms situate themselves between the palladium atoms rather easily. When the hydrogen atoms sit between the palladium atoms in this way the substance is called palladium hydride. The hydrogen atoms can also easily leave the palladium. Each time hydrogen enters or leaves the palladium structure, a change in how the palladium nanoparticle interacts with electromagnetic waves occurs.

Scattered intensity of light from a palladium.

Researchers measured how an incoming electromagnetic wave in the visible region was scattered off of the palladium nanoparticle. Each time hydrogen atoms were absorbed or released from the palladium the light scattered in a different way, however the measurements were not so obvious, as shown in the first image below. Researchers tried to enhance the signal to improve their measurements. A gold antenna, of just the right dimensions to make it resonant with the electromagnetic waves involved, was brought nearby. The antenna’s sharp tip is strongly affected by the scattered electromagnetic waves causing an oscillation of the electrons within the gold antenna tip that travels down the antenna. The detected signal is increased, becoming very clear as shown below, and this is music to any researcher’s ear.

 

Nano-antennas are useful for converting solar radiation into electricity. Adamant supplies of clean energy result in the growth of economic prosperity, global stability and quality of life. A nano-antenna is a type of solar cell that makes use of infrared radiation to create electricity instead of harnessing visible light to create electricity where infrared radiation is often believed as heat and exists beyond the visible range for humans. Infrared light is emitted from the Earth and also from various industrial processes like waste energy and coal-fired power plants. One version of the nano-antenna takes the shape of a microscopically small gold square or spiral of metal wire about 1/25th the diameter of a human hair that is embedded in a flexible polyethylene plastic sheet. In researches, the devices have been shown to be as high as 92% efficient at converting the frequencies of infrared light which they capture and convert into electrical energy.

Nano antennas that generates directed infrared light for data transfer

For the first time, physicists from the University of Würzburg have successfully converted electrical signals into photons and radiated them in specific directions using a low-footprint optical antenna that is only 800 nanometres in size.

 

Directional antennas convert electrical signals to radio waves and emit them in a particular direction, allowing increased performance and reduced interference. This principle, which is useful in radio wave technology, could also be interesting for miniaturised light sources. After all, almost all Internet-based communication utilises optical light communication. Directional antennas for light could be used to exchange data between different processor cores with little loss and at the speed of light. To enable antennas to operate with the very short wavelengths of visible light, such directional antennas have to be shrunk to nanometre scale.

 

The antenna was developed by the nano-optics working group of Professor Bert Hecht, who holds the Chair of Experimental Physics 5 at the University of Würzburg. The name “Yagi-Uda” is derived from the two Japanese researchers, Hidetsugu Yagi and Shintaro Uda, who invented the antenna in the 1920s. What does a Yagi-Uda antenna for light look like? “Basically, it works in the same way as its big brothers for radio waves ,” explains Dr. René Kullock, a member of the nano-optics team. An AC voltage is applied that causes electrons in the metal to vibrate and the antennas radiate electromagnetic waves as a result. “In the case of a Yagi-Uda antenna, however, this does not occur evenly in all directions but through the selective superposition of the radiated waves using special elements, the so-called reflectors and directors,” says Kullock. “This results in constructive interference in one direction and destructive interference in all other directions.”
Accordingly, such an antenna would only be able to receive light coming from the same direction when operated as a receiver.

 

Applying the laws of antenna technology to nanometre scale antennas that radiate light is technically challenging. Some time ago, the Würzburg physicists were already able to demonstrate that the principle of an electrically driven light antenna works. But in order to make a relatively complex Yagi-Uda antenna, they had to come up with some new ideas. In the end, they succeeded thanks to a sophisticated production technique: “We bombarded gold with gallium ions which enabled us to cut out the antenna shape with all reflectors and directors as well as the necessary connecting wires from high-purity gold crystals with great precision,” explains Bert Hecht.

 

In a next step, the physicists positioned a gold nano particle in the active element so that it touches one wire of the active element while keeping a distance of only one nanometre to the other wire. “This gap is so narrow that electrons can cross it when voltage is applied using a process known as quantum tunnelling,” explains Kullock. This charge motion generates vibrations with optical frequencies in the antenna which are emitted in a specific direction thanks to the special arrangement of the reflectors and directors.

 

The antenna will need further development before it is used in practice. The physicists will have to work on the antenna’s counterpart that receives light signals. The signal’s efficiency and stability will also need to be improved.

 

Optimized coupling between quantum dots and nanoantennas resulted in a record-high collection efficiency of single photons.

Efficient single photon sources have applications in various quantum technologies, such as quantum key distribution and quantum metrology. Quantum dot emitters provide on-demand production of single photons, but the photons are emitted in all directions, which results in low collection efficiency.

 

Abudayyeh et al. increased the directionality of photons emitted from quantum dots operating at room temperature by placing them in nanoantennas. They achieved a record-high collection efficiency of 85% of the emitted single photons. The nanoantennas directed the photons in a single direction, increasing the number of collected photons. The authors optimized the coupling between the antennas and quantum dots with improved antenna fabrication techniques and enhanced quantum dots known as CdSe/CdS core/thick-shell or giant quantum dots, which are non-blinking and non-photobleaching at room temperature. “We have come up with a novel fabrication and placement method that enables us to reach record-high collection efficiencies even with such broadband emitters,” said author Hamza Abudayyeh.

 

The authors hope the nanoantenna fabrication method they developed will aid in the eventual application of the antennas. Unlike previously used indeterministic or single-try methods, their placement method, dip-pen nanolithography, allowed them to directly and precisely write the quantum dots in the nanoantennas. This method is more suitable for scaling. The quantum dots also demonstrated high photon rates of many emitted photons.

 

The authors plan couple these on-chip, room temperature nanoantenna-emitter devices with a fiber to produce plug-and-play single photon sources with high collection efficiencies. Source: “Single photon sources with near unity collection efficiencies by deterministic placement of quantum dots in nanoantennas,” by Hamza Abudayyeh, Boaz Lubotzky, Anastasia Blake, Jun Wang, Somak Majumder, Zhongjian Hu, Younghee Kim, Han Htoon, Riya Bose, Anton V. Malko, Jennifer A. Hollingsworth, and Ronen Rapaport, APL Photonics (2021).

Nanomaterials for Nanoantennas

Carbon nanotubes (CNTs) are hollow cylindrical tubes formed by rolling a sheet of carbon atoms arranged in a hexagonal ring, as in a sheet of graphite, either in monolayer (single walled nanotube, SWCNT) or multilayer (multi-walled nanotube, MWCNT) form. Their diameter may range from 0.7 (SWCNT) to   50  naometers (MWCNT) and few tens of micron in length.

 

CNTs can radiate as a small nano-dipole antenna when it is electromagnetically excited. With nanometer length of CNTs dipole antenna, the electromagnetic (EM) radiation from this antenna is expected to cover a range within terahertz and optical frequency.

 

CNTs antenna can be a novel solution to reduce the gap of communication between the microscopic world and nanotechnology devices. It would also be advantageous to the applications requiring a wireless connection with the nano-scale devices like nano-sensors. SWCNTs-dipole antenna is one of the most potential CNTs antennas in the nanotechnology antenna field, especially for the infrared (IR) and terahertz (THz) frequency ranges.

 

Nanomaterial based patch antenna

The numerous advantages of planar or microstrip antenna, such as its low weight, small volume, and ease of fabrication using printed circuit technology, led to the design of several configurations for various personal and mobile applications.

 

Copper and Silicon were known the best materials to be used as interconnects and semi-conducting devices. But as the technology is scaling to nano-scale dimensions, new problems are arising. Graphene and Carbon Nanotubes (CNTs) are two important allotropes of carbon to be used as remedy of these problems. Due to high current carrying capacity and thermal stability, these materials can be used as patches. In a design of a patch antenna, one side of a dielectric substrate acts as a radiating patch and other side of substrate acts as ground plane.

 

Fibers made of carbon nanotubes configured as wireless antennas can be as good as copper antennas but 20 times lighter, according to Rice University researchers. The antennas may offer practical advantages for aerospace applications and wearable electronics where weight and flexibility are factors.

 

 

Nanotube fiber antennas as capable as copper

Rice lab of chemist and chemical engineer Matteo Pasquali have developed antenna based on strong, lightweight nanotube fibers. The research could help engineers who seek to streamline materials for airplanes and spacecraft where weight equals cost. Increased interest in wearables like wrist-worn health monitors and clothing with embedded electronics could benefit from strong, flexible and conductive fiber antennas that send and receive signals, Pasquali said.

 

Contrary to earlier results by other labs (which used different carbon nanotube fiber sources), the Rice researchers found the fiber antennas matched copper for radiation efficiency at the same frequencies and diameters. Their results support theories that predicted the performance of nanotube antennas would scale with the density and conductivity of the fiber.

 

“Not only did we find that we got the same performance as copper for the same diameter and cross-sectional area, but once we took the weight into account, we found we’re basically doing this for 1/20th the weight of copper wire,” Bengio said.

 

Applications for this material are a big selling point, but from a scientific perspective, at these frequencies carbon nanotube macro-materials behave like a typical conductor,” he said. Even fibers considered “moderately conductive” showed superior performance, he said. Although manufacturers could simply use thinner copper wires instead of the 30-gauge wires they currently use, those wires would be very fragile and difficult to handle, Pasquali said.

 

“Amram showed that if you do three things right—make the right fibers, fabricate the antenna correctly and design the antenna according to telecommunication protocols—then you get antennas that work fine,” he said. “As you go to very thin antennas at high frequencies, you get less of a disadvantage compared with copper because copper becomes difficult to handle at thin gauges, whereas nanotubes, with their textile-like behavior, hold up pretty well.”

 

Nano-Material Makes Spray-On Antennae

ChamTech Operations has developed a mixture made of nanoparticles that can be sprayed on any vertical surface, from a light pole to a tree, to create powerful antennae. The nanoparticles in the spray act as nanocapacitors which “charge and discharge very quickly and don’t create any heat that can reduce the efficiency of your typical copper antenna.” The engineers’ toughest obstacles was arranging the nanoparticles in the correct pattern.

 

The efficiency of the nano-spray, which does not leak heat like copper wiring, makes antennae more powerful, meaning data can be transferred over the same distance using half the energy or twice the distance using the same amount of energy. The spray has the ability to integrate wireless infrastructure into our landscapes—imagine rural fence posts sprayed to create a nation-wide wireless network or highway lane lines which can give our cars and mobile devices clear Internet reception at all times.

 

References and Resources also include:

https://bigthink.com/ideafeed/nano-material-makes-spray-on-antennae

https://phys.org/news/2017-10-nanotube-fiber-antennas-capable-copper.html

https://www.nanowerk.com/nanotechnology-news2/newsid=54323.php

https://www.physicscentral.com/explore/action/nanoantennas.cfm

About Rajesh Uppal

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