A new electronics technique that could allow a radio device to transmit and receive on the same channel at the same time (“full duplex,” or simultaneous, two-way transmission) has been developed by researchers at the University of Bristol’s Communication Systems and Networks research group. The technique can estimate and cancel out the interference from a device’s own transmission.

Today’s cell phones and other communication devices use twice as much of the radio spectrum as necessary. The new system requires only one channel (set of frequencies) for two-way communication,so it uses only half as much spectrum compared to current technology.

The new technology combines electrical balance isolation and active radio frequency cancellation. Their prototype can suppress interference by a factor of more than 100 million and uses low-cost, small-form-factor technologies, making it well suited to use in mobile devices such as smartphones.

Significant impacts on mobile and WiFi systems

For future cellular systems (such as 5G systems), the new technology would deliver increased capacity and data rates, or alternatively, the network operators could provide the same total network capacity with fewer base-station sites, reducing the cost and environmental impact of running the network.

In today’s mobile devices, a separate filtering component is required for each frequency band, and because of this, today’s mobiles phone do not support all of the frequency channels available internationally. Different devices are manufactured for different regions of the world, so there are currently no 4G phones capable of unrestricted global roaming.

In Wi-Fi systems, the new design would double the capacity of a Wi-Fi access point, allowing for more simultaneous users or higher data rates.

Replacing these filters with the research team’s duplexer circuit would create smaller and cheaper devices, and would allow manufacturers to produce a single model for the entire world. This would enable global roaming on 4G and would further decrease cost through greater economies of scale.

The team had published papers about their research in the IEEE Journal on Selected Areas in Communications special issue on full duplex radio, and in this month’s issue of the IEEE Communications Magazineand has filed patents.

Abstract of Electrical balance duplexing for small form factor realization of in-band full duplex

Transceiver architectures utilizing various self-interference suppression techniques have enabled simultaneous transmission and reception at the same frequency. This full-duplex wireless offers the potential for a doubling of spectral efficiency; however, the requirement for high transmit-to-receive isolation presents formidable challenges for the designers of full duplex transceivers. Electrical balance in hybrid junctions has been shown to provide high transmit- to-receive isolation over significant bandwidths. Electrical balance duplexers require just one antenna, and can be implemented on-chip, making this an attractive technology for small form factor devices. However, the transmit-toreceive isolation is sensitive to antenna impedance variation in both the frequency domain and time domain, limiting the isolation bandwidth and requiring dynamic adaptation. Various contributions concerning the implementation and performance of electrical balance duplexers are reviewed and compared, and novel measurements and simulations are presented. Results demonstrate the degradation in duplexer isolation due to imperfect system adaptation in user interaction scenarios, and requirements for the duplexer adaptation system are discussed.

Abstract of Optimum Single Antenna Full Duplex Using Hybrid Junctions

This paper investigates electrical balance (EB) in hybrid junctions as a method of achieving transmitter-receiver isolation in single antenna full duplex wireless systems. A novel technique for maximizing isolation in EB duplexers is presented, and we show that the maximum achievable isolation is proportional to the variance of the antenna reflection coefficient with respect to frequency. Consequently, antenna characteristics can have a significant detrimental impact on the isolation bandwidth. Simulations that include embedded antenna measurements show a mean isolation of 62 dB over a 20-MHz bandwidth at 1.9 GHz but relatively poor performance at wider bandwidths. Furthermore, the operational environment can have a significant impact on isolation performance. We present a novel method of characterizing radio reflections being returned to a single antenna. Results show as little as 39 dB of attenuation in the radio echo for a highly reflective indoor environment at 1.9 GHz and that the mean isolation of an EB duplexer is reduced by 7 dB in this environment. A full duplex architecture exploiting EB is proposed.

A new graphene roll-to-roll continuous manufacturing process developed by MIT and University of Michigan researchers could finally take wonder-material graphene out of the lab and into practical commercial products.

The new process is an adaptation of a chemical vapor deposition method widely used to make graphene, using a small vacuum chamber into which a vapor containing carbon reacts on a horizontal substrate, such as a copper foil. The new system uses a similar vapor chemistry, but the chamber is in the form of two concentric tubes, one inside the other, and the substrate is a thin ribbon of copper that slides smoothly over the inner tube.

Gases flow into the tubes and are released through precisely placed holes, allowing for the substrate to be exposed to two mixtures of gases sequentially. The first region is called an annealing region, used to prepare the surface of the substrate; the second region is the growth zone, where the graphene is formed on the ribbon. The chamber is heated to approximately 1,000 degrees Celsius to perform the reaction.

The researchers have designed and built a lab-scale version of the system, and found that when the ribbon is moved through at a rate of 25 millimeters (1 inch) per minute, a very uniform, high-quality single layer of graphene is created. When rolled 20 times faster, it still produces a coating, but the graphene is of lower quality, with more defects.

A “big leap”

Graphene is a material with a host of potential applications, including use in solar panels that could be integrated into windows, and membranes to desalinate and purify water. But all these possible uses face the same big hurdle: the need for a scalable and cost-effective method for continuous manufacturing of graphene films.

For these practical uses, “You’re going to need to make acres of it, repeatedly and in a cost-effective manner,” says MIT mechanical engineering Associate Professor A. John Hart, senior author of the open-access Scientific Reportspaper.

Making such quantities of graphene would represent a big leap from present approaches, where researchers struggle to produce small quantities of graphene — often laboriously pulling these sheets from a lump of graphite using adhesive tape, or producing a film the size of a postage stamp using a laboratory furnace.

The new method promises to enable continuous production, using a thin metal foil as a substrate, in an industrial process where the material would be deposited onto the foil as it smoothly moves from one spool to another. The resulting sheets would be limited in size only by the width of the rolls of foil and the size of the chamber where the deposition would take place.

Applications

Because a continuous process eliminates the need to stop and start to load and unload materials from a fixed vacuum chamber, as in today’s processing methods, it could lead to significant scale-up of production. That could finally unleash applications for graphene, which has unique electronic and optical properties and is one of the strongest materials known.

Some potential applications, such as filtration membranes, may require very high-quality graphene, but other applications, such as thin-film heaters may work well enough with lower-quality sheets, says Hart, who is the Mitsui Career Development Associate Professor in Contemporary Technology at MIT.

So far, the new system produces graphene that is “not quite [equal to] the best that can be done by batch processing,” Hart says — but “to our knowledge, it’s still at least as good” as what’s been produced by other continuous processes. Further work on details such as pretreatment of the substrate to remove unwanted surface defects could lead to improvements in the quality of the resulting graphene sheets, he says.

The team is studying these details, Hart adds, and learning about tradeoffs that can inform the selection of process conditions for specific applications, such as between higher production rate and graphene quality. Then, he says, “The next step is to understand how to push the limits, to get it 10 times faster or more.”

Hart says that while this study focuses on graphene, the machine could be adapted to continuously manufacture other two-dimensional materials, or even to growing arrays of carbon nanotubes, which his group is also studying.

“This is high-quality research that represents significant progress on the path to scalable production methods for large-area graphene,” says Charlie Johnson, a professor of physics and astronomy at the University of Pennsylvania who was not involved in this work. “I think that the concentric tube approach is very creative. It has the potential to lead to significantly lower production costs for graphene, if it can be scaled to larger copper-foil widths.”

The work was supported by the National Science Foundation and the Air Force Office of Scientific Research.

Using electrochemistry, North Carolina State University (NCSU) researchers have created a reconfigurable, voltage-controlled liquid metal antenna that may play a role in future mobile devices and the coming Internet of Things.

By placing a positive or negative electrical voltage across the interface between the liquid metal and an electrolyte, they found that they could cause the liquid metal to spread (flow into a capillary) or contract, changing its operating frequency and radiation pattern.

“Using a liquid metal — such as eutectic gallium and indium — that can change its shape allows us to modify antenna properties [such as frequency] more dramatically than is possible with a fixed conductor,” explained Jacob Adams, an assistant professor in the Department of Electrical and Computer Engineering at NCSU and a co-author of anopen-access paper in the Journal of Applied Physics, from AIP Publishing.

The positive voltage “electrochemically deposits an oxide on the surface of the metal that lowers the surface tension, while a negative [voltage] removes the oxide to increase the surface tension,” Adams said. These differences in surface tension dictate which direction the metal will flow.

This advance makes it possible to “remove or regenerate enough of the ‘oxide skin’ with an applied voltage to make the liquid metal flow into or out of the capillary. We call this ‘electrochemically controlled capillarity,’ which is much like an electrochemical pump for the liquid metal,” Adams noted.

Although antenna properties can be reconfigured to some extent by using solid conductors with electronic switches, the liquid metal approach greatly increases the range over which the antenna’s operating frequency can be tuned. “Our antenna prototype using liquid metal can tune over a range of at least two times greater than systems using electronic switches,” he pointed out.

Previous liquid-metal designs typically required external pumps that can’t be easily integrated into electronic systems.

Extending frequencies for mobile devices

“Mobile device sizes are continuing to shrink and the burgeoning Internet of Things will likely create an enormous demand for small wireless systems,” Adams said. “And as the number of services that a device must be capable of supporting grows, so too will the number of frequency bands over which the antenna and RF front-end must operate. This combination will create a real antenna design challenge for mobile systems because antenna size and operating bandwidth tend to be conflicting tradeoffs.”

This is why tunable antennas are highly desirable: they can be miniaturized and adapted to correct for near-field loading problems such as the iPhone 4′s well-publicized “death grip” issue of dropped calls when by holding it by the bottom. Liquid metal systems “yield a larger range of tuning than conventional reconfigurable antennas, and the same approach can be applied to other components such as tunable filters,” Adams said.

In the long term, Adams and colleagues hope to gain greater control of the shape of the liquid metal in two-dimensional surfaces to obtain nearly any desired antenna shape. “This would enable enormous flexibility in the electromagnetic properties of the antenna and allow a single adaptive antenna to perform many functions,” he added.

Abstract of A reconfigurable liquid metal antenna driven by electrochemically controlled capillarity 

We describe a new electrochemical method for reversible, pump-free control of liquid eutectic gallium and indium (EGaIn) in a capillary. Electrochemical deposition (or removal) of a surfaceoxide on the EGaIn significantly lowers (or increases) its interfacial tension as a means to induce the liquid metal in (or out) of the capillary. A fabricated prototype demonstrates this method in a reconfigurable antenna application in which EGaIn forms the radiating element. By inducing a change in the physical length of the EGaIn, the operating frequency of the antennatunes over a large bandwidth. This purely electrochemical mechanism uses low, DC voltages to tune the antenna continuously and reversibly between 0.66 GHz and 3.4 GHz resulting in a 5:1 tuning range. Gain and radiation pattern measurements agree with electromagnetic simulations of the device, and its measured radiation efficiency varies from 41% to 70% over its tuning range.