Power/Performance Bits: April 28

Flat microwave reflector; underwater power through light; stretchy thermoelectric generators.


Flat microwave reflector
Researchers from Los Alamos National Laboratory developed a new flat reflector for microwaves that could improve communications while providing a better form factor. It also breaks reciprocity, effectively turning it into a one-way mirror.

The flat reflector can be reconfigured on the fly electronically, allowing it to be used for beam steering, customized focusing, and other functions that are difficult to achieve with conventional antenna designs.

“Our new reflectors offer lightweight, low-profile alternatives to conventional antennas. This is a potential boon for satellites, where minimizing weight and size is crucial,” said Abul Azad, of the MPA-CINT group at Los Alamos National Laboratory. “The panels could be easily incorporated onto surfaces of buildings or terrestrial vehicles as well.”

What goes in is not what comes out with a spatio-temporally modulated metasurface reflector. (Credit: Los Alamos National Laboratory)

An array of finely structured electronic components on a planar surface makes up the reflector. Applying signals to the components allows the 2D reflector to act like a 3D antenna, as well as provides control over the direction and frequency of reflected light. The nonreciprocal response of the reflector can help prevent antennas from picking up echoes from their outgoing broadcasts and protect delicate circuitry from powerful, potentially damaging incoming signals.

“We have demonstrated the first dynamic metasurface capable of achieving extreme non-reciprocity by converting microwaves into plasmons, which are electric charge waves on the reflector’s surface,” said Diego Dalvit, of the T-4 group at Los Alamos. “This is key to controlling the way the reflectors function.”

The researchers see a range of applications, including optics that can adapt to distortion, one-way wireless transmissions, and new antenna designs. The team also thinks miniaturized versions could improve chip-based circuitry by ensuring that signals go only to the intended components and don’t lead to inadvertent signals in other parts of the circuit.

Underwater power through light
Researchers at King Abdullah University of Science and Technology (KAUST) designed a way to both power and transfer information from underwater devices, wirelessly. Called simultaneous lightwave information and power transfer (SLIPT), the system targets “internet of underwater things” devices where other communication methods run into problems.

“Underwater acoustic and radio wave communications are already in use, but both have huge drawbacks. Acoustic communication can be used over large distances but lacks stealth (making it detectable by a third party) and can only access a small bandwidth,” said Jose Filho, a master’s student at KAUST. “Furthermore, radio waves lose their energy in seawater, which limits their use in shallow depths. They also require bulky equipment and lots of energy to run.”

By contrast, “SLIPT can help charge devices in inaccessible locations where continuous powering is costly or not possible,” said Filho.

The team was able to charge and transmit instructions across a 1.5-meter-long water tank to a solar panel on a submerged temperature sensor. The sensor recorded temperature data and saved it on a memory card, later transmitting it to a receiver when information in the light beam instructed it to do so.

In another experiment, the battery of a camera submerged at the bottom of a tank supplied with Red Sea water was charged via its solar panel within an hour and a half by a partially submerged, externally powered laser source. The fully charged camera was able to stream one-minute-long videos back to the laser transmitter.

Applications for the system include underwater sensors for tracking climate change effects on coral reefs, detecting seismic activity, and monitoring oil pipelines, as well as potentially autonomous search-and-rescue robots.

Next, the team is working on the deployment of underwater SLIPT configurations, including ways to overcome the effects of turbulence on underwater reception and looking into the use of ultraviolet light for transmissions that face underwater obstructions. They are also developing smart underwater optical positioning algorithms that could help locate relay devices set up to extend the communication ranges of underwater devices.

Stretchy thermoelectric generators
Researchers at Linköping University, University of Auckland, and University of Mons built a soft and stretchable organic thermoelectric module that can harvest energy from body heat.

The material is a composite comprised of the conducting polymer PEDOT:PSS for thermoelectric properties, a water-soluble polyurethane rubber for elasticity, and an ionic liquid that also aids in softness.

A common conducting polymer used in many applications, PEDOT:PSS provides good thermoelectric properties. But thick polymer film is too hard and brittle to be successfully integrated into wearable electronics.

“Our material is 100 times softer and 100 times more stretchable than PEDOT:PSS,” said Klas Tybrandt, a senior lecturer at Linköping’s Laboratory of Organic Electronics. “The ability to control the structure of the material both at the nanoscale and the microscale allows us to combine the excellent properties of the different materials in a composite.”

The new composite is also printable, noted Nara Kim, a postdoc and principal research engineer in Linköping’s Laboratory of Organic Electronics. “The composite was formulated by water-based solution blending and it can be printed onto various surfaces. When the surface flexes or folds, the composite follows the motion. And the process to manufacture the composite is cheap and environmentally friendly.”

The researchers see a huge range of new possibilities using the material to create soft and elastic organic conducting materials, including smart clothing, wearable electronics and electronic skin.

According to Xavier Crispin, a professor at Linköping’s Laboratory of Organic Electronics, “There are many ionic liquids, conducting polymers and traditional elastomers that can be combined to give new nanocomposites for many applications, such as thermoelectric generators, supercapacitors, batteries, sensors, and in wearable and implantable applications that require thick, elastic and electrically conducting materials.”

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