Power/Performance Bits: March 30

Harvesting body heat; printable thermoelectric generators; silicon photonics and CMOS lidar.


Harvesting body heat
Researchers at University of Colorado Boulder, Harbin Institute of Technology, Southeast University, and Huazhong University of Science and Technology designed a stretchy thermoelectric generator that can be worn against the skin to power small wearable electronics using body heat.

The stretchy material polyimine is used as the base of the device. A series of thin thermoelectric chips are added to the base, connected with liquid metal wires. The polyimine allows for flexibility without introducing too much strain to the brittle thermoelectric material. It is also self-healing and fully recyclable.

It can generate about 1 volt of energy for every square centimeter of skin space, which is less voltage per area than what most existing batteries provide but still enough to power electronics like watches or fitness trackers, the team said. “In the future, we want to be able to power your wearable electronics without having to include a battery,” said Jianliang Xiao, an associate professor in the Paul M. Rady Department of Mechanical Engineering at CU Boulder.

“Whenever you use a battery, you’re depleting that battery and will, eventually, need to replace it,” Xiao said. “The nice thing about our thermoelectric device is that you can wear it, and it provides you with constant power.”

Xiao also noted that more blocks of generators can be added to increase power. “What I can do is combine these smaller units to get a bigger unit,” he said. “It’s like putting together a bunch of small Lego pieces to make a large structure. It gives you a lot of options for customization.”

The researchers calculated that a person taking a brisk walk could use a device the size of a typical sports wristband to generate about 5 volts of electricity, more than that of many watch batteries.

While they are still working out some issues with the design, the team thinks these devices could be on the market in five to ten years.

Printable thermoelectric generators
Thermoelectric generators, or TEGs, hold potential for powering sensors and IoT devices by converting ambient and waste heat into electrical power. Researchers at Karlsruhe Institute of Technology (KIT) and Otego GmbH are working on making them cheaper to manufacture by using printable materials.

“Thermoelectric generators directly convert thermal into electrical energy. This technology enables operation of autonomous sensors for the Internet of Things or in wearables, such as smart watches, fitness trackers, or digital glasses without batteries,” said Professor Uli Lemmer, Head of the Light Technology Institute (LTI) of KIT.

“Conventional TEGs have to be assembled from individual components using relatively complex manufacturing methods,” Lemmer said. “To avoid this, we studied novel printable materials and developed two innovative processes and inks based on organic as well as on inorganic nanoparticles.”

The first process uses screen printing to apply a 2D pattern onto an ultrathin flexible substrate foil using thermoelectric printing inks. Then, a generator having about the size of a sugar cube is folded by means of an origami technique.

With the help of newly developed inks and special production techniques, such as origami, inexpensive thermoelectric generators can be produced for various applications. (Photo: Andres Rösch, KIT)

The second process consists of printing a 3D scaffold and applying a silver selenide (Ag2Se)-based n-type printable thermoelectric ink to the surfaces.

Roll-to-roll screen printing and 3D printing are key technologies, noted Lemmer. “The new production processes not only enable inexpensive scalable production of these TEGs. Printing technologies also allow the component to be adapted to the applications. We are now working on commercializing the printed thermoelectrical system.”

Lidar integrates silicon photonics and CMOS
Researchers from University of Southampton and Pointcloud Inc developed a 3D lidar system that integrates silicon photonic components and CMOS electronic circuits.

“Lidar has been promising a lot but has not always delivered on its potential in recent years because, although experts have recognized that integrated versions can scale down costs, the necessary performance has not been there. Until now,” said Graham Reed, Professor of Silicon Photonics within the Optoelectronic Research Centre at University of Southampton.

“The silicon photonics system we have developed provides much higher accuracy at distance compared to other chip-based lidar systems to date, and most mechanical versions, showing that the much sought-after integrated system for lidar is viable.”

Remus Nicolaescu, the CEO of Pointcloud Inc, added, “The combination of high performance and low cost manufacturing, will accelerate existing applications in autonomy and augmented reality, as well as open new directions, such as industrial and consumer digital twin applications requiring high depth accuracy, or preventive healthcare through remote behavioral and vital signs monitoring requiring high velocity accuracy.”

The latest tests of the prototype, a large-scale 2D coherent detector array consisting of 512 pixels, show that it has an accuracy of 3.1 millimeters at a distance of 75 meters.

The research teams are now working to extend the pixels arrays and the beam steering technology to make the system even better suited to real-world applications and further improve performance.

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