中文 English

System Bits: Oct. 15

Minimizing damage; lithium-sulfur batteries; electro-adhesive stamps.

popularity

When self-driving cars collide
As self-driving car technology develops and evolves, it is inevitable that there will be collisions while the tech matures.

“What can we do in order to minimize the consequences?” asks Amir Khajepour, a professor of mechanical and mechatronics engineering at the University of Waterloo. “That is our focus.”

The first rule for the autonomous vehicle (AV) crash-mitigation technology is avoiding collisions with pedestrians.

From there, it weighs factors such as relative speeds, angles of collision, and differences in mass and vehicle type to determine the best possible maneuver, such as braking or steering in one direction or another.

“We consider the whole traffic environment perceived by the autonomous vehicle, including all the other vehicles and obstacles around it,” said Dongpu Cao, also a mechanical and mechatronics engineering professor at Waterloo.

Khajepour, director of the Mechatronic Vehicle Systems Lab, said the system is needed because the popular idea that AVs of the future will completely eliminate crashes is a myth.

Although safety should improve dramatically, he said, there are just too many uncertainties for self-driving vehicles to handle them all without some mishaps.


Image source: Pixabay

“There are hundreds, thousands, of variables we have no control over,” he said. “We are driving and all of a sudden there is black ice, for instance, or a boulder rolls down a mountain onto the road.”

AVs are capable of limiting damage when a crash is unavoidable because they always know what is happening around them via sensors, cameras and other sources, and routinely make tens and even hundreds of decisions per second based on that information.

The new system decides how an AV should respond in emergency situations based primarily on pre-defined mathematical calculations considering the severity of crash injuries and damage.

Researchers didn’t attempt to factor in extremely complex ethical questions, such as whether an AV should put the safety of its own occupants first or weigh the well-being of all people in a crash equally.

But when carmakers and regulators eventually hammer out the ethical rules for self-driving vehicles, Khajepour said, the system framework is designed to integrate them.

A paper on their work, Crash Mitigation in Motion Planning for Autonomous Vehicles, recently appeared in IEEE Transactions on Intelligent Transportation Systems.

Simplifying production of lithium-sulfur batteries
Scientists at Singapore’s NanoBio Lab (NBL) of A*STAR have developed a novel approach to prepare next-generation lithium-sulfur cathodes, which simplifies the typically time-consuming and complicated process for producing them. This represents a promising step towards the commercialization of lithium-sulfur batteries, and addresses industry’s need for a practical approach towards scaling up the production of new materials that improve battery performance.

While the lithium-ion battery is widely recognized as an advanced technology that can efficiently power modern communication devices, it has drawbacks such as limited storage capacity and safety issues due to its inherent electrochemical instability. This is set to change with a new simplified technique developed by NBL’s team of researchers, in the development of lithium-sulfur cathodes from inexpensive commercially available materials. Sulfur’s high theoretical energy density, low cost, and abundance contribute to the popularity of lithium-sulfur battery systems as a potential replacement for lithium-ion batteries.

Theoretically, lithium-sulfur batteries are capable of storing up to 10 times more energy than lithium-ion ones, but to date are unable to sustain this over repeated charging and discharging of the battery. NBL’s lithium-sulfur cathode demonstrated excellent specific capacity of up to 1,220 mAh/g, which means that 1 gram of this material could store a charge of 1,220 mAh. In contrast, a typical lithium-ion cathode has a specific energy capacity of 140 mAh/g. In addition, NBL’s cathode could maintain its high capacity over 200 charging cycles with minimal loss in performance. Key to this was NBL’s unique two-step approach of preparing the cathode.

By first building the carbon host before adding the sulfur source, the researchers obtained a 3D interconnected porous nanomaterial. This approach prevents NBL’s carbon scaffold from collapsing when the battery is charged, unlike those of conventionally prepared cathodes. The latter collapses during the initial charge and discharge cycle, resulting in a structural change. As such, the conventional cathodes become highly dense and compact with a lower surface area and smaller pores, resulting in lower battery performance than NBL’s carbon scaffold. In fact, NBL’s cathode offered 48% higher specific capacity and 26% less capacity fade than conventionally prepared sulfur cathodes. When more sulfur was added to the material, NBL’s cathode achieved a high practical areal capacity of 4 mAh per square centimeter.

“We have shown that the preparation technique of sulfur cathodes has a strong influence on the electrochemical performance in lithium-sulfur batteries,” said Professor Jackie Y. Ying, who leads the NBL research team. “Our method is industrially scalable, and we anticipate that it would have a significant impact on the future design of practical lithium-sulfur batteries.”

The NBL researchers are working on designing and optimizing not just the cathode, but also the anode, separator and electrolyte through nanomaterials engineering. The goal is to develop a full cell system for lithium-sulfur battery that has superior energy storage capacity, as compared to conventional lithium-ion batteries. Such a new battery system can last much longer than current batteries, and would be of great interest for electronic devices, electric vehicles, and grid energy storage.

Shrinking components while enabling assemblies
The ever-shrinking devices, including chiplets, that go into smartphones and other compact electronics call for technology that can grip such devices and place them on a printed circuit board. That’s an area of research at the Massachusetts Institute of Technology.

“Electronics manufacturing requires handling and assembling small components in a size similar to or smaller than grains of flour,” says Sanha Kim, a former MIT postdoc and research scientist who worked in the lab of mechanical engineering associate professor John Hart. “So, a special pick-and-place solution is needed, rather than simply miniaturizing [existing] robotic grippers and vacuum systems.”

Now Kim, Hart, and others have developed a miniature “electro-adhesive” stamp that can pick up and place down objects as small as 20 nanometers wide — about 1,000 times finer than a human hair. The stamp is made from a sparse forest of ceramic-coated carbon nanotubes arranged like bristles on a tiny brush.

When a small voltage is applied to the stamp, the carbon nanotubes become temporarily charged, forming prickles of electrical attraction that can attract a minute particle. By turning the voltage off, the stamp’s “stickiness” goes away, enabling it to release the object onto a desired location.

Hart says the stamping technique can be scaled up to a manufacturing setting to print micro- and nanoscale features, for instance to pack more elements onto ever smaller computer chips. The technique may also be used to pattern other small, intricate features, such as cells for artificial tissues. And the team envisions macroscale, bioinspired electro-adhesive surfaces, such as voltage-activated pads for grasping everyday objects and for gecko-like climbing robots.

“Simply by controlling voltage, you can switch the surface from basically having zero adhesion to pulling on something so strongly, on a per unit area basis, that it can act somewhat like a gecko’s foot,” Hart says.

The team has published its results in the journal Science Advances.

This research was supported in part by the Toyota Research Institute, the National Science Foundation, and the MIT-Skoltech Next Generation Program.



Leave a Reply


(Note: This name will be displayed publicly)