Power/Performance Bits: Nov. 6

Camera for object recognition
Researchers from the University of Illinois at Urbana-Champaign developed a new camera that could improve object detection in vehicles. Inspired by the visual system of mantis shrimp, the camera detects the polarization of light and has a dynamic range about 10,000 times higher than today’s commercial cameras.

“In a recent crash involving a self-driving car, the car failed to detect a semi-truck because its color and light intensity blended with that of the sky in the background,” said Viktor Gruev of the University of Illinois at Urbana-Champaign. “Our camera can solve this problem because its high dynamic range makes it easier to detect objects that are similar to the background and the polarization of a truck is different than that of the sky.”

Mantis shrimp have a logarithmic response to light intensity. This makes the shrimp sensitive to a high range of light intensities, allowing them to perceive very dark and very bright elements within a single scene.

The dynamic range and polarization capability can be seen in the light intensity image (left) and two polarization images (middle and right) acquired with the new camera. The scene imaged included a black plastic horse, an LED flashlight and a cone-shaped piece of silicon. (Source: Viktor Gruev, University of Illinois at Urbana-Champaign)

To achieve a similarly high dynamic range for their new camera, the researchers tweaked the way the camera’s photodiodes convert light into an electrical current. Instead of operating the photodiodes in reverse bias mode, traditionally used for imaging, the researchers used forward bias mode. This changed the electrical current output from being linearly proportional to the light input to having a logarithmic response like the shrimp.

For the polarization sensitivity, the researchers mimicked the way that the mantis shrimp integrates polarized light detection into its photoreceptors by depositing nanomaterials directly onto the surface of the imaging chip that contained the forward biased photodiodes. “These nanomaterials essentially act as polarization filters at the pixel level to detect polarization in the same way that the mantis shrimp sees polarization,” said Gruev.

Tested under different driving lighting conditions, such as in tunnels and fog, the camera worked without problems.

The researchers say the camera could be mass-produced for as little as $10 apiece. They are now working with a company that manufactures air bags to see if the new camera’s high dynamic range and polarization imaging capability can be used to better detect objects to either avert a collision or deploy the air bag a few milliseconds earlier than is currently possible.

Replaceable EV battery
Researchers at the Ulsan National Institute of Science and Technology (UNIST) propose a new way of approaching electric vehicle power by using replaceable, rather than rechargeable, batteries. The new aluminum-air flow battery has higher energy density, lower cost, longer cycle life, and higher safety than traditional lithium-ion batteries, the team says.

Aluminum-air batteries produce electricity from the reaction of oxygen in the air with aluminum and cannot be recharged via conventional means. Instead, the battery’s aluminum plate and electrolyte would be replaced. In an electric vehicle, the battery has a higher energy density than gasoline.

“Gasoline has an energy density of 1,700 Wh/kg, while an aluminum-air flow battery exhibits a much higher energy densities of 2,500 Wh/kg with its replaceable electrolyte and aluminum,” said  Jaephil Cho, a professor at UNIST. “This means, with 1kg of aluminum, we can build a battery that enables an electric car to run up to 700km.”

A new type of aluminum-air flow battery is more energy efficient than the existing lithium-ion batteries. (Source: UNIST)

The team’s battery uses silver nanoparticle-mediated silver manganate nanoplates as a highly active and chemically stable catalyst for oxygen reduction. The patterns on the surface of the silver manganite nanoplates create a high concentration of dislocations in the crystal lattice, providing high electrical conductivity with low electrode resistance.

Compared to the conventional aluminum air batteries, the new battery’s discharge capacity increased 17 times. Additionally, the capacity of newly developed silver-manganese oxide-based catalysts was comparable to that of the conventional platinum catalysts. Silver is 50 times less expensive than platinum, making the new battery competitive in terms of the price, the team said.

3D printed Li-ion batteries
Researchers at Duke University and Texas State University created a new method for 3D printing of lithium-ion batteries that allows them to be almost any shape. The process can be done using inexpensive consumer 3D printers.

One challenge was using poly(lactic acid) (PLA), which is a common material for 3D printing but not an ionic conductor. The team was able to increase the ionic conductivity of PLA by infusing it with an electrolyte solution of ethyl methyl carbonate, propylene carbonate, and LiClO4. To boost the battery’s electrical conductivity, graphene was incorporated into the anode and multi-walled carbon nanotubes into the cathode. Lithium titanate was blended into the PLA used for the anode, while lithium manganese oxide was added for the cathode.

This LED bangle, including a lithium-ion battery, was made entirely by 3D printing. (Source: American Chemical Society)

To test the process, the team 3D printed an LED bangle bracelet with an integrated lithium-ion battery. The bangle battery could power a green LED for about 60 seconds. According to the researchers, the capacity of the first-generation 3D-printed battery is about two orders of magnitude lower than that of commercial batteries, which is too low for practical use. However, they say that they have several ideas for increasing the capacity, such as replacing the PLA-based materials with 3D-printable pastes.