Power/Performance Bits: Sept. 15

Higher-res lidar
Researchers from Purdue University and École Polytechnique Fédérale de Lausanne (EPFL) devised a way to improve lidar and provide higher-resolution detection of nearby fast-moving objects through mechanical control and modulation of light on a silicon chip.

“Frequency modulated continuous wave” (FMCW) lidar detects objects by scanning laser light from the top of a vehicle. A single laser beam splits into a comb of other wavelengths, called a microcomb, to scan an area. Light bounces off of an object and goes to the detector through an optical isolator or circulator, which ensures all reflected light ends up at the detector array.

By using acoustic waves, the team was able to tune these components more quickly. The system incorporates MEMS transducers made of aluminum nitride to modulate the microcomb at high frequencies ranging from megahertz to gigahertz. The transducers were then integrated with a silicon nitride photonics wafer.

An array of phased MEMS transducers stirs light at gigahertz frequencies by launching a corkscrew-like stress wave into a silicon chip. “The stirring motion modulates light such that it can only travel in one direction,” said Sunil Bhave, a Purdue professor of electrical and computer engineering.

Additionally, “the tight vertical confinement of the bulk acoustic waves prevents cross-talk and allows for close placement of the actuators,” noted Hao Tian, a Purdue Ph.D. candidate in electrical and computer engineering at Purdue.

Other transducers excite an acoustic wave that shakes the chip at megahertz frequencies, demonstrating sub-microsecond control and tuning of the laser pulse microcomb or soliton.

This light modulation technique not only integrates mechanics with optics, but also the fabrication processes involved, making the technology more commercially viable, the researchers said. The MEMS transducers are simply fabricated on top of the silicon nitride photonics wafer with minimal processing.

“This achievement, bridging integrated photonics, MEMS engineering and nonlinear optics, represents a new milestone for the emerging chip-based microcomb technology,” said Junqiu Liu, who leads the fabrication of silicon nitride photonics chips at the EPFL Center of MicroNanoTechnology.

Beyond lidar, the researchers see the light modulation technique boosting microcomb applications in power-critical systems such as in space, data centers and portable atomic clocks, or in extreme environments such as those with cryogenic temperatures.

EMI-shielding MXene
Researchers from Drexel University and Korea Institute of Science and Technology (KIST) investigated titanium carbonitride and found it has exceptional electromagnetic interference shielding properties.

Titanium carbonitride is part of the MXene family of two-dimensional materials, which have shown promising properties in a number of areas. Titanium carbonitride, in particular, was able to block and absorb electromagnetic interference more effectively than any known material, including the metal foils currently used in most electronic devices.

“This discovery breaks all the barriers that existed in the electromagnetic shielding field. It not only reveals a shielding material that works better than copper, but it also shows an exciting, new physics emerging, as we see discrete two-dimensional materials interact with electromagnetic radiation in a different way than bulk metals,” said Yury Gogotsi, PhD, Distinguished University and Bach professor in Drexel’s College of Engineering.

Initially, the group was investigated an MXene called titanium carbide, which showed to be an effective shielding material. As the team investigated other materials, they came across something even better.

“Titanium carbonitride has a very similar structure by comparison to titanium carbide – they’re actually identical aside from one replacing half of its carbon atoms with nitrogen atoms – but titanium carbonitride is about an order of magnitude less conductive,” said Kanit Hantanasirisakul, a doctoral candidate in Drexel’s Department of Materials Science and Engineering. “So we wanted to gain a fundamental understanding of the effects of conductivity and elemental composition on EMI shielding application.”

In tests, a film of the titanium carbonitride material could block EMI interference about 3-5 times more effectively than a similar thickness of copper foil.

It also operates differently. While most EMI shielding materials simply prevent the penetration of the electromagnetic waves by reflecting it away, titanium carbonitride actually blocks EMI by absorbing the electromagnetic waves. The material’s layered, porous structure and chemical structure give it these particular characteristics, which emerge during annealing,

“This is a much more sustainable way to handle electromagnetic pollution than simply reflecting waves that can still damage other devices that are not shielded,” Hantanasirisakul said. “We found that most of the waves are absorbed by the layered carbonitride MXene films. It’s like the difference between kicking litter out of your way or picking it up – this is ultimately a much better solution.”

This means it could be used to individually coat components inside a device to contain their EMI even while they are being placed closely together, the researchers said.

Backpack camera for beetles
Researchers from the University of Washington built a tiny wireless, steerable camera that is small enough to be carried by a beetle. The camera can stream video to a smartphone at 1 to 5 frames per second and sits on a mechanical arm that can pivot 60 degrees. It weighs about 250 milligrams.

“We have created a low-power, low-weight, wireless camera system that can capture a first-person view of what’s happening from an actual live insect or create vision for small robots,” said Shyam Gollakota, a UW associate professor in the school of computer science & engineering. “Vision is so important for communication and for navigation, but it’s extremely challenging to do it at such a small scale. As a result, prior to our work, wireless vision has not been possible for small robots or insects.”

Capturing wide-angle, high-resolution images requires power, and the batteries to support such a system are too heavy for insects or tiny robots. Drawing inspiration from the eyes of a fly, where only a small area is high-resolution vision, the system uses an ultra-low-power black-and-white camera that can sweep across a field of view with the help of a mechanical arm. When a voltage is applied to the arm, it bends to move the camera into the desired position where it will stay for about a minute unless more power is applied. The camera and arm are controlled via Bluetooth from a smartphone from a distance up to 120 meters away, and a video shows the camera in action.

A Pinacate beetle explores the UW campus with the camera on its back. (Credit: Mark Stone/University of Washington)

“One advantage to being able to move the camera is that you can get a wide-angle view of what’s happening without consuming a huge amount of power,” said Vikram Iyer, a UW doctoral student in electrical and computer engineering. “We can track a moving object without having to spend the energy to move a whole robot. These images are also at a higher resolution than if we used a wide-angle lens, which would create an image with the same number of pixels divided up over a much larger area.”

The researchers attached their removable system to the backs of two different types of beetles, a death-feigning beetle and a Pinacate beetle. “We made sure the beetles could still move properly when they were carrying our system,” said Ali Najafi, a UW doctoral student in electrical and computer engineering. “They were able to navigate freely across gravel, up a slope and even climb trees.” The beetles also lived for at least a year after the experiment ended.

“We added a small accelerometer to our system to be able to detect when the beetle moves. Then it only captures images during that time,” added Iyer. “If the camera is just continuously streaming without this accelerometer, we could record one to two hours before the battery died. With the accelerometer, we could record for six hours or more, depending on the beetle’s activity level.”

The researchers also applied the camera to a low power, insect-sized terrestrial robot that uses vibration to move. Applications include biology observations and exploring hard-to-reach places.