Nuts and Volts - May/June 2018

MEMS + Lens = Compact LIDAR

If you see a car driving down the road and it looks as if there is a rotating ice bucket on the top, it’s likely a self-driving car, and the bucket is its LIDAR unit. The system works, but is relatively bulky, slow, and may amass a layer of bug splats over time. Fortunately, researchers at Argonne National Laboratory ( www.anl.gov) and Harvard University ( www.harvard.edu) have come up with a technology that combines a microelectromechanical system (MEMS) with newly crafted metasurface lenses to produce a much more compact infrared light-focusing system.

Their device is based on a metasurface lens that measures only 900 microns in diameter and 10 microns in thickness (less than 0.04 by 0.0004 inches). As you may know, metamaterials are synthetic structures that exhibit properties not generally found in natural materials. Hence, a metasurface is an artificial sheet material of subwavelength thickness whose structure imposes unusual phase shifts on transmitted or reflected light.

Interestingly, it can display a negative refractive index within a particular frequency range (i.e., it causes the light to travel faster than it would in a vacuum).

In the new optical system, MEMS mirrors reflect scanned light, which is focused by the metalens without the need for additional optical components such as a focusing lens. The trick was to integrate the two technologies without hurting their performance.

The eventual goal is to fabricate all components of an optical system with the same technology used to manufacture today’s electronics. According to Argonne’s Daniel Lopez, “These devices are key today for many technologies. They have become technologically pervasive and have been adopted for everything from activating automobile air bags to the global positioning systems of smart phones ... In principle, optical systems could be made as thin as credit cards.” ▲

ADVANCED TECHNOLOGY

Fusion is Coming! Again!

Every few years, someone announces a “breakthrough” in fusion technology that promises to provide the world with clean, safe, cheap, inexhaustible power. In 2005, Bill Gates assured us, “Two years from now, spam will be solved.” So much for promises. However, if at first you don’t succeed, raise a big wad of money and try, try again.

The latest to take the fusion pledge is a collaboration between MIT ( web.mit.edu) and a new company called Commonwealth Fusion Systems (CFS, www.cfs.energy). CFS is basically an MIT spinoff, created by former Plasma Science and Fusion Center staff and students who have cleverly siphoned an initial $50 million from Eni — an Italian multinational energy company founded in 1953.

The key to CFS’ plans is an effort to develop the world’s most powerful large-bore superconducting electromagnets, which are to be used to keep the hot plasma from escaping the donut-shaped chamber and ruining everyone’s day. The result will be a much more compact tokamak than, say, the large-scale ITER currently under construction in France.

Whereas ITER is aiming for an output of 500 MW, the CFS project — dubbed SPARC — has a more modest final goal of 200 MW; this is comparable to most existing commercial power plants.