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Global Technology

Most smartphones contain gyroscopes to detect the orientation of the screen and help figure out which way it is facing, but their accuracy is poor. They’re the reason why phones often incorrectly indicate which direction a user is facing during navigation.

It doesn’t matter much to a human on the street or behind the wheel, but a driverless car could get lost quickly with a loss of GPS signal. Inside their backup navigation systems, autonomous vehicles currently use high-performance gyroscopes that are larger and much more expensive.

However, high-performance gyroscopes are a bottleneck, and they have been for a long time. And now, a small, inexpensive, and highly accurate gyroscope developed at the University of Michigan can remove this bottleneck by enabling the use of high-precision and low-cost inertial navigation in most autonomous vehicles. The new gyroscope is 10,000 times more accurate but only ten times more expensive than the gyroscopes now used in your typical cell phone. Importantly, this gyroscope is 1,000 times less expensive than much larger gyroscopes with similar performance.

It could form the core of an improved backup navigation system that could help soldiers find their way in areas where GPS signals have been jammed. Or, in a more mundane scenario, accurate indoor navigation could speed up warehouse robots.

The device that enables navigation without a consistent orienting signal is called an inertial measurement unit. It is made up of three accelerometers and three gyroscopes, one for each axis in space. But getting a good read on which way you’re going with existing inertial measurement units is so expensive that they have been out of range for most applications, even for applications as expensive as autonomous automobiles.

The key to making this affordable is a small gyroscope with a nearly symmetrical mechanical resonator. It looks like a one centimeter wide “Bundt pan” crossed with a wine glass. As with wine glasses, the duration of the ringing tone produced when the glass is struck on the quality of the glass - but instead of being an aesthetic feature, the ring is crucial to the gyroscope’s function. The complete device uses electrodes placed around the glass resonator to push and pull on the glass, making it ring and keeping it going.

The glass resonator vibrates in a specified pattern, and if you suddenly rotate it, the vibrating pattern wants to stay in its original orientation. So, by monitoring the vibration pattern, it is possible to directly measure the rotation rate and angle.  The way that the vibrating motion moves through the glass reveals when, how fast and by how much the gyroscope spins in space.

To make their resonators as perfect as possible, the Michigan team starts with a nearly ideal sheet of pure glass, known as fused-silica, about a quarter of a millimeter thick. They use a blowtorch to heat the glass and then mold it into a Bundt-like shape - known as a “birdbath resonator” since it also resembles an upside-down birdbath.

Then, they add a metallic coating to the shell and place electrodes around it that initiate and measure vibrations in the glass. The whole thing is encased in a vacuum package, about the footprint of a postage stamp and half a centimeter tall, which prevents air from damping out the vibrations.

The research, funded by DARPA, was recently presented at the 7th IEEE International Symposium on Inertial Sensors & Systems.

References
University of Michigan, March 23, 2020, “Small, Precise and Affordable Gyroscope for Navigating without GPS,” Nicole Casal Moore and Kate McAlpine.  ⓒ 2020 The Regents of the University of Michigan.  All rights reserved.

To view or purchase this article, please visit:
https://news.umich.edu/small-precise-and-affordable-gyroscope-for-navigating-without-gps/

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An international team has developed a new method for generating quantum-entangled photons in a previously inaccessible spectral range, making the encryption of satellite-based communications much more secure in the future.

A 15-member research team from the UK, Germany, and Japan has developed a new method for generating and detecting quantum-entangled photons at a wavelength of 2.1 micrometers. In practice, entangled photons are used in encryption methods such as quantum key distribution to completely secure telecommunications between two partners against eavesdropping attempts. The research results are presented to the public for the first time in a recent issue of Science Advances.

Until now, it has been possible to implement such encryption mechanisms only in the near-infrared range of 700 to 1550 nanometers. These shorter wavelengths have disadvantages, especially in satellite-based communication, because they are disturbed by light-absorbing gases in the atmosphere as well as the background radiation of the sun. With the existing technology, end-to-end encryption of transmitted data can only be guaranteed at night.

Entangled photon pairs at two micrometers wavelength are significantly less influenced by the solar background radiation. Also, a so-called “transmission window” exists in the earth’s atmosphere for wavelengths of two micrometers.  That means these photons are less absorbed by atmospheric gases, allowing more effective communication.

For their experiment, the researchers used a nonlinear crystal made of lithium niobate. When they sent ultrashort light pulses from a laser into the crystal a nonlinear interaction produced entangled photon pairs with a new wavelength of 2.1 micrometers.

The next crucial step will be to miniaturize this system by converting it into photonic integrated devices, making it suitable for mass production and use in other application scenarios.

References
Science Advances, March 27, 2020, “Two-Photon Quantum Interference and Entanglement at 2.1 μm,” by Shashi Prabhakar et al. ⓒ 2020 American Association for the Advancement of Science. All rights reserved.

To view or purchase this article, please visit
https://advances.sciencemag.org/content/6/13/eaay5195