Researchers have developed a small, highly accurate gyroscope that is 10,000 times more accurate but only 10 times more expensive than gyroscopes used in typical cellphones. Most smartphones contain gyroscopes to detect the orientation of the screen and help figure out which way the user is facing but their accuracy is poor. They are the reason why cellphones often incorrectly indicate which direction a user is facing during navigation. In another example, a driverless car could get lost quickly with a loss of Global Positioning System (GPS) signal. And better backup navigation equipment could help soldiers find their way in areas where GPS signals have been jammed or speed up warehouse robots.
The device that enables navigation without a consistent orienting signal is an inertial measurement unit (IMU). It is made up of three accelerometers and three gyroscopes, one for each axis in space. But existing IMUs are very pricey, even for equipment as expensive as autonomous vehicles.
The key to making the affordable, small gyroscope is a nearly symmetrical mechanical resonator that looks like a Bundt pan crossed with a wine glass, made one centimeter wide. With wine glasses, the duration of the ringing tone produced when the glass is struck depends 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 certain pattern. If it is suddenly rotated, the vibrating pattern wants to stay in its original orientation. So, by monitoring the vibration pattern, it is possible to directly measure rotation rate and angle. The way the vibrating motion moves through the glass reveals when, how fast, and by how much the gyroscope spins in space.
To make their resonator as perfect as possible, the team started with a nearly perfect sheet of pure glass, known as fused-silica, about a quarter of a millimeter thick. They used a blowtorch to heat the glass and then mold it into a Bundt-cake-like shape known as a “birdbath” resonator since it also resembles an upside-down birdbath. Then, they added a metallic coating to the shell and placed electrodes around it that initiate and measure vibrations in the glass. The whole thing was encased in a vacuum package about the footprint of a postage stamp and half a centimeter tall that prevents air from quickly damping out the vibrations.