What is a Gyroscope? 

A gyroscope is a device that consists of a wheel or disc or circulating beam of light mounted such that it can spin rapidly about an axis; this axis is free to change in any direction. The orientation of the axis is not impacted by the tilting of the mounting, so the gyroscope is in effect used to detect and measure the deviation of an object from its desired orientation, even maintain the said orientation and angular velocity. 

In their most rudimentary form, gyroscopes are a spinning wheel/disk on an axle. The more complex ones are typically mounted on a metal frame, or set of moveable frames or gimbals for the apparatus to function with greater precision. These are typically multi-axis gyroscopes that allow for a wide bandwidth in all their axes. Gyroscopes can seem like simple objects and when the wheel is not spinning, they can be reduced to being over-engineered paperweights. But they have several complex uses today: they are used in compasses and automatic pilots on ships and aircraft, in the steering mechanisms of torpedoes, and in the inertial guidance systems installed in space launch vehicles, ballistic missiles, and orbiting satellites. 

 

A Brief History of Gyroscopes

Essentially, a gyroscope is a top combined with a pair of gimbals. Such tops were invented in many different civilizations, including Greece, Rome, and China, although most of them were not really used as instruments. The first known apparatus similar to a gyroscope was the Whirling Speculum or the Serson’s Speculum and it was invented by John Serson in 1743. It was used as a level, to locate the horizon in foggy or misty conditions.

It was in 1817 that Germany’s Johann Bohnenberger wrote about using the instrument like an actual gyroscope. In 1852, French physicist Léon Foucault used it in an experiment involving the earth’s rotation and gave the device its modern name, with scope deriving from Greek word skopeein, which means to see and gyro coming from Greek word gyros, meaning circle or rotation.

In the 1860s, the advent of electric motors made it possible for a gyroscope to spin indefinitely; what followed was a spate of improvisations with the first functional gyrocompass patented in 1904 by German inventor Hermann Anschütz-Kaempfe.  Soon nations became aware of the military importance of the invention as they realised how gyroscopes can be used for automatic steering and to correct turn and pitch motion in cruise and ballistic missiles. 

Thus, during World War II, the gyroscope became a main component for aircraft and anti-aircraft gun sights. After the war, gyroscopes were miniaturized for use in guided missiles and weapons navigation systems; these midget gyroscopes weighed less than 3 ounces (85 g) and had a diameter of approximately 1 inch (2.5 cm).

 

How does a Gyroscope Work? 

The gyroscope is basically a massive rotor that is fixed in light supporting rings called gimbals. The gimbals have frictionless bearings that isolate the central rotor from outside torques. The spin axis is defined by the axle of the spinning wheel. The rotor spins about an axis, with three degrees of rotational freedom. Having thus acquired extraordinary stability of balance at high speeds, it maintains the high speed rotation axis of its central rotor. 

Now when the gyroscope is applied with external torques or rotations about the given axis, one can measure the orientation using a precession phenomenon (precession refers to the change in the orientation of the rotational axis of a rotating body). In other words, upon the application of external torque - along a direction perpendicular to the rotational axis - on an object rotating about an axis, precession takes place. This rotation about the spin axis is identified and information on this rotation is passed on to a motor or other device that applies torque in an opposite direction thus canceling the precession and maintaining the orientation. Precession can also be avoided by using two gyroscopes arranged perpendicular to each other. The rotation rate can be measured by the pulsation of counteracting torque at constant time intervals. 

 

Types of Gyroscopes

Microelectromechanical systems (MEMS) gyroscopes

MEMS gyroscopes are basically miniaturized gyroscopes found in electronic devices. These are built on the idea of the Foucault pendulum and use a vibrating element.

Hemispherical Resonator Gyroscope (HRG)

Also known as a wine-glass gyroscope or mushroom gyro, the HRG makes use of a thin solid-state hemispherical shell, anchored by a thick stem. This shell is driven to a flexural resonance by electrostatic forces generated by electrodes which are deposited directly onto separate fused-quartz structures enveloping the shell. The inertial property of the flexural standing waves helps produce a gyroscopic effect.

 

Vibrating Structure Gyroscope

Also known as a Coriolis Vibratory Gyroscope (CVG), a vibrating structure gyroscope is a gyroscope that uses a vibrating structure to determine the rate of rotation. 

Dynamically Tuned Gyroscope (DTG)

A DTG is a rotor suspended by a universal joint with flexure pivots. The flexure spring stiffness is independent of spin rate. But the dynamic inertia (from the gyroscopic reaction effect) from the gimbal lends a negative spring stiffness proportional to the square of the spin speed. So at a particular speed, the two moments cancel each other, freeing the rotor from torque, making it an ideal gyroscope.

Ring Laser Gyroscope

A ring laser gyroscope uses the Sagnac effect to calculate rotation by measuring the shifting interference pattern of a beam split into two-halves, even as the two-halves move around the ring in opposite directions. In the Sagnac effect, a beam of light is split and the two beams are made to follow the same path but in opposite directions. On return to the point of entry the two light beams are allowed to exit the ring and undergo interference.

Fiber Optic Gyroscope

A fiber optic gyroscope uses the interference of light to detect mechanical rotation. The split beam’s two-halves go in opposite directions in a coil of fiber optic cable as long as 5 km. 

 

Uses/ Applications of Gyroscopes Today

 

How a gyroscope works in a ship 

a. With steadicam: During the filming of the speeder bike chase scene in the movie Return of the Jedi, a steadicam - aka camera stabilizer - rig was used along with two gyroscopes for extra stabilization. 

b. In Heading indicators: Gyroscopes are used in heading indicators, also known as directional gyros. A heading indicator is a flight instrument used in aircrafts to inform the pilots of the aircraft’s heading / course. The heading indicator has an axis of rotation that is set horizontally, pointing north. But unlike a magnetic compass, it does not seek north. In an airliner, the heading indicator slowly drifts away from north and needs to be reoriented at regular intervals, using a magnetic compass as a reference.

c. As gyrocompass: The directional gyro may not seek out north, but a gyrocompass does. It does so by detecting the rotation of the earth about its axis and then seeking the true north, instead of the magnetic north. Usually, they have built-in damping to prevent overshoot when re-calibrating from sudden movement. 

d. With accelerometers: Gyroscopes are also used along with accelerometers, which are used to measure proper acceleration. It is important to note here that measuring an object’s acceleration and integrating over time, the velocity of the object can be arrived at. Integrating again, the object’s position can be determined. While a simple accelerometer consists of a weight that can freely move horizontally, a more complicated design comprises a gyroscope with a weight on one of the axes. (For more information about accelerometers, check out our blog on accelerometers. 

e. In Consumer Electronics: Given the fact that the gyroscope helps calculate orientation and rotation and is used for maintaining a reference direction or providing stability in navigation, designers have incorporated them into modern technology. In addition to being used in compasses, aircraft, computer pointing devices, gyroscopes are now also used in consumer electronics. In fact, Apple founder Steve Jobs was the first one to popularize the usage or application of the gyroscope in consumer electronics; he did so by using them in the Apple iPhone. Since then, gyroscopes have come to be commonly used in smartphones. Moreover, a few features of Android phones - think PhotoSphere or 360 Camera and VR feature - can not work without a gyroscope sensor in the phone.

It is the Gyro sensor in our smartphones that senses angular rotational velocity and acceleration. This is what makes it possible for us to play using motion senses in our phones, tablets. Similarly, the smartphone’s gyroscope helps us watch 360-degree videos or photos. When we move our phone, the photo or the video moves due to the presence of a tiny gyroscope in the phone.

f. In toys: Gyroscopes are also used in toys, in fact there are toy gyroscopes which make for great educational tools as they help kids understand how gyroscopes work. 

g. In bicycles: Electric powered flywheel gyroscopes inserted in bicycle wheels are said to be a good alternative to training wheels.

h. In cruise ships: Cruise ships use gyroscopes for leveling motion-sensitive devices such as self-leveling pool tables.

Nuclear Spins Detect Subtle Rotations

A small device performs rotational measurements using nuclear spins in a diamond wafer, paving the way for microchip-size gyroscopes.

Hold that tilt. Like a toy gyroscope, the nuclear spins inside a diamond crystal maintain a stable orientation—which can be used to measure rotations.

Future technologies for unmanned and autonomous vehicles need precise gyroscopes for reliable flight and navigation, but these devices are typically too large to be suitable for lightweight microscopic electronics. Now researchers have demonstrated a tiny gyroscope that exploits the behavior of atomic nuclei in diamond [1]. Compared with previous diamond-based sensors, the device can measure slower rotational speeds—in a range (tens of degrees per second) that is relevant for aviation applications. The researchers expect that further development could lead to a new generation of commercially viable and ultrasensitive microchip gyroscopes.

A gyroscope detects changes in the orientation of an object like an airplane. Today’s most accurate gyroscopes employ laser light traveling on a closed path around a ring. But the accuracy of such devices depends on the area enclosed by the ring, so shrinking the gyroscopes would make them less reliable. Realizing small but still sensitive gyroscopes requires a different approach, and researchers have been developing alternatives based on exploiting the behavior of elementary particles that possess spin.

The spin state of a particle will stay fixed—like the spin axis of a toy gyroscope—unless acted on by some external force. Hence, a conceptually simple design for a gyroscope involves setting the spin of a particle in some state, leaving it alone, and then measuring the spin again. Any change would reveal a rotation of the object that encompasses the particle, which could be a flying vehicle, for example.

Making such a gyroscope work in practice, however, is challenging. Some researchers have been trying with atomic gases held in small traps, but collisions with walls tend to perturb the atomic spins. Using diamond avoids this problem. Diamond is made almost entirely of carbon atoms but also contains sites where a nitrogen atom replaces a carbon, while also leaving a nearby atomic vacancy in the lattice. These nitrogen vacancy (NV) centers have spins, both electronic and nuclear, that researchers have used to detect rotation (see Focus: Detecting the Rotation of a Quantum Spin) but not yet at the sensitivity level needed for a gyroscope.

Alexey Akimov of the Lebedev Physical Institute in Russia and colleagues have now demonstrated a gyroscope based on NV centers in a thin diamond wafer. Unlike previous work that focused on the spins of electrons or of carbon nuclei associated with NV centers, the researchers selected the spins of nitrogen nuclei as their rotation detectors. The nitrogen spins are less susceptible to perturbations than the other spins. However, the electron spins still proved useful in initializing and reading out the nuclear spins.

To demonstrate the operation of the gyroscope, the researchers placed their diamond wafer on a rotating platform embedded in a magnetic field. In such a field, the electron and nitrogen spins in an NV center are coupled through a light-mediated interaction. Taking advantage of this property, the team used a sequence of light pulses to set the nitrogen spins in an ensemble of NV centers into one spin state. They then let the spins evolve for 2 milliseconds before reading out the new spin state using a second sequence of pulses.

A schematic of the nitrogen-vacancy (NV) gyroscope, placed on a rotating platform. The nitrogen nuclear spins in a diamond wafer are set by pulses from a laser (green), as well as inputs from microwave (MW) and radio-frequency (RF) components controlled by a field-programmable gate array (FPGA). After a free evolution period, the spin states are measured by reading out their emission

 

This read-out step took advantage of another convenient property of NV centers: the state of the electron spins—and hence the nuclear spins—can be inferred from the amount of light emitted from the NV centers. Rotating the platform slowly, at a speed of less than one revolution per second, the researchers measured the intensity of the emitted light and used this signal to calculate the platform rotation speed.

Besides providing setup and readout, the electron spins also played a secondary role in greatly improving the accuracy of the measurements, Akimov says. By monitoring the electron spins, the team could correct for a magnetic-field effect that causes an additional rotation of the nuclear spins. The team checked their gyroscope against a commercial microelectromechanical systems (MEMS) gyroscope and found good agreement. Akimov says the NV gyroscope could have an advantage over other gyroscopes in that it would not need constant recalibration.

Another advantage is that diamond crystals can be integrated into existing microchip technology more easily than gas-based devices can. “The solid-state nature of the sensor is a huge advantage,” says physicist Dmitry Budker of the Johannes Gutenberg University in Germany, whose research group first suggested this approach in 2012. Akimov and colleagues are now miniaturizing their gyroscope so that it might eventually fit on a microchip. “Many things can be improved to make the device smaller,” Akimov says.

–Mark Buchanan

Mark Buchanan is a freelance science writer who splits his time between Abergavenny, UK, and Notre Dame de Courson, France.

Atomic-scale gyroscope uses diamond defects

Spinning around: physicists have created a gyroscope using nuclear spins in diamond. (Courtesy: Shutterstock/Inna Bigun)

Researchers in Russia have built a highly accurate, atomic-scale gyroscope that detects rotation through changes in the coupled spins of electrons and nitrogen nuclei. Led by Alexey Akimov at the Lebedev Physical Institute in Moscow, the team created its device by exploiting defects in the atomic structure of diamond. The approach could enable tiny gyroscopes to be integrated onto inexpensive microchips that could be used on lightweight aerial vehicles.

Within a traditional gyroscope, conservation of angular momentum ensures that the rotational axis of a spinning disk remains fixed even as its casing rotates. As a result, a gyroscope can be used to detect rotation, which makes it useful for navigation.

On a much smaller scale, electrons and some atoms and nuclei have intrinsic angular momenta called spin. It is therefore possible to detect rotation by measuring transitions in the quantum spin states of these particles. Previously, this has been attempted using trapped atomic gasses – but because such atoms can drift and collide with their surrounding walls, these measurements have been unreliable.

Focus on nuclear spins

Instead of using drifting atoms, Akimov’s team used nitrogen vacancy (NV) centers in diamond. These occur when two adjacent carbon atoms in a diamond lattice are replaced with a nitrogen atom and a lattice vacancy. An NV centre has both nuclear and electronic spins, but unlike atoms in a gas it cannot move. An important feature of an NV centre is that the spin state of the electron can be read-out by shining light on it, which causes it to emit distinctive light of its own.

Previously, electron spins in NV centres have been used to detect extremely rapid rotation. In this latest experiment, however, the focus was on the nuclear spins, which are much less susceptible to noise and therefore more suitable for detecting much slower rotations.

Diamond wafer

The team’s set-up comprised an ensemble of NV centres within a thin diamond wafer that was placed rotating platform. Using an applied magnetic field along with laser, microwave and radio-frequency pulses, the team set the nuclear spins to all point in the same direction.

 

Defect spins slow diamond motion

The diamond then rotated slowly for 2 ms, after which the researchers coupled the nuclear and electronic spins. This allowed them to measure the orientations of the nuclear spins. They then used this information to determine the platform’s rotational speed with no stationary reference required.

The team says that the performance of the new device is on par with commercially available gyroscopes based on microelectromechanical (MEMs) systems. These use vibrating, rather than rotating, masses but suffer from a lack of long-term stability. Akimov and colleagues say that their diamond-based system could be readily integrated into existing microchips and could be used to improve the navigational abilities of lightweight aerial vehicles, including unmanned drones.

 

References

1. V. V. Soshenko et al., “Nuclear spin gyroscope based on the nitrogen vacancy center in diamond,” Phys. Rev. Lett. 126, 197702 (2021).

2. Nuclear Spin Gyroscope based on the Nitrogen Vacancy Center in Diamond

3. Vladimir V. Soshenko, Stepan V. Bolshedvorskii, Olga Rubinas, Vadim N. Sorokin, Andrey N. Smolyaninov, Vadim V. Vorobyov, and Alexey V. Akimov
4. Phys. Rev. Lett. 126, 197702 (2021)
5. https://physicsworld.com/a/atomic-scale-gyroscope-uses-diamond-defects/
6. https://www.youngwonks.com/blog/What-is-a-Gyroscope-and-How-Does-It-Work
7. https://physicsworld.com/a/how-to-measure-a-single-quantum-spin-in-a-rapidly-rotating-diamond/