How Gyroscopes Work in Phones: MEMS Sensors, Motion Tracking, and Applications

Gyroscope in a phone is a miniature sensor that measures angular velocity and enables a smartphone to track rotation around three axes. This technology is essential for mobile games, video stabilization, augmented reality, and other features that rely on device movement detection.

What Is a MEMS Gyroscope and How Is It Built?

A MEMS gyroscope (Micro-Electro-Mechanical Systems) is a micromechanical angular velocity sensor made using microelectronics technologies. Its sensitive elements are so tiny they fit inside a compact microchip package.

The sensor is based on silicon structures capable of small mechanical oscillations. These are formed directly on a silicon substrate using microfabrication techniques similar to those applied in semiconductor manufacturing.

Inside a typical MEMS gyroscope you'll find:

• Moving mass - a microscopic element set into oscillatory motion.
• Spring suspensions - thin elastic structures allowing the mass to shift in specific directions.
• Electrodes - components that excite oscillations and measure displacements.
• Electronic circuit - processes the signals from the sensitive elements and calculates angular velocity.

These moving parts are usually housed within a hermetically sealed microcavity. A controlled gas environment or reduced pressure helps ensure optimal oscillation properties and protects the structure from external influences.

Unlike classic gyroscopes with a spinning rotor, MEMS gyros use vibrating masses that respond to sensor body rotation. This design allows for multiple measurement axes in a compact, energy-efficient chip, enabling their use not only in smartphones but also in smartwatches, game controllers, drones, and other electronic devices.

To learn more about micromechanical structure technology, see the article MEMS: Micro-Electro-Mechanical Systems in Modern Electronics.

How a MEMS Gyroscope Works: Vibrations and the Coriolis Force

The operation of a MEMS gyroscope is based on the Coriolis force - a physical effect arising when an object moves within a rotating reference frame. This effect enables the sensor to detect smartphone rotation without a traditional mechanical rotor.

Inside the gyroscope, a microscopic silicon mass continuously vibrates due to electrostatic forces. When the phone is still, oscillations occur mostly along a designated direction. As the device rotates, the mass experiences additional movement that can be detected.

How the Coriolis Force Measures Rotation

Imagine the moving mass oscillates along the X axis. If the smartphone rotates around the Z axis, the Coriolis force causes an extra displacement along the Y axis. The higher the angular velocity, the greater the impact on the vibrating element.

The measurement process includes several stages:

1. Oscillation excitation: Electrodes make the silicon mass vibrate at a set frequency.
2. Coriolis force generation: When the device rotates, an additional force acts on the moving mass, perpendicular to the initial motion.
3. Displacement registration: The distance between moving and fixed electrodes changes, altering electrical capacitance.
4. Signal processing: The electronic circuit extracts the signal, applies calibration, and computes angular velocity.

Since these displacements are extremely small, highly sensitive electronics are used to register capacitance changes. Vibrations are typically maintained near the mechanical structure's resonance frequency to yield a strong measurement signal.

Measuring Rotation Along Three Axes

Modern smartphone gyroscopes measure angular velocity relative to three mutually perpendicular axes:

• X - rotation around the phone's transverse axis
• Y - rotation around the longitudinal axis
• Z - rotation around the axis perpendicular to the screen

This requires several sensitive structures or special designs with multiple vibration modes. Results are given in degrees per second (°/s) or radians per second (rad/s). For example, 90 °/s means the device is currently rotating at 90 degrees per second around the respective axis.

It's important to note that a MEMS gyroscope measures angular velocity, not the angle of rotation. To determine how much the smartphone has rotated over time, the system must process a sequence of measurements.

How Smartphones Detect Rotation and Position in Space

The gyroscope in a smartphone constantly measures angular velocity across all three axes. The system uses this data to calculate orientation changes during turns and tilts.

For instance, if the phone rotates at 90°/s around one axis and maintains this speed for half a second, the rotation angle is 45 degrees. The phone sequentially adds up these small orientation changes over short intervals - a process known as integrating angular velocity.

This method has a drawback: even minor measurement errors accumulate over time. If the gyroscope records a nonzero velocity when the phone is still, the calculated orientation will gradually drift from reality - a phenomenon known as gyroscope drift.

Combining Data from Multiple Sensors: Sensor Fusion

To improve orientation accuracy, smartphones use Sensor Fusion - combining readings from several sensors:

• Gyroscope - tracks rotational speed and rapid orientation changes.
• Accelerometer - measures acceleration (including gravity) to determine the vertical direction.
• Magnetometer - gauges the magnetic field to help find direction relative to magnetic north.

Each sensor compensates for the others' limitations. The gyroscope accurately detects fast turns but accumulates errors. The accelerometer corrects tilt relative to gravity, though it's also affected by movement. The magnetometer adds directional information, but its readings may be distorted by nearby metal objects, magnets, or electronics.

How Sensor Fusion Works

Sensor fusion algorithms compare measurements and estimate the most probable smartphone orientation. For abrupt turns, the system primarily uses gyroscope data, as it reacts quickly. When the device stops moving, the accelerometer's input corrects accumulated tilt errors.

Data may be processed using complementary filters, Kalman filters, and other state estimation algorithms, providing more stable orientation than a gyroscope alone. Results can be given as rotation angles or quaternions - a mathematical way to describe 3D orientation.

Note: orientation and position in space are different concepts. The gyroscope determines where the smartphone is pointing, but not its coordinates or traveled distance. Additional sources like cameras, satellite navigation, and other sensors are used for movement tracking.

Read more about sensor integration in the article How Inertial Navigation Works Without GPS: IMU in Everyday Life.

Gyroscope vs. Accelerometer: What's the Difference?

Gyroscopes and accelerometers often work together but measure different physical quantities. The gyroscope detects angular velocity, while the accelerometer registers acceleration acting on the device, including gravity.

For example, when a phone lies still on a table, the gyroscope reads nearly zero angular velocity, while the accelerometer detects acceleration due to gravity, indicating the vertical direction. If you rotate the phone around its vertical axis, the gyroscope records the turn, but the accelerometer might not register significant changes since gravity's direction relative to the phone hardly shifts.

Gyroscope vs. Accelerometer: Comparison Table

Why One Sensor Isn't Enough

An accelerometer can determine the phone's tilt relative to vertical when the device is stationary or moving without significant acceleration. However, it can't reliably track rotation around the direction of gravity. The gyroscope, by contrast, detects rotation around any axis but loses orientation accuracy over time due to accumulating errors.

Combining these sensors allows smartphones to distinguish between tilts, turns, and linear movements. For example, in mobile games the gyroscope tracks turning direction, while the accelerometer provides tilt and acceleration information. Automatic screen rotation typically relies on the accelerometer, so a separate gyroscope isn't required for switching between portrait and landscape modes.

What Is the Gyroscope Used for in Smartphones?

The gyroscope in a phone is essential for features requiring fast and precise rotation tracking. It enables motion-based game controls, video stabilization, and orientation detection in virtual environments.

Motion Control in Mobile Games

In mobile games, the gyroscope lets you control the camera or aiming by physically turning your phone. For instance, in PUBG Mobile and similar shooters, you can fine-tune your aim with small device movements without touching the screen. The sensor data translates into game commands, and sensitivity settings determine how much the virtual camera responds to phone rotation.

Photo and Video Stabilization

During video capture, the gyroscope detects small phone rotations caused by hand shake. These data are used by stabilization systems to reduce unwanted image vibrations. Depending on the camera's design, different technologies are used:

• Optical Image Stabilization (OIS): The lens or sensor physically shifts to counteract device movement.
• Electronic Image Stabilization (EIS): The image is digitally corrected using gyroscope data and frame analysis.
• Hybrid stabilization: Combines optical and electronic corrections.

The gyroscope is especially valuable for electronic stabilization, as it can assess camera movement independently of image content.

Augmented and Virtual Reality

In augmented reality (AR) applications, the gyroscope tracks phone rotations and promptly updates virtual object positions relative to the camera. For example, when you turn your phone, the system must quickly adjust the virtual model's perspective to match the real environment. In virtual reality (VR), gyroscope readings track head turns, but additional sensors or tracking systems are necessary for spatial movement detection.

Gesture and Motion Recognition

Gyroscope data also enable recognition of various device movements: turns, shakes, and complex gestures. These features are found in apps, game controllers, and fitness tracking systems. Usually, the gyroscope works alongside the accelerometer, as combining angular velocity and linear acceleration improves movement detection accuracy. However, not every app uses gyroscope data - developers choose the necessary sensors based on specific functions.

Conclusion

A MEMS gyroscope enables a smartphone to detect rotation using microscopic vibrating structures. As the device turns, the Coriolis force causes additional displacement of sensitive elements, which is converted into an electrical signal. The sensor then calculates angular velocity along three axes.

By itself, the gyroscope does not determine the phone's absolute orientation. For more precise motion tracking, its data is combined with inputs from the accelerometer and magnetometer. This integrated system is crucial for mobile gaming, video stabilization, and augmented reality applications.

For basic automatic screen rotation, the accelerometer is sufficient. However, if your phone is used for motion-controlled games, AR apps, or advanced image stabilization, the presence of a gyroscope becomes much more important.