IMU

An inertial measurement unit (IMU) is a device that provides information about motion and orientation by measuring forces and rotations. A typical IMU combines accelerometers and gyroscopes to sense linear acceleration along three axes and angular velocity around three axes. Many modern IMUs also include a magnetometer to provide a measure of the ambient magnetic field, enabling improved absolute attitude estimation. Most consumer and industrial IMUs are based on microelectromechanical systems (MEMS), offering compact size and low cost. In strapdown configurations, sensors are fixed to the body, and their outputs are integrated by a processor to obtain orientation and motion estimates without a gimbaled platform.

The accelerometers measure specific force, which includes both actual acceleration and the gravity vector, while gyroscopes provide angular rates. Magnetometers sense the magnetic field vector and help anchor heading relative to Earth's field. Raw sensor data are typically processed by sensor fusion algorithms, such as Kalman filters or complementary filters, to produce stable estimates of attitude (often expressed as Euler angles or quaternions) and, in some systems, velocity or position. High-rate IMU data are commonly fused with external references such as GPS to reduce drift and improve accuracy. Calibration is essential to correct biases, scale factors, misalignments, and temperature effects; MEMS devices are particularly prone to bias instability and noise.

Applications span a wide range of fields, including mobile devices, drones and unmanned vehicles, robotics, aerospace, automotive stability systems, and virtual/augmented reality. Differences among IMUs are often described by degrees of freedom (e.g., 6-DOF for accelerometers and gyroscopes, 9-DOF when a magnetometer is included) and by sensor technology (MEMS versus fiber-optic or ring-laser gyros in high-end systems). IMUs remain a foundational component for inertial navigation and motion tracking.