Electromagnetic tracking is a method for determining an object’s precise position and orientation in three-dimensional space. A feature of this technology is its ability to function without a direct line of sight, allowing it to track objects through other non-metallic materials. This capability has led to its adoption in a variety of fields where knowing the exact location and angle of an object is important.
The Science Behind Electromagnetic Tracking
Electromagnetic tracking (EMT) operates by generating a localized, low-frequency magnetic field and detecting how sensors move within it. A field generator, or transmitter, contains coils that produce this magnetic environment. The fields generated can be either alternating current (AC) or direct current (DC), depending on the system’s design. These fields are carefully controlled and have a known geometry, which is fundamental for the tracking calculations.
When a sensor, which also contains small coils, enters this magnetic field, the field induces small electrical currents within the sensor’s wires. The characteristics of these induced currents—such as their strength and phase—change predictably based on the sensor’s distance and orientation relative to the field generator. By measuring these electrical signals, the system can compute the sensor’s location and its rotational state, known as its six degrees of freedom (6DOF).
An EMT system consists of three main parts. The field generator creates the magnetic tracking volume. One or more sensors are attached to or embedded within the object being tracked. A central processing unit energizes the generator, receives the raw signal data from the sensors, and performs the calculations to determine the final position and orientation data.
Core Applications Across Industries
During surgical navigation, EMT allows for the real-time tracking of instruments like catheters, endoscopes, or biopsy needles inside a patient’s body. Surgeons can visualize the instrument’s path on a screen, enhancing precision during minimally invasive procedures where direct sight is impossible. This reduces reliance on other imaging methods and can improve procedural safety and efficiency.
In virtual and augmented reality (VR/AR), EMT is used to track the movement of head-mounted displays and handheld controllers. This tracking provides the low-latency, high-accuracy positional data needed for immersive digital experiences. As a user moves their head or hands, their digital avatar or viewpoint is updated in real-time for natural interaction. The ability to operate without line-of-sight is an advantage over optical systems.
EMT provides feedback for robotic systems. Robotic arms in manufacturing or logistics can be equipped with sensors to verify their exact position and orientation, ensuring tasks are performed with high precision. For autonomous mobile robots, EMT can supplement other navigation systems, offering reliable positioning in environments where GPS or vision-based systems might fail. The data helps these robots understand their location and perform their functions accurately.
Another application is in motion capture for biomechanics research and animation. By placing sensors on a person’s body, researchers can study human movement in detail. This data is used to analyze athletic performance, design ergonomic products, or diagnose movement disorders. In the entertainment industry, this same process is used to translate an actor’s performance into the movements of a digital character for movies and video games.
Understanding System Accuracy and Limitations
The performance of an electromagnetic tracking system is subject to several factors. A primary challenge is the distortion of the magnetic field. When ferromagnetic materials like steel or highly conductive non-ferromagnetic materials like aluminum are present near the tracking volume, they can alter the shape of the magnetic field. This distortion can introduce errors into the position and orientation calculations, reducing the system’s accuracy.
Electromagnetic interference (EMI) from other electronic devices is another source of error. Devices such as motors, power lines, and computer monitors can emit their own electromagnetic fields, which can interfere with the tracking system’s weaker fields. This interference can corrupt the signals detected by the sensors, leading to inaccurate readings. Careful placement of the system and shielding can help mitigate these effects.
EMT systems have a defined tracking range, the volume within which sensors can be accurately tracked. This volume is determined by the field generator’s strength, and accuracy decreases as a sensor moves toward the outer edges. Other performance metrics include resolution, the smallest movement the system can detect, and its update rate, or how frequently it provides new position data.
The physical size of the sensors and their connecting cables can also be a limitation. This can impact usability in applications requiring minimal intrusion.
Innovations in Electromagnetic Tracking Technology
To address existing limitations, researchers are developing new technologies to improve the performance of electromagnetic tracking. One area of innovation is the creation of software algorithms for real-time distortion compensation. These algorithms can identify and correct errors caused by metallic objects in the tracking field, enhancing accuracy in challenging environments.
Miniaturization is also driving progress. Advances in manufacturing have led to the development of smaller sensors and more compact field generators. These smaller components are less intrusive, making them suitable for new medical procedures and allowing for easier integration into consumer devices. The development of wireless EM tracking systems is also helping to reduce clutter and improve ease of use by eliminating physical cables.
Hybrid tracking systems are another area of development. These systems combine electromagnetic tracking with other technologies, such as inertial measurement units (IMUs) or optical tracking. By fusing data from multiple sources, hybrid systems can leverage the strengths of each technology. For example, an IMU can provide high-frequency motion data while the EMT system corrects for drift, resulting in a more accurate tracking solution.