Foreign object detection (FOD) is a core technology for ensuring charging safety and efficiency in car electric wireless charging stands. Its implementation relies on electromagnetic characteristic monitoring, temperature change sensing, power loss analysis, and multi-sensor fusion. These technologies capture the interference of metallic foreign objects on the magnetic field, circuit, or thermal field, forming a multi-layered protection system to ensure a stable and reliable charging process.
Electromagnetic characteristic monitoring is the foundation of FOD detection. When a metallic foreign object enters the charging area, it alters the electromagnetic field distribution between the transmitting and receiving coils. For example, a metallic object induces a current due to eddy currents, causing a decrease in the inductance and an increase in the resistance of the transmitting coil, thus affecting the quality factor (Q value) of the entire resonant circuit. By monitoring Q value changes in real time, the system can determine the presence of a foreign object. Some high-end products employ high-order composite resonant topologies, improving detection sensitivity through optimized circuit design, enabling the detection of even tiny metal pieces (such as earrings).
Temperature change sensing is a direct means of FOD detection. Metallic foreign objects in a magnetic field heat up rapidly due to eddy currents; for example, a coin can reach a high temperature within 10 seconds. The charging bracket's built-in temperature sensor monitors the coil surface temperature in real time. When abnormal temperature rise is detected (e.g., exceeding 40°C), the system immediately reduces charging power or stops operation to prevent equipment damage or fire risks. Some products incorporate infrared array sensors, using thermal imaging technology to pinpoint the exact location of foreign objects, further improving detection accuracy.
Power loss analysis achieves indirect detection through the principle of energy conservation. The system compares the total energy output from the transmitter with the actual energy received by the receiver. If the difference exceeds a threshold (e.g., 15%), it determines that a foreign object is "stealing" energy. This method is suitable for high-power charging scenarios (such as electric vehicles) and can identify additional losses caused by small metal fragments (e.g., 0.3 mm iron pieces). Some products combine current and voltage sensors to improve detection response speed by calculating the dynamic changes in power loss.
Multi-sensor fusion technology is key to improving detection reliability. Single detection methods may have blind spots or false positive risks; for example, Q-value detection is insensitive to non-metallic foreign objects, and temperature detection has a lag. Therefore, high-end charging stands integrate multiple technologies such as inductance monitoring, temperature sensing, and infrared imaging, using data fusion algorithms for comprehensive judgment. For example, the system only confirms the presence of a foreign object and triggers a protection mechanism when inductance monitoring detects a decrease in the Q value, the temperature sensor detects localized temperature rise, and the infrared camera captures the outline of the foreign object.
Electromagnetic compatibility design is crucial for foreign object detection. The high-frequency current of the wireless charging system may cause electromagnetic interference to the sensors, leading to distorted detection data. To address this, charging stands employ shielding designs (such as metal casings and magnetic absorbing materials) to isolate interference sources, while optimizing sensor layout (such as moving them away from the coil center and adding filtering circuits) to improve signal stability. Some products also use software algorithms (such as Kalman filtering) to reduce noise in the detection data, ensuring accurate identification of foreign objects even in complex electromagnetic environments.
In the future, foreign object detection in car electric wireless charging stands will evolve towards intelligence and precision. With the introduction of artificial intelligence technology, the system can automatically identify foreign objects of different materials and shapes through machine learning models and adapt to interference factors in different environments (such as changes in temperature and humidity). Meanwhile, advancements in sensor technology will drive detection accuracy to the millimeter level, even enabling precise location of tiny foreign objects, providing a more robust guarantee for the safety of wireless charging.
The foreign object detection function of the car electric wireless charging stand constructs a multi-layered protection system from the physical layer to the algorithm layer through technologies such as electromagnetic characteristic monitoring, temperature sensing, power analysis, and multi-sensor fusion. These technologies not only solve the safety hazards caused by metallic foreign objects but also improve charging efficiency and user experience, becoming a key support for promoting the widespread adoption of wireless charging technology.
