1. FOD Risk Classification
| Object Type | Detection Difficulty | Examples |
| Metallic | High | Coins/Keys/Clips |
| Magnetic | Medium | Cards/RFID Tags/Earbuds |
| Biological | Very High | Fingers/Skin |
Source: WPC Qi 1.3 Section 12 Safety Requirements
Requires specialized biological detection
2. Detection Technologies Comparison
2.1 Electrical Methods
| Technology | Principle | Precision | Limitations |
| Q-factor Monitoring | Coil resonance shift | ±1mm metal | Poor non-metal detection |
| Impedance Analysis | Equivalent resistance change | >50mg metal | Requires 1kHz+ sampling |
| Power Loss Method | Input-output power delta | >100mW error margin | Temperature-sensitive |
3. Qi v2.0 Certification Requirements
| Test Item | Test Condition | Pass Criteria |
| Static Metal Test | 5 coins (Φ18mm) | Charging power <2W |
| Dynamic FOD Test | Moving metal (1cm/s) | Response time <500ms |
| Temperature Safety | Continuous operation + FOD | ΔT≤8°C (EN 62368-1) |
Multi-technology FOD mandatory from 2024
4. Engineering Challenge Solutions
4.1 Small Metallic Detection (<Φ5mm)
- 3D Coil Array: 4×4 detection coils with 3mm pitch
- Pulsed Eddy Current: μs-level pulses for metal identification
4.2 False Alarm Reduction
AI Algorithm: 100k+ sample training for component recognition (99.2% accuracy)
5. Design Checklist
Mandatory Requirements
- Dual detection: Q-factor + temperature sensing (IEC 63002 compliant)
- Redundant shutdown: Hardware watchdog + software protection
Prohibited Designs
- Aluminum enclosures (EMI shielding)
- Detection thresholds >50% above Qi limits
Glossary
| Term | Definition |
| Quality Factor (Q-value) | Resonant circuit efficiency metric |
| Eddy Current Loss | Energy dissipation in conductors |
| Thermal Runaway | Uncontrolled temperature increase |
| Fail-Safe | Default-to-safe failure mode |
Qi v2.0 pre-certified modules available (false positive rate <0.01%)