The final part of the series covers what turns a resonant link into a shippable product: safety engineering, and the measured numbers we design against. (Start at Part 1 for the physics.)
7. Foreign object detection and safety
An alternating field induces eddy-current heating in any intruding metal (Part 2, §4.2). Our transmitters integrate two layers of protection:
- Power accounting. Input power is continuously reconciled against the load ledger; when $\Delta P = P_{in} - P_{load}$ crosses a threshold, the system derates and enters intermittent probing.
- $Q$-monitoring. Metal foreign objects change the resonant cavity's equivalent loss resistance $R_{eq}$; tracking $Q$ drift via the ratio of circulating current to cavity voltage catches them.
Every touchable voltage on the receiver side stays below 60 V SELV (IEC 62368); the resonant cavity peak voltage is inherently clamped by the topology at $(2 \sim 3.5) \times V_{bus}$ — no shock hazard. The transmit frequency sits in the ISM/Qi band, with EMC designed to EN 55011 / CISPR 11 limits.
8. Measured data anchors
| Platform | Input | Coils | Measured performance |
|---|---|---|---|
| Long-range module (reference platform) | 12 V | Ø200 mm coil pair | 3 W at 160 mm, 0.7 W at 290 mm, limit 380 mm |
| Levitation lighting system | 12 V | Compact coil pair | 150–200 mW continuous across a 10–25 mm float gap, in a permanent-magnet eddy environment |
| 50 mm wireless lamp panel (in development) | 12 V | Ø180 mm ring | Target 50 mm / 200 mW, RGB pixel-programmable |
9. Application matrix
| Scenario | Gap | Power | Key challenge | Our approach |
|---|---|---|---|---|
| Levitating bulbs / display stands | 10–50 mm | 0.2–3 W | Permanent-magnet eddy loss, levitation EMC | Hollow ring coil + magnetic-path separation + frequency optimization |
| Through-stone / through-wood decorative lighting | 20–50 mm | 5–15 W | Material thickness adds to the gap | Ø150–200 mm large coils + PP compensation |
| Long-range sensor power | 100–400 mm | 0.1–3 W | Extremely low $k$ | Large-diameter thin ring coils + high-$Q$ resonance + asymmetric turn ratios |
| Cable-free home lighting | 5–30 mm | 5–20 W | Efficiency and temperature rise | Flux-guide plates to constrain the magnetic path + constant-current direct drive |
Closing note
There is no magic in wireless power — only the trade-off between three variables: $k$, $Q$, and $f$. We build every product on derivable physics and reproducible measurements. That is the ground under our promise: the distance you see is the distance you get.
Need a wireless power feasibility evaluation for a specific product structure? Talk to our engineering team.
The Wireless Power Transfer Engineering Series — Part 1 · Part 2 · Part 3 · Part 4