Apple Patents a Wireless Charger That Detects Stray Metal Before It Gets Hot
A coin sitting on your wireless charger can silently drain power and get dangerously warm. Apple's new patent describes a system that catches that in real time, by doing a little math before things go wrong.
What Apple's foreign-object power check actually does
A credit card sits on a wireless charging pad all night while a phone charges nearby. By morning the card's chip is fried, and the pad ran hot the whole time. That scenario is exactly what this patent tries to prevent.
Apple's system has the charger and the phone talk to each other during charging. The phone tells the charger how much power it's actually receiving. The charger compares that number to how much it's sending out, and then checks whether the gap is bigger than a formula predicts it should be. If the gap is too large, something is stealing energy in the middle, and the charger knows to slow down or shut off.
The key word is predicted. Every charging pair has a known baseline for how much power normally disappears between transmitter and receiver. This patent builds that baseline into the math, so the system isn't just reacting to raw numbers but to whether those numbers look wrong for this specific setup.
… determining that a foreign object is present if the measured power loss exceeds the predicted power loss by more than a threshold; and responsive to determining that the foreign object is present, mitigating presence of the foreign object by reducing a power level of or suspending the wireless power transfer …
Translation: It spots stray metal by noticing unexpected energy drops, then cuts power to prevent overheating.
How the transmitter compares measured vs. Predicted power loss
The patent covers controller and communication circuitry inside a wireless power transmitter. During a charging session, the transmitter and receiver constantly share power readings, and the controller runs a four-step check.
- Receive a power report: the phone (receiver) sends back how many watts it's actually taking in.
- Measure the gap: the charger compares that figure to what it's putting out, producing a measured power loss.
- Compute a predicted loss: using one or more stored coefficients (think of them as calibration numbers tuned to how this charger-and-phone pair normally behave), the system calculates how much loss is expected under normal conditions.
- Compare and decide: if the measured loss exceeds the predicted loss by more than a preset threshold, the controller flags a foreign object as present and either reduces power or stops charging entirely.
The predicted-loss formula is what separates this from cruder detection methods. Earlier approaches often used fixed thresholds, which could be fooled by normal variation between different phone models or charger positions. By anchoring the threshold to a baseline specific to this transmitter-receiver pair, the system becomes much harder to trick with ordinary power fluctuations.
The patent also covers the receiver side, meaning a phone could run the same logic and report its conclusion back, giving the charger a second opinion.
Transmitters and/or receivers in a wireless power transfer system predict power losses to account for presence of foreign objects.
Translation: The charging system anticipates normal energy loss so it can spot unwanted items.
What this means for safer everyday wireless charging
For everyday users, the practical benefit is a charger that doesn't silently cook a hotel key card, a ring, or a spare coin left on the pad overnight. Wireless charging standards already require some foreign-object detection, but accuracy varies widely between products. A predictive model tied to the specific device pair is a tighter safety net than a generic power-cutoff rule.
Apple's steady filing activity around wireless power suggests the company sees wireless charging as infrastructure worth protecting carefully, not just a convenience feature. If this approach reaches production, it could also improve charging efficiency: a system that can precisely identify genuine loss from interference wastes less energy second-guessing normal variation.
This is the 19th Apple filing we've tracked in Battery & power coverage since May, adding to work like smarter wireless charging negotiation and a sliding port cover.
The system's accuracy depends entirely on having a reliable starting point. If the charger and phone's physical relationship shifts after that baseline is established, say because a case was added or the phone slid slightly, the stored reference goes stale and the system either misses a real hazard or shuts down unnecessarily.
The approach also assumes both the charger and the phone are sharing detailed performance data with each other, which works cleanly when Apple makes both. A third-party charger that can't supply that information leaves the safety check running on half the picture.
Given those limits, the core idea still reads as worth it. A safety threshold that learns the specific behavior of one charger-and-phone pair will catch far more real problems than a fixed cutoff designed for the average case, and the setup cost is just a brief calibration when the two devices first meet.
There are more where this came from
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The drawings
7 drawing sheets from US 2026/0269656 A1 · click any drawing to enlarge
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