Differences

This shows you the differences between two versions of the page.

--- foreign_object_detection_in_the_qi_standard [2025/04/30 15:19] – tm
+++ foreign_object_detection_in_the_qi_standard [2025/05/01 14:17] (current) – [1.Q-factor detection] tm
@@ Line 1: / Line 1: @@
-=====Foreign Object Detection in the Qi standard=====
+======Foreign Object Detection in the Qi standard======
-====Classification of FOD methods====
+=====Classification of FOD methods=====
-In the Qi standard, the transmitter emits power to the receiver via an high-frequency alternating magnetic field. Qi technology is defined as a low-power transfer standard which implies that it poses no health risk to living objects (LOs). In the Qi standard, no living object detection (LOD) is performed as there is no space between the charging pads where LOs (e.g. animals) can enter and interfere with the WPT.
+In the Qi standard, the transmitter emits power to the receiver via an high-frequency alternating magnetic field. Qi technology is defined as a [[Introduction of the Qi standard|low-power transfer standard]] which implies that it poses no health risk to living objects (LOs). In the Qi standard, no living object detection (LOD) is performed as there is no space between the charging pads where LOs (e.g. animals) can enter and interfere with the WPT.
 However, this does not mean that this magnetic field between the transmitter and receiver is weak. Metal objects (MOs), such as keys or coins, can induce eddy currents within themselves when present in the magnetic field. This can cause overheating of the MO and bring forth high-risk situations like fire hazard. (Zhang et al., 2019, p. 1,2).
@@ Line 13: / Line 13: @@
 | Figure 1 FOD methods (Zhang et al., 2019, p. 3) |
-====FOD technology applied in Qi standard====
+=====FOD technology applied in Qi standard=====
 Analysis of a Qi-authorized 15 W transmitter: the Infineon WLC1515, reveals that it uses three distinct FOD methods based on system parameter detection. These include Q-factor measurement, power loss monitoring and over-temperature protection (Technologies, 2023, p. 29).
-**1.	Q-factor detection**
+====1.	Q-factor detection====
 The Q-factor (quality factor) of a coil is a measure of its efficiency in storing energy relative to the energy it loses. It is defined by the formula in Equation 1.
@@ Line 30: / Line 30: @@
 When a metal object (MO) enters the coil’s magnetic field, it disturbs the field and induces eddy currents in the object. These eddy currents cause the coil’s inductance 𝐿 to decrease and its resistance 𝑅 to increase due to additional energy losses. As a result, the Q-factor drops, which can be used as an indication of a foreign object in wireless power transfer systems. As examined by Tian et al., when metal objects enter the charging zone, the quality factor of the Rx coil exhibits a significant downward trend, making it a suitable index for MOD within WPT systems such as the Qi standard (Tian et al., 2022, p. 3; Wireless Power Consortium (WPC), n.d.).
 Practically, the quality factor of the receiver coil will be measured in a [[Power transfer architecture of the Qi standard|pre-power transfer phase]]. Next, Figure 2 shows how Q-factor FOD is created (Infineon, 2023, p. 5; Technologies, 2023, p. 25).
@@ Line 35: / Line 36: @@
 | Figure 2 Q-factor FOD (Infineon, 2023, p. 5) |
-**2.	Power loss detection**
+====2.	Power loss detection====
 Power loss-based FOD is a real-time method used during active power transfer. This approach involves periodically measuring the transmitter output power and comparing it to the power values reported by the receiver via the Received Power Packet (RPP). The MO is detected when the measured system power loss exceeds the system power loss threshold value, as shown in Figure 3. By forcing the threshold breach to last for three consecutive readings, it prevents the system from responding to single outliers before cutting power. This increases detection reliability and user experience (Infineon, 2023, p. 9).
-As Tian et al. note, power loss-based FOD methods are easily affected by coil misalignment, making it difficult to distinguish between actual foreign object-induced losses and normal fluctuations in power transfer. The recent updates in magnetic alignment via the Magnetic Power Profile (MPP) mitigates this issue by ensuring consistent coil positioning (Tian et al., 2022, p. 12)
+As Tian et al. note, power loss-based FOD methods are easily affected by coil misalignment, making it difficult to distinguish between actual foreign object-induced losses and normal fluctuations in power transfer. The recent updates in magnetic alignment via the magnetic power profile (MPP) mitigates this issue by ensuring consistent coil positioning (Tian et al., 2022, p. 12)
 | {{:power_loss_detection.png?400|}} |
 | Figure 3 power loss FOD (Infineon, 2023, p. 9) |
-**3.	Over-temperature detection**
+====3.	Over-temperature detection====
 The last system parameter detection method is a non-electrical one which implies that an additional temperature sensor will monitor the temperature of the transmitter coil. This is typically a negative temperature coefficient (NTC) thermistor.