IEC 63563-7:2025

IEC 63563-7 ®
Edition 1.0 2025-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Qi Specification version 2.0 –
Part 7: Foreign Object Detection

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IEC 63563-7 ®
Edition 1.0 2025-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Qi Specification version 2.0 –

Part 7: Foreign Object Detection

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.240.99, 35.240.99 ISBN 978-2-8327-0190-4

- 2 - IEC 63563-7:2025 © IEC 2025
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
QI SPECIFICATION VERSION 2.0 –
Part 7: Foreign Object Detection
FOREWORD
 The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprisingall
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preparatory work. International, governmental and non-governmental organizationsliaising with the IEC also
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(ISO) in accordance with conditions determined by agreement between the twoorganizations.
 The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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 IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
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thereof. As of the date of publication of this document, IECKDGQRW received notice of (a) patent(s),which may be
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information, which may be obtained from the patent database available athttps://patents.iec.ch. IEC shall
not be held responsible for identifying any or all such patent rights.
IEC 635-7 has been prepared by technical area 15: Wireless Power Transfer, of IEC
technical committee 100: Audio, video and multimedia systems and equipment. It is an
International Standard.
It is based on Qi Specification version 2.0, Foreign Object Detection and was submitted as a
Fast-Track document.
The text of this International Standard is based on the following documents:
Draft Report on voting
//FDIS //RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
The structure and editorial rules used in this publication reflect the practice of the organization
which submitted it.
This document was developed in accordance with ISO/IEC Directives, Part 1 and ISO/IEC
Directives, IEC Supplement available at www.iec.ch/members_experts/refdocs. The main
document types developed by IEC are described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
x reconfirmed,
x withdrawn, or
x revised.
- 4 - IEC 63563-7:2025 © IEC 2025
WIRELESS POWER
CONSORTIUM
Qi Specification
Foreign Object Detection
Version 2.0
April 2023
DISCLAIMER
Theinformationcontainedhereinisbelievedtobeaccurateasofthedateofpublication,
butisprovided“asis”andmaycontainerrors.TheWirelessPowerConsortiummakesno
warranty,expressorimplied,withrespecttothisdocumentanditscontents,includingany
warrantyoftitle,ownership,merchantability,orfitnessforaparticularuseorpurpose.
NeithertheWirelessPowerConsortium,noranymemberoftheWirelessPower
Consortiumwillbeliableforerrorsinthisdocumentorforanydamages,includingindirect
orconsequential,fromuseoforrelianceontheaccuracyofthisdocument.For any further
explanation of the contents of this document, or in case of any perceived inconsistency or ambiguity
of interpretation, contact: info@wirelesspowerconsortium.com.
RELEASE HISTORY
Specification Version Release Date Description
v2.0 Final Draft April 2023 Initial release of the 2.0 Qi Specification.

- 6 - IEC 63563-7:2025 © IEC 2025
Table of Contents
1  General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1 Structure of the Qi Specification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Compliance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.5 Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.6 Power Profiles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2  Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3  Avoidance of Foreign Object heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1 Representative Foreign Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4  Pre-power transfer FOD methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1 Empty surface test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.2 Resonance change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5  In-power transfer FOD methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.1 Basic power loss accounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.2 Calibrated power loss accounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Annex A: Determining the reference FOD values (normative). . . . . . . . . . . . . . . . . 35
Annex B: Open-air Q test (informative) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
B.1 General flow for the open-air Q test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
B.2 Measuring the quality factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
B.3 Impact of objects on the Q deflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
B.4 Compensated Q-deflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
B.5 Choosing a threshold. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
B.6 Temperature compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
B.7 Potential implementation issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

1 General
The Wireless Power Consortium (WPC) is a worldwide organization that aims to develop and
promote global standards for wireless power transfer in various application areas. A first
application area comprises flat-surface devices such as mobile phones and chargers in the
Baseline Power Profile (up to 5 W) and Extended Power Profile (above 5 W).
1.1 Structure of the Qi Specification
General documents
ƒ Introduction
ƒ Glossary, Acronyms, and Symbols
System description documents
ƒ Mechanical, Thermal, and User Interface
ƒ Power Delivery
ƒ Communications Physical Layer
ƒ Communications Protocol
ƒ Foreign Object Detection
ƒ NFC Tag Protection
ƒ Authentication Protocol
- 8 - IEC 63563-7:2025 © IEC 2025
1.2 Scope
The QiSpecification,ForeignObjectDetection (this document) defines methods for ensuring that
the power transfer proceeds without heating metal objects in the magnetic field of a Power
Transmitter. Although the Power Transmitter may optionally use any of these methods, some of
them require assistance by the Power Receiver.
1.3 Compliance
All provisions in the QiSpecification are mandatory, unless specifically indicated as recommended,
optional, note, example, or informative. Verbal expression of provisions in this Specification follow
the rules provided in ISO/IEC Directives, Part 2.
Table 1: Verbal forms for expressions of provisions
Provision Verbal form
requirement “shall” or “shall not”
recommendation “should” or “should not”
permission “may” or “may not”
capability “can” or “cannot”
1.4 References
For undated references, the most recently published document applies. The most recent WPC
publications can be downloaded from http://www.wirelesspowerconsortium.com.

1.5 Conventions
1.5.1 Notation of numbers
ƒ Real numbers use the digits 0 to 9, a decimal point, and optionally an exponential part.
ƒ Integer numbers in decimal notation use the digits 0 to 9.
ƒ Integer numbers in hexadecimal notation use the hexadecimal digits 0 to 9 and A to F, and are
prefixed by "0x" unless explicitly indicated otherwise.
ƒ Single bit values use the words ZERO and ONE.
1.5.2 Tolerances
Unless indicated otherwise, all numeric values in the QiSpecification are exactly as specified and do
not have any implied tolerance.
1.5.3 Fields in a data packet
A numeric value stored in a field of a data packet uses a big-endian format. Bits that are more
significant are stored at a lower byte offset than bits that are less significant. Table 2 and Figure 1
provide examples of the interpretation of such fields.
Table 2: Example of fields in a data packet
b b b b b b b b
7 6 5 4 3 2 1 0
(msb)
B
16-bit Numeric Data Field
B
(lsb)
B Other Field (msb)
B 10-bit Numeric Data Field (lsb) Field
Figure 1. Examples of fields in a data packet
16-bit Numeric Data Field
b b b b b b b b b b b b b b b b
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
B B
0 1
10-bit Numeric Data Field
b b b b b b b b b b
9 8 7 6 5 4 3 2 1 0
B B
2 3
- 10 - IEC 63563-7:2025 © IEC 2025
1.5.4 Notation of text strings
Text strings consist of a sequence of printable ASCII characters (i.e. in the range of 0x20 to 0x7E)
enclosed in double quotes ("). Text strings are stored in fields of data structures with the first
character of the string at the lowest byte offset, and are padded with ASCII NUL (0x00) characters
to the end of the field where necessary.
EXAMPLE: The text string “WPC” is stored in a six-byte fields as the sequence of characters 'W', 'P', 'C', NUL,
NUL, and NUL. The text string “M:4D3A” is stored in a six-byte field as the sequence 'M', ':', '4', 'D',
'3', and 'A'.
1.5.5 Short-hand notation for data packets
In many instances, the QiSpecification refers to a data packet using the following shorthand
notation:
/
In this notation, refers to the data packet's mnemonic defined in the QiSpecification,
CommunicationsProtocol, and refers to a particular value in a field of the data packet.
The definitions of the data packets in the QiSpecification,CommunicationsProtocol, list the
meanings of the modifiers.
For example, EPT/cc refers to an End Power Transfer data packet having its End Power Transfer
code field set to 0x01.
1.6 Power Profiles
A Power Profile determines the level of compatibility between a Power Transmitter and a Power
Receiver. Table 3 defines the available Power Profiles.
ƒ BPPPTx: A Baseline Power Profile Power Transmitter.
ƒ EPP5PTx: An Extended Power Profile Power Transmitter having a restricted power transfer
()pot
capability, i.e. P = 5 W.
L
ƒ EPPPTx: An Extended Power Profile Power Transmitter.
ƒ BPPPRx: A Baseline Power Profile Power Receiver.
ƒ EPPPRx: An Extended Power Profile Power Receiver.
Table 3: Capabilities included in a Power Profile
Feature BPP PTx EPP5 PTx EPP PTx BPP PRx EPP PRx
Ax or Bx design Yes Yes No N/A N/A
MP-Ax or MP-Bx design No No Yes N/A N/A
Baseline Protocol Yes Yes Yes Yes Yes
Extended Protocol No Yes Yes No Yes
Authentication N/A Optional Yes N/A Optional

- 12 - IEC 63563-7:2025 © IEC 2025
2 Introduction
In a normal use case of a power transfer according to the QiSpecification, the Power Signal
(magnetic field) of the Power Transmitter interacts with the Power Receiver Product only.
However, sometimes a user accidentally places metallic objects such as coins, paper clips, keys, or
pieces of aluminum foil next to or underneath the Power Receiver Product, either before the power
transfer starts, or while it is ongoing. The QiSpecification refers to such objects as Foreign Objects.
A problem with Foreign Objects is that they can dissipate power from the magnetic field, and as a
result heat up to unsafe temperature levels. The system should therefore not initiate the power
transfer, limit the power level, or stop the power transfer when it detects that one or more Foreign
Objects are present.
Figure 2. Power transfer system including a Foreign Object
Friendly Metal
Shielding
Coil
Magnetic Field Line
PRx Product
Foreign Object
PTx Product
Coil
Ferrite Shielding
A factor complicating Foreign Object Detection (FOD) is the presence of Friendly Metals in the
magnetic field. A Friendly Metal is similar to a Foreign Object in the sense that it can dissipate
power from the magnetic field. However, unlike a Foreign Object, it is an integral part of the Power
Receiver Product or Power Transmitter Product. In many cases, it is hard for a Power Transmitter
to distinguish properly between Foreign Objects and Friendly Metals. Typically, no single method is
sufficient to solve the problem. Accordingly, the Power Transmitter should use multiple methods to
maximize the probability of detecting Foreign Objects, while minimizing the probability of false
alarms.
3 Avoidance of Foreign Object heating
As explained in Section 2, Introduction, the Power Signal can heat up Foreign Objects that are
present in the Operating Volume. Therefore, a Power Transmitter Product shall ensure that such
Foreign Objects do not reach unsafe temperature levels. This may involve limiting or terminating
the power transfer.
The Power Transmitter can use several approaches to prevent excessive of heating Foreign Objects
and apply those before starting the power transfer and/or while the latter is in progress. The main
use cases that FOD should address include
ƒ A user placing a Foreign Object before placing a Power Receiver Product
ƒ A user placing a Foreign Object together with a Power Receiver Product
ƒ A user placing a Foreign Object after placing a Power Receiver Product
The methods described in Section 4, Pre-powertransferFODmethods, address the first two use
cases. Detecting a Foreign Object before starting the power transfer lets the Power Transmitter take
one or more of the following actions.
ƒ Warn the user of a potential unsafe situation
ƒ Refuse to start the power transfer until a user has removed the Foreign Object
ƒ Proceed to transfer power but at a reduced level
The methods described in Section 5, In-powertransferFODmethods, address the third use case.
They also address the use case in which the Power Transmitter proceeds with the power transfer
even though it suspects a Foreign Object is present. In general, these methods enable the Power
Transmitter to limit the power loss to Foreign Objects (by reducing the power level), with the aim
to limit their heating.
If the Power Transmitter does not detect a Foreign Object before starting the power transfer, it may
use that knowledge to calibrate the system to improve its sensitivity for power loss (see Section 5.2,
Calibratedpowerlossaccounting, for details). However, when it detects a Foreign Object and
proceeds to transfer power at a reduced level anyway, it should ensure that any of such calibrations
it may perform do not degrade its sensitivity.
Some of the methods described in Section 4, Pre-powertransferFODmethods, and Section 5, In-
powertransferFODmethods, involve the Power Receiver sending information about its design
properties to the Power Transmitter. The Power Receiver shall provide the design information
associated with all those methods.
In addition to the methods described in Section 4, Pre-powertransferFODmethods, and Section 5,
In-powertransferFODmethods, the Power Transmitter can monitor the temperature of its
Interface Surface for hot spots. Moreover, it can actively cool its Interface Surface to drain heat
away from the Power Receiver and Foreign Objects.

- 14 - IEC 63563-7:2025 © IEC 2025
3.1 Representative Foreign Objects
Foreign Objects can have many different sizes, shapes, and material compositions. To address this
diversity, the QiSpecification,ForeignObjectDetection (this document) defines the required FOD
capabilities of a Power Transmitter in terms of a set of Representative Foreign Objects. Table 4 lists
these objects.
Table 4: Representative Foreign Objects
Designator Shape Material Dimensions Limit / C°
RFO#1 Disk Steel 1.1011 ø15 mm, 60
DIN RFe160 1 mm thick
RFO#2 Ring DIN 3.2315 ø20 mm (inner) 60
EN AW-6082 ø22 mm (outer)
ISO AlSi1MgMn 1 mm thick
RFO#3 Foil EN AW-1050 ø20 mm, 80
DIN 3.0255 0.1 mm thick
Al99.5
RFO#4 Disk DIN 3.2315 ø22 mm, 60
EN AW-6082 1 mm thick
ISO AlSi1MgMn
When one of the Representative Foreign Objects is present in the Operating Space, the Power
Transmitter shall not heat it to a temperature above the limit associated with that object.

4 Pre-power transfer FOD methods
A Power Transmitter can use different methods to detect Foreign Objects before initiating a power
transfer to a Power Receiver. Some of these methods depend on the Power Receiver providing
information about its design properties.
With the method described in Section 4.1, Emptysurfacetest, the Power Transmitter ensures that
it will only start the power transfer if its Interface Surface was empty just before a user placed a
Power Receiver Product. It does so by waiting for a user to place an object, determining if it is a
Foreign Object, and if that is the case, waiting for the user to remove it.
The Power Transmitter typically uses an Analog Ping to determine whether there is an object in its
Operating Volume. It applies a weak Power Signal and looks for changes to its resonance properties
as a sign of the presence of an object. If an object is present, the Power Transmitter follows up with
a Digital Ping, to which only a Power Receiver Product will respond. If there is no response to the
Digital Ping, the Power Transmitter assumes that the object on its surface is a Foreign Object.
The empty-surface test cannot detect a Foreign Object that arrives simultaneously with a Power
Receiver Product (e.g., a piece of aluminum foil sticking to the Power Receiver Product). To
distinguish the Foreign Object from Friendly Metal within the Power Receiver Product, the Power
Transmitter can quantify the changes in its resonance properties and look for differences with the
expected changes that the presence of the Power Receiver Product alone would induce.
Accordingly, with the method described in Section 4.2, Resonancechange, the Power Receiver
provides the expected inductance of a reference tank circuit when the Power Receiver Product is
placed on the Power Transmitter Product. The Power Transmitter can use this information to
determine if there is a Foreign Object between itself and the Power Receiver Product. To make a
sufficiently accurate determination, the Power Transmitter should account for differences of its
design with the reference tank circuit.
NOTE: Because the Power Receiver provides the relevant information in the negotiation phase of the
Enhanced Protocol (see the QiSpecification,CommunicationsProtocol, for details), the resonance
change method is available to EPP and EPP5 products only.

- 16 - IEC 63563-7:2025 © IEC 2025
4.1 Empty surface test
Figure 3 shows a conceptual flow diagram that describes how the empty-surface test fits in the pre-
power startup flow. Basically, the flow contains two loops. In the first loop the Power Transmitter
waits for a user to place an object. Next, if the object responds to a Digital Ping, the object is a Power
Receiver Product, and the Power Transmitter proceeds to deliver power. Otherwise, the object is a
Foreign Object, and in the second loop, the Power Transmitter waits for the user to remove it (back
in loop 1). Accordingly, at the start of the first loop, the Interface Surface is empty.
Figure 3. Conceptual flow diagram of the empty-surface test at startup
Start
Analog Ping Digital Ping Analog Ping
Loop 1 Loop 2
N N
Object Response Empty
N
detected? ? pad?
Y Y Y
Deliver power
Practical implementations should enhance this conceptual flow to address corner cases such as
ƒ The user initially placing the Power Receiver Product in a misaligned position, where it does
not respond to a Digital Ping, and subsequently moving it to a better-aligned position
ƒ The Analog Ping not being able to detect the presence of a Power Receiver Product when the
latter has only a weak impact on the Power Transmitter's properties
ƒ Communications errors corrupting the response to the Digital Ping
Examples of enhancements to address these corner cases include the use of timeouts, flags, multiple
thresholds, and more. In more detail, when waiting for a user to place a Power Receiver Product, the
Power Transmitter can issue Digital Pings occasionally to ensure that its Analog Pings did not miss
detecting a Power Receiver Product. This approach can also help to deal with initially misaligned
Power Receiver Products when combined with continuous monitoring of any changes in the Power
Transmitter's properties.
When initiating an Analog Ping, the Power Transmitter generates a weak Power Signal and
measures the quality factor of its tank circuit. If the measured value is sufficiently different from
the empty pad value (as stored in the Power Transmitter), an object is present. Annex B:, Open-air
Qtest(informative), provides details on how to measure the quality factor, how to evaluate the
impact of an object on the measured value, how to choose an appropriate threshold, and how to
compensate for various drifts in the system.

4.2 Resonance change
When a user places a Power Receiver Product in a Power Transmitter's Operating Volume, the
inductance of the Power Transmitter's coil typically increases due to the proximity of the Power
Receiver's Shielding. This results in a decrease of the Power Transmitter's resonance frequency. At
the same time, power absorption in the Friendly Metals of the Power Receiver Product causes the
quality factor of the resonance to decrease.
Figure 4 shows an example of this effect, with the curves in the diagram illustrating the behavior of
the resonance under various conditions. When the Operating Volume is empty, the resonance
occurs at the frequency f (dark curve). When a Power Receiver Product is present in the Operating
t
Volume, the resonance shifts to a (typically lower) frequency f ′ . The magnitude of the shift
t
depends on the design properties of the Power Transmitter and the Power Receiver Product, as
well as on the position of the latter in the Operating Volume. For example, the shift is typically
smaller for a phone in a protective case than for the same phone without such a case. The reason is
the increased distance between the phone's Shielding and the Power Transmitter's coil.
Figure 4. Resonance shift caused by a Power Receiver Product and Foreign Objects
f ’ f
t t
Operating frequency
The dashed curves in Figure 3 show the shift of the resonance curve when a Foreign Object is
present in the Operating Volume in addition to the Power Receiver Product. Typically, the Foreign
Object counters the shift induced by the Power Receiver Product, and reduces the strength of the
resonance (i.e. the quality factor). The reason is that the Foreign Object introduces a power loss
and shields ferrites in the Power Receiver Product from the Power Transmitter's coil.
The Power Transmitter can use the change in the resonance frequency to determine whether a
Foreign Object is present in the Operating Volume. However, it needs help from the Power Receiver
to do so. This is because one Power Receiver Product can produce the same change as another
Power Receiver Product and a Foreign Object combined. To support the resonance change FOD
()ref
method, the Power Receiver shall send a Reference Resonance Frequency f ' and a Reference
t
()ref
Quality Factor Q' using FOD data packets in the negotiation phase of the communications
t
protocol.
Coil current
- 18 - IEC 63563-7:2025 © IEC 2025
The Reference Resonance Frequency and the Reference Quality Factor are the resonance
frequency and quality factor of a reference tank circuit loaded with the Power Receiver Product.
See Section 4.2.2, Obtainreferencevalues, for details. To ensure that contributions of Foreign
Objects to the resonance change dominate over those of Friendly Metals, an EPP Power Receiver
()ref
Product shall have a Reference Quality Factor of Q′ ≥ 25 .
t
NOTE: The Reference Resonance Frequency and the Reference Quality factor are not properties of the
resonance in the Power Receiver's tank circuit. Instead, they reflect how Friendly Metals and ferrites
in the Power Receiver Product affect the resonance in the Power Transmitter's tank circuit.
The resonance-change based FOD method therefore consists of the following steps.
1. Measure the resonance properties, i.e. f ′ and Q′ .
t t
()ref ()ref
2. Obtain reference values for these quantities, i.e. f ' and Q' .
t t
3. Determine the probability that a Foreign Object is present.
4. Inform the Power Receiver if the probability exceeds a threshold.
5. Stop the power transfer if the risk of heating a Foreign Object to an unsafe temperature is too
high.
The following section describe steps of the method in detail.
4.2.1 Measure the resonance properties
The Power Transmitter should measure its resonance properties—as affected by the presence of a
Power Receiver in the Operating Volume—before executing a Digital Ping and waking up the Power
Receiver. If the Power Receiver would wake up, the additional load adds to the Q factor, yielding a
spurious result. Accordingly, the Power Transmitter should use as low a Power Signal as possible.
NOTE: The Power Signal is low enough if the Power Transmitter keeps the rectified voltage of TPR#MP3
below 0.85 V.
The recommended method of measuring the resonance properties is to make a frequency sweep,
while measuring the voltage u applied to the tank circuit as well as the resulting voltage u across
ti tl
the coil. The ratio u /u of these two voltages at the highest point of the shifted resonance yields the
tl ti
quality factor Q′ .
t
Figure 5. Measuring the resonance properties
f ’
t
࢛
ܜ܋
࢛ ࢛
ܜܑ ܜܔ
Operating frequency
Voltage ratio
4.2.2 Obtain reference values
Once the Power Transmitter has measured the properties of its resonance, it should execute a
Digital Ping to wake up the Power Receiver. The latter shall send FOD/rf and FOD/qf data packets in
the negotiation phase of the communications protocol to provide its Reference Resonance
()ref ()ref
Frequency f ' and Reference Quality Factor Q' ; see the QiSpecification,Communications
t t
Protocol, for details.
The Reference Resonance Frequency and Reference Quality Factor are the properties of a
reference coil assembly as affected by the proximity of the Power Receiver Product. Figure 5
provides an illustration of the reference coil assembly, which consists of a ferrite, a coil, and a cover.
()ref ()ref
Table 5 defines its properties. For details about determining f ' and Q' , see Annex A:,
t t
DeterminingthereferenceFODvalues(normative).
NOTE: The reference coil assembly is based on the A10 and MP-A1 Power Transmitter designsǤ
Figure 6. Reference coil assembly

- 20 - IEC 63563-7:2025 © IEC 2025
Table 5: Properties of the reference coil assembly
Dimension Value Unit
Ferrite: relative permeability μ = 650 + j × 25
r
Length 53.3 mm
Width 53.3 mm
Thickness 2.54 mm
Coil; centered on the ferrite; 105 × 40 AWG type 2 litz wire
Outer diameter 43 mm
Inner diameter 20.5 mm
Thickness 2.1 mm
Number of turns per layer 10 N/A
Number of layers 2 N/A
Cover: magnetically passive material
Thickness 2.5 mm
At an operating frequency of 100 kHz, the inductance of the reference coil assembly is about
()ref ()ref
L = 25 μH with a resistance of about R = 100 mё.
t t
4.2.3 Determine the presence of a Foreign Object
The Power Transmitter should use the measured resonance frequency f ' , the measured quality
t
()ref
factor Q′ , the received Reference Resonance Frequency f ' , and the received Reference Quality
t t
()ref
Factor Q' to determine the probability that a Foreign Object is present in its Operating Volume.
t
In the calculations involved, the Power Transmitter should account for its design differences with
the reference coil assembly used to determine the reference values.

4.2.4 Inform the Power Receiver
The Power Transmitter shall inform the Power Receiver about the probability that a Foreign
Object is present in the Operating Volume. If the probability is below a threshold, it shall respond to
the FOD Status data packet with ACK. If the probability is above the threshold, it shall respond with
NAK. See the QiSpecification,CommunicationsProtocol, for details about aborting the power
transfer when the Power Transmitter discovers a Foreign Object.
NOTE: When the Power Transmitter has not yet received both reference values, it may not be able to
confidently determine the probability of a Foreign Object being present. In that case, it may respond
with ACK to FOD Status data packets until it has all values it needs.
4.2.5 Stop the power transfer
Upon receiving a NAK response to an FOD data packet, a Power Receiver shall switch to the power
transfer phase of the Baseline Protocol (see the QiSpecification,CommunicationsProtocol) limiting
its Load Power level to 5 W or less. If the Power Transmitter assesses that the risk of heating a
Foreign Object to unsafe temperatures is too high, it may remove the Power Signal.

- 22 - IEC 63563-7:2025 © IEC 2025
5 In-power transfer FOD methods
A Power Transmitter can use several methods to detect Foreign Objects while the power transfer to
a Power Receiver is in progress. Most of these methods depend on the Power Receiver providing
information about the ongoing power transfer.
One method involves estimating the power loss to Foreign Objects by balancing the Transmitted
Power and Received Power levels. To enable this method, the Power Receiver shall provide
sufficiently accurate Received Power level data to the Power Transmitter on a regular basis.
Because this FOD method involves one-way communications from the Power Receiver to the
Power Transmitter only, it applies to products in all power profiles. Section 5.1, Basicpowerloss
accounting, describes this method in detail.
An improvement of this basic method is calibrated power loss accounting. This more advanced
method is available to EPP and EPP5 products only because it uses properties of the Enhanced
Protocol (see the QiSpecification,CommunicationsProtocol, for details). Moreover, it assumes that
at least one pre-power transfer FOD method is available as well. Typically, the Power Transmitter
and Power Receiver calibrate the estimated power loss at the start of the power transfer phase.
Section 5.2, Calibratedpowerlossaccounting, describes this method in detail.
5.1 Basic power loss accounting
In this FOD method, the Power Transmitter estimates the amount of power P dissipated in
FO
Foreign Objects using the Received Power level data it receives from the Power Receiver. If the
()thr
estimated power loss exceeds a threshold ΔP ≈ 500 mW for some period, there is a risk of
FO
heating Foreign Objects to unsafe temperatures. In that case, Power Transmitter may take one of
the following actions.
ƒ Request the Power Receiver to reduce its power consumption (Extended Protocol only)
ƒ Ignore the Power Receiver's CE data packets and change its operating point to reduce the
Transmitted Power level (and therefore the amount of power dissipated in the Foreign
Objects)
ƒ Abort the power transfer
NOTE: Experiments and simulations of the temperature rise in Foreign Objects of various sizes, shapes and
materials compositions have shown that a power dissipation of up to about 500 mW such objects is
acceptable in most cases.
5.1.1 Method
The power P that Foreign Objects dissipate from the Power Signal is equal to the difference of the
FO
Transmitted Power P and Received Power P , i.e.
t r
(loss) (loss)
ΔP==P –P –
FO t r P –P P +P
i t o r
In this equation, P represents the input power to the Power Transmitter; P the output power from
i o
()loss ()loss
the Power Receiver; ΔP the power loss in the Power Transmitter; and ΔP the power loss
t r
in the Power Receiver. Figure 7 illustrates the equation.
Figure 7. Power loss accounting
Foreign Object
(loss) (loss)
ȴP ȴP ȴP
t FO r
Tank Tank
Inverter Rectifier
Circuit Circuit
P P P P
i t r o
Power Transmitter Power Receiver
The power loss incurred in a Power Receiver Product typically includes the following contributions.
ƒ The power loss in the tank circuit
ƒ The power loss in the rectifier
ƒ The power loss in ferrite(s) that serve to constrain the magnetic field
ƒ The power loss in metal parts of the Power Receiver Product that are exposed to the magnetic
field
By measuring its operating current, the Power Receiver can determine its tank circuit and rectifier
losses with relatively good accuracy. However, it is more difficult for the Power Receiver to measure
its ferrite and Friendly Metal losses. Moreover, the latter can depend strongly on the position of the
Power Receiver Product in the Operating Volume. As a result, the Power Receiver can typically
determine its ferrite and Friendly Metal losses with much less accuracy than its circuit losses.
The power loss incurred in a Power Transmitter Product typically includes a similar set of
contributions.
ƒ The power loss in the inverter
ƒ The power loss in the tank circuit
ƒ The power loss in ferrite(s) that serve to constrain the magnetic field
ƒ The power loss in metal parts of the Power Transmitter Product that are exposed to the
magnetic field
...