SIST EN IEC 63563-7:2026

Qi specification version 2.0 - Part 7: Foreign object detection (IEC 63563-7:2025)

IEC 63563-7:2025 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.

Qi Spezifikation Version 2.0 - Teil 7: Fremdobjekt Erkennung (IEC 63563-7:2025)

Spécification Qi version 2.0 - Partie 7: Détection de corps étrangers (IEC 63563-7:2025)

IEC 63563-7:2025 définit des méthodes permettant de s'assurer que le transfert de puissance se déroule sans échauffement des objets métalliques dans le champ magnétique d'un émetteur de puissance. Bien que l'Exigence puisse utiliser l'une ou l'autre de ces méthodes, certaines d'entre elles requièrent l'assistance du Récepteur de Puissance.

Različica specifikacije Qi 2.0 - 7. del: Odkrivanje, zaznavanje tujkov (IEC 63563-7:2025)

General Information

• Status: Not Published
• Public Enquiry End Date: 14-Jul-2024
• ICS: 29.240.99 - Other equipment related to power transmission and distribution networks
• ICS: 33.160.99 - Other audio, video and audiovisual equipment
• ICS: 35.200 - Interface and interconnection equipment
• ICS: 35.240.99 - IT applications in other fields
• Technical Committee: AVM - Audio, video and multimedia systems and equipment
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 30-Jul-2025
• Due Date: 04-Oct-2025
• Ref Project: EN IEC 63563-7:2025 - Qi Specification version 2.0 - Part 7: Foreign Object Detection

Standards Content (Sample)

SLOVENSKI STANDARD
oSIST prEN IEC 63563-7:2024
01-julij-2024
Različica specifikacije Qi 2.0 - 7. del: Odkrivanje, zaznavanje tujkov (Hitri
postopek)
Qi specification version 2.0 - Part 7: Foreign object detection (Fast track)
Ta slovenski standard je istoveten z: prEN IEC 63563-7:2024
ICS:
29.240.99 Druga oprema v zvezi z Other equipment related to
omrežji za prenos in power transmission and
distribucijo električne energije distribution networks
33.160.99 Druga avdio, video in Other audio, video and
avdiovizuelna oprema audiovisual equipment
35.200 Vmesniška in povezovalna Interface and interconnection
oprema equipment
oSIST prEN IEC 63563-7:2024 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN IEC 63563-7:2024
oSIST prEN IEC 63563-7:2024
100/4128/CDV
COMMITTEE DRAFT FOR VOTE (CDV)
PROJECT NUMBER:
IEC 63563-7 ED1
DATE OF CIRCULATION: CLOSING DATE FOR VOTING:
2024-05-03 2024-07-26
SUPERSEDES DOCUMENTS:
IEC TA 15 : WIRELESS POWER TRANSFER
SECRETARIAT: SECRETARY:
Korea, Republic of Mr Ockwoo Nam
OF INTEREST TO THE FOLLOWING COMMITTEES: PROPOSED HORIZONTAL STANDARD:

TC 106,TC 108
Other TC/SCs are requested to indicate their interest, if any,
in this CDV to the secretary.
FUNCTIONS CONCERNED:
EMC ENVIRONMENT QUALITY ASSURANCE SAFETY
SUBMITTED FOR CENELEC PARALLEL VOTING NOT SUBMITTED FOR CENELEC PARALLEL VOTING

This document is still under study and subject to change. It should not be used for reference purposes.
Recipients of this document are invited to submit, with their comments, notification of any relevant patent rights of which they
are aware and to provide supporting documentation.
Recipients of this document are invited to submit, with their comments, notification of any relevant “In Some Countries”
clauses to be included should this proposal proceed. Recipients are reminded that the CDV stage is the final stage for
submitting ISC clauses. (SEE AC/22/2007 OR NEW GUIDANCE DOC).

TITLE:
Qi Specification version 2.0 - Part 7: Foreign Object Detection (Fast track)

PROPOSED STABILITY DATE: 2029
NOTE FROM TC/SC OFFICERS:
This document is only in PDF format. IEC and WPC have agreed to use the pdf files as this is an adoption.

electronic file, to make a copy and to print out the content for the sole purpose of preparing National Committee positions.
You may not copy or "mirror" the file or printed version of the document, or any part of it, for any other purpose without
permission in writing from IEC.

oSIST prEN IEC 63563-7:2024
WIRELESS POWER
CONSORTIUM
Qi Specification
Foreign Object Detection
Version 2.0
April 2023
oSIST prEN IEC 63563-7:2024
COPYRIGHT
© 2023 by the Wireless Power Consortium, Inc. All rights reserved.
The QiSpecification is published by the Wireless Power Consortium and has been prepared by the
members of the Wireless Power Consortium. Reproduction in whole or in part is prohibited
without express and prior written permission of the Wireless Power Consortium.
DISCLAIMER
The information contained herein is believed to be accurate as of the date of publication,
but is provided “as is” and may contain errors. The Wireless Power Consortium makes no
warranty, express or implied, with respect to this document and its contents, including any
warranty of title, ownership, merchantability, or fitness for a particular use or purpose.
Neither the Wireless Power Consortium, nor any member of the Wireless Power
Consortium will be liable for errors in this document or for any damages, including indirect
or consequential, from use of or reliance on the accuracy of this document. For any further
explanation of the contents of this document, or in case of any perceived inconsistency or ambiguity
of interpretation, contact: [e-mail].
RELEASE HISTORY
Specification Version Release Date Description
v2.0 Final Draft April 2023 Initial release of the 2.0 Qi Specification.

oSIST prEN IEC 63563-7:2024
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

oSIST prEN IEC 63563-7:2024
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
 Introduction
 Glossary, Acronyms, and Symbols
System description documents
 Mechanical, Thermal, and User Interface
 Power Delivery
 Communications Physical Layer
 Communications Protocol
 Foreign Object Detection
 NFC Tag Protection
 Authentication Protocol
Reference design documents
 Power Transmitter Reference Designs
 Power Receiver Design Examples
Compliance testing documents
 Power Transmitter Test Tools
 Power Receiver Test Tools
 Power Transmitter Compliance Tests
 Power Receiver Compliance Tests
NOTE: The compliance testing documents are restricted and require signing in to the WPC members’
website. All other specification documents are available for download on both the WPC public website
and the WPC website for members.

oSIST prEN IEC 63563-7:2024
1.2 Scope
The QiSpecification, Foreign Object Detection (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. In addition, the
QiSpecification references documents listed below. Documents marked here with an asterisk (*)
are restricted and require signing in to the WPC website for members.
 Product Registration Procedure Web page*
 Qi Product Registration Manual, Logo Licensee/Manufacturer*
 Qi Product Registration Manual, Authorized Test Lab*
 Power Receiver Manufacturer Codes,* Wireless Power Consortium
 The International System of Units (SI), Bureau International des Poids et Mesures
 Verbal forms for expressions of provisions, International Electotechnical Commission
For regulatory information about product safety, emissions, energy efficiency, and use of the
frequency spectrum, visit the regulatory environment page of the WPC members’ website.

oSIST prEN IEC 63563-7:2024
1.5 Conventions
1.5.1 Notation of numbers
 Real numbers use the digits 0 to 9, a decimal point, and optionally an exponential part.
 Integer numbers in decimal notation use the digits 0 to 9.
 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.
 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
oSIST prEN IEC 63563-7:2024
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,
Communications Protocol, and refers to a particular value in a field of the data packet.
The definitions of the data packets in the QiSpecification, Communications Protocol, 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.
oSIST prEN IEC 63563-7:2024
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.
 BPP PTx: A Baseline Power Profile Power Transmitter.
 EPP5 PTx: An Extended Power Profile Power Transmitter having a restricted power transfer
()pot
capability, i.e. P = 5 W.
L
 EPP PTx: An Extended Power Profile Power Transmitter.
 BPP PRx: A Baseline Power Profile Power Receiver.
 EPP PRx: 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

oSIST prEN IEC 63563-7:2024
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.
oSIST prEN IEC 63563-7:2024
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
 A user placing a Foreign Object before placing a Power Receiver Product
 A user placing a Foreign Object together with a Power Receiver Product
 A user placing a Foreign Object after placing a Power Receiver Product
The methods described in Section 4, Pre-power transfer FOD methods, 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.
 Warn the user of a potential unsafe situation
 Refuse to start the power transfer until a user has removed the Foreign Object
 Proceed to transfer power but at a reduced level
The methods described in Section 5, In-power transfer FOD methods, 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,
Calibrated power loss accounting, 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-power transfer FOD methods, and Section 5, In-
power transfer FOD methods, 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-power transfer FOD methods, and Section 5,
In-power transfer FOD methods, 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.

oSIST prEN IEC 63563-7:2024
3.1 Representative Foreign Objects
Foreign Objects can have many different sizes, shapes, and material compositions. To address this
diversity, the QiSpecification, Foreign Object Detection (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.

oSIST prEN IEC 63563-7:2024
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, Empty surface test, 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, Resonance change, 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, Communications Protocol, for details), the resonance
change method is available to EPP and EPP5 products only.

oSIST prEN IEC 63563-7:2024
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
 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
 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
 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
Q test (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.

oSIST prEN IEC 63563-7:2024
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
oSIST prEN IEC 63563-7:2024
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, Obtain reference values, 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. See QiSpecification, Power Transmitter Test Tools, for details on the construction of this
TPR.
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
oSIST prEN IEC 63563-7:2024
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.
Table 5 defines its properties, and the QiSpecification, Power Transmitter Test Tools, provides details
()ref ()ref
for constructing and calibrating it. For details about determining f ' and Q' , see Annex A:,
t t
Determining the reference FOD values (normative).
NOTE: The reference coil assembly is based on the A10 and MP-A1 Power Transmitter designs; see the
QiSpecification, Power Transmitter Reference Designs, for additional details.
Figure 6. Reference coil assembly

oSIST prEN IEC 63563-7:2024
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 mΩ. See the Qi Specification, Power
t t
Transmitter Test Tools, for details.
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.

oSIST prEN IEC 63563-7:2024
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, Communications Protocol, 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, Communications Protocol) 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.

oSIST prEN IEC 63563-7:2024
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, Basic power loss
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, Communications Protocol, 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, Calibrated power loss accounting, 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.
 Request the Power Receiver to reduce its power consumption (Extended Protocol only)
 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)
 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.
oSIST prEN IEC 63563-7:2024
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.
 The power loss in the tank circuit
 The power loss in the rectifier
 The power loss in ferrite(s) that serve to constrain the magnetic field
 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.
 The power loss in the inverter
 The power loss in the tank circuit
 The power loss in ferrite(s) that serve to constrain the magnetic field
 The power loss in metal parts of the Power Transmitter Product that are exposed to the
magnetic field
oSIST prEN IEC 63563-7:2024
Like a Power Receiver, a Power Transmitter can determine its inverter and tank circuit losses with
relatively good accuracy, and its ferrite and Friendly Metal losses with more difficulty. However,
since the latter typically depend only weakly on the position of the Power Receiver Product in the
Operating Volume, the Power Transmitter can determine them with relatively good accuracy as
well—and in most cases with much better accuracy than a Power Receiver can determine its ferrite
and Friendly Metal losses.
In the power loss accounting method, the Power Transmitter monitors the Foreign Object loss ΔP
FO
while the power transfer is ongoing. Hereto, the Power Receiver shall determine its Received Power
level and regularly send this information to the Power Transmitter. The reported Received Power
level is the average over a time window preceding the data packets used to communicate it. The
offset and size of this window are elements of the Power Transfer Contract. For details, see the
QiSpecification, Communications Protocol. To estimate the Foreign Object loss P as accurately as
FO
possible, the Power Transmitter should determine its Transmitted Power level in a time window
that matches the Power Receiver's time window as closely as possible. Because the Power
Transmitter does not know when the Power Receiver will report its Received Power level next, it
should determine its Transmitted Power level in sliding windows and select the best match. See
Figure 7 for an illustration.
To estimate the Foreign Object loss P as accurately as possible, the Power Transmitter should
FO
determine its Transmitted Power level in a time window that matches the Power Receiver's time
window as well as possible. Because the Power Transmitter does not know when the Power
Receiver will report its Received Power level next, it should determine its Transmitted Power level
in sliding windows and select the best match. See Figure 8 for an illustration.
Figure 8. Sliding windows for determining the Transmitted Power level
࢚
࢚
ܟܑܖ܌ܗܟ ܗ܎܎ܛ܍ܜ
Data Packet RP or RP8 Response
࢚
ܛܔܑ܌܍
࢚
ܟܑܖ܌ܗܟ
ȴP = P – P
FO t r
In this example, the Power Transmitter starts to measure its Transmitted Power level after
receiving a data packet. It uses a window size equal to the one in the Power Transfer Contract, and
an appropriate sliding offset t . Smaller sliding offsets yields larger overlaps between the Power
slide
Transmitter and Power Receiver windows. For example, a sliding offset of 25% of the window size
yields an overlap of 75% in the worst-case misalignment. When the Power Transmitter detects the
preamble of a data packet, it stops taking measurements. If the received data packet was an RP8 or
RP data packet, it takes the last measured Transmitted Power value from the appropriate sliding
window and calculates the Foreign Object loss. If this loss is below the threshold, it sends an ACK
response (mode 0, 1, and 2 of RP data packets only) and starts measuring its Transmitted Power
level again. If the loss is above the threshold several times in a row, the Power Transmitter should
conclude that a Foreign Object is present and take appropriate action to prevent heating it.

oSIST prEN IEC 63563-7:2024
5.1.2 Received power accuracy
The effectiveness of the power loss accounting method depends on the accuracy with which the
Power Transmitter and Power Receiver can determine their Transmitted Power and Received
Power levels. As discussed in Section 5.1.1, Method, the Power Receiver typically does not
determine its Received Power level by measuring it directly, but instead by calculating it from a
measured output power (to the Load), an estimate of its circuit loss (tank circuit, rectifier, etc.), and
an estimate of its ferrite and Friendly Metal losses.
()est
The Power Receiver shall report an overestimated Received Power value P in its RP8 and RP
r
data packets such that
()est
P≤≤P P + ΔP
r r r r
()est
where P represents the Received Power level, and P represents a margin as provided in Table 6.
r r
Table 6: Estimated Received Power accuracy
Estimated Received Power ΔP Unit
r
()est
350 mW
P ≤ 5 W
r
()est
500 mW
5 W < P ≤ 10 W
r
()est
750 mW
10 W < P
r
()est
NOTE: Table 6 implies that a reported amount of Received Power P = 5 W, implies an actual amount of
r
Received Power P in the range of 4.65 W up to and including 5 W.
r
It is hard—if not impossible—for a Power Receiver to estimate the contributions of the power loss
in its Friendly Metals to the Received Power level with an accuracy that is independent of its
position and orientation in the Operating Volume. The estimate therefore suffers from a systematic
error or bias that depends on the position and orientation. If the latter represent too large a
misalignment between the Power Transmitter and Power Receiver, the Estimated Received Power
accuracy may fail the above requirement.
5.1.3 FOD threshold
The diagrams in Figure 9 illustrate the impact of the estimated Received Power and Transmitted
Power level accuracies on the FOD threshold. The horizontal axes represent the power level, which
increases towards the right. According to the requirement given in section 5.1.2, Received Power
accuracy, the actual Received Power level is somewhere in the vertically hatched area to the left of
()est
P
the Estimated Received Power level . Assuming that the Power Transmitter estimates its
r
Transmitted Power level with an accuracy of ±ΔP , the actual Transmitted Power level is
t
somewhere in the horizontally hatched area centered on the estimated Transmitted Power
()est
P
level .
t
oSIST prEN IEC 63563-7:2024
A Foreign Object that can heat up to unacceptably high temperatures is present in the Operating
()thr
Volume if the actual Foreign Object loss ΔP exceeds a threshold ΔP , i.e.
FO FO
()thr
ΔP = P –P > ΔP
FO t r FO
Since the Power Transmitter only knows the estimated power levels, it should use the following
condition
()est ()est ()est ()thr ()margin
ΔP = P –P > ΔP – ΔP
FO t r FO
()margin
where ΔP = ΔP + ΔP helps the Power Transmitter to ensure that the actual Foreign
r t
()thr
Object loss ΔP does not exceed the threshold ΔP , regardless of the uncertainty in the
FO FO
estimated power loss. See the example b
...