Blog – What is Foreign Object Detection in Wireless Charging, Anyway?

What is Foreign Object Detection in Wireless Charging, Anyway?
What is Foreign Object Detection in Wireless Charging, Anyway?

Nobody can argue that Wireless Charging is an incredibly convenient way to keep our favorite handheld devices charged up, and to provide some remedy for battery anxiety.  Wireless charging is (almost) everywhere nowadays — in our phones, in our cars, in our airports, in our restaurants and coffee shops, and soon to be in places we haven’t even thought of yet.  But is it safe?  We have seen internet articles about wireless charging shortening the life of your smartphone’s battery, or other ways wireless charging can harm your device.  But unfortunately, those articles are not written by people who understand wireless charging, and are false and misleading.  (Spoiler:  There is no difference in charging your phone from a wire or from wireless — it’s just another way of getting energy.)

Back to our question:  Is wireless charging safe?  The answer, of course, is a resounding “yes”, provided it is done correctly.  One of the biggest safety topics to understand in a modern-day wireless charger is how to prevent the wireless charger from heating metal objects to unsafe levels.  Because the frequency used by the wireless charger is very effective at heating metal objects, it is up to us as system designers to ensure that any stray metal objects, such as wayward coins, that present themselves in the middle of a charging session are not a cause for alarm (as in “fire alarm”).  In order to protect ourselves from these “foreign” metal objects, we try to detect this safety threat with something called “Foreign Object Detection”, or FOD.

Historically, ever since the introduction of Foreign Object Detection (FOD) methods in the Wireless Power Consortium Qi (pronounced “chee”) standard, the general public has had a misunderstanding of what FOD really means.

If a random person is asked what FOD must do, in most cases the answer would be that if a coin is placed on the transmitter surface, the transmitter should indicate the presence of a foreign object. This is basically the functionality of a metal detector.

In practice most receivers like phones and battery packs have metal elements around the receiving coil. User experience can be negatively affected if these metal elements are wrongly classified as foreign objects. According to the Qi specification, a foreign object is detected only after a Qi receiver is placed on the transmitter surface, information is exchanged between the two devices and a decision is made about the foreign object presence based on the estimation of how much power would actually be dissipated into the foreign object during power transfer. It is perfectly acceptable to have an object on the transmitter surface during power transfer if it does not heat above certain thresholds.

 

OBJECT PLACEMENT ON THE TRANSMITTER SURFACE

The most popular method to detect the presence of an object on the transmitter surface is the Direct Q Measurement. It monitors for changes to the quality factor (Q factor) of the transmitter coil or for changes in its inductance or resistance. Other methods that detect the presence of objects on the transmitter coil can be based on change in capacitance, light reflection or transmission, changes in weight/pressure, resonance at 1MHz, metal detectors using auxiliary coils, etc.

The Qi specification has an informative section reserved for these mechanisms. The resonance shift method is already described and is related to the change in quality factor. The fact that a resistance change is also induced by most (but not all) receivers can be used to improve the detection of the object but it is not enough to determine if the presumed foreign object would actually absorb enough energy during power transfer to cause a significant increase in its temperature.

 

CONFUSION BETWEEN THE DIRECT Q MEASUREMENT AND THE EXISTING PRE-POWER FOD METHOD

These values are measured when a receiver is placed on a MP-A1 transmitter coil and they are reported by the receiver during the negotiation phase.

The transmitter may not use a MP-A1 coil and in that case its measurements of Q and resonant frequency must be converted from the actual transmitter coil to how they would look like on the MP-A1 coil before a decision can be made regarding the mismatch between the measured values and the reported values from the receiver.

The Qi specification has a high-level description of the pre-power FOD methods but the mechanism used to calculate the Q factor seen by a MP-A1 coil is not provided.

The direct measurement of the transmitter coil quality factor without a receiver present can at most inform the transmitter of the existence of metallic objects on the charging surface, and the transmitter can use this data to inform the user to clear these objects before placing the receiver on the surface. This method can also be used after a confirmed FOD event and subsequent removal of power.  In that case, the transmitter uses this method to ensure the user has removed all objects from the charging surface before allowing the receiver to be placed to restart charging.

This method alone cannot determine if the metallic object will consume sufficient power to heat the object, but it can be used in combination with other power loss methods to educate the user to always remove all metal objects from the transmitter surface before/during/after charging.

Confusing?  The key is in the name of the action:  Foreign Object Detection.  It’s one thing to detect a metal object, but it’s a whole different ballgame to determine if that object will lead to an unsafe situation if we charge a phone while that object is present.  As a charger, what you want to do is charge a user’s battery — that is, after all, the reason you exist.  Therefore a charger must have a robust and deterministic plan for deciding which objects are clearly unsafe, and which objects can still be present during a charging cycle without cause for alarm.  If I am too conservative, then nobody gets to charge.  But if I am too lenient, then somebody gets burned (maybe literally).  Striking the right, and safe, balance is the art of good transmitter design.

Emanuel Stingu Spark Connected, CTO

“It is perfectly acceptable to have an object on the transmitter surface during power transfer if it does not heat above certain thresholds.” – Emanuel Stingu, Chief Technology Officer at Spark Connected.

About Spark Connected

Spark Connected | powering the world, wirelessly

Spark connected is an industry leader specializing in multiple advanced and safe wireless power technologies that benefits a wide variety of applications in the Automotive, Industrial, Infrastructure, Medical, Telecom and Security, Robotics, Factory Automation, IOT, Smart Home, and Consumer markets.

Spark is transforming wireless power delivery and intelligent battery charging with innovative platforms, disruptive technology and breakthrough products enabling an enhanced user experience for all. The company specializes in Product Development and Engineering Solutions with a team of passionate innovators with decades of combined deep domain expertise.

Spark Connected is a Full Member of the Wireless Power Consortium.

Please forward inquiries to:
Marina Wolf/Ruwanga Dassanayake
(972) 855-8026
sales(at)sparkconnected.com

Blog – The Leap Beyond 15W Wireless Charging

Powered By Spark - Wireless power and wireless charging blog

INTRODUCTION

Since the public announcement of near-field coupled magnetic-field based resonant wireless power transfer (WPT) in 2006, wireless charging technology has been undergoing significant development. Since then standards bodies such as Qi Wireless Power Consortium (WPC) as well as PMA/Airfuel Alliance have been formed, among which, Qi WPC has been the main driving force in advancing and establishing the standards for the WPT and wireless charging.

Different wireless chargers including 5W legacy and 15W next-generation have been certified and utilized in the market. With the success at these power levels the industry is leaping for the next big step to hit the market with the power levels of 30W, 45W, 60W, and beyond.  The application for these power levels could involve laptops, drones, autonomous robots, power tools, etc.

OPERATION PRINCIPLES

The near-field wireless power transfer operates based on the magnetic-filed coupling of the transmitter (TX) and receiver (RX) coils. The magnetic field is stablished with alternative current (ac) at different frequencies including radio frequency (RF), resonant, or near resonant frequencies, where the latter is designed for inductive charging. Figure 1 depicts a near-field coupled WPT/WC system. Depending on the switching frequency of the TX driver as well as LC tanks resonant frequency the system could be designed to operate in one of the three aforementioned operation modes.

The Leap Beyond 15W Wireless Charging - WPT/WC system by Malek Ramezani
The TX driver output is an ac voltage with a fundamental frequency at which the system is designed for. This voltage supplies the TX LC tank with an ac current establishing a magnetic field in the TX coil. When a wireless power receiver is at the presence of this filed, the coupling between the TX and RX coils induces an ac voltage across the RX coil which yields to an ac voltage at the input of RX rectifier. This ac voltage is then rectified to either charge a battery or supply a load.

The deceptively simple appearance of this system has demanded enormous effort from EE engineers to improve its efficiency and reliability in competition with the wire-based chargers. Although, 5W WC systems have shown a promising dependability and met the market’s demand, the 15W is still challenging the technology leading companies and agencies. The challenge is not only optimizing the  systems for a higher efficiency but also their reliability is highly dependent on the communication system between TX and RX. The communication system provides a negotiation mechanism through which the TX and RX establish a power transfer agreement. The traditional communication between the TX and RX in the 5W systems has been based on a low-bandwidth in-band communication where the message is modulated on top of the power signals at its origin and then is demodulated from the power signals at its destination. The in-band modulation is usually implemented through amplitude shift keying (ASK), frequency shift keying (FSK), or phase shift keying (PSK), or a combination of these methods. It can be conceived that this communication method could be affected by the dynamics of the power signal. Therefore, the gateway to the higher reliability of WC systems at power levels of 15W  and beyond is  enhancing their communication robustness independent from the power signals dynamics and therefore improving overall system reliability. The possible solution could be the out-of-band communication with high bandwidth and bit rate such as Bluetooth, NFC, or similar technologies.

Development of higher power WC systems for applications where simultaneous power and data transfer are needed could be a revolutionary transition to a cord-less world. The  application of these WCs in consumer electronics, especially in laptops would be the beginning of an integrated wireless charging and data transfer unit. In this outlook a transmitter unit, e.g., a laptop docking station at the power levels of 45 – 200 Watts could be utilized as both power and data transfer wireless link. At the front-line of battle between the wired and wireless world a technology leader such as Spark Connected is fulfilling its mission towards Powering the world, wirelesslyby developing the most advance and reliable 45 – 200  Watts  WPT and WC systems.

Malek Ramezani - WPC Co-Chair and Senior Power Electronics Systems Engineer at Spark Connected

Malek Ramezani

  • Senior Power Electronics Engineer
  • PhD in Electrical Engineering from The University of Alabama
  • Co-chair for Foreign Object Detection (FOD) at the Wireless Power Consortium (WPC/Qi)

About Spark Connected

Spark Connected | powering the world, wirelessly

Spark connected is an industry leader specializing in multiple advanced and safe wireless power technologies that benefits a wide variety of applications in the Automotive, Industrial, Infrastructure, Medical, Telecom and Security, Robotics, Factory Automation, IOT, Smart Home, and Consumer markets.

Spark is transforming wireless power delivery and intelligent battery charging with innovative platforms, disruptive technology and breakthrough products enabling an enhanced user experience for all. The company specializes in Product Development and Engineering Solutions with a team of passionate innovators with decades of combined deep domain expertise.

Spark Connected is a Full Member of the Wireless Power Consortium.

Please forward inquiries to:
Marina Wolf/Ruwanga Dassanayake
(972) 855-8026
sales(at)sparkconnected.com

Malek Ramezani has been elected to the Foreign Object Detection Task Force co-chair position at the WPC

Spark Connected has been awarded co-chair positions at the Wireless Power Consortium.
Spark Connected has been awarded co-chair positions at the Wireless Power Consortium.

Dallas, TX. May 26, 2020.

Spark Connected, a global leader in developing advanced and innovative wireless power technology and system level solutions, has been elected to another co-chair position at the Wireless Power Consortium.

Spark Connected, a global leader in developing advanced and innovative wireless power technology and system level solutions, has been elected to another co-chair position at the Wireless Power Consortium.

Malek Ramezani, Senior Power Electronics Systems Engineer at Spark Connected, has been elected as the Co-Chair of the WPC Enhanced Foreign Object Detection Task Force (EFOD TF).

This task force works towards enhancing the current FOD approaches of Qi-certified wireless power solutions as well as developing new FOD practices to promote and guarantee the safe operation of any wireless power system seeking  Qi certification.

 


About WPC

Established in 2008, the Wireless Power Consortium is an open, collaborative standards development group of more than 500 member companies from around the globe. WPC’s member companies are large and small competitors and ecosystem partners representing brands from all parts of the industry and all parts of the globe. Members collaborate with a single purpose: worldwide compatibility of all wireless chargers and wireless power sources.

As wireless charging continues to evolve beyond consumer handheld devices, there are myriad of other new applications, such as laptops, tablets, drones, robots, connected car and the intelligent cordless kitchen. The WPC maintains and develops standards for a variety of different wireless power applications. This includes:

  • The Qi standard, for smartphones and other portable mobile devices. Qi delivers up to 15W today. A future extension will also deliver up to 60W to enable laptop charging in addition to charging smartphones and other portable mobile devices with wide positioning freedom.
  • The Ki Cordless Kitchen standard, for kitchen appliances, for delivering up to 2,200W.
  • The Medium Power standard, a simple low-cost solution delivering 30 – 200W for power tools, robotic vacuum cleaners, e-bikes, and other battery-powered devices that don’t require compatibility with the Qi standard for mobile phones charging.

With more than 5000 different Qi Certified wireless charging products in the market, the WPC uses a network of independent authorized test labs around the globe that test specific properties for safety, interoperability, and usability. Spark Connected is proud to serve on these committees and task forces, and advance the future of wireless charging and power in the market.

Malek Ramezani - WPC Co-Chair and Senior Power Electronics Systems Engineer at Spark Connected
Malek Ramezani, Senior Power Electronics Systems Engineer

About Spark Connected

Spark Connected | powering the world, wirelessly

Spark connected is an industry leader specializing in multiple advanced and safe wireless power technologies that benefits a wide variety of applications in the Automotive, Industrial, Infrastructure, Medical, Telecom and Security, Robotics, Factory Automation, IOT, Smart Home, and Consumer markets.

Spark is transforming wireless power delivery and intelligent battery charging with innovative platforms, disruptive technology and breakthrough products enabling an enhanced user experience for all. The company specializes in Product Development and Engineering Solutions with a team of passionate innovators with decades of combined deep domain expertise.

Spark Connected is a Full Member of the Wireless Power Consortium.

Please forward inquiries to:
Marina Wolf/Ruwanga Dassanayake
(972) 855-8026
sales(at)sparkconnected.com