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Wireless Power: The View from the Other Side of the Chasm

Chris Stephens – General Manager, Wireless Power Division – IDT
Laurence McGarry – Director of Marketing, Wireless Power Division – IDT

Introduction

In his book, Crossing the Chasm, Geoffrey Moore describes a gap or “chasm” between early adopters and mainstream market acceptance in the lifecycle of disruptive new technologies.

The first smartphone with integrated wireless charging capability was launched in 2011. In the intervening half-decade, the ecosystem and technology have evolved significantly to the point today where the drop-and-go convenience of wireless charging is becoming a critical feature in smartphones, smartphone accessories and smartwatches.

Entering 2017, wireless power has effectively crossed the chasm into mainstream adoption. 

Looking Back Over the Last 5 Years

It has been quite a journey from modest beginnings in a single smartphone model.  The steadily increasing popularity of wireless charging and the path it has taken can perhaps best be illustrated with a few statistics: 

  • 200 Million wireless power ICs sold in 2016. (source: I.H.S)
  • Wireless charging is integrated into more than 25 smartphone models.
  • Wireless power is integrated into the center-consoles of greater than 50 automobile models as standard or manufacturer optional equipment.
  • The majority of smartwatches sold today utilize wireless charging. More than 20 smartwatch models feature it.
  • Over 150 wireless charging smartphone cases and over 200 wireless charging pads are commercially available today.
  • Many of the largest, most recognized corporations and consumer brands have announced and deployed wireless power, including: Samsung, LG, Sony, Motorola, Apple, HP, Belkin, iHome, Ikea, Starbucks, McDonald’s, Marriott, Toyota, Honda, General Motors and Mercedes-Benz.

Entering 2017, wireless power has effectively crossed the chasm into mainstream adoption.

Several key catalysts lifted wireless power technology across the chasm: 

  • IC vendors drove die sizes and test times down with scale, allowing IC costs to penetrate key price barriers.
  • Coil technology continuously improved to allow for low cost, low loss Rx coils at 0.35 mm thickness for ease of integration into a smartphone.
  • SOC (system-on-chip) based architectures with RAM, programmable ROM and microcontrollers greatly streamlined the certification and interoperability testing/optimization process.

Standards: Emerging Clarity on the Other Side of the Chasm

avt-201701-idt-cliffWireless power growth and deployment have been impressive to date, but it has been slowed by a long-lived standards battle among competing interests. The clear winner as we enter 2017 is the Qi standard administered by the Wireless Power Consortium. Qi is a highly flexible, high-performance magnetic induction-based wireless power transfer protocol that benefits from a robust ecosystem.

At the heart of the entire wireless power ecosystem lays the core 5 W Qi protocol, also known as WPC baseline power. Over 90% of all wireless power ICs deployed to date operate according to this Qi protocol. This includes smartwatch transmitters and receivers that may not be Qi certified but still closely follow the Qi protocol for wireless power transfer.

A second less common standard is PMA (Power Matters Alliance). This standard is administered by the AirFuel Alliance. The PMA protocol for wireless power transfer is also based on magnetic induction and is similar enough to Qi that receiver and transmitter ICs can incorporate both protocols such that they can operate on either standard with minimal material cost penalty.

A third standard that garners a lot of attention, but without significant deployments to date, is called AirFuel Resonant (formerly called Rezence A4WP). This standard is also administered by the AirFuel Alliance but operates on the magnetic resonance principle and at a much higher frequency (6.78 MHz for AirFuel Resonant vs. 87 kHz – 205 kHz for Qi and PMA). There may be some key benefits with AirFuel Resonant with regard to performance in the presence of nearby metal and high power transmission (the transmit and receive coils can be implemented with fewer windings). To date, though, AirFuel Resonant deployment has been stymied by EMC (Electromagnetic Compatibility) issues, high transmitter solution cost, and lack of ecosystem development.

A fourth method of wireless power is generally referred to as “microwave charging.” A number of small startups have invested in this method to try to realize the dream of charging smartphones and other devices at distances of up to 15 feet. Generally speaking, these microwave charging schemes use the ISM 2.45 GHz and 5.80 GHz bands – the same bands utilized for Wi-Fi®. Wi-Fi interoperability issues, safety concerns, FCC regulations, and transmitter solution cost economics have kept these microwave charging-at-a-distance schemes outside the realm of practical application to date and likely will continue to do so for the foreseeable future.

At any rate, the Qi standard is the clear and unquestioned winner at this juncture. Qi provides the best tradeoffs by far in terms of ecosystem maturity, performance and solution cost. When considering wireless power for your next project or purchase look for the Qi Certified logo. This will assure that the device is genuine and not counterfeit, and has been thoroughly tested and shown to adhere strictly to the Qi standard, ensuring the best end-customer experience.

Looking Ahead to the Next 5 Years

Now that the chasm has been crossed, the view looking forward is coming into focus.

First up is higher power charging. The WPC 1.2 specification was recently released and this allows for charging at up to 15 Watts. This is comparable to or even sometimes exceeds wired charging power today in smartphones. WPC 1.2 is viable because of advances in power transmission efficiency. This month, vendors were expected to demonstrate their 15 Watt WPC 1.2 kits at CES in Las Vegas.

Qi provides the best tradeoffs by far in terms of ecosystem maturity, performance and solution cost.

It cannot be stressed enough that these improvements in power transfer efficiency are most critical to enhancing charging power and thus reducing charging time. Smartphone charging is governed by a thermal loop that will cease charging if a certain temperature is exceeded. For example, the total heat from a wireless power transfer protocol can be expressed in terms of efficiency as follows:

Heat = PR * (1/η – 1)

Where PR = desired receive charging power and η = the (DC in Tx) to (Rx DC out)
power transfer system efficiency. For example, 70% efficiency with 5 Watts of power transferred to the smartphone would result in 2.14 Watts of wasted heat raising the temperature of the smartphone. 70% efficiency is what was achieved on the earlier wireless power systems and would be pretty poor performance compared to the performance of systems today. Note the following graph with recently measured laboratory benchmarks with 0.35 mm thick receiver coils.

Charging power and efficiency evolution – 15 Watt systems in development for 2018 have LESS waste heat than the original 5 Watt systems in 2011!

Another area of evolution is commonly referred to as “placement forgiveness.”  Early wireless power systems were very fickle and required a high degree of X and Y dimension alignment between the transmitter and receiver to effect a charge.  Furthermore, the Z-distance (or height) at which a smartphone could be charged was highly limited.  This has changed over the last 5 years to the point where the placement forgiveness is truly in the realm of “drop-and-go.” Consider the following diagram based on laboratory measurements:

Placement forgiveness evolution – XY alignment precision necessary for charging is extremely easy to achieve with current Qi systems. Evolution to greater Z-height is in development and will soon allow for under desk mount!

Another notable area of evolution to expect is transmitter infrastructure convergence. Currently, PMA, Qi, and AirFuel Resonant and semi-custom pads/stands for Qi-based smartwatches are usually sold separately and they don’t often interoperate to charge any device regardless of standard. As the infrastructure in hotels, coffee shops, automobiles, airports and other key places proliferates, the designs will have to converge so that one pad will be able to charge just about any device between 2 Watts and 15 Watts. The wireless power IC vendors are well on their way to making this a reality with ICs already being commonly offered as “dual-mode” (Qi and PMA) and ICs and reference designs slated for release in 2017 that operate as “tri-mode” (Qi, AirFuel PMA and Resonant).

…the designs will have to converge so that one pad will be able to charge just about any device between 2 Watts and 15 Watts.

Conclusion

From the other side of the chasm, we can now reflect and realize the ideas of the pioneers, such as Faraday and Tesla. Adoption of wireless power continues to proliferate in new smartphone and smartwatch introductions – driving transmitter infrastructure adoption in home, office, automobile and leisure facilities and creating an ecosystem of wireless installations and users. As the technology continues to mature and user awareness increases, we enter the next phase of the “chasm” curve and see
the emergence of new applications from medical equipment, benefiting from waterproofing during frequent sterilization – to electronic drones, conveniently landing and re-charging on wireless charge pads.


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