Wireless power is slowly evolving to help make charging second-nature to the consumer. In Japan, for instance, several portable devices are available that support wireless charging.1 As more portable devices that offer wireless charging capabilities enter the market, the need for standards naturally will follow. Organizations have emerged to help grow the market and provide standards for designers, which include the Alliance for Wireless Power (A4WP), and The Wireless Power Consortium’s Qi (pronounced “chee”) Specification. To find out more about wireless power, emerging standards and what they mean for the designer, I posed some questions to Menno Treffers, Chairman of the Wireless Power Consortium.

ECN: Can you describe the main benefits of the Qi standard for designers?

Menno Treffers: The Qi specification is available as a free public download from our website: A large ecosystem of suppliers provides components and services for product developers. You can get coils, shielding, ICs, test tools, certification services, engineering services, ODM manufacturing. And you can use these components and services from many different companies in many countries.

ECN: Can you describe the main benefits of the Qi standard for the consumer/end user?

MT: The key benefit of wireless charging is the convenience. Consumers that made the switch don’t want to go back to plugging in a connector. The advantage of Qi is that it can be (and has been) integrated in mobile phones.

ECN: Can you describe the technology behind the Qi standard and what makes it unique?

MT: The Qi standard is the only non-proprietary solution for wireless charging available in products today. It works by generating a safe electromagnetic field between a charger and a device through a well-established process called magnetic induction. Qi chargers have a built-in transmitting coil, so any Qi device will work with any Qi charger, now and in the future. Qi is superior to other wireless power solutions as it offers the widest range of features to optimize user convenience and product choices: support for both inductive and resonant charging, spatial freedom, and intelligent power management.

ECN: Given the wide variety of mobile devices – now and in the future – how is the amount of design requirements for the mobile device kept to a minimum?

MT: The Qi specifications are interface specification. We try to avoid specifying product implementations. In the end, the only thing that matters is compatibility: a receiver with the Qi logo must work on all transmitters with the Qi logo. A product that passes all certification test procedures will get the logo, independent of the implementation.

ECN: How is system control handled in the power transfer?

MT: The receiver transmits control signals to the transmitter by modulating the load. The receiver is in control of power transmission and regulates power transmission up and down, depending on the need (battery charge status, for example). The receiver transmits control signals to the transmitter by modulating the load. The receiver is in control of power transmission and regulates power transmission up and down, depending on the need (battery charge status, for example).In the system control process, how does the base station reduce any errors toward zero?

ECN: What should the designer know about the communications interface between the base station and mobile device?

MT: That depends on what you design. If you design the system ICs you have to understand the control protocol in great detail. For others it will depend on the chipset that you use.

ECN: What environmental considerations (ie., interference) should the designer be aware of when designing to your standards?

MT: Products have to stay within EMF limits and avoid interference (EMI) with other products. With Qi, it is easy to comply with EMF regulations. EMI is more challenging, particularly in a sensitive environment such as a car. The Qi guidelines for automotive aftermarket products (free download from the website).

ECN: Will wireless charging of low power devices already on the market be affected in any way?

MT: The Qi certification process makes sure that Qi products that are on the market now will work with all future Qi-certified products.

ECN: Describe the certification process for new designs and what kind of help will your organization offer designers toward that end?

MT: A new receiver (e.g. a new mobile phone) or base station (a Qi charger) must be submitted to one of the authorized test labs. That test lab verifies compliance with the Qi specification by executing the tests that are prescribed in the test specification. This test is followed by an interoperability test in which the new product is tested against all previously certified products.

ECN: What will it take for wireless power to gain widespread adoption and how will your standard be a part of it?

MT: The key factor for mass adoption is when manufacturers completely integrate the technology into their products. As the market for mobile devices with wireless power expands, wireless charging surfaces embedded into infrastructure will soon follow. This is something we’re seeing developing now with Qi. The hottest new smartphones including HTC Droid DNA, HTC 8X, Google Nexus 4, LG Spectrum, and the Nokia Lumia 920, have Qi integrated into the devices as an out-of-the box feature and do not require a backdoor option to facilitate charge.

ECN: How will the Qi standard adapt to future mobile devices and/or consumer preferences?

MT: We are gradually increasing the amount of power that can be delivered. At Mobile World Congress you will see the first 7.5 Watt base stations and receivers. That will increase to 15 Watt. We can add features, such as this power increase, to the specification when needed, under the condition that they can be introduced backwards compatible with the installed base of Qi products.

ECN: What other types of technologies will benefit from your standard?

MT: Qi chargers can be integrated into many products. We already see integration in speaker docks (to play music while charging a phone) and televisions (to play video while charging the phone). Qi receivers are not only integrated in mobile phones, but also in digital still cameras. Products that need to be sealed (underwater cameras, for example) in particular benefit from wireless charging.

ECN: What kinds of accessories can we expect in the future?

MT: In the near future, we’ll start to see additional charging pads and more innovative charging products like the Nexus 4 Wireless Charging Orb, the JBL Wireless Charging Speaker, and the charging console featured in the 2013 Toyota Avalon Limited.

1 Jessica Leber, “Wireless Charging—Has Its Time Finally Arrived?”, MIT Technology Review, September 11, 2012.