Nobody Likes Power Cords! Wireless Power is Happening
GaN Talk – Alex Lidow, Ph.D.
Sep 30, 2017
I have yet to meet someone who likes power cords.
Take for example Keith. In figure 1 is a photo of all the power-related accessories Keith lugs around in his backpack to make certain he will be able to run his phone, tablet, and computer wherever he goes. What Keith and others may not realize is that the technology is available that can eliminate every one of these cords – today! So, why is it taking so long for wireless power solutions to become a household technology?
Figure 1: Keith’s “kit” of power cords.
Certainly, wireless charging is not a new topic having been talked about for quite a while. But now, with a recently developed innovative approach to the design of transmission and receiver antennae (coils), ubiquitous wireless power is ready to be incorporated into our daily lives throughout furniture, walls, and floors to efficiently and economically power all the gadgets we need for our electronic lives.
Setting the Conditions for Widespread Adoption: Competing Wireless Power Standards
Two industry standards groups have been leading the charge to take wireless power to consumers. The first standards group to promote wireless charging was the Wireless Power Consortium (WPC) with their Qi standard, which is based on inductive charging technology. The second group, AirFuel™ Alliance, utilizes highly resonant magnetic fields as one of their standards. It is resonant magnetic technology that holds the promise of widespread wireless power and will make wireless power an everyday, everywhere technology.
The primary limitation of inductive charging is that it requires precise position alignment between transmitter and receiver, and can only power one device at a time. This technology is currently the most recognizable to the consumer, since it was first to market with the technology employed to charge toothbrushes, Samsung phones, and most recently iPhones. A second, and equally severe, limitation of this technology is the fact that it requires precise placement of the receiving device (e.g. toothbrush or cell phone) relative to the transmitter (cradle or charging spot) that houses the power source used to charge the device. In contrast, the AirFuel resonance magnetic standard technology provides power simultaneously to multiple receiving devices anywhere they are placed on the transmission coil surface area.
So, When Will Wide Spread Applications Be Commonplace?
If the technology exists, where are all the wirelessly powered furniture, cell phones, televisions, and computers? They are on the way with Taiwan and China leading the charge. Inclusion of wireless power transmitters in furniture, table-tops, and on trains, planes and in automobiles has started, and the introduction of end-user receiving devices is picking up momentum. For example, Dell Computers recently launched their Dell 7285 2-in-1 Latitude computer that has the capability to be charged wirelessly (see figure 2). In addition, AirFuel reports that now there are about 6,000 installations worldwide for resonant magnetic and expanding.
Figure 2: Dell’s Latitude 7285 2-in-1 laptop is wirelessly charged using a highly resonant magnetic power-transmitting unit (PTU) based on the AirFuel standard.
But why so slow an uptake for this seemingly superior resonant magnetic standard?
Being able to power several items simultaneously and without having to worry about positioning receiving units directly over a transmitting surface over extremely large areas is ideal. Unfortunately, transmitting power over a large surface (e.g. a tabletop) turns out to be surprisingly difficult to achieve. The problem can be broken into three main challenges:
- Powering multiple devices simultaneously creates an infinite number of use scenarios for transmitter/receiver pairing combinations.
- The larger the charging area, the larger the transmitting antenna. Unfortunately, larger antennae are more susceptible to off-resonance shifting, which severely impacts transmission efficiency and transmitter system cost (see figure 3).
- Receivers that translate the AirFuel standard transmission 6.78 MHz signal rate into a controlled voltage with adequate power to operate devices as diverse as computers and table lamps, have not been very efficient.
Figure 3: As the resonant magnetic antenna grows in size, so do the magnetic fields, thus increasing the likelihood of interference with other electronics within range.
Device Receive Units Solving These Challenges For Transmitting Power Wirelessly Over A Large Surface Area
Solving issue number 1, charging multiple devices simultaneously, has been addressed in the AirFuel standard by defining a pre-determined set of source (transmitter) and device (receiver) paring combinations. An example of an AirFuel Alliance defined combination is a class 3 source, rated at 16 W, that is paired with two category 3 devices, rated at 6.5 W each, or one category 4 device, rated at 13 W. For reference, a typical smart phone (receiving device) is within category 3, whereas a small laptop computer requires more power and falls within a category 4 rating.
Although this power-level matching reduces the impact of maximum power demand imposed on the system to within the capability of its amplifier, unfortunately it does not address the fundamental need for the growth of the consumer ecosystem over the long term. In support of growing the wireless power ecosystem, EPC has created a range of products including development kits for class 2, 3, and 4 power transmitting units (PTU), as well as for category 3 and 4 power receiving units (PRU) to help end-system wireless power developers design and deliver products to the ultimate end-user consumer market faster.
Solving problem number 2, having an antenna (coil) able to cover large surface areas, is significantly more difficult to achieve then providing power to a small, well defined single spot, as is the case with inductive technology (Qi). Today, commercially available PTUs have an area of less than one square foot (0.1 sq. meters). There are two issues at the core of the problem: (a) large antennae are hard to keep in resonance over the entire area: and, (b) large antennae tend to interfere (EMI) with electronics even at distances beyond the X and Y dimensions of the antenna being used.
To address this problem, EPC has recently achieved a breakthrough in wireless power transmission systems with an innovative, scalable large area antenna (coil) design. This antenna design provides the uniform magnetic field required under the AirFuel standard. In addition, this antenna design is scalable to cover small or large surface areas of virtually any shape.
The key to this breakthrough innovation was an antenna design that limits the magnetic field distance used for power transfer. In traditional wireless power systems, as the coil area becomes larger, so does the magnetic field with its susceptibility to impedance shifting. In addition, the emission of the magnetic field causing interference with other devices also increases with size. At a certain point, the larger field becomes undesirable for various reasons, such as the high cost of abating impedance variation susceptibility, increased difficulty in passing electromagnetic interference (EMI) standards, and having to address human safety concerns associated with specific absorption ratio (SAR). Due to the unique structure of EPC’s new coil design, interference between various wireless power devices and other objects placed on or near it are further reduced.
The coil can be manufactured using standard processes available today, thus keeping costs low. Also, this new antenna design can be used in wireless powered devices, particularly those needing higher power and/or large areas. The reduced impedance of the coil makes it ideal for keeping unregulated voltage variation low between no load and full power within the device. This novel antenna design can extend to any surface, regardless of size and orientation – for example entire walls, floors, furniture, and countertops.
A transmission system using this antenna design was first demonstrated at the IEEE APEC 2017 exhibition held in Tampa, Florida in March 2017. The wireless power transmitter and antenna demonstration were an integral part of a 20” x 40” (0.5 meter x 1 meter) tabletop that could simultaneously power a variety of common products, including a desk lamp, an Amazon Echo Dot, a notebook computer, a computer monitor, and a smart phone (see figures 4 and 5).
Figure 4: Small and inexpensive antennae are used as power receivers for the variety of loads powered wirelessly.
Of significant note is the fact that this tabletop goes beyond wireless charging to provide continuous power to devices wirelessly over a large surface. In the tabletop demonstration, the computer monitor, Amazon Echo, and table lamp do not have batteries, but are powered directly by the transmitter positioned below the tabletop’s surface. At the same time, the cell phone, which has a battery, is being charged.
To extend resonant magnetic wireless power technology beyond this tabletop example, the flexible design transmission coil can be economically incorporated into walls, upon which flat-screen TVs, speakers, and wall lamps can be hung – without the need to be physically “plugged in.” Likewise, kitchen countertops can become platforms for powering blenders, toasters, and coffee machines without the danger of mixing water and electricity. Conference room tables can power the laptops and charge the phones of the participants without having a labyrinth of wires snaking across the table and, in the near future, can power augmented reality systems used to enhance the presentation of the meeting.
Having solutions to the first two of the three problems confronting resonant magnetic power delivery, the third problem – receiver efficiency – is the next to be addressed.
EPC has developed two wireless power receiver demonstration systems, the Category 3 EPC9513 (5 V, 5 W) and the Category 4 EPC9515 (5 V, 10 W). Soon these systems will be joined by additional demonstration systems producing regulated 19 V and 110 V outputs at higher power levels. The efficiency of these first-generation systems is about 87% and future improvements in architecture and GaN IC technology should bring this number into the 95% range. These demonstration systems operate to the Airfuel standard, excluding Bluetooth® Low Energy (BLE) communications.
With the wide range of efficient receivers that can be used to power anything from lamps to laptops to tablets, while remaining compatible with cell phone charging, the system designer now has all the tools needed to create an entire wireless power, large area, efficient ecosystem.
Wireless Power Is Ready For Prime Time
We can now help Keith and all of us…we are ready to cut the cord and have wireless power available everywhere! The complete, ubiquitous wireless power transmission system is at hand. Our homes and offices can be wirelessly powered, finally eliminating those unsightly, inconvenient, and at times, dangerous power cords.
Employing resonant magnetic wireless power technology over large surface areas is now possible with the recently developed innovative approach to the design of transmission and receiver antennae (coils) by EPC. Wireless power transmission systems are destined to be incorporated into furniture, walls and floors, and to efficiently and economically power all the receiver-equipped gadgets we use in our everyday lives.
The time has come to Cut the Cord, after all…nobody likes power cords!