The Future of Wireless Charging
Mr. Akshay
Dattatray Shelke
B.E. Electronics and telecommunication
Email: (akky487@gmail.com)
Ref (European
Editors)
Wireless charging for mobile phones is finally
taking off. After a decade of development, and a wide array of different
specifications, the technology and the market are maturing and consolidating
sufficiently for mainstream adoption.
This is highlighted by companies
such as furniture supplier IKEA adopting the Qi specification in tables and
other products, and providing its own wireless-enabled cases called Vitahult
for those phones such as the iPhone that don’t support that particular
technology.
Similarly, Starbucks is using a
competing technology from Power mat, which has been working on wireless
charging for a decade. This involves a ring (essentially an inductive coil with
a controller) that plugs into the power socket of a phone, which is then placed
on a Power mat to charge.
Figure 1: Starbucks has been
rolling out wireless charging using technology from Power mat.
These maturing technologies are
leading to new options for designers in consumer, medical and industrial
applications.
*Wireless charging
specifications
One of the reasons for the slow adoption of
wireless charging has been the fragmented specifications. Two industry
associations have merged over the last year to create a group that can take on
the market leader.
This new group, called Rezence, brings together the Alliance
for Wireless Power (A4WP) and Power Matters Alliance (PMA) to bridge two core
wireless charging technologies. The group aims to use this combined
specification for a core-charging standard supporting a wide range of consumer,
medical, military and industrial applications, not just mobile phones and cars.
The merged Rezence group has over 170 member
companies, including board member companies AT&T, Broadcom, Flextronics,
Gill Electronics, Integrated Device Technologies, Intel, MediaTek, Power mat
Technologies, Procter & Gamble, Qualcomm, Samsung Electronics, Samsung
Electro-Mechanics, Starbucks, and WiTricity.
It sees wireless charging being used in wider
applications, from Bluetooth headsets to wearables and up to tablets, notebooks
and laptops, as well as medical and embedded product designs.
It aims to challenge the Qi Wireless Power Standard
Specification, which is overseen by the Wireless Power Consortium (WPC). This
has seen over 50 million units of 80 mobile devices from 200 companies using
the technology since it was established in 2008.
The latest version of the specification supports
the delivery of 15 W to mobile phones for fast charging, up from the previous 1
A at 5 V (5 W). Some phone makers offer wired fast charging that provides a 60
percent charge in as little as 30 minutes, and the aim of the latest Qi
specification is to extend this to existing units that use the Qi wireless
charging as well. This sits well with the coffee shop charging model where
there is limited time.
The group also approved the test procedures and
tools needed to verify that fast charging products are compliant with the new
Qi specification, as well as being backward compatible with all existing Qi
products.
WPC’s members include Belkin, Convenient Power, Delphi,
Freescale, Haier, HTC, IKEA, LG, Microsoft, Motorola, Nokia, Panasonic, Power by
Proxy, Royal Philips, Samsung, Sony, TDK, Texas
Instruments, Verizon Wireless, and ZTE. This has given the group significant
momentum with implantations in Motorola and Samsung mobile phones, Philips
consumer equipment, and cars with systems from Delphi.
*Implementation
The Qi specification uses small
inductive coils that can handle resonant frequencies of 100 – 205 kHz, but this
means that the terminal has to be placed close to the charging surface and
directly over the charging coil. The Qi receiving coils, like the 30 mm x 30 mm
single loop such as the WR303050 from
TDK, have a thickness of just 0.92 mm with an inductance of 12.3 µH at 100 kHz.
The efficiency of around 66% is another reason for using this approach to
reduce the losses.
Figure 2: The WR303050 wireless
charging receiver coil from TDK is just 0.92 mm thick for integration into a
mobile terminals using the Qi specification.
Laird Signal Integrity
Products has created a transmitter module that is designed to meet the Qi specification.
The WPC A1 module uses
a ferrite base to provide a high Q (quality) factor for a sharp resonant peak.
This means as much power as possible is transferred to the receiving coil for
faster charging with fewer losses. This can be used with a wide range of
designs, from office equipment to power tools, embedded in surfaces.
Qi also has a relatively simple
communications protocol that is limited to one device being charged,
controlling the rate of charge and putting the terminal into a low-power mode
once it has reached full charge to avoid over-charging. For more flexibility, a
base station (or charging mat) can have multiple inductors to charge multiple
devices, and each has its own controller, but each terminal has to be placed in
a particular position.
Wurth and Texas Instruments have developed a wireless power demonstration kit that combines transmission
and receive coils with the charging and communications controllers. This uses
version 1.1 of the specification with the 5 W charging controller and
high-efficiency coils from Wurth such as the 13 A, 6.3 µH transmission coil (in
Figure 3a) and the receiver coil (in Figure 3b). The inductance of each coil is
already matched with the resistance and capacitance on the boards to provide
the highest available Q-factor for efficient operation. However, designers can
change the coil to test out larger devices or coils with multiple levels.
Figure 3a: The wireless power
demonstration kit combines technology from Wurth and Texas Instruments to show
how wireless charging can be implemented in a design with a transmission board.
This is a fundamental difference
from the Rezence approach, which uses a much larger induction coil so that
multiple devices can be placed anywhere on a charging mat. However, this
creates a challenge for the communications protocol. The charging controller
has to vary the frequency (the PMA specification uses a 277-357 kHz range) as
well as vary the charging rate for all the different terminals on the charging
mat. However, this higher frequency does allow for a higher charging rate and
supports a greater depth of field so that the charging mat can be embedded into
a surface such as a tabletop.
The two technologies that make up
the Rezence specification have been consolidated over the last year, and this
is now allowing designers to adopt the revised technology in designs that will
come to market in 2016.
*Future wireless power
Wireless power is not just about
inductive charging. There is increasing interest in beaming power through free
space.
Researchers at MIT have
demonstrated the transmission of 60 W of power over a distance of 2 meters
using strongly coupled resonant devices (Figure 4). The power source,
left, is connected to AC power. The blue lines represent the magnetic near
field induced by the power source. The yellow lines represent the flow of
energy from the source to the capture coil, which is shown powering a light
bulb. This also shows how the magnetic field (blue lines) can wrap around a
conductive obstacle between the power source and the capture device.
This technology has been
commercialized by WiTricity, which has teamed up with Great batch, a global
developer and manufacturer of medical devices and components, to use the
technology in medical device applications. Great batch will use the wireless
charging systems for medical devices of its own design, as well as systems and
solutions for Original Equipment Manufacturers (OEMs).
Figure 4: The strongly coupled
resonators used by WiTricity for wireless power across free space.
The technology allows flexible
positioning and the ability to charge through non-metallic materials such as
plastic and glass. This allows designers to remove contacts and create closed
systems that charge batteries through completely sealed cases, easing sterilization,
reducing maintenance, and increasing reliability and availability in medical
applications. This can also reduce the battery size, particularly for implanted
devices that can be charged through the skin.
The company is also part of the
A4WP Rezence specification to use the technology for standards-based wireless
charging systems.
It’s not just electromagnetic
waves that are being used for wireless power, either. A startup in California
called Ubeam is aiming to use ultrasound to beam power across a room. This
would use high frequency ultrasound energy that would then be converted back
into electrical power by a transducer. The company has developed a high-powered
ultrasonic transducer, transmitter, receiver and power converter, along with a
highly secure ultrasonic data transmission system for the controller.
*Conclusion
Wireless charging is reaching a
critical point. As the specification consolidates to two choices from WPC and
Rezence, designers will see a wider range of components available for system
development. While WPC’s Qi provides a stable, cost-effective implementation of
wireless charging that is available now with high-speed charging, Rezence
offers more flexibility for charging multiple devices but with increased
complexity and cost. It also opens up the opportunity for longer distance
charging through the technology of WiTricity and others, which will give
developers in the embedded and industrial markets more flexibility in the
overall system design.
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