Market demand for convenient charging options is on the rise. Which power transfer technology will emerge victorious? Who will influence the standards? Find out more.

Wireless power transmission has actually been in existence for over 100 years. Nikolas Tesla used to demonstrate the concept of magnetic resonance coupling back in the 19th Century. The concept, particularly in the area of wireless charging, has recently gained popularity as manufacturers seek to cut the cord and increase mobility of their devices. Some of the advantages include:

  • No cables/contact-free charging
  • Universal charging
  • On-demand charging
  • Smaller devices without bulky batteries
  • Improved flexibility for wearables

Unfortunately, the wireless transfer of power is not very efficient due to inherent technological limitations and in some cases a health hazard. While we are still some distance away from making Tesla’s dream of widespread wireless power transfer, there are several applications being realized now from consumer devices to cars and public transport. Last month, we covered the rumors that Apple was introducing a wireless charging mat. Today, we discuss patent filings related to different power transfer technologies for wireless charging.

What is wireless charging?

On the most basic level, wireless charging is the transmission of electromagnetic energy through air to charge a device. Actually, the device’s battery. The wireless charging market was estimated at $11 billion in 2019 and is expected to grow at 14.4% CAGR into 2026 (Source: link). One of the key drivers appears to be the use of gallium arsenide (GaA) and gallium nitride (GaN), which are wide-bandgap semiconductors that allow for more efficient transfer of power at higher frequencies. This is due to their high temperature tolerance which means these devices can be operated at higher power levels and with a much higher critical electrical field density, that allows them to operate at much higher voltages and currents. This makes them highly valuable in military, radio and energy conversion applications.

While most of the existing solutions are based on inductive or resonant charging, the market is now witnessing the entry of other power transfer approaches, such as microwave/RF coupling, ultrasonic coupling, light/laser coupling, and capacitive coupling. Each of these is discussed briefly below.

Inductive Coupling:

Inductive coupling works on the basis that an alternating current passing through a first conductor creates an alternating magnetic field around it, which when exposed to a second conductor, induces an electromotive force (EMF or voltage) in the second conductor. Inductive charging uses a transmitter coil in the charger to generate an alternating current in a devices receiving coil to either power the device and/or charge a battery in the device. Charging devices used in smartphones typically use inductive coupling.

Resonant Coupling

Resonant coupling works on the same principle as inductive coupling. However, it takes advantage of the fact that coils with identical resonances exhibit strong coupling due to the highly directional nature when the resonance values of the coils match. The strong coupling characteristics of this technique allows the transmitter and receiver to be positioned a bit further away from each other compared to Inductive coupling

Capacitive Coupling:

To understand capacitive coupling, one needs to understand the basic principle on which a capacitor works. A capacitor is made of two conductors, often parallel metal plates separated by a dielectric medium. It works on the principle of Coulomb’s law which states that a charge on one conductor will exert a force on the charge carriers of the other conductor inducing an opposite polarity. To transfer power wirelessly using capacitive coupling, a first conductive plate is placed in a transmitting device and another conducting plate in a receiving device. When these two devices are aligned with each other as in a capacitor, a charge to the transmitting plate will induce an opposite charge in the receiving plate, which can then be used to power or charge a battery in the receiving device.

Light/Laser Coupling

Wireless power transmission using light or lasers for coupling a transmitter and a receiver work similar to a solar power generator. The receiver device is lined with highly efficient photovoltaic cells, which when exposed to light (e.g. lasers) emitted by a transmitting device, generate the power required for the receiving device.

Ultrasonic Coupling

This method, in particular, uses an electro-acoustic (rather than electromagnetic) conversion material to convert electrical energy into acoustic energy in the ultrasonic spectrum at the transmitter and convert the received acoustic energy into electrical energy through acoustic-electric conversion materials at the receiver. Ultrasonic power transfer occurs from a first device that can emit ultrasound to a second device that captures the frequency and generate voltage through the use of a crystal via a medium such as air, water, polymers, or even the human body.

Microwave/RF Coupling

Power transmission using microwaves or radio frequency waves uses the respective waves as carriers for transmitting power. At the transmitting end, electrical power is converted into RF signals and transmitted via an antenna to a receiver antenna that collects the RF waves and converts them back to electrical power to be supplied to a connected load.

Wireless Charging Standards

There are two standard setting organizations that compete on wireless charging:

  • AirFuel Alliance – The standard setting organization was formed by Alliance for Wireless Power (A4WP) and Power Matters Alliance (PMA) in 2015. Members include Duracell, Dell, Samsung, Energous, and Qualcomm. These standards focus on electromagnetic resonance and radio frequency operating at the ISM band.
  • Wireless Power Consortium (WPC) – The WPC, created the popular Qi standard, boasts a wider membership that includes Google, Blackberry, Nokia, Samsung, Qualcomm, Bosch, and Apple. The Qi standard focuses on powering small devices based on inductive charging. It operates between 100-300 KHz. Another standard that is being developed by WPC is the higher power Ki for household applications.

Patent Landscape

We searched and retrieved approximately 50,000 patents and applications published worldwide to identify research trends, active players, partnerships, M&A, competitor comparison, opportunities/gaps under each coupling type identified above and developed a detailed technical taxonomy.

A quick look at the overall filing trend shows a steady increase in worldwide patent filings since 2005. The number of new applications disclosing wireless charging related technologies increased from 942 applications in 2008 to 5,568 in 2018.

*Forecasted number of new filings

Fig 1: Application Filing Trend

The top twenty-five (25) assignees share 40% of the overall patents/applications indicating that the top players have a strong foothold, likely the result of their R&D efforts or through consolidation or M&A activities. Our analysis of the assignees supports the assertion that consumer electronics (smartphones, wearable, etc.), healthcare, and automobile segments are driving the demand for wireless power transmission.

Fig 2: Assignee Trend

Resonant and inductive coupling contributes to the majority of the patent landscape while microwave/RF coupling seems to be the third most common area of focus for assignees in this space.

One of the possible reasons for the low number of patents/publications disclosing capacitive coupling may be due to the limitation of the technology, itself. Capacitive coupling needs to be operated at very high frequencies to avoid non-linear distortions which are not desired in any power transmitting or receiving circuits. Similarly, for light-based and ultrasound-based power transmission, there are exponential power losses associated with distance and there must be a clear line of sight between the transmitter and receiver which limits its application areas. Other aspects, such as the overall applicable industry size for each coupling type, the cost of implementation, a lack of public infrastructure, the cost of individual components, regulatory burdens, and safety issues can also be factors in their widespread application.

Fig 3: Coupling Type Distribution

As shown in the Assignee vs Coupling Type distribution graph below, most assignees (e.g. Toyota) are focused on adapting resonant and inductive coupling technologies rather than other technologies more suitable for transmitting power over long distances. This may be due to their intent on enabling wireless power transmission within a vehicle or from an external transmitter only when it is stationary and near-by (at a charging dock).

Fig 4: Coupling Type Distribution for Top Assignees

Of the available coupling types, microwave/RF coupling appears to be the only type suitable for long range transmission and that is not limited to a clear line of sight. Drilling down into these patents revealed that Qualcomm is leading the pack in terms of total number of filings. Despite being the top patent filer, Qualcomm’s recent filings are sparse, with the majority of filings having occurred between 2010 and 2011. This may be an indication the company’s focus has shifted to resonant and inductive coupling. By comparison, most of the microwave/RF coupling filings from assignees like Energous, Samsung, BASF and Ossia are more recent in nature.

Fig 5: Top Assignees for Microwave/RF coupling

Companies working in enabling wireless power transmission vary from automobile manufacturers (Toyota, Nissan, etc), consumer electronics manufacturers (Samsung, LG, Apple, etc), semiconductor companies (Qualcomm, Intel, etc.), home appliances (BSH Hausgeräte), chemical manufacturers (BASF), and others indicating that there is interest for wireless power transmission across industries. A number of startups were also identified during our analysis, some with working prototypes and FCC approved products making them targets for investment.

The Qi standard dominates the market while Airfuel is not far behind. While radiative wireless charging through microwave/RF was traditionally less used, in recent times there are several examples of commercial systems including WattUp (Energous), Cota (Ossia), PRIMOVE (Bombardier), and Lifetime Power (Powercast) systems. Wireless charging technology using newer approaches may represent an opportunity area for entrenched companies looking to diversify or new entrants looking to make R&D investments.


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