Wireless Charging: All Set for Takeoff

Mobile device solutions
Convenience is one of the key drivers for consumer mobile solutions being the first adopters of wireless power technology. Devices such as cellphones, tablets, media players, and mobile TVs require different adaptors with different interface connectors, meaning one needs to carry many connectors and adaptors to serve the same purpose of transferring charge into a device. A universal wireless adaptor with a powerful supporting infrastructure and ECO system can address this inconvenience. Having the solution available in cars, coffee shops, restaurants, trains, airplanes, offices etc. will support the need for this convenience.

Another important factor is technology upgrades in mobile solutions that generate a greater demand for power from the device’s battery, meaning the convenience of wireless charging is of even greater interest.

Referring to Figure 1 , we can see that for maximum flexibility, we need a sophisticated system to control the transmission and reception of the power.

Figure 1

Wireless Charger System: Transmitter and Receiver Block Diagram.

Wireless Charger System: Transmitter and Receiver Block Diagram.

There are many similarities between the architectures of MI and MR technologies. For example, both use a magnetic field as a bridge to transfer power.

In both technologies, current through a resonant circuit creates a magnetic field to transfer power. The alignment of the receive and transmit coils in the flux field and the distance between them determines how efficiently energy is transferred; greater separation between transmit and receive coils results in less efficient power transfer. Resonant frequency, the ratio of transmit to receive coil dimensions, coupling factor, coil impedance, skin effect, AC and DC elements, and the parasitics of the coil are other factors that have a large impact on how efficiently energy is transferred.

It is given that as the X, Y, and Z separation and the proportional angle between transmit and receive coils increases, the losses and efficiency will be greatly impacted.

Depending on the requirement, including cost and size considerations, a single or multiple coil solution can be employed in both MI and MR technologies. Figure 2 provides an overview of typical coil structures.

Figure 2

Magnetic coupling fields - inductive and resonant.

Magnetic coupling fields – inductive and resonant.

Power management
Development of high-performance power management architectures has a big impact on the implementation of successful MI and MR solutions. On the transmitter side, in order to induce current into the resonant circuit, a DC-to-AC conversion takes place. In MI technology, a half-bridge or full-bridge inverter is used for this conversion whereas in MR technology current is supplied from a power amplifier. Conclusion
It is reasonable to conclude that the best potential solution for a specific application will be based on the required features and performance. If free positioning or multi-device charging capability in X, Y, and Z directions is required, magnetic resonance is probably the preferred solution. If high efficiency performance with strong standards-compliance is required, then WPC-compliant solutions may represent the optimum choice. However, there is no question that a multimode solution able to seamlessly recognize the coupled MI- or MR-based device and transfer power effectively and efficiently will be the ideal solution to serve such applications.

12 comments on “Wireless Charging: All Set for Takeoff

  1. amrutah
    February 6, 2013

    Siamak, Thanks for the interesting post.

    Like Wi-Fi, the Qi standard for wireless charging (most popular deivce I know is Nokia Lumia 920) will help charging different devices with a single wireless charger and we need not carry different adapters for different devices.

    Said that, Are there any other standards used for wireless charging and that will compete with Qi?

  2. amrutah
    February 6, 2013

    We know that the wireless charging has still time to evolve, to reduce the resistive heating and waste to improve efficiency for single device…

    Further as you quoted, “The alignment of the receive and transmit coils in the flux field and the distance between them determines how efficiently energy is transferred”

    This would directly mean that we cannot charge 2 or more devices at the same time (even at the cost of reduced efficiency)???

  3. jkvasan
    February 6, 2013


    Yet to see any standard that would compete with the Qi. While Google and Samsung are trying to bring their own devices with varied specifications, the industry is yet to come in terms with something which could revolutionize many industries, especially, the automotive industry. If electric vehicles could be charged fast with standardized devices, it is going to be big time.

  4. SunitaT
    February 6, 2013

    Siamak, Thanks for the post.

    As of today to charge a phone without a cord, most phone owners would have to buy a smartphone case or battery pack with an embedded receiver, and then use a charging mat with a compatible transmitter. But these adoption barriers could soon disappear with adoption of a universal wireless charging standard.

    A universal standard will allow us to have charging mats in public places, where users can recharge without having to carry around a power pack.

  5. SunitaT
    February 6, 2013


    Presently innovation is going on Adaptive Resonance wireless charging where we can simultaneously charge multiple devices. These charging mats makes use of adaptive resonance techniques which are smart enough to know which device needs what kind of power.

  6. amrutah
    February 6, 2013


    I agree that there are some wireless power transmitters that use Adaptive resonance charging technique to charge multiple devices of different power formats (inductive coupling (MI), magnetic resonance (MR), and Qi technology into one solution, which means, whatever be format of the device adaptive Resonance technology will allow you to charge it with the same format).  I am excited to know if a single transmitter could charge multiple devices at the same time whose power requirement (or charge time) are different. Any idea??

    I assume, the mats that you mentioned have multiple receivers points, with each device using a different charging format.

    An interesting info about wireless charging on the wireless power consortium page.

  7. eafpres
    February 6, 2013

    The EPA estimates there might be 2.4 billion power adapters in the US.  The efficiency of these, as well as their consumption when plugged in but not charging a device is a big concern on total energy footprint.  Any thoughts on the efficiency of these wireless charging systems vs. wired?

  8. jkvasan
    February 8, 2013

    SB I agree it is convenient to just place the device on the charging mat. However, with wired charging method, one could still use the device while it is charging. Can this be done with wireless charging?

  9. jkvasan
    February 11, 2013

    Is automatic detection and hence charging possible. If so the charger can sleep till a device is placed on the mat thus reducing power wastage.

  10. Brad Albing
    February 12, 2013

    Uh-oh – hadn't thought of that. You'd need to lay your head on the mat to use your phone. Just slightly impractical.

  11. eafpres
    February 14, 2013

    I think if people start putting their heads on wireless charging mats the FCC will quickly issue SAR limits which will kill the technology!!  Let's hope that isn't the outcome.

  12. Brad Albing
    March 28, 2013

    Good way to sneak a nap tho' – “Sorry boss, just charging my phone…Zzzzz.”

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