Apple Files Patent for “Reverse Charging” Tech for Multiple Devices
After Apple's failed AirPower program, it appears the Cupertino-based company is bouncing back with “reverse charging” for multiple devices.
In collaboration with its partner Belkin, Apple is taking another swing at multi-device wireless charging technology.
The company recently filed a patent to incorporate wireless charging capabilities into its Macbook and iPad products. With these imminent solutions, Apple hopes to remedy design issues with AirPower and offer more efficient, higher-performance wireless charging platforms that meet global standards.
Mobile device wireless charging with Apple Macbook. Image used courtesy of Patently Apple
According to Bloomberg, the new charging technology will enable horizontal charging and offer 33 percent faster charging speed for the Apple Watch Series 7.
Why exactly did AirPower fail in the first place? And how is Apple approaching wireless charging anew with its recently-granted patent?
Why Apple's First Wireless Charger Blundered
To understand the cause of AirPower's failure, it may be useful to review the principles behind the technology. The two most common methods for wireless power transfer (WPT) include electromagnetic induction and magnetic resonance.
Electromagnetic induction, which the Qi Standard relies upon, offers low power transfer because it lacks a common transformer magnetic core. Distance and inadequate orientation between the transmission and receiving coils adversely affect the efficiency of this method.
The other method, magnetic resonance, functions regardless of distance and orientation by incorporating series capacitors into the transmission and receiving coils. These capacitors resonate with similar frequencies to continuously provide high-efficiency WPT.
Overlapping transmission coils in Apple’s AirPower. Image used courtesy of the United States Patent Application Publication
Since Apple did not officially state specific reasons for pulling the plug on AirPower, many speculations surfaced—most loosely pointing to overheating issues. AirPower adopted the electromagnetic induction method for WPT. However, to efficiently charge multiple devices regardless of position or alignment, Apple incorporated multiple overlapping transmission coils into AirPower.
This decision caused some functional issues, including coil-induced interference, power wastage, and massive heat generation. Additionally, the device required high amounts of current to meet multiple-device wireless charging demands. Since Apple engineers could not offer adequate solutions to these challenges, the company canceled its AirPower launch.
The Challenges of Multi-device Wireless Charging
Qi is a wireless charging standard developed by the Wireless Power Consortium. Although the Qi standard offers some key benefits, including safety and compatibility, its stringent requirements limit some applications, such as free-positioning and multi-device charging.
The Qi standard requires proper alignment of both transmitting and receiving coils in the wireless charger and mobile device, respectively, before charging can commence. This strict requirement can decrease efficiency and convenience, thwarting the idea of a hassle-free charging experience for the user.
Additionally, manufacturers find it challenging to implement multi-device charging, which is dependent on free-positioning. Free-positioning technology also faces several challenges, including coil misalignment, magnetic field interference, and the limited adoption of wireless charging protocols.
Qi coils require proper alignment for efficient charging. Image used courtesy of Aira
The holes at the center of transmitting and receiving coils, widely referred to as “hot spots” or “sweet spots,” are the most active areas of the coils. The Qi standard requires proper alignment of these spots for efficient charging, which impedes multi-device charging.
Many manufacturers try to circumvent this issue by incorporating multiple arrays of transmitting coils into the wireless charger. Still, device makers find it challenging to meet the three top requirements of a free-position, multi-device charging coil matrix: high precision, manufacturability, and thinness.
Moreover, since multi-device charging requires numerous transmitting sweet spots on the same pad simultaneously, promptly locating a sweet spot for each device is a challenge that adversely impacts the user experience.
Will Apple Take Another Swing at the Charging Pad?
Although Apple ended its AirPower project in 2019, the company continued to work on its wireless charging solution. One clear indication of this continual work is its recently-granted U.S. patent for inductive power transfer (IPT). This IPT technology includes an inductive power transmitter coil and an inductive power receiver coil.
With this updated technology, how is Apple remedying the design issues it faced with AirPower?
A key functionality Apple hopes to incorporate into this new solution is something called reverse charging. MacBook and iPad devices will be able to reverse-charge multiple mobile devices, including phones, watches, electronic styluses, remote controllers, earbuds, and more. This functionality allows power transfer between Apple devices during or after charging.
In addition, Apple plans to integrate detectable sensing elements with other components in its wireless charging pad. These sensing elements will locate electronic devices and detect orientation via pressure sensing, promising higher efficiencies in free-positioning and multi-device charging.
Location and orientation detection via pressure sensing. Image (modified) used courtesy of Patently Apple
The patent offers a description of what Apple aims to achieve with its new wireless charging technology from an electrical engineering standpoint. The technology will incorporate an inductive power transmitter system—comprising a power transmitting coil and transmission, detection, and control circuitries.
The strength of the IPT will depend on a few factors:
- WPT efficiency
- Peak and RMS magnitudes of the transmitting coil-bound AC
- Peak and RMS magnitudes of the receiving coil AC
- Magnitude of the inductive power receiver output DC
A typical block diagram for IPT. Image (modified) used courtesy of Patently Apple
Additionally, the technology is designed to control the inductive power transmitter via a method that can detect, control, and respond to the WPT of intended devices. Apple’s innovation may include a charging mat, which can either act as a standalone device or can be incorporated into other platforms, such as furniture, laptops, tablets, or other electronic devices.
Details are Still Under Wrap
Many engineers still see true wireless charging as a myth. Now, Apple hopes to make this technology a reality. Because of its past failures with AirPower, the company will leverage new approaches to achieve wireless charging, especially for multiple mobile devices.
In addition to incorporating detectible sensing elements, the reverse charging capability of this device will make it more efficient and higher-performing than AirPower if Apple successfully pulls it off. Although Apple is yet to officially announce a release date for this technology, Bloomberg reports that the company will be releasing more details within the next year or two.