It was interesting to see these comments from Qualcomm in this recent Computerworld article by Lucas Mearian: Samsung uses Qi charging for Galaxy S4, but sees A4WP as the future.
“The frequencies at which tightly coupled solutions operate are not that far from the frequencies that are used for conductive cooking,” he said. “The tightly coupled solutions today have a problem where they can heat the metal surfaces in the smartphone & or metal objects. The result is that a lot of times [with] the tightly coupled solutions, the foreign object detection either dials back the power or simply turns the power off”
Let’s get a few things clear first of all:
You can have tightly coupled systems operating at high frequencies and loosely coupled systems operating at low frequencies.
And the good news here at PowerbyProxi is that in none of these cases do we design wireless charging systems like you would design induction cookers! With an induction cooker inefficiency is the target, the less efficient the better – it’s how you create heat. The opposite is true for any respectable wireless power supply. High efficiency is the target.
PowerbyProxi continues to demonstrate real wireless power solutions that prove loosely coupled systems operating at low frequencies, when designed properly, actually have better thermal performance to tightly coupled systems (when measured on all key areas of the phone like the LCD, back cover and battery as well as the transmitter surface area). This is because loosely coupled systems operating a low frequencies have superior average efficiency. Average efficiency is what the user experiences day to day (peak efficiency is what only test engineers experience). Please see Kunal’s blog on average efficiency if you don’t know what I am talking about.
Let’s remember that the user does not care about how you achieve loosely coupled or what the frequency is. The user wants to place his or her phone and other electronics devices anywhere on the pad without any thought and have it recharge as fast as a wired charger. Furthermore they want to know that is is safe to use, will not cause interference with other devices and is environmentally friendly.
The average efficiency of PowerbyProxi’s Proxi Smartphone pad (loosely coupled and operating at low frequencies) is almost triple that of a loosely coupled system operating at high frequencies. I know which one our customers call the induction cooker.
If you would like more information please contact us directly at firstname.lastname@example.org.
In my previous blog I talked about efficiency and using it to measure “how loose” a loosely coupled system actually is. The next question is how much does an end-user actually care about the efficiency of sub 20W consumer device charging solutions. When was the last time you checked the efficiency of your wall wart for your smartphone or your laptop for that matter? Is this data even easily available to curious end-users?
To get an appreciation for how close to the thermal edge smartphones operate at today, you only need to play music or stream a video over 3G / WiFi on a sunny day and see how long it takes before smartphone goes into self-preservation mode. It is said that computer design is more like refrigerator design these days to see who can design the best heat sinks. For a long time Apple did not put i7 processors in their MacBook Pros due to the inability to get heat outside the slick Aluminium shell.
To ensure that wireless charging for consumer devices is widely adopted (such as smartphones & tablets), the technology should not limit the usability of devices while charging is taking place. In my view efficiency is actually a means to achieving thermal performance which is the “end”, and NOT the “end” itself. Other parameters that matter are; cost, Human RF Exposure, EMC performance, Rx size, and how quickly the device charges.