PowerbyProxi > loosely coupled

Wireless Charging & Induction Cooking: Opposite ends of the efficiency spectrum

April 2, 2013 / 0 Comments / 1239 / Features, Technical

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:

  1. Tightly coupled does not equal low frequency (eg 100kHz -500kHz)
  2. Loosely coupled does not equal high frequency (eg 6.78MHz – 13.56MHz)

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 info@powerbyproxi.com.

Fady Mishriki is Co-Founder, EVP and Chief Tesla Officer at PowerbyProxi

Charging efficiency – a means to an end, or the end itself?

January 29, 2013 / 1 Comments / 163 / Technical

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.

Kunal Bhargava is Engineering Manager for PowerbyProxi

Measuring efficiency for 2D wireless charging zones – which metric is best?

January 21, 2013 / 2 Comments / 334 / Consumer Electronics Solutions

Efficiency is a commonly referenced performance metric for Wireless Power systems so I thought I would take the opportunity via blog to examine:

a) how it is measured, and

b) how it is analysed to compare the performance of various systems – specifically ones with two-dimensional charging zones i.e. charging pads.

Having been in the industry for almost a decade now I have seen multiple dimensions ranging from transmitter only efficiency, receiver only efficiency, efficiency of coils and so on and so forth. Our efficiency measurements here at PowerbyProxi are more simplistic. We define efficiency as total DC power out divided by DC power in @ the rated load “fast charging” load. This rated fast charging load tends to be 3.5W to 5W for most smartphones. If there are multiple devices, the DC power out is the sum of DC power to all devices.

Looking at the voltage and max current stated on your wall wart wired charger you can calculate the rated load. Wired power supply manufacturers rarely over-spec the current rating of their power supplies, in order to keep cost and size down.

With this methodology you will be able to measure efficiency at any given point.

So how do you analyse a system with a 2D charging area?

What we think really matters is not just how efficiency changes as you move a receiver around the charging area of a transmitter,  but also the size of the transmitter coil(s) vs. the area in which the the centre of the receiver coil can move while the receiver still receives rated power (charging area).

Take the following scenarios for example:

  • You have system A with a 100cm2 transmitter coil with a charging area of 25cm2 at an efficiency of 65-70%
  • You have system B with a 100cm2 transmitter coil with a charging area of 50cm2 area at efficiency of 55-60%

Which system is better?

According to a basic analysis of minimum and maximum efficiency, system A wins – hands down!

However  if we apply weighting for the charging area, we will get a better insight into overall system performance. Let us walkthrough the above example using really simple numbers:

  • System A has a 100cm2 transmitter coil with a charging area of 25cm2 area at an efficiency of 70% everywhere in this charging area
  • System B with a 100cm2 transmitter coil with a charging area of 50cm2 area at an efficiency of 60% everywhere in this charging area

In this case the charging area weighted efficiency is:

  • System A 25/100 x 0.7 = 17.5%
  • System B 50/100 x 0.6 = 30%

So actually system B is better if you use the charging area weighted efficiency.

The charging area weighted efficiency helps define “how loose” a loosely coupled system actually is.

We believe this is the right metric for comparing efficiency of wireless power systems. What are other people’s views?

Kunal Bhargava is Engineering Manager for PowerbyProxi

What does loose coupling mean??

August 29, 2012 / 0 Comments / 645 / Features, Technical

Coupling is a term widely used in discussing wireless power systems – it refers to a coupling coefficient ‘k’ which defines how well a transmitter and receiver are magnetically “linked” as a percentage. Generally  something like transformers have extremely high coupling coefficients approaching 100%.

Technically, tightly coupled systems are interpreted as having high or transformer like coupling coefficients while loose coupling is interpreted as systems with low coupling coefficients. There is some debate around the cut-off for high and low – 50% is one proposed transition point.

From a usability perspective I would define tightly coupled as a system which requires some form of mechanical alignment to fix orientation and transmission distance. This can be done via a magnet or a mechanical alignment feature on the transmitter and receiver. A loosely coupled system would allow complete flexibility of orientation / misalignment in a 2D target zone. A 2D target zone would be a planar area such as a matt (i.e. Proxi-2D), which can wirelessly charge devices imbedded with a receiver that is a few cm above it.

Systems like the Proxi-3D which enables receivers to work in a  three dimensional target zone with an omni-directional receiver are what a user may call as beyond loosely coupled!

In my opinion the usability definition is more relevant for anyone buying the system as really the technical definition is really just a means to an end – the end being ensuring customers don’t have to carefully align their devices with a wireless charger.

Kunal Bhargava is Engineering Manager for PowerbyProxi

Making a Wireless Power Charging Standard, What is Best for Consumers

August 8, 2012 / 0 Comments / 139 / Consumer Electronics Solutions

Continuing from my blog last week regarding wireless power charging of smartphones and the current debate around industry standards.…

The CEA has formed 2 working groups to drive specifications, with the goal of establishing a large market for Consumer Electronics:

WG4 System Requirements for Highly Resonant Wireless Power Systems
Summary: “WG4 is developing ANSI/CEA-2042.4. This standard will define system requirements for highly resonant wireless power systems. Highly resonant wireless power systems are systems that transfer power wirelessly using magnetic induction, and that require magnetic resonance.” This is also referred to in the industry as loosely coupled.

WG5 System Requirements for Tightly-Coupled Wireless Power Transfer
Summary: “WG5 is developing ANSI/CEA-2042.5. This standard will define system requirements for a tightly coupled wireless power system. A tightly coupled wireless power system is an inductive wireless power transfer system with a strong magnetic linkage between the primary and secondary coil.”

Why would any consumer care for another tightly coupled solution?   Isn’t this just another manifestation of the specification released by the Wireless Power Consortium with all its limitations?

I believe WG4 is solving real customer needs to enable practical solutions for Consumer Electronics.  Don’t you?

PowerbyProxi is a member of WG4 and one of the main contributors to this specification.  We are leveraging our world class team in wireless power and many years of delivering practical solutions that customers want.

Let me now your thoughts.

 Tony Francesca is VP of Business Development – Consumer Technologies