PowerbyProxi > wireless power systems

Defining power ranges for charging ecosystems – what does a universal solution look like?

September 3, 2012 / 0 Comments / 149 / Technical

A wireless power standard is essential to achieving true ubiquity of wireless charging of electronic devices. This is something wired charging has struggled to achieve just ask anyone who has owned a couple or more laptops. Lets not even get started about the iPhone 5 wired charger!

One of the key questions is what is the magic power level or range that will create the most user friendly ecosystems. Ecosystem being defined as compatible transmitters and recievers. Is there an ecosystem for cellphones / smartphones, another for laptops and so on? Or is the real need to have compatibility across the board for all “general” household consumer devices.

The downside of having a one size fits all type of solution is that you will need to trade-off performance and cost against ecosystem expansion from 0-3.5W to 0-100W. A transmitter that can charge 2 smartphones @ 3.5W each only, will look very different to one that can charge 2 smartphones @ 3.5W each as well as a laptop at 90W.

Most of the smaller consumer electronics devices would only require an ecosystem operating in the sub 10W range – this includes smartphones, cellphones, tablets and the like. On the face of it then, a logical demarcation point for ecosystems might be <10W for smaller devices, and 11W to 100W per receiver for larger capacity devices like laptops?

What do you think?

Read more about wireless power technology.

Kunal Bhargava is Engineering Manager for PowerbyProxi

Frequency selection in wireless charging – what’s efficient and safe?

July 31, 2012 / 0 Comments / 1324 / Technical

When we talk about wireless power, one of the first design questions we consider is… “at what resonant frequency should the system transfer its power?”.  Selecting the system’s resonant frequency helps increase the distance for power transfer and improves the efficiency of the wireless power solution. But what are the health implications? and are wireless charging products being accurately measured?

Resonant frequency refers to the frequency at which an object naturally vibrates or oscillates.  It is at this frequency that objects are able to achieve their maximum amplitude – whereas it is difficult to get them to vibrate at other frequencies.  In the case of inductive power transfer (IPT), the principle of resonance is applied to induce an electrical current between coils of the same frequency over greater distances.

Naturally the resonant frequency will depend on the problem or application, however there are other factors which influence this decision.  As with all electronic products, the foremost issue is safety.

Usually safety is determined by how much radio frequency (RF) exposure can be applied without being harmful to human health.  Guidleines do exist which provide reference to what are acceptable and safe limits of exposure…or so we think.

Most would consider the 1998 and the 2009 ICNIRP (International Council on Non-Ionizing Radiation Protection) guidelines as a reference to those limits. Yet the guidelines lack any specific mention or reference to the behaviour of wireless power systems.  What this means is that the “limits” identfied may not accurately apply to RF radiation created by wireless charging.

That is not to say that wirelss power systems operating under these guidleines are unsafe –  electromagnetic fields created by this technology are considered to be at the lower end of the exposure spectrum. But surely more specific and conclusive measurements of IPT applications are required to understand the appropriate exposure limits?

Otherwise how do we know if limits are too harsh? (impacting the quality of solutions), or  conversely, not harsh enough?

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