PowerbyProxi > Technical > Frequency range and wireless power systems – what works best?

Frequency range and wireless power systems – what works best?

August 9, 2012 / 5 Comments / 1295 / Technical
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In my post last week I started to examine issues around frequency selection for wireless power systems.  This week I want to take the discussion a bit further and talk about the benefits (as we perceive) of using lower frequencies (in the kHz range) vs. higher frequencies (MHz) as an industry standard.

As the standards debate rages on, different parties continue to put forward their various interpretations on the ideal frequency range. Various standards utilize higher frequency ranges than others.  PowerbyProxi, through the CEA working group, continues to argue that standards that use lower frequency ranges (kHz) are more appropriate based on what we believe is in the best interest for you – the consumer.

There are several factors that need to be taken into account.

Complexity. How complex is the device to manufacture. Controllers used for wireless power systems are far more complex at the MHz range ultimately impacting the cost of manufacture and thus the price that the end-consumer (you) pays.

Interference. As we as we are aware there are no wireless devices operating in the MHz range that meet EMC radiated emission compliance.  What it means is that at the moment, there is no proof that they wont cause interference on other devices.

Other factors such as charging distance, transmission efficiency, thermal properties and form factor tend to be implementation specific or require further research to be able to draw clear comparisons.

On the balance of the research done so far, lower frequencies at the kHz allow for more user friendly and functional wireless power systems to be developed.  Isn’t that ultimately what it should be all about?

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


Comments (3)

  1. Konstantin Lakirovich

    Witricity uses resonance frequency in MHz range, which allows them to transfer power of tens of watts over distance of 2 meters. Even in this frequency range they utilize near filed properties. If they have 10 MHz working frequency – wave length will be around 30 meters. As it is known, the boundary between near field and far field lays around 1/6 of wavelength, which will be 5 meters from the source for frequency 10 MHz. It means that Witricity also relies on the energy of magnetic field as other inductively coupled devices, such as transformers or loosely coupled coils.  Only the energy level which they manage to transmit is much higher than we may achieve by using KHz range.  Witricity defines the transmitting waves as evanescent waves, which intensity diminishes exponentially with the distance from the source. 
    It would be greatly appreciated to learn more about evanescent waves and how they differ from electromagnetic waves in near field in KHz range.
    My experience is in hundreds KHz range  and I can state, that loosely coupled resonance pairs do not manifest with very high electromagnetic emission. The main reason is that even if there is an open space between resonating elements, field goes down very fast and in addition, sinewave form of emission makes it very easy to filter for surrounding devices.
    It would be good to hear more about advantages or disadvantages of these two approaches: low and high resonance frequency. 

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