Wireless power

Wireless Charging

by on July 21, 2017 10:35 am
Categories: summer2017
Tags: , , ,

Last year I got my first bluetooth speaker. I kept it in my bathroom (of course) and it was really nice, no cables – no problems. Except of course when it ran out of batteries and I had to jump out of the shower and search for the cable all wet. With IoT and bluetooth connected devices coming more and more popular, one really has to wonder how long we have to wait for wireless charging (WC). The idea has been around since Nicola Tesla (1856-1943) so what’s the hold up? In this blog I will go over the basics of WC and it’s applications.

The general WC as we know it uses electromagnetic fields (EM fields) to transfer power between objects. [1] Like the name suggests, the medium for EM fields is often air, making the physical connection redundant. Those fields are typically induced by the use of coils in the transmitting source, resulting in a current in the receiving device. This method is not restricted to using air as a medium though and can also be applied through materials such as wood, plastics and granit.

 

How Em fields are used for WC

 

According to PowerByProxi [2] it’s no longer about when this technology will be robust. Instead, the question is about which type of wireless power setup will best meet your needs. When designing a wireless power system, therer are two key considerations, coil geometry and frequency of operation. The first one depends on the users need, summarized with [3]:

Coil array is optimal is any environment where you want:

  • High efficiency (70%+)
  • Multiple simultaneous device charging (e.g. a laptop, tablet, cell phone, or wearable device)
  • Compliance with safety regulations without limiting transmit output power
  • The ability to provide high power levels for multiple devices

Perimeter coil is optimal in situations where:

  • Power needs are lower
  • Efficiency is not important, and the lower cost of the coil will not be outweighed by higher energy costs
  • Cross-talk between transmitters is avoided due to proximity
  • Multi-device charging and high power levels or charging speed are not important

However the latter one addresses power efficiency and human safety where humans exposure to radio frequency is measured by the specific absorption rate (SAR). The problem here is that both power efficiency and SAR increases with increasing frequency. At a low KHz frequency you could transfer power to useful devices but as it gets closer to MHz, you’ll have to be more careful. This is the biggest headache since the two most recognized frequency-ranges are around 110KHz and 6.78MHz. Of course if you are running, for an example, an automatic factory of some kind, you don’t have to worry about human health.

Some other very interesting techniques are now being invaded in this area. Researchers at Disney are now using aluminum walls to expand the use of EM fields to make electrical power as ubiquitous as Wi-Fi. [4] But other than getting rid of your annoying cables, WC has many benefits. It reduces costs associated with the cables, eases the production of devices that are hermetically sealed (waterproof) and eliminates sparks from the cables. With the speed of this innovation you don’t have to wait long until you’ll be charging your car as you stop on a red light, leaving your phone uncharged overnight and enjoying good music in the shower with dry floor.

 

 

[1] https://powerbyproxi.com/wireless-charging/

[2] https://powerbyproxi.com/2014/11/design-considerations-modern-wireless-power-transfer-systems-frequency-operation/

[3] http://www.planetanalog.com/author.asp?section_id=3306&doc_id=563498

[4] https://www.cnet.com/news/disney-builds-prototype-room-with-ubiquitous-wireless-charging/

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5 comments on “Wireless Charging”

  1. Hi Helgi,
    You chose a very relevant topic to talk about. WC can bring a transformative change in the way we interact with electronic devices. But a serious issue I can foresee is of compatibility. How can we create EM fields as per the requirement of the device. Surely, the power requirements of a phone and a car will vary significantly. If the technology is to become ubiquitous, a new mechanism needs to be put in place. Maybe the EM fields need to be specific for a specific device., and the device also should have the capability to recognize the corresponding EM waves.
    I think this is a design principle the manufacturers are definitely thinking about.

    PS: My section is MS&E 238 A.

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  2. Love this topic, nice choice Helgi. If one can charge a toothbrush wirelessly, why not a vehicle? And it appears that inductive charging is safe to the human body: the electromagnetic field is small and weak, especially if over short distances. “The International Commission on Non-Ionizing Radiation Protection (ICNIRP) has found no evidence of adverse effects on human health when exposed to inductive charging.” [1]

    [1]: https://www.chargespot.com/news/how-safe-is-wireless-charging/

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  3. Hey,

    Nice post Helgi. I have often been in that situation when I am in the middle of something and suddenly loose power. Totally not cool, so I got really interested in your post and did a little bit of reading on my own:
    I found this article (http://news.stanford.edu/2017/06/14/big-advance-wireless-charging-moving-electric-cars/) that was published just a month ago. The next generation of chargers will be quantum instead of inductive, and will be able to send higher currents over longer distances (currently 3 feet). This is supposed to target the long charge time for electric vehicles by adopting stations through out the road systems. Although they still have some ways to go, but the advances seam promising.

    MS&E 238A,
    Sara Dabzadeh

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    1. Hi and thanks for the comment!
      Amazing stuff going on in that article and really shows how close we are to things like charging moving cars and so on.
      Funny that it is actually happening here in Stanford.

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  4. Thank you for the interesting topic Helgi. I agree that the ease of wireless charging simply makes sense for a lot of products and thus the slow development from research to actual products is rather surprising. One of the larger obstacles is agreeing on global standards, which is essential for at least charging cars, so public charging on roads and parking lots would be viable. One of the biggest push towards these standards comes from the AirFuel Alliance [1], but with much new research on different kinds of charging technologies it is likely to take a good while before agreement is achieved. One interesting wireless charging company aiming for diverse markets, including consumer electronics and electric vehicles, and seems to have developed products is WiTricity [2]. The company is backed up by Inte[3]l and uses magnetic resonance for charging, which is according to their site, capable of charging multiple devices with different energy requirements. However, the company only sells their products to manufacturers, so consumer products like these seem to still remain part of the future.

    [1] https://www.airfuel.org/index.php/home/about-us-2
    [2] http://witricity.com/
    [3] http://witricity.com/intel-licenses-witricity/
    MS&E 238A

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