FCC approves first 'power-at-a-distance' wireless charging device

This kind of wireless charging will never work, simply because of the RF path losses. The free space path loss at 5.8GHz over 15 feet is appr. 60 dB. This means that if we need 1mW delivered to a device at 15 feet from the charger, this charger must transmit 1000W of RF. If this transmitter is limited to 4W, the power at 15 feet would be 4uW (micro-watt!). What could you possibly charge with that amount of energy???

 

Think 30 cm wavelength, 2 or 3 feet separation, 10 watts, and highly directional antennas.

Look better?

 

they didn't 3 feet away !!

 

Just showing path loss not a killer at 900 MHZ ISM at 2- 3 feet

15 feet utility is BS, IMO

 

Flaky argument - this is consumer product apparently aimed , no pun intended, to charge anything in three feet range. As an OF I have a "difficulty" to aim TV clicker...

Still waiting for some (high school ) viz to come up with a math answer

given the "spec" ISM , < 3 feet range - how may years it will take to KEEP TRICKLE charging 100 mAH battery.
Other technical assumptions are allowed - such as the actual device time in service - actual load etc.
73 Shirley

 

No it does not look better, actually worse because it no longer meets the spec.

That is where the other part of voodoo "electronics" comes in.
Show us the math! PE1GRV did!

You cannot argue with physic, but you can keep dreaming and argue with QRZ forum.

73 Shirley

 

Indeed. I am delighted to invoke the physics.

Well, try again Shirley. Try these values:

Pt= 10 watts
Gr =10
Gt=10
Lambda =0.3 meters
Distance = 0.8 meters

Pr = ?

 

My calculation started off from ERP. Your example is even more dangerous if you put 10 watts in a highly directional antenna of, say 25db, resulting in 316W ERP. I wouldn't want to be walking through that field at that frequency...

 

Ok, that results in 10dB path loss so you end up with 1W in the receiver. But if you walk in front of that antenna at "nut height", all sorts of unwanted effects start to happen...
And moving away another 0.8m reduces the received power to 250mW. Remember that loss increases with the square of the distance?

 

Kindly read my earlier posts: that was exactly the point I made, with kitty cats;-)

 

Gee, I hope so!

BTW the path loss does NOT go as the square of the distance in the near-field.....with 20 dB total gain(Gt Gr), you are actually near at the transition to near field at 0.8 meters.

The point is that one can contrive a situation where you can do 'at a distance' charging. And I certainly don't want to be around a 100 watt ERP either;-)

 

EMC issues aside...
The wallstreet sizzle story for consumer applications of WattUP mainly hypes charging of handheld or small tabletop consumer devices.

Given that same consumer market, a power-at-distance VHF system benefiting from near field or transition field... would surely force some design tradeoffs into the consumer handheld/tabletop device packaging.

The nitty gritty, is that the biggest design tradeoff faced by this entire power-at-distance technology field is the package size-vs-charge rate balancing act.

The VHF power-at-distance physics are probably more well suited to physically larger devices where packaging size is not a big issue.
Unfortunately, this is literally only inches away from the sweet spot for ~200 kHz type power induction (less than a meter) which already has a good market foothold.

There is room for an entire spectrum of intellectual property in this field

 

Not to put a damper on dreams - here are some things to consider

Quoted from unidentified source , just for info.

Simple Guidelines for Charging Lithium-based Batteries

• Turn off the device or disconnect the load on charge to allow the current to drop unhindered during saturation. A parasitic load confuses the charger.
• Charge at a moderate temperature. Do not charge at freezing temperature. (See BU-410: Charging at High and Low Temperatures)
• Lithium-ion does not need to be fully charged; a partial charge is better.
• Not all chargers apply a full topping charge and the battery may not be fully charged when the “ready” signal appears; a 100 percent charge on a fuel gauge may be a lie.
• Discontinue using charger and/or battery if the battery gets excessively warm.
• Apply some charge to an empty battery before storing (40–50 percent SoC is ideal). (See BU-702: How to Store Batteries.)

Last updated 2017-05-09

 

See what I mean?

Bonnie tells the story and the issues in a nutshell..

HNY Bonnie, and best in 2018

73
Chip W1YW

 

I must confess that lithium ion batteries are a huge disaster. Too damn dangerous.