Friday, June 2, 2017

What Does It Take To Switch a "Phone Charging" Light On?

A few follow up points on the post from yesterday on the uBeam wireless charging.

I did like seeing this quote from the journalist:

Asked why the battery percentage didn’t appear to increase rapidly, Perry shakes her head.

“You’re thinking about it the wrong way, this is about a paradigm shift,” she says. “If you’re moving from your car to a coffee shop to work and your phone is charging while you’re using it, it’s no long about what percentage you’re at. You could stay at 1% all day.”

So it's an artful dodge of the question (that the journalist didn't press on), and perhaps an admission that the charge rate is not 'faster than a wire' as has been stated before by uBeam. It's more the "trickle charge" route, where you get tiny amounts of power over a long period of time. That "faster than a wire" claim was made at a time when the company was stating 1.5 Watts minimum charging which is much more than "trickle charge", and would fully fill your phone in 3 to 4 hours. Saying you stay at the same charge rate all day implies you are charging at an overall average of around 0.5 Watts, including all the times you are not around any uBeam transmitters, but if the charge rate is much greater than 0.5 Watts, why not say?

I noticed in that article the transmitter and receiver 'prototypes' back then in November 2015 were much smaller as well.


If there is actually a "trickle charge" regime, then the phones need charged as they are in use, and most use is a person standing or sitting holding the phone, fingers around the back, at around 45 degrees. Given line of sight, and assuming the 'bezel free front' of most modern phones, this implies the transmitters will need to be on the floor or base of the wall to get access, but will also likely be cluttered. Fingers on the phone case will prevent charging - unless of course you want to hold your phone by the edges as you use it (unlike in the picture above). I'm not seeing how trickle charge works with a mobile user, you need rapid charge in such circumstances. The practicality here, I'm not seeing. Maybe uBeam can layout the actual use-case scenarios they envision?

Also interesting was the quote from technical adviser Matt O'Donnell:

“When Meredith called me in 2015, I was curious and skeptical as hell, because you just hadn’t seen efficient airborne transducers,” says O’Donnell, dean emeritus at the University of Washington’s college of engineering, who now serves as uBeam’s chief technology advisor. “But holy moly, the leaps they’ve made in the past 18 months have been impressive.”

Hmmm, so all this advancement was made in the last 18 months, they had much, much less back then. But I'm confused because in September 2015 uBeam made this statement (among others):

“We’re at a massive inflection point,” said 26-year old uBeam co-founder and Chief Executive Meredith Perry. “We are about to head into a completely new phase of growth.”...In order to ease the transition into production, uBeam said today it has hired former Cisco Vice President of Supply Chain Management Jeff Devine as chief operating officer...“When we were seeking out an operations candidate we were looking at someone with decades of experience from taking a product from prototype to production,” said Perry. “He’s going to be the one that’s going to help us take this from our small shop to what will become our massive multi-million (unit) production next year.”

So which of those is true? Production ready in September 2015, or not? As with the "faster than a wire" claims from 2015 there are some implications as to 'perception vs reality' over the last few years if what Prof O'Donnell says is accurate. (COO Devine left his role at uBeam earlier this year before 'inflection' happened). For a further point of reference, I left the company at roughly the time these claims were being made.

The current receiver case is pretty interesting too. Looking at it, I'd guess 6 by 11 by 1.5cm which is larger than the phone itself, for around 100 cm^3 of volume. A standard battery for a Galaxy S5 is about 15cm^3 so you could have around 7 of those packed into that volume, giving you around 4 days of continuous use before recharging, and would cost about $70. If uBeam are using Murata (or Murata style) transducers in that case, there's around 60 of them at $3 each, so $180 just in transducers there. I'm not seeing the practicality or economics here.

(For those wondering - Murata are the primary maker of the parking sensors that are used in many cars, using ultrasound as the detection method. They're the small circles you see on bumpers, and individually look like cylinders about 1 cm each in diameter and height. They sell millions of them every years to the auto industry, and are around $3 each in bulk. You can go buy them yourself if you like.)

I did notice they have two different arrays that are used at different times, and I wonder if they are operating in the same manner, or if they are specced to handle different test conditions, and what is seen in these demos can't all be done on the one demo system. It's a little hard to tell from the videos as shown.

Now I could make a few more comments, especially on the posters in the background of the video and what they give away, but that's just going way too detailed even for my blog. 


Last point for now - the above picture shows a Kindle Fire on the right, and if you look in the bottom it's indicating "charging", but what rate is it charging at? 4.62 volts and 10 mAmps - basically  under 50 mW. To give you an idea of what that amount is, a typical phone batter is in the 5 to 6 Wh range, which means at this rate it would take over 100 hours to charge your phone at that rate. That's also assuming the phone is switched off, as it's typically consuming at around 500 mW so without that level of 'charging' it's consuming power faster than it's receiving it. I'm not seeing the practicality if that's the case. (A demo of a charging indicator coming on can be found in a newer post, here)

All this indicates is that the floor to show a device charge light come on is not the same as actually charging it - you need to see something like the screen on the left with voltage and current to know actual charging rate. This floor varies by device (iPhone seems to trigger at a higher floor than Android, and the floor varies with charge level IIRC), it's possible it's charging much faster (faster than a wire even?), but if it is, why not say?

As has been said before - physics doesn't prevent you sending power via ultrasound, or RF like Energous does, but can you send enough power to be useful, safely, efficiently, simply, and cost effectively?

11 comments:

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  2. A knowledgeable ultrasound person wrote this to me earlier today, stated they're fine with it being published here. I thought it may be of interest to people who've read this far.

    "Just a few tidbits I noticed:

    Those 1cm transducers have been on the market for several decades (at least 20-30 years, probably more), so there's little room for improvement. The specific model they're using I don't know, but most are pretty comparable, and they haven't changed appreciably over time. In quantity some are closer to $1-$2, but assembly costs and power requirements will still be astronomical.

    For those hexagon arrays, I doubt they are annularly phased; I think it's more likely they're tilting the outer panels slightly inward for a modest but helpful focusing effect. I think this is why the phones had to be very specifically placed at a short distance. I noticed there was a cut between the guy holding moving the phone closer with a red screen, and when charging was shown.

    The square array is believably phased, using video tracking to aim the beam(s) (noted reflective rectangles on the receiver); technically it's pretty straightforward, but it's quite a lot of hardware required, as we can see. At an 8mm wavelength, having interelement spacing of >10mm will clearly make grating lobes, as you note.

    The phone sleeve/receiver is clearly another array of similar (or the same) transducers. I did notice that during one of the demos, the phone was off while charging, and in another, it was in airplane mode, probably to reduce power consumption while still showing that it's charging.

    The stunt of buying the phone at the store was effective for PR, but as you note not meaningful."

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    1. I'm beginning to agree with this commentator's thinking on the hex panel - it's geared to a single point focus for higher power density, and may simply be mechanically focused. It performs a different function than the square array, and the two are not interchangeable.

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  3. I have a different concern: who cares?

    Qi wireless charging has been available in Samsung phones for years, and I personally love it!! But I see nobody else using it. I.e. it's not selling phones.

    Worse, USB-C and the Pixel are leading phones to charge faster, while phones already carry 8-12+ hours of charge.

    I could see niche applications in wireless speakers or wireless LED lighting, but unclear how big those markets are. Perhaps if they own the IP on directional wireless power, then faster underside car charging?

    Paul, penny for your thoughts!

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    1. I agree - it's no longer a driving factor for many people. Unlike a few years ago, our infrastructure has adapted and there's a lot more places to charge your phone. In your home and office you have charging cables in key locations, previously problematic places like aircraft now are providing outlets.

      Qi is interesting but to be honest it's more limiting than a wire. I can still use the phone on a USB cable, but harder when I have to leave it on the charging mat.

      As you note, USB-C potentially charging at 100W (more limited in that the battery in a phone simply won't accept that fast a charge yet) but once that's here then a phone charges in 3 minutes (OK that's a way off but you get the idea)

      There's just not a key demand. Where's the 10x gain in utility? There are other cheaper solutions like "phone case that has a large battery in it" or "carry a $2 charge cable with you". Why pay $1000 for a transmitter (or $10,000), and for a receiver $100 (or $500)?

      Under-car charging? Witricity is looking at that I think, and is probably a reasonable solution.

      Rapid answer for you - I'll maybe write a more detailed article later.

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    2. Wow, thx for the detailed reply! super helpful...

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  4. Don't you need to be d^2/lambda away from the array to be in the far field where beam steering will work? I'd assume that's many meters in this case.

    Seems that would be a fundamental limitation in power generation. You need a large array to generate the power, which means a longer far-field, which also means more 1/r^2 loss.

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    1. The nearfield/farfield boundary occurs around there and you do get a peak at that point, though not necessarily the largest peak. Prior to that there are a number of maxima in the near field. Some info and images here:

      http://www.bostonpiezooptics.com/the-ultrasonic-transducer

      You do make a very good point about something that would need considered during beamforming and a possible limiting factor.

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