Talk-Powered Cell Phones Won't Need Batteries

alphadogg writes "It's possible that in the future conversations on your cell phone could generate enough electrical power to run the phone, without batteries. That's one possible outcome of recent work by a team of Texas researchers, who appear to have discovered that by building a certain type of piezoelectric material to a specific thickness (about 21 nanometers, compared to a typical human hair of 100,000 nanometers), you can boost its energy production by 100 percent. And the technology could power not just phones, but a whole range of low-power mobile devices and sensors. The breakthrough is an example of 'energy harvesting' that can convert one kind of energy, such as vibrations or solar rays, into electricity."

Why don't they use body heat?

[www.sorehands.com]

And, no I am not talking about the Matrix...ok...it crossed my mind.

I remember there was also a digital watch that worked on body heat. I could not find that one, but I found another, non-digital. http://www.roachman.com/thermic [roachman.com] .

Physics might say otherwise

[Anonymous Coward]

Lets assume that a minimum channel capacity (bits/s) is required to support a conversation, even if we use the absolute best vocoder that eliminates all redundant information. Shannon's Law [wikipedia.org] then says that for a given noise power (set by the environment) there is a minimum signal power which must be transmitted to get error free transmission. Again we are assuming we have an optimal codec, which achieves Shannon's bound. This sets the absolute minimum power consumption of an ideal radio telephone. A real life phone will use more than this. My guess is that this theoretical minimum power is greater than the power which can be harvested from the human voice.

Bah. Back in my day...

[Anonymous Coward]

...we had talk powered land lines. [wikipedia.org]

Re:not enough energy to power a modern cell phone

[orkybash]

Regarding your last idea, I've interned in the medical device industry so I might have some perspectives... basically, if something like this couldn't power a cell phone it certainly couldn't power sustained operation of a pacemaker! Charge a battery for a defibrillator maybe, but even then you're taking huge risks with rechargable batteries with regard to memory. Basically, even if you were able to use this to increase battery life, you would still decrease *predictability* of the battery life, which is a huge no-no in that industry (doctors need to know pretty well when the thing needs to come out!)

Marine Sound Powered Phones

[TOGSolid]

As a maritime employee, I use sound powered phones on a daily basis. While they work great and definitely get the job done, they're always a little on the quiet side and tinny sounding. They generate just enough juice to get that low quality voice across. Even if boosted by 100%, I highly doubt that'd be enough for a cellphone, not one capable of doing anything besides just talking at least. There still would have to be some sort of battery in the device to allow you to dial and establish the initial cell signal. I could see some clever implementations of an improved piezoelectric device though. It'd help slow down battery drain if you're constantly on the cellphone at least a little.

Re:If you can get the power down

[sexconker]

?
Your math. It is very wrong.

A typical AAA battery is 1.5v @ about 900 mAH.
Round that up and you get 1500 mWH.

1500 mWH / 10 mW = 150 hours.

Re:Physics might say otherwise

[Anonymous Coward]

I agree, the power generated by a human voice can't possibly exceed a few milliwatts, and is likely less than 1 milliwatt.

However, assuming the average person weighs 150lbs, the energy potential of each step is quite a reasonable amount. Perhaps by putting a miniature generator in each shoe that compresses 1/4" with each step and turns that compression force into electricity we could power something like a current tech. cell phone. Then all one would have to do is pace back and forth while talking (a fairly common practice even without shoe-generation), and never worry about battery life.

The biggest hurdle with such a plan would be transmission of the power from the feet to the phone, but at least the power generation potential is sufficient.

Re:Isn't this fairly common already

[NicknamesAreStupid]

It takes 1000 screaming people to generate a watt's worth of energy (one joule of energy per second).

Re:Do the math, Barbie

[goodmanj]

A little help for those too lazy to do the math:

Power per area transmitted by a sound wave:

F = p^2 / (rho0 c)
where
p = rms pressure variations in the sound wave (.01-.05 Pa or so for human voice)
rho0 = density of air (1.3 kg/m3 typ.)
c = speed of sound in air (330 m/s)

I get 1 microwatt per square meter. So for a 20-cm2 cell phone, 2 nanowatts, ignoring the receiver-coupling issues mentioned by the parent post.

No way, Jose, and by at least three zeros after the "1".

Let's make that nine.

Re:not enough energy to power a modern cell phone

[caladine]

OTOH, future cellular devices might incorporate enough improvements into power efficiency (e.g., e-ink displays [wikipedia.org]), such that you could significantly extend battery life and perhaps even power a very basic subset of the phone when the battery runs out.

IMO, future cellular devices will probably use something based on IMOD display technology [wikipedia.org]. It has all the power benefits of e-ink, but considerably faster switching. They're also already available, albeit at pretty small sizes. There's also color versions of these IMOD displays avaliable, but they also suffer from the current size problems.

The Wikipedia article is somewhat short on the details, so the Qualcomm PR page is here [qualcomm.com]. Like I said, it's really a PR page trying to promote their solution, but the whitepapers do have some interesting information on how it all works.