At CES 2010, a company called RCA has presented a device called 'Airnergy', which is supposedly able to harvest energy from WiFi (and GSM) networks, for instance to charge your cellphone. Now this raises immediate suspicions: if that is possible, why aren't mobile devices powered by these networks in the first place? However, given the feeling that we are surrounded by a vast multitude of such networks, it still sounds remotely plausible. The only way to determine whether this makes sense, is to actually crunch the numbers:
My phone has a 0.9 Ah battery, at 3.7V. This means the battery holds 12kJ. With an uptime of 200 hours, this means a mobile phone consumes 17 mW on average.
A wireless accesspoint emits EM radiation in the order of of 100mW. If a device harvesting this power has an active area of 10x10cm and is, on average, located 1 meter from the accesspoint, it will pick up 0.01/(4*pi) * 100 = 0.08 mW, assuming the radiation is the same in all directions.
If the device in question can harvest 0.08 mW, it takes17/0.08 ~ 209 accesspoints and 200 hours to accumulate 12 kJ. My only conclusion can be that this product is completely bogus. Even at a conference, with perhaps 100 nearby cellphones as additional radiation sources, it wouldn't be useful.
This analysis grossly overestimates the power that could be harvested, as it assumes a 100% conversion of EM radiation into electricity and situates the accesspoints within one meter of the device. Is it a hoax? Is it fraud? Is it idiocy? Or is my calculation wrong?
Given the examples (though not all of them), that seems to make sense: at some point something is just so good that you couldn't wish for a better version. If you can't buy a better version of something that will work for twenty years, then the number of products sold will decline fast and the manufacturer has a problem. However, that line of though misses three important points
- Every product has always reached a mature phase and manufacturers are usually prepared for that to happen. There haven't been major improvements in world receiver radio's for quite some time, but they are still being produced and sold.
- When the improvement upon the previous model decreases, the time to general adoption grows. This is usually because the price lowers with time and the cost-benefit ratio increases. If the time grows too large, steps may be skipped: 100GB video discs may well be the next big thing, even if blu-ray fails.
- It is about perceived improvement more than about real improvement. Did I actually need this 32" LCD television? Is it actually that much better than my previous 24" CRT version? I don't think so, yet I bought it.
Nevertheless, this does leave us with one really interesting question: will there ever be a time when no technological improvements are marketable anymore? When you have your range of Star Trek technology: holosuite, replicator, spaceship, transporter, ..., would there still be a consumer market for new technology? If not, then the question is when the effective end would be reached.