"To estimate the impact of energy harvesting on the phone, we modifying an iPod Touch to measure battery current and voltage. We play an audio file that generates the required 22 kHz tone and find that the iPod draws 91 mA at 4.04 V when the harvester is attached and 37 mA at 4.04 V when the harvester is not attached.
These figures illustrate the substantial inefficiency of this approach compared with directly supplying power to a peripheral. We note, however, that the power output of an iPod is higher than an iPhone, making the numbers appear worse than they are on the iPhone."
Speaking of figures, I wonder how this would compare to what can be gathered from ambient radiowaves with a device of a similar size.
I remember a posting from somewhere where Nokia claimed to reach in the miliwatt range only using ambient radiowaves. Can't seem to find it again though.
"To estimate the impact of energy harvesting on the phone, we modifying an iPod Touch to measure battery current and voltage. We play an audio file that generates the required 22 kHz tone and find that the iPod draws 91 mA at 4.04 V when the harvester is attached and 37 mA at 4.04 V when the harvester is not attached.
These figures illustrate the substantial inefficiency of this approach compared with directly supplying power to a peripheral. We note, however, that the power output of an iPod is higher than an iPhone, making the numbers appear worse than they are on the iPhone."