Thermoelectric generators go to infinity and way beyond

This week’s post on IMEC’s body-heat-powered thermoelectric generator sparked my interest in thermopiles. A thermopile is what you get when you string a series of thermocouples together. Thermocouples work on the Seebeck affect, where two dissimilar metals placed together can produce a voltage proportional to the difference in temperature of the two metals. Thermocouples are usually used as temperature sensors, but with the right metals you can apply heat, crank up the temperature differential, and produce some serious voltage. There are some very neat (and very old) thermoelectric generators on this page, including pictures of generators that go back to the 1860s, and an ad for a generator to power your radio from the 1930s.

Steve Leibson pointed out that the HP 3400A true-rms meter used a thin-film thermopile to get true RMS readings to 10 MHz by measuring the heat rise generated by the signal. A resistor did the RMS-to-heat conversion and the thermopile did the heat-to-dc voltage conversion to drive the meter aft (after amplification). The 3400A was introduced in 1963.

Steve also pointed out that thermoelectric generators in the form of radioisotope thermoelectric generators (RTGs) have boldly gone farther than any other power-producing device as they enable the deep space spacecraft such as Cassini, which operate where solar energy is unavailable and fuel cells would poop out way too soon. RTGs use the heat from radio-active decay, most commonly Plutonium-238, which has a half-life of 87.7 years.

Ok, Powersource covered a new battery introduced last spring that was designed for medical implantation. Long battery life is important for implanted medical devices – having to open a patient up surgically to change a battery should happen as seldom as possible. (Hence the interest in transmitting power wirelessly for medical devices.) You know where this thought is going – here’s another application for RTGs! Sure enough, heart pacemakers powered by radioactive decay  have been made (and some may still be in use). From the article:

“ … They pose a hazard if the wearer is shot in the chest with a gun. If the wearer dies and the generator is not removed before cremation the device will be subject to great heat. It is unlikely however, if the plutonium is in the form of the dioxide, that contamination will occur. Note that plutonium 238 is more able to disperse than plutonium 239, but the dioxide is an air stable solid which is normally sintered in air at a temperature much higher than that used in the cremation of human remains (although they are designed to survive cremation).”

You are, hands-down, the coolest kid on the block with a plutonium-238-powered heart. But don’t get shot in the chest.