Direct generation of a voltage and current by gas flow over carbon nanotubes and semiconductors

We report here a direct generation of measurable voltages and currents when a gas flows over a variety of solids even at the modest speed of a few meters per second. The underlying mechanism is an interesting interplay of Bernoulli's principle and the Seebeck effect: Pressure differences along streamlines give rise to temperature differences across the sample; these in turn produce the measured voltage. The electrical signal is quadratically dependent on the Mach number M and proportional to the Seebeck coefficient of the solids. Results are presented for doped Si and Ge, single wall and multiwall carbon nanotubes, and graphite. Our results show that gas flow sensors and energy conversion devices can be constructed based on direct generation of electrical signals.