A walkie talkie doesn’t work in a mine, and this could potentially be used there. Radio doesn’t work underwater, but nuclear subs trail an antenna out of the back to receive messages using Extremely Low Frequency radio. The application for this sort of antenna is ideally for where regular radio doesn’t work. For contrast, if this were a wire quarter-wave antenna it would be tens of kilometers long. The key is that it’s these soundwaves bouncing around that define the resonant frequency, and the speed of sound in lithium niobate is a lot slower than the speed of light, but they’re translated into electric signals because of its piezoelectricity. An AC voltage is applied to the rod makes it vibrate, and this triggers an oscillating electric current flow that’s emitted as VLF radiation. Instead of pushing pixies through an antenna, this antenna uses a rod-shaped crystal of lithium niobate, a piezoelectric material. They’ve developed a piezoelectric transmitter for very long wavelengths. Now there might be an easier way to play with VLF radiation, thanks to developers at the National Accelerator Laboratory. There is more information on Extremely Low Frequency radio in Michael Crichton’s Sphere than there is in the normal parts of the Internet. Very low frequency and Extremely Low Frequency radio isn’t practiced very much, ultimately because it’s impractical and you simply can’t transmit much information when your carrier frequency is measured in tens of Hertz. If you want to talk about antennas, the amateur radio community has you covered, with one glaring exception.