Cymatics, the study of wave phenomena (often of material media on a vibrating substrate), was popularized by Swiss MD Hans Jenny (1904-1972). Though often discussed in the context of "new age" ideas, DIY techies and artists have expanded interest in the phenomena.
There's more at PVC in Making sound visible through Cymatics. For now, here's a recent example of cymatics from Nigel Stanford, Ferro Fluid: