Nice book if you got time to read it,
"Ether technology: a rational approach to antigravity"
http://www.zamandayolculuk.com/cetinbal/PDFdosya/EtherTech.pdf
A tad old (1977) but ahead of its time. Written by RHO SIGMA (Dr. Rolf Schaffranke). He was nice enough to verify his persona as RHO SIGMA at the time of writing. He wanted to keep his research under cover at the time. His analysis of the Biefield/Brown effect was right on. 8)