Tesla distinguished his wireless system from Hertzian radiation in lectures and patents from the 1890s onward, describing conduction through the earth. Andrija Puharich proposed ELF waves embedded in or enveloped by scalar waves as carriers of psi information in works like Beyond Telepathy (1962). Thomas Bearden promoted 'scalar EM' weapons theories from the 1980s. Physics texts treat the psi-era 'scalar wave' as unsupported: longitudinal EM waves in free space are not a solution of Maxwell's equations.
The concept survived because it answered a need: psi researchers wanted a physical carrier for telepathy, and scalar waves offered one that explained both speed-of-thought transmission and penetration of shielding. Soviet psychotronics literature leaned heavily on similar ideas during the Cold War, which fed Western interest in kind.
Believers hold that ELF-penetrating, cage-crossing signals explain reported remote influences on minds, and that classified programs would hardly publish the physics. Skeptics note that a century of looking has produced patents and books but no instrument reading.
If scalar waves do not exist, why do a century of researchers, patents, and military interest keep circling the concept, and if they do, what else rides on them?