What is the Frey effect?

The United States of America’s military’s thesaurus defines voice to skull V2K devices as follows.Nonlethal weapons which includes 1. A Neuro electromagnetic device which uses microwave transmission of sound into the skull of persons or animals by way of pulse modulated microwave radiation; and 2. A silent sound device which can transmit sound into the skull of persons or animals. Neural electromagnetic devices and V2K are used to send transmissions of sound into the skull through pulse modulate