The phenomenon is tunable in that the characteristic sounds and intensities of those sounds depend on the characteristics of the RF energy as delivered... Because the frequency of the sound heard is dependent on the pulse characteristics of the RF energy, it seems possible that this technology could be developed to the point where words could be transmitted to be heard like the spoken word, except that it could only be heard within a person..s head. In one experiment, communication of the words from one to ten using ..speech modulated.. microwave energy was successfully demonstrated. Microphones next to the person experiencing the voice could not pick up these sounds