SWD (Short wave Diathermy) and IFT(Interferential current) these 2 have a mode of action.
see for the case of LBA with sciatica we need to go deeper to the nerve root level where the compression is? IFT is also giving the choice as the 2 carrier waves takes care of the superficial structute and the interference zone produced of low frequency penetrates to the deeper structure without getting the enery lost in the superficial structure. the penetration of anythig decreases with depth and hence to avoid this loss the carrier waves are used and for the pain relief the interference zone do the rest.