Soluble compounds to absorb radio-frequency electromagnetic radiation
Of course! Salt water is effective, because it is an ionic solution. Submarines and SCUBA divers cannot use radio-frequency (RF) communication over any distance because of that issue. Very high power, very-low-frequency (VLF) land-based transmitters can penetrate to perhaps 20 meters depth to subs, but salt water is essentially opaque to RF and microwaves.