Darkshield is a fully sintered compoundable ferrite powder designed for maximum microwave energy absorption at 19GHz only $17.95 for 25g sample, volume discounts.
A 1mm thick layer of this material mixed with epoxy can attenuate a signal by nearly 14db at 19GHz. Thicker layers or stacked layers can reduce the signal even further. Click on the Specifications tab for a detailed, downloadable pdf file full details.
Download this data sheet on Darkshield fully compoundable sintered ferrite powder for attentuating cellphone frequency microwaves.
The image below shows a 1mm thick plate made with Darkshield ferrite powder. The plate is roughly 25x40mm in size & is 80% ferrite powder by weight. Our 25g size vial has enough powder to make a plate large enough to cover one side (the non-antenna size) of 2 cell phones or any device you care to use it with.