You can 3D print a functionally graded (varied composition) titanium alloy pin and have it surgically inserted in your foot. To decode, cut pin into thin slices and read with an XRF gun, and apply your decoding scheme. No one will expect it!
You can 3D print a functionally graded (varied composition) titanium alloy pin and have it surgically inserted in your foot. To decode, cut pin into thin slices and read with an XRF gun, and apply your decoding scheme. No one will expect it!