An encoded particle 8 includes a particle substrate 10; at least a portion of the substrate having at least one diffraction grating disposed therein, the grating having a resultant refractive index variation at a grating location, the grating being embedded within a substantially single material of the...http://www.google.com.au/patents/US7106513?utm_source=gb-gplus-sharePatent US7106513 - Diffraction grating-based encoded particle
