US Patent 10929730 Retroreflective multiscale codes

In some examples, an article includes a substrate having a surface; a parent optical element set comprising one or more parent optical elements disposed on the surface of the substrate, a child optical element set comprising one or more child optical elements disposed on the surface of the substrate. Each of the parent optical elements has a first retroreflective property and each of the child optical elements has a second retroreflective property different from the first retroreflective property.