A selectively reflective construct, and a method for making the construct, are described. Embodiments of the incised cannula exhibit reduced tissue trauma compared with screw-threaded cannula, improved fixation andor retention compared with an unthreaded cannula, and good sealing between the cannula and the incision. The remote units recover the master carrier and master clock and synchronize local oscillators in each remote unit to these master carrier and master clock signals to generate reference carrier and clock signals for use by the remote unit receiver. A characteristic structure is that the polycrystalline MgO deposition material is formed of a sintered pellet of polycrystalline MgO, of which MgO purity is more than 99.