A wristband assembly comprising a wristband strap having a first portion, a second portion, and a fold line between the first portion and the second portion. The lens system comprises an excitation coil providing a magnetic flux to a pole piece unit having a first pole piece, a second pole piece and at least two openings for charged particle beams, wherein the two openings are arranged in one row, thereby forming a lens row, and wherein the pole piece unit has an elongated shape. A liquid polymer precursor composition comprising both carbonizing and noncarbonizing templating polymers is deposited on the porous metal support.