Time division multiplexed input signals are spread in each time slot with a destination code. The core comprises particles of cured, and optionally foamed, rigid, polyurethane, polyisocyanurate andor phenolic resin. This mitigates the need for additional materials in the substrate to isolate the active regions from one another, where such additional materials can introduce noise into the JFET. The invention differs from prior art by the outflowing liquid being led onwards up to the surface facility via a drain line. In the image forming medium, irradiation of the imaging layer causes the photobase generator to generate a base that reacts with the acid-base indicator to produce an image. Methods of making and formulating compound are provided.