In one embodiment, air is automatically sampled within a zone of interest in response to an event caused by a mammal. The liquid thermosetting insulating resin composition comprises an epoxy resin assuming a liquid state at room temperature, preferably in combination with a phenolic resin assuming a liquid state at room temperature, a curing catalyst, and a filler, wherein the filler contains a spherical filler and a ground filler. The pulses of each pair are transmitted in rapid succession to minimize motional artifacts.