An apparatus (22, 122) for filtering a substance (13) includes an
electrically insulating substrate (30, 130) that separates a source volume
(12) containing the substance (13) from a target volume (18). The
substrate (30, 130) has a first side in fluid communication with the
source volume (12) and a second side in fluid communication with the
target volume (18). The substrate (30, 130) further includes a plurality
of openings (42, 142) connecting the first side with the second side. The
openings (42, 142) are sized to provide filtering fluid communication
between the source volume (12) and the target volume (18) for at least one
phase of the substance. A heater film (32) is deposited over selected
portions of the substrate (30, 130). The heater film (32) contacts the
substrate (30, 130) to heat at least a portion of the openings (42, 142).
