“…In the beginning, the smallest microchannel was made for the flow sensor, but in such a case the sensitivity was high and the dynamic range was too small. Therefore, the adopted channel size was relatively big (2 mm w × 1 mm d), although the target flow range was below 50 µl min Time-of-flight types [6][7][8] are reliable for flow rate monitoring, but it was necessary to have a continuous signal for feedback control. Also, a small and inexpensive sensor with low-power consumption is a necessary condition for incorporating it into µGAS.…”