Anomalous pulse change in gravity-driven microfluidic oscillator and its application to photodiode switching

Electrofluidic analogy is useful because it provides a method to significantly reduce the reliance of microfluidic chips on dynamic off-chip controllers. Among the functions developed by the analogy, conversion from constant to pulsatile pressure is critical and is yet to be studied. Here, unlike its counterpart electrical oscillator generating square pulses more slowly with decreasing the input voltage, we report that a microfluidic oscillator generates sawtooth pressure pulses more rapidly with decreasing the input pressure (P_I) at 1–2 kPa. Further, with decreasing P_I, the oscillator generates square pulses at P_I > 3.4 kPa, but its operation unexpectedly stops at 2.1 < P_I < 3.4 kPa. We analyze its underlying mechanism with a sophisticated model including a dynamic interaction of the oscillator components and reveal the critical role of the dynamic property of oscillator valves. Additionally, we show electrofluidic switching of a photodiode with the oscillator. The understanding obtained in this study would be essential for developing microfluidic circuits using electrofluidic analogy.