Charge synchronization for a piezoelectric droplet generator

Improvements to an existing piezoelectric droplet generator are reported. This instrument produces monosize droplets from the periodic breakup of a liquid jet. Droplets tend to be closely spaced because of the method of generation, so increased separation is obtained by selectively charging and deflecting some of the droplets from the main stream to a drain. A phase-shifting circuit is used to synchronize the charging signal with droplet formation so that droplets are properly charged or discharged, as required. Originally, charge synchronization was obtained by controlling the amplitude of the piezoelectric transducer voltage and thus, altering the breakup length of the jet which was observed to lead to the production of satellite droplets or loss of control at large amplitudes. The present circuit avoids these problems.