Figure 2.

(a) USB ultrasonic humidifier containing a piezoelectric transducer and high-frequency generating circuit used to spray specimen. (b) The piezoelectric transducer and high-frequency generating circuit extracted from the humidifier shown in (a). A wire that allows the circuit to be activated out of water is circled in blue. (c) A droplet (1 µl) applied to the piezoelectric transducer surface opposite to the direction of liquid spray. (d) Design for the piezoelectric transducer mounting connector. (e) Piezoelectric transducer, tweezers and grid in the specimen-application position (i), showing spray from the piezoelectric transducer (ii) and with the piezoelectric transducer retracted in the ready-to-plunge position (iii).