ElectroPen: An ultra-low–cost, electricity-free, portable electroporator
(a) (i) Image of the striking mechanism (hammer action) found within the piezo igniter in a lighter (arrow indicates location of crystal). (ii) The parts include, from top to bottom, metal conductor (gold-colored region) housing the piezoelectric crystal, springs, hammer, release spring, and geometrical latch. The presence of two springs is to decouple the loading and release phase for consistent voltage output. (b) Images of the hammer and PZT crystal. The circular surface area of the hammer comes into direct contact with a pin that strikes the piezoelectric crystal, generating a voltage through the piezoelectric effect. (c) (i) Snapshots from high-speed video illustrating the position of the hammer during the loading, latch-release, and relaxation phases (S4 Video). (ii) Free-body diagram indicating movement of each part through each phase of the hammer action, including activation and deactivation of spring forces. (d) Plot of displacement of the hammer and the lower case as a function of time obtained using high-speed image video. (e–g) Zooming into the dynamics of the hammer during the latch-release phase reveals that the hammer achieves a peak velocity of 8 ms−1 in 0.5 ms, which corresponds to an acceleration of 30,000 ms−2. The explosive acceleration results in a 10-N force (mass of hammer is 0.3 g) exerted over a tiny area of the PZT crystal. The data for d–g can be found on GitHub under the S2 Data file, under the sheets titled Fig 3D, 3E and 3F and 3G, respectively. PZT, lead zirconate titanate.