Pulled microcapillary tube resonators for high precision microdroplet size measurements

This paper reports the high-precision microdroplet size measurement using a pulled microcapillary tube resonator (PμTR) which is fabricated by a microfabrication-free approach-pulling a glass capillary and fixing it on top of a machined jig. The pulled section in the middle makes simple contact with a piezoactuator (actuation node) and a quartz tuning fork (QTF, sensing node) while un-pulled sections at both ends provide easy connection with standard adapters and fluidic tubings. We introduce microscale oil droplets into the PμTR and demonstrate that the PμTR exhibits the resolution of 31 nm for the radius change of oil droplets at around the average radius of 28.47 μm. This resolution is far superior to the diffraction limit of conventional optical microscopy based techniques.