THE DOUBLE-RING ELECTRODYNAMIC BALANCE FOR MICROPARTICLE CHARACTERIZATION

A simple form of the electrodynamic balance, suitable for a wide range of microparticle measurements, is described and analyzed. The ac electrode of the device consists of a pair of parallel rings, and the dc endcaps are either simple disks or they can be eliminated entirely by applying suitable dc bias voltages to the rings. The stability characteristics of the device are determined by extension of well-established stability theory, and experiments are compared with that theory. The device is particularly well-suited for detection of radioactive aerosols, for it has significant advantages over the bihyperboloidal device for radioactivity measurement. The detection of radioactivity levels of less than 20 pCi is feasible. Coupled with a Raman spectrometer the balance serves as a stable "platform" for the study of the chemistry of microparticles, and both qualitative and quantitative analysis of microdroplet chemistry are demonstrated for binary droplets of 1-octadecene and 1-bromoctadecane.