Design and characterization of a modular tunable ring electrode aerosol charge conditioner

A tunable ring electrode aerosol charge conditioner is introduced. Bipolar ions are created by means of radioactive decay. The device creates a stream of unipolar ions by separating positive and negative ions using an axial electric field with electric field strengths up to 2 kV cm⁻¹. Varying the electric field strength enables changing the charge conditioner output from bipolar (V = 0) to unipolar for positively charged particles (V > 0) or negatively charged (V < 0). The steady-state ion field and aerosol charge distributions are predicted using a numerical model. Charge conditioner performance is characterized using tandem differential mobility analyzer measurements. Results show that the mean charge per particle increases approximately logarithmically with the applied DC voltage. There is good agreement between model-predicted and observed charge distributions over a wide range of DC voltages and particle sizes. The design is open hardware providing an adaptable platform that can be used as a starting point to modify the charge conditioner design to optimize performance for specific applications.