Front cover: Measurement of the real part of the Clausius–Mossotti factor of dielectrophoresis for Brownian particles

DOI: 10.1002/elps.201900345 The cover picture shows a method for measuring the real part of the Clausius‐Mossotti factor of dielectrophoresis for Brownian particles based on the theory of Smoluchowski, using a designed microchannel with planar hyperbolic electrodes. An approximate two‐dimensional spring‐like dielectrophoretic force is generated in the device, and the data necessarily measured is the probability density function of the particle displacement undergoing confined Brownian motion. The idea can be extended to the measurement of total polarizability and permanent dipole moment of proteins and other macromolecules.