RF field is sensed to produce an incoming voltage that drives a microarray of electron guns in a sweep pattern towards a detector array. A toner for developing an electrostatic latent image comprising such a charge control agent, a binder resin and a colorant. The ratio of Ca to Zr in the secondary phases is smaller than the ratio of Ca to Zr in the primary phase, and the number of secondary phases with a diameter of 100 nm or greater in a cross section of the dielectric layers averages 30 or less per 10 square \u03bcm.