Jan Bares

Electrical conductivity of packed particle beds

The dependence of conductivity on particle size is derived for the case of insulating particles exhibiting surface conductivity and particle-to-particle contact resistance. Experimental results obtained on glass particle beds agree well with the physical model that emphasizes surface conductivity as a controlling factor. The proportionality of the DC resistivity to the particle size proposed in the present report was verified by the experimental data and surprisingly found to hold even for AC equivalent parallel resistance. The frequency dependence of the dielectric permittivity and of the equivalent parallel resistance was found to be well approximated by a law with exponents generally different from -1/2. For sufficiently high probing frequencies, the AC response is unencumbered by the particle-to-particle contacts and is characteristic of the bulk material. >

Looking ahead through a rearview mirror

Electrophotography, as an original invention, was just another way to make a copy. Its development into a continuous process made it historic. As with any technology, the evolution proceeded along several fronts, in particular the advancement of enabling components including stimulation and sponsorship of research in related scientific disciplines, development of technology and engineering solutions, and expansion of the market while satisfying existing demand. The evolution, driven by customer and market requirements, has followed the paradigm of any other technology-based appliance: growth in performance and reliability and reduction in size and cost, ultimately enabling the transition all the way from highly functional centralized machines to personal devices. Besides this traditional evolution, xerography expanded when it could link with other technologies. The most dramatic breakthroughs that led to rapid market expansion occurred when digital electronics enabled printing and image processing, and the proliferation of personal computers launched a robust color creation and hardcopy market. The electrophotography industry was prepared for this opportunity and made possible desktop publishing, distributed printing, and recently, color copying and printing with acceptable color fidelity. What early indicators signaled the evolutionary paths, and the divergences, electrophotography would take? In this paper, we examine the history, including relevant publications, to find such indicators. Current literature is also considered in that light.