John S. Moore

A survey of color graphics printing: User needs for permanent copies of charts, graphs, and other illustrations are growing rapidly, and the technology is catching up to meet the demand

The requirements posed for color printers by various applications are discussed, and the remaining mechanical problems are described. The various types of printers available are examined, and their advantages and disadvantages discussed.

Helium permeation in plasma-addressed liquid-crystal displays

Full color liquid crystal (LC) displays with 5 inch diagonals are readily available today, and manufacturers are ramping up production of 10 inch full color displays for laptop computers. These displays require an integrated thin film transistor (TFT) as well as a capacitor to capture and store analog data voltage for a sixtieth of a second at each display element. For large displays there can be a million or so of these switching and data storage elements that comprise, in effect, a megasample analog memory. Fabricating such arrays is proving to be a formidable task. The concept for replacing the array of integrated TFTs with functionally identical plasma switches to address LC displays was first disclosed in the May, 1990. These switches consist of a channel of ionized gas that can be turned on and off quickly and that are capacitively coupled to the storage elements of the display. To achieve rapid data capture as well as fast turn-off of the columns of ionized gas it appears that at least one component of the gas must have a low atomic weight. To ensure long term stability, nonreactive gases are needed. Helium is an obvious choice since it is light and nonreactive, and furthermore, only a low level of visible light is generated when it is ionized in the channels. Unfortunately helium permeates through the glass enveloped of a liquid crystal display faster than any other gas. Containing it for the five to ten year life of a display is a challenge, and progress toward meeting that challenge is discussed here after a brief review of the plasma addressing (PA) concept.

A physical explanation of how air-assist improves the performance of drop-on-demand ink jets: based upon experimental observations

Drop formation characteristics of a jet with and without air-assist are compared. While the normalized drop breakoff process and drop velocity profiles were similar in both cases, the impact of a lower absolute drop velocity and a larger range of time-to media for the jet without air-assist was enough to lower the maximum addressability of the jet. The dynamic range of the jet remained the same despite removal of the air-assist. An ink jet with the dynamic range of 20 kdps can be achieved without the use of air-assist if the system response is designed to permit such a dynamic range. The important element to control is surface wetting.<<ETX>>