Shield
The Holtzman energy field worn as personal armour across the Imperium, which is why its soldiers fight with blades, and which cannot be worn long on Arrakis.
A shield, sometimes called a Holtzman shield, is a protective energy field thrown around whatever it is meant to protect. A Holtzman generator produces it, and it can be calibrated to admit matter travelling below a set speed. That calibration matters in a personal shield, since anyone inside one that admitted nothing would suffocate. Shields over installations can be set far tighter, because life support can recycle the air behind them. Because shields are everywhere, firearms and directed-energy weapons became largely obsolete or too dangerous to use, so fighting went back to blades and precise technique, and anyone of the slightest importance wears a body shield. The danger is in the interaction: a lasgun beam striking a Holtzman field sets off sub-atomic fusion and a nuclear explosion, and whether it goes off at the shield, at the gun, or both is a matter of chance.
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