Robotics and automation

La barrière immatérielle is the light curtain: a row of infrared beams across the opening that halts the arm the moment anything breaks them. The adjective is a trap laid for English in particular. Immatériel in French means having no physical body — no bar, no mesh, nothing to lay a hand on. « Immaterial » in English has drifted almost entirely off that reading. In a courtroom or a meeting it means irrelevant, of no consequence: « that objection is immaterial ». So an engineer told that a barrier is immaterial hears that the barrier does not matter, which is the exact opposite of what the device is for. The two senses do share an ancestor, since what has no substance is easy to reinterpret as what carries no weight in an argument, but only French kept the first branch in daily use: le patrimoine culturel immatériel is what English calls intangible heritage, and les biens immatériels are intangible assets. Read immatériel as « with nothing there to touch », and on the shop floor say light curtain.