You searched for: “variable time fuse
electronic fuse, radio-frequency heating, influence fuse, variable-time fuse, vt fuse
1. A fuse that is ignited by a self-contained electronic element; for example, a proximity fuse or an electronically triggered device designed to detonate an explosive charge in a missile, etc., at a predetermined distance from the target.
2. A fuse; such as, the radio proximity fuse, set off by an electronic device incorporated within it.

A fuse that detonates a warhead when the target is within some specified region near the fuse.

Radio, radar, photoelectric, or other devices may be used as activating elements.