查了一下，外文说的是就是雷达原理，用的三个电子管比硬币还小
VT-M532 VT RF Tubes
Miniaturized RF Tubes
![tubes.jpg]()
used inside the VT M532
(Shown at left)
Proximity Fuzes
Proximity fuze technology was developed during WWII, and two types were produced.
The first (British) was used for anti-aircraft rockets and relied on optics. A sensor was calibrated for broad daylight. As the missile approached the target the daylight shining into that sensor was reduced. When the sensor was shaded enough, an electrical circuit would close and detonate the warhead. While successful, it was useless when it came to shooting at night.
The second concept (U.S.) applied radio waves,
using the same principle as Radar. The fuze transmits a signal which is reflected by the target and received by the fuze. This reflected signal increases in strength as distance is reduced. When the reflected signal intensity reaches a certain level, a triggering circuit electrically fires the detonator.
These early radio "VT" fuzes were large and fragile, using mechanical and vacuum tube components, but they were very successful in a number of applications and used to good effect.
With the advent of transistor technology in the 1950's electronics could be reduced in size, resulting in smaller more robust fuzes which could be applied to smaller munitions.
