A phase-based radar that detects a standing-cow even when she has not moved for a while.
Sprinkler solenoid triggered by a phase-modulated radar module. Senses the 3-D volume under the sprinkler and opens only when a cow is present — including a cow that is standing still.
Advantage over plain microwave detection: does not require the animal to micro-move to stay "present" — the neck-yoke case where a cow stands still for a long time is handled correctly.
Advantage over vision detection: not affected by dust, spray or low light.
Tradeoff: hardware cost is roughly 20% higher than the microwave module. Choose this where precision matters more than unit cost.