I'm interested in developing timing gates to measure running speed something like this https://store.simplifaster.com/product/freelap-pro-bt112/.
The description says that the cones use an electromagnetic field combined with a wearable "chip" to detect when the athlete runs through the gate. I'm curious what kind of hardware would be used to emit a strong enough electromagnetic field and what would sense it? (current running through a coil or AC and hall effect sensor?) I'm aware of how an electromagnetic field can be created but specifically how can it be so precise as to measure exactly when the person crosses the line almost like a laser beam? Also I would think that it would take a high amount of current to create a strong enough magnetic field to be detected from a few feet away. And if the current is high enough I would think it would create a lot of heat. Anyone have any insight or experience with this application of EMF and precise timing?