A protective reduction in output power triggered when a device's internal temperature exceeds a safe operating limit. In PEMF devices running at high frequency or high duty cycle, resistive losses in the coil and driver circuit generate heat. If the device doesn't have sufficient thermal mass or cooling, temperature rises until firmware or hardware limits reduce drive current, pulse width, or repetition rate to protect components. The result is that measured output at the beginning of a session may be higher than output after several minutes of operation. Thermal throttling is a sign that the device is being pushed near its sustained power limit.
Every pulse turns a little energy into heat in the coil, the heat per pulse. At a low pulse rate that heat has time to shed, but at a high rate it stacks up and the coil temperature climbs, step by step, toward the device safe limit. When it reaches that limit the device throttles, stepping the drive current, pulse width, or repetition rate down to hold the temperature, so measured output later in a session can read lower than at the start.
