When the sensor input impedance matched with the impedance of peripheral circuit, it can achieve the maximum output power.
Starting from the equipment, only when the sensor and the transmission lines realize the impedance matching, the peripheral circuit can receive the partial discharge signals that coupled by the sensor for maximum efficiency.
From macro available, Impedance matching can be measured by reflection coefficient or standing wave ratio.
In radio frequency circuit, on a point of the transmission line, the reflection coefficient (voltage) is defined as the reflected wave voltage ratio the incident wave voltage, such as type 1.
U2 is the reflected wave voltage, U1 is the incident wave voltage. Standing wave coefficient (voltage) is defined as the
signal antinode point voltage and the ratio of the node voltage, such as type 2.