A method of maintaining a desired level of sub-transient reactance in a superconducting machine includes specifying a desired level of sub-transient reactance. The sensing element senses a change in magnetic field caused by the presence of a target. The components of the circuit design then can be placed to minimize critical connections. A method is provided that defines a burst period for sending the reference signals, determines an interval between the reference signals, and sends a timing instruction message that includes the burst period and the determined interval. The intermediate layer contains an ethylene-acrylic acid binary copolymer and a polyolefin resin in which repeating structural units are contained in a particular ratio.