A module for use in a wireless power transfer system, the module comprising: a first inductive element formed by at least one loop of electrically conductive material; and additional circuitry connected to the first inductive element and comprising terminals for connection to a power supply or electrical load, wherein the first inductive element forms a high-Q resonator with at least a portion of the additional circuitry, the resonator having an intrinsic Q value greater than 100; and wherein the additional circuitry comprises: a first capacitor connected in series with the first inductive element to form a first circuit pathway; a second capacitor connected in parallel to the first circuit pathway and forming a second circuit pathway; and a second inductive element connected in series with the first and second circuit pathways, wherein a capacitance value of the second capacitor, C 1, is given by C 1 = 1 ω ⋅ X + X 2 R n − R 2 1 − R n X 2 + R 2 and an inductance value of the second inductive element, L 2, is given by L 2 = − 1 ω ⋅ 1 − Xω C 1 − R n R n ω C 1. wherein ω is an angular frequency of operation of the module, R is the real component of a complex impedance of the first inductive element and the first capacitor, X is the imaginary component of the complex impedance of the first inductive element and the first capacitor, and R n = R/Z 0, where Z 0 is a characteristic impedance of a coupled external circuit. a first inductive element formed by at least one loop of electrically conductive material; and additional circuitry connected to the first inductive element and comprising terminals for connection to a power supply or electrical load, wherein the first inductive element forms a high-Q resonator with at least a portion of the additional circuitry, the resonator having an intrinsic Q value greater than 100; and wherein the additional circuitry comprises: a first capacitor connected in series with the first inductive element to form a first circuit pathway; a second capacitor connected in parallel to the first circuit pathway and forming a second circuit pathway; and a second inductive element connected in series with the first and second circuit pathways, wherein a capacitance value of the second capacitor, C 1, is given by C 1 = 1 ω ⋅ X + X 2 R n − R 2 1 − R n X 2 + R 2 and an inductance value of the second inductive element, L 2, is given by L 2 = − 1 ω ⋅ 1 − Xω C 1 − R n R n ω C 1. wherein ω is an angular frequency of operation of the module, R is the real component of a complex impedance of the first inductive element and the first capacitor, X is the imaginary component of the complex impedance of the first inductive element and the first capacitor, and R n = R/Z 0, where Z 0 is a characteristic impedance of a coupled external circuit. a first capacitor connected in series with the first inductive element to form a first circuit pathway; a second capacitor connected in parallel to the first circuit pathway and forming a second circuit pathway; and a second inductive element connected in series with the first and second circuit pathways, wherein a capacitance value of the second capacitor, C 1, is given by C 1 = 1 ω ⋅ X + X 2 R n − R 2 1 − R n X 2 + R 2 and an inductance value of the second inductive element, L 2, is given by L 2 = − 1 ω ⋅ 1 − Xω C 1 − R n R n ω C 1. wherein ω is an angular frequency of operation of the module, R is the real component of a complex impedance of the first inductive element and the first capacitor, X is the imaginary component of the complex impedance of the first inductive element and the first capacitor, and R n = R/Z 0, where Z 0 is a characteristic impedance of a coupled external circuit.