A tunable magnetic inductor

For integrated radio-frequency applications, tunable magnetic inductors are expected. A tunable magnetic inductor, based on magnetoimpedance effect, is presented in this paper. The proposed inductor is constructed with a magnetic inductor body, wound by an insulated coil, inducing a longitudinal dc bias magnetic field when a dc control current is flowing through. Formed by a conductive core coated by a high-permeability magnetic layer, the magnetic inductor body can be realized by either a thin-film structure or a composite wire. The reluctance models for both thin-film and composite wire structures are studied. A prototype tunable magnetic inductor, using a composite wire element, has been characterized. The results show that by varying the dc control current, the inductance L of the magnetic inductor can be tuned. The tunable range depends on the frequency of the current flowing through the inductor. A relative variation of inductance ΔL/L₀, up to 18% at low frequency (around 5 MHz), is achieved by applying a bias current of magnitude merely up to 15 mA. The quality factor varies from 5 to 17 in the measured frequency range. The proposed tunable inductor may be further optimized for high-frequency applications and has the potential to be realized in micro-electromechanical systems technology.