A coin detection antenna includes a substrate and an air core coil in a track shape including a wiring pattern provided on the substrate, and a width of an air core of the air core coil in a short-side direction is equal to or less than twice a thickness of a smallest coin having a smallest thickness of coins to be detected.

A variable inductor includes a three-limbed core first section having an inductor winding wound about a medial limb. An air gap is disposed in the medial limb. The inductor includes a second section having a control limb in which a first end of the control limb is connected to a first outer limb of the three-limbed core, and a second end of the control limb is connected to a second outer limb of the three-limbed core. A control winding is wound about the control limb. The inductor may be used in a control circuit to control a power signal driving a transducer. The inductor may be controlled by a signal derived from a comparison of a voltage phase of a power signal to the transducer and a phase of the current traversing the transducer. A system may include the control circuit, including the variable inductor, and the transducer.

A variable inductor includes a three-limbed core first section having an inductor winding wound about a medial limb. An air gap is disposed in the medial limb. The inductor includes a second section having a control limb in which a first end of the control limb is connected to a first outer limb of the three-limbed core, and a second end of the control limb is connected to a second outer limb of the three-limbed core. A control winding is wound about the control limb. The inductor may be used in a control circuit to control a power signal driving a transducer. The inductor may be controlled by a signal derived from a comparison of a voltage phase of a power signal to the transducer and a phase of the current traversing the transducer. A system may include the control circuit, including the variable inductor, and the transducer.

A mechanical hub is provided. The mechanical hub is attachable to a cable and includes an outer shell and tiles. The outer shell surrounds the cable. The tiles are spaced to surround the circumference of the cable. The tiles may be positioned between the outer shell and the cable such that a translation of the outer shell alters the distance between the tiles and the cable. The mechanical hub may improve signals that are transmitted over segments of a cable that have degraded signal quality.

Disclosed in the present invention is an adjustable inductor, and a transmission circuit for magnetic resonance. The adjustable inductor comprises a fixing assembly, an inductance assembly and a sliding assembly. The inductance assembly is electrically connected to the fixing assembly. The sliding assembly is electrically connected to the fixing assembly and the inductance assembly, and is configured to be able to change the contact position with the inductance assembly so as to change the inductance value of the inductance assembly.