We have studied electromagnetic flux guidance and confinement effects in NiFe cores, interconnecting three Al rings, to form a mesoscopic transformer-like device. Applying ac signals (of low amplitude and kHz frequency) to the contact pads of a semiclosed ring induced time-varying magnetic fields, which could be transferred to a nearby, closed ring, via the aid of a NiFe core. Similarly, a second core carried the fields of this ring, resulting from the induced signals, over to a third, semiclosed ring where readouts were performed over an applied load, using a lock-in amplifier. Highly linear curves of output versus input signal at stable phase were obtained with effective mutual inductance in the muH regime, giving an improvement of the order of 10(6) on the free field. (C) 2004 American Institute of Physics.