Converse Magnetoelectric Composite Resonator for Sensing Small Magnetic Fields.

Magnetoelectric (ME) thin film composites consisting of sputtered piezoelectric (PE) and magnetostrictive (MS) layers enable for measurements of magnetic fields passively, i.e. an AC magnetic field directly generates an ME voltage by mechanical coupling of the MS deformation to the PE phase. In order to achieve high field sensitivities a magnetic bias field is necessary to operate at the maximum piezomagnetic coefficient of the MS phase, harnessing mechanical resonances further enhances this direct ME effect size. Despite being able to detect very small AC field amplitudes, exploiting mechanical resonances directly, implies a limitation to available signal bandwidth along with the inherent inability to detect DC or very low frequency magnetic fields. The presented work demonstrates converse ME modulation of thin film Si cantilever composites of mesoscopic dimensions (25 mm × 2.45 mm × 0.35 mm), employing piezoelectric AlN and magnetostrictive FeCoSiB films of 2 µm thickness each. A high frequency mechanical resonance at about 515 kHz leads to strong induced voltages in a surrounding pickup coil with matched self-resonance, leading to field sensitivities up to 64 kV/T. A DC limit of detection of 210 pT/Hz1/2 as well as about 70 pT/Hz1/2 at 10 Hz, without the need for a magnetic bias field, pave the way towards biomagnetic applications.

Dielectric properties of Co-gamma-irradiated and microwave-heated rat tumour and skin measured in vivo between 0.2 and 2.4 GHz.

The dielectric properties of a rat tumour (rhabdomyosarcoma R1H), skin and muscle were measured in vivo with an open-ended coaxial line and a computer-controlled system based on a network analyser. The permittivity of the tumour R1H and of the normal tissues in anaesthetised rats was determined at frequencies between 0.2 and 2.4 GHz. No significant differences were observed either between rat tumour and muscle or between normal and 15 Gy irradiated rat tumour and skin. However, after a hyperthermia treatment at 43 degrees C for 60 min the dielectric properties, especially of the rat skin, changed due to the hyperthermic induced oedema which is related to an increase in tissue water content. The process of the oedema modifies the dielectric properties of the skin to a higher degree than those of the tumour.