Magnetic field sensors such as flux gate and magnetoimpedance elements have been sonsidered to be useful tools for indicating the direction of a terrestrial field. Downsizing of these sensors is essential for then to be used in highly integrated electronic devices such as mobile phones and computers. We developed a new type of magnetic field sensor that has a great advantage in this respect. The sensor has a composite structure cosisting of a mechanical resonator with a high Q factor and magnetostrictive layers. With the high sensitivity of the magnetostrictive layers to external fields, the resonance frequency of the resonator is expected to be shifted by the ΔE effect. Since the shift in frequency is independent of the resonator size, appreciable downsizing of the sensor is possible. In this paper we describe our initial experiments to verify that the composite resonator is sufficiently sensitive to detect terrestrial fields. The results show that it has a sensitivity of 40 Hz/Oe for a resonator with a resonance frequency of 120 kHz.
