Development of the Johns Hopkins xylophone bar magnetometer

A novel xylophone resonating bar magnetometer, invented by APL's Research a nd Technology Development Center, is being developed in collaboration with the Space Department: into a compact, high-sensitivity, wide dynamic range sensor suitable for space physics applications. The magnetometer's principl es of operation are presented and are demonstrated in experimental situatio ns. The sensor uses the Lorentz force and the xylophone bar's mechanical re sonance to yield subnanotesla sensitivity. This resonance technique offers large mechanical gains at the expense of bandwidth (typically a few hertz). However, the device can be used as a mixer to detect alternating magnetic fields. This capability is demonstrated at low frequencies (a few hertz) an d at radio frequencies (a few megahertz). The sensor incorporates no magnet ic materials and, therefore, can be used to detect small fields while rejec ting large out-of-band signals. The resonator's temperature sensitivity is mitigated using feedback. The device is in an early engineering prototype s tage. Eventually, using micro-machining and chip-on-board techniques, it is expected to be implemented as a "magnetometer on a chip."