BOOMERANG spectrometer
The BOOMERANG spectrometer. Two neodymium iron boron pole magnets P magnetize a cylindrically symmetric array formed by ring magnets R and detector magnets D, which are made of mu-metal. A spherical volume A, filled with a liquid or solid sample, is placed inside coil C, which provides RF pulses to modulate the sample's magnetization. The magnet assembly, which may be viewed as a pair of pole pieces slightly perturbed by removal of the material to form the gap around the detector magnets D, provides a homogeneous field of around 0.65 T at the sample. One of the detector magnets is fixed to a single-crystal silicon beam O forming a z axis mechanical resonator with fundamental frequency around 450 Hz.
(Inset) This cross section shows the forces exerted by the sample on the components of the magnet array when the magnetizations of the sample and all of the magnets are aligned along vector M. Cyclic inversion of the sample's magnetization induces mechanical oscillations of O, which are detected with a fibre optic interferometer (image and text: Proc. Nat. Acad. Sci. 101 12804)