Resonator force transducer

Abstract

A vibratory, force transducer includes a pair of elongate, generally parallel bars coupled together at their ends in a type of double-ended tuning fork arrangement. The bars each have a thickness of t, a width of w and a length between fixed ends of L. The distance separating the points where the bars are coupled together is m. Apparatus is provided to cause the bars to vibrate in a transverse direction and in substantially 180.degree. phase opposition. Apparatus is also provided for determining the frequency of vibration of the bars so that when the bars are subjected to either compressive or tensile forces along the longitudinal axis of the bars, the magnitude of such forces can be readily determined by simply determining the magnitude of the frequency change. The values of w and t are selected so that 0.4<t/w<4, and this reduces the likelihood of buckling the transducer when it is subjected to compressive forces while also maintaining a configuration which is relatively easy to fabricate using a photolithographic process. The values of t, w, L and m are selected so that various spurious modes of oscillation of the transducer, which causes a reduction in the mechanical Q and thus an erroneous reading of applied forces, are avoided. The disclosed selection processes for t, w, and L may be applied also to single beam flexure mode transducers to avoid spurious modes of oscillation while maintaining a configuration which is relatively easy to fabricate using photolithographic processes.