Xikai Liu, Dong Ma, Liang Chen and Xiangdong Liu *
MOE Key Laboratory of Fundamental Physical Quantities Measurement & Hubei Key Laboratory of Gravitation
and Quantum Physics, School of Physics, Huazhong University of Science and Technology, Wuhan 430074,
China; liuxikai@hust.edu.cn (X.L.); madong@hust.edu.cn (D.M.); liangchen@hust.edu.cn (L.C.)
* Correspondence: liuxd@mail.hust.edu.cn; Tel.: +86-027-8755-8394; Fax: +86-027-8754-2391
Received: 5 January 2018; Accepted: 5 February 2018; Published: 8 February 2018
Abstract: Tuning the stiffness balance is crucial to full-band common-mode rejection for a
superconducting gravity gradiometer (SGG). A reliable method to do so has been proposed and
experimentally tested. In the tuning scheme, the frequency response functions of the displacement of individual test mass upon common-mode accelerations were measured and thus determined a characteristic frequency for each test mass. A reduced difference in characteristic frequencies between the two test masses was utilized as the criterion for an effective tuning. Since the measurement of the characteristic frequencies does not depend on the scale factors of displacement detection, stiffness tuning can be done independently. We have tested this new method on a single-component SGG and obtained a reduction of two orders of magnitude in stiffness mismatch.
