A Nano-g Metal Flexure Accelerometer Featuring Tunable Magnetic Negative Stiffness

High-precision accelerometers featuring large dynamic ranges are critical for gravity gradient measurements conducted on airborne and shipborne platforms, where lowering the fundamental frequency has been demonstrated as an effective dynamic range enhancement strategy. Although negative stiffness mechanisms are widely adopted, conventional designs suffer from compromised structural simplicity and limited tuning precision. In this article, we proposed a metal flexure accelerometer employing magnetic negative stiffness (MFAEMNs), where the magnetic negative stiffness (MN) element is integrated in parallel with the spring–mass system; when the accelerometer senses the changing of the acceleration, the MNs’ generated force dynamically counteracts the leaf spring’s restoring force, enabling precise stiffness compensation while preserving high spurious mode rejection. A prototype was fabricated and tested to validate the design concept of the MFAEMNs. During the experiments, the gap thickness between the magnets was tuned precisely to obtain different configurations of the MFAEMNs. The experiment results demonstrated that the resonant frequency of the proposed accelerometer was tuned from 9.3 to 3 Hz continuously, which is threefold lower than the accelerometer without MNs. The sensitivity increased from 815 to 8305 V/g, representing a 10.2-fold enhancement. Moreover, the noise floor of the proposed accelerometer reduces from 9 to 1 ng/ $(\rm Hz)^{1/2}$ @0.4–2 Hz, yielding a nine-fold improvement in noise resolution over the baseline configuration. The experimental results demonstrate promising validation with potential for enhanced performance through systematic optimization in subsequent studies.