A teeny device can measure subtle shifts in Earth’s gravitational field about miniaturized gravimetry operating at room temperature based on a diamagnetic levitated micro-oscillator with a proof mass of only 215 mg placed in the aluminum frame stabilizing the temperature of the permanent magnets with the PID controller. A vacuum chamber and thermal isolators are used to avoid ambient temperature disturbances and magnetic shields are placed outside the aluminum frame to shield against external magnetic field. Tilt adjusters are used to level the setup.

A 633-nm laser beam reaches the displacement sensor and is then sent to a photodetector through optical fibers. Piezoelectric positioners are used to control the position of displacement sensor to ensure that the copper wire is exactly at the focal point of the laser beam. The laser beam is focused by a lens. The copper wire is placed on the focal point, where displacement sensitivity in the Z direction is maximum.

Instead of a weight and spring, Huang and his team used two magnets, one levitated by the other. The levitated magnet acted like the weight, moving up and down in response to a shifting gravitational field. The intangible force of magnetism between the magnets worked akin to the solid spring. A laser measured changes in the position of the levitated magnet, allowing the researchers to watch the Earth’s gravitational field fluctuate over several days in response to tidal forces from the moon. They also detected two earthquakes, one off the coast of Honshu, Japan, and one in the Bali Sea of Indonesia.

• Measurement of the Earth tides with a diamagnetic-levitated micro-oscillator at room temperature
• Measurement of the Earth tides with a MEMS gravimeter.