【工学】重力の擾乱を測定できる小型デバイス

A portable, cheap-to-produce device for measuring tiny perturbations in local gravity, such as those caused by a subterranean tunnel or an underground body of oil, is described in a paper published in Nature. The silicon-based device is sensitive enough to measure the Earth’s tides - the deformation of the Earth’s crust caused by the gravity of the Sun and Moon - and has applications in geoscience, engineering, oil and gas prospecting, and environmental monitoring.

Gravimeters measure tiny variations in local gravitational acceleration and are used in scientific applications, such as volcanology (to measure magma buildup before an eruption, for example), and also have industrial and commercial use, including in civil engineering and the detection of hydrocarbon reservoirs. Although several technologies exist that have the sensitivity for such applications, they are almost all limited by high cost (more than $100,000) and mass (over 8 kilograms).

Giles Hammond and colleagues developed a miniaturized gravimeter, comprising a 15-millimetre-square piece of silicon weighing 25 milligrams. Their technique is based on fabrication processes used to make the micro-electromechanical system (MEMS) accelerometers found in smart phones, which can be reproduced in large volumes and at low cost. They find the MEMS gravimeter has a gravitational sensitivity of about 40 microgal per hertz1/2 - and long term stability which is superior to current MEMS. The authors suggest that this miniature gravimeter may, among other applications, allow gravity-mapping exploration surveys to be conducted with drones, limiting the need for dangerous low-altitude aeroplane flights.