New Tech: Pocket-sized Gravimetry

In the “less is more” department, researchers at the University of Glasgow in Scotland are developing a device that could potentially revolutionize the field of gravity sensing.

Borrowing from smart phone technology, they have developed and demonstrated a fingernail-size gravimeter.

Richard Middlemiss and several colleagues with the university’s Institute for Gravitational Research published results of their research in the journal Nature.

“Gravimeters have been around for decades. The problem with them is they generally cost hundreds of thousands of pounds, or dollars, and they weigh 10 kilograms, 20 kilograms, up to hundreds of kilograms,” he said.

Middlemiss said the device could be produced much more economically than current gravimeters.

“What we’ve done is we’ve taken the technology that’s used in a mobile phone — that’s the thing that turns the screen sideways when you tilt it (an accelerometer). … We’ve made this thing massively more sensitive and massively more stable and we’re now able to use that as a gravimeter,” he added.

Image Caption

The new gravimeter created by researchers at the University of Glasgow in Scotland’s Institute for Gravitational Research uses the same type of micro-electromechanical system (MEMS) used in smartphones’ internal accelerometers. Image courtesy of the University of Glasgow.

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In the “less is more” department, researchers at the University of Glasgow in Scotland are developing a device that could potentially revolutionize the field of gravity sensing.

Borrowing from smart phone technology, they have developed and demonstrated a fingernail-size gravimeter.

Richard Middlemiss and several colleagues with the university’s Institute for Gravitational Research published results of their research in the journal Nature.

“Gravimeters have been around for decades. The problem with them is they generally cost hundreds of thousands of pounds, or dollars, and they weigh 10 kilograms, 20 kilograms, up to hundreds of kilograms,” he said.

Middlemiss said the device could be produced much more economically than current gravimeters.

“What we’ve done is we’ve taken the technology that’s used in a mobile phone — that’s the thing that turns the screen sideways when you tilt it (an accelerometer). … We’ve made this thing massively more sensitive and massively more stable and we’re now able to use that as a gravimeter,” he added.

Application in the Field

AAPG Member Joseph P. Fagan Jr., president of Centennial Geoscience Inc. in Littleton, Colo., agreed that if the device can be fully developed and mass-produced commercially, it could be an important advancement for the field and for energy exploration.

“We’re going to have to watch and see how it develops. It has a lot of promise and it really is exciting,” Fagan said. “If it can be effectively mass-produced, it would reduce overall costs. You could place gravimeters in the field for real-time or ongoing monitoring,” he said.

“To me, acquiring gravity and magnetic data is the logical first step to help design an exploration program,” Fagan said.

He said gravimetry, especially airborne, has been advancing in quality and cost-effectiveness, and a further reduction in cost and improvement in convenience would go a long way.

“If it (gravimetry) helps and prevents you from shooting a couple square miles (of seismic) you didn’t need, it has probably already paid for itself,” he said.

He said airborne geophysical methods have extra value when land access is a problem.

“Since these data are all acquired remotely, there are no feet on the ground,” he said.

How It Works

The team’s new device, which they have named “Wee-g,” uses the same cheap, mass-producible micro-electromechanical systems (MEMS) used in smartphones’ internal accelerometers. While the MEMS technology in phones uses relatively stiff and insensitive springs to maintain the orientation of the screen relative to the Earth, Wee-g employs a silicon spring about a tenth of the thickness of a human hair. This allows Wee-g’s 12 millimeter-square sensor to detect very small changes in gravity, according to the university release.

The team used the device to measure the Earth tides from the basement of the university’s Kelvin building. Earth tides are a subtle effect from the moon and the sun exerted on the Earth’s crust. The pull of the sun and the moon displace the crust, creating a very slight expansion and contraction of the planet of around 40 centimeters.

“The Earth tides are a well-established phenomenon, which we’re able to accurately predict using mathematical models,” said Giles Hammond of the university’s School of Physics and Astronomy, one of the co-authors of the paper.

“One of the factors which separates gravimeters from simple accelerometers is stability, allowing users to monitor variations in gravity over the course of several days or weeks. We used our Wee-g system to monitor the Earth tides under Glasgow over the course of several days, and our results aligned perfectly with the variations in gravity that the model had predicted,” Hammond continued.

“The significance of this is two-fold: firstly, we’ve shown that a MEMS device can maintain its stability over a long period of time, and secondly, that a device which could easily be built using existing mass-production technology can act as a very accurate gravimeter,” Hammond added.

“Wee-g opens up the possibility of making gravity measurement a much more realistic proposition for all kinds of industries,” said Middlemiss. “Gravity surveys for geophysical exploration could be carried out with drones instead of planes and networks of MEMS gravimeters could be placed around volcanoes to monitor the intrusion of magma that occurs before an eruption – acting as an early warning system.”

The detector, built at the university’s James Watt Nanofabrication Centre, is a collaboration between the School of Physics and Astronomy (Institute for Gravitational Research) and the School of Engineering (Electrical and Nanoscale). The work is one of the first research outcomes from QuantIC, the UK’s “centre of excellence for research, development and innovation in quantum enhanced imaging,” which was established in late 2014.

“What’s going on here is we’re taking our fundamental core research and we’re actually translating it into applications that can be taken up by industry,” said Hammond.

“In this particular application, the industries involved might be oil and gas prospecting, defense security or industries interested in environmental monitoring,” noted Hammond.

Fagan said he agreed the research is promising.

“There are lots of applications, not just in oil and gas but in greater geophysics as well,” he said.

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