Researchers at the National Institute of Standards and Technology have developed an accelerometer that uses laser light instead of mechanical strain to produce a signal.
Called an optomechanical accelerometer, it is only a millimeter thick and provides higher accuracy, NIST said this week.
The NIST device is made up of two silicon chips with infrared laser light entering at the bottom chip and exiting at the top. The top chip contains a proof mass suspended by flexible silicon beams just one-fifth the width of a human hair, which means it can move up and down freely in response to acceleration.
A proof mass is a part of all accelerometers, including the new NIST device. It is a freely moving mass that is tracked relative to a fixed reference point inside a device. The distance between the proof mass and a reference point changes when an accelerometer slows down, speeds up or switches direction. The motion of a proof mass creates a detectable signal. Many common electronics devices use accelerometers, including smartphones that detect when a phone is picked up, which activates the screen for viewing.
In the NIST device, a mirrored coating on the proof mass and a microfabricated concave mirror attached to the bottom chip form an optical cavity. The wavelength of the infrared laser light is picked to nearly match the resonant wavelength of the cavity, which enables the light to build in intensity as it bounces back and forth between the two mirrored surfaces many times before exiting.
When the device accelerates, the proof mass moves, changing the length of the cavity and shifting the resonant wavelength. This in turn alters the intensity of the reflected light. With an optical readout, it is possible to convert the change in intensity into a measurement of acceleration.
Other accelerometers use light, but the design of the NIST device makes measuring more straightforward and more accurate, NIST said. The device also operates over a great frequency range and has undergone more testing than similar devices.
It also does need time-consuming periodic calibrations. It might be usable as a portable reference standard to calibrate other accelerometers now on the market to make them more accurate, NIST said.
It could be useful for improvements in inertial navigation in critical military, submarine and satellite systems when GPS is not available. NIST researchers Jason Gorman, Thomas LeBrun, David Long and their colleagues described their work on the device in Optica. Their research is part of a NIST program called NIST on a Chip.
The NIST device allows scientists to lower the uncertainty of measurements over a wide range of acceleration frequencies, from 1 kilohertz to 20 kilohertz without the need for calibration. The researchers are making improvements that should decrease uncertainty to near 1%.
It is capable of sensing displacements of the proof mass that are less than one hundred-thousandth of the diameter of a hydrogen atom. The optomechanical accelerometer can detect accelerations as tiny as 32 billionths of a g, which is a measure of acceleration from the Earth’s gravity.
That level of sensitivity is higher than all accelerometers now on the market with similar size and bandwidth, NIST said.
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