Ultra-precise optomechanical accelerometer needs no calibration

March 29, 2021 // By Rich Pell
Ultra-precise optomechanical accelerometer needs no calibration
Researchers at the National Institute of Standards and Technology (NIST) say they have developed an accelerometer measuring only a millimeter thick that uses laser light instead of mechanical strain to produce a signal.

Known as an optomechanical accelerometer, the device is designed to address the increasing demand to accurately measure acceleration in smaller navigation systems and other devices. Consisting of two silicon chips, with infrared laser light entering at the bottom chip and exiting at the top (see image), the design of the instrument makes the measuring process more straightforward, providing higher accuracy, say the researchers.

The device also operates over a greater range of frequencies and has been more rigorously tested than similar light-based devices. Not only is device much more precise than the best commercial accelerometers, it does not need to undergo the time-consuming process of periodic calibrations.

In fact, say the researchers, because the instrument uses laser light of a known frequency to measure acceleration, it may ultimately serve as a portable reference standard to calibrate other accelerometers now on the market, making them more accurate. The device also has the potential to improve inertial navigation in such critical systems as military aircraft, satellites and submarines, especially when a GPS signal is not available.

Accelerometers record changes in velocity by tracking the position of a freely moving mass, dubbed the "proof mass," relative to a fixed reference point inside the device. The distance between the proof mass and the reference point only changes if the accelerometer slows down, speeds up, or switches direction.

The motion of the proof mass creates a detectable signal. The new NIST accelerometer relies on infrared light to measure the change in distance between two highly reflective surfaces that bookend a small region of empty space. The proof mass - which is suspended by flexible beams one-fifth the width of a human hair so that it can move freely - supports one of the mirrored surfaces. The other reflecting surface, which serves as the accelerometer’s fixed reference point, consists of an immovable microfabricated concave mirror.

Together, the two reflecting surfaces and the empty space between them

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