Gaithersburg, Maryland, March 12, 2021-A laser-driven accelerometer (a sensor that detects sudden changes in speed) operates in a larger frequency range than similar non-optical instruments and has a higher Accuracy. Researchers at NIST have developed a photomechanical accelerometer device with a thickness of 1 mm that bypasses the dependence on mechanical strain by using light as its activator. The researchers said that the device does not require regular calibration.
Although there are other light acceleration sensors, the NIST design provides higher accuracy than similar and similar instruments.
All accelerometers record speed changes by tracking the position of a mass proof or freely moving mass relative to a fixed reference point inside the accelerometer itself. The distance between the inspection mass and the reference point will only change when the accelerometer changes speed or direction.
For example, in a vehicle moving at a constant speed, the distance between the seated passenger and the dashboard remains constant. However, if the car brakes suddenly and throws it at the passengers, the distance will change.
In motion, the detection mass produces a detectable signal that can be sensed by the accelerometer. Researchers at NIST use infrared lasers to measure the distance difference between two highly reflective surfaces, which are pre-determined with a blank space. They use flexible beams to dangle one-fifth of the width of a person’s hair. If the free matter moves freely, it will support one of the mirrors. The other reflecting surface is composed of a fixed micro-machined concave mirror and is used as a fixed reference point.
The mechanism of the surface and free space forms a cavity in which infrared light resonates or reflects back and forth at a precise wavelength, which is determined by the distance between the mirrors. With this intensity, if the detection mass moves in response to acceleration, thereby changing the interval between the mirrors, the resonance wavelength will also change.
Researchers use stable single-frequency lasers, lock them on the cavity, and track any changes in resonant wavelength with high sensitivity. In this way, coupled with optical frequency combs, they can measure light in the cavity with high accuracy.
The NIST device consists of two silicon chips, the infrared laser enters the bottom chip, and then shoots out from the top. The top chip contains an inspection mass suspended by a silicon beam, which allows the mass to move up and down freely in response to acceleration. The mirror coating on the inspection mass and the hemispherical mirror connected to the bottom chip form an optical cavity. When the device accelerates, the inspection mass will move, thereby changing the length of the cavity and changing the resonance wavelength. This changes the intensity of the reflected light. The optical reading converts the change in intensity into a measure of acceleration. Provided by F. Zhou/NIST.
When the mass moves during the acceleration point, which changes the length of the cavity, the intensity of the reflected light changes as the wavelengths associated with the frequency comb move in and out. resonance With cavity.
This design ensures the quality of the verification and the support beam acts as a harmonic oscillator or a simple spring, and vibrates a single frequency within the working range of the accelerometer. Researchers say that converting the displacement of the detection mass into acceleration is an operation that plagues existing optomechanical accelerometers.
In the test, the accelerometer allows the engineering team to obtain the smallest measurement uncertainty, with an acceleration frequency ranging from 1 to 20 kHz. They do not need to calibrate the instrument. The current iteration of the device is capable of detecting displacements of standard masses less than one thousandth of the diameter of a hydrogen atom. The acceleration it detects is as small as 32 parts per billion ag (where “g” is the acceleration due to the gravity of the earth).
The research team said that further improvements will enable the optomechanical accelerometer to be used as a portable, high-precision reference device for calibrating accelerometers other than laboratory settings.
NIST researchers Jason Gorman, Thomas LeBrun, David Long and colleagues at Optical (www.doi.org/10.1364/OPTICA.413117).
