Scanning electron microscope image of an array of optomechanical accelerometer devices. Green squares are proof masses suspended by nano-scale tethers. Near the green blocks are optical cavities, slightly pink, which senses motion of the proof masses. (via Martin Winger & Caltech)
Accelerometers allow our devices to move with us in a 3D world. They are embedded into most of our mobile tech and serve to be used as a motion input devices for a wide range of applications such as gaming, image stabilization and interface control (among a host of other uses). They are also used to determine the user’s relative position much like GPS but aren’t the most accurate over satellite positioning systems. In order for them to be more accurate, such as those used on airplanes, they have to be larger in size to accommodate the electrical circuitry needed for precision. Researchers at Caltech (California Institute of Technology) are looking to change that by miniaturizing a new sensor system which makes use of laser-light over electronic circuits. Accelerometers work by measuring ‘proper acceleration’ (physical acceleration) associated with a weight per unit of flexible test mass which is detected by an electrical circuit. Those sensors are accurate to a point but tend to become larger in size when increased accuracy is needed. It’s widely known that laser-light is extremely accurate when used to pinpoint a position and making a laser-light device with an optical readout has been done before such as the Laser Interferometer Gravitational-Wave Observatory (using optical interferometers to detect cosmic gravitational waves) at Caltech. These too rely on a larger proof of mass to detect subtle movement. To overcome these limitations the researchers, led by professor of applied physics Oskar Painter, embedded all the components needed, such as the lasers, detectors and interferometer) for the new sensor on one nano-scaled silicon chip.
According to Profess Painter the key to getting the new sensor to function accurately lies within the sensors optical cavity that was engineered to ‘read-out the motion.' The optical cavity itself is incredibly small and measures only 20 microns long, 1 micron wide and a few tenths of a micron thick. It’s equipped with 2 silicon nano-beams with one positioned on the proof of mass while the other is stationary. These two nano-beams act as ‘light-pipes’ and when laser-light is introduced it bounces back and forth through the nano-beams holes. This in-turn moves the proof of mass which moves one of the nano-beams and as a result changes the intensity of light being reflected out of the system. The sensor is so accurate that movements can be measured all the way down to a few femtometers (the diameter of a single proton) making it ultra-sensitive to the slightest movement! The researchers hope to see their accelerometer sensor integrated in future microchips not only for mobile devices but use with oil and gas exploration, incorporated in fighter jets for increased flight stabilization and even biomedical applications.
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