Accelerometers and Gyroscopes: The Stars Amongst the Sensors

Have you ever wondered how a smartphone quickly senses its location, adjusts screen orientation and creates beautiful parallax effects with the background of floating icons? Let us find out how this happens and what are the choices available to the designers -- Sneha A. and Dilin Anand

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Rugged seems to be the keyword
It comes as no surprise though, that the sensor which is used to detect a free-fall should not be the first one to bonk out on impact.

The bias stability for gyros may be pretty numbers in the datasheet, but everything goes out of the window once you get your device out into the real world. Gravity sensitivity and environmental factors like heat, all play a part here. This is why bias stability and vibration rejections are some of the key parameters being looked at. Analog Devices’ ADXRS64x family of low-noise, vibration-rejecting yaw rate gyroscopes are drop-in performance upgrades to existing designs using the ADXRS62x family.

For modern applications such as oil-downhole monitoring, UAV inertial measurements and industrial robotics, there is an increased demand for rugged accelerometers. Of course, another area that requires these accelerometers is the exponentially growing mobile devices segment. With this demand in mind, the last year has seen the launch of tougher accelerometers that can withstand heavy impacts.

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A new line of sensors that are insensitive to temperature changes or gradients, with signal output unaffected by electromagnetic interference, and requiring no warm-up time was brought out by Silicon Designs in the last half of 2013. All Silicon Designs’ accelerometers feature a custom-integrated circuit with onboard sending amplifier and differential output stage, with a 0.5V-4.5V single-ended or ±4V differential output, proportional to the amount of measured acceleration.

Laser accelerometers
Researchers at Caltech, the California University of Technology, are working on accelerometers that work with lasers. An accelerometer normally uses an electrical circuit, whilst a laser accelerometer uses laser light instead of electricity. The optical cavity of this accelerometer is very small (about 20 microns long, only a single micron deep and few tenths of a micron thick). It contains two silicon nanobeams that are situated in an accelerometer as the two sides of a zipper that has a proof mass attached to one of its sides.

The moment a laser light enters the accelerometer, the nanobeams act as a ‘light pipe.’ These nanobeams guide the light to be bounced back and forth in between its holes. The movement of the proof mass results in the change of the intensity of the laser light that is reflected out. This reflected laser light is so sensitive to the motion of the proof mass that it helps in the determination of even the slightest displacement.

The laser accelerometers are still under research to find the cost-effective ways of using laser with accelerometers.

Sneha A. is technical journalist at EFY, Gurgaon and Dilin Anand is senior technical correspondent at EFY, Bengaluru




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