MEMS: The technology of tiny devices
MEMS stands for microelectromechanical systems, which is the technology of micro-fabricated devices. The main idea behind this technology is to combine basic mechanical parts and tools – like cantilevers and membranes – with silicon technology of the type found in computer processors.
The result is a microfabricated electronic chip that unites multiple sensors in a small space, and which can be used to build various systems, including accelerometers, gyroscopes, and magnetic sensors. Accordingly, MEMS’ small size has made them ideal for smartphones, GPS, game controllers, and other modern inventions.
IMUs: Tiny devices for sensing
An inertial measurement unit, or IMU, is an electronic chip composed of several micro-fabricated sensors: an accelerometer, which senses force or gravity; a gyroscope, which reports the angular rate; and sometimes a magnetic sensor, which acts as a compass.
These sensors collect data that are processed by an external or onboard microprocessor to provide information about the attitude, orientation, and rotational speed of an object.
Depending on the model and the manufacturer, each of these internal sensors is available in 1-, 2-, or 3-axis versions. However, the 3-axis devices are the most commonly used today, since they provide extra information which may be required for certain applications such as robotics.
If you want to learn more about IMUs, consider taking a look at our previous article titled An Introduction to IMU.
The difference between them
As you can see, MEMS and IMUs are both electronic chips. Since IMUs can be made using different technologies, including MEMS, the difference is that some IMUs are a type of MEMS.
How MEMS-based IMUs work
MEMS-based IMUs use the Coriolis Effect, which is based on vibrating mass deflection resulting from rotation to measure the angular speed or acceleration. This technology is prone to drift significantly over time, so gyroscopic sensors use an advanced Kalman filter to correct for this effect.
For example, the Variense VMU931 is a MEMS IMU with 9 degrees of freedom. It uses a customized Kalman filter algorithm for excellent orientation and motion detection. This IMU is built for a range of applications – from UAV (drone) navigation to clinical research, for instance – in fields including industry, sports, and medicine.
Other types of IMUs
For tactical-grade applications which require high accuracy, Ring Laser Gyros (RLGs ) are generally considered to be the most accurate option. The RLG-based IMUs have excellent stability and repeatability characteristics. However, they are also very expensive.
Fiber-optic (FOG) technology is an alternative to the more expensive RLGs. FOGs are more accurate than their MEMS counterparts. They provide more precise rotational rate information, since they are less dependent on using mechanical movement to conduct the transduction. However, while FOGs are not quite as costly as RLGs, they are still significantly more expensive than MEMs.
As MEMS inertial measurement sensors improve in performance, they’re more accepted for use in the latest industrial and research applications, like unmanned vehicle control and biomechanics research, to name just a few. With their small size, low cost, and and multi-axis sensing, MEMs-based IMUs are rightfully poised to become the most popular type of sensors.