MEMS Demystified with 3D Printing

Today we take it for granted that a smartphone screen automatically rotates upwards, and that you can perform other motion-based actions–such as turning on the flashlight by flicking your wrist. But how is your phone actually able to sense this spacial motion? The short answer is via MEMS (micro-electromechanical system) technology, which senses rotation and acceleration in the form of IMUs (inertial measurement units).

But how do MEMS IMUs actually work?

The answer is conceptually simple, but mind-blowing in scale. As seen in the Breaking Taps video below, inside each MPU-6050 IMU is a relatively heavy mass that wants to stay stationary as an accelerometer, while a vibrating tuning form distorts when twisted as a gyroscope. Or more accurately, there are three of each, one for each translational and rotational axis.

The accelerometer, as introduced at 4:45 the easiest to understand of these two devices. A mass is fixtured to a spring, and moves with respect to the device’s overall structure based on linear motion. A series of capacitive combs is used to sense these changes.

The gyroscope uses similar concepts of distortion and capacitive sensing. In this case, however, vibration is actively induced in the sensing element, instead of a using a static mass. Under rotation, the vibrating element induces a Coriolis force on the system, which can be picked up and passed along as data.

Both types of sensing elements are illustrated in the video via a 3D-printed model, available here if you’d like to print one yourself. At that scale, these concepts are interesting, but approachable. What’s mind-boggling is that billions of this type of device can be made cheaply, and at a physical scale that makes a microSD card look gigantic.