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A 3D Printed Ti6Al4V Alloy Uniaxial Capacitive Accelerometer

Published in : IEEE Sensors Journal (Volume: 21, Issue: 18, September 2021)
Authors : Valentina Zega, Luca Martinelli, Riccardo Casati, Emanuele Zappa, Giacomo Langfelder, Alfredo Cigada, Alberto Corigliano
Summary Contributed by:  Anupama

The currently prevalent Micro-Electro-Mechanical sensors (MEMS) can have minimal dimensions and are cheap when mass produced. However, their cost rises significantly in the case of customization for niche applications. Recently, 3D-printing technology has gained attention as a fabrication process that promises customization at a low cost. 3D-printed sensors can be fabricated either by embedding sensors into printed structures or by intrinsically printing the entire sensor.

A 3D-printed metal capacitive accelerometer prototype is presented here. A Ti6Al4V uniaxial accelerometer was designed, fabricated, and evaluated in an experimental environment.

An additive manufacturing technique, Laser Powder Bed Fusion (L-PBF), is regarded as the most versatile 3D-printing technique for metal sensors with good mechanical properties and resolution.

The uniaxial accelerometer design comprises a proof mass suspended through folded springs that allow pure translation along the y-axis. To ensure low cross-axis sensitivity, the springs are designed to maintain the desired mode at an approximate frequency of 200 Hz.

A Renishaw AM 250 3D printer was used to print the accelerometer using a gas atomized Ti6Al4V powder. The printer applies a meander scanning strategy and could produce specimens with a layer thickness of 60 microns. The printer system achieved overall dimensions for the device as small as 28 x 23 x 15 cubic mm.

The accelerometer was assembled with two Cu electrodes and glued to a printed circuit board. The proof mass and the electrodes are isolated by two PVC sheets. The sheets are roughly 300 microns thick, which corresponds to the nominal distance between the proof mass and the electrodes.

Both the proof mass and the electrodes are kept at a constant voltage. In response to an external acceleration applied along the y-axis, the proof mass is displaced toward or away from the electrodes. The change in the distance between the proof mass and the electrodes results in a differential capacitance change. Thus, the external acceleration can be measured as a capacitance variation between the proof mass and electrodes.

The printed prototype was tested in an experimental setup to evaluate its mechanical and electrical characteristics. The results show the linear behavior of the accelerometer to be within the considered range of frequency.

The differential sensitivity of the prototype was determined by measuring the capacitances between the electrodes and the proof mass with the PCB mounted first in the horizontal direction and then in the vertical direction. Upon comparison, the proposed device was found to be strongly comparable to existing state-of-art MEMS accelerometers. The alloy Ti6Al4V has a specific heat of 553J/Kg K and a thermal conductivity of 6.6–6.8W/m K, guaranteeing a much better thermal behavior than polymer-based sensors.

The 3D-printed metal accelerometer prototype presented here failed to achieve dimensions as low as that of MEMS sensors. However, the accuracy and versatility of the proposed 3D-printed sensor were proven by both visual and electrostatic measurements. The prototype has demonstrated the possibility of a new class of 3D-printed sensors that can be customized for specific purposes at a low cost.

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