Fabrication, Modeling, and Evaluation of a Digital Output Tilt Sensor With Conductive Microspheres

Abstract

Abstract-Recent advances in wearable computing ask for bendable and conformable electronic circuits and sensors, allowing an easy integration into everyday life objects. Here, we present a novel flexible tilt sensor on plastic using conductive microspheres as gravity sensitive pendulum. The sensor provides a digital output of the measurement signal without the need for any additional electronics (e.g. amplifiers) close to the sensing structure. The sensor is fabricated on a free-standing polyimide foil with SU-8 photoresist defining the cavity for the pendulum. The pendulum consists of freely movable conductive microspheres which, depending on the sense of gravity, connect different electric contacts patterned on the polyimide foil. We develop a model of the sensor and identify the amount of microspheres as one of the key parameters in the sensor design which influences the performance of the sensor. The presented tilt sensor with eight contacts achieves an angular resolution of 22.5• with a hysteresis of 10• and less at a tilt of the sensor plane of 50• . Analysis of the microsphere movements reveals a response time of the sensor at ∼ 50 ms.

Flexible Sensors—From Materials to Applications

“…Resolution and hysteresis are generally regarded as the most significant parameters for orientation sensors. Büthe et al [557,558] built a digital tilt sensor based on conductive microspheres acting as a pendulum. Depending on the orientation of the sensor structure, the conductive microspheres create an electrical connection between the ground pads and the respective contact pads.…”

“…An additional example includes biomimetic skins which mimic the ability of organisms to orientate themselves with the Earth's magnetic field [496]. Additionally, detecting rotation and tilt angles can endow robots with the ability to correctly self-detect moving parts' position information [557][558][559]. Soft and deformable robots safely interact with humans [614,615], and, at the same time, flexible and stretchable sensors perfectly fit with the demanding requirements of biologically inspired soft robots in terms of conformability to the bending structures in which large strains are involved [90,616,617].…”

Electric-Contact Tilt Sensors: A Review

“…Aiming at further miniaturization, conventional steel balls used in bearings must be replaced with some other members. For example, using conductive microspheres (made of tin, silver, and copper alloy, which is usually used for soldering of ball-grid arrays) having diameter of 0.25 mm in the tilt sensor has already been successful, presented in [ 59 ]. Moreover, at the Institute of Micromechanics and Photonics, Warsaw University of Technology, a research project “Ultra-Efficient WIreless POwered Micro-robotic joint” (UWIPOM2) has been realized [ 60 ], which is aimed, among other things, at building a rolling bearing having external diameter of 300 µm and utilizing balls with diameter of 30–70 µm.…”

Liquid‐Based Digital Readable Tilt Sensor

“…Direction detection in 12 directions was possible because the sensor fabricated in this study had 12 wires. Büthe et al [ 26 ] proposed the use of micrometal spheres to fabricate a digital reed tilt sensor using conductive materials. In contrast to the aforementioned liquid metal sensor, this sensor could measure inclination angles up to 360°.…”