Abstract
Energy-autonomous bistable threshold sensor switches have the potential to reduce costs because they do not need any electrical energy supply for monitoring physical quantities, such as relative humidity. In previous work, a bistable beam-like sensor switch with switching hysteresis was manufactured from sheet metal and a partially coated water vapor-sensitive hydrogel (poly(vinyl alcohol)/poly(acryl acid)). Based on the beam theory, a corresponding mechanical model was developed. However, bending plates should be used instead of bending beams to separate the humidity to be measured from the electrical contacts. For this reason, this work deals with the development and realization of a mechanical model based on the plate theory to describe the deflection of a silicon bimorph bending plate partially coated with hydrogel that swells with increasing humidity. For implementing a switching hysteresis a plasma-enhanced chemical vapor deposition silicon dioxide (SiO2) layer is used, which was deposited and structured on top of the silicon plate. The hydrogel layer itself is patterned on the surface of the bending plate using a stamp technique. To validate the mechanical model, the switching hysteresis of the miniaturized sensor switch was measured optically by a camera measurement device.
Highlights
The demand on sensors and sensor systems that combine data acquisition and signal processing increases in several fields, like industrial production, building automation, and automobile technology
From the mechanical model with axial compression (Equation (82)), the S-shape curve progression shows an increase in the width of the hysteresis, which depends on the axial compression
This work deals with the miniaturization and development of a rectangular-shaped, siliconbased sensor switch with switching hysteresis for humidity sensing
Summary
The demand on sensors and sensor systems that combine data acquisition and signal processing increases in several fields, like industrial production, building automation, and automobile technology. Numerous sensors and sensor systems can be used for humidity sensing [1,2]. 90% of all sensors are used as threshold switches and, in process control, some 70% [3]. A novel approach for a non-powered humidity threshold switch based on the binary zero-power sensor principle (BIZEPS) was proposed in Reference [4,5,6,7,8,9,10]. With this principle, the energy for the switching process is taken directly from the measured variable. The basic part is a humidity-dependent polymer film in which swelling has both a sensory effect and an actuator function that causes switching
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