Differential Capacitive Bias Stability under Non-Uniform Substrate Thermal Fields
Spatial thermal gradients disrupt differential capacitive balance, requiring symmetric substrate layout and strain isolation to preserve bias stability.
Dielectric Permittivity Drift
Property Instability
Long-term variations in the polarizability of insulating materials alter the baseline capacitance of sensing elements and transmission lines. This phenomenon, known as dielectric permittivity drift, compromises the stability of capacitive sensors and high-frequency printed circuit boards. It changes the electrical impedance and propagation velocity without any physical movement of the electrodes.
Environmental Sensitivity
Adsorption of water vapor and exposure to high temperatures are the primary drivers of material property changes. Because water has a high dielectric constant, even trace amounts of moisture absorbed by the polymer or ceramic insulation lead to a rise in permittivity. This dielectric permittivity drift is often reversible by baking out the sensor, but permanent chemical aging can occur after prolonged exposure.
These environmental effects introduce measurement errors that mimic physical deflection in capacitive pressure or position sensors.
Material Influence
Polyimide and epoxy glass laminates exhibit higher susceptibility to aging and moisture absorption than quartz or specialized fluoropolymers. Choosing materials with low moisture absorption coefficients reduces the risk of long-term capacitance changes. High-reliability sensors utilize ceramic or glass substrates to minimize structural and material degradation over their operating life.
Compensation Technique
Dual-capacitor structures containing a sealed reference channel exposed to the same thermal conditions provide a differential measurement that cancels the drift. While the active capacitor responds to the target physical parameter and environmental changes, the sealed reference tracks only the dielectric permittivity drift. Subtracting the reference signal from the measurement signal isolates the true physical parameter.