Fundamentals of Sagnac Phase Shift and Thermal Shupe Effect Cancellation
Quadrupolar winding cancels thermal Shupe non-reciprocity by spatially pairing symmetric fiber segments equidistant from the coil center.
Elastomeric Potting
Protective Encapsulation
The application of flexible polymeric compounds to enclose and protect electronic assemblies secures delicate circuitry against moisture and mechanical shock. Known as elastomeric potting, this process involves dispensing liquid silicones or polyurethanes over assemblies within a housing where they cure into soft, resilient solids. This encapsulation technique prevents the ingress of water, dust, and corrosive chemicals that would otherwise cause electrical failure.
The flexible nature of the material ensures that thermal expansion does not damage fragile solder joints.
Material Selection
Selecting the appropriate compound requires balancing curing temperature, viscosity, and chemical compatibility with the substrate. Silicone-based systems are preferred for their stability over wide temperature limits, while polyurethane compounds provide superior adhesion to various housing plastics and metals. The liquid must flow easily around components to avoid leaving air pockets which could fail under high pressure or high voltage.
Vacuum degassing before dispensing is commonly used to remove entrapped air and prevent voids in the cured material.
Mechanical Damping
Damping of shock and vibration is achieved through the low modulus of the cured elastomer. When external forces are applied to the housing, the elastomeric potting deforms, absorbing the kinetic energy and distributing the stress away from sensitive sensors. This behavior is valuable in aerospace applications where constant mechanical vibration is present.
Calibration Adjustment
Metrological validation of the encapsulated sensor must account for any mechanical load that the cured resin applies to the transducer element. In high-precision pressure sensors, the presence of the potting material can shift the zero point and introduce temperature-dependent measurement errors. Technicians perform calibration cycles before and after the potting process to measure these shifts and program the appropriate offset corrections into the sensor’s firmware.
Regular testing of the curing oven ensures that the polymer reaches its designed cross-link density, keeping any calibration drift within the allowable limits.