Piezoresistive Sensor Unit for Monitoring Mechanical Force in Connected Components

Simple SummaryContent extracted from patent full text and abstract with AI.

This invention is a thin-film sensor unit designed to be placed under a bolt or screw — essentially built into or around a standard washer — to continuously monitor whether the fastener remains properly tightened. The sensor layer is made from a carbon nanotube–polymer nanocomposite whose electrical resistance changes in direct proportion to the mechanical force pressing on it, allowing even tiny loosening events to be detected in real time. The sensor connects via a plug-in electronics module containing a signal processor, wireless or wired transmitter, and a small battery that can power the system for at least six months without external power. The entire assembly is designed to be a drop-in replacement for an ordinary washer, requiring no modification to existing bolted joints.

Use CasesContent extracted from patent full text and abstract with AI.

• Continuous real-time monitoring of bolted flange connections in oil and gas pipelines to detect loosening or leakage at critical joints before a failure occurs.
• Structural health monitoring of high-strength bolts in bridges, wind turbine towers, and steel-frame buildings where dynamic loads or thermal cycling can cause gradual loosening.
• Quality assurance during assembly of industrial machinery by verifying that the correct tightening torque has been reached and maintained, replacing manual torque-wrench checks.
• Monitoring of bolted connections in railway infrastructure (rail joints, track fasteners) where vibration-induced loosening poses a safety risk.
• Leak detection at pipe coupling points in water distribution or chemical processing networks by sensing the drop in clamping force that precedes or accompanies a seal failure.
• Condition monitoring of dental or orthopaedic implant screws, where the sensor washer can alert clinicians to implant loosening without requiring invasive inspection.

BenefitsContent extracted from patent full text and abstract with AI.

• Enables real-time, continuous monitoring of fastener preload force with a reaction time below 500 µs, detecting force changes as small as a few millinewtons caused by rotations of less than 1°.
• The layered thin-film design is compatible with standard commercial washers and requires no modification to existing bolted joints, making retrofit installation straightforward.
• Carbon nanotube nanocomposite sensitivity can be tuned by adjusting filler concentration or polymer type, allowing the sensor to be optimised for a wide range of torque levels and bolt sizes.
• Mass-production-compatible printing and coating processes (screen printing, inkjet, spray coating, etc.) keep manufacturing costs significantly lower than piezoelectric or RFID-based alternatives.
• The self-contained plug-in module with an integrated battery eliminates the need for external power wiring and can operate autonomously for at least six months in wireless mode.
• An optional ring-shaped secondary piezoresistive sensor adds fluid-leak detection capability at the joint, providing a dual-function monitoring solution in a single compact unit.

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Patent Abstract

A sensor unit (4) for monitoring connectable components is proposed, which comprises a base unit (5), an electrode layer (6), and a sensor layer (7), wherein the electrode layer (6) is formed on the base unit (5), wherein the electrode layer (6) comprises at least one electrode which is formed in electrical contact with the sensor layer (7). Furthermore, the sensor layer (7) is formed on a side of the electrode layer (6) facing away from the base unit (5), and the sensor layer (7) is formed from a piezoresistive material, so that a mechanical force can induce an electrical resistance change in the sensor layer (7).