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62 DESIGN007 MAGAZINE I OCTOBER 2025 alerts the driver when one or more tires are signifi- cantly underinflated. Typically mounted in the valve stem, a TPMS sensor contains a MEMS (micro- electromechanical system) pressure sensor, ASICs (application-specific integrated circuits), an RF transmitter, and a battery within a compact enclo- sure. By helping drivers maintain proper tire pres- sure, TPMS technology improves fuel efficiency, extends tire life, and enhances overall safety. These sensors operate in extremely harsh con- ditions, enduring continuous vibration, mechanical shock, wide temperature swings, and the stresses of tire rotation. Moisture, humidity, road debris, and even tire sealant chemicals also threaten their long- term reliability. Specialized polyurethane-based potting materi- als are widely used to encapsulate and protect sen- sitive electronics in TPMS sensors. Specifically engi- neered, these formulations provide an ideal combi- nation of material properties, including: • Flexibility with sufficient mechanical strength • Strong adhesion to electronic assemblies • Ability to absorb stresses associated with thermal expansion and contraction • RF transparency • Resistance to moisture and chemicals These attributes make polyurethane potting com- pounds effective at damping vibration and absorb- ing mechanical shock. Unlike rigid epoxies, they flex with temperature changes, eliminating issues caused by CTE mismatch. Tailored formulations also provide excellent water resistance while main- taining RF signal integrity. Because TPMS modules must meet stringent auto- motive requirements, they undergo a comprehensive series of durability and reliability tests. The primary standard is the ISO 16750 Series, which defines sys- tem-level electrical, mechanical, climatic, and chemi- cal testing for automotive electronics, including: • ISO 16750-3: Mechanical load testing includ- ing vibration and shock • ISO 16750-4: Climatic stress testing including thermal cycling, temperature shock, humidity changes, and ingress of moisture and particulates • ISO 16750-5: Chemical exposure testing for automotive fluids (e.g., brake fluid and tire sealant), salt spray, and cleaning agents • ISO 20653 (IP67/IP68): Ingress protection against moisture and contaminants Beyond these standards, TPMS assemblies undergo further stress testing to simulate long- term field conditions. These include PCTs, salt fog exposure, 85°C /85% humidity damp heat tests, thermal cycling (-40°C to 125°C ) and mechanical drop tests. Throughout testing, the potting material must maintain adhesion, flexibility, and mechanical integrity to ensure reliable operation over the life- time of the vehicle. When Sensors Get Wet: How Potting Protects Water Monitoring Devices Today's smart water meters and sensors are often deployed in harsh outdoor environments where water ingress (both liquid and vapor) is a persistent threat. These devices must reliably deliver accurate measurements and data transmissions throughout a 10–15-year service life. In agriculture, water sensors are key compo- nents of smart farming systems. These devices enable controlled and efficient irrigation and water management based on real-time data collected on weather and soil conditions. Using temperature and moisture sensors, they provide continuous monitor- ing and send alerts when an action, such as adjust- ing irrigation schedules, is needed. In urban settings, remote water metering has become an essential technology, improving water management for both consumers and utilities. Real- time data on water consumption enables early leak T P M S s e n s o r d u r i n g p ot t i n g p ro c e s s . ▼