Electronics Guide

Tire Pressure Monitoring Systems

Tire pressure monitoring systems (TPMS) are mandated in much of the world: the United States required direct or indirect TPMS on new light vehicles under 10,000 pounds from September 2007 under the TREAD Act, and the European Union has required TPMS on all newly registered passenger cars since November 2014 under UN Regulation 64. Direct-measurement sensors mounted inside the wheel are difficult to service, so the rotating, vibration-rich tire is an attractive target for energy harvesting that could remove the coin cell entirely.

Piezoelectric harvesters capture energy from the cyclical deformation of the tire as the contact patch passes, at a fundamental rate set by wheel rotation. Electromagnetic and inertial generators exploit centrifugal and gravitational effects during rotation, and hybrid designs combine mechanisms to broaden the speed range over which useful power is produced. Reported laboratory and on-wheel prototypes generate on the order of milliwatts—for example, a piezoelectric rotational harvester demonstrating roughly 9 mW near 8 Hz rotation—which is enough to support intermittent pressure measurement and radio transmission.

In practice, virtually all TPMS sensors in series production today remain battery powered, with service lives of roughly five to ten years; batteryless, harvester-driven TPMS is an active research area rather than a mainstream commercial product. The motivation is clear: a self-powered sensor would last the life of the tire, eliminate scheduled battery replacement, and reduce the disposal of lithium cells, which is especially valuable for commercial fleets where tire-related stops are costly.

Wheel and Hub Monitoring

Beyond tire pressure, wheel assemblies benefit from monitoring of bearing temperature, vibration, and load. Energy harvesting sensors on wheel hubs and brake assemblies can detect developing faults before they cause failures. Thermoelectric generators draw on the heat of brakes and bearings, while vibration and rotational harvesters capture mechanical energy from the turning assembly.

Bearing temperature monitoring provides early warning of lubrication failure and wear. Vibration analysis detects bearing defects and wheel imbalance. Load sensing supports stability control and weight management. Together these measurements improve safety and lower maintenance cost while sparing the routine of replacing wheel-mounted batteries.

Engine and Powertrain Monitoring

Engine-compartment sensors monitor temperature, pressure, vibration, and fluid condition throughout the powertrain. Harvesting from engine vibration and waste heat can power sensors in locations that are difficult to wire. Thermoelectric generators placed against exhaust manifolds and engine surfaces exploit large temperature differences, although practical sensor-scale modules deliver modest power and the Seebeck conversion efficiency of automotive thermoelectric materials is low—commonly only a few percent—so harvested power is best matched to low-duty-cycle sensing rather than continuous high loads.

Oil-condition monitoring detects contamination and degradation that indicate maintenance needs. Coolant sensors track temperature and level to help prevent overheating. Exhaust-gas sensors support emissions control and combustion tuning. The high temperatures of the engine bay stress sensor electronics but provide abundant thermal gradients for harvesting.

Vehicle Body Sensors

Collision detection, occupant sensing, and body-condition monitoring benefit from distributed sensors throughout the vehicle structure. Energy harvesting allows sensor placement without routing wiring through panels and structural members. Photovoltaic cells integrated into roof panels and glazing capture ambient and cabin light to power body sensors and auxiliary functions where illumination is reliable.

Structural Health Monitoring

Aircraft structural integrity monitoring is critical to flight safety. Sensors distributed throughout the airframe detect fatigue cracks, corrosion, and impact damage. Eliminating sensor wiring saves weight, which is valuable in aircraft where every kilogram affects fuel consumption and payload. Vibration from engines and aerodynamic flow, together with thermal gradients across the skin, provides energy for harvesting.

Strain gauges monitor stress at critical locations. Acoustic emission and guided-wave sensors detect crack initiation and growth. Corrosion sensors track degradation of aluminum alloys and composite structures. Because harvesters remove the wiring penalty, designers can place the dense sensor coverage that comprehensive monitoring requires; demonstrated systems power acoustic-emission and guided-wave nodes from piezoelectric and thermoelectric sources.

Vibration levels vary sharply between flight phases. Takeoff and landing produce high excitation, while cruise can be comparatively smooth. Harvesting systems must bridge low-vibration periods with energy storage, and multi-source designs combining vibration, thermal gradients, and solar energy improve availability across the mission.

Engine Health Monitoring

Engine monitoring helps prevent in-flight failures and refine maintenance scheduling. Sensors on nacelles and pylons capture vibration from engine operation, while thermoelectric generators draw on the heat of engine cases and exhaust. The large temperature gradients of the engine environment offer real thermoelectric potential, though packaging must tolerate severe heat and vibration.

Vibration analysis detects bearing wear, blade damage, and compressor health. Temperature monitoring tracks hot-section condition and cooling effectiveness. Oil-debris monitoring identifies component wear before failure. Continuous engine-health data supports condition-based maintenance that reduces both failures and unnecessary scheduled work.

Cargo and Cabin Monitoring

Cabin environmental monitoring affects passenger comfort and safety. Self-powered sensors track temperature, humidity, and air quality throughout passenger compartments. Cargo-hold monitoring detects fire, smoke, and hazardous atmospheres. Photovoltaic cells harvest cabin lighting, while piezoelectric floor elements can sense passenger presence and movement.

Landing Gear Monitoring

Landing gear experiences severe stress during takeoff and landing. Sensors monitor strut pressure, brake temperature, and structural condition. The shock absorbed on touchdown provides significant mechanical energy for harvesting. Weight-on-wheels sensing enables automatic reconfiguration of systems between ground and flight operations.

Track Condition Monitoring

Track condition affects safety, ride quality, and maintenance demand. Sensors along the right-of-way monitor rail stress, geometry, and joint condition. Solar panels and vibration harvesters energized by passing trains supply distributed power across rail networks that often lack trackside electrical service.

Rail temperature monitoring helps prevent heat-related buckling in summer and cold-related fractures in winter. Stress sensors detect loads exceeding safe limits from overweight cars. Geometry sensors measure gauge, alignment, and surface that govern ride quality. Joint sensors detect loosening fasteners and deteriorating rail ends.

The intermittent nature of train passage complicates vibration harvesting. Storage must accumulate energy during passages to sustain monitoring between trains. Supercapacitors suit this pulsed pattern well, offering rapid charge acceptance and long cycle life, and are frequently paired with a small rechargeable cell for longer holdover.

Rolling Stock Monitoring

Cars and locomotives contain many systems that require monitoring for safety and maintenance. Sensors on wheelsets, suspensions, and car bodies track condition throughout the network. Vibration from travel provides mechanical energy, while the temperature difference between hot running gear and ambient air enables thermoelectric harvesting.

Wheel-flat detection identifies damaged wheels that batter the track and degrade ride quality. Bearing monitors detect overheating that signals imminent failure, complementing trackside hot-box detectors. Draft-gear sensors monitor coupling forces and alignment. Load sensors confirm that weight limits are respected and cargo is properly distributed.

Wayside Detection Systems

Trackside detectors identify problems on passing trains, including hot bearings, dragging equipment, and shifted loads. Solar-powered stations operate at remote sites without power infrastructure, inspecting every passing train without an operator present.

Signal and Communication Systems

Rail signaling and communication infrastructure spans long distances of track. Solar-powered signal monitoring and repeater stations reduce infrastructure cost in remote areas. Self-powered sensors on signaling equipment detect failures and degradation before they affect train operations.

Hull Structural Monitoring

Ship hulls endure continuous stress from wave loading, cargo forces, and temperature variation. Sensors distributed through the hull monitor strain, fatigue, and corrosion. Wave-induced motion provides mechanical energy, ocean and machinery temperature gradients enable thermoelectric harvesting, and deck-mounted solar panels supplement other sources.

Hull-stress monitoring helps prevent structural failure in heavy weather. Fatigue tracking at critical locations supports condition-based surveys. Corrosion monitoring follows coating degradation and steel thickness loss. Watertight-integrity sensors detect flooding before it becomes critical.

Propulsion System Monitoring

Marine propulsion systems—engines, shafts, and propellers—require continuous monitoring. Self-powered sensors capture vibration from machinery and heat from engine exhaust. Condition monitoring enables predictive maintenance that helps prevent breakdowns far from port.

Shaft vibration analysis detects misalignment and bearing wear. Propeller monitoring tracks blade condition and cavitation damage. Engine monitoring covers lubrication, cooling, and combustion. Pairing harvested energy with these functions yields autonomous diagnostic nodes that operate without external power.

Cargo Monitoring

Container and bulk-cargo monitoring tracks condition, temperature, and security throughout voyages. Self-powered cargo sensors operate independently across multi-week crossings. Solar panels on container tops, thermoelectric generators that exploit cargo-to-ambient temperature differences, and kinetic harvesters that capture ship motion supply the power.

Temperature monitoring protects perishable and temperature-sensitive cargo. Shock and vibration recording documents handling for damage claims. Security sensors detect unauthorized container access. Location tracking through the supply chain provides visibility for shippers and receivers.

Navigation Aid Monitoring

Buoys, beacons, and other aids mark channels and hazards throughout waterways. Solar-powered navigation aids have operated reliably for decades. Energy harvesting extends them with additional sensing, including environmental monitoring, vessel tracking, and health monitoring of the aid-to-navigation equipment itself.

Truck and Trailer Monitoring

Commercial trucking benefits from comprehensive monitoring of tractors, trailers, and cargo. Energy harvesting is especially useful on trailers, which are routinely uncoupled from tractor power. Solar panels on trailer roofs and refrigeration units capture ample energy, while vibration harvesters draw on road travel.

Refrigerated-trailer temperature monitoring helps ensure cold-chain integrity. Tire and brake monitoring improves safety and reduces roadside breakdowns. Cargo sensors track loading, weight distribution, and security. Door sensors document access for chain-of-custody verification.

Bus and Transit Vehicle Monitoring

Public transit vehicles require monitoring of passenger systems, safety equipment, and vehicle condition. Self-powered sensors throughout buses and rail cars operate without battery replacement by maintenance staff. Passenger counting, air-quality monitoring, and verification of emergency systems all benefit from removing the wiring and battery burden.

Fleet Management Integration

Harvested-sensor data integrates with fleet-management systems for vehicle tracking, maintenance planning, and operational optimization. Telematics platforms aggregate sensor readings with vehicle location and driver behavior. Analytics then surface trends that warrant attention before they become failures.

Vibration Environment Characterization

Transportation vibration environments vary widely by mode, location, and operating condition. Effective harvester design requires understanding the frequency content, amplitude ranges, and temporal patterns of the source. On-platform measurement characterizes the actual environment so the harvester can be optimized to it.

Resonant harvesters tuned to a dominant frequency maximize power extraction in narrowband conditions. Broadband and nonlinear harvesters accommodate variable-speed operation and multiple sources, and frequency-tuning mechanisms adapt to changing conditions. The quality of vibration characterization strongly influences harvester effectiveness.

Temperature Extremes

Transportation systems expose sensors to temperature extremes, from arctic cold to engine-bay heat. Harvesting electronics must operate reliably across the full range. The capacity and internal resistance of batteries and capacitors vary considerably with temperature, which drives careful component selection and energy management.

Wide-temperature automotive electronics commonly operate from roughly -40 to +125 degrees Celsius (AEC-Q100 grade 1), with grade 0 parts reaching +150 degrees Celsius for the harshest underhood locations. Thermal management protects sensitive components, and temperature compensation maintains measurement accuracy across the operating range.

Shock and Vibration Survival

Transportation shock and vibration can damage sensitive electronics. Ruggedized packaging protects harvesting and sensing components. Shock isolation reduces transmitted peak forces while still allowing the steady vibration energy needed for harvesting to reach the transducer. Validation through shock and vibration testing confirms survival in service.

Regulatory Compliance

Transportation systems are heavily regulated for safety. Energy harvesting sensors must meet applicable requirements for electromagnetic compatibility, flammability, and hazardous materials, and any radio link must comply with regional spectrum rules. Automotive, aerospace, rail, and maritime sectors each impose specific standards, and compliance documentation supports certification and customer acceptance.

Fail-Safe Design

Safety-critical transportation systems require fail-safe design that prevents dangerous conditions if monitoring fails. The variability of harvested energy must not compromise the availability of safety functions. Redundant sources and adequate storage provide holdover for critical monitoring, and a known-safe state on power loss bounds the consequences of harvester starvation.

Data Integrity

Transportation monitoring data informs safety-critical decisions. Integrity mechanisms ensure that information is accurate and trustworthy. Error detection and correction guard against communication faults, and message authentication helps prevent spoofing of safety-relevant data on wireless links.

Maintenance Integration

Harvested-sensor data must integrate with established maintenance programs. Standard data formats allow use with existing maintenance-management systems. Alarm thresholds align with defined maintenance actions. The monitoring system must support, rather than complicate, maintenance operations.

Autonomous Vehicle Integration

Autonomous vehicles require extensive sensing beyond today's monitoring systems. Energy harvesting can power redundant sensors that improve the reliability of the autonomy stack and add monitoring capability without increasing the complexity of the vehicle's electrical distribution.

Electric Vehicle Applications

Electric vehicles present new harvesting opportunities and constraints. Regenerative braking already recovers kinetic energy at the vehicle scale. At the sensor scale, the battery pack's thermal-management gradients and road-induced vibration can power monitoring of cells, modules, and chassis. Self-powered sensing of pack temperature and structural condition is attractive because the pack is sealed and safety critical, and it avoids adding low-voltage wiring across a high-voltage enclosure.

Urban Air Mobility

Emerging urban air mobility vehicles, including electric vertical takeoff and landing (eVTOL) aircraft, will require comprehensive monitoring. Energy harvesting offers weight-efficient sensing for these mass-sensitive aircraft, and the distinctive vibration and thermal signatures of distributed electric propulsion create new sources to harvest.