The importance of structural health monitoring and its supporting technology

By Mark Patrick, Mouser Electronics

This article originally appeared in the April'24 magazine issue of Electronic Specifier Design – see ES's Magazine Archives for more featured publications.

SHM is the continuous, on-board monitoring of a structure during its operational life by systems that integrate sensors, transmission networks, and data analysis software. SHM is used to conduct testing  and health and performance monitoring of structures such as bridges, buildings, dams, and stadiums, and can also be applied to aircraft and industrial machinery.

According to Grand View Research, the global SHM market was valued at $2.66 billion in 2022 and is forecast to grow at a CAGR of 18.8% between 2023 and 2030. The market can be segmented  according to application, with the key segments being bridges and dams, buildings and stadiums,  vessels and platforms, airframes and wind turbines, and large machines and equipment.

Significant opportunities exist in this dynamic market and the challenge for existing players and new entrants is to choose the right technology for the specific SHM requirement. However, the challenge doesn’t stop there. The successful solution developer knows how to leverage the supply chain to  accelerate time to market and achieve the optimum cost profile.

The role of sensors and technology in SHM

The rapid growth of the IoT has driven an unprecedented wave of innovation in the electronics market, and SHM developers have access to an almost infinite choice of components and modules.  In addition, most semiconductor manufacturers are focused on helping their customers accelerate development cycles by offering tools such as pre-certified modules, development environments,  evaluation boards, reference designs, and software libraries.

SHM sensors measure different parameters relating to the state of the structure, along with  environmental factors such as stress, strain, vibration, inclination, humidity, and temperature. A  wide range of sensors are available to SHM developers, which fall into five common categories:

Strain gauges monitor variables such as loads, compression, tension, bending, and torsion in a  structure. They are used extensively in SHM systems designed to monitor structures that are subject  to heavy loads, including bridges, overpasses, and buildings.

Crack-detection sensors monitor the position and length of cracks in concrete structures, including  roads, buildings, and tunnels. Cracks in these structures may indicate an underlying problem, and  any movement in these cracks may warn of larger issues.

Vibration sensors such as the Amphenol Wilcoxon LVEP-TO5 Embedded Accelerometers monitor the g-force experienced by a structure. Changes in vibration can signal an impending issue in a structure or piece of equipment. The LVEP-TO5 series offers extremely high sensitivities, up to 50mV/g with the LVEP050. With ultra-low power consumption levels down to 80μW, the devices are easily  integrated into battery-powered wireless vibration sensors.

Inclinometers, also known as tilt sensors, use MEMS technology to monitor slippage in embankments, piers, abutments, and retaining walls. The Murata Electronics SCL3300 inclinometer  range (Figure 1) delivers best-in-class characteristics for inclination measurement, with its high accuracy, three-axis measurement, and industry-leading shock durability. With four user-selectable measurement modes, this low-noise device can easily be optimised for different applications, and  with a typical current draw of 3μA in sleep mode, it is ideally suited for battery-powered applications.

Piezometers are typically used for monitoring fluid or pore water pressure in embankments,  boreholes, standpipes, reservoirs, and tanks. Water can be highly destructive when in the wrong place or at the wrong pressure, so water monitoring is a core function of SHM.

Other common SHM sensors include resistance and temperature detectors, thermocouples, load cells, fibre optic sensors, and acoustic emission sensors.

Other key SHM technologies

While sensors are key components at the front end, other IoT technologies are equally important in an overall SHM system, principally wireless communications, and microcontroller units (MCUs).

Wireless communications

Wireless communications remove the need for cumbersome and expensive cabling runs and enable significant flexibility in the positioning of sensors. Various wireless protocols have evolved to support the needs of different applications. For example, LPWAN targets use cases where relatively small  amounts of data must be transmitted over long distances. LPWAN is ideal for battery-powered sensors in remote, inaccessible locations. Bluetooth Low Energy is another common, low-power protocol supporting higher data rates and Wi-Fi 6E offers high data throughputs and larger  bandwidths for data-hungry SHM applications. Cellular technologies, although more expensive, offer the security of licensed spectrum. Many manufacturers offer multi-mode communication modules, which combine two or more wireless protocols (for example, Wi-Fi and Bluetooth Low Energy or 5G and Wi-Fi).

Edge processing

Shrinking component sizes have led to a proliferation of MCUs which can be integrated at the front  end of SHM solutions. Powerful multi-core Arm devices can execute software which was once confined to the data centre. However, the trusty 8-bit device continues to be a stalwart of the IoT, offering ease of programming and low power consumption through sleep modes for battery-driven

Conclusion

The deployment of SHM systems is growing rapidly in response to key trends such as the  acceleration of new infrastructure projects and the ageing and deterioration of existing structures like dams and bridges. This expansion of structural monitoring is aided by the evolution of IoT  technologies, such as sensors, wireless technologies, and embedded processing capabilities. Advanced sensors based on MEMS technology, such as accelerometers, inclinometers, and strain gauges, are ideally suited to the requirements of SHM systems. The civil engineering industry is one of a growing number of sectors leveraging the power of the IoT to improve the safety and efficiency of a mission-critical technology like SHM.