Strainmeters

Strainmeters are instruments designed to measure strain, the fractional change in length that a material or structure experiences. They convert mechanical deformation into electrical or optical signals, enabling quantitative records of how objects deform over time. Strainmeters are used in civil engineering for structural health monitoring and in geophysics to study crustal deformation, tectonics, and seismic processes.

Several families of strainmeters exist. Resistive foil strain gauges are among the most common and are typically bonded to a surface as part of a Wheatstone bridge. They convert strain into a change in electrical resistance, with a gauge factor around 2, and are suited to surface measurements on infrastructure. Fiber-optic strainmeters use optical fibers and include methods based on fiber Bragg gratings, interferometry, or phase shifts. They offer high sensitivity, immunity to electrical noise, and the ability to monitor long distances and harsh environments, including boreholes. Interferometric meters, such as Michelson or Fabry-Perot configurations, provide very high sensitivity to small strains and can be deployed in precision applications.

In practice, strainmeters measure either surface deformation or subsurface strain fields. Borehole strainmeters extend sensing into rock or sediment and are valuable in geophysical campaigns and earthquake research. The measurement can cover ranges from microstrain to millistrain, with resolutions ranging from microstrain to nanostrain depending on the sensor and electronics.

Key considerations for use include temperature sensitivity, calibration needs, installation method, and data acquisition requirements. Modern deployments often integrate multiple sensors along with data loggers and remote telemetry to produce continuous monitoring of structural or geological processes.