Table 4 Comparison of FBG sensors and traditional methods for monitoring soil aggregation forces.

Measurement Circuit

Optical fiber system requires an interrogation unit for wavelength detection.

Mechanical or electronic force measurement system.

Wheatstone bridge circuit measures strain as a change in resistance.

Electrical system measures force as a voltage output.

Measured Type

Wavelength shift corresponding to strain or force.

Penetration resistance (force per unit area).

Resistance change proportional to strain.

Voltage change proportional to applied load

Limit of Spatial Resolution

High (can measure at multiple discrete points with spacing as small as 1 mm).

Very low (point measurements only).

Low (requires physical attachment; limited to sensor placement).

Low (sensitive to overall load but not spatial distribution).

Strain Resolution

Very high (in the range of nano-strain, ~ 1 µε).

Low (force resolution is coarse).

Moderate (~ 10–50 µε).

Moderate (~ 5–20 µε).

Sensitivity

High sensitivity due to direct optical signal measurement.

Low sensitivity to small variations in soil texture or moisture.

Moderate; influenced by environmental noise and setup quality.

High for large forces but less sensitive to minute changes.

Accuracy

Extremely accurate (~ ± 0.1%).

Moderate (± 2–5%).

Moderate (± 1–2%).

High (± 0.5%).

Maximum Strain

~ 10,000 µε (10%) without permanent deformation.

Low; measures penetration resistance, not strain.

Moderate (~ 5,000 µε).

High for load but not designed to measure strain.

Cost

Higher initial cost due to optical interrogation unit.

Low to moderate; mechanical penetrometers are inexpensive, electronic ones cost more.

Low initial cost, but frequent recalibration increases long-term cost.

Moderate initial cost, but higher maintenance.

Durability

High; resistant to environmental conditions like moisture and temperature.

High for mechanical types; moderate for electronic types.

Moderate; prone to temperature and humidity effects.

Moderate; susceptible to corrosion and wear.

Response Time

Fast (in milliseconds).

Moderate to slow, depending on operator skill and system.

Moderate (seconds).

Slow (seconds, depending on load and system).

Integration Capabilities

Easily integrates with smart systems for real-time monitoring and data analytics.

Not designed for integration with digital systems.

Limited integration into automated systems.

Requires additional systems for real-time applications.

Size and Weight

Compact and lightweight (fiber diameter ~ 125 μm).

Portable but often heavy for field use.

Bulkier; attached to surfaces or embedded in materials.

Larger and heavier; not suitable for small-scale studies

Environmental Tolerance

Excellent resistance to corrosion, electromagnetic interference (EMI), and temperature fluctuations.

High for mechanical; moderate for electronic versions.

Moderate; sensitive to EMI and environmental degradation

Moderate; sensitive to harsh environmental conditions.

Calibration Needs

Minimal; calibration is typically stable over time.

Minimal for mechanical types; periodic for electronic.

Requires regular recalibration to maintain accuracy.

Requires periodic recalibration.