Installation of Fiber Optic Strain Sensors

Proper installation of fiber optic strain sensors involves careful surface preparation, adhesive selection, and protective measures to ensure accurate and reliable strain measurements.

Surface Preparation

Before installing a fiber optic strain sensor, the surface must be cleaned, abraded, and conditioned to ensure strong adhesion and accurate strain transfer. This process is similar to the preparation used for traditional foil strain gauges. For metallic or composite surfaces, remove any dirt, grease, or oxidation, and lightly abrade the surface to improve bonding.

Conditioning or neutralizing the surface may also be necessary depending on the adhesive used.

Adhesive Selection

Adhesives such as M-Bond 200 or AE-10 are commonly used for bonding fiber optic sensors to surfaces.

M-

Bond 200 is a single-part cyanoacrylate that cures rapidly at room temperature and provides strong adhesion for short-term applications. The adhesive's operating temperature range should be considered: for M-Bond 200, short-term use is -185°C to 95°C, and long-term use is -32°C to 65°C. After curing, a protective layer, such as RTV silicone, is recommended to shield the fiber and adhesive from environmental effects like moisture, temperature fluctuations, and mechanical abrasion.

Installation Methods

Surface Bonding

Surface bonding is the most common method for fiber optic strain sensors. The fiber is laid along the prepared surface and bonded using the selected adhesive. Minimal glue is used to avoid altering the fiber's mechanical response.

For temporary or non-critical applications, double-sided tape can be used, though it is less reliable under environmental stress.

Embedment

Fiber optic sensors can also be embedded within materials, such as concrete or composite layers, which is particularly useful in civil engineering and aerospace applications. Embedment provides excellent strain transfer and protects the fiber from external damage.

Cable Considerations

For distributed fiber optic sensing (DFOS) in structural monitoring, the cable type, installation method, and environmental conditions are critical. Cables may be attached to or embedded in structures, direct-buried, or placed in conduits. Proper installation ensures efficient strain transfer and long-term reliability.

Protective Measures

After installation, a protective coating or layer is recommended to prevent damage from mechanical, thermal, or chemical exposure.

RT

V silicone or similar materials are commonly applied over the bonded fiber. For embedded fibers, the surrounding material itself often provides sufficient protection.

Verification

Once installed, it is important to verify sensor performance by comparing measurements with reference strain gauges or known load conditions. High-resolution fiber optic sensors can provide hundreds to thousands of sensing points along a single fiber, offering detailed strain mapping.

Summary

Prepare the surface: clean, abrade, and condition. Select appropriate adhesive: M-Bond 200 or AE-10 for surface bonding. Install the fiber: surface bond or embed depending on application.

Apply protective layer: RTV silicone or equivalent. Verify performance: compare with reference measurements. Following these steps ensures accurate, high-fidelity strain measurements and long-term reliability of fiber optic strain sensors in various applications.