# Experimental Study on Dual-Structure Polymer Optical Fiber Sensors for Turbidity Detection

## TL;DR

This paper studies polymer optical fiber sensors for measuring water turbidity, finding that one sensor type is more sensitive at high particle concentrations.

## Contribution

The study introduces and compares two polymer optical fiber sensor designs for turbidity detection with different particle types and concentrations.

## Key findings

- Gap-POF sensors showed higher sensitivity to turbidity changes, especially at high particle concentrations.
- Silica powder caused more light intensity fluctuations compared to clay particles due to aggregation and larger size.
- White and green light wavelengths were most responsive to turbidity changes in the sensors.

## Abstract

This study presents a comprehensive investigation of turbidity monitoring using two different types of polymer optical fiber (POF) sensors: the reflection–refraction type (RR-POF) and the gap type (Gap-POF). Both sensors were used to visualize and monitor the turbidity changes in suspensions with varying concentrations and different particle compositions, namely silica powder and clay particles. The experiments were conducted by introducing silica powder and clay into water at various concentrations, and the resulting turbidity was measured using both types of POF sensors. The results revealed a significant correlation between particle concentration and light intensity for both kinds of POF sensors. As the particle concentration increased, the light intensity decreased due to increased scattering and absorption effects. For both silica powder and clay suspensions, the light intensity stabilized at lower values as the concentration increased, with the Gap-POF sensor exhibiting higher sensitivity to turbidity changes, particularly at high particle concentrations. Additionally, the study found that the particle composition influenced the sensor response. Silica powder particles caused more irregular fluctuations in light intensity at higher concentrations due to their larger particle size and tendency to aggregate, while clay particles, due to their smaller size and better dispersion, resulted in more stable and gradual changes in light intensity. This highlighted the differences in optical responses between different particle types. Furthermore, the multi-wavelength measurements showed consistent results, with white and green lights exhibiting the strongest response to turbidity changes, while red and blue lights were less sensitive. This wavelength-dependent response was attributed to the scattering and absorption properties of the particles in the suspensions. Both RR-POF and Gap-POF sensors proved to be effective for turbidity monitoring, with Gap-POF demonstrating superior performance in high-concentration suspensions. The findings suggest that POF sensors, particularly Gap-POF, are highly suitable for real-time turbidity monitoring in various particle suspension systems.