Contactless RF sensor for low-concentration chlorine detection in water

Overview

This solution offers a contactless method for detecting low concentrations of chlorine ions in treated water using radio-frequency (RF) or microwave reflection (S11) spectrum analysis. By eliminating the need for physical contact with the water sample, the sensor avoids corrosion and fouling issues that limit conventional probe-based sensors, potentially extending operational life beyond 10 years. The technology is designed to detect chlorine at concentrations below 0.01 mg/L (10 ppb) with an accuracy of ±20%, making it suitable for water treatment facilities, municipal water quality monitoring, and industrial process control where reliable low-level chlorine measurement is critical.

Technical specifications

Core technology:

• Loop gap resonator (LGR) used to measure RF/microwave reflection (S11) spectra
• Ion mass and charge produce distinguishable spectral signatures at varying concentrations
• Quasi-static measurement assumption: RF reflection is significantly faster than ion mobility and flow rates between 100 and 1,500 ml/min
• Machine learning algorithm for data analysis, including temperature sensitivity compensation
• In-line sensor form factor with integrated coupler, designed to be less than 10 cm³

Validated performance:

• Lead (Pb) detection below 1 ppb (0.001 mg/L) in DI water and city water
• Water hardness measurement at 10 ppm level
• Salt ion concentrations (NaCl, MgCl, KCl) detected at 0.1 mg/L resolution
• All prior testing performed under static conditions

Technology readiness level

The technology is at an early-to-mid stage of development. Proof-of-concept validation has been completed in static laboratory conditions, demonstrating the ability to detect various metal and salt ions at low concentrations. Future work will focus on optimizing LGR operating frequencies specifically for chlorine ions, miniaturizing the sensor design for in-line deployment, implementing machine learning–based data analysis, and validating performance under flowing water conditions. Additional characterization of temperature sensitivity and long-term operational stability will be required before commercial deployment.