Abstract
In this study, we propose a highly sensitive multichannel pH sensor that is based on an optical-fiber pulse width modulation (PWM) technique. According to the optical-fiber PWM method, the received sensing signal’s pulse width changes when the optical-fiber pH sensing-element of the array comes into contact with pH buffer solutions. The proposed optical-fiber PWM pH-sensing system offers a linear sensing response over a wide range of pH values from 2 to 12, with a high pH-sensing ability. The sensitivity of the proposed pH sensor is 0.46 µs/pH, and the correlation coefficient R2 is approximately 0.997. Additional advantages of the proposed optical-fiber PWM pH sensor include a short/fast response-time of about 8 s, good reproducibility properties with a relative standard deviation (RSD) of about 0.019, easy fabrication, low cost, small size, reusability of the optical-fiber sensing-element, and the capability of remote sensing. Finally, the performance of the proposed PWM pH sensor was compared with that of potentiometric, optical-fiber modal interferometer, and optical-fiber Fabry–Perot interferometer pH sensors with respect to dynamic range width, linearity as well as response and recovery times. We observed that the proposed sensing systems have better sensing abilities than the above-mentioned pH sensors.
Highlights
Over the last several decades, the development and applications of chemical and biosensors have grown very rapidly [1]
In the proposed pulse width modulation (PWM) system, the control port is the change of index of the sensing membrane of the sensing element
The pulse width is proportional to the pH, which corresponds to changes in the refractive index of the overlay waveguide as well as the absorption of the evanescent field into the waveguide
Summary
Over the last several decades, the development and applications of chemical and biosensors have grown very rapidly [1]. For optical-fiber intensity modulation pH sensors, different types of pH-sensitive materials/dyes are used on the optical-fiber core or polished cladding. They measure the pH value of a given fluid by observing optical parameters such as absorption, reflection, transmission of optical power, and fluorescence. The sensors have several features including a wide pH sensing range, linear sensing response, and good stability This sensor has several disadvantages including a complex fabrication process, low sensitivity, and long response and recovery times (about 60 s and 80 s, respectively). The proposed optical-fiber PWM pH sensor has several other features: simple construction, ease of cost, reusability, and light weight.
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