Fiber-optic pulse width modulation sensor for low concentration VOC gas

A high response butanol gas sensor based on ZnO hollow spheres

“…Volatile organic compounds (VOCs) such as alcohols and aromatic hydrocarbons can easily evaporate at room temperature, which causes them to be one kind of main origin of pollutions in the air [2,3]. For instance, n-butanol, a flammable, stimulating and narcotic liquid with characteristic odor, which is widely present in industrial waste streams (stationary sources) and can be released into the atmosphere when used as a solvent for paints, coatings, varnishes, resins, gums, vegetable oils, etc, is also deleterious for human health [4].…”

Highly Sensitive and Wide-Dynamic-Range Multichannel Optical-Fiber pH Sensor Based on PWM Technique

“…${\mathrm{normaln}}_1$ and ${\mathrm{normaln}}_2$ are the refractive index of the fiber cladding and the material of the overlay waveguide, respectively. Now, if a light pulse with time period $\mathrm{normalT}$ is transmitted through the side-polished optical-fiber waveguide, then the received light pulse width ${\mathrm{normalT}}_{\mathrm{normalH}}$ can be written mathematically as [41,42] ${\mathrm{normalT}}_{\mathrm{normalH}}=\frac{\mathrm{normalT}}{{\mathrm{normaln}}_2{\left(\frac{\mathsf{\gamma }\mathrm{L}}{\mathrm{sans-serif\alpha }}\right)}^{0.5}},$ where $\mathrm{normalL}$ is the length of the polished cladding, $\mathrm{sans-serif\gamma }$ is the evanescent wave absorption coefficient, and $\mathrm{sans-serif\alpha }$ is the phenomenological ion-specific parameter. Therefore, by observing the pulse width of the received sensing signal, the pH-value can be determined.…”

“…In our study, we proposed a fast, highly sensitive, wide-dynamic-range side-polished optical-fiber pH sensor array that is based on optical-fiber pulse width modulation (PWM) [41,42] principles. According to the optical-fiber PWM technique, the pulse width of the received sensing signal from the optical-fiber pH-sensing element of the array changes if the sensing element of the array comes into contact with a pH buffer solution.…”

Optical fiber detector for monitoring volatile hydrocarbons during electrokinetic treatment of polluted soil

“…Moreover, fiber‐based VOCs sensors are inherently safe due to the lack of spark or short circuit in optical fibers. Most optical fiber VOC sensors reported so far are based on monitoring the changes caused by the presence of VOC gases, of the sensitive layer properties deposited over the fiber surface . The exposure of the coated‐fiber to VOC gas modifies the physical (e.g.…”