Simultaneous Real-Time Measurements of Temperature, Liquid Level, Humidity, and pH by ZnSe/Co Nanostructure-Coated Polymer Films

In this work, the surface of long-period fiber grating (LPFG) and polarization maintaining fiber (PMF) is functionalized based on the interaction between the resonance wavelength and external environment. LPFG coated with a 150 nm ZnSe/Co film is fixed on a hollow bracket, prestressed, and annealed many times. A highly sensitive liquid level sensor with adjustable sensitivity, an adjustable measurement range, and a high liquid level early warning is prepared. The waveguide layer controlled by humidity is constructed by filling poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT/PSS) in a periodically etched PMF. The surface is coated with a poly(vinyl alcohol) (PVA) and carbon nanotube (CNT) composite polymer. After laser processing, a honeycomb porous film is obtained, and the humidity sensor with wavelength modulation is prepared. The pH-sensitive polymer is successively adsorbed on the surface of PMF coated with a 120 nm indium tin oxide (ITO) film by electrostatic self-assembly (ESA). Poly(allylamine hydrochloride) (PAH), poly(acrylic acid) (PAA), and poly(styrene sulfonate) (PSS) constitute a composite film with rapid deposition and high permeability that is covered with polyaniline/poly(methyl methacrylate) (PMMA) as the protective layer. After laser processing, a fluffy porous film structure is formed. The pH sensor is obtained and the preparation steps are greatly reduced. Finally, based on the wavelength division multiplexing (WDM) and multiwavelength matrix (MWM), the problem of crosstalk is solved. An integrated sensor is constructed to realize the simultaneous measurement of temperature, liquid level, humidity, and pH. It has been successfully applied to monitor the overall environment of a chemical waste liquid storage tank. The sensor has the advantages of remote monitoring, safety, efficiency, and labor-saving.