A review of the use of fibre-optic sensor technologies for humidity sensing is presented. The paper first provides a brief overview on the basic concept of what is meant by humidity and on conventional detection methods. This is followed by an extensive review on the various fibre-optic techniques reported for humidity sensing, covering both intrinsic and extrinsic sensor configurations.

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Fibre-optic sensor technologies for humidity and moisture measurement

■ CONTENTS Books, Reviews, and Articles of General Interest 488 Sensors for (Dissolved) Gases and Vapors 489 Hydrogen 489 Hydrocarbons 490 Oxygen 491 Ammonia 493 Carbon Dioxide 494 Nitrogen Oxides 494 Vapors of Organic Solvents 495 Sensors for Humidity, Water Fractions, Hydrogen Peroxide, and Hydrazine 495 Humidity 495 Water Fractions 496 Hydrogen Peroxide and Hydrazine 496 Sensors for pH Values, Ions, and Salinity 496 pH Values 496 Ions 497 Salinity and Ionic Strength 499 Sensors for Organic Species 499 Biosensors 500 Immunosensors 500 PNA-Based Biosensors (DNA, Aptamers) 501 Other Affinity Sensors 501 Enzymatic Biosensors 502 Whole Cell Sensors 502 Advanced Optical Sensing Schemes and Materials 503 Author Information 505 Corresponding Author 505 Notes 505 Biographies 505 Acknowledgments 505 References 505

Fiber-Optic Chemical Sensors and Biosensors (2008–2012)

We have reviewed the humidity sensors based on ceramic materials. We first discuss the operating principle of ceramic humidity sensors. This is followed by a section on the relationship between the conduction mechanism and microstructure characteristics of the sensing elements of ceramic humidity sensors. This part of the review is also focused on the methods for optimization of the microstructure of ceramic porous elements. The next section summarizes the information on the materials used for the ceramic humidity sensors fabrication and effect of dopants or hybrid compositions on the sensing ceramic-based materials. Then we analyze state-of-the-art techniques for producing ceramic sensors. The key research and technological challenges in the field are discussed at the end of the review. The review is based on 424 references published during from 1998–2013.

Recent trends of ceramic humidity sensors development: A review

Gas detection is important for controlling industrial and vehicle emissions, household security and environmental monitoring. In recent decades many devices have been developed for detecting CO2, CO, SO2, O2, O3, H2, Ar, N2, NH3, H2O and several organic vapours. However, the low selectivity or the high operation temperatures required when most gas sensors are used have prompted the study of new materials and the new properties that come about from using traditional materials in a nanostructured mode. In this paper, we have reviewed the main research studies that have been made of gas sensors that use nanomaterials. The main quality characteristics of these new sensing devices have enabled us to make a critical review of the possible advantages and drawbacks of these nanostructured material-based sensors.

Gas sensors based on nanostructured materials.

Controllable preparation of Nano-MgO and investigation of its bactericidal properties

The present paper reports the various physico-chemical properties of MgO film obtained by using a precursor prepared by sol–gel technique. The aim of this work is to produce films with nano size particles so as to employ them for sensor applications, as adsorption in such films increases many folds due to increase in surface area. Infra-red spectroscopic and thermal studies indicate the presence of solvent in the precursor, which perhaps helps in decomposition to nano-particles during the nucleation of the film. The films have been deposited on the glass rod bend in U-shape for humidity sensor. The results as obtained are encouraging to use MgO film as humidity sensor.

Nano-like magnesium oxide films and its significance in optical fiber humidity sensor

Polyaniline (PANI) was prepared in emeraldine via chemical oxidation method using CuSO4 as initiating agent. The chemical characterizations were made using UV-vis (ultraviolet-visible spectrophotometry), FT-IR (Fourier transform spectroscopy), TG- DTA (thermo-gravimetric/differential thermal analysis), ESI-MS (electrospray ionization mass spectrometry), XRD (X-ray diffraction), SEM (scanning electron microscopy) techniques. The results revealed the formation of homogeneous, crystalline PANI with sub-micron size particles. The PANI thin film of 0.5 µm thickness has been fabricated using spin coating technique. The resulting PANI film was exposed to controlled humid condition and change in resistance has been recorded. The resistance was continuously decreased from 13.5 to 3.75 MΩ with a linear change in humidity ranging from 3 to 95%. The result was reproducible and checked by repeating observation. Copyright © 2010 VBRI press.

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Synthesis And Characterization Of Highly Crystalline Polyaniline Film Promising For Humid Sensor

Exploring fiber optic approach to sense humid environment over nano-crystalline zinc oxide film

Thin films of titanium dioxide in anatase form have been prepared using isobutyl titanate as precursor. The resulting TiO2 was coated on an U-shaped pyrex glass rod to sense the humidity of a contr ...

Fabrication Of Ultra-sensitive Optical Fiber Based Humidity Sensor Using TiO2 thin Film

A new sensitive and selective derivative spectrophotometric procedure is developed for trace‐level determination of Tl3+ in the range of 680 × 10−2 to 380 µg mL−1; molar absorption coefficient and detection limit of a 1:1 complex with 2‐(5‐bromo‐2‐pyridylazo)‐5‐diethylaminophenol in the presence of cetylpyridinium chloride are 525 × 104 L mol−1 cm−1 and 420 × 10−2 ng mL−1, respectively The developed method, by using the measurement of the derivative amplitude of the analyte (Tl3+) at the zero crossover point of the interfering metal ion (Ga3+), is applied for the determination of Tl3+ in the presence of Ga3+, and vice versa for Ga3+ ions The determination range of Tl3+ and Ga3+ in the presence of each other is 010–246 µg mL−1 and 004–105 µg mL−1, respectively; the relative standard deviation for sample containing 123 µg mL−1 Tl3+ and 042 µg mL−1 Ga3+ is 143 and 165%, respectively The proposed procedure is successfully applied for simultaneous determination of the two metal ions in 

A Method for Nonextractive Simultaneous Determination of Thallium (III) and Gallium (III) in Environmental and Standard Samples with 2‐(5‐Bromo‐2‐pyridylazo)‐5‐diethylaminophenol in Cationic Micellar Medium

G. K. Parashar

Papers

Nano-like magnesium oxide films and its significance in optical fiber humidity sensor

Synthesis And Characterization Of Highly Crystalline Polyaniline Film Promising For Humid Sensor

Exploring fiber optic approach to sense humid environment over nano-crystalline zinc oxide film

Fabrication Of Ultra-sensitive Optical Fiber Based Humidity Sensor Using TiO2 thin Film

A Method for Nonextractive Simultaneous Determination of Thallium (III) and Gallium (III) in Environmental and Standard Samples with 2‐(5‐Bromo‐2‐pyridylazo)‐5‐diethylaminophenol in Cationic Micellar Medium