Simultaneous Measurement Of Relative Humidity Research Articles

Miniature all-silica fiber-optic sensor for simultaneous measurement of relative humidity and temperature.

This Letter presents a miniature fiber-optic sensor created at the tip of an optical fiber suitable for simultaneous measurement of relative humidity and temperature. The proposed sensor is based on two cascaded Fabry-Perot interferometers, the first configured as a relative humidity sensing element made from silica micro-wire coated with thin porous SiO2 layer, and the second as a temperature sensing element made from a segment of a standard single-mode fiber. The sensor has linear characteristics for both measurement parameters and a sensitivity of 0.48 deg/%RH and 3.7 deg/°C.

An open-cavity Fabry-Perot interferometer with PVA coating for simultaneous measurement of relative humidity and temperature

A fiber-optic open-cavity Fabry-Perot (FP) interferometer (FPI) with polyvinyl alcohol (PVA) coating is proposed and experimentally demonstrated for simultaneous measurement of relative humidity (RH) and temperature. The FPI consists of an etched side-hole fiber (SHF) sandwiched in between two leading single-mode-fibers. The PVA film is plated on the fiber surface functioning as a humidity-to-refractive index (RI) transducer. Theoretical analysis details the RH and temperature influence on the spectral fringes of the FPI. Experimental results confirms and show that, the reflection loss of the FPI nonlinearly decreases more than 15dB when the RH increases from 30%RH to 90%RH with a highest sensitivity of −1.2dB/%RH, while the dip wavelength of the spectral fringe exhibits linear RH and temperature sensitivities of −23.1pm/%RH and −6.14pm/°C, respectively. Thus, by monitoring the reflection and wavelength of the interference dip, the proposed sensor enables accurate simultaneous measurement of RH and temperature. A fast and reversible time response has also been demonstrated. Such excellent sensing performance with compactness, ease of fabrication makes our sensing structure a highly promising candidate for RH and temperature monitoring applications.

Hygroscopic polymer microcavity fiber Fizeau interferometer incorporating a fiber Bragg grating for simultaneously sensing humidity and temperature

This work proposes a hygroscopic polymer microcavity fiber Fizeau interferometer (PMFFI) incorporating a fiber Bragg grating (FBG) for the simultaneous measurement of relative humidity (RH) and temperature (T). The PMFFI was fabricated by attaching the hygroscopic polymer to a single-mode fiber endface to form a low-finesse Fabry–Perot resonant microcavity. This work is the first to investigate polymer of the Norland Optical Adhesive (NOA) series with particular porous structures that responds well to the moisture and can thus be used in the fiber-optic sensing of relative humidity. Additionally, the NOA materials have a high thermal expansion coefficient and so can be used in the highly sensitive measurement of temperature. The adsorption/desorption of water molecules and variations in temperature both change the optical path of the microcavity, shifting the fringes in the interference spectra. Incorporating a general FBG that is nonreactive to RH but sensitive to T judges the variation in T. The combined sensor supports the simultaneous measurement of both parameters RH and T by gauging of the individual spectral responses of PMFFI and FBG, respectively. Experimental results demonstrate that the RH and T can be simultaneously measured with high sensitivity and accuracy using the proposed sensing configuration.

Novel Knob-integrated fiber Bragg grating sensor with polyvinyl alcohol coating for simultaneous relative humidity and temperature measurement.

A novel high performance optical fiber sensor for simultaneous measurement of relative humidity (RH) and temperature based on our newly designed knob-integrated fiber Bragg grating (FBG) is proposed and experimentally demonstrated. The knob-shaped taper followed by an FBG works as a multifunctional joint that not only excites the cladding modes but also recouples the cladding modes reflected by the FBG back into the leading single mode fiber. Polyvinyl alcohol (PVA) film is plated on the fiber surface by dip-coating technique as a humidity-to-refractive index (RI) transducer, and affects the intensity of reflected cladding modes by way of evanescent fields. By monitoring the intensity and wavelength of the reflected cladding modes, the RH and temperature variance can be determined simultaneously. Experimental results show an RH sensitivity of up to 1.2 dB/%RH within an RH range of 30-95%, which is significantly better than previously reported values. And the temperature sensitivity of 8.2 pm/°Ccould be achieved in the temperature range of 25-60°C. A fast and reversible time response has also been demonstrated, enabling to pick up a humidity change as fast as 630 ms. The capability of simultaneous measurement of RH and temperature, the fast response, the reusability and the simple fabrication process make this structure a highly promising sensor for real-time practical RH monitoring applications.

Simultaneous measurement of relative humidity and temperature with PCF-MZI cascaded by fiber Bragg grating

Simultaneous measurement of relative humidity and temperature has been realized by using an optical fiber sensor formed by cascading a photonic crystal fiber (PCF)-based in-fiber Mach-Zehnder interferometer (MZI) and a fiber Bragg grating (FBG). The PCF-MZI was fabricated by using a short PCF fusion-spliced between two single-mode fibers with its air holes in the cladding area being collapsed in the splicing regions. It was then coated with a layer of polyvinyl alcohol (PVA), whose refractive index is sensitive to humidity. Because the PCF-MZI and FBG have different responses to humidity and temperature, simultaneous measurement has been achieved with resolutions of 0.13% RH and 1.0°C for humidity and temperature, respectively. The relative humidity measurement range is up to 30%–95% RH.

A Handpiece for the Simultaneous Measurement of Photosynthetic Rate and Leaf Diffusive Conductance: II. CALIBRATION

The design and construction of a handpiece for the simultaneous measurement of photosynthetic rate and diffusive conductance of cereal leaves in almost natural conditions in the field is described. Photosynthetic rate is found from the assimilation of l4C02 by part of the leaf which is temporarily enclosed in a small hand-held chamber. This chamber also acts as a stirred, steady-state water vapour diffusion porometer, allowing the simultaneous measurement of relative humidity from which the leaf diffusive conductance is estimated. The instrument also measures the leaf and air tempera tures and incident photon flux density. The important criteria of the performance of such a handpiece are discussed, and the sensors which measure the physical variables of humidity, temperature, and photon flux density are described. An automatic sequencing system built from logic circuits which displays the measured values of these variables and times the operations is also described.