Cavity Sensor Research Articles

Wireless passive polymer-derived SiCN ceramic sensor with integrated resonator/antenna

This paper presents a passive wireless polymer-derived silicon carbonitride (SiCN) ceramic sensor based on cavity radio frequency resonator together with integrated slot antenna. The effect of the cavity sensor dimensions on the Q-factor and resonant frequency is investigated by numerical simulation. A sensor with optimal dimensions is designed and fabricated. It is demonstrated that the sensor signal can be wirelessly detected at distances up to 20 mm. Given the high-temperature stability of the SiCN, the sensor is very promising for high-temperature wireless sensing applications.

Towards more accurate microcavity sensors: maximum likelihood estimation applied to a combination of quality factor and wavelength shifts

Optical microcavities are widely used for biological and chemical sensing applications. In these devices, a sensing event is estimated by measuring the shift in the resonant wavelength, or in the quality factor of the microcavity. However, all published works to date only use one of these measures to estimate the sensing event. Here, we show that the estimation accuracy of a sensing event can be improved by employing a combination of both the quality factor and the resonant wavelength measurements in a microcavity sensor. We further demonstrate an experimental application of this model by introducing a refractive index change for a microtoroidal cavity sensor immersed in a liquid. By further using the finite element method simulations in conjunction with the estimator model, we show the existence of three distinct measurement regimes as a function of the quality factor of the microcavity. Finally, the estimator model is extended to develop a sensing metric to compare performance of optical or non-optical sensors.

Analysis of Water Pollution by a Microwave Cavity Sensor

Analysis of Water Pollution by a Microwave Cavity Sensor

Simultaneous measurement of absolute strain and differential strain based on fiber Bragg grating Fabry–Perot sensor

We present a fiber Bragg grating Fabry–Perot (FBG-FP) sensor using the fast Fourier transform (FFT) demodulation for measuring the absolute strain and differential strain simultaneously. The amplitude and phase characteristics of Fourier transform spectrum have been studied. The relation between the amplitude of Fourier spectrum and the differential strain has been presented. We fabricate the fiber grating FP cavity sensor, and carry out the experiment on the measurement of absolute strain and differential strain. Experimental results verify the demodulation method, and show that this sensor has a good accuracy in the scope of measurement. The demodulating method can expand the number of multiplexed sensors combining with wavelength division multiplexing and time division multiplexing.

Hybrid microcavity humidity sensor

This work presents an optical humidity sensing technique based on the combination of a whispering gallery mode microtoroidal cavity sensor and a nm-scale thick humidity-responsive polymer coating deposited via the initiated chemical vapor deposition process. As a result of the conformational change by the polymer in response to humidity, the sensitivity is increased by nearly two orders of magnitude in comparison to conventional refractometric sensing. Additionally, the dependence of the device performance on the film thickness is studied. Specifically, the thinner film enabled a faster response rate, yet a slower recovery rate, as compared to the thicker films.

Gasoline properties determination with phononic crystal cavity sensor

In order to optimize the combustion process, engine performance and meeting the EPA emission standards, information should be gained in real time about properties of gasoline, which is supplied nowadays in a wide range with different compositions. This study presents a new sensor platform based on a phononic crystal (PnC) sensor comprising a cavity and its application as in-line real-time measuring system to determine gasoline properties. The method is based on the analysis of the transmission spectrum of a phononic crystal sensor filled with the liquid gasoline blend. We could reveal a strong correlation between gasoline properties and the frequency of maximum transmission.Obtained experimental results show that the phononic crystal sensors can be considered as a prospective, competitive and inexpensive device specifically for ethanol in gasoline detection and distinguishing fuels with different octane numbers.

Fabry-Pérot cavity sensor-based optofluidic gas chromatography using a microfabricated passive preconcentrator/injector

This study reports on dual on-column Fabry-Pérot (FP) cavity sensor-based gas chromatography (GC) of mixtures of volatile organic compounds (VOCs) utilizing an on-chip device, the so called "microfabricated passive preconcentrator/injector (μPPI)". Comprehensive analysis of the sampling, desorption/injection, and compound separation performance of the μPPI-based optofluidic GC system is described. Here, the combined use of the μPPI and on-column FP cavity sensors in a common GC platform enabled diffusion-based passive sampling, rapid (<7 min) chromatographic separation, and optical detection for the quaternary VOC mixtures of benzene, TCE, toluene, and m-xylene at sub-ppm concentrations with a simpler fluidic setup than conventional GC systems. The FP cavity sensor arrangement provided the means to study the dynamics of the thermal desorption/injection of VOCs by the μPPI and its effect on the GC separation resolution. Our analysis of obtained chromatograms revealed a presence of the competitive adsorptions of VOC mixtures onto the adsorption sites of trapping materials in the μPPI, which decreased the effective sampling rate by ~50% for compounds with high volatility. The validated performance of the optofluidic GC system promises future development of a field deployable GC microsystem incorporating the μPPI and the FP cavity sensors.

High-Temperature Capacitive Mode Pressure Sensor Based on SiC

In order to realize high-accuracy pressure measurement in harsh environment, a new kind of Double-notches Touch Mode Capacitive Pressure Sensor (DTMCPS) based on SiC material is presented. Through research to material properties of the sensor, the sensor can be applied in high-temperature field. Using Finite Element Method (FEM) to simulate and solve capacitance, the results show that DTMCPS can immensely improve the sensitivity and the linear range of traditional single cavity sensor because of its double notches structure. Consequently, the sensor has outstanding measurement performance in high-temperature environment.

Self-repairing, interferometric waveguide sensor with a large strain range

We demonstrate a polymer waveguide, Fabry-Perot interferometer strain sensor fabricated through a self-writing process in a photopolymerizable resin bath between two silica optical fibers. The measurable strain range is extended through sensor self-repair and strain measurements are demonstrated up to 150% applied tensile strain. The sensor fabrication and repair is performed in the ultraviolet wavelength range, while the sensor interrogation is performed in the near-infrared wavelength range. A hybrid sensor is fabricated by splicing a short segment of multimode optical fiber to the input single-mode optical fiber. The hybrid sensor provides the high quality of waveguide fabrication previously demonstrated through self-writing between multimode optical fibers with the high fringe visibility of single-mode propagation. The peak frequency shift of the reflected spectrum Fabry-Perot sensor is extremely linear with applied strain for the hybrid sensor, with a sensitivity of 2.3×10(-3) per nanometer per percent strain. The calibrated peak frequency shift with applied strain is the same for both the original sensor and the repaired sensor; therefore, the fact that the sensor has self-repaired does not need to be known. Additionally, this calibration is the same between multiple sensor fabrications. In contrast to a conventional air gap Fabry-Perot cavity sensor, no decrease in the fringe visibility is observed over the measurable strain range.

Optical fiber Fabry-Perot interferometer cavity fabricated by femtosecond laser micromachining and fusion splicing for refractive index sensing

We demonstrate a fiber in-line Fabry-Perot interferometer cavity sensor for refractive index measurement. The interferometer cavity is formed by drilling a micro-hole at the cleaved fiber end facet, followed by fusion splicing. A micro-channel is inscribed by femtosecond laser micromachining to vertically cross the cavity to allow liquid to flow in. The refractive index sensitivity obtained is ~994 nm/RIU (refractive index unit). Such a device is simple in configuration, easy for fabrication and reliable in operation due to extremely low temperature cross sensitivity of ~4.8 × 10(-6) RIU/°C.

Optimized light–matter interaction and defect hole placement in photonic crystal cavity sensors

Photonic crystal slab cavities were investigated for increased light-matter interaction based on selective placement of sublattice hole sized defect holes inside L3 cavities. A multiple-hole defect (MHD) consisting of three defect holes placed in the regions of highest cavity mode field intensity were demonstrated through finite-difference time-domain simulations and experiments to exhibit the strongest light-matter interaction without introducing significant scattering losses. Compared to an L3 cavity without defect holes, these strategically designed three-hole MHD cavities presented higher quality factor and more than double the resonance wavelength shift upon exposure to a thin oxide and two small chemical molecules.

Noninvasive in vitro measurement of pig-blood d-glucose by using a microwave cavity sensor

We have developed an electromagnetic microwave cavity sensor based on the resonant frequency shift for real time measurement of the glycemia in pig blood. We could determine the concentration of d-glucose in pig blood in the range of 150–550mg/dl at the resonance frequency near 4.75GHz with a bandwidth of 300MHz. The change in the d-glucose concentration in blood brings microwave reflection coefficient S11 changes of about 6.26dB and resonance frequency shifts of about 11.25MHz due to the electromagnetic interaction between the cavity resonator and the blood filled plastic tube inserted into the cavity. This proposed system provides a unique approach for real time noninvasive and contactless glucose monitoring.

The Study on Amended Method for the Measurement of Humidity with Microwave Cavity Sensor

While measuring the steam humidity using microwave cylindrical cavity, thanks to the thermal expansion effect of metal, the resonant frequency changes as temperature changes. Such phenomenon reduces the measurement accuracy. This paper analyses the phenomenon, and discusses an amended calculation method which will increase the test accuracy. Compared with lab test results, this amended method becomes more convictive.

Intrinsic Fabry–Pérot Cavity Sensor Based on Etched Multimode Graded Index Fiber for Strain and Temperature Measurement

Two Fabry-Perot interferometers based on chemical etching in multimode graded index fibers are fabricated and their response to temperature and strain are compared. Chemical etching is applied in the graded index fiber end creating an air cavity. The interferometric cavity is formed when the graded index fiber with the air concavity is spliced to a single-mode fiber. The intrinsic sensors present high sensitivity to strain and low sensitivity to temperature. For the 62.5 μm core fiber, sensitivities of 6.99 pm/με and, 0.95 pm/°C were obtained for strain and temperature, respectively. The sensor based in the 50 μm core fiber, on the other hand, presented sensitivities of 4.06 pm/με and -0.84 pm/°C for strain and temperature, respectively.

Application Study on Microwave Resonance Cavity for Non-Electrical Quantity Detection

In order to detect the humidity and the density of cigarette, we designed a type of microwave resonance cavity sensor which is called repeating-entry model. We used TM010 resonance model to the real-time detection of cigarette humidity and density. Under two conditions: vacuum resonance and cigarette in existence, through the swept technique we obtain resonance frequency，peak powerand half power point bandwidth from amplitude-frequency peculiarity (Figure I). According to mathematical formulas (6) and (7), we get cigarette humidity and density respectively. The detection technique has many advantages such as speediness, continuation, high resolution rate, non-pollution, safe and convenient operation, etc. And it is applicable to industrial survey on the spot.

Application Study on Microwave Resonance Cavity for Non-Electrical Quantity Detection

In order to detect the humidity and the density of cigarette, we designed a type of microwave resonance cavity sensor which is called repeating-entry model. We used TM010 resonance model to the real-time detection of cigarette humidity and density. Under two conditions: vacuum resonance and cigarette in existence, through the swept technique we obtain resonance frequency，peak powerand half power point bandwidth from amplitude-frequency peculiarity (Figure I). According to mathematical formulas (6) and (7), we get cigarette humidity and density respectively. The detection technique has many advantages such as speediness, continuation, high resolution rate, non-pollution, safe and convenient operation, etc. And it is applicable to industrial survey on the spot.

End-Point Control of Holding Phase Based on Cavity Pressure for Injection Molding

While the switchover from filling to packing is particularly crucial during injection molding, the transfers from holding to screw recovery also significantly affects the quality of molded parts. In this study, the end-point control of the holding phase based on cavity pressure was presented. It was compared with the traditional control method by holding time. The purpose of this study was to validate the feasibility of the end-point control of holding phase by cavity pressure, and to examine its consistency. The weight of the molded parts served as the main measure to probe the process’s capabilities. The results of the verification experiments revealed that the end-point control mode based on cavity pressure could yield better consistency of part weight than the traditional control method by holding time, however, the benefits were not significant. The trigger value of cavity pressure and sensor position should be considered for achieving such high process capabilities.

Multivariate regression modeling for monitoring quality of injection moulding components using cavity sensor technology: Application to the manufacturing of pharmaceutical device components

There is an increased demand within the moulding industry to improve the quality of moulded parts by maintaining consistent tolerances and overall dimensions. This interest is more important in areas of the moulding industry that are dedicated to pharmaceutical devices, where a quality by design approach is now expected to be adopted. A pharmaceutical device is an assembly of different plastic components which are manufactured by injection moulding; many have critical quality parameters which affect not only the device appearance but also more importantly its performance for drug delivery. Hence, the need of better understanding and control of injection moulding processes. This study presents the use of multivariate regression modeling approach to monitor the quality of the final product using cavity sensor technology (CST). The influence of the injection moulding process parameters on the quality of the final parts have been investigated using a design of experiment approach. The results demonstrate that the Partial Least Squares (PLS) regression model based on cavity pressure sensor data could be successfully used to monitor the quality (weight, dimensions) of the final product in plastic injection moulding.

Characterization of variable reflectivity of a polarization-maintaining fiber Sagnac mirror for long-distance remote fiber Bragg gratings cavity sensors

Variation of broadband reflectivity is experimentally characterized for a polarization-maintaining fiber (PMF) Sagnac mirror. Theoretical analysis is also demonstrated using the Jones matrices of the PMF Sagnac mirror. Variable reflectivity is useful to enhance the signal performance of a long-distance remote fiber Bragg gratings (FBGs) cavity sensor at a range of tens of km. Controlling both the reflecting bandwidth and partial reflectivity assists the effective multi-wavelength lasing from the linear-type resonance cavity with FBG mirrors at one side and a PMF Sagnac mirror at the other. The FBG sensing signal achieves a high SNR of greater than ∼45 dB due to the cavity mirror effect.

Hepa Filter Material Load Detection Using a Microwave Cavity Sensor

Abstract This paper presents a novel microwave cavity sensor application for the detection of HEPA filter particulate loading. The sensor resonates at 3.435GHz and 8.570GHz when empty, where the TM010 and TM020 modes dominate respectively. Experimental results show that the resonant frequency of the sensor shifts significantly when filters of different particulate loadings are presented to it. This is a significant finding, and means that the sensor could present an effective solution for determining the loading of periodic use HEPA filters (e.g. those used in personal respirators), which are often disposed of unnecessarily.