Environmental Sensing

Miniature In Vivo Chitosan Diaphragm-Based Fiber-Optic Ultrasound Sensor

Li Han Chen, Chi Chiu Chan, Xiu Min Ang, Weiyong Yuan, Peng Zu, Wei C. Wong, YiFan Zhang, and Kam Chew Leong

Published in IEEE Journal of Selected Topics in Quantum Electronics

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Abstract

A fiber-optic Fabry–Perot interferometric chitosan membrane hydrophone for in vivo ultrasound measurements is proposed. The hydrophone is based on a thin chitosan film acting as a low-finesse Fabry–Perot cavity that is formed at the tip of hol- low core fiber. Chitosan membrane provides maximum acoustic impedance matching for in vivo ultrasound measurement and opti- mizes the matched-loading condition due to its permeable property. The transduction mechanism is based on acoustically induced me- chanical deformation of the chitosan sensing interferometer, which exhibits a voltage sensitivity of 0.5 mV/MPa or ?06 dB re 1 V/μPa without the use of filtering and external preamplifiers. The sensor shows frequency response from 1 to 20 MHz in the presence of acoustic amplitude level up to 4 MPa with a minimum detectable pressure of 40 kPa. The wideband sensitive response, biocompat- ibility, and easy functionalization of chitosan membrane suggest the possibility for accurate and reliable measurements of exposure levels encountered in in vivo ultrasound measurements and may find applications as an alternative to piezoelectric hydrophone for ultrasound characterizations.

Sensitivity-enhanced Michelson interferometric humidity sensor with waist-enlarged fiber bitaper

Pengbing Hu, Xinyong Dong, Kai Ni, Li Han Chen, Wei Chang Wong, and Chi Chiu Chan

Published in Sensors and Actuators B-Chemical

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Abstract

A fiber-optic humidity sensor composed of a chitosan-coated, waist-enlarged bitaper-based Michelson interferometer (WEBMI) is proposed and experimentally demonstrated. Humidity changes interference pattern of the sensor head through refractive index of the chitosan coating thus relative humidity level can be determined from corresponding wavelength shift. The achieved sensitivity is further enhanced by more than 5 times, from 26 pm/%RH to 135 pm/%RH, by reducing the fiber cladding thickness and oxidizing the chitosan film. Experimentations show that the measurement is fully reversible and repeatable with fast response and recovery time of ? s and 3 s, respectively.

Photonic Crystal Fiber Loop Mirror-Based Chemical Vapor Sensor,

Luo Niu, Chun-liu Zhao, Liang Qi, Chi Chiu Chan, Juan Kang, Shangzhong Jin, Jiangtao Guo, and Huifeng Wei

Published in Journal of Lightwave Technology

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Abstract

A compact chemical vapor sensor based on a fiber loop mirror (FLM) inserted with a high-birefringent photonic crys- tal fiber (HiBi-PCF) is proposed and experimentally demonstrated. Because the resonant dips of the HiBi-PCF FLM are sensitive to the phase difference between two counter-propagating waves in the FLM, a highly sensitive chemical vapor can be achieved by mea- suring the resonant dip shifts when chemical vapor diffuses into the air holes of the HiBi-PCF. Experimental results show a high sensitivity of 15.5 pm/ppm for ethanol is obtained when a 5.1 cm long HiBi-PCF is used in the FLM. Three different mechanisms for the high sensitivity of the proposed sensor are discussed. A lique- faction model with a full-vector finite element method is proposed and is regarded as the main contribution.

Chitosan based Fiber-optic Fabry–Perot Humidity Sensor

L.H. Chen, T. Li, C.C. Chan, R. Menon, P. Balamurali, M. Shaillender, B. Neu, X.M. Ang, P. Zu, W.C. Wong, K.C. Leong

Published in Sensors and Actuators B-Chemical

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Abstract

A relative humidity fiber sensor based on Fabry–Perot interferometry configuration is presented. The proposed fiber sensor is functionalized with a thin layer of a moisture-sensitive natural polymer chitosan to form a low fineness Fabry–Perot sensor. The sensing scheme used in this work is based on the swelling effect of chitosan sensing film (degree of swelling varies as a function of relative humidity) which will induce optical path modulation when relative humidity is changed. As observed, the proposed sensor exhibits a sensitivity of 0.13 nm/%RH for relative humidity ranging from 20%RH to 95%RH with a RH uncertainty of ±1.68%RH and fast response time of 380 ms.

Chitosan-Coated Polarization Maintaining Fiber-Based Sagnac Interferometer for Relative Humidity Measurement

Li Han Chen, Chi Chiu Chan, Tao Li, Mutukumaraswamy Shaillender, Bjo ̈rn Neu, Papusamy Balamurali, Rahul Menon, Peng Zu, Xiu Min Ang, Wei Chang Wong, Chueh Loo Poh, and Kam Chew Leong

Published in IEEE Journal of Selected Topics in Quantum Electronics

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Abstract

A relative humidity fiber sensor based on polarization maintaining (PM) fiber Sagnac interferometery configuration is presented. The proposed sensor is functionalized with a thin layer of a moisture-sensitive natural polymer chitosan, whose degree of swelling varies as a function of relative humidity. The sensing scheme used in this study is based on the strain effect induced on the PM fiber to modulate its birefringence property through the swelling effect of chitosan. To optimize the sensor’s response, the experiments were first conducted to evaluate the effect of chitosan concentration on the PM fiber, followed by investigating effects of chemically etched PM fiber and analyzing modified chitosan sens- ing film effect on the sensor’s performance. As observed from the results, the optimized sensor exhibits a sensitivity of 81 pm/%RH for the relative humidity ranging from 20% RH to 95% RH with an uncertainty of ±2.04% RH.