In this article, we propose a novel multipoint gas detection scheme based on the photothermal (PT) effect and interferometer working at different wavelengths. Several fiber Bragg gratings (FBGs) with ...different central wavelengths were incorporated in the linear Sagnac-like interferometer, which served as the wavelength-dependent reflection mirrors, to extract the gas concentration information from different gas cells. This structure allows for a more straightforward and efficient installation and layout, as it eliminates the need for sophisticated servo control and lock-in amplifiers. The experiment used a novel frequency-domain signal processing method to collect weak gas signals, and the results showed that an 18-cm-long gas cell can detect gas concentrations as low as 47 ppb with current technology. This method can significantly reduce noise, and crosstalk can be lowered to less than 30 dB. A three-point acetylene detection system is validated through experiments. The proposed method has potential application in the multipoint, multigas monitor in the monitoring field.
Compared with its counterparts, polarization sensitive optical time-domain reflectometry (P-OTDR) has two typical problems in terms of multi-point disturbance detection and high precision ...positioning, which restrict its practical applications. In this paper, we propose a novel method by using two-dimensional (2-D) image processing and statistical clustering. In place of the traditional spatial or temporal signal analysis way, the idea employs the temporally and the spatially uneven/inconsistent evolving patterns induced by the multiple individual events, and the proposed method is carried out to accumulate the temporally differentiated OTDR traces and then build up a 2-D temporal-spatial evolving graph, by using edge detection and automatic clustering to distinguish different disturbing points with precise locations. Through series of multi-point disturbance tests, the proposed method has been proved to have better performance than the conventional direct differentiation method and the fast Fourier transform spectrum analysis.
With the development of wearable devices, strain sensors have attracted large interest for the detection of human motion, movement, and breathing. Various strain sensors consisting of stretchable ...conductive materials have been investigated based on resistance and capacitance differences according to the strain. However, this method requires multiple electrodes for multipoint detection. We propose a strain sensor capable of multipoint detection with a single electrode, based on the ultrasound pulse-echo method. It consists of several transmitters of carbon nanotubes (CNTs) and a single polyvinylidene fluoride receiver. The strain sensor was fabricated using CNTs embedded in stretchable polydimethylsiloxane. The received data are characterized by the different times of transmission from the CNTs of each point depending on the strain, i.e., the sensor can detect the positions of the CNTs. This study demonstrates the application of the multipoint strain sensor with a single electrode for measurements up to a strain of 30% (interval of 1%). We considered the optical and acoustic energy losses in the sensor design. In addition, to evaluate the utility of the sensor, finger bending with three-point CNTs and flexible phantom bending with six-point CNTs for the identification of an S-curve having mixed expansion and compression components were carried out.
We developed a novel fiber optic Surface Plasmon Resonance (SPR) hydrogen sensor based on heterocorestructured fiber optics with multi-layer films of gold (Au), tantalum pentaoxide (Ta2O5), ...andpalladium (Pd) that are uniformly coated on a cladding surface. In a light intensity-based experimentwith Light Emitting Diode (LED) operation at 850 nm, we induced a transmitted loss change ofapproximately 0.23 dB with a response time of 15 s for 4% hydrogen in 25-nm Au, 60-nm Ta2O5, and3-nm Pd multi-layer films. In addition, multi-point detection for hydrogen was successfully achievedusing a combination of an SPR hydrogen tip sensor and an interrogating system based on PseudorandomNoise-code Correlation Reflectometry (PNCR). The sensor gives optical loss changes with and withouthydrogen absorption and shows Pd hydrogenation process in real time with high sensitivity, such asmore than 0.4 dB.
Phase sensitive Surface Plasmon Resonance (SPR) techniques are a popular means of characterizing biomolecular interactions. However, limitations due to the narrow dynamic range and difficulty in ...adapting the method for multi-point sensing have restricted its range of applications. This paper presents a compact phase sensitive SPR technology using a custom CMOS camera. The system is exceptionally versatile enabling one to trade dynamic range for sensitivity without altering the optical system. We present results showing sensitivity over the array of better than 10−6 Refractive Index Units (RIU) over a refractive index range of 2×10−2RIU, with peak sensitivity of 3×10−7RIU at the center of this range. We also explain how simply altering the settings of polarization components can give sensitivity on the order of 10−8RIU albeit at the cost of lower dynamic range. The consistent response of the custom CMOS camera in the system also allowed us to demonstrate precise quantitative detection of two Fibrinogen antibody–protein binding sites. Moreover, we use the system to determine reaction kinetics and argue how the multipoint detection gives useful insight into the molecular binding mechanisms.
•We introduced a SPR sensor with an optimal sensitivity of 3×10−7RIU.•Sensitivity better than 10−6RIU was achieved for refractive index 1.33 ~1.35RIU.•Relation between responsivity and dynamic range was illustrated.•Potential performance (sensitivity of 4.7×10−8RIU) was estimated.•New AC detector enabling multi-point sensing was introduced.
A novel device was designed for the multipoint addressable detection of DNA hybridization. Row and column electrodes array were orthogonally arranged, and the microwells were assembled on the ...crossing points of the row/column electrodes to form a 4
×
4 microwell array. Amperometric signals at the individual microwells could be detected separately on the basis of redox cycling of localized electroactive species occurring between the electrodes. Immobilization and hybridization of DNA could block the redox cycling of Fe(CN)
6
4−/Fe(CN)
6
3− at the designated microwells, resulting in the reduction of current response. This device had been used to detect DNA hybridization with excellent sensitivity (0.03
μM) and selectivity. The device can be applied to comprehensive and high-throughput detection and imaging of biochemical species.
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