The precise detection of volatile organic compounds plays a pivotal role in addressing environmental concerns, industrial safety, and medical diagnostics. The accurate identification and quantification of these compounds because of their ubiquity and potential health hazards has fueled the development of advanced sensing technologies. This work presents a sensing system in the realm of long-wavelength infrared spectroscopy for achieving enhanced selectivity and sensitivity of benzene, toluene, and propane detection through quartz-enhanced photoacoustic spectroscopy. High-resolution gas spectroscopy is made possible by the use of specially designed InAs/AlSb-based quantum cascade lasers, emitting in the wavelength range 13–15 μm, and quartz tuning forks. The sensor system, characterized by its robustness and precision, demonstrates exceptional capabilities in benzene, toluene, and propane detection. The system's capacity for practical applications in environmental monitoring and medical diagnostics is demonstrated by its ability to distinguish these volatile organic compounds with a minimum detection limit of 113 ppb, 3 ppb, and 3 ppm for toluene, benzene, and propane at an integration time of 10 s, even in complex gas matrices. This work advances gas sensing technology while also offering insightful information on spectral interferences, a persistent problem in the field. The results usher in a new era of sophisticated and reliable gas sensing techniques meeting the growing demand for precise volatile organic compounds detectors for environmental monitoring purposes.

This paper addresses the analysis and design of a high-resolution and temperature-insensitive inclination sensor using Fiber Bragg Grating (FBG). The sensor uses a pendulum-based structure with FBG attached to its cantilever arm. Initially, strain analysis of the proposed inclination sensor is carried out using the Finite Element Method (FEM) to optimize the structure and materials for its fabrication. Experimental analysis is carried out on the inclination sensors by varying the inclination angle, and its results are compared with FEM based results. The shift in Bragg wavelength of FBG due to generated strain at cantilever arm is observed on optical interrogator. To measure the sub-picometer wavelength shift with enhanced resolution and lower uncertainty, eigendecomposition of the reflection spectrum using Karhunen–Loève Transform (KLT) is implemented. The range of measurement of tilt angle is found to be 0° to 3°: with a resolution of 0.0008°. The satisfactory linearity of measured angle versus true angle, excellent repeatability, and very high resolution validates the feasibility of the proposed inclination sensor.

Fiber Bragg Gratings (FBGs) are known for their high sensitivity towards strain and temperature variation. In this manuscript, the strain sensing property of FBG is utilized and explored for measuring weight using a common binocular shaped cantilever type load cell. The shift in Bragg wavelength due to load application is converted into optical power variation using edge filter detection technique. Furthermore, change in optical power is converted into voltage variation and is feed to the Raspberry Pi via analog to digital converter (ADC ADS1115) for real-time and continuous online monitoring of weights. The optical load cell has shown linear response for applied weight up to 8kg. Mechanical properties of optical load cell such as nonlinearity, hysteresis, repeatability, creep and safe over load are studied in detail. Message Queuing Telemetry Transport (MQTT) protocol is used to send data from Raspberry Pi to IoT cloud. The system has achieved resolution of 20g with error of ± 50g.

Benzene is a gas known to be highly pollutant for the environment, for the water and cancerogenic for humans. In this paper, we present a sensor based on Quartz Enhanced Photoacoustic Spectroscopy dedicated to benzene analysis. Exploiting the infrared emission of a 14.85 µm quantum cascade laser, the sensor is working in an off-beam configuration, allowing easy alignment and stable measurements. The technique provides a very good selectivity to the sensor and a limit of detection of 30 ppbv in 1 s, i.e. a normalized noise equivalent absorption of 1.95 × 10⁻⁸ W.cm⁻¹.Hz^−1/2. The achieved performances of the sensor have enabled measurements on several air samples of a gas station showing a non-neglectable risk in case of long exposure.

We report InAs-based quantum cascade lasers (QCLs) operating near 14 µm with a threshold current density J_th as low as 0.6 kA/cm² at room temperature. The threshold obtained is lower than the J_th of the best reported InP-based QCLs to date without facet treatment. The achieved performance improvement is partially due to an increased separation between the upper transition level and the next one in the active quantum wells of the employed QCL design.

Psychophysiological measurement can be very crucial in critical conditions faced in aviation, military, hospitals, etc. Respiration rate is one of the primary parameters to determine the psychophysiological condition of a person. An effective respiration rate measurement system is developed using Fiber Bragg Grating (FBG), and a comparison of its response with an electronic sensor is carried out in this paper. An edge filter detection technique is employed to interrogate the optical sensing data. Arduino Uno is used for acquiring data from both electronic and optical sensors simultaneously. Both the electronic and optical sensors are fitted inside the same PVC mask, and their responses are compared. The experiment is carried out on five subjects, and every time it is found, that optical sensor is much more reliable and responsive. Optical sensor has better rise and decay constants for instantaneous temperature sensing making it a superior candidate to diagnose various respiration abnormalities. Respiration rate calculation is also carried out during coughing and headshaking. In the events of coughing, response of the optical sensor is much more prominent as compared to the electronic sensor. However, respiration rate calculation remains unaffected and reliable.