Portable Environmental Monitoring Research Articles

High-efficiency mid-infrared CW-seeded optical parametric generation in PPLN waveguide

Mid-infrared optical sources have been extensively used in a variety of applications, including gas sensing and metrology, by exploiting the fingerprint fundamental vibrational absorption bands of molecules in this spectral region. Parametric frequency conversion techniques, such as optical parametric generation (OPG) and optical parametric oscillator (OPO), represent common methodologies for mid-infrared generation. Notably, continuous-wave (CW)-seeded OPG exhibits superior stability and performance compared to conventional OPG. Here, we present a simple method for mid-infrared source generation based on femtosecond OPG in periodically poled lithium niobate (PPLN) waveguides. In addition to its robustness and simplicity, mid-infrared CW-seeded OPG features a high quantum conversion efficiency of 46.5% and a low threshold. The phase of CW-seeded OPG was passively referenced to the CW laser, making it suitable for dual-comb applications. This system shows great promise in the miniaturization of mid-infrared combs and will be applied to non-laboratory applications, including open-path atmospheric gas sensing and portable environmental monitoring.

A Wide Dynamic Range Multi-Sensor ROIC for Portable Environmental Monitoring Systems With Two-Step Self-Optimization Schemes

This article presents a wide-dynamic-range multi-sensor readout interface for portable environmental monitoring systems with two-step self-optimization schemes. It proposes two-step self-optimization methods of adaptive range detection and coarse self-cancelation (CSC) for current-type sensor interfaces, and range-based path control and current DAC-based correlated double sampling (CDS) for resistive sensing interfaces. Their digital conversions are provided by two kinds of high-resolution ADCs, namely, an incremental ΔΣ current detector and a two-step SAR- ΔΣ ADC. The proposed ROIC prototype is fabricated in a 180-nm CMOS process, achieving a dynamic range (DR) of 136.5 dB and 160.9 dB, and a maximum SNR of 109.8 dB and 108.6 dB for current and resistance detection, respectively. For system-level feasibility, an environmental monitoring system prototype based on the ROIC is also manufactured and functionally verified by integrating two kinds of in-house micro-electro-mechanical systems (MEMS) sensor devices, the MCU, and the Bluetooth module, supporting wireless air quality and water pollution monitoring capabilities.

MICROPROCESSOR SYSTEM FOR INVESTIGATION OF SENSOR CHARACTERISTICS ON THE BASIS OF POROUS SILICON

Development of integrated sensors is a promising scientific and technical direction to create components for measurement and information systems. Among the different types of analyser one of the places are occupied by sensors of hydrogen containing compounds in gaseous and liquid condition (especially poisonous and carcinogenic). Fixing the presence of a substances in the gas or liquid environment is an actual task for scientific, industrial and medical application areas. The main goal of this paper an inexpensive microprocessor system for measuring and analyzing electrical properties of nanocomposite sensing material such as porous silicon on the base of current and capacity-voltage characteristics and its hardware and software applying is represented. The microprocessor system is designed for measuring sensors current-voltage and capacity-voltage characteristics based on porous silicon and nanocomposite structures and consists of the following units: power supply unit, DC voltage regulator, control and measurement module, RLC-meter E7-22, UART/USB and RS232/USB converters, measuring cell, PC. The software of the microprocessor system for measuring consists of the software for the control and measurement module implemented on the Atmega 128 microcontroller and the main device management software for the PC. The main program algorithm and software are implemented in the C# programming language in the Visual Studio 2017 environment The results of the comparison allow us to conclude that the implemented modules of the microprocessor system for sensors I-V- and C-V characteristics testing can be used in the development of portable environmental monitoring devices, to study porous silicon sensors using them. Keywords — porous silicon, nanocomposite; sensor, microcontroller, microprocessing system, current-voltage characteristic

Sandwiched Platinum Thin Film TCD for 3-Omega Technique for Detection of Ammonia Gas

Over the past few decades, sensor technology has been revolutionized by exploring the disciplines of nanotechnology and nanofabrication process. As a result, environmental sensors including gas sensors have been miniaturized and become more advanced in the terms of sensitivity and accuracy. Todays, gas sensors can cover a broader range of volatile compounds with a limit of detection (LOD) as low as single ppm. Despite these advances, ammonia sensing is still challenging because of its corrosive nature. The chemical-based gas sensors for ammonia are not reliable due to several factors such as slow recovery time, sensor base-line drifting, vulnerability to degradation and false alarm [1]. On the other hand, physical-based ammonia sensing approaches have the advantage of fast response time and long-term durability [2]. The Thermal Conductivity Detector (TCD) limit of detection has been improved to 30 ppm by making use of the 3-omega measurement technique, however the sensor requires a robust geometrical design, and careful material selection to withstand the higher temperature during operation [3,4]. To enhance LOD further, a new design including design elements which eliminates the shortcomings in the current cantilever design. The temperature difference in the deposition process for Al203 and platinum layer causes the sensor to bend away from the silicon wafer surface, and be vulnerable to fluid velocity. Hence a supporting platinum layer has been added underneath of Al2O3 layer so that thermal stresses introduced during fabrication, and generated in operation are compensated. The new design of micro wire TCD also includes optimized shape to bear the high thermal stresses caused by continuous current needed for the 3-omega measurement technique, and a higher stability of the temperature coefficient of resistance with platinum film to improve reproducibility of response. [1] Azad, A. M., Akbar, S. A., Mhaisalkar, S. G., Birkefeld, L. D., & Goto, K. S. (1992). Solid‐state gas sensors: A review. Journal of the Electrochemical Society, 139(12), 3690-3704. [2] Mahdavifar, A., Navaei, M., Hesketh, P. J., Dimandja, J. D., Stetter, J. R., & McMurray, G. (2015). Implementation of a polysilicon micro electro-thermal detector in gas chromatography system with applications in portable environmental monitoring. ECS Journal of Solid State Science and Technology, 4(10), S3062-S3066. [3]Lotfi, Ardalan, Milad Navaei, and Peter J. Hesketh. "A Platinum Cantilever-Based TCD for 3-Omega Sensing of Gas Mixtures." ECS Transactions 86.16 (2018): 79-86. [4] Lotfi, A., Mahdavifar, A., Struk, D., Stetter, J. R., Navaei, M., & Hesketh, P. (2017). Ultimate Sensitivity of Physical Sensor for Ammonia Gas Detection Exploiting Full Differential 3-Omega Technique. ECS Transactions, 80(10), 1571-1578 Figure 1

Platinum Thin Film TCD Designed for 3 Omega Sensing of Gas Mixtures

Over the last few decades, the world of sensors has been revolutionized by exploring the disciplines of nanotechnology and sophisticated Nano-fabrication process. As a result, gas sensors have become smaller and more robust in the terms of sensitivity and accuracy. Furthermore, these sensors are able to cover a broader range of gases and volatile compounds increasing detection capabilities, allowing detection down to single ppm. However, challenges still exist in detecting certain gases, specifically ammonia. The chemical-based gas sensors for ammonia are not reliable due to several factors such as slow recovery time, sensor base-line drifting, vulnerability to degradation and false alarm [1]. On the other hand, the physical-based ammonia sensing approach has the advantage of fast response time and long-term durability [2], while the thermal conductivity detector suffers a lack of high sensitivity and selectivity. In an effort to address these challenges, this study is designed to improve the limit of detection of a micro wire thermal conductivity gas sensor that enables the system to detect 100 parts per million for ammonia. The differential 3-Omega measurement technique uses two sensors, one as sensing sensor and the other as a reference [3,4]. It is a harmonic excitation technique that needs a sinusoidal current can produce high thermal stresses that shorten the sensor life-time. To increase the reproducibility of sensor fabrication process, the micro wire TCD sensor material is replaced with platinum. In summary, the new design of micro wire TCD includes optimized shape to bear the high thermal stresses caused by continuous current needed by 3-omega technique and higher stability of the temperature coefficient of resistance with platinum film. [1] Azad, A. M., Akbar, S. A., Mhaisalkar, S. G., Birkefeld, L. D., & Goto, K. S. (1992). Solid‐state gas sensors: A review. Journal of the Electrochemical Society, 139(12), 3690-3704. [2] Mahdavifar, A., Navaei, M., Hesketh, P. J., Dimandja, J. D., Stetter, J. R., & McMurray, G. (2015). Implementation of a polysilicon micro electro-thermal detector in gas chromatography system with applications in portable environmental monitoring. ECS Journal of Solid State Science and Technology, 4(10), S3062-S3066. [3] Lotfi, A., Mahdavifar, A., Struk, D., Stetter, J. R., Navaei, M., & Hesketh, P. (2017). Ultimate Sensitivity of Physical Sensor for Ammonia Gas Detection Exploiting Full Differential 3-Omega Technique. ECS Transactions, 80(10), 1571-1578 [4] Kommandur, S., Mahdavifar, A., Hesketh, P. J., & Yee, S. (2015). A microbridge heater for low power gas sensing based on the 3-Omega technique. Sensors and Actuators A: Physical, 233, 231-238. Figure 1

Implementation of a Polysilicon Micro Electro-Thermal Detector in Gas Chromatography System with Applications in Portable Environmental Monitoring

Thermal conductivity detectors work based on electro-thermal interaction between rate of heat loss to the surrounding gas from a hot element and resistance change due to temperature variation of the heater. Our developed ultra-low power polysilicon microbridge TCD provides ultra-fast response time and high sensitivity along with lower power consumption that makes it suitable for portable GC in environmental and bioengineering applications. In this work we modeled and tested the microTCD operation as a detector in a GC system. MicroTCD was packaged and connected to a 3 m long separation column in GC and was tested with injections of hexane and mixture of six standard compounds in helium carrier. Modeling and experimental results show that the effect of carrier gas flow speed on power consumption and heat loss from the microbridge is small and therefore the microTCD is insensitive to various typical flow rates. A new method of excitation and measurement of the detector was utilized to avoid base temperature drifting and achieve superior resolution in extended range of operations while consuming only 0.4 mW power. The microTCD response for different compound was obtained and compared with standard Flame Ionization Detector (FID) results.

Atomic Layer Deposition of SnO2 for Selective Room Temperature Low ppb Level O3 Sensing

This work demonstrates ultra-low power ozone sensors for real time, continuous, and portable monitoring. Atomic Layer Deposition (ALD) of SnO2 enables precise control of ultrathin film thickness on the order of the Debye length to enhance sensitivity at room temperature. Correlation between ozone concentration and the rate of resistance change is used to maintain fast response times and ultraviolet (UV) illumination hastens recovery. ALD SnO2 ultrathin film sensors realize room temperature operation with highly selective detection of 50 ppb ozone with average power consumption of 150 μW making them well suited for real time, portable environmental monitoring systems.

A chip scale nanofluidic pump using electrically controllable hydrophobicity

The traditional microfluidic systems and devices faced limitations such as power consumption and high driving force in the attempt for implementation as chemical analysis and environmental monitoring systems. The up-to-date development of chemistry and biology has generated great demand for lab-on-a-chip performing specific chemical and biological analysis, clinical diagnostics and biomedical processing. Manipulation of ultrasmall amount and great varieties of biofluids has also been a major issue challenging many researchers. Here we demonstrate in this article, a device utilizing electrically controllable surface tension as the driving force to deliver fluid flow in the order of nanoliters per minute or even smaller, without a dedicated actuator. This device is capable of pumping a continuous liquid column. This actuation mechanism of fluid flow in this device is based on electrowetting-on-dielectric (EWOD) effect and the physics of the fluid dynamics is governed by Navier–Stokes equation. It also has a built-in metering feature to precisely determine the flow rate without an additional flow sensor. The experimental results show that water can be electrically actuated successfully to flow in the microchannel at a flow rate of 18 nl/min under a potential of as low as 20 V. This is very attractive for applications which require an ultra miniaturized metering pump operated at a low power for portable environmental monitoring instruments, chemical analysis systems, implantable medical devices, drug delivery systems and clinical diagnostic systems.

A portable integrated wide-range gas sensing system with smart A/D front-end

In this paper, the development of a portable environmental monitoring system based on a gas sensor array is proposed. The most critical issues related to the microsensor, the interface circuit and the data analysis have been addressed. The complete system is designed to exhibit high precision and large dynamic range. Experimental results on a prototype, obtained by injecting ethanol on a microsensor coated with Pd-doped SnO2, have confirmed the theoretical expectations, demonstrating that the system is suitable for high-precision gas sensing applications.

Watershed-Based Integration of Hydrology, Geochemistry, and Geophysics in an Environmental Geology Curriculum

Inquiry-based study focused on the campus watershed was initiated at Binghamton University after creation of an undergraduate Environmental Geology Track within the Geological Sciences curriculum. Use of the watershed in environmental geology courses has been implemented to 1) promote active learning outside of the classroom; 2) allow students to work with state of the art field and laboratory equipment and “real world” data; and 3) encourage interdisciplinary thinking. The longer-term goal is to enable undergraduates to conduct meaningful, field based, “capstone” research projects. A grant from the National Science Foundation supported instrumentation of the entire campus watershed into a readily accessible field laboratory; included are groundwater monitoring wells, equipment for measuring and sampling stream flow, a meteorological station, a wet and dry deposition collector for sampling atmospheric quality, and portable environmental monitoring equipment. In addition, geophysical equipment, including seismic refraction and reflection, DC electrical resistivity, and gravity anomaly measurements, is used to determine subsurface structure at various locations on campus. The undergraduates are now able to explore differences in physical and chemical processes between and within the atmosphere, hydrosphere, and lithosphere on real-time scales. The use of this equipment and the watershed focus has been fully incorporated into three inquiry-based undergraduate courses (Environmental Hydrology, Environmental Geophysics, and Environmental Measurements) to foster interdisciplinary learning about the complexity of watershed-based processes. This manuscript describes the campus field stations, presents examples of field exercises, and assesses the impacts of the program to date.

A Portable Environmental Monitoring System to Assess Barn Worker Indoor Air Exposure

A personal environmental sampling backpack (PESB) was constructed to assessacute worker exposure in poultry and swine operations. The PESB is capable ofrecording, on a minute-by-minute basis over an 8-h period, the followingenvironmental parameters: temperature (40 to 70C, 1C), relative humidity (RH)(0-100% @ 25C, 2%), ammonia (NH 3 ) (0-50 ppm, 5% of reading), carbon dioxide(CO 2 ) (0-5000 ppm, 5% of reading), and dust (0.3, 0.5, 1 and 5 m). Theseenvironmental conditions are measured via thermistor (temperature), capacitance (RH),electrochemical (NH 3 ), non-dispersive infrared (CO 2 ), and laser (dust). For endotoxinand gravimetric dust measurements, the PESB contains two constant airflow pumps,which can deliver airflow rates of 0.5 to 3.0 L/min. By sampling barn air within thebreathing zone of the worker (a 0.3 m radius around the mouth) the PESB canmonitor a workers personal exposure over their entire work shift. The PESB has alsobeen designed to minimize equipment cleaning between barns, required by stringentbiosecurity protocols. Through the use of a watertight case and an anti-microbialexhaust filter for sampled air, only the carrying pack and external tubing needs to besubjected to thorough cleaning and disinfection to maintain biosecurity. The PESBweighs 8.42 kg (18.57 lbs) with dimensions of 388 mm (h) 288 mm (w) 173 mm(d) (15.28 in. 11.34 in. 6.81 in.).