Heyu Yin | Midlands State University (original) (raw)
Teaching Documents by Heyu Yin
Papers by Heyu Yin
ESSCIRC 2022- IEEE 48th European Solid State Circuits Conference (ESSCIRC)
Microchemical Journal, 2021
Abstract Airborne particulate matter (PM), especially fine particles with a diameter smaller than... more Abstract Airborne particulate matter (PM), especially fine particles with a diameter smaller than 2.5 µm (PM2.5 classification) are a deadly air quality concern. One possible solution to reduce individual exposure to fine PM is to develop a low-cost and wearable PM monitor. This paper introduces a new approach for continuous quantification of particles that expresses a resolution suitable for fine PM measurement and a capacity for miniaturization to support wearable monitoring using a unique combination of particle size fractionation and electrochemical quantification. High efficiency size fractionation is performed through a microfluidic device utilizing an I-shape pillar based deterministic lateral displacement (DLD) method to provide particles of uniform size for downstream quantification. Measurement of PM concentration was explored using different electrochemical methods and electrode materials, and differential pulse voltammetry (DPV) with gold electrodes was found to give the best sensitivity and repeatability. Our results show that the mechanism responsible for the particle’s electrochemical response is the ionic electret effect, linking this effect to PM measurement for the first time. A compact electrochemical instrumentation system was implemented to demonstrate this detection scheme as a wearable PM monitoring platform. DPV results with polystyrene particles demonstrate a sensitivity of for 1 µm particles of 3 aA/particle. Both size fractionation and quantification results show that this platform is a promising option for portable fine PM monitoring.
2018 IEEE Biomedical Circuits and Systems Conference (BioCAS), 2018
ECoG electrode arrays offer great potential for high-channel-count monitoring of large scale brai... more ECoG electrode arrays offer great potential for high-channel-count monitoring of large scale brain activity. However, scaling ECoG recording systems to high channel count is challenging due to the large silicon area demanded by the coupling capacitors necessary for DC offset voltage rejection. This paper presents a new approach to reduce the perchannel area of recording circuits by introducing a capacitorembedded ECoG electrode structure that implements coupling capacitors within the existing electrode area. For proof of concept, a 4x4 array of 8 pF capacitor-embedded electrodes was fabricated in a 2mm x 2mm area using a three-mask process to form a capacitor stack of Cu, Ta2O5, and Ti/Cu/Au. In vivo experiments performed on an adult rat show that physiologically-evoked activity was accurately detected according to the placement of the electrodes for manual whisker deflection, shoulder tapping and hindlimb tapping. The capacitor-embedded ECoG electrode structure provides a new method for achieving high channel count neural recording.
2016 IEEE International Symposium on Circuits and Systems (ISCAS), 2016
The integration of biosensors, microfluidics and CMOS instrumentation provides a compact lab-on-C... more The integration of biosensors, microfluidics and CMOS instrumentation provides a compact lab-on-CMOS microsystem well suited for high throughput measurement. This paper describes a screen-printed planar metallization technique for lab-on-CMOS that overcomes challenges associated with traditional thin film metallization. Utilizing a chip-in-carrier packaging approach with an epoxy carrier, screen-printed electrical interconnects are shown to reliably resolve up to 10μm step height differences between the CMOS chip and the surrounding carrier that supports microfluidics. The metallization process presented in this paper is also shown to be compatible with subsequent microfluidic integration to complete the lab-on-CMOS device platform.
Advanced Materials, 2021
In article number 2007764, Changyong Cao and co-workers review the progress in smart agriculture ... more In article number 2007764, Changyong Cao and co-workers review the progress in smart agriculture systems, consisting of soil sensors, plant wearables, and remote sensing devices, for detecting the health condition of soil and crops to advance the management of modern farms and increase agriculture production, while protecting the environment.
2017 IEEE International Symposium on Circuits and Systems (ISCAS), 2017
Airborne particulate matter (PM) pollution, especially fine particles with a diameter of 2.5 μm o... more Airborne particulate matter (PM) pollution, especially fine particles with a diameter of 2.5 μm or smaller (PM2.5), has caused severe air quality issues that threaten human life and contribute to global mortality. Thus a low cost, portable or wearable platform for individual PM2.5 monitoring is of great interest. This paper introduces a platform for portable real-time PM2.5 monitoring that combines a particle separation microfluidic channel and electrochemical detection. The microfluidic device utilizes an I-shape pillar based deterministic lateral displacement method to achieve high separation efficiency of different particle sizes. Electrochemical detection was implemented for particles measurement to achieve high sensitivity and simplify the instrumentation compared to conventional optical methods. Both separation and detection results show that this platform is a promising option for portable PM2.5 monitoring.
2020 IEEE International Symposium on Circuits and Systems (ISCAS), 2020
Deterministic lateral displacement (DLD) devices have demonstrated great promise in separation of... more Deterministic lateral displacement (DLD) devices have demonstrated great promise in separation of micro and nano-sized particles, with important applications in biomedical research and healthcare monitoring. This paper introduces a new cascaded multi-section DLD approach toward expanding the dynamic range of particle sizes separated. A robust model has been developed to analyze the design tradeoffs and practical fabrication limits of this new approach. Results show that by cascading multiple sections of increasingly smaller gap size and critical separation dimension, a wide spectrum of size fractionation dynamic ranges and minimum separation resolutions can be achieved. Moreover, the presented model allows designers to visualize the cost of achieving various performance goals in terms of overall device size. Model results based on DLD theoretical equations are first presented, followed by model results for both circle and I-shaped pillar options that apply scaling restrictions associated with their practical fabrication limits.
2021 IEEE International Midwest Symposium on Circuits and Systems (MWSCAS), 2021
PM2.5 is one of the main sources of air pollution and could negatively affect the human health. T... more PM2.5 is one of the main sources of air pollution and could negatively affect the human health. The available commercial PM monitoring devices are often bulky and expensive and thus not useful for personal use. Toward the implementation of personal/wearable PM monitoring devices, this paper presents a low-cost, liquid-based capacitive monitoring device that uses in-house fabricated electrodes and a custom PCB with off-the-shelf components. The fabricated device is designed to detect concentration of particles in a liquid environment which enables integration of the capacitive detection with future electrochemical-based analysis of PM elemental composition. In this liquid-based detection scheme, a minimum detection level of 4.6 x 106 particles/µL is achieved which corresponds to the particles sampled from an unhealthy level of PM2.5 in the air. The detection response shows a linearity of R2=0.9934 during the experiments.
Advanced Materials, 2021
a compelling need to utilize advanced technologies in the agriculture sector to increase agricult... more a compelling need to utilize advanced technologies in the agriculture sector to increase agricultural productivity and reduce food losses to guarantee food security. [2] In this regard, "smart agriculture" or "precision agriculture" has been attracting increasing attention due to its capability for using less to grow more compared to traditional agricultural practices. In addition, it improves the quality of the work environment and social aspects of farming, ranching, and other relevant professions. [4] Smart agriculture comprises a set of technologies that combines sensors, information systems, enhanced machinery, and informed management to optimize production by accounting for variabilities and uncertainties within sustainable agricultural systems. [3-5] Among the set of technologies, advanced sensing systems that monitor soil health and conditions and crop developments are of paramount importance because they collect and evaluate critical data for decision making and management, especially when crop growth conditions vary considerably over space and time. Spatial variation may result from soil properties, diseases, weeds, pests, and previous land management. In particular, some soil properties (e.g., moisture, pH, nutrients) and plant diseases may form long-term spatial patterns. Temporal variability arises from weather patterns and management practices. In summary, the soil properties relevant to crop growth include a range of soil conditions including soil gas, moisture, temperature, nutrients, pH, and pollutants in the soil (Figure 1). [6,7] Monitoring the soil conditions will provide key information not only to improve resource utilization to maximize farming outputs and minimize environmental side effects but also to build site-specific databases of relationships between soil conditions and plant growth for intelligent and sustainable agriculture systems. Traditionally, soil properties are measured by soil sampling and offsite laboratory analysis or by on-site measurement to provide an extensive knowledge of soil information. [8] Seasonally varying crop growth conditions, such as water stress, lack of nutrients, diseases, weeds, and insects, are evaluated by visual inspection and laboratory analysis of plant tissues. The relatively periodically coarse sampling/measurement rate of these conventional strategies may not be sufficient to reveal variation at the appropriate spatial and temporal resolution. Novel technologies for collecting soil information with sufficient spatiotemporal resolutions are in demand to build efficient smart or precision agriculture systems. With the Soil sensors and plant wearables play a critical role in smart and precision agriculture via monitoring real-time physical and chemical signals in the soil, such as temperature, moisture, pH, and pollutants and providing key information to optimize crop growth circumstances, fight against biotic and abiotic stresses, and enhance crop yields. Herein, the recent advances of the important soil sensors in agricultural applications, including temperature sensors, moisture sensors, organic matter compounds sensors, pH sensors, insect/pest sensors, and soil pollutant sensors are reviewed. Major sensing technologies, designs, performance, and pros and cons of each sensor category are highlighted. Emerging technologies such as plant wearables and wireless sensor networks are also discussed in terms of their applications in precision agriculture. The research directions and challenges of soil sensors and intelligent agriculture are finally presented.
2016 IEEE Healthcare Innovation Point-Of-Care Technologies Conference (HI-POCT), 2016
The growing impact of airborne pollutants and explosive gases on human health and occupational sa... more The growing impact of airborne pollutants and explosive gases on human health and occupational safety has escalated the demand for sensors to monitor hazardous gases. Existing gas sensors lack the miniaturization and real-time measurement capability necessary to quantify point-of-care exposure to gaseous hazards. To overcome these challenges and enable cost-effective monitoring of personal exposure in local environments, this paper presents a robust microfabricated planar electrochemical gas sensor featuring room temperature ionic liquid (RTIL) as the electrolyte. Together with carefully selected electrochemical methods, the miniaturized gas sensor is capable of measuring multiple gases important to human health and safety. Compared to its larger predecessor, our manually-assembled Clark-cell sensor, this microsensor provides better sensitivity, linearity and repeatability, as validated for oxygen and methane monitoring. The microfabricated planar RTIL electrochemical gas sensor is well suited for personal point-of-exposure monitoring of hazardous gases in a real world environment.
IEEE Transactions on Instrumentation and Measurement, 2019
This paper introduces a novel compact low-power amperometric instrumentation design with current-... more This paper introduces a novel compact low-power amperometric instrumentation design with current-to-digital output for electrochemical sensors. By incorporating the double layer capacitance of an electrochemical sensor's impedance model, our new design can maintain performance while dramatically reducing circuit complexity and size. Electrochemical experiments with potassium ferricyanide, show that the circuit output is in good agreement with results obtained using commercial amperometric instrumentation. A high level of linearity (R 2 = 0.991) between the circuit output and the concentration of potassium ferricyanide was also demonstrated. Furthermore, we show that a CMOS implementation of the presented architecture could save 25.3% of area, and 47.6% of power compared to a traditional amperometric instrumentation structure. Thus, this new circuit structure is ideally suited for portable/wireless electrochemical sensing applications.
Sensors and Actuators B: Chemical, 2018
Tunable and quantitative serial dilution on a multichannel microfluidic electrochemical platform ... more Tunable and quantitative serial dilution on a multichannel microfluidic electrochemical platform Highlights for review This work implements tunable and quantitative serial dilution on a multichannel microfluidic electrochemical platform. The electrochemical platform can continuously share and dilute samples from prior channels, which effectively reduces sample cost with only one outlet required. The miniaturized electrochemical platform was established with microfabrication process and tested to validate its performance.
IEEE Sensors Journal, 2018
The growing demand for personal healthcare monitoring requires a challenging combination of perfo... more The growing demand for personal healthcare monitoring requires a challenging combination of performance, size, power, and cost that is difficult to achieve with existing gas sensor technologies. This paper presents a new CMOS monolithic gas sensor microsystem that meets these requirements through a unique combination of electrochemical readout circuits, post-CMOS planar electrodes, and room temperature ionic liquid (RTIL) sensing materials. The architecture and design of the CMOS-RTIL-based monolithic gas sensor are described. The monolithic device occupies less than 0.5 mm 2 per sensing channel and incorporates electrochemical biasing and readout functions with only 1.4 mW of power consumption. Oxygen was tested as an example gas, and results show that the microsystem demonstrates a highly linear response (R 2 = 0.995) over a 0-21% oxygen concentration range, with a limit of detection of 0.06% and a 1 s response time. Monolithic integration reduces manufacturing cost and is demonstrated to improve limits of detection by a factor of five compared to a hybrid implementation. The combined characteristics of this device offer an ideal platform for portable/wearable gas sensing in applications such as air pollutant monitoring.
IEEE transactions on biomedical circuits and systems, Apr 1, 2018
The integration of biosensors, microfluidics, and CMOS instrumentation provides a compact lab-on-... more The integration of biosensors, microfluidics, and CMOS instrumentation provides a compact lab-on-CMOS microsystem well suited for high throughput measurement. This paper describes a new epoxy chip-in-carrier integration process and two planar metalization techniques for lab-on-CMOS that enable on-CMOS electrochemical measurement with multichannel microfluidics. Several design approaches with different fabrication steps and materials were experimentally analyzed to identify an ideal process that can achieve desired capability with high yield and low material and tool cost. On-chip electrochemical measurements of the integrated assembly were performed to verify the functionality of the chip-in-carrier packaging and its capability for microfluidic integration. The newly developed CMOS-compatible epoxy chip-in-carrier process paves the way for full implementation of many lab-on-CMOS applications with CMOS ICs as core electronic instruments.
Sensors and Actuators B: Chemical, 2017
The growing impact of airborne pollutants and explosive gases on human health and occupational sa... more The growing impact of airborne pollutants and explosive gases on human health and occupational safety has escalated the demand of sensors to monitor hazardous gases. This paper presents a new miniaturized planar electrochemical gas sensor for rapid measurement of multiple gaseous hazards. The gas sensor features a porous polytetrafluoroethylene substrate that enables fast gas diffusion and room temperature ionic liquid as the electrolyte. Metal sputtering was utilized for platinum electrodes fabrication to enhance adhesion between the electrodes and the substrate. Together with carefully selected electrochemical methods, the miniaturized gas sensor is capable of measuring multiple gases including oxygen, methane, ozone and sulfur dioxide that are important to human health and safety. Compared to its manually-assembled Clark-cell predecessor, this sensor provides better sensitivity, linearity and repeatability, as validated for oxygen monitoring. With solid performance, fast response and miniaturized size, this sensor is promising for deployment in wearable devices for real-time point-of-exposure gas pollutant monitoring.
Sensors and actuators. B, Chemical, 2017
Intense study on gas sensors has been conducted to implement fast gas sensing with high sensitivi... more Intense study on gas sensors has been conducted to implement fast gas sensing with high sensitivity, reliability and long lifetime. This paper presents a rapid amperometric method for gas sensing based on a room temperature ionic liquid electrochemical gas sensor. To implement a miniaturized sensor with a fast response time, a three electrode system with gold interdigitated electrodes was fabricated by photolithography on a porous polytetrafluoroethylene substrate that greatly enhances gas diffusion. Furthermore, based on the reversible reaction of oxygen, a new transient double potential amperometry (DPA) was explored for electrochemical analysis to decrease the measurement time and reverse reaction by-products that could cause current drift. Parameters in transient DPA including oxidation potential, oxidation period, reduction period and sample point were investigated to study their influence on the performance of the sensor. Oxygen measurement could be accomplished in 4 s, and th...
2013 IEEE SENSORS, 2013
ABSTRACT This paper presents a real-time, electrochemical gas sensor array system featuring room ... more ABSTRACT This paper presents a real-time, electrochemical gas sensor array system featuring room temperature ionic-liquid interfaces and targeting safety monitoring in underground mines. A prototype system was constructed using a custom ionic-liquid sensor array, a custom multi-mode electrochemical sensor readout board, and a commercial low power microcontroller board. Gas sensors for multiple mine gases were implemented in a 2 by 2 miniaturized array. A novel resource-sharing circuit tailored to our gas sensor array was utilized to significantly decrease power, cost and size while implementing two electrochemical detection modes. The system achieves a resolution as high as 0.01% vol in amperometry mode and 0.06% vol in impedance spectroscopy mode for oxygen as an example target gas.
Rare Metals, 2014
ABSTRACT The superconducting nanowire single photon detector (SNSPD) draws much attention because... more ABSTRACT The superconducting nanowire single photon detector (SNSPD) draws much attention because of its attractive performance at ultra violet, visible, and near-infrared wavelengths, and it can be widespread in quantum information technologies. However, how to increase the absorption which can dramatically increase the quantum efficiency of the SNSPD is still a top research issue. In this study, the effect of incident medium and cavity material on the optical absorptance of cavity-integrated SNSPDs was systematically investigated using finite-element method. The simulation results demonstrate that for photons polarized parallel to nanowire orientation, even though the maximum absorptance of the nanowire is insensitive to cavity material, it does increase when the refractive index of incident medium decreases. For perpendicularly polarized photons, both incident medium and cavity material play significant roles, and the absorptance curves get closer to the parallel case as the refractive index of cavity material increases. Based on these results, two cavity-integrated SNSPDs with front-illumination structure which can enhance the absorptance for both parallel and perpendicular photons are proposed. Finally, a design to realize polarization-independent SNSPDs with high absorptance is presented.
ESSCIRC 2022- IEEE 48th European Solid State Circuits Conference (ESSCIRC)
Microchemical Journal, 2021
Abstract Airborne particulate matter (PM), especially fine particles with a diameter smaller than... more Abstract Airborne particulate matter (PM), especially fine particles with a diameter smaller than 2.5 µm (PM2.5 classification) are a deadly air quality concern. One possible solution to reduce individual exposure to fine PM is to develop a low-cost and wearable PM monitor. This paper introduces a new approach for continuous quantification of particles that expresses a resolution suitable for fine PM measurement and a capacity for miniaturization to support wearable monitoring using a unique combination of particle size fractionation and electrochemical quantification. High efficiency size fractionation is performed through a microfluidic device utilizing an I-shape pillar based deterministic lateral displacement (DLD) method to provide particles of uniform size for downstream quantification. Measurement of PM concentration was explored using different electrochemical methods and electrode materials, and differential pulse voltammetry (DPV) with gold electrodes was found to give the best sensitivity and repeatability. Our results show that the mechanism responsible for the particle’s electrochemical response is the ionic electret effect, linking this effect to PM measurement for the first time. A compact electrochemical instrumentation system was implemented to demonstrate this detection scheme as a wearable PM monitoring platform. DPV results with polystyrene particles demonstrate a sensitivity of for 1 µm particles of 3 aA/particle. Both size fractionation and quantification results show that this platform is a promising option for portable fine PM monitoring.
2018 IEEE Biomedical Circuits and Systems Conference (BioCAS), 2018
ECoG electrode arrays offer great potential for high-channel-count monitoring of large scale brai... more ECoG electrode arrays offer great potential for high-channel-count monitoring of large scale brain activity. However, scaling ECoG recording systems to high channel count is challenging due to the large silicon area demanded by the coupling capacitors necessary for DC offset voltage rejection. This paper presents a new approach to reduce the perchannel area of recording circuits by introducing a capacitorembedded ECoG electrode structure that implements coupling capacitors within the existing electrode area. For proof of concept, a 4x4 array of 8 pF capacitor-embedded electrodes was fabricated in a 2mm x 2mm area using a three-mask process to form a capacitor stack of Cu, Ta2O5, and Ti/Cu/Au. In vivo experiments performed on an adult rat show that physiologically-evoked activity was accurately detected according to the placement of the electrodes for manual whisker deflection, shoulder tapping and hindlimb tapping. The capacitor-embedded ECoG electrode structure provides a new method for achieving high channel count neural recording.
2016 IEEE International Symposium on Circuits and Systems (ISCAS), 2016
The integration of biosensors, microfluidics and CMOS instrumentation provides a compact lab-on-C... more The integration of biosensors, microfluidics and CMOS instrumentation provides a compact lab-on-CMOS microsystem well suited for high throughput measurement. This paper describes a screen-printed planar metallization technique for lab-on-CMOS that overcomes challenges associated with traditional thin film metallization. Utilizing a chip-in-carrier packaging approach with an epoxy carrier, screen-printed electrical interconnects are shown to reliably resolve up to 10μm step height differences between the CMOS chip and the surrounding carrier that supports microfluidics. The metallization process presented in this paper is also shown to be compatible with subsequent microfluidic integration to complete the lab-on-CMOS device platform.
Advanced Materials, 2021
In article number 2007764, Changyong Cao and co-workers review the progress in smart agriculture ... more In article number 2007764, Changyong Cao and co-workers review the progress in smart agriculture systems, consisting of soil sensors, plant wearables, and remote sensing devices, for detecting the health condition of soil and crops to advance the management of modern farms and increase agriculture production, while protecting the environment.
2017 IEEE International Symposium on Circuits and Systems (ISCAS), 2017
Airborne particulate matter (PM) pollution, especially fine particles with a diameter of 2.5 μm o... more Airborne particulate matter (PM) pollution, especially fine particles with a diameter of 2.5 μm or smaller (PM2.5), has caused severe air quality issues that threaten human life and contribute to global mortality. Thus a low cost, portable or wearable platform for individual PM2.5 monitoring is of great interest. This paper introduces a platform for portable real-time PM2.5 monitoring that combines a particle separation microfluidic channel and electrochemical detection. The microfluidic device utilizes an I-shape pillar based deterministic lateral displacement method to achieve high separation efficiency of different particle sizes. Electrochemical detection was implemented for particles measurement to achieve high sensitivity and simplify the instrumentation compared to conventional optical methods. Both separation and detection results show that this platform is a promising option for portable PM2.5 monitoring.
2020 IEEE International Symposium on Circuits and Systems (ISCAS), 2020
Deterministic lateral displacement (DLD) devices have demonstrated great promise in separation of... more Deterministic lateral displacement (DLD) devices have demonstrated great promise in separation of micro and nano-sized particles, with important applications in biomedical research and healthcare monitoring. This paper introduces a new cascaded multi-section DLD approach toward expanding the dynamic range of particle sizes separated. A robust model has been developed to analyze the design tradeoffs and practical fabrication limits of this new approach. Results show that by cascading multiple sections of increasingly smaller gap size and critical separation dimension, a wide spectrum of size fractionation dynamic ranges and minimum separation resolutions can be achieved. Moreover, the presented model allows designers to visualize the cost of achieving various performance goals in terms of overall device size. Model results based on DLD theoretical equations are first presented, followed by model results for both circle and I-shaped pillar options that apply scaling restrictions associated with their practical fabrication limits.
2021 IEEE International Midwest Symposium on Circuits and Systems (MWSCAS), 2021
PM2.5 is one of the main sources of air pollution and could negatively affect the human health. T... more PM2.5 is one of the main sources of air pollution and could negatively affect the human health. The available commercial PM monitoring devices are often bulky and expensive and thus not useful for personal use. Toward the implementation of personal/wearable PM monitoring devices, this paper presents a low-cost, liquid-based capacitive monitoring device that uses in-house fabricated electrodes and a custom PCB with off-the-shelf components. The fabricated device is designed to detect concentration of particles in a liquid environment which enables integration of the capacitive detection with future electrochemical-based analysis of PM elemental composition. In this liquid-based detection scheme, a minimum detection level of 4.6 x 106 particles/µL is achieved which corresponds to the particles sampled from an unhealthy level of PM2.5 in the air. The detection response shows a linearity of R2=0.9934 during the experiments.
Advanced Materials, 2021
a compelling need to utilize advanced technologies in the agriculture sector to increase agricult... more a compelling need to utilize advanced technologies in the agriculture sector to increase agricultural productivity and reduce food losses to guarantee food security. [2] In this regard, "smart agriculture" or "precision agriculture" has been attracting increasing attention due to its capability for using less to grow more compared to traditional agricultural practices. In addition, it improves the quality of the work environment and social aspects of farming, ranching, and other relevant professions. [4] Smart agriculture comprises a set of technologies that combines sensors, information systems, enhanced machinery, and informed management to optimize production by accounting for variabilities and uncertainties within sustainable agricultural systems. [3-5] Among the set of technologies, advanced sensing systems that monitor soil health and conditions and crop developments are of paramount importance because they collect and evaluate critical data for decision making and management, especially when crop growth conditions vary considerably over space and time. Spatial variation may result from soil properties, diseases, weeds, pests, and previous land management. In particular, some soil properties (e.g., moisture, pH, nutrients) and plant diseases may form long-term spatial patterns. Temporal variability arises from weather patterns and management practices. In summary, the soil properties relevant to crop growth include a range of soil conditions including soil gas, moisture, temperature, nutrients, pH, and pollutants in the soil (Figure 1). [6,7] Monitoring the soil conditions will provide key information not only to improve resource utilization to maximize farming outputs and minimize environmental side effects but also to build site-specific databases of relationships between soil conditions and plant growth for intelligent and sustainable agriculture systems. Traditionally, soil properties are measured by soil sampling and offsite laboratory analysis or by on-site measurement to provide an extensive knowledge of soil information. [8] Seasonally varying crop growth conditions, such as water stress, lack of nutrients, diseases, weeds, and insects, are evaluated by visual inspection and laboratory analysis of plant tissues. The relatively periodically coarse sampling/measurement rate of these conventional strategies may not be sufficient to reveal variation at the appropriate spatial and temporal resolution. Novel technologies for collecting soil information with sufficient spatiotemporal resolutions are in demand to build efficient smart or precision agriculture systems. With the Soil sensors and plant wearables play a critical role in smart and precision agriculture via monitoring real-time physical and chemical signals in the soil, such as temperature, moisture, pH, and pollutants and providing key information to optimize crop growth circumstances, fight against biotic and abiotic stresses, and enhance crop yields. Herein, the recent advances of the important soil sensors in agricultural applications, including temperature sensors, moisture sensors, organic matter compounds sensors, pH sensors, insect/pest sensors, and soil pollutant sensors are reviewed. Major sensing technologies, designs, performance, and pros and cons of each sensor category are highlighted. Emerging technologies such as plant wearables and wireless sensor networks are also discussed in terms of their applications in precision agriculture. The research directions and challenges of soil sensors and intelligent agriculture are finally presented.
2016 IEEE Healthcare Innovation Point-Of-Care Technologies Conference (HI-POCT), 2016
The growing impact of airborne pollutants and explosive gases on human health and occupational sa... more The growing impact of airborne pollutants and explosive gases on human health and occupational safety has escalated the demand for sensors to monitor hazardous gases. Existing gas sensors lack the miniaturization and real-time measurement capability necessary to quantify point-of-care exposure to gaseous hazards. To overcome these challenges and enable cost-effective monitoring of personal exposure in local environments, this paper presents a robust microfabricated planar electrochemical gas sensor featuring room temperature ionic liquid (RTIL) as the electrolyte. Together with carefully selected electrochemical methods, the miniaturized gas sensor is capable of measuring multiple gases important to human health and safety. Compared to its larger predecessor, our manually-assembled Clark-cell sensor, this microsensor provides better sensitivity, linearity and repeatability, as validated for oxygen and methane monitoring. The microfabricated planar RTIL electrochemical gas sensor is well suited for personal point-of-exposure monitoring of hazardous gases in a real world environment.
IEEE Transactions on Instrumentation and Measurement, 2019
This paper introduces a novel compact low-power amperometric instrumentation design with current-... more This paper introduces a novel compact low-power amperometric instrumentation design with current-to-digital output for electrochemical sensors. By incorporating the double layer capacitance of an electrochemical sensor's impedance model, our new design can maintain performance while dramatically reducing circuit complexity and size. Electrochemical experiments with potassium ferricyanide, show that the circuit output is in good agreement with results obtained using commercial amperometric instrumentation. A high level of linearity (R 2 = 0.991) between the circuit output and the concentration of potassium ferricyanide was also demonstrated. Furthermore, we show that a CMOS implementation of the presented architecture could save 25.3% of area, and 47.6% of power compared to a traditional amperometric instrumentation structure. Thus, this new circuit structure is ideally suited for portable/wireless electrochemical sensing applications.
Sensors and Actuators B: Chemical, 2018
Tunable and quantitative serial dilution on a multichannel microfluidic electrochemical platform ... more Tunable and quantitative serial dilution on a multichannel microfluidic electrochemical platform Highlights for review This work implements tunable and quantitative serial dilution on a multichannel microfluidic electrochemical platform. The electrochemical platform can continuously share and dilute samples from prior channels, which effectively reduces sample cost with only one outlet required. The miniaturized electrochemical platform was established with microfabrication process and tested to validate its performance.
IEEE Sensors Journal, 2018
The growing demand for personal healthcare monitoring requires a challenging combination of perfo... more The growing demand for personal healthcare monitoring requires a challenging combination of performance, size, power, and cost that is difficult to achieve with existing gas sensor technologies. This paper presents a new CMOS monolithic gas sensor microsystem that meets these requirements through a unique combination of electrochemical readout circuits, post-CMOS planar electrodes, and room temperature ionic liquid (RTIL) sensing materials. The architecture and design of the CMOS-RTIL-based monolithic gas sensor are described. The monolithic device occupies less than 0.5 mm 2 per sensing channel and incorporates electrochemical biasing and readout functions with only 1.4 mW of power consumption. Oxygen was tested as an example gas, and results show that the microsystem demonstrates a highly linear response (R 2 = 0.995) over a 0-21% oxygen concentration range, with a limit of detection of 0.06% and a 1 s response time. Monolithic integration reduces manufacturing cost and is demonstrated to improve limits of detection by a factor of five compared to a hybrid implementation. The combined characteristics of this device offer an ideal platform for portable/wearable gas sensing in applications such as air pollutant monitoring.
IEEE transactions on biomedical circuits and systems, Apr 1, 2018
The integration of biosensors, microfluidics, and CMOS instrumentation provides a compact lab-on-... more The integration of biosensors, microfluidics, and CMOS instrumentation provides a compact lab-on-CMOS microsystem well suited for high throughput measurement. This paper describes a new epoxy chip-in-carrier integration process and two planar metalization techniques for lab-on-CMOS that enable on-CMOS electrochemical measurement with multichannel microfluidics. Several design approaches with different fabrication steps and materials were experimentally analyzed to identify an ideal process that can achieve desired capability with high yield and low material and tool cost. On-chip electrochemical measurements of the integrated assembly were performed to verify the functionality of the chip-in-carrier packaging and its capability for microfluidic integration. The newly developed CMOS-compatible epoxy chip-in-carrier process paves the way for full implementation of many lab-on-CMOS applications with CMOS ICs as core electronic instruments.
Sensors and Actuators B: Chemical, 2017
The growing impact of airborne pollutants and explosive gases on human health and occupational sa... more The growing impact of airborne pollutants and explosive gases on human health and occupational safety has escalated the demand of sensors to monitor hazardous gases. This paper presents a new miniaturized planar electrochemical gas sensor for rapid measurement of multiple gaseous hazards. The gas sensor features a porous polytetrafluoroethylene substrate that enables fast gas diffusion and room temperature ionic liquid as the electrolyte. Metal sputtering was utilized for platinum electrodes fabrication to enhance adhesion between the electrodes and the substrate. Together with carefully selected electrochemical methods, the miniaturized gas sensor is capable of measuring multiple gases including oxygen, methane, ozone and sulfur dioxide that are important to human health and safety. Compared to its manually-assembled Clark-cell predecessor, this sensor provides better sensitivity, linearity and repeatability, as validated for oxygen monitoring. With solid performance, fast response and miniaturized size, this sensor is promising for deployment in wearable devices for real-time point-of-exposure gas pollutant monitoring.
Sensors and actuators. B, Chemical, 2017
Intense study on gas sensors has been conducted to implement fast gas sensing with high sensitivi... more Intense study on gas sensors has been conducted to implement fast gas sensing with high sensitivity, reliability and long lifetime. This paper presents a rapid amperometric method for gas sensing based on a room temperature ionic liquid electrochemical gas sensor. To implement a miniaturized sensor with a fast response time, a three electrode system with gold interdigitated electrodes was fabricated by photolithography on a porous polytetrafluoroethylene substrate that greatly enhances gas diffusion. Furthermore, based on the reversible reaction of oxygen, a new transient double potential amperometry (DPA) was explored for electrochemical analysis to decrease the measurement time and reverse reaction by-products that could cause current drift. Parameters in transient DPA including oxidation potential, oxidation period, reduction period and sample point were investigated to study their influence on the performance of the sensor. Oxygen measurement could be accomplished in 4 s, and th...
2013 IEEE SENSORS, 2013
ABSTRACT This paper presents a real-time, electrochemical gas sensor array system featuring room ... more ABSTRACT This paper presents a real-time, electrochemical gas sensor array system featuring room temperature ionic-liquid interfaces and targeting safety monitoring in underground mines. A prototype system was constructed using a custom ionic-liquid sensor array, a custom multi-mode electrochemical sensor readout board, and a commercial low power microcontroller board. Gas sensors for multiple mine gases were implemented in a 2 by 2 miniaturized array. A novel resource-sharing circuit tailored to our gas sensor array was utilized to significantly decrease power, cost and size while implementing two electrochemical detection modes. The system achieves a resolution as high as 0.01% vol in amperometry mode and 0.06% vol in impedance spectroscopy mode for oxygen as an example target gas.
Rare Metals, 2014
ABSTRACT The superconducting nanowire single photon detector (SNSPD) draws much attention because... more ABSTRACT The superconducting nanowire single photon detector (SNSPD) draws much attention because of its attractive performance at ultra violet, visible, and near-infrared wavelengths, and it can be widespread in quantum information technologies. However, how to increase the absorption which can dramatically increase the quantum efficiency of the SNSPD is still a top research issue. In this study, the effect of incident medium and cavity material on the optical absorptance of cavity-integrated SNSPDs was systematically investigated using finite-element method. The simulation results demonstrate that for photons polarized parallel to nanowire orientation, even though the maximum absorptance of the nanowire is insensitive to cavity material, it does increase when the refractive index of incident medium decreases. For perpendicularly polarized photons, both incident medium and cavity material play significant roles, and the absorptance curves get closer to the parallel case as the refractive index of cavity material increases. Based on these results, two cavity-integrated SNSPDs with front-illumination structure which can enhance the absorptance for both parallel and perpendicular photons are proposed. Finally, a design to realize polarization-independent SNSPDs with high absorptance is presented.
IEEE Transactions on Applied Superconductivity, 2013
A novel photon-number-resolving detector based on serially connected superconducting nanowires is... more A novel photon-number-resolving detector based on serially connected superconducting nanowires is presented. The serial nanowire detector (SND) uses spatial multiplexing on a subwavelength scale, the same as the parallel nanowire detector (PND), to provide an output signal proportional to the number of incident photons and avoids the problem of leakage current that the PND suffers from, thus allowing both high quantum efficiency and large number of resolvable photons. Electrothermal simulation results of the SND exhibit a better linearity than that of the PND, and the influence of some important design parameters on the detector's performance is investigated. In addition, noise analysis is done in order to estimate the upper limit of the element number of the SND. Finally, a modified segmental current supply scheme is proposed to overcome the problem of constrictions.