A microcontroller-based interface circuit for data acquisition and control of a micromechanical thermal flow sensor

Flow measurement has been an essential requirement in many commercial and industrial applications; one of the urgent needs is the low-power flow-sensing node for the Internet of Things (IoT) in the smart Energy-efficient Building (EeB). With the mature CMOS fabrication techniques, the low-cost MEMS flow devices combined with the highly integrated circuits (ICs) and micro mechanical components are able to be carried out. In particular, the target of this thesis, thermal flow sensors do not require any moving parts that make them perhaps the easiest flow devices to be implemented in the CMOS process due to the structural and electronic simplicity. This thesis mainly focuses on the systematic design and fabrication of the low-cost micromachined calorimetric flow sensors by using the CMOS-MEMS technology. Primarily, a unified design platform with the theoretical modeling and simulation was proposed to get a comprehensive deep study of the thermoresistive micro calorimetric flow (TMCF) sensor system. Wherein, a general 1D model of TMCF sensor for two types of packaging: the open-space type and the channel type was proposed. Besides, the equivalent circuit model (ECM) for the TMCF sensor system was built and validated. This proposed unified design platform could be effectively applied in the design and optimization of CMOS TMCF sensor system. Accordingly, two batches of TMCF sensors were successfully designed and fabricated with the commercial CMOS MEMS technology, respectively. The batch of monolithically integrated TMCF sensors was fabricated by using a 0.35μm 2P4M CMOS MEMS process. The fabricated TMCF sensors achieved a highest normalized sensitivity of 230mV/(m/s)/mW with the bidirectional flow detection of nitrogen (-11 ~ 11 m/s), which was two orders of magnitude higher than the previous CMOS flow sensors. Besides, the responses of TMCF sensors predicted by the 1D model and CFD model were in good agreement with the experimental data. Remarkably, an advanced T<sup>2</sup>MCF sensor was achieved, where the common issue of inconsistent output in the thermal flow sensor due to the variation of ambient temperature T<sub>a</sub> was compensated and minimized. The T<sup>2</sup>MCF sensor showed the excellent temperature insensitive output with the maximum normalized variation of 0.5% under the different T<sub>a</sub> of 22°C ~ 48°C. Compared to the uncompensated counterpart (49%), the measuring accuracy and stability of T<sup>2</sup>MCF sensor were greatly improved. Furthermore, a flow regime map (protrusion d* vs. reduced chip Reynolds number Re*) under different channel aspect ratio Ar was constructed to serve as a useful guideline for designing a well-packaged, reliable and accurate TMCF sensor system. Another wafer-level encapsulated TMCF sensors was designed and fabricated by using the proprietary InvenSense CMOS MEMS technology. Thereinto, the fabricated Mo TMCF sensor with the pulsed operated CTD mode achieved an excellent normalized sensitivity of 112.4μV/(m/s)/mW with the bidirectional detection of nitrogen flow (-26 ~ 26 m/s). Besides, the measured TMCF sensor response time (τ<sub>max</sub> < 3.63ms) shows good agreement with the proposed theoretical thermal RC model. Remarkably, an integrated CMOS MEMS Mo flow sensor which demonstrates a very compact system on chip (SoC) that features a very low-power Current Feedback Instrumentation Amplifier (CFIA) as a front-end readout circuit was also implemented, where the measured sensitivity of this SoC flow sensor was 35mV/sccm. For the sake of higher-order sensor value, a compact and low-cost micro BTU (μBTU) sensor system prototype, including a Mo TMCF sensor and a Poly-Si RTD fused on the same chip, integrated with a digital signal processing (DSP) unit, was proposed. The μBTU system achieved a detection range of 1.5 ~ 15milli-BTU/h and a sensor system accuracy of less than 6%. The performance achieved by these CMOS MEMS flow/energy sensors, including the high sensitivity, low power consumption, large flow range, and rapid response ability, combined with the high level of integration and low-cost makes them possible to deploy as the flow/thermal sensing nodes of Internet of Things (IoT) for the flow and energy monitoring in the smart EeB.

A system for measuring flow of liquids (water) based on heat loss was formed of two thick film segmented thermistors, power supply with constant voltages RCV, 8 voltage dividers RN, acquisition card and PC with custom IWF software. The thermistors were placed in two metal or plastic housings connected in series like and filled with liquid,(water).The first thermistor Th1 is referent and measures the temperature of water incoming to the sensor, while the second thermistor Th2 is the flow sensor and it is selfheated with self current at a constant supply voltage from power source. Using the command from the PC the RCV power source generates constant voltages for powering Th2 in steps of 2V per 5°C of input water temperature increase. The self-heating current I of the Th2 thermistor is measured vs. the water flow rate Q. The water flow rate is defined from the function Q=F(I). The acquisition card measures in multiplex 8 voltages on voltage dividers: each voltage is measured 10 times per second and the computer calculates the average value for each second.

Airflow sensor is a crucial component for monitoring environmental airflow conditions in many engineering fields, especially in the field of aerospace engineering. However, conventional airflow sensors have been suffering from issues such as complexity and bulk in structures, high cost in fabrication and maintenance, and low stability and durability. In this work, we developed a facile direct-writing method for fabricating a low-cost piezoresistive element aiming at high-performance airflow sensing, in which a commercial pen was utilized to drop solutions of single-walled carbon nanotubes onto tissue paper to form a piezoresistive sensing element. The encapsulated piezoresistive element was tested for electromechanical properties under two loading modes: one loading mode is the so-called pressure mode in which the piezoresistive element is pressed by a normal pressure, and another mode is the so-called bending mode in which the piezoresistive element is bended as a cantilever beam. Unlike many other developed airflow sensors among which the sensing elements are normally employed as cantilever beams for facing winds, we designed a fin structure to be incorporated with the piezoresistive element for airflow sensing; the main function of the fin is to face winds instead of the piezoresistive element, and subsequently transfer and enlarge the airflow pressure to the piezoresistive element for the normal pressure loading mode. With this design, the piezoresistive element can also be protected by avoiding experiencing large strains and direct contact with external airflows so that the stability and durability of the sensor can be maintained. Moreover, we experimentally found that the performance parameters of the airflow sensor could be effectively tuned by varying the size of the fin structure. When the fin sizes of the airflow sensors were 20 mm, 30 mm, and 40 mm, the detection limits and sensitivities of the fabricated airflow sensors were measured as 8.2 m/s, 6.2 m/s, 3.2 m/s, 0.0121 (m/s)−2, 0.01657 (m/s)−2, and 0.02264 (m/s)−2, respectively. Therefore, the design of the fin structure could pave an easy way for adjusting the sensor performance without changing the sensor itself toward different application scenarios.

Difficulties that emerge in the development of micromechanical inertial sensors operating in self-oscillation mode are considered. Possible ways of how to analyze parameters of such sensors based on the analysis of information and energy characteristics are shown. The feasibility of micromechanical sensors using modern electronic elements, such as optoelectronic position sensors and magnetoelectric force-balance transducers, is discussed. The advantages of such devices are described.

Unmanned aerial vehicles (UAVs) carry sensing instruments to interesting, often remote areas with difficult access to collect in situ data. Atmospheric sensors can providing critical real-time data for environmental monitoring and other earth science applications. However, there remains a significant technology gap in the development of high performance trace gas sensors that meet the stringent requirements for UAV deployment. Most gas sensors are costly, bulky, and too slow to capture data in a speeding aircraft. In order to integrate with UAVs, airborne sensing systems should meet the UAV payload size, weight and power limitations. In addition, the UAV-carried sensors should be able to perform sensitive measurements with large variations of temperature, pressure and altitude and be compatible with the UAV’s cruise speed. This paper presents the investigation of a miniature, lightweight, ultra-low power (microwatts), ultra-fast, thermal conductivity (TCD) sensor platform to enable high resolution, fast analysis of methane (CH4) in the atmosphere. KWJ’s MEMS TCD sensor consists of a microfabricated polysilicon element that is low mass for rapid response and low power operation. The sensor elements are heated to a specified temperature by constant voltage or constant current. The thermal conductivity of the target gas in which the device resides will be reflected in the rate of cooling and equilibrium temperature of the device. TCD sensors with different geometries and dimensions were exposed to CH4 in air mixtures over a range of concentrations (100ppm - 1000ppm). The results showed that the sensor’s response is linearly dependent on the CH4 concentration. A lower limit of detection (LLD) for CH4 of ~100 ppm in dry air was obtained using the TCD sensors. Fabrication of MEMS TCD sensors. KWJ fabricated sensor elements are comprised of passivated polysilicon and fabricated with multiple sensing structures on one chip. Some of the elements are designed to accommodate a coating for high sensitivity and selectivity but these are not discussed herein. Figure 1 below is an SEM image of a 50 x1 µm TCD element suspended over a cavity. Characterization of TCD sensors. A benchtop measurement system, including testing chamber, environmental control system, gas delivery system, sensor control/measurement electronics and data acquisition system, was used for characterizing the response of the TCD sensors. The sensor element was placed in the test chamber and exposed to CH4/air gas mixtures with different concentrations. A pulse current waveform is applied to excite the sensor. The typical pulse comprised a hot excitation (1.5mA) applied for 40 ms and the cold excitation (0.25mA) for 4960 ms to provide a total pulse and measurement cycle of 5 seconds. Both the sensor control and data acquisition were timed in a coordinated fashion via the PC interface (Labview) such that the TCD resistance was acquired during the correct portion of the repetitive heating and cooling cycles. With the pulse excitation, the power consumption is very low (1.5mA*4V = 6mW continuous and 6*0.04/5=48 µW) per reading duration of 40 ms. The UAV would only move about 2.3 feet at a 40 mph air speed and thus the airborne readings at 40 ms would provide a resolution of a few feet. Of course, the response time of the device is measured in microseconds and so resolution of a few inches or less could be obtained with optimization of this device. The TCD sensor element was exposed to dry CH4 with different concentrations (1000ppm, 750ppm, 500ppm, 250ppm and 100ppm) in air at ambient temperature. The linear sensor response is illustrated below. These results provide a Lower Limit of Detection (LLD) for CH4 of about ~100 ppm CH4. Because of its small size, low mass, rapid response, and low power consumption, the novel sensor platform can be easily adapted to be deployed with different UAV platforms (balloons or different types of aircrafts). The structure of the novel sensor elements can accommodate metal electrodes and, therefore, can be used with selective and high sensitivity coatings for specialized applications. These features will be explored in future work. The MEMS approach used here provides a platform that can bridge the gap between the current large gas sensing equipment and the requirements for tiny payload UAV carrying gas sensor instrumentation for environmental measurements and earth science applications. Figure 1. MEMS TCD bridge (50 x 1 μm) and CH4 calibration curve. Figure 1

A thermal mass flow sensor with high dynamic flow range in silicon bulk micromachining membrane technology is presented. The response behavior of this sensor based on a two hot wire principle is described. This sensor configuration uses two hot wires mounted closely spaced one behind the other within a thin membrane, kept at the same temperature. The power to compensate cooling of and the interaction between the two hot wires are used to calculate mass flows and directionality of flows of gaseous and liquid fluids in a small channel. The response shows both anemometric and calorimetric behavior, depending on fluid, channel height and flow range. The hot wires are heated relative to temperature sensors located also on an isolated membrane on the same chip. Choosing an appropriate evaluation procedure an independence of the signal from the ambient temperature is achieved. This configuration will be discussed in view of the published results of single heater flow sensors, being of calorimetric or anemometric type. A calculation method for the determination of linear and power law range of the response is given.

Chemical production activities cause large amounts of ammonia to evaporate into the atmosphere, degrading air quality and even endangering public health, so monitoring ammonia in real time is significant. Traditional detection techniques, including spectrometers, chromatography, and pumping methods, are characterized by high costs, complex operation, significant delays, and limited compatibility, which obstructs the immediate identification of ammonia and the timely provision of information. Due to their distinct benefits such as compact size, affordability, quick response time, and lack of need for manual operation, resistive ammonia sensors hold significant promise for the real-time tracking of ammonia emissions in chemical manufacturing processes. In recent years, sensors utilizing metal-oxide semiconductor (MOS) nanomaterials have become a popular area of research due to their high sensitivity, strong stability, and acceptable response and recovery times. However, the interface circuits of existing MOS gas sensors mainly focus on sensor configuration and data acquisition. These interface circuits lack the functions of array timing control and data processing; gas detection and identification cannot be realized directly by them, which reduces the system integration and increases the application complexity. This paper begins by examining key design strategies for MOS-based resistive sensors aimed at enhancing ammonia sensing capabilities, offering researchers a foundation for their work in creating high-performance ammonia sensors. Based on this, a complete measuring system and a programmable interface circuit for an MOS gas sensor are introduced, which can integrate sensor configuration, signal acquisition, data processing, and output of recognition results. Finally, the current challenges and future opportunities of MOS-based resistive ammonia sensor systems are presented. The purpose of this review is to offer researchers suggestions for creating high-performance MOS-based resistive ammonia sensor systems and to promote the use of these sensors in upcoming chemical manufacturing processes.

Application of quartz tuning forks for detection of endotoxins and Gram-negative bacterial cells by monitoring of Limulus Amebocyte Lysate coagulation

.SignificanceMicrofluidic flow phantom studies are commonly used for characterizing the performance of laser speckle contrast imaging (LSCI) instruments. The selection of the flow control system is critical for the reliable generation of flow during testing. The majority of recent LSCI studies using microfluidics used syringe pumps for flow control.AimWe quantified the uncertainty in flow generation for a syringe pump and a pressure-regulated flow system. We then assessed the performance of both LSCI and multi-exposure speckle imaging (MESI) using the pressure-regulated flow system across a range of flow speeds.ApproachThe syringe pump and pressure-regulated flow systems were evaluated during stepped flow profile experiments in a microfluidic device using an inline flow sensor. The uncertainty associated with each flow system was calculated and used to determine the reliability for instrument testing. The pressure-regulated flow system was then used to characterize the relative performance of LSCI and MESI during stepped flow profile experiments while using the inline flow sensor as reference.ResultsThe pressure-regulated flow system produced much more stable and reproducible flow outputs compared to the syringe pump. The expanded uncertainty for the syringe pump was 8 to higher than that of the pressure-regulated flow system across the tested flow speeds. Using the pressure-regulated flow system, MESI outperformed single-exposure LSCI at all flow speeds and closely mirrored the flow sensor measurements, with average errors of and , respectively.ConclusionsPressure-regulated flow systems should be used instead of syringe pumps when assessing the performance of flow measurement techniques with microfluidic studies. MESI offers more accurate relative flow measurements than traditional LSCI across a wide range of flow speeds.

Compact sensor systems for on-site monitoring of groundwater for trace organic compounds in the liquid phase are currently under development in our laboratories. Potential challenges include sensor baseline drift and the presence of outliers in the data, along with difficulties extracting the contribution of individual BTEX compound (benzene, toluene, ethylbenzene, and xylenes) from the sensor response to mixtures containing multiple chemically similar compounds. As a first step, the approach presented here permits online estimation of analyte concentrations in binary mixtures of BTEX compounds in the presence of linear baseline drift and outliers. This paper investigates a sensor signal-processing approach based on estimation theory, specifically, Kalman filter (KF), extended KF, and discrete low-pass filter. The approach permits online linear baseline drift correction, filtering of outlier points, and estimation of analyte concentration(s) in binary mixtures and single analyte samples, before the sensor response reaches steady state. Sensor signals from mixtures of BTEX compounds were analyzed because these compounds are good indicators of accidental releases of fuel and oil into groundwater. Models were first developed for the sensor response so that estimation theory can be used to obtain the sensor parameters. The baseline-drift correction technique uses KF to perform online linear extrapolation or interpolation. The presented combination of sensor signal-processing techniques was simultaneously tested using actual measured data. Unknown sensor parameters and identification of analytes in samples were obtained within a relatively short period of time (8 min or less for the present sensor system), well before the sensor response reaches equilibrium.

We report the fabrication of a highly sensitive field-effect transistor (FET) biosensor using thermally-reduced graphene oxide (TRGO) sheets functionalized with gold nanoparticle (NP)-antibody conjugates. Probe antibody was labeled on the surface of TRGO sheets through Au NPs and electrical detection of protein binding (Immunoglobulin G/IgG and anti-Immunoglobulin G/anti-IgG) was accomplished by FET and direct current (dc) measurements. The protein binding events induced significant changes in the resistance of the TRGO sheet, which is referred to as the sensor response. The dependence of the sensor response on the TRGO base resistance in the sensor and the antibody areal density on the TRGO sheet was systematically studied, from which a correlation of the sensor response with sensor parameters was found: the sensor response was more significant with larger TRGO base resistance and higher antibody areal density. The detection limit of the novel biosensor was around the 0.2 ng/mL level, which is among the best of reported carbon nanomaterial-based protein sensors and can be further optimized by tuning the sensor structure.

According to basic electromagnetic theory, the response of a capacitive sensor depends on the structural parameters of the sensor and the dielectric permittivity between the plates. Here, the effect on the response of a capacitive sensor is investigated by changing its structural parameters. In the experiments, a nozzle is used to make wet steam and to control its humidity. A heating method is used to calibrate humidity of the steam. A Schmitt oscillation circuit is used to measure the capacitance of the sensors. Three sensors with different structural parameters are investigated. The standard k-e turbulence model, the wall function and the Semi-Implicit Method for Pressure Linked Equations (SIMPLE) algorithm are used to simulate the coupled performance of the electric field and the flow field in different structured sensors. There was a linear relationship with the humidity of the steam and the capacitance of the humidity sensor decreased with an increasing plate thickness. The capacitance change ratio was dependent on the humidity of the steam and increased with an increasing plate length. The capacitance change ratio decreased with an increasing plate separation. The stability and error of the sensors increased as the ratio between the plate length and plate separation increased. The linear relationship between the capacitance of the sensors and the steam humidity increased initially and then decreased as the ratio between the plate length and plate separation increased..

Investigating the potential of using gold nanoparticle-functionalized micromechanical sensors for gamma radiation detection

Operating modes and power considerations of microhollow cathode discharge devices with elongated trenches

In solid oxide cells (SOCs), the choice between galvanostatic (constant current) and potentiostatic (constant voltage) modes does not significantly affect the performance of SOCs as long as the cell components remain unchanged and intact. However, the degradation of cell components, which leads to changes in electrochemical and physical properties of the cell, elevates the importance of the selected operating mode. This paper aims to investigate the effects of galvanostatic and potentiostatic operating modes on the evolving properties of SOCs and their subsequent influence on performance durability. Employing non-equilibrium thermodynamic analysis, a crucial approach for understanding the degradation phenomena within an active electrochemical system, this study aims to provide in-depth insights into how these operating modes affect the longevity and efficacy of SOCs. Key findings include: In cases where oxygen electrode (OE) degradation is accelerated by higher partial pressure of oxygen ( pO2 ), operating under constant voltage electrolysis can mitigate the high pO2 at the OE|electrolyte (OE|EL) interface. Conversely, if OE degradation occurs more rapidly under a lower pO2, constant current electrolysis is more effective in suppressing degradation by achieving a high pO2 at the OE|EL interface. For degradation of the fuel electrode (FE) due to higher pO2, constant current electrolysis is beneficial for more stable performance, which helps maintain low pO2 at the FE|EL interface. When FE degradation is accelerated by lower pO2, constant voltage electrolysis can avert low pO2 at the FE|EL interface. In practical scenarios, more complex degradation mechanisms come into play, especially when pO2 significantly deviates from initial conditions. Degradation in one electrode can influence pO2 in the other electrode, a phenomenon more pronounced in potentiostatic than in galvanostatic electrolysis.