A simple interface circuit to measure very small capacitancechanges in capacitive sensors

This paper presents an easy-to-design interface circuit to measure very small-percentage capacitance variations in capacitive sensors, especially suitable for industrial measurements. A computer-controlled 24-bit A/D converter is employed to obtain a higher resolution. This interface circuit can be used with various types of capacitive sensors. The most interesting thing is, that the measurement results through this interface circuit are independent of the initial capacitance of the sensor. In addition, the double differential operating principle used here minimizes the error caused by coupling and stray capacitance of sensor probes. The operating principle of the designed interface circuit, the major assumptions made, test data, and possible future developments are discussed     

Emerging MXene-Based Flexible Tactile Sensors for Health Monitoring and Haptic Perception

Due to their potential applications in physiological monitoring, diagnosis, human prosthetics, haptic perception, and human–machine interaction, flexible tactile sensors have attracted wide research interest in recent years. Thanks to the advances in material engineering, high performance flexible tactile sensors have been obtained. Among the representative pressure sensing materials, 2D layered nanomaterials have many properties that are superior to those of bulk nanomaterials and are more suitable for high performance flexible sensors. As a class of 2D inorganic compounds in materials science, MXene has excellent electrical, mechanical, and biological compatibility. MXene-based composites have proven to be promising candidates for flexible tactile sensors due to their excellent stretchability and metallic conductivity. Therefore, great efforts have been devoted to the development of MXene-based composites for flexible sensor applications. In this paper, the controllable preparation and characterization of MXene are introduced. Then, the recent progresses on fabrication strategies, operating mechanisms, and device performance of MXene composite-based flexible tactile sensors, including flexible piezoresistive sensors, capacitive sensors, piezoelectric sensors, triboelectric sensors are reviewed. After that, the applications of MXene material-based flexible electronics in human motion monitoring, healthcare, prosthetics, and artificial intelligence are discussed. Finally, the challenges and perspectives for MXene-based tactile sensors are summarized.     

Incorporation of fiber-optic sensors in concrete specimens: testing and evaluation

As series of tests has been carried out on the performance of several fiber-optic temperature sensors, operating on the fluorescence lifetime principle using neodymium-doped fiber and configured into ruggedized temperature probes, mounted in a number of different concrete samples. The aim has been to evaluate the performance of probes fitted into concrete specimens to simulate the conditions experienced in structures used in civil applications, such as bridges and dams. A key feature of the investigation was observing the integrity of the sensors under investigation while obtaining temperature data from the device. The results show the sensors operated well from below room temperature to beyond 300/spl deg/C, preserving their integrity under adverse test conditions.     

Nanosized Metal-Oxide Semiconducting SrTi1 ±xO3 − δ Oxygen Gas Sensors for Low-Temperature Application

The X-ray diffraction and transmission electron microscope results show that nanosized-SrTi_1plusmnxO_3-delta material series (27 nm) with perovskite structure can be synthesized using the high-energy ball milling technique. The thick-film screen-printed nanosized-SrTi_1plusmnxO_3-delta-based sensor series with annealing temperature of 400 degC are found to have good oxygen-sensing property at near human-body temperature for the first time for such a low temperature. The effect of the deviating stoichiometry of the nanosized-SrTi_1plusmnxO_3-delta -based sensors on their sensing properties was also investigated. The optimal relative resistance (R_nitrogen/R_20%oxygen ) value of 6.35 was obtained by a nanosized-SrTiO_3-delta -based sensor at 40 degC operating temperature. Their near human-body operating temperature is much lower than that of the conventional low-temperature semiconducting oxygen gas sensors (300degC-500degC) and SrTiO₃ oxygen sensors (>700degC). This can extend the application of the semiconducting oxygen gas sensors from the conventional high and medium temperature to the lower operating temperature areas such as the medical, environmental, and domestic fields, etc     

Optical Microresonators for Sensing and Transduction: A Materials Perspective

Optical microresonators confine light to a particular microscale trajectory, are exquisitely sensitive to their microenvironment, and offer convenient readout of their optical properties. Taken together, this is an immensely attractive combination that makes optical microresonators highly effective as sensors and transducers. Meanwhile, advances in material science, fabrication techniques, and photonic sensing strategies endow optical microresonators with new functionalities, unique transduction mechanisms, and in some cases, unparalleled sensitivities. In this progress report, the operating principles of these sensors are reviewed, and different methods of signal transduction are evaluated. Examples are shown of how choice of materials must be suited to the analyte, and how innovations in fabrication and sensing are coupled together in a mutually reinforcing cycle. A tremendously broad range of capabilities of microresonator sensors is described, from electric and magnetic field sensing to mechanical sensing, from single‐molecule detection to imaging and spectroscopy, from operation at high vacuum to in live cells. Emerging sensing capabilities are highlighted and put into context in the field. Future directions are imagined, where the diverse capabilities laid out are combined and advances in scalability and integration are implemented, leading to the creation of a sensor unparalleled in sensitivity and information content.     

Investigation on New Types of Semiconducting Ceramic Gas Sensors

A series of new types of semiconducting ceramic gas-sensing materials, Al₂O₃-based semiconducting ceramics, have been invented. Hydrogen and methane gas sensors have been made from these materials with different metal oxide additives. These gas sensors have various advantages, such as very good gas selectivity, nearly linear relationship between sensitivity and gas concentration, lower operating temperature, fast recovery time, and good anti-humidity property. The preparation and properties of these semiconducting ceramic gas sensors are presented in this paper.     

Sensors--an effective approach for the detection of explosives

The detection of explosives and explosive related illicit materials is an important area for preventing terrorist activities and for putting a check on their deleterious effects on health. A number of different methods, based on different principles, have been developed in the past for the detection of explosives. Sensors are one of those methods of detection which have capability to mimic the canine system and which are known to be the most reliable method of detection. The objective of this review is to provide comprehensive knowledge and information on the sensors operating on different transduction principles, ranging from electrochemical to immunosensors, being used for the detection of explosives as they pose a threat for both health and security of the nation. The review focuses mainly on the sensors developed in the recent 5 years and is prepared through summary of literature available on the subject.     

Design of inductive sensors for magnetic testing of steel ropes

The design and operating principles of four inductive sensors for magnetic testing of steel ropes are presented. The magnetic concentrators can maintain the same shape as in Hall-effect leakage flux sensors, but the output signals of the inductive sensors are quite different and depend on the speed of testing. Although the inductive sensors are not as versatile as Hall-effect sensors, they are simpler in operation and can still find applications, especially in the initial and middle stages of the deterioration of the rope.     

Temperature profile investigation of SnO/sub 2/ sensors for CO detection enhancement

SnO/sub 2/ sensors are widely used for the detection of air contaminants such as CO. Nevertheless, their application encounters several problems, mainly the effect of interfering gases. The low selectivity is, in fact, a well-known problem of these sensors. Moreover, the high operating temperature of metal oxide sensors implies, in general, high power consumption. We present a study aimed at the selection of an appropriate measurement technique for detection of CO for indoor applications (lower threshold 100 ppm), in the presence of high concentrations of ethanol (up to 1000 ppm), by using only one sensor. Moreover, the paper aims at developing portable CO detectors that are very small, low power, and could be battery operated.     

Creating gold nanoprisms directly on quartz crystal microbalance electrodes for mercury vapor sensing

A novel electrochemical route is used to form highly {111}-oriented and size-controlled Au nanoprisms directly onto the electrodes of quartz crystal microbalances (QCMs) which are subsequently used as mercury vapor sensors. The Au nanoprism loaded QCM sensors exhibited excellent response-concentration linearity with a response enhancement of up to ～ 800% over a non-modified sensor at an operating temperature of 28?°C. The increased surface area and atomic-scale features (step/defect sites) introduced during the growth of nanoprisms are thought to play a significant role in enhancing the sensing properties of the Au nanoprisms toward Hg vapor. The sensors are shown to have excellent Hg sensing capabilities in the concentration range of 0.123-1.27 ppm(v) (1.02-10.55 mg m(-3)), with a detection limit of 2.4 ppb(v) (0.02 mg m(-3)) toward Hg vapor when operating at 28?°C, and 17 ppb(v) (0.15 mg m(-3)) at 89?°C, making them potentially useful for air monitoring applications or for monitoring the efficiency of Hg emission control systems in industries such as mining and waste incineration. The developed sensors exhibited excellent reversible behavior (sensor recovery) within 1 h periods, and crucially were also observed to have high selectivity toward Hg vapor in the presence of ethanol, ammonia and humidity, and excellent long-term stability over a 33 day operating period.     

Oscillator-based interface for measurand-plus-temperature readoutfrom resistive bridge sensors

A signal conditioning circuit based on a relaxation oscillator is proposed for use with resistive bridge sensors. The circuit provides a rectangular-wave output whose frequency is related to the bridge unbalance, and duty-cycle is a function of the overall sensor bridge resistance, hence of the sensor operating temperature. In this way, two measurement values are simultaneously and independently carried on the same output signal. The circuit makes use of a constant current bridge excitation which enables the connection of remote sensors without accuracy degradation, and moreover, for silicon piezoresistive sensors, provides a first-order temperature compensation. A frequency-doubling output stage significantly reduces the nonlinearity due to switching delay times, at the parity of output center frequency and span. Experimental results are reported on the characterization of both the circuit alone and interfaced to a silicon pressure sensor     

Optimization of gas-sensitive polymer arrays using combinations of heterogeneous and homogeneous subarrays

Results for optimizing an array of conducting polymer gas sensors for sensing one of five analytes in the presence of up to four interferents are presented. The optimized array consists of subarrays of homogeneous (like) sensors contributing to a larger heterogeneous array of up to ten points (unlike sensors) in multidimensional sensor space. The optimization techniques presented here are linear, since the polymer sensors in their useful (low concentration) operating range exhibit linear and additive response characteristics. The optimization of these arrays produces maximum separability between analytes, demonstrating the trade-off between the addition of both information and variability induced by increasing the size of the heterogeneous array. Optimization results for sensing acetone, hexane, THF, toluene, and ethanol in the presence of interferents result in array sizes that are significantly less than the maximum available number of sensors (ten in the heterogeneous partition of the array). This result adds fuel to the argument that fewer sensors are better; the argument for more sensors, however, is also made in the context of the electronic nose systems where significant chemical diversity is required. Homogeneous subarrays of up to four elements each improve the separability of analytes in these optimized heterogeneous arrays by over 10% and also effectively flag broken or unhealthy sensors in a manner that is independent of analyte and concentration.     

Intraocular Pressure Monitoring Sensors

Continuous measurement of intraocular pressure is important in the detection and treatment of glaucoma. While a point check of intraocular pressure in a doctor's office using indirect measurements such as the tonometer is helpful, it is inadequate to track circadian variation. Circadian variation is an independent risk factor in addition to elevated pressure levels. This paper is aimed at providing an up-to-date review of various intraocular pressure sensing techniques and in vivo sensor design approaches. The basic operating principles of various implantable sensors are reviewed and categorized into groups to delineate their differences. A discussion is presented identifying the drawbacks of existing designs and key design questions are proposed for future progress.     

Superconducting helium level sensor

A superconducting helium level sensor is described which can be constructed in the laboratory and therefore be adapted to the actual experimental arrangement. Geometrical dimensions and case material can be chosen arbitrarily. Concept, construction and operating characteristics of such a level sensor are presented. Corrections are given for temperature influence on resistance which is relevant to long sensors.     

Improving sensitivity and selectivity of SnO/sub 2/ gas sensors by temperature variation

A microcontroller-based gas-sensing system is presented in this paper. The analysis presented here exploits the differences in the steady-state performance of SnO/sub 2/ gas sensors at different operating temperatures and the potential use of such differences for improving their selectivity and sensitivity. Sets of experimental measurements of sensitivity versus temperature are used for the detailed presentation of the proposed approach. The results indicate that selective identification and rather accurate measurement of a mixture of CH/sub 4/ and CO gases are quite possible. Finally, a microcontroller-based configuration is presented as a working example of a small-size implementation, which may offer measurements of improved sensitivity and selectivity along with high accuracy and reliability.     

Minimizing data collection for field calibration of steady-state virtual sensors for HVAC equipment

The paper presents an algorithm to minimize the amount of data collection for calibration of steady-state virtual sensors when obtained during normal operation of HVAC equipment in the field. If virtual sensors were calibrated using laboratory data, the amount of the calibration data could be minimized using design of experiment techniques. However, these techniques are not applicable to data from field operating equipment since most of the operating conditions are not controllable (e.g., ambient temperature, loads). In this paper, an algorithm to minimize the data collection period for calibration of steady-state virtual sensors is developed based on sensor accuracy, reliability and applicability. Application of the method is demonstrated for calibration of hourly electricity consumption virtual sensors for 3 packaged air conditioners that are serving a small commercial building, and the method terminated the calibration process after about 3 weeks of data collection for all units with very accurate estimates of electricity consumption.     

强度调制型光纤传感器用电路研究

在强度调制型光纤传感器中,光源发光强度和光电接收器工作的稳定性,是决定测量精度的关键因素。设计了具有软启动功能和恒亮度控制的光源驱动电路,所用光电接收器能满足测量系统要求。实验表明,该电路软启动效果明显,能抑制电压波动冲击,输出电压稳定度优于0.8%,为提高该类传感器测量精度提供了有效的手段。     

Investigation of cryogenic level sensors for LN2 and LOX

Investigations of two different types of cryogenic level sensors (capacitance and High Temperature Superconductor (HTS) for level measurement of liquid nitrogen (LN₂) and liquid oxygen (LOX) are presented here. They were tested for an active length of 400 mm in LOX and LN₂. A discrete diode array level sensor was used as a primary standard for calibrating these sensors. Comparative studies on linearity, sensitivity and other parameters at the operating temperatures are presented.     

High Sensitivity,Wearable, Piezoresistive Pressure Sensors Based on Irregular Microhump Structures and Its Applications in Body Motion Sensing

A pressure sensor based on irregular microhump patterns has been proposed and developed. The devices show high sensitivity and broad operating pressure regime while comparing with regular micropattern devices. Finite element analysis (FEA) is utilized to confirm the sensing mechanism and predict the performance of the pressure sensor based on the microhump structures. Silicon carbide sandpaper is employed as the mold to develop polydimethylsiloxane (PDMS) microhump patterns with various sizes. The active layer of the piezoresistive pressure sensor is developed by spin coating PEDOT:PSS on top of the patterned PDMS. The devices show an averaged sensitivity as high as 851 kPa^?1, broad operating pressure range (20 kPa), low operating power (100 nW), and fast response speed (6.7 kHz). Owing to their flexible properties, the devices are applied to human body motion sensing and radial artery pulse. These flexible high sensitivity devices show great potential in the next generation of smart sensors for robotics, real‐time health monitoring, and biomedical applications.     

Investigation of the scaling rules determining the performance of film bulk acoustic resonators operating as mass sensors

Solidly mounted (SMR-type) thin film bulk acoustic resonators operating at 2.2, 4.1, and 8.0 GHz and with lateral extents from 30 to 500 microm were fabricated and their performance as mass sensors was evaluated theoretically as well as experimentally. It was found that increasing the frequency leads to a principally improved performance of these devices. Problems arising for the horizontal as well as the vertical dimension and structure are investigated.