Inductive Voltage Dividers with Calculable Relative Corrections

Inductive voltage dividers are now used in measurement laboratories for the production of audio-frequency voltage ratios with errors (deviations from turns ratio) of a few parts in ten million of input. A major component of error arises from the interaction between distributed shunt impedances and leakage impedances in the windings. Correction for this systematic error in dividers of special design can result in an order-of-magnitude improvement in accuracy. A solution using network equations has been obtained for the corrections to the relative errors of inductive voltage dividers of specific design. Earlier theoretical considerations, confirmed by measurements of limited accuracy, indicated an S-shaped curve of ratio error vs nominal ratio, and quadrature component vs nominal ratio. The results from recent calculations are in agreement with the earlier measurements and provide much better definition of the true shape of the S-curve. An algebraic equation has been derived for the limiting form of this S-shaped characteristic curve. A resistance analog of an inductive voltage divider was constructed to represent the lumped circuit parameters equivalent to the distributed shunt admittances and the winding impedances. Measurements of the gross errors in the analog have yielded experimental results in excellent agreement with those calculated from the network equations.     

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.     

Inductive and Transformative Transducers with Short-Circuiting Ring

An ideal short-circuiting ring (R = 0) represents an infinite magnetic resistance for magnetic flux. A core of suitable shape allows an influence to be exercised upon the path of magnetic flux in a ferromagnetic circuit by displacing a short-circuiting ring. This fact may be utilized to construct transformative or inductive transducers. Two practical arrangements are described, and the effects on the characteristics of various parameters such as short-circuit resistance, core geometry, frequency of the energizing current, etc., are explained. The transducers examined attain a linearity error of 0.3 percent for displacement of 10 cm. The transducers, as described, do not show any wear, and the force of the short-circuiting ring exerted on the object of measurement remains a factor of 1000 below the force of the transducer used previously. Consequently, transducers (for linear travel or angular rotation) with short-circuiting rings are suitable both for use as rugged shop instruments and for precision transducers in metrology and control.     

An ASIC Front End for Planar High-Frequency Contactless Inductive Position Sensors

We describe an application-specific integrated circuit (ASIC) front end for readout and control of planar high-frequency contactless inductive position sensors that contain transmitter and receiver coils on a fixed printed circuit board and a moving passive resonant target. Such an inductive position sensor suffers from transmitter-to-receiver signal coupling, which can result in a phase-sensitive offset; hence, an error in the position measurement occurs. For the receiver front end, we consider two analog synchronous mixer demodulators, which we call mixer-1 and mixer-2, and analyze their ability to reject phase-sensitive offsets due to transmitter signal breakthrough. The mathematical analysis is validated with measured results from the fabricated ASIC in a 0.35-$muhbox{m}$ CMOS process technology. The ASIC front end contains the transmitter driver, the two receiver mixer variants, a frequency divider/shifter, and an amplifier low-pass filter. Measurements from five ASIC samples connected to the sensor show that, with a system gain of 320, the average output offset variation with phase difference from $-$ 99 to $+117^{circ}$ is more than 237 mV with mixer-1 compared to less than 7 mV with mixer-2.      

State of the Art in Alcohol Sensing with 2D Materials

Since the discovery of graphene,the star among new materials,there has been a surge of attention focused on the monatomic and monomolecular sheets which can be obtained by exfoliation of layered compounds.Such materials are known as two-dimensional(2D)materials and offer enormous versatility and potential.The ultimate single atom,or molecule,thickness of the 2D materials sheets provides the highest surface to weight ratio of all the nanomaterials,which opens the door to the design of more sensitive and reliable chemical sensors.The variety of properties and the possibility of tuning the chemical and surface properties of the 2D materials increase their potential as selective sensors,targeting chemical species that were previously difficult to detect.The planar structure and the mechanical flexibility of the sheets allow new sensor designs and put 2D materials at the forefront of all the candidates for wearable applications.When developing sensors for alcohol,the response time is an essential factor for many industrial and forensic applications,particularly when it comes to hand-held devices.Here,we review recent developments in the applications of 2D materials in sensing alcohols along with a study on parameters that affect the sensing capabilities.The review also discusses the strategies used to develop the sensor along with their mechanisms of sensing and provides a critique of the current limitations of 2D materials-based alcohol sensors and an outlook for the future research required to overcome the challenges.     

State-of-the-art and recent developments in micro/nanoscale pressure sensors for smart wearable devices and health monitoring systems

Small-sized, low-cost, and high-sensitivity sensors are required for pressure-sensing applications because of their critical role in consumer electronics, automotive applications, and industrial environments. Thus, micro/nanoscale pressure sensors based on micro/nanofabrication and micro/nanoelectromechanical system technologies have emerged as a promising class of pressure sensors on account of their remarkable miniaturization and performance. These sensors have recently been developed to feature multifunctionality and applicability to novel scenarios, such as smart wearable devices and health monitoring systems. In this review, we summarize the major sensing principles used in micro/nanoscale pressure sensors and discuss recent progress in the development of four major categories of these sensors, namely, novel material-based, flexible, implantable, and selfpowered pressure sensors.     

Supercapacitive Iontronic Nanofabric Sensing

The study of wearable devices has become a popular research topic recently, where high‐sensitivity, noise proof sensing mechanisms with long‐term wearability play critical roles in a real‐world implementation, while the existing mechanical sensing technologies (i.e., resistive, capacitive, or piezoelectric) have yet offered a satisfactory solution to address them all. Here, we successfully introduced a flexible supercapacitive sensing modality to all‐fabric materials for wearable pressure and force sensing using an elastic ionic–electronic interface. Notably, an electrospun ionic fabric utilizing nanofibrous structures offers an extraordinarily high pressure‐to‐capacitance sensitivity (114 nF kPa^?1), which is at least 1000 times higher than any existing capacitive sensors and one order of magnitude higher than the previously reported ionic devices, with a pressure resolution of 2.4 Pa, achieving high levels of noise immunity and signal stability for wearable applications. In addition, its fabrication process is fully compatible with existing industrial manufacturing and can lead to cost‐effective production for its utility in emerging wearable uses in a foreseeable future.     

Advances in Rational Design and Materials of High‐Performance Stretchable Electromechanical Sensors

Stretchable and wearable sensor technology has attracted significant interests and created high technological impact on portable healthcare and smart human–machine interfaces. Wearable electromechanical systems are an important part of this technology that has recently witnessed tremendous progress toward high‐performance devices for commercialization. Over the past few years, great attention has been paid to simultaneously enhance the sensitivity and stretchability of the electromechanical sensors toward high sensitivity, ultra‐stretchability, low power consumption or self‐power functionalities, miniaturisation as well as simplicity in design and fabrication. This work presents state‐of‐the‐art advanced materials and rational designs of electromechanical sensors for wearable applications. Advances in various sensing concepts and structural designs for intrinsic stretchable conductive materials as well as advanced rational platforms are discussed. In addition, the practical applications and challenges in the development of stretchable electromechanical sensors are briefly mentioned and highlighted.     

ZnO Nanosheets Abundant in Oxygen Vacancies Derived from Metal‐Organic Frameworks for ppb‐Level Gas Sensing

Surmounting the inhomogeniety issue of gas sensors and realizing their reproducible ppb‐level gas sensing are highly desirable for widespread deployments of sensors to build networks in applications of industrial safety and indoor/outdoor air quality monitoring. Herein, a strategy is proposed to substantially improve the surface homogeneity of sensing materials and gas sensing performance via chip‐level pyrolysis of as‐grown ZIF‐L (ZIF stands for zeolitic imidazolate framework) films to porous and hierarchical zinc oxide (ZnO) nanosheets. A novel approach to generate adjustable oxygen vacancies is demonstrated, through which the electronic structure of sensing materials can be fine‐tuned. Their presence is thoroughly verified by various techniques. The sensing results demonstrate that the resultant oxygen vacancy‐abundant ZnO nanosheets exhibit significantly enhanced sensitivity and shortened response time toward ppb‐level carbon monoxide (CO) and volatile organic compounds encompassing 1,3‐butadiene, toluene, and tetrachloroethylene, which can be ascribed to several reasons including unpaired electrons, consequent bandgap narrowing, increased specific surface area, and hierarchical micro–mesoporous structures. This facile approach sheds light on the rational design of sensing materials via defect engineering, and can facilitate the mass production, commercialization, and large‐scale deployments of sensors with controllable morphology and superior sensing performance targeted for ultratrace gas detection.     

Applications of remote sensing techniques to geology

Remote sensing is a new emerging field of technological development and has made a very significant impact on the geological surveys and studies. The work done so far in geological remote sensing has indicated the scope, utility and limitations of these modern techniques in different geological problems. The utility of airborne surveys and aerial photography has now been well established whereas satellite remote sensing at present has two main constraints—resolution and lack of stereoscopy. With the developments in sensor technology to provide sensors with improved resolution, more spectral bands and stereoscopy, substantial new results are anticipated in the geological remote sensing from space. Brief overview of applications of remote sensing techniques to geology is discussed in this paper.     

薄膜热阻微传感器技术

在工业生产中,人们对温度传感器超小型化的要求越来越迫切,而薄膜传感器的出现满足这一要求.薄膜温度传感器由于其优异的性能,在工业生产中越来越得到广泛应用.本文介绍了薄膜温度传感器的特点、种类、应用,着重介绍了薄膜热敏电阻传感器测温机理、膜系、影响其测温精度的主要因素及薄膜热敏电阻主要制备工艺、设备等,并探讨了薄膜热敏电阻的标定方法,最后论述了热敏电阻传感功能薄膜的国内外发展现状及其目前制备热敏电阻传感功能薄膜需要解决的关键技术问题.     

Microfabricated Inductive Micropositioning Sensor for Measurement of a Linear Movement

An inductive device with a moving core will change its inductance as a function of the core position. By extending this principle to a microtransformer with multiple evenly spaced cores, a measurement system combining features of analog (variable reluctance) and incremental positioning may be devised. For detecting the direction of motion system (to know in which direction to count), an incremental length-measurement system not only requires one, but two output signals, which have to be offset by 90deg. This paper presents a microtransformer-based positioning system fulfilling these requirements. It presents the fabrication technology employed and discusses experimental test results     

Inductive Teaching and Learning Methods: Definitions,Comparisons, and Research Bases

Traditional engineering instruction is deductive, beginning with theories and progressing to the applications of those theories. Alternative teaching approaches are more inductive. Topics are introduced by presenting specific observations, case studies or problems, and theories are taught or the students are helped to discover them only after the need to know them has been established. This study reviews several of the most commonly used inductive teaching methods, including inquiry learning, problem‐based learning, project‐based learning, case‐based teaching, discovery learning, and just‐in‐time teaching. The paper defines each method, highlights commonalities and specific differences, and reviews research on the effectiveness of the methods. While the strength of the evidence varies from one method to another, inductive methods are consistently found to be at least equal to, and in general more effective than, traditional deductive methods for achieving a broad range of learning outcomes.     

RF Energy Transmission for a Low-Power Wireless Impedance Sensor Node

The proper management of energy resources is essential for any wireless sensing system. With applications that span industrial, civil, and aerospace infrastructure, it is necessary for sensors and sensor nodes to be physically robust and power efficient. In many applications, a sensor network must operate in locations that are difficult to access, and often these systems have a desired operational lifespan which exceeds that of conventional battery technologies. In the present study, the use of microwave energy is examined as an alternate method for powering compact, deployable wireless sensor nodes. A prototype microstrip patch antenna has been designed to operate in the 2.4 GHz ISM band and is used to collect directed radio frequency (RF) energy to power a wireless impedance device that provides active sensing capabilities for structural health monitoring applications. The system has been demonstrated in the laboratory, and was deployed in field experiments on the Alamosa Canyon Bridge in New Mexico in August 2007. The transmitted power was limited to 1 W in field tests, and was able to charge the sensor node to 3.6 V in 27 s. This power level was sufficient to measure two piezoelectric sensors and transmit data back to a base station on the bridge.      

Chemical sensors for portable, handheld field instruments

A review of three commonly used classes of chemical sensor technologies as applicable to implementation in portable, handheld field instruments is presented. Solid-state gas and chemical sensors have long been heralded as the solution to a wide variety of portable chemical sensing system applications. However, advances in optical sensing technology have reduced the size of supporting infrastructure to be competitive with their solid-state counterparts. Optical, solid-state, and hybrid arrays of sensors have application for portable instruments, but issues of insufficient selectivity and sensitivity continue to hamper the widespread introduction of these miniaturized sensors for solving chemical sensing problems in environments outside the laboratory. In this article, we evaluate three of the major classes of compact chemical sensors for portable applications: (solid-state) chemiresistors, (solid-state) CHEMFETs, and (optical) surface plasmon resonance sensors (SPR). These sensors are evaluated and reviewed, according to the current state of research, in terms of their ability to operate at low-power, small-size, and relatively low-cost in environments, with numerous interferents and variable ambient conditions     

Methanol, ethanol and hydrogen sensing using metal oxide and metal (TiO(2)-Pt) composite nanoclusters on GaN nanowires: a new route towards tailoring the selectivity of nanowire/nanocluster chemical sensors

We demonstrate a new method for tailoring the selectivity of chemical sensors using semiconductor nanowires (NWs) decorated with metal and metal oxide multicomponent nanoclusters (NCs). Here we present the change of selectivity of titanium dioxide (TiO(2)) nanocluster-coated gallium nitride (GaN) nanowire sensor devices on the addition of platinum (Pt) nanoclusters. The hybrid sensor devices were developed by fabricating two-terminal devices using individual GaN NWs followed by the deposition of TiO(2) and/or Pt nanoclusters (NCs) using the sputtering technique. This paper present the sensing characteristics of GaN/(TiO(2)-Pt) nanowire-nanocluster (NWNC) hybrids and GaN/(Pt) NWNC hybrids, and compare their selectivity with that of the previously reported GaN/TiO(2) sensors. The GaN/TiO(2) NWNC hybrids showed remarkable selectivity to benzene and related aromatic compounds, with no measurable response for other analytes. Addition of Pt NCs to GaN/TiO(2) sensors dramatically altered their sensing behavior, making them sensitive only to methanol, ethanol and hydrogen, but not to any other chemicals we tested. The GaN/(TiO(2)-Pt) hybrids were able to detect ethanol and methanol concentrations as low as 100 nmol mol(-1) (ppb) in air in approximately 100 s, and hydrogen concentrations from 1 μmol mol(-1) (ppm) to 1% in nitrogen in less than 60 s. However, GaN/Pt NWNC hybrids showed limited sensitivity only towards hydrogen and not towards any alcohols. All these hybrid sensors worked at room temperature and are photomodulated, i.e. they responded to analytes only in the presence of ultraviolet (UV) light. We propose a qualitative explanation based on the heat of adsorption, ionization energy and solvent polarity to explain the observed selectivity of the different hybrids. These results are significant from the standpoint of applications requiring room-temperature hydrogen sensing and sensitive alcohol monitoring. These results demonstrate the tremendous potential for tailoring the selectivity of the hybrid nanosensors for a multitude of environmental and industrial sensing applications.     

Sensitivity Tunable Inductive Fluid Conductivity Sensor Based on RF Phase Detection

New results are presented for a sensitivity-tunable, inductive fluid conductivity sensor based on RF phase detection. An electronically controlled RF phase shifter allows the sensor to function in a wide range of conductivities from 2-70 mS/cm and helps tune the sensitivity of the response in a selected conductivity range. The noncontact nature of the sensor makes it suitable for corrosive fluids. Furthermore, the small size of the sensing element (1 inch. Sq X 6 mm thick) makes it suitable for compact in-line and hand held monitoring systems.     

Organic Transistors in Optical Displays and Microelectronic Applications

Organic thin‐film transistors (OTFTs) offer unprecedented opportunities for implementation in a broad range of technological applications spanning from large‐volume microelectronics and optical displays to chemical and biological sensors. In this Progress Report, we review the application of organic transistors in the fields of flexible optical displays and microelectronics. The advantages associated with the use of OTFT technology are discussed with primary emphasis on the latest developments in the area of active‐matrix electrophoretic and organic light‐emitting diode displays based on OTFT backplanes and on the application of organic transistors in microelectronics including digital and analog circuits.     

Advances in the Application of Magnetic Nanoparticles for Sensing

Magnetic nanoparticles (MNPs) are of high significance in sensing as they provide viable solutions to the enduring challenges related to lower detection limits and nonspecific effects. The rapid expansion in the applications of MNPs creates a need to overview the current state of the field of MNPs for sensing applications. In this review, the trends and concepts in the literature are critically appraised in terms of the opportunities and limitations of MNPs used for the most advanced sensing applications. The latest progress in MNP sensor technologies is overviewed with a focus on MNP structures and properties, as well as the strategies of incorporating these MNPs into devices. By looking at recent synthetic advancements, and the key challenges that face nanoparticle‐based sensors, this review aims to outline how to design, synthesize, and use MNPs to make the most effective and sensitive sensors.     

Flow-through vs flow-over: analysis of transport and binding in nanohole array plasmonic biosensors

We quantify the efficacy of flow-through nanohole sensing, as compared to the established flow-over format, through scaling analysis and numerical simulation. Nanohole arrays represent a growing niche within surface plasmon resonance-based sensing methods, and employing the nanoholes as nanochannels can enhance transport and analytical response. The additional benefit offered by flow-through operation is, however, a complex function of operating parameters and application-specific binding chemistry. Compared here are flow-over sensors and flow-through nanohole array sensors with equivalent sensing area, where the nanohole array sensing area is taken as the inner-walls of the nanoholes. The footprints of the sensors are similar (e.g., a square 20 μm wide flow-over sensor has an equivalent sensing area as a square 30 μm wide array of 300 nm diameter nanoholes with 450 nm periodicity in a 100 nm thick gold film). Considering transport alone, an analysis here shows that given equivalent sensing area and flow rate the flow-through nanohole format enables greatly increased flux of analytes to the sensing surface (e.g., 40-fold for the case of Q = 10 nL/min). Including both transport and binding kinetics, a computational model, validated by experimental data, provides guidelines for performance as a function of binding time constant, analyte diffusivity, and running parameters. For common binding kinetics and analytes, flow-through nanohole arrays offer ～10-fold improvement in response time, with a maximum of 20-fold improvement for small biomolecules with rapid kinetics.