In-situ sugar-templated porous elastomer sensor with high sensitivity for wearables

Fabrication of elastic pressure sensors with low cost, high sensitivity, and mechanical durability is important for wearables, electronic skins and soft robotics. Here, we develop high-sensitivity porous elastomeric sensors for piezoresistive and capacitive pressure detection. Specifically, a porous polydimethylsiloxane (PDMS) sponge embedded with conductive fillers of carbon nanotubes (CNTs) or reduced graphene oxide (rGO) was fabricated by an in-situ sugar template strategy. The sensor demonstrates sensitive deformation to applied pressure, exhibiting large and fast response in resistance or capacitance for detection of a wide range of pressure (0‒5 kPa). PDMS, as a high-elasticity framework, enables creation of sensors with high sensitivity, excellent stability, and durability for long-term usage. The highest sensitivities of 22.1 and 68.3 kPa⁻¹ can be attained by devices with 5% CNTs and 4% rGO, respectively. The geometrics of the sponge sensor is tailorable using tableting technology for different applications. The sensors demonstrate finger motion detection and heart-rate monitoring in real-time, as well as a capacitive sensor array for identification of pressure and shape of placed objects, exhibiting good potential for wearables and human-machine interactions.     

Plasmonic refractive index sensor based on metal–insulator-metal waveguides with high sensitivity

A plasmonic square ring resonator sensor design based on metal–insulator-metal waveguide is proposed. The transmission spectra and electric field distribution of the resonator are simulated using the finite element method (FEM). The numerical simulation results achieved from the transmission spectra are used to investigate the sensing characteristics of the structure. The effect of structural parameters on the spectral characteristics and sensing performance are investigated in detail. The sensitivity is obtained to a value as high as 1367?nm/RIU with a figure of merit of ～25. The suggested design can possibly be applied in optical network-on-chip and on-chip nanosensors.     

Novel fabrication of an SnO(2) nanowire gas sensor with high sensitivity

We fabricated a nanowire-based gas sensor using a simple method of growing SnO(2) nanowires bridging the gap between two pre-patterned Au catalysts, in which the electrical contacts to the nanowires are self-assembled during the synthesis of the nanowires. The gas sensing capability of this network-structured gas sensor was demonstrated using a diluted NO(2). The sensitivity, as a function of temperature, was highest at 200?°C and was determined to be 18 and 180 when the NO(2) concentration was 0.5 and 5?ppm, respectively. Our sensor showed higher sensitivity compared to different types of sensors including SnO(2) powder-based thin films, SnO(2) coating on carbon nanotubes or single/multiple SnO(2) nanobelts. The enhanced sensitivity was attributed to the additional modulation of the sensor resistance due to the potential barrier at nanowire/nanowire junctions as well as the surface depletion region of each nanowire.     

Quantized dissipation of the quantum Hall effect at high currents

Quantized dissipative voltage states are observed when large currents are passed through a high-quality quantized Hall resistance device. These dissipative states are interpreted as occurring when electrons are excited to higher Landau levels and then return to the original Landau level. The author shows that the quantization is more complicated than previously thought. For example, the quantization can be a function of magnetic field. Therefore, the dissipative voltage quantization can, in general, be difficult to verify and determine     

Multipoint diffraction strain sensor with variable sensitivity

In our earlier work, a multipoint diffraction strain sensor using a microlens array was developed for measurement of whole-field strains. The method is extended to a system with variable sensitivity and measurement range. In the present system, two collimated laser beams, 3 mm in diameter, symmetrically strike the grating attached to the specimen surface at prescribed angles. The diffracted wavefronts, magnified by a microscope objective, are sampled by a lenslet array with each microlens acting as an individual strain sensor. In-plane strain components over the full field can be measured by what is to our knowledge a new sensor with variable sensitivity by changing the distance from the microscope objective to the microlens array. Both a theoretical explanation and experimental verification are provided.     

Single-crystal magneto-optic sensor with electrically adjustable sensitivity

A novel magneto-optic sensor with electrically adjustable sensitivity is proposed that is based on the approximate multiplication correlation between the linear electro-optic phase retardation and the Faraday magneto-optic rotation angle in a single bismuth germanate crystal. The measurement sensitivity and its temperature stability, linear and monotonic measurement ranges of the proposed sensor can be controlled in real time by adjusting the modulating voltage applied to the sensing crystal. In particular, the proposed sensor can be used for the precise measurement of dc magnetic field or dc current. The basic sensing performance is theoretically analyzed and experimentally demonstrated by dc current measurement.     

Facilely prepared layer-by-layer graphene membrane-based pressure sensor with high sensitivity and stability for smart wearable devices

With the prosperous development of artificial intelligence, medical diagnosis and electronic skins, wearable electronic devices have drawn much attention in our daily life. Flexible pressure sensors based on carbon materials with ultrahigh sensitivity, especially in a large pressure range regime are highly required in wearable applications. In this work, graphene membrane with a layer-by-layer structure has been successfully fabricated via a facile self-assembly and air-drying(SAAD) method. In the SAAD process,air-drying the self-assembled graphene hydrogels contributes to the uniform and compact layer structure in the obtained membranes. Owing to the excellent mechanical and electrical properties of graphene, the pressure sensor constructed by several layers of membranes exhibits high sensitivity(52.36 kPa~(-1)) and repeatability(short response and recovery time) in the loading pressure range of 0–50 kPa. Compared with most reported graphene-related pressure sensors, our device shows better sensitivity and wider applied pressure range. What's more, we demonstrate it shows desired results in wearable applications for pulse monitoring, breathing detection as well as different intense motion recording such as walk,run and squat. It's hoped that the facilely prepared layer-by-layer graphene membrane-based pressure sensors will have more potential to be used for smart wearable devices in the future.     

A magnetic-field bending resonance sensor with maximum generated magnetoelectric voltage

A bending resonance magnetoelectric (ME) sensor with maximum generated response voltage is theoretically described. Based on the proposed model, the frequency dependence of the ME coefficient is determined. The optimum thickness of a piezoceramic layer is proposed, which provides a twofold increase in the response voltage. The phenomenon of antiresonance suppression of oscillations in the region of the third bending resonance at 95 Hz is discovered.     

On acoustic sensor sensitivity

Acoustic sensor sensitivity expressed as frequency change per unit of measurand can result in the erroneous conclusion that higher-frequency sensors are superior to lower-frequency ones. It is argued that, when compared on the bases of reproducibility and resolution capability, good low-frequency sensors are superior to good high-frequency ones     

Theq factor and absolute maximum of random gravitation-neutrino coincidences

A calculation is made of the integrated q-factor distribution function which was used when performing a computer simulation of experimental data in order to analyze the truth of the gravitation-neutrino correlation effect during the SN 1987A supernova burst. Translated from Izmeritel'naya Tekhnika, No. 4, pp. 3–4, April, 1999.     

Fiber Bragg grating temperature sensor with controllable sensitivity

We demonstrate a fiber Bragg grating (FBG) sensor with controllable sensitivity by connecting two metal strips that have different temperature-expansion coefficients. By changing the lengths of the metal strips we successfully controlled and improved the temperature sensitivity to 3.3 times of that of bare FBG.     

用于非线性兰姆波检测的高灵敏度宽带光纤光栅传感器

光纤传感器因其灵敏度高,已逐渐应用于超声检测的研究中,但大多数光纤传感器的频带响应范围有限,约为几百k Hz,很难检测到更高频率的信号。所提出的光纤布拉格光栅(Fiber Bragg Grating,FBG)传感器的高频检测范围可以达到4 MHz左右,大大提高了其检测带宽范围。文中将传感器应用于304不锈钢板兰姆波的非线性检测,同时与传统超声换能器的检测结果做对比。实验结果表明,用脉冲波激励信号时,FBG传感器可以检测到钢板兰姆波的基频到五倍频信号,表明FBG在检测兰姆波非线性上是有很大潜力的。     

Long-period grating refractive index sensor with a modified cladding structure for large operational range and high sensitivity

What is believed to be a novel long-period grating (LPG) refractive index sensor with a modified cladding structure is proposed and studied. In the proposed structure, the cladding of the fiber has a two-layer structure, i.e., a cladding layer of low refractive index with a reduced radius and an overlay of high refractive index. The sensitivity of the structure-modified LPG sensor to the ambient refractive index change as a function of the cladding layer and overlay parameters is investigated by way of modeling. It is found that an increase of the ambient refractive index causes a field redistribution of the cladding mode into the overlay when the parameters of the overlay are properly selected. It is shown that by reducing the radius of the cladding layer, the operational range of the LPG refractive index sensor can be as large as 0.195 (from 1.244 to 1.440) with a minimum sensitivity of 660 nm/refractive index, which represents a 31% increase of operational range in comparison with the operational range obtained from the reported structure. The design guidelines for achieving this large operation range and high sensitivity are explained by investigating the dependence of the cladding modes on the radius of the cladding layer.     

A surface acoustic wave humidity sensor with high sensitivity based on electrospun MWCNT/Nafion nanofiber films

Humidity detection has been widely used in a variety of fields. A humidity sensor with high sensitivity is reported in this paper. A surface acoustic wave resonator (SAWR) with high resonance frequency was fabricated as a basic sensitive component. Various nanotechnologies were used to improve the sensor's performance. A multi-walled carbon nanotube/Nafion (MWCNT/Nafion) composite material was prepared as humidity-sensitive films, deposited on the surface of an SAWR by the electrospinning method. The electrospun MWCNT/Nafion nanofiber films showed a three-dimensional (3D) porous structure, which was profitable for improving the sensor's performance. The new nano-water-channel model of Nafion was also applied in the humidity sensing process. Compared to other research, the present sensor showed excellent sensitivity (above 400 kHz/% relative humidity (RH) in the range from 10% RH to 80% RH), good linearity (R(2) > 0.98) and a short response time (～3 s@63%).     

Hall sensor response to an inhomogeneous magnetic field

The response of a Hall-effect sensor to a spatially dependent magnetic field is of importance for many applications such as magnetic microscopy and nondestructive testing. Using the analytical expression of the response of a Greek cross Hall sensor response to an ideal field dot published a few years ago, we have calculated its sensitivity and its full width at half maximum for the field produced by a magnetic dipole and by two coplanar lines. The experimental results are in good agreement with theory. They show that the spatial resolution is roughly equal to the dimension of the central part of the Greek cross and that a flux-meter approximation is not appropriate for modeling such Hall-effect sensors for very close field sources.