Miniature Sensor Research Articles

Optimization of light-analyte interaction in Si3N4/polymer hybrid waveguide for sensitive sensing of pyridine vapor with ppb-level detection limit

High-sensitivity and miniature volatile organic compound (VOC) sensor is considerably significant for environment monitoring. Herein we performed the theoretical and experimental optimization of waveguide sensor to realize the sensitive detection of volatile toxic pyridine vapor with ppb-level detection limit. The miniature sensor is based on the CMOS-compatible silicon nitride (Si3N4) Mach-Zehnder interferometer (MZI) waveguide with dipolar polycarbonate as sensitive cladding material. Theoretical optimization by varying the waveguide width and the thickness of sensitive cladding is carried out to tune the group refractive index and evanescent field. Experimentally, two MZIs with distinct waveguide widths and sensitive cladding thickness are fabricated to compare their performance in pyridine vapor sensing. The sensing results show that the thickness of sensitive layer plays a key role in sensing sensitivity and response time. The final obtained pyridine sensing sensitivity can reach 63 pm/ppm and the detection limit can be as low as 476 ppb. Our demonstration provide a simple and efficient strategy for sensitive sensing of hazardous chemical vapors, which may find application in biochemical sensing.

In vivo detection of L-tryptophan in cucumbers using poly (9-Aminoacridine) film modified pencil graphite electrode

• A miniature sensor for detecting L-Trp is constructed using PAA modified PGE. • Detecting L-Trp in vivo is realized in cucumber fruit. • L-Trp levels in cucumbers in different categories are monitored. The rapid quantitative detection of L-tryptophan (L-Trp) is essential for promoting agricultural development. A miniature electrochemical sensor was constructed with the pencil graphite electrode(PGE) modified with poly (9-aminoacridine) film(PAA) for the detection of L-Trp in cucumber. The electropolymerization of PAA could greatly increase the sensitivity and selectivity, resulting in the constructed sensor with a linear range of 5-200 μM and the limit of detection as 0.035 μM. The miniature electrochemical sensor is a reliable electrochemical platform for the detection of L-Trp in cucumber fruit both in vivo and in vitro.

Development of highly sensitive capacitive proximity sensor based on stacked monocharged electrets

Recently, the demand for miniaturization and high sensitivity of the capacitive proximity sensors has increased noticeably for development of sensor networks. However, the volume and weight of conventional sensor devices are emerging as limitations in the practical application. In this paper, the stacked electrets-based highly sensitive noncontact capacitive sensor system (SENS) is proposed. The SENS is fabricated in compact-sized and light weight because electrets, which are dielectric materials that have quasi-permanent injected electric charges so can form external electric field, substitute the transmitter electrode and the external power source. Also, sensitivity of the SENS is effectively improved by stacking electrets. For experimental analysis, the electrostatic properties of the stacked electrets, which are due to the injected charges, and resultant influences on the sensitivity of the SENS are studied. In addition, based on experimental results, a proximity notification system with the SENS is developed using a LabVIEW program to demonstrate the practicality of the SENS.

Viscosity Sensors Based on III-Nitride Optical Devices Integrated With Droplet Sliding Channels

In this letter, we demonstrate a miniature viscosity sensor based on GaN-on-sapphire optical device integrated with an inclined flow channel. The monolithic device, consisting of a pair of GaN diodes responsible for light emission and detection, can monitor droplet sliding. Without the need for external optical components, the proposed elegant design of a few centimeters in size is capable of distinguishing the liquid viscosities from 2 to 600 mPa <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot \text{s}$ </tex-math></inline-formula> in tens of seconds. The proposed optical sensor exhibits attractive features, such as compactness, low cost, ease of operation, and small liquid volume required, making it suitable for practical applications in liquid viscosity measurement.

Modular electromagnetic railgun accelerator for high velocity impact studies.

A modular electromagnetic railgun accelerator facility named "RAFTAR" (i.e., Railgun Accelerator Facility for Technology and Research) has been commissioned and its performance has been characterized for high velocity impact testing on materials in a single-shot mode. In the first tests, RAFTAR demonstrated an acceleration of more than 1000m/s for an 8g solid aluminum-7075 armature projectile. The current fed was 220kA, having a muzzle time of about 1.75ms. It is a single pulse breech-fed rectangular bore (14 × 13mm2) railgun, and its 1.15m long barrel assembly consists of two parallel copper bars with an inter-gap of 13mm that are encased within 50mm thick high strength reinforced fiberglass sheets (Garolite G10-FR4) and bolted from both the sides. RAFTAR is powered by two capacitor bank modules that have a maximum stored energy of 160 kJ each (containing eight 178 μF/15kV capacitors), two high power ignitron switches, and a pulse shaping inductor. To obtain consistent acceleration of the armature inside the barrel, reversal of driving current is prevented, and its pulse duration is stretched by tactical integration of the crowbar switch and bitter coil inductor in the circuit. Armature projectile velocity measurement in-bore and outside in free space was performed by the time-of-flight technique using indigenously made miniature B-dot sensors and a novel shorting-foil arrangement, respectively. The time resolved measurement of the in-bore armature evidenced a velocity-skin-effect in the high acceleration phase. There is good agreement between the experimentally measured and theoretically predicted efficiency, confirming the optimal choice of operating parameters. The conclusion summarizes important experimental findings and analyzes the underlying causes that limit the performance of railguns.

Frictional Anisotropic Locomotion and Adaptive Neural Control for a Soft Crawling Robot.

Crawling animals with bendable soft bodies use the friction anisotropy of their asymmetric body structures to traverse various substrates efficiently. Although the effect of friction anisotropy has been investigated and applied to robot locomotion, the dynamic interactions between soft body bending at different frequencies (low and high), soft asymmetric surface structures at various aspect ratios (low, medium, and high), and different substrates (rough and smooth) have not been studied comprehensively. To address this lack, we developed a simple soft robot model with a bioinspired asymmetric structure (sawtooth) facing the ground. The robot uses only a single source of pressure for its pneumatic actuation. The frequency, teeth aspect ratio, and substrate parameters and the corresponding dynamic interactions were systematically investigated and analyzed. The study findings indicate that the anterior and posterior parts of the structure deform differently during the interaction, generating different frictional forces. In addition, these parts switched their roles dynamically from push to pull and vice versa in various states, resulting in the robot's emergent locomotion. Finally, autonomous adaptive crawling behavior of the robot was demonstrated using sensor-driven neural control with a miniature laser sensor installed in the anterior part of the robot. The robot successfully adapted its actuation frequency to reduce body bending and crawl through a narrow space, such as a tunnel. The study serves as a stepping stone for developing simple soft crawling robots capable of navigating cluttered and confined spaces autonomously.

Room-Temperature Semiconductor Gas Sensors: Challenges and Opportunities.

Our demand for ubiquitous and reliable gas detection is spurring the design of intelligent and enabling gas sensors for the next-generation Internet of Things and Artificial Intelligence. The desire to introduce gas sensors everywhere is fueled by opportunities to create room-temperature semiconductor gas sensors with ultralow power consumption. In this Perspective, we provide an overview of the recent achievement of room-temperature gas sensors that have been translated from the advances in the design of the chemical and physical properties of low-dimensional semiconductor nanomaterials. The emergence of solution-processable nanomaterials opens up remarkable opportunities to integrate into high-performance and flexible room-temperature gas sensors by using low-temperature, large-area, solution-based methods instead of costly, high-vacuum, high-temperature device manufacturing processes. We review the fundamental factors which affect the receptor and transducer functions of semiconductor gas sensors. We also discuss challenges that must be addressed in the move to the continuous miniaturization and evolution of semiconductor gas sensors.

Silver Nanoflakes-Enhanced Anisotropic Hybrid Composites for Integratable Pressure Sensors.

Flexible pressure sensors based on polymer elastomers filled with conductive fillers show great advantages in their applications in flexible electronic devices. However, integratable high-sensitivity pressure sensors remain understudied. This work improves the conductivity and sensitivity of PDMS-Fe/Ni piezoresistive composites by introducing silver flakes and magnetic-assisted alignment techniques. As secondary fillers, silver flakes with high aspect ratios enhance the conductive percolation network in composites. Meanwhile, a magnetic field aligns ferromagnetic particles to further improve the conductivity and sensitivity of composites. The resistivity of the composite decreases sharply by 1000 times within a tiny compression strain of 1%, indicating excellent sensing performance. On the basis of this, we demonstrate an integratable miniature pressure sensor with a small size (2 × 2 × 1 mm), high sensitivity (0.966 kPa-1), and wide sensing range (200 kPa). Finally, we develop a flexible E-skin system with 5 × 5 integratable sensor units to detect pressure distribution, which shows rapid real-time response, high resolution, and high sensitivity.

Analysis of Front Leg Kinematics of Cricket Bowler Using Wearable Sensors and Machine Learning

A fast bowler in the game of cricket is exposed to high-intensity actions and is more prone to lumbar stress fractures, ankle sprains, and knee, shoulder, and lower back injuries. There are different phases of bowling, from running to ball release, viz., run-up, predelivery stride (PDS), mid-bound (MB), front foot contact (FFC), ball release, and follow through. The front leg motion of the bowler plays a crucial role in delivering the ball efficiently. An improper landing after the jump causes most of the injuries as more strain is induced on the knee, ankle, and groin region. Loss of balance during the follow-through is the other most common reason for injury. A braced front leg at FFC helps the bowler transfer the momentum gained during the run-up into a fast-bowling action. For a refined understanding of the motion of the bowler and the causes of injuries, the identification of bowling phases is crucial. This article proposes the design of a miniature and economical wearable sensor unit using a Bosch BNO055 inertial measurement unit (IMU) sensor that the players can comfortably wear during the game. A novel method for calculating knee flexion of bowlers at FFC using quaternion data gathered from sensors is presented. Two wearable units were placed on the bowler’s front leg to collect motion data. Supervised machine-learning algorithms have been evaluated for classifying bowling phases using statistical features extracted from the sensor data to assist coaches and players with data-driven and evidence-based bowlers’ training.

Design of microfluidic radionuclide sensors: Combining microscale 3D printing based on 2-photon polymerization with nanoscale polymer brush scintillators

Development of miniature sensors for radionuclides is a challenging goal. In this paper we have applied specially developed vinyl-functionalized organic fluorophores for fabrication of nanoscale polymer brush scintillator coatings on artificially created 3D mesoporous structures. The applied 3D printing based on 2-photon polymerization is a modern approach, which extends the concept of additive manufacturing to the micro/nano-scale. One of the fundamental limitations of the 3D printing based on 2-photon polymerization (2PP) is a limited range of suitable photo-resins and, thus, limited functionalities of the resulting structures. To address this challenge, various post-processing technological steps, such as overcoating with conformal oxide layers and/or pyrolysis have been suggested. In this study, we demonstrate how chemical modification of 3D printed polymer structures with nanoscale polymer brush scintillators can be applied as a viable technological strategy for microfluidic radionuclide sensors. Application of new polymerizable organic fluorophores allowed “grafting to” or “grafting from” modifications of the photoresist surface with high concentration and precisely controlled location of the active scintillating units within the coating.

Challenges and Opportunities of Chemiresistors Based on Microelectromechanical Systems for Chemical Olfaction.

Microelectromechanical-system (MEMS)-based semiconductor gas sensors are considered one of the fastest-growing, interdisciplinary high technologies during the post-Moore era. Modern advancements within this arena include wearable electronics, Internet of Things, and artificial brain-inspired intelligence, among other modalities, thus bringing opportunities to drive MEMS-based gas sensors with higher performance, lower costs, and wider applicability. However, the high demand for miniature and micropower sensors with unified processes on a single chip imposes great challenges. This review focuses on recent developments and pitfalls in MEMS-based micro- and nanoscale gas sensors and details future trends. We also cover the background of the topic, seminal efforts, current applications and challenges, and opportunities for next-generation systems.

Miniature vacuum sensor based on gas adsorptions from carbon nanotube field emitters

A mini-type vacuum sensor based upon current enhancement from gas adsorption for multi-walled carbon nanotube (MWNT) field emitters is developed. The current increase rates in low emission state are proportional to gas pressures in nitrogen, hydrogen, and mixed gas environments. The field emission energy distribution (FEED) measurement demonstrated the reductions of electron tunneling energy barriers in H2 and N2 ambiences. The first-principles simulation indicates that the energy barrier reduction, which is related to the surface energy well from nitrogen adsorption, is attributed to the sensing effect for nitrogen. Both experiments and first-principles simulation affirmed that the high MWNT crystallinity benefits the sensing performance. The miniature sensor in millimeter dimensions based on MWNT field emitter with simple diode configuration can operate in a wide vacuum range from 10−7 to 10−2 Pa. The sensor was assembled inside the X-ray tube to measure the in-situ device vacuum, showing great potentials for vacuum electronic device applications.

Effect of irradiation and annealing performed with bias voltage applied across the coupling capacitors on the interstrip resistance of ATLAS ITk silicon strip sensors

The powering configuration of the silicon strip modules developed for the new Inner Tracker of the ATLAS experiment includes a voltage of up to 0.5 V across the coupling capacitor of each individual strip. However, this voltage is usually not applied in the sensor irradiation studies due to the significant technical and logistical complications. To study the effect of an irradiation and a subsequent beneficial annealing on the strip sensors in real experimental conditions, four prototype ATLAS17LS miniature sensors were irradiated by 60Co source and annealed, both with and without the bias voltage of 0.5 V applied across the coupling capacitors. The values of interstrip resistance measured on irradiated samples before and after annealing indicate that increase of radiation damage caused by the applied voltage can be compensated by the presence of this voltage during annealing.

Piezoelectric Gas Sensors with Polycomposite Coatings in Biomedical Application

When developing methods for diagnosing pathologies and diseases in humans and animals using electronic noses, one of the important trends is the miniaturization of devices, while maintaining significant information for diagnostic purposes. A combination of several sorbents that have unique sorption features of volatile organic compounds (VOCs) on one transducer is a possible option for the miniaturization of sensors for gas analysis. This paper considers the principles of creating polycomposite coatings on the electrodes of piezoelectric quartz resonators, including the choice of sorbents for the formation of sensitive layers, determining the mass and geometry of the formation of sensitive layers in a polycomposite coating, as well as an algorithm for processing the output data of sensors to obtain maximum information about the qualitative and quantitative composition of the gas phase. A comparative analysis of the efficiency and kinetics of VOC vapor sorption by sensors with polycomposite coatings and a set of sensors with relevant single coatings has been carried out. Regression equations have been obtained to predict the molar-specific sensitivity of the microbalance of VOC vapors by a sensor with a polycomposite coating of three sorbents with an error of 5-15% based on the results of the microbalance of VOC vapors on single coatings. A method for creating "visual prints" of sensor signals with polycomposite coatings is shown, with results comparable to those from an array of sensors. The parameters Aij∑ are proposed for obtaining information on the qualitative composition of the gas phase when processing the output data of sensors with polycomposite coatings. A biochemical study of exhaled breath condensate (EBC) samples, a microbiological investigation of calf tracheal washes, and a clinical examination were conducted to assess the presence of bovine respiratory disease (BRD). An analysis of the gas phase over EBC samples with an array of sensors with polycomposite coatings was also carried out. The "visual prints" of the responses of sensors with polycomposite coatings and the results of the identification of VOCs in the gas phase over EBC samples were compared to the results of bacteriological studies of tracheal washes of the studied calves. A connection was found between the parameters Aij∑ of a group of sensors with polycomposite coatings and the biochemical parameters of biosamples. The adequacy of replacing an array of piezoelectric sensors with single coatings by the sensors with polycomposite coatings is shown.

Bio-Inspired Micro- and Nanorobotics Driven by Magnetic Field.

In recent years, there has been explosive growth in the number of investigations devoted to the development and study of biomimetic micro- and nanorobots. The present review is dedicated to novel bioinspired magnetic micro- and nanodevices that can be remotely controlled by an external magnetic field. This approach to actuate micro- and nanorobots is non-invasive and absolutely harmless for living organisms in vivo and cell microsurgery, and is very promising for medicine in the near future. Particular attention has been paid to the latest advances in the rapidly developing field of designing polymer-based flexible and rigid magnetic composites and fabricating structures inspired by living micro-objects and organisms. The physical principles underlying the functioning of hybrid bio-inspired magnetic miniature robots, sensors, and actuators are considered in this review, and key practical applications and challenges are analyzed as well.

Design of Uniform Magnetic Field Coil by Quasi-Elliptic Function Fitting Method With Multiple Optimizations in Miniature Atomic Sensors

This article presents a design method of cylindrical uniform field coil based on quasi-elliptic function fitting (EFF) method with multiple optimizations. The EFF method is a type of discrete wire techniques aiming at simplifying the coil structure. Combing with particle swarm optimization (PSO) algorithm, the optimized parameters of EFF coil are obtained for highly uniform magnetic field. To further improve the uniformity of magnetic field in the central space, a new regional points selection optimization method is proposed. The calculation results show that after PSO optimization, the absolute maximum relative error in the target region is optimized to 0.098% by EFF coil comparing with modified single saddle coil (3.08%), nest coil (2.4%), and target field method (TFM) coil (0.11%). After regional points selection optimization, the volume proportion of absolute magnetic field relative error less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$1\times 10^{-4}$</tex-math></inline-formula> increases from 35.24% to 54.38% by EFF coil comparing with TFM coil. In addition, the simple EFF coil structure is verified to be easy to process and keep high performance through experiments. As the EFF coil’s high uniformity and simple structure, the new method has important significance for the miniaturization of atomic sensors.

A fully-actuated quadcopter representation using quaternions

Recent advances in practical fields like robotics and the miniaturisation of many sensors and actuators have turned autonomous vehicles into a reality. These systems come in many shapes and forms depending on the medium and their design but can be classified in one of two categories according to their mechanical configuration and number of actuators: fully-actuated and under-actuated vehicles; the second group still poses many challenges for the automatic control and robotics communities. This work introduces an easy methodology, based on quaternions, for designing controllers for a class of under-actuated systems, such as multicopter vehicles. The methodology starts from a fully-actuated representation of the system and adapts it to be implemented in under-actuated systems. In addition, it allows the easy development of controllers without taking care the coupled dynamics of the system. The proposed approach is based on Lyapunov's stability theory and is proven for certain criteria of the system's dynamics. The quadcopter configuration is used to validate the proposed methodology in simulations and in experimental tests. Abbreviations: AGV: autonomous ground vehicle; AUV: autonomous underwatervehicle; DoF: degree(s) of freedom; ESC: energy shaping controller; SFC: statefeedback controller; SSC: separated saturations controller; UAV: unmanned aerialvehicle

Electrochemical Sensor for Bilirubin Detection Using Paper-Based Screen-Printed Electrodes Functionalized with Silver Nanoparticles.

A notable diagnostic for the detection of hemolytic diseases is bilirubin, a by-product of haemoglobin breakdown. The concentration of bilirubin ranges from 0.3 to 1.9 mg in 100 mL of blood. Low blood bilirubin levels are associated with a greater risk of coronary heart disease and anaemia. Hyperbilirubinemia results from a serum bilirubin level of more than 2.5 mg/100 mL. Therefore, it is very crucial to check the serum bilirubin level. Analytical equipment for point-of-care testing must be portable, small, and affordable. A unique method is used to detect bilirubin selectively using paper-based screen-printed carbon electrodes that were covalently linked with nanoparticles, that serves as a key biomarker for jaundice. In order to create an electrochemical biosensor, bilirubin oxidase was immobilised on electrodes modified with AgNPs. The morphology of Ag nanoparticles in terms of size and shape was determined using both UV- Vis Spectroscopy and transmission electron microscopy (TEM). The biosensor's analytical response was assessed using potentiostat (Cyclic voltammetry (CV) and linear sweep voltammetry (LSV)). The developed paper-based sensor provided optimum feedback and a broad linear range of 1 to 9 µg/mL for bilirubin, with a lower LOD of 1 µg/mL. Through tests of bilirubin in artificial blood serum, the viability is confirmed. The method that is being used makes it possible to create and use an inexpensive, miniature electrochemical sensor.

Ultra-compact displacement and vibration sensor with a sub-nanometric resolution based on Talbot effect of optical microgratings.

Based on Talbot effect of optical microgratings, we report an ultra-compact sensor for displacement and vibration measurement with resolution down to sub-nanometer level. With no need of optical components such as reflectors, splitters, polarizers, and wave plates, the proposed sensor based on a common-path structure shows a high compactness. Using gratings with period of 3 µm, displacement measurement within a range of 1 mm is demonstrated experimentally. Associated with an interpolation circuit with subdividing factor of 4096, a resolution of 0.73 nm is obtained. The experimental results also show the ability for the sensor to detect in-plane vibration with frequency below 900 Hz. With a sub-nanometer resolution and an ultra-compact structure, the miniature sensor shows potential in applications such as high-precision machinery manufacturing and semiconductor processing.

Combination of an optical waveguide platform and ultra-thin spectrometer that enables increased surface plasmon resonance sensor compactness.

A novel integrated surface plasmon resonance (SPR) sensor that combines an optical waveguide platform and an ultra-thin spectrometer is proposed. The core of the proposed method is a special-shaped optical waveguide structure that employs a wedge-shaped incident surface, which changes the position of the total reflection of the incident light on the sagittal plane without affecting the direction of propagation on the tangential plane. The parameters of the sensing module with the integrated SPR sensor and spectrometer module were designed and optimized to achieve higher performance in a compact optical waveguide platform. An experimental system was built based on the theoretical model, and the spectral sensitivity of the system was analyzed before sample detection, and the results showed that the spectral resolution in the working range could reach 9.9 nm. The refractive index sensitivity of this novel SPR sensor was 3186 nm/RIU with good stability by detecting different concentrations of sodium chloride samples. This new structure does not require an external spectrometer, thereby enabling an increase in the compactness of the SPR sensing system. The proposed method can provide a novel idea for the miniaturization of SPR sensors.