Low Hysteresis Error Research Articles

Outstanding dielectric permittivity and humidity sensitivity in (Y/Sb) co[sbnd]doped TiO2 ceramics with rapid response/recovery time

The synthesized (Y0.5Sb0.5)xTi1-xO2 (YSTO) ceramics (x=0.005 and 0.05) were investigated for their potential application in humidity sensors. The rutile phase of TiO2 for YSTO ceramics was confirmed. SEM images revealed dense microstructures, with relative densities and average grain sizes decreasing with doping concentrations. YSTO ceramics exhibited outstanding dielectric constants (ε′∼ 6.617.31×104) and low loss tangents (tanδ∼0.0190.067) at 25°C and 1 kHz. Capacitive humidity sensing properties demonstrated significant increases in capacitance with rising relative humidity (%RH) levels, with sensitivities of 165 and 386 pF/%RH. Hysteresis analysis showed narrow loops with low hysteresis error (γH∼1.4 and 2.0 %). Rapid response (∼9 s) and recovery (∼7 and 4 s) times, with stable repeatability, were observed. The presence of VO•• and SbTi• was confirmed, enhancing humidity sensing through chemical absorption reactions. This analysis underscores the potential of YSTO ceramics for humidity sensors, emphasizing the role of microstructural characteristics and induced defects in sensor performance, which is vital for the development of advanced sensing technology.

Highly sensitive surface acoustic wave magnetic field sensor based on the loss mechanism

Currently, the surface acoustic wave (SAW) magnetic field sensing technique utilises the SAW velocity/frequency mechanism of magnetoacoustic interaction as an indicator of the magnetic sensitivity mechanism. However, this method has low sensitivity and poor stability. To address this problem, a dynamic magnetoelastic coupling theoretical model is constructed to theoretically simulate the influence of the ΔE effect of magnetically sensitive thin films on SAW propagation attenuation. This study describes a high-sensitivity SAW magnetic field sensing mechanism based on magnetoacoustic attenuation. The simulation results show a clear relationship between the acoustic propagation loss and external magnetic field, indicating a structure-property relationship. An amorphous soft magnetic material (Fe90Co10)78Si12B10 was used as a magnetically sensitive thin film due to its high permeability, low coercivity (Hc), low hysteresis, ease of magnetisation and demagnetisation. SAW magnetosensitive device operating on a frequency of 200 MHz has been experimentally developed using a standard semiconductor photolithography process. A SiO2 layer was deposited on a 36° YX-LiTaO3 substrate as a waveguide, and a (Fe90Co10)78Si12B10 layer was on the top of the propagation area as a magnetosensitive film. The experimental results showed that the acoustic loss change due to the magnetic field variation was 4.63 dB within a magnetic field range of 0 Oe to ±10 Oe, which agreed with the theoretical results. The sensor had a sensitivity of 0.7546 dB Oe−1 within the range of 0–4 Oe and the lower detection limit of magnetic fields was 0.272 Oe, low hysteresis error of 0.54%, multiple repeatability error of 0.13%, excellent repeatability and stability were achieved in the experiments from the developed sensing device.

Pentaerythritol tetraacrylate microcavity sensor for high performance relative humidity detection

A pentaerythritol tetraacrylate (PETA) microcavity sensor for high performance relative humidity (RH) detection is presented. The fiber tip all-polymer microcavity, with a maximum size of 99.27 µm, consists of a circular truncated cone on the fiber tip end surface and is manufactured by photopolymerization of PETA using two-photon polymerization technology, which is characterized by miniaturization and rapid manufacturing. Experimental results show that its RH sensitivity reaches 108.05 pm/%RH in the range of 14.7–84.3%RH. In particular, respiration monitoring experiments show that its response time and recovery time are 0.55 s and 2.5 s, respectively. The sensor shows the inherent advantages of compact structure, fast response, good repeatability, low hysteresis error, good stability, and high sensitivity. Therefore, it is a promising candidate for potential applications in chemical, medical and biological fields related to RH detection.

A high sensitivity and multi-axis fringing electric field based capacitive tactile force sensor for robot assisted surgery

This paper presents a design of multi-axis tactile force sensor using the fringe effect of an electric field between stationary patterned electrodes. The unique configuration of the electrodes consisting of four separate square-shaped sensing electrodes, with each encircled by excitation electrodes, allows to achieve enhanced fringe field effect and hence sensitivity. The proposed sensor can decouple the normal, shear and angular shear applied forces. The sensor is fabricated using low-cost rapid prototyping techniques with flexible Ecoflex 00–30 and silicone rubber RTV-528 as the elastomers for contact with the environment. An analytical model is developed that correlates the nominal capacitance of the sensor with that of the geometric dimensions of the stationary electrodes and air cavity height between the electrodes and elastomer. The force measurement ranges in the normal, shear, and angular axis are 5 N, 1.5 N, and 1 N respectively. The sensor shows a perfectly linear response, repeatability, and a low hysteresis error, thermal stability and robustness to the environmental interferences that makes it suitable to be used for force feedback in minimally invasive robotic surgery.

Pressure and Electromechanical Behaviors of Elastic Pressure Exerting and Sensing Fabrics for Monitoring Pressure of Compression Textiles

AbstractSensing fabrics have received great attention due to various applications in medical area, healthcare, and smart clothes. However, there are very few studies on sensing fabrics that can be used to monitor the pressure of compression garments. In this study, a pressure exerting and sensing fabric is fabricated by interweaving highly sensitive yarn sensor into woven fabric using industrial‐scale weaving technology. By using a new method for measuring the pressure sensing capabilities under external stresses from a curved surface, effects of fabric structure and operation mode on the pressure and electromechanical properties are evaluated. New fabric structures are proposed to deliberately arrange the yarn sensing elements in a less‐ or even non‐binding form within the fabric for good elasticity and sensing properties. Arising from the appropriate material selection and structure feature, the sensing fabric realizes a suitable and stable amount of induced pressure as well as very low stress relaxation. Consequently, the sensing fabric with sateen structure demonstrates very good pressure sensing performance with sensitivity of 1.22 kPa−1, low hysteresis error of 8.06%, and linearity of 0.98 in the desired pressure range from 0.58 to 3.83 kPa. Furthermore, the fabric exhibits excellent stability over 4500 pressing cycles.

KIT-5-Assisted Synthesis of Mesoporous SnO2 for High-Performance Humidity Sensors with a Swift Response/Recovery Speed

Developing highly efficient semiconductor metal oxide (SMOX) sensors capable of accurate and fast responses to environmental humidity is still a challenging task. In addition to a not so pronounced sensitivity to relative humidity change, most of the SMOXs cannot meet the criteria of real-time humidity sensing due to their long response/recovery time. The way to tackle this problem is to control adsorption/desorption processes, i.e., water-vapor molecular dynamics, over the sensor's active layer through the powder and pore morphology design. With this in mind, a KIT-5-mediated synthesis was used to achieve mesoporous tin (IV) oxide replica (SnO2-R) with controlled pore size and ordering through template inversion and compared with a sol-gel synthesized powder (SnO2-SG). Unlike SnO2-SG, SnO2-R possessed a high specific surface area and quite an open pore structure, similar to the KIT-5, as observed by TEM, BET and SWAXS analyses. According to TEM, SnO2-R consisted of fine-grained globular particles and some percent of exaggerated, grown twinned crystals. The distinctive morphology of the SnO2-R-based sensor, with its specific pore structure and an increased number of oxygen-related defects associated with the powder preparation process and detected at the sensor surface by XPS analysis, contributed to excellent humidity sensing performances at room temperature, comprised of a low hysteresis error (3.7%), sensitivity of 406.8 kΩ/RH% and swift response/recovery speed (4 s/6 s).

Design and Characterization of Three-Axis High-Range Inductive Tactile Force Sensor Utilizing Magnetorheological Elastomer for Robotic Surgical Applications

This article presents a three-axis inductive tactile force sensor utilizing a magnetorheological elastomer (MRE) marker for inducing inductance change in square-shaped coils, in response to an input force. The sensor consists of copper coils on a printed circuit board (PCB) and a patterned elastomer layer between the marker and coils. The proposed configuration of the coils reduces the mechanical crosstalk between the applied three-axis forces, thus decoupling the force axes. Finite-element method (FEM)-based analyses are carried out to optimize the sensing gap between the coils and the marker. To observe the effect of the elastomer material on the sensor performance, two types of silicone rubbers, Ecoflex-30 and RTV-528, are used to make the patterned elastomer and the marker. The sensor with Ecoflex-30 elastomer can measure forces up to 25 N in normal and 2.5 N in shear directions, whereas the sensor with RTV-528 elastomer has a higher force range of up to 30 N for normal and 6 N for shear directions but has a lower sensitivity. A resolution of 12.71, 7.96, and 6.61 mN is achieved with Ecoflex-30, whereas for RTV-528, the force resolution is 76.52, 11.7, and 23.98 mN for normal, shear, and angular shear directions, respectively. The hysteresis error for the proposed sensors is 7.2% and 5.3% for Ecoflex-30 and RTV-528 elastomers, respectively. The proposed inductive tactile force sensor can be used in a wide range of robotic surgical applications for sensing multidirectional forces with better resolution and low hysteresis error.

A Soft Multi-Axis High Force Range Magnetic Tactile Sensor for Force Feedback in Robotic Surgical Systems.

This paper presents a multi-axis low-cost soft magnetic tactile sensor with a high force range for force feedback in robotic surgical systems. The proposed sensor is designed to fully decouple the output response for normal, shear and angular forces. The proposed sensor is fabricated using rapid prototyping techniques and utilizes Neodymium magnets embedded in an elastomer over Hall sensors such that their displacement produces a voltage change that can be used to calculate the applied force. The initial spacing between the magnets and the Hall sensors is optimized to achieve a large displacement range using finite element method (FEM) simulations. The experimental characterization of the proposed sensor is performed for applied force in normal, shear and 45° angular direction. The force sensitivity of the proposed sensor in normal, shear and angular directions is 16 mV/N, 30 mV/N and 81 mV/N, respectively, with minimum mechanical crosstalk. The force range for the normal, shear and angular direction is obtained as 0–20 N, 0–3.5 N and 0–1.5 N, respectively. The proposed sensor shows a perfectly linear behavior and a low hysteresis error of 8.3%, making it suitable for tactile sensing and biomedical applications. The effect of the material properties of the elastomer on force ranges and sensitivity values of the proposed sensor is also discussed.

Finger motion detection based on optical fiber Bragg grating with polyimide substrate

Gestures play an important role in human-computer interaction, which provides a natural way for human-machine communication. In this paper, we proposed a new finger motion detection method based on optical fiber Bragg grating (FBG) with polyimide substrate. Several FBGs with polyimide substrate were fixed on the forearm to monitor the deformation around the forearm caused by finger motion. Firstly, the sensors layout was determined according to the distribution of forearm muscles which control finger motions, and the arrangement of FBGs was optimized. Then, through a series of tests, the response characteristics and applicability of the proposed FBG with polyimide substrate were verified. The tests results show that FBG with polyimide substrate has a high sensitivity, good linearity, low hysteresis error and good creep resistance compared with other two substrates. In the experiment of finger motion detection, test data based on six static gestures was adopted to evaluate the availability of the FBGs. The experimental results show that the proposed method can detect six static gestures effectively, and the FBG output signal has good repeatability under the same gesture. This is the first attempt to use FBGs to detect fingers’ monitor by monitoring deformations at the forearm, which is a technique with wide application prospects.

Highly stretchable-compressible coiled polymer sensor for soft continuum manipulator

In recent years, soft continuum robots have become emerging research hotspots, but sensing of the robot shape needs to be addressed for precise control. To solve this problem, we present an optical coiled polymer sensor that can measure strain based on macro bending power loss. Proposed sensor is fabricated by coiling and annealing a polymer optical fiber of diameter 0.25 mm. Under applied strain, the bending curvature of the coiled sensor changes which leads to light intensity change. Due to its coiled design, the proposed sensor is highly stretchable and can measure both tensile and compressive strain of the coiled sensor structure in a wide range (>250%). Static and dynamic responses of the proposed sensor were observed by controlling the design parameters, such as spring diameter and number of coils. Fabricated coiled polymer sensor with a light-weight (<0.5 g) and compact structure showed a high stretchability-compressibility, high stability, and low hysteresis error. By placing three fabricated sensors inside the soft continuum manipulator, a 3-degree-of-freedom (DOF) configuration including bending and torsion motions can be obtained. We used an artificial neural network to derive the relationship between the sensor outputs and the 3 DOFs configuration of the soft continuum manipulator. The results showed that the configuration of the soft continuum manipulator can be obtained in real-time with high accuracy (error < 2.17%).

Enhanced Sensitivity of FeGa Thin-Film Coated SAW Current Sensor

A surface acoustic wave (SAW) device is proposed for sensing current by employing the patterned FeGa thin film as the sensitive interface. The layered media structure of FeGa/SiO2/LiNbO3 was established to reveal the working principle of the sensors, and an SAW chip patterned by delay-line and operating at 150 MHz was fabricated photolithographically on 128° YX LiNbO3 substrate. The FeGa thin film with a larger magnetostrictive coefficient was sputtered onto the acoustic propagation path of the SAW chip to build the sensing device. The prepared device was connected into the differential oscillation loop to construct the current sensor. The FeGa thin film produces magnetostrictive strain and so-called ΔE effect at the magnetic field generated by the applied current, which modulates the SAW propagation velocity accordingly. The differential frequency signal was collected to characterize the measurand. Larger sensitivity of 37.9 kHz/A, low hysteresis error of 0.81%, excellent repeatability and stability were achieved in the experiments from the developed sensing device.

Texture Identification of Objects Using a Robot Fingertip Module with Multimodal Tactile Sensing Capability

Modern robots fall behind humans in terms of the ability to discriminate between textures of objects. This is due to the fact that robots lack the ability to detect the various tactile modalities that are required to discriminate between textures of objects. Hence, our research team developed a robot fingertip module that can discriminate textures of objects via direct contact. This robot fingertip module is based on a tactile sensor with multimodal (3-axis force and temperature) sensing capabilities. The multimodal tactile sensor was able to detect forces in the vertical (Z-axis) direction as small as 0.5 gf and showed low hysteresis error and repeatability error of less than 3% and 2% in the vertical force measurement range of 0–100 gf, respectively. Furthermore, the sensor was able to detect forces in the horizontal (X- and Y-axes) direction as small as 20 mN and could detect 3-axis forces with an average cross-talk error of less than 3%. In addition, the sensor demonstrated its multimodal sensing capability by exhibiting a near-linear output over a temperature range of 23–35 °C. The module was mounted on a motorized stage and was able to discriminate 16 texture samples based on four tactile modalities (hardness, friction coefficient, roughness, and thermal conductivity).

Compact Flat Fabric Pneumatic Artificial Muscle (ffPAM) for Soft Wearable Robotic Devices

A pneumatic artificial muscle (PAM) has been widely adopted in a wide range of wearable applications, but the bulkiness and the slow response of the actuator have remained a challenge. In this work, we developed a flat fabric PAM (ffPAM), achieving high compactness, rapid response, and low hysteresis error. Our ffPAM exerts a maximum force of 118.0 N ± 0.1 N at 172 kPa, an average maximum contraction ratio of 23.84% ± 0.06%, and a maximum hysteresis error of 6.2%. Using the thin fabric as a base material, the actuator's total weight is 34.8 g. Based on dynamic response experiments, the ffPAM was verified to have a response time of 0.0318 s ± 0.0012 s for contraction, and the bandwidth of more than 4 Hz, regarding the contraction length with respect to input pressure. Moreover, a maximum contraction length was maintained during 10 000 cycles. Additionally, we embedded a fabric-based soft contractile sensor for the measurement of the contraction. We validated that the capacitance of the embedded capacitive contractile sensor has a linear relationship with the contraction length at constant pressures. To emphasize the compactness of the ffPAM in practical wearable applications, the actuator was placed between the legs, and its compactness was compared with that of previous PAMs.

Ultrahigh sensitive and ultrafast relative humidity sensing using surface enhanced microcantilevers

Active control of relative humidity (RH) and real-time monitoring in a sustained manner are of paramount importance in numerous fields and it is necessary to develop state-of-the-art RH sensors with high sensitivity and fast response times. In the present work, we propose and experimentally demonstrate a high-performance RH sensor using SiO2 microcantilevers (MCs) with controlled micro-patterns on their surface. SiO2 MCs with and without controlled surface micro-patterns were fabricated using direct laser writer and wet chemical etching methods. RH sensing experiments were performed, by measuring the shift in resonance frequency of MCs, when RH is varied between 20% and 90%. RH sensitivity of micro-patterned MCs was found to be significantly higher than the unpatterned ones and is explained on the basis of gel-like water layer formation inside the micro-patterns which facilitates the enhanced uptake of water molecules. Micro-patterned MCs exhibited an unprecedented RH sensitivity (10.45 Hz/% RH), ultrafast response/recovery times (∼ 1 s) and outstanding stability (variation < 5%) along with low hysteresis error (< 3%RH). These superior characteristics of micro-patterned MCs allowed the real-time monitoring of human respiration during normal and slow inhale/exhale cycles. Introduction of controlled micro-patterns on MC surface provides a simple and efficient way to enhance the sensitivity of MC based sensors without compromising other sensor characteristics such as response and recovery times.

Flexible capacitive pressure sensors fabricated by 3D printed mould

In this Letter, flexible capacitive pressure sensors are developed. Compared to the current mainstream design, the structure is easier to get a large deformation in the dielectric layer and its deformation is more controllable. Since the structure is symmetrical, it deforms uniformly and its Poisson's ratio is near zero when pressure is applied. Besides that, by moderating the structure dimension, sensors with different sensitivity and detection pressure range can be achieved. The fabrication process of these flexible sensors is mainly based on the 3D printing technology, with which the moulds of the sensor are made. The mixture of polydimethylsiloxane and hardening solution is dripped into the printed mould to form the dielectric layer. When it is completely solidified, the dielectric layer is demoulded from the mould. Four moulds with different inner sizes are printed and then four sensors are fabricated and tested. The measurement results show that the capacitance of the sensors increases when the applied pressure increases. The sensor with thinner supporting structure in the dielectric layer has higher sensitivity. The sensor with a thicker supporting structure in the dielectric layer has a larger pressure detection range. All the sensors have low hysteresis error and excellent repeatable performance.

Understanding the effect of sourcing voltage and driving circuit in the repeatability of measurements in force sensing resistors (FSRs)

Force sensing resistors (FSRs) are manufactured by the vigorous mixing of conductive particles with an insulating polymer resulting in a conductive polymer composite (CPC). FSRs have found great acceptance in biomechanical applications due to their low profile and light weight. However, FSRs exhibit considerable amounts of hysteresis and repeatability error that currently limit their usage. In an attempt to overcome this limitation, the hysteresis and repeatability errors of FSRs were assessed under different conditions of sourcing voltages (VFSR) and driving circuits. It was found that the hysteresis error exhibits a strong dependency on VFSR; this observation opposes the general belief that FSRs’ performance is voltage independent. In general, it was observed that incremental VFSR results in lower hysteresis error. The phenomenon of sensitivity degradation (SD) was also studied at the aforementioned conditions; it was found that SD is also a voltage-related phenomenon occurring at large VFSR. An electrical model was presented for the voltage-dependent response of FSRs; such a model can explain—up to some extent—the different performance of FSRs in regard to voltage changes. In order to obtain representative results, the experimental tests comprised 32 specimens of commercial FSRs from the brands: FlexiForce A201-1 and Interlink FSR 402. Only the Interlink FSR 402 sensor showed a slight dependency between VFSR and the repeatability error.

A Novel Soft Pneumatic Artificial Muscle with High-Contraction Ratio.

There is a growing interest in soft actuators for human-friendly robotic applications. However, it is very challenging for conventional soft actuators to achieve both a large working distance and high force. To address this problem, we present a high-contraction ratio pneumatic artificial muscle (HCRPAM), which has a novel actuation concept. The HCRPAM can contract substantially while generating a large force suitable for a wide range of robotic applications. Our proposed prototyping method allows for an easy and quick fabrication, considering various design variables. We derived a mathematical model using a virtual work principle, and validated the model experimentally. We conducted simulations for the design optimization using this model. Our experimental results show that the HCRPAM has a 183.3% larger contraction ratio and 37.1% higher force output than the conventional pneumatic artificial muscle (McKibben muscle). Furthermore, the actuator has a compatible position tracking performance of 1.0 Hz and relatively low hysteresis error of 4.8%. Finally, we discussed the controllable bending characteristics of the HCRPAM, which uses heterogeneous materials and has an asymmetrical structure to make it comfortable for a human to wear.

Fabrication of ZnO nanorods and Chitosan@ZnO nanorods on MEMS piezoresistive self-actuating silicon microcantilever for humidity sensing

This paper reports the fabrication method and humidity sensing performances of zinc oxide nanorods (ZONRs) and chitosan self-assembled monolayers (SAMs) modified ZONRs patterned piezoresistive silicon MEMS microcantilevers. The self-actuating and self-sensing microcantilevers were fabricated using standard silicon wafers and bulk-micromachining techniques; a p-diffused heating resistor was patterned at the clamped end of the microcantilever as the self-actuator. Moreover, the resonant frequency shift induced by the mass change of adsorbed water on the hybrid sensing nanostructure can be read-out directly by a p-diffused full Wheatstone bridge. Aligned high-surface-to-volume-ratio ZONRs were selectively deposited on the microcantilever as the sensing material using a simple low-temperature chemical-bath deposition (CBD) process based on a DC sputtering/annealing ZnO seed-layer. In addition, for comparison, a low-cost seed-layer method using aqueous chemical growth (ACG) method was also applied to deposit ZONRs. Furthermore, chitosan SAMs were self-assembled on the ZONRs, yielding a microcantilever-based gravimetric relative humidity (RH) sensor with good stability and repeatability (± 0.06%RH over 90 min), high sensitivity (ZONRs: 4.4 ppm/%RH; chitosan-SAMs@ZONRs: 16.9 ppm/%RH), and low hysteresis error (2.1%RH).

Grating-patterned FeCo coated surface acoustic wave device for sensing magnetic field

This study addresses the theoretical and experimental investigations of grating-patterned magnetostrictive FeCo coated surface acoustic wave (SAW) device for sensing magnetic field. The proposed sensor is composed of a configuration of differential dual-delay-line oscillators, and a magnetostrictive FeCo grating array deposited along the SAW propagation path of the sensing device, which suppresses effectively the hysteresis effect by releasing the internal binding force in FeCo. The magnetostrictive strain and ΔE effect from the FeCo coating modulates the SAW propagation characteristic, and the corresponding shift in differential oscillation frequency was utilized to evaluate the measurant. A theoretical model is performed to investigate the wave propagation in layered structure of FeCo/LiNbO3 in the effect of magnetostrictive, and allowing determining the optimal structure. The experimental results indicate that higher sensitivity, excellent linearity, and lower hysteresis error over the typical FeCo thin-film coated sensor were achieved from the grating-patterned FeCo coated sensor successfully.

A Two-Axis Goniometric Sensor for Tracking Finger Motion.

The study of finger kinematics has developed into an important research area. Various hand tracking systems are currently available; however, they all have limited functionality. Generally, the most commonly adopted sensors are limited to measurements with one degree of freedom, i.e., flexion/extension of fingers. More advanced measurements including finger abduction, adduction, and circumduction are much more difficult to achieve. To overcome these limitations, we propose a two-axis 3D printed optical sensor with a compact configuration for tracking finger motion. Based on Malus’ law, this sensor detects the angular changes by analyzing the attenuation of light transmitted through polarizing film. The sensor consists of two orthogonal axes each containing two pathways. The two readings from each axis are fused using a weighted average approach, enabling a measurement range up to 180 and an improvement in sensitivity. The sensor demonstrates high accuracy (±0.3), high repeatability, and low hysteresis error. Attaching the sensor to the index finger’s metacarpophalangeal joint, real-time movements consisting of flexion/extension, abduction/adduction and circumduction have been successfully recorded. The proposed two-axis sensor has demonstrated its capability for measuring finger movements with two degrees of freedom and can be potentially used to monitor other types of body motion.