Sensitive Force Sensor Research Articles

Single-Molecule Mechanoresistivity by Intermetallic Bonding.

The metal-electrode interface is key to unlocking emergent behaviour in all organic electrified systems, from battery technology to molecular electronics. In the latter, interfacial engineering has enabled efficient transport, higher device stability, and novel functionality. Mechanoresistivity - the change in electrical behaviour in response to a mechanical stimulus and a pathway to extremely sensitive force sensors - is amongst the most studied phenomena in molecular electronics, and the molecule-electrode interface plays a pivotal role in its emergence, reproducibility, and magnitude. In this contribution, we show that organometallic molecular wires incorporating a Pt(II) cation show mechanoresistive behaviour of exceptional magnitude, with conductance modulations of more than three orders of magnitude upon compression by as little as 1 nm. We synthesised series of cyclometalated Pt(II) molecular wires, and used scanning tunnelling microscopy - break junction techniques to characterise their electromechanical behaviour. Mechanoresistivity arises from an interaction between the Pt(II) cation and the Au electrode triggered by mechanical compression of the single-molecule device, and theoretical modelling confirms this hypothesis. Our study provides a new tool for the design of functional molecular wires by exploiting previously unreported ion-metal interactions in single-molecule devices, and develops a new framework for the development of mechanoresistive molecular junctions.

Single‐Molecule Mechanoresistivity by Intermetallic Bonding

AbstractThe metal‐electrode interface is key to unlocking emergent behaviour in all organic electrified systems, from battery technology to molecular electronics. In the latter, interfacial engineering has enabled efficient transport, higher device stability, and novel functionality. Mechanoresistivity – the change in electrical behaviour in response to a mechanical stimulus and a pathway to extremely sensitive force sensors – is amongst the most studied phenomena in molecular electronics, and the molecule‐electrode interface plays a pivotal role in its emergence, reproducibility, and magnitude. In this contribution, we show that organometallic molecular wires incorporating a Pt(II) cation show mechanoresistive behaviour of exceptional magnitude, with conductance modulations of more than three orders of magnitude upon compression by as little as 1 nm. We synthesised series of cyclometalated Pt(II) molecular wires, and used scanning tunnelling microscopy – break junction techniques to characterise their electromechanical behaviour. Mechanoresistivity arises from an interaction between the Pt(II) cation and the Au electrode triggered by mechanical compression of the single‐molecule device, and theoretical modelling confirms this hypothesis. Our study provides a new tool for the design of functional molecular wires by exploiting previously unreported ion‐metal interactions in single‐molecule devices, and develops a new framework for the development of mechanoresistive molecular junctions.

An ultrasensitive flexible force sensor with nature-inspired minimalistic architecture to achieve a detection resolution and threshold of 1 mN for underwater applications

Highly sensitive flexible force sensors enable precise detection of underwater signals for monitoring biological activity, environmental conditions, and vehicle movement. Multilayer stack assembly and micro/nano structure array are often seen in most force/pressure sensors which are toughly hard to control the interlayer spacing and micro/nano structures alignment precisely, resulting in poor consistency and stability. Herein, we first reported a new force sensor with a nature-inspired minimalistic architecture, addressing such issues in an elegant and surprising approach by using a single-layer arched functional membrane with one microgroove. Inspired by the scorpions’ slit sensilla and mantis’ campaniform sensilla, a highly sensitive and waterproof flexible force sensor was fabricated. It is demonstrated that the force sensor has a sensitivity of 27.6 N−1, a high force resolution (1 mN), a fast response time of 70 ms, excellent stability over 5000 cycles and linearity (0.996), and a small force detection limit (≤ 1 mN), showing great potential in underwater environment sensing and motion monitoring of vehicles. This novel but minimalistic architecture provides a new direction in the development of sensors with advanced performance.

Modeling Electronic Devices with a Casimir Cavity

The Casimir effect has been exploited in various MEMS (micro-electro-mechanical system) devices, especially to make sensitive force sensors and accelerometers. It has also been used to provide forces for a variety of purposes, for example, for the assembly of considerably small parts. Repulsive forces and torques have been produced using various configurations of media and materials. Just a few electronic devices have been explored that utilize the electrical properties of the Casimir effect. Recently, experimental results were presented that described the operation of an electronic device that employed a Casimir cavity attached to a standard MIM (metal–insulator–metal) structure. The DC (direct current) conductance of the novel MIM device was enhanced by the attached cavity and found to be directly proportional to the capacitance of the attached cavity. The phenomenological model proposed assumed that the cavity reduced the vacuum fluctuations, which resulted in a reduced injection of carriers. The analysis presented here indicates that the optical cavity actually enhances vacuum fluctuations, which would predict a current in the opposite direction from that observed. Further, the vacuum fluctuations near the electrode are shown to be approximately independent of the size of the optical cavity, in disagreement with the experimental data which show a dependence on the size. Thus, the proposed mechanism of operation does not appear correct. A more detailed theoretical analysis of these devices is needed, in particular, one that uses real material parameters and computes the vacuum fluctuations for the entire device. Such an analysis would reveal how these devices operate and might suggest design principles for a new genre of electronic devices that make use of vacuum fluctuations.

A Highly Sensitive 3D-Printed Flexible Sensor for Sensing Small Pressures in Deep-Sea High-Pressure Environment.

The origin of life on Earth is believed to be from the ocean, which offers abundant resources in its depths. However, deep-sea operations are limited due to the lack of underwater robots and rigid grippers with sensitive force sensors. Therefore, it is crucial for deep-sea pressure sensors to be integrated with mechanical hands for manipulation. Here, a flexible stress sensor is presented that can function effectively under high water pressure in the deep ocean. Inspired by biological structures found in the abyssal zone, our sensor is designed with an internal and external pressure balance structure (hollow interlocking spherical structure). The digital light processing (DLP) three-dimensional (3D) printing technology is utilized to construct this complex structure after obtaining optimized structural parameters using finite element simulation. The sensor exhibits linear sensitivity of 0.114 kPa-1 within the range of 0-15 kPa and has an extremely short response time of 32 ms, good dynamic-static load response capability, and excellent resistance cycling stability. It shows high sensitivity of 1.74 kPa-1 even under 30 MPa static water pressures and the theoretical working pressure can exceed 110 MPa, which provides a new solution for deep-sea robots.

A Highly Sensitive MEMS Three-Dimensional Force Sensor based on Piezoresistive Cantilever with Stress Concentration

A Highly Sensitive MEMS Three-Dimensional Force Sensor based on Piezoresistive Cantilever with Stress Concentration

Highly Sensitive Force Sensor Based on High-Q Asymmetric V-Shaped CaF2 Resonator.

Whispering gallery mode (WGM) resonators have high-quality factors and can be used in high-sensitivity sensors due to the narrow line width that allows for the detection of small external changes. In this paper, a force-sensing system based on a high-Q asymmetric V-shaped CaF2 resonator is proposed. Based on the dispersion coupling mechanism, the deformation of the resonator is achieved by loading force, and the resonant frequency is changed to determine the measurement. By adjusting the structural parameters of the asymmetric V-shaped resonator, the deformation of the resonator under force loading is improved. The experimental results show that the sensitivity of the V-shaped tip is 18.84 V/N, which determines the force-sensing resolution of 8.49 μN. This work provides a solution for force-sensing measurements based on a WGM resonator.

Highly sensitive fiber force sensor based on cascaded Fabry-Perot cavities and Vernier effect

In this article, we introduce a new concept for an in-line optical fiber force sensor probe, which is based on two cascaded Fabry-Perot (F-P) cavities to generate the Vernier effect and enhance sensitivity. Due to the significantly low Young’s modulus of UV-cured adhesive within the sensing cavity, extremely high force sensitivity is obtained. In our initial sample, we achieved an impressive force sensitivity of −61,301 nm/N. To improve that, the optical path difference between the two cavities is further reduced, exhibiting a remarkable increased force sensitivity of −140,813 nm/N. As an application, we conducted an experiment using this highly sensitive force sensor probe to measure the evaporation rate of ethanol, a common solvent, which is 7.79 × 10−5 g/s at room temperature. The proposed sensor features advantages of high sensitivity, simple structure, ease of fabrication, compactness, which is an ideal fiber sensor probe for sensitive force measurement.

Printed Composite Film with Microporous/Micropyramid Hybrid Conductive Architecture for Multifunctional Flexible Force Sensors.

Porous structures and micropatterning surfaces play a crucial role in the development of highly sensitive force sensors. However, achieving these two conductive architectures typically requires the synthesis of complex materials and expensive manufacturing processes. In this study, we introduce a novel conductive composite film featuring a microporous/micropyramid hybrid conductive architecture, which is achieved through a straightforward process of materials mixing and one-step screen printing. By utilizing a deep eutectic solvent in the ink component, micropores are induced in the printed composite, while the mesh of the screen mask acts as a template, resulting in a micropyramid film surface. We have successfully realized highly sensitive flexible force sensors (0.15 kPa-1) with multifunctional capabilities for perceiving normal force and shear force.

Hardware and software for automated examination of defects of hard tissues of teeth after endodontic intervention for fatigue and destruction

The work developed circuit engineering, design and software of the loading machine for automated examination of dental hard tissue defects after endodontics intervention for fatigue and destruction. The advantage of this development is the combination as cyclic loading methods simulating chewing movements and force effects on compression in a compact small-sized case, with low power consumption and small noise level. Thanks to the use of a screw transmission and a stepper motor in combination with a sensitive tensoresistive force sensor, it was possible to achieve high accuracy and resolution of 0.1 microns.
 A series of tests was conducted on real samples of endodontically treated teeth restored using fiberglass pins and cast metal stump inserts. It is shown that methods of restoring incisors and premolars of the upper jaw with the help of fiberglass pins have an advantage when the residual structure of the tooth is lacking due to a more uniform distribution of deformation stresses, since their elastic modulus is close to the elastic modulus of dentin.

A sub-millinewton resolution biaxial force sensor with temperature self-compensation for vascular intervention

This article presents a fiber Bragg grating (FBG)-based highly sensitive micro-biaxial force sensor for vascular intervention surgery. It features a 3D-printed integrated structure incorporating an FBG- embedded cavity at its front end for temperature decoupling and an elliptical arc ball hinge to improve lateral sensitivity. Four FBG-embedded fibers are suspended in a circular array within the flexible hinge to minimize lateral strain crosstalk and increase measurement accuracy. Finite-element analysis has been implemented to validate the flexure performance, while both static and dynamic loading experiments have been performed to validate the sensor performance. The experiments revealed resolutions of 0.761 and 0.765 mN, respectively for the two lateral forces within a range of −1 to 1 N, and dynamic measurement error lower than 0.67 % of full scale. Temperature compensation experiments are conducted under loaded conditions for both axes, showing errors of lower than 1.6 % and 1.2 %. The ability to decouple force and temperature will benefit its broad application for vascular intervention surgery.

Multifractality in stride-to-stride variations reveals that walking involves more movement tuning and adjusting than running

Introduction: The seemingly periodic human gait exhibits stride-to-stride variations as it adapts to the changing task constraints. The optimal movement variability hypothesis (OMVH) states that healthy stride-to-stride variations exhibit “fractality”—a specific temporal structure in consecutive strides that are ordered, stable but also variable, and adaptable. Previous research has primarily focused on a single fractality measure, “monofractality.” However, this measure can vary across time; strideto-stride variations can show “multifractality.” Greater multifractality in stride-tostride variations would highlight the ability to tune and adjust movements more.Methods: We investigated monofractality and multifractality in a cohort of eight healthy adults during self-paced walking and running trials, both on a treadmill and overground. Footfall data were collected through force-sensitive sensors positioned on their heels and feet. We examined the effects of self-paced walking vs. running and treadmill vs. overground locomotion on the measure of monofractality, α-DFA, in addition to the multifractal spectrum width, W, and the asymmetry in the multifractal spectrum, WAsym, of stride interval time series.Results: While the α-DFA was larger than 0.50 for almost all conditions, α-DFA was higher in running and locomoting overground than walking and locomoting on a treadmill. Similarly, W was greater while locomoting overground than on a treadmill, but an opposite trend indicated that W was greater in walking than running. Larger WAsym values in the negative direction suggest that walking exhibits more variation in the persistence of shorter stride intervals than running. However, the ability to tune and adjust movements does not differ between treadmill and overground, although both exhibit more variation in the persistence of shorter stride intervals.Discussion: Hence, greater heterogeneity in shorter than longer stride intervals contributed to greater multifractality in walking compared to running, indicated by larger negative WAsym values. Our results highlight the need to incorporate multifractal methods to test the predictions of the OMVH.

Wearable multisource quantitative gait analysis of Parkinson's diseases

As the motor symptoms of Parkinson's disease (PD) are complex and influenced by many factors, it is challenging to quantify gait abnormalities adequately using a single type of signal. Therefore, a wearable multisource gait monitoring system is developed to perform a quantitative analysis of gait abnormalities for improving the effectiveness of the clinical diagnosis. To detect multisource gait data for an accurate evaluation of gait abnormalities, force sensitive sensors, piezoelectric sensors, and inertial measurement units are integrated into the devised device. The modulation circuits and wireless framework are designed to simultaneously collect plantar pressure, dynamic deformation, and postural angle of the foot and then wirelessly transmit these collected data. With the designed system, multisource gait data from PD patients and healthy controls are collected. Multisource features for quantifying gait abnormalities are extracted and evaluated by a significance test of difference and correlation analysis. The results show that the features extracted from every single type of data are able to quantify the health status of the subjects (p < 0.001, ρ > 0.50). More importantly, the validity of multisource gait data is verified. The results demonstrate that the gait feature fusing multisource data achieves a maximum correlation coefficient of 0.831, a maximum Area Under Curve of 0.9206, and a maximum feature-based classification accuracy of 88.3%. The system proposed in this study can be applied to the gait analysis and objective evaluation of PD.

Inhibitory Effects of Epithelial Cells on Fibrosis Mechanics of Microtissue and Their Spatiotemporal Dependence on the Epithelial-Fibroblast Interaction.

Cell-generated contraction force is the primary physical drive for fibrotic densification of biological tissues. Previous studies using two-dimensional culture models have shown that epithelial cells inhibit the myofibroblast-derived contraction force via the regulation of the fibroblast/myofibroblast transition (FMT). However, it remains unclear how epithelial cells interact with fibroblasts and myofibroblasts to determine the mechanical consequences and spatiotemporal regulation of fibrosis development. In this study, we established a three-dimensional microtissue model using an NIH/3T3 fibroblast-laden collagen hydrogel, incorporated with a microstring-based force sensor, to assess fibrosis mechanics. When Madin-Darby canine kidney epithelial cells were cocultured on the microtissue's surface, the densification, stiffness, and contraction force of the microtissue greatly decreased compared to the monocultured microtissue without epithelial cells. The key fibrotic features, such as enhanced protein expression of α-smooth muscle actin, fibronectin, and collagen indicating FMT and matrix deposition, respectively, were also significantly reduced. The antifibrotic effects of epithelial cells on the microtissue were dependent on the intercellular signaling molecule prostaglandin E2 (PGE2) with an effective concentration of 10 μM and their proximity to the fibroblasts, indicating paracrine cellular signaling between the two types of cells during tissue fibrosis. The effect of PGE2 on microtissue contraction was also dependent on the time point when PGE2 was delivered or blocked, suggesting that the presence of epithelial cells at an early stage is critical for preventing or treating advanced fibrosis. Taken together, this study provides insights into the spatiotemporal regulation of mechanical properties of fibrosis by epithelial cells, and the cocultured microtissue model incorporated with a real-time and sensitive force sensor will be a suitable system for evaluating fibrosis and drug screening.

A novel topographically patterned MXene@MnO2/PVDF piezo-active hybrid for flexible real-time and sensitive force sensor

Flexible force sensors capable of real-time and sensitive analysis have gained immense popularity because of their great potential to be integrated into potable and wearable electronics. Herein, a novel flexible force sensor constructing from topographically patterned piezo-active MXene@MnO2/poly(vinylidene fluoride) (PVDF) hybrid that allows for real-time precise pressure detection is proposed. Benefiting from the synergistic effect of topographical patterning and nano-reinforcement filling, the piezo-active hybrids with convex microarrays patterns demonstrate outstanding piezoelectric coefficient d33 (49 pC/N) and output upon mechanical stimuli, enabling the resultant force sensors with high voltage sensitivity of 0.450 V/N, fast response time of 16–19 ms and excellent operation stability. Furthermore, the feasibility of sensors in effectively detecting water droplets, gas flow and finger bending is demonstrated, confirming their viability for real applications.

31‐4: Sharp Force Touch for On‐Screen User Interface in LCD and Foldable OLED Display Application

We describe ultra‐high sensitive force sensor on flat display that can detect and differentiate between feather touch and press touch or tapping. The proposed unique sensor pattern design and pressure‐sensitive material enables ultra‐high force sensitivity, multi force detection (10 points). Our force touch technology with button‐shaped bumps cover enables blind input operations and usability as good as mechanical buttons. Therefore, our technology provides reduced input errors and yield more intuitive and safedrive. In addition, the proposed novel algorithm enables an operating temperature range for automotive applications.

Near-infrared microfiber Bragg grating for sensitive measurement of tension and bending.

Fiber-optic devices working in the visible and near-infrared windows are attracting attention due to the rapid development of biomedicine that involves optics. In this work, we have successfully realized the fabrication of near-infrared microfiber Bragg grating (NIR-µFBG), which was operated at the wavelength of 785 nm, by harnessing the fourth harmonic order of Bragg resonance. The NIR-µFBG provided the maximum sensitivity of axial tension and bending to 211 nm/N and 0.18 nm/deg, respectively. By conferring the considerably lower cross-sensitivity, such as response to temperature or ambient refractive index, the NIR-µFBG can be potentially implemented as the highly sensitive tensile force and curve sensor.

Flexible force-sensitive distributed pressure sensing system for soft connection of aircraft Cockpit Cover

With respect to the actual application of the edge bonding of transparent part of the fighter jet cockpit cover by soft connection, the flexible force-sensitive distributed pressure sensor system is developed, which covers the flexible force-sensitive sensor, calibration device, circuit and data analysis software. The pressure distribution during pressurizing of the edge bonding of multidimensional curved surface transparent parts is vividly showcased by 2D and 3D images. A number of people are assigned to carry out operation. Based on the pressure distribution map and data acquisition, it is determined that the existing bonding process has the serious decificiency of uneven pressure distributio that cannot be addressed, and there is huge potential for improvement.

On-Site Safety-Valves Testing in Thermal Power Plants

Abstract The paper describes the function and importance of safety devices on pressure equipment, legal regulations for the necessary scope and periods of functional inspections of safety valves in thermal power plants. The mode of operation of the apparatus for in-site testing and adjustment of safety valves on pressure vessels is described, as well as a comparative presentation of the obtained test results compared to the results obtained by the conventional method that uses hydraulic pressure of the medium for valve spring load. The on-site method uses a motor drive to load the valve spring, and uses sensitive displacement, force and sound sensors to generate signals, which are processed in a suitable software application to obtain test results. Unlike the conventional method, the on-site method allows testing of safety valves without their disassembly from the installation site. A comparison of the test results obtained by the modern method with the test results by the conventional method was made on several safety valves. It has been shown that in addition to better precision, which is important for valves with lower operating pressures, the application of the on-site method shortens the test time several times.

Reaching silicon-based NEMS performances with 3D printed nanomechanical resonators

The extreme miniaturization in NEMS resonators offers the possibility to reach an unprecedented resolution in high-performance mass sensing. These very low limits of detection are related to the combination of two factors: a small resonator mass and a high quality factor. The main drawback of NEMS is represented by the highly complex, multi-steps, and expensive fabrication processes. Several alternatives fabrication processes have been exploited, but they are still limited to MEMS range and very low-quality factor. Here we report the fabrication of rigid NEMS resonators with high-quality factors by a 3D printing approach. After a thermal step, we reach complex geometry printed devices composed of ceramic structures with high Young’s modulus and low damping showing performances in line with silicon-based NEMS resonators ones. We demonstrate the possibility of rapid fabrication of NEMS devices that present an effective alternative to semiconducting resonators as highly sensitive mass and force sensors.