Flexible Strain Gauge Research Articles

Sensory artificial cilia for in situ monitoring of airway physiological properties

Continuously monitoring human airway conditions is crucial for timely interventions, especially when airway stents are implanted to alleviate central airway obstruction in lung cancer and other diseases. Mucus conditions, in particular, are important biomarkers for indicating inflammation and stent patency but remain challenging to monitor. Current methods, reliant on computational tomography imaging and bronchoscope inspection, pose risks due to radiation and lack the ability to provide continuous real-time feedback outside of hospitals. Inspired by the sensing ability of biological cilia, we report wireless sensing mechanisms in sensory artificial cilia for detecting mucus conditions, including viscosity and layer thickness, which are crucial biomarkers for disease severity. The sensing mechanism for mucus viscosity leverages external magnetic fields to actuate a magnetic artificial cilium and sense its shape using a flexible strain-gauge. Additionally, we report an artificial cilium with capacitance sensing for mucus layer thickness, offering unique self-calibration, adjustable sensitivity, and range, all enabled by external magnetic fields. To enable prolonged and wireless data access, we integrate Bluetooth Low Energy communication and onboard power, along with a wearable magnetic actuation system for sensor activation. We validate our method by deploying the sensor independently or in conjunction with an airway stent within a trachea phantom and sheep trachea ex vivo. The proposed sensing mechanisms and devices pave the way for real-time monitoring of mucus conditions, facilitating early disease detection and providing stent patency alerts, thereby allowing timely interventions and personalized care.

A flexible resistive strain gauge with reduced temperature effect via thermal expansion anisotropic composite substrate

Strain gauge plays vital roles in various fields as structural health monitoring, aerospace engineering, and civil infrastructure. However, traditional flexible strain gauge inevitably brings the pseudo-signal caused by the substrate temperature effect and determines its accuracy. Here, we present an anisotropic composite substrate designed to modify the thermal expansion performance via Micro-electro-mechanical System (MEMS) technology, which facilitates the development of strain gauges that are minimally affected by substrate temperature-induced effect. Compared to the isotropic flexible substrate, the simulated expansion displacement in the thermal insensitive direction is reduced by 53.6% via introducing an anisotropic thermal expansion structure. The developed strain gauge exhibits significantly reduced sensitivity to temperature-induced effect, with a temperature coefficient of resistance decreasing from 87.3% to 10%, along with a notable 47.1% improvement in TCR stability. In addition, the strain gauge displays a sensitivity of 1.99 and boasts a wide strain operational range of 0–6000 µε, while maintaining excellent linearity. Furthermore, stress response conducted on a model of an aircraft wing illustrates the rapid monitoring of the strain gauge, which can detect strain as low as 100 µε. This study strongly highlights the potential applicability of the developed strain gauge in the aircraft, ships, and bridges for monitoring stress.

A Review Paper on Designing of Knee Support System for Elderly People

Knee pain can now occur in people as young as their 30s, not just in their 60s and 70s. As the elderly population grows, hospitals will have a hard time accepting more patients due to the high demand for services. The focus will shift from post-accident care to preventative care, especially for people with knee pain. The first step in designing and developing a successful knee exoskeleton is to conduct high-quality research on the following topics: knee structure, the diseased state of osteoarthritis, knee kinematics, gait analysis, the existing market for knee exoskeletons, actuation methods, novel software, sensors, and more. The study found that applying heat to the knee increases tissue temperature, softens surrounding tissues, reduces tissue viscosity, increases connective tissue extensibility, reduces pain, and increases joint mobility. Flexible sensors are used in wearable devices such as electric skin, flexible strain gauge sensors, motion detectors, and self-repairing sensors. A self-adjusting knee joint is being developed to allow passive self-alignment with the ICR of the natural knee. Neoprene rubber is a synthetic closed-cell rubber used in medical devices, but it lacks breathability and restricts the movement of water vapor, moisture, and heat. Knitted stretch fabrics provide warmth and compression to injured areas, and foam provides shock protection and pressure points to promote healing. Test methods are used to evaluate the dimensional, mechanical, and thermo-physiological properties for material selection. A wearable suit design was studied using a Design of Experiments approach, with eight key parameters identified and an optimization method developed. Robotics and automation technology were used to address discomfort issues in the body-worn knee exoskeleton design.

Modulating saturation magnetization and topological Hall resistivity of flexible ferrimagnetic Mn4N films by bending strains

The ferrimagnetic rare-earth-free Mn4N films are considered as a good candidate in spintronics due to its low saturation magnetization (MS) and high Néel temperature. Here, Mn4N films are directly deposited on flexible mica to investigate strain-related magnetic and electronic transport properties. The MS variation of 11.0 nm Mn4N film reaches 453% at tensile strain of radius of curvature (ROC) = 2 mm. Bending strains cannot affect anomalous Hall resistivity and magnetoresistance. However, the topological Hall resistivity of 147.0 nm Mn4N film increases by 58% at tensile strain of ROC = 5 mm due to frustrated exchange interactions. The flexible Mn4N films have great potential applications in flexible magnetic sensor and strain gauge due to strain modulated MS, resistance, and stable magnetoresistance.

Investigation of textured sensing skin for monitoring fatigue cracks on fillet welds

Load-induced fatigue cracking in welds is a critical safety concern for steel transportation infrastructure, and the automation of their detection using commercial sensing technologies remains challenging due to the randomness in crack initiation and propagation. The authors have previously proposed a corrugated soft elastomeric capacitor (cSEC), which is a flexible and ultra-compliant thin-film strain gauge that transduces strain into a measurable change in capacitance. The cSEC technology has been successfully demonstrated for measuring bending strain as well as angular rotation in a folded configuration. This study builds on prior discoveries to characterize the sensor’s capability at monitoring fatigue cracks in corner welds, for which the sensor needs to be installed in a folded configuration. A crack monitoring algorithm is developed to fuse the cSEC data into actionable information. Experimental work is conducted on an orthogonal welded connection, mimicking a plate-to-web joint in steel bridges, with cSECs folded over the fillet welds. The sensor’s electromechanical behavior is characterized, and results confirm that the cSEC is capable of fatigue crack detection and quantification. In particular, results show that the cSEC can detect a minimum crack length of 0.48 mm and that its overall sensing performance, including signal linearity, resolution, and accuracy, is adequate under no damage, yet decreases with increasing crack size, likely attributable to the simplification of the electromechanical model and higher noise produced by the loading equipment under smaller applied displacement.

A Flexible Chip-Film Patch and a Flexible Strain Gauge Sensor Suitable for a Hybrid System-in-Foil Integration

Hybrid Systems-in-Foil (HySiF) encompass large-area thin-film electronics and ultrathin, high performance CMOS chips, which are integrated into a flexible polymeric foil substrate. In this work, the individual components of a customized flexible sensor system are characterized in detail, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i.e.</i> , a strain gauge and a readout ASIC, and the system functionality is proved. We employ the Chip-Film Patch (CFP) technology, where an ultra-thin readout ASIC is embedded in spin-coated polyimide foil in order to monitor resistance variations of strain gauges. These two components are suitable to be integrated on the same foil, whereas the envisioned system is intended to monitor the respiratory system of newborns and premature infants. The latest developments in the CFP process using the aromatic polyimide PI-2611 are shown. In particular, the optimization of the spin-coating and evaluation of polyimide uniformity above the embedded chip are highlighted. Furthermore, we demonstrate a flexible strain gauge sensor using thin-film metals embedded in polyimide PI-2611, which is usable at up to 30% strain under electromechanical load. This also demonstrates the mechanical reliability of the CFP circuit interconnects. The electrical characterization of the readout ASIC, after back-thinning and embedding into the CFP, reveals no stress induced performance degradation.

Bioinspired Cilia Sensors with Graphene Sensing Elements Fabricated Using 3D Printing and Casting.

Sensor designs found in nature are optimal due to their evolution over millions of years, making them well-suited for sensing applications. However, replicating these complex, three-dimensional (3D), biomimetic designs in artificial and flexible sensors using conventional techniques such as lithography is challenging. In this paper, we introduce a new processing paradigm for the simplified fabrication of flexible sensors featuring complex and bioinspired structures. The proposed fabrication workflow entailed 3D-printing a metallic mold with complex and intricate 3D features such as a micropillar and a microchannel, casting polydimethylsiloxane (PDMS) inside the mold to obtain the desired structure, and drop-casting piezoresistive graphene nanoplatelets into the predesigned microchannel to form a flexible strain gauge. The graphene-on-PDMS strain gauge showed a high gauge factor of 37 as measured via cyclical tension-compression tests. The processing workflow was used to fabricate a flow sensor inspired by hair-like ‘cilia’ sensors found in nature, which comprised a cilia-inspired pillar and a cantilever with a microchannel that housed the graphene strain gauge. The sensor showed good sensitivity against both tactile and water flow stimuli, with detection thresholds as low as 12 µm in the former and 58 mm/s in the latter, demonstrating the feasibility of our method in developing flexible flow sensors.

Micropatterned flexible strain gauge sensor based on wet electrospun polyurethane/PEDOT: PSS nanofibers

Extremely elastic and sensitive strain gauge sensors are highly demanded to keep track of strains in flexible electronics, skin deformation, and human movement. This report discusses a new approach to fabricate a stretchable, electrically conductive and sensitive strain gauge sensor which uses a polymeric nanofibrous composite of thermoplastic polyurethane (TPU) elastomer and conductive poly (3,4-ethylene dioxythiophene) poly(styrene sulfonate) (PEDOT: PSS) polymer as its basis. The nanofibrous composite was prepared using wet electrospinning technique. The designed TPU/PEDOT: PSS membrane loaded on a silicon rubber (SR) substrate holds an electrical resistance of 3 KΩ and a stable gauge factor of 20 up to 40% strains at room temperature. A single Wheatstone bridge was implemented to calibrate a micro-patterned strain sensor grid for voltage output versus an applied bending moment/force. The obtained results inferred that the fabricated sensor could be used to sense rapid and minute deformation actions in a wide range of engineering applications.

Transition States of Nanocrystal Thin Films during Ligand-Exchange Processes for Potential Applications in Wearable Sensors

Ligand exchange is an advanced technique for tuning the various properties of nanocrystal (NC) thin films, widely used in the NC thin-film device applications. Understanding how the NC thin films transform into functional thin-film devices upon ligand exchange is essential. Here, we investigated the process of structural transformation and accompanying property changes in the NC thin films, by monitoring the various characteristics of silver (Ag) NC thin films at each stage of the ligand-exchange process. A transition state was identified in which the ligands are partially exchanged, where the NC thin films showed unexpected electromechanical features with high gauge factors up to 300. A model system was established to explain the origin of the high gauge factors, supported by the observation of spontaneously formed nanocracks and metal-insulator transition from the structural analysis and charge transport study, respectively. Taking advantages of the unique electromechanical properties of the NC thin films, we fabricated flexible strain gauge sensor devices with high sensitivity, reliability, and stability. We introduce a one-step fabrication process, namely, "the time- and spatial-selective ligand-exchange process", for the design of low-cost and high-performance wearable sensors that effectively detect human motion, such as finger or neck muscle movement. This study provides a fundamental understanding of the ligand-exchange process in NCs, as well as an insight into the functionalities of the NC thin films for technological applications.

Sleep monitoring sensor using flexible metal strain gauge

This paper presents a sleep monitoring sensor based on a flexible metal strain gauge. As quality of life has improved, interest in sleep quality, and related products, has increased. In this study, unlike a conventional single sensor based on a piezoelectric material, a metal strain gauge-based array sensor based on polyimide and nickel chromium (NiCr) is applied to provide movement direction, respiration, and heartbeat data as well as contact-free use by the user during sleeping. Thin-film-type resistive strain gage sensors are fabricated through the conventional flexible printed circuit board (FPCB) process, which is very useful for commercialization. The measurement of movement direction and respiratory rate during sleep were evaluated, and the heart rate data were compared with concurrent electrocardiogram (ECG) data. An algorithm for analyzing sleep data was developed using MATLAB, and the error rate was 4.2% when compared with ECG for heart rate.

A large-area strain sensing technology for monitoring fatigue cracks in steel bridges

This paper presents a novel large-area strain sensing technology for monitoring fatigue cracks in steel bridges. The technology is based on a soft elastomeric capacitor (SEC), which serves as a flexible and large-area strain gauge. Previous experiments have verified the SEC’s capability to monitor low-cycle fatigue cracks experiencing large plastic deformation and large crack opening. Here an investigation into further extending the SEC’s capability for long-term monitoring of fatigue cracks in steel bridges subject to traffic loading, which experience smaller crack openings. It is proposed that the peak-to-peak amplitude (pk–pk amplitude) of the sensor’s capacitance measurement as the indicator of crack growth to achieve robustness against capacitance drift during long-term monitoring. Then a robust crack monitoring algorithm is developed to reliably identify the level of pk–pk amplitudes through frequency analysis, from which a crack growth index (CGI) is obtained for monitoring fatigue crack growth under various loading conditions. To generate representative fatigue cracks in a laboratory, loading protocols were designed based on constant ranges of stress intensity to limit plastic deformations at the crack tip. A series of small-scale fatigue tests were performed under the designed loading protocols with various stress intensity ratios. Test results under the realistic fatigue crack conditions demonstrated the proposed crack monitoring algorithm can generate robust CGIs which are positively correlated with crack lengths and independent from loading conditions.

Cardiac microphysiological devices with flexible thin-film sensors for higher-throughput drug screening.

Microphysiological systems and organs-on-chips promise to accelerate biomedical and pharmaceutical research by providing accurate in vitro replicas of human tissue. Aside from addressing the physiological accuracy of the model tissues, there is a pressing need for improving the throughput of these platforms. To do so, scalable data acquisition strategies must be introduced. To this end, we here present an instrumented 24-well plate platform for higher-throughput studies of engineered human stem cell-derived cardiac muscle tissues that recapitulate the laminar structure of the native ventricle. In each well of the platform, an embedded flexible strain gauge provides continuous and non-invasive readout of the contractile stress and beat rate of an engineered cardiac tissue. The sensors are based on micro-cracked titanium-gold thin films, which ensure that the sensors are highly compliant and robust. We demonstrate the value of the platform for toxicology and drug-testing purposes by performing 12 complete dose-response studies of cardiac and cardiotoxic drugs. Additionally, we showcase the ability to couple the cardiac tissues with endothelial barriers. In these studies, which mimic the passage of drugs through the blood vessels to the musculature of the heart, we regulate the temporal onset of cardiac drug responses by modulating endothelial barrier permeability in vitro.

Nanoparticle monolayer-based flexible strain gauge with ultrafast dynamic response for acoustic vibration detection

The relatively poor dynamic response of current flexible strain gauges has prevented their wide adoption in portable electronics. In this work, we present a greatly improved flexible strain gauge, where one strip of Au nanoparticle (NP) monolayer assembled on a polyethylene terephthalate film is utilized as the active unit. The proposed flexible gauge is capable of responding to applied stimuli without detectable hysteresis via electron tunneling between adjacent nanoparticles within the Au NP monolayer. Based on experimental quantification of the time and frequency domain dependence of the electrical resistance of the proposed strain gauge, acoustic vibrations in the frequency range of 1 to 20,000 Hz could be reliably detected. In addition to being used to measure musical tone, audible speech, and creature vocalization, as demonstrated in this study, the ultrafast dynamic response of this flexible strain gauge can be used in a wide range of applications, including miniaturized vibratory sensors, safe entrance guard management systems, and ultrasensitive pressure sensors.

A contact stress sensor based on strain gauge

In this paper a sensor with flexible strain gauge is proposed. The sensor can monitor the contact stress between two surfaces in some extreme environments such as thin slits. The force sensitive element inside the sensor is made up of film grid, supporting layer with holes and deforming layer for smoothing load. The device with this structure can easily convert the positive pressure into pulling stress of film grid. The sensor performance related to the number of holes, thickness of layers and elastic constant of layers is investigated. The response of the sensor is simulated and analyzed with finite element analysis software. Based on simulation results, several parameters are optimized and the corresponding sensor is manufactured. The whole sensor thickness is less than 300 μm. Based on the load test in 0–4 MPa, the results show that the linearity error is ±1.77% of full-scale output (FSO), the average deviation is ±0.98% FSO and the hysteresis is ±0.92% FSO. The proposed sensor has advantages of simple structure, easy package, excellent performance and great practicality.

Electrical conduction of nanoparticle monolayer for accurate tracking of mechanical stimulus in finger touch sensing.

A flexible strain gauge is an essential component in advanced human-machine interfacing, especially when it comes to many important mobile and biomedical appliances that require the detection of finger touches. In this paper, we report one such strain gauge made from a strip of nanoparticle monolayer onto a flexible substrate. This proposed gauge operates on the observation that there is a linear relationship between electrical conduction and mechanical displacement in a compressive state. Due to its prompt temporal response, the gauge can accurately track various mechanical stimuli running at the frequencies of interest. Experiments have confirmed that the proposed strain gauge has a strain detection limit as low as 9.4 × 10(-5), and its gauge factor can be as large as 70, making this device particularly suitable for sensitive finger touch sensing. Furthermore, negligible degradation in the gauge's output electrical signal is observed even after 9000 loading/unloading cycles.

A flexible strain gauge exhibiting reversible piezoresistivity based on an anisotropic magnetorheological polymer

A flexible, anisotropic and portable stress sensor (logarithmic reversible response between 40–350 kPa) was fabricated, in which i) the sensing material, ii) the electrical contacts and iii) the encapsulating material, were based on polydimethylsiloxane (PDMS) composites. The sensing material is a slide of an anisotropic magnetorheological elastomer (MRE), formed by dispersing silver-covered magnetite particles (Fe3O4@Ag) in PDMS and by curing in the presence of a uniform magnetic field. Thus, the MRE is a structure of electrically conducting pseudo-chains (needles) aligned in a specific direction, in which electrical conductivity increases when stress is exclusively applied in the direction of the needles. Electrical conductivity appears only between contact points that face each other at both sides of the MRE slide. An array of electrical contacts was implemented based on PDMS-silver paint metallic composites. The array was encapsulated with PDMS. Using Fe3O4 superparamagnetic nanoparticles also opens up possibilities for a magnetic field sensor, due to the magnetoresistance effects.

Highly flexible capacitive strain gauge for continuous long-term blood pressure monitoring

An innovative procedure for measuring blood pressure, with none of the disadvantages of current procedures, is proposed. A highly-flexible capacitive strain gauge has been designed to measure changes in the diameter of a blood vessel; such changes are indicative of blood pressure. The sensor is implanted and wrapped around an arterial blood vessel during the normal course of a surgical procedure. In vivo tests, demonstrating the feasibility of this concept, are reported, along with in vitro tests and notes on sensor design and fabrication. These continuous blood pressure monitoring sensors may be used for a continuous long-term monitoring of blood pressure and pulse. They may also be combined with a real-time nerve stimulation technique or a course of medication to create a closed-loop system for blood-pressure control.

Flexible Strain Gauge Sensors with Long-term Stability and Low Power Consumption for Self-sufficient Sensor Systems

Abstract In this paper we present a flexible sensor element with low power consumption and long-term stability under typical aeronautical conditions. Titanium (Ti) is used as thin film metallization material, because of its high corrosion and heat resistance. Polyimide foil and also ultrathin glass substrates are used as substrate. Parylene C is used as passivation layer for the whole sensor. Long-term stability of a Ti based strain gauge sensor with high resistance and low energy consumption on different substrates are investigated.

Flexible polysilicon sensor array modules using “etch-release” packaging scheme

A flexible polysilicon strain gauge array has been designed and fabricated using surface-micromachining with a SiO2 sacrificial layer. The realized sensor array is mechanically flexible, which can be attached on a non-planar surface. To realize the flexible polysilicon strain gauge array, a new packaging scheme using polysilicon/oxide-based surface-micromachining was developed. The proposed packaging scheme completes the strain sensor and the circuit board on a single process, which eliminates additional assembly and alignment problems. The measured gauge factor shows that it is more sensitive than conventional metal strain gauges. Unlike a single-crystal silicon strain gauge, a crystal direction does not affect its sensitivity in a polysilicon sensor, and this isotropic property makes the realization of an omni-directional strain gauge array possible. The proposed flexible strain sensor array can be used in a measurement of stress distribution of an arbitrary and non-planar surface.

A direct reading flexible strain gauge for large strains

StrainVolume 6, Issue 3 p. 144-144 Free Access A direct reading flexible strain gauge for large strains First published: July 1970 https://doi.org/10.1111/j.1475-1305.1970.tb01679.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume6, Issue3July 1970Pages 144-144 RelatedInformation