Repeatability and Extended Time Stability Study of an Additively Printed Strain Gauge Under Different Load Conditions

Abstract Printed electronics has found new applications in wearable electronics owing to the opportunities for integration, and the ability of sustaining folding, flexing and twisting. Continuous monitoring necessitates the production of sensors, which include temperature, humidity, sweat, and strain sensors. In this paper, a process study was performed on the FR4 board while taking into account multiple printing parameters for the direct-write system. The process parameters include ink pressure, print speed, and stand-off height, as well as their effect on the trace profile and print consistency using white light interferometry analysis. The printed traces have also been studied for different sintering conditions while keeping the FR4 board’s temperature limit in mind. The paper also discusses the effect of sintering conditions on mechanical and electrical properties, specifically shear load to failure and resistivity. The data from this was then used to print strain gauges and compared them to commercially available strain gauges. By reporting the gauge factor, the printed strain gauge has been standardized. The conductive ink’s strain sensing capabilities will be studied under tensile cyclic loading (3-point bending) at various strain rates and maximum strains. Long-term performance testing will be carried out using cyclic tensile loads.

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Preparation and Characterization of Polypropylene/Carbon Nanotubes (PP/CNTs) Nanocomposites as Potential Strain Gauges for Structural Health Monitoring

Nanomaterials ◽

10.3390/nano10040814 ◽

2020 ◽

Vol 10 (4) ◽

pp. 814 ◽

Cited By ~ 5

Author(s):

Bartolomeo Coppola ◽

Luciano Di Maio ◽

Loredana Incarnato ◽

Jean-Marc Tulliani

Keyword(s):

Carbon Nanotubes ◽

Thermo Gravimetric Analysis ◽

Tensile Tests ◽

Strain Gauges ◽

Gauge Factor ◽

Gravimetric Analysis ◽

Strain Sensing ◽

Scanning Calorimetry ◽

Impedance Variation ◽

Mechanical Tensile

Polypropylene/carbon nanotubes (PP/CNTs) nanocomposites with different CNTs concentrations (i.e., 1, 2, 3, 5 and 7 wt%) were prepared and tested as strain gauges for structures monitoring. Such sensors were embedded in cementitious mortar prisms and tested in 3-point bending mode recording impedance variation at increasing load. First, thermal (differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA)), mechanical (tensile tests) and morphological (FE-SEM) properties of nanocomposites blends were assessed. Then, strain-sensing tests were carried out on PP/CNTs strips embedded in cementitious mortars. PP/CNTs nanocomposites blends with CNTs content of 1, 2 and 3 wt% did not show significant results because these concentrations are below the electrical percolation threshold (EPT). On the contrary, PP/CNTs nanocomposites with 5 and 7 wt% of CNTs showed interesting sensing properties. In particular, the best result was highlighted for the PP/CNT nanocomposite with 5 wt% CNTs for which an average gauge factor (GF) of approx. 1400 was measured. Moreover, load-unload cycles reported a good recovery of the initial impedance. Finally, a comparison with some literature results, in terms of GF, was done demonstrating the benefits deriving from the use of PP/CNTs strips as strain-gauges instead of using conductive fillers in the bulk matrix.

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Aerosol jet printed capacitive strain gauge for soft structural materials

npj Flexible Electronics ◽

10.1038/s41528-020-00095-4 ◽

2020 ◽

Vol 4 (1) ◽

Author(s):

Kiyo T. Fujimoto ◽

Jennifer K. Watkins ◽

Timothy Phero ◽

Doug Litteken ◽

Kevin Tsai ◽

...

Keyword(s):

Strain Gauge ◽

Structural Integrity ◽

Superior Performance ◽

Strain Gauges ◽

Gauge Factor ◽

Destructive Testing ◽

Flexible Polymer ◽

Load Monitoring ◽

High Elongation ◽

Aerosol Jet Printing

AbstractSoft structural textiles, or softgoods, are used within the space industry for inflatable habitats, parachutes and decelerator systems. Evaluating the safety and structural integrity of these systems occurs through structural health monitoring systems (SHM), which integrate non-invasive/non-destructive testing methods to detect, diagnose, and locate damage. Strain/load monitoring of these systems is limited while utilizing traditional strain gauges as these gauges are typically stiff, operate at low temperatures, and fail when subjected to high strain that is a result of high loading classifying them as unsuitable for SHM of soft structural textiles. For this work, a capacitance based strain gauge (CSG) was fabricated via aerosol jet printing (AJP) using silver nanoparticle ink on a flexible polymer substrate. Printed strain gauges were then compared to a commercially available high elongation resistance-based strain gauge (HE-RSG) for their ability to monitor strained Kevlar straps having a 26.7 kN (6 klbf) load. Dynamic, static and cyclic loads were used to characterize both types of strain monitoring devices. Printed CSGs demonstrated superior performance for high elongation strain measurements when compared to commonly used HE-RSGs, and were observed to operate with a gauge factor of 5.2 when the electrode arrangement was perpendicular to the direction of strain.

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Strain sensing fabric integrated with carbon nanotube yarn for wearable applications

Textile Research Journal ◽

10.1177/0040517518807441 ◽

2018 ◽

Vol 89 (15) ◽

pp. 3048-3055

Author(s):

Wei Liu ◽

Ningjuan Liu ◽

Yang Gao ◽

Shuang Wang ◽

Qiong Cheng ◽

...

Keyword(s):

Carbon Nanotube ◽

Mechanical Performance ◽

Great Influence ◽

Gauge Factor ◽

Poly Vinyl Alcohol ◽

Wearable Electronics ◽

Strain Sensing ◽

Single Strain ◽

Sensing Properties ◽

Woven Structure

Textiles, as a desired platform for wearable smart technology, can be integrated with smart elements in the hierarchical levels of the fabric structure. In this study, a new way to make strain sensing fabric was developed by embedding a single strain sensing carbon nanotube (CNT)-based yarn into the woven structure. To overcome the abrasion during insertion, the yarn was coated with poly(vinyl alcohol) (PVA) to achieve higher mechanical performance. The gauge factor of the yarn was improved from 0.91 to 1.64. The sensing properties of CNT/PVA yarn integrated strain sensing fabric showed a gauge factor of over 1.1, a degree of linearity of more than 97% and good stability and repeatability during cyclic loading. Fabric with different integrated yarn lengths, patterns and output connections has also been investigated. The results showed that the yarn length and bend over section had a great influence on the strain sensing properties of the fabric. Furthermore, the fabric strain sensor exhibited a quick and precise response to the finger motion detection, demonstrating potential in wearable electronics.

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A Low-Cost Strain Gauge Displacement Sensor Fabricated via Shadow Mask Printing

Sensors ◽

10.3390/s19214713 ◽

2019 ◽

Vol 19 (21) ◽

pp. 4713 ◽

Cited By ~ 1

Author(s):

Ying Yi ◽

Bo Wang ◽

Amine Bermak

Keyword(s):

Strain Gauge ◽

Printed Electronics ◽

Low Cost ◽

Flexible Substrate ◽

Displacement Sensor ◽

Gauge Factor ◽

Shadow Mask ◽

Resistance Response ◽

Thermal Compression ◽

Sensing Material

This work presents a cost-effective shadow mask printing approach to fabricate flexible sensors. The liquid-state sensing material can be directly brushed on a flexible substrate through a shadow mask. The ink leakage issue which often occurs in printed electronics is addressed with a custom taping scheme. A simple thermal compression bonding approach is also proposed to package the functional area of the sensor. To verify the feasibility and robustness of the proposed fabrication approach, a prototyped strain gauge displacement sensor is fabricated using carbon ink as the sensing material and a flexible polyimide (PI) film as the substrate. Once the substrate is deformed, cracks in the solidified ink layer can cause an increased resistance in the conductive path, thus achieving function of stable displacement/strain sensing. As a demonstration for displacement sensing application, this sensor is evaluated by studying its real-time resistance response under both static and dynamic mechanical loading. The fabricated sensor shows a comparable performance (with a gauge factor of ~17.6) to those fabricated using costly lithography or inkjet printing schemes, while with a significantly lower production cost.

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Design of a CMOS readout circuit on ultra-thin flexible silicon chip for printed strain gauges

Advances in Radio Science ◽

10.5194/ars-15-123-2017 ◽

2017 ◽

Vol 15 ◽

pp. 123-130

Author(s):

Mourad Elsobky ◽

Yigit Mahsereci ◽

Jürgen Keck ◽

Harald Richter ◽

Joachim N. Burghartz

Keyword(s):

Circuit Design ◽

Flexible Electronics ◽

Strain Gauge ◽

Output Voltage ◽

High Performance ◽

Wheatstone Bridge ◽

Strain Gauges ◽

Wearable Electronics ◽

Readout Circuit ◽

Interface Circuit

Abstract. Flexible electronics represents an emerging technology with features enabling several new applications such as wearable electronics and bendable displays. Precise and high-performance sensors readout chips are crucial for high quality flexible electronic products. In this work, the design of a CMOS readout circuit for an array of printed strain gauges is presented. The ultra-thin readout chip and the printed sensors are combined on a thin Benzocyclobutene/Polyimide (BCB/PI) substrate to form a Hybrid System-in-Foil (HySiF), which is used as an electronic skin for robotic applications. Each strain gauge utilizes a Wheatstone bridge circuit, where four Aerosol Jet® printed meander-shaped resistors form a full-bridge topology. The readout chip amplifies the output voltage difference (about 5 mV full-scale swing) of the strain gauge. One challenge during the sensor interface circuit design is to compensate for the relatively large dc offset (about 30 mV at 1 mA) in the bridge output voltage so that the amplified signal span matches the input range of an analog-to-digital converter (ADC). The circuit design uses the 0. 5 µm mixed-signal GATEFORESTTM technology. In order to achieve the mechanical flexibility, the chip fabrication is based on either back thinned wafers or the ChipFilmTM technology, which enables the manufacturing of silicon chips with a thickness of about 20 µm. The implemented readout chip uses a supply of 5 V and includes a 5-bit digital-to-analog converter (DAC), a differential difference amplifier (DDA), and a 10-bit successive approximation register (SAR) ADC. The circuit is simulated across process, supply and temperature corners and the simulation results indicate excellent performance in terms of circuit stability and linearity.

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Performance Characteristics of Additively Printed Strain Gauges Under Different Conditions of Temperature and High Stress Loads

10.1115/ipack2021-74074 ◽

2021 ◽

Author(s):

Pradeep Lall ◽

Tony Thomas ◽

Jinesh Narangaparambil

Keyword(s):

Strain Gauge ◽

High Stress ◽

Consumer Electronics ◽

Performance Characteristics ◽

Curing Temperature ◽

Strain Gauges ◽

Gauge Factor ◽

Direct Write ◽

Commercial Strain ◽

Silver Ink

Abstract Applications of printed sensors have increased to industrial, consumer electronics, and medical fields with the advancements in the technology of printing and the adaptability of ink. These sensors are used to monitor a variety of measurements, including temperature, humidity, strain, and sweat, with different systems. This paper studies the performance characteristics of additively printed strain sensors using a nScrypt machine with a direct-write printing technique. The ink used in this study is silver ink which is thermally cured and also has a solderable property. The thermal curing temperature and trace width of the printed silver trace is optimized for better performance in the strain measurements, shear load to failure, and resistivity. Once the printing characteristics of the trace are defined, strain gauges are printed on printed wiring boards (PWB) and are tested at different loading and temperature environments. The sustainability and repeatability of the sensor measurements at high-stress conditions are studied using combined temperature and vibration loads of up to 50 degrees Celsius and 10g acceleration levels. The strain characteristics of the printed strain gauges are studied by comparing them to a commercial strain gauge at a similar position on the test substrate. The repeatability and variation of the strain profile are studied with different conditions of temperature and acceleration conditions at different time instants during vibration. The gauge factor of the printed strain gauge is quantified using a 3-point bending experiment with printed and commercial strain gauges at symmetrical locations of the substrate.

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High Degree of Freedom Hand Pose Tracking Using Limited Strain Sensing and Optical Training

Volume 1B: 38th Computers and Information in Engineering Conference ◽

10.1115/detc2018-85870 ◽

2018 ◽

Author(s):

Wentai Zhang ◽

Jonelle Z. Yu ◽

Fangcheng Zhu ◽

Yifang Zhu ◽

Nurcan Gecer Ulu ◽

...

Keyword(s):

American Sign Language ◽

Strain Gauge ◽

Strain Gauges ◽

Support Vector ◽

Leap Motion ◽

Strain Sensing ◽

Joint Angles ◽

Linear Quadratic ◽

Feed Forward Neural Network ◽

Pose Tracking

The ability to track human operators’ hand usage when working in production plants and factories is critically important for developing realistic digital factory simulators as well as manufacturing process control. We propose an instrumented glove with only a few strain gauge sensors and a micro-controller that continuously tracks and records the hand configuration during actual use. At the heart of our approach is a trainable system that can predict the fourteen joint angles in the hand using only a small set of strain sensors. First, ten strain gauges are placed at the various joints in the hand to optimize the sensor layout using the English letters in the American Sign Language as a benchmark for assessment. Next, the best sensor configurations for three through ten strain gauges are computed using a support vector machine classifier. Following the layout optimization, our approach learns a mapping between the sensor readouts to the actual joint angles optically captured using a Leap Motion system. Three regression methods including linear, quadratic and neural regression are then used to train the mapping between the strain gauge data and the corresponding joint angles. The final proposed model involves four strain gauges mapped to the fourteen joint angles using a two-layer feed-forward neural network.

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Giant gauge factor of Van der Waals material based strain sensors

Nature Communications ◽

10.1038/s41467-021-22316-8 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Wenjie Yan ◽

Huei-Ru Fuh ◽

Yanhui Lv ◽

Ke-Qiu Chen ◽

Tsung-Yin Tsai ◽

...

Keyword(s):

Carrier Mobility ◽

Large Range ◽

Van Der Waals ◽

High Sensitivity ◽

Strain Sensors ◽

Strain Gauges ◽

Gauge Factor ◽

Proof Of Concept ◽

High Flexibility ◽

Small Deformations

AbstractThere is an emergent demand for high-flexibility, high-sensitivity and low-power strain gauges capable of sensing small deformations and vibrations in extreme conditions. Enhancing the gauge factor remains one of the greatest challenges for strain sensors. This is typically limited to below 300 and set when the sensor is fabricated. We report a strategy to tune and enhance the gauge factor of strain sensors based on Van der Waals materials by tuning the carrier mobility and concentration through an interplay of piezoelectric and photoelectric effects. For a SnS2 sensor we report a gauge factor up to 3933, and the ability to tune it over a large range, from 23 to 3933. Results from SnS2, GaSe, GeSe, monolayer WSe2, and monolayer MoSe2 sensors suggest that this is a universal phenomenon for Van der Waals semiconductors. We also provide proof of concept demonstrations by detecting vibrations caused by sound and capturing body movements.

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Anisotropic, Wrinkled, and Crack-Bridging Structure for Ultrasensitive, Highly Selective Multidirectional Strain Sensors

Nano-Micro Letters ◽

10.1007/s40820-021-00615-5 ◽

2021 ◽

Vol 13 (1) ◽

Author(s):

Heng Zhang ◽

Dan Liu ◽

Jeng-Hun Lee ◽

Haomin Chen ◽

Eunyoung Kim ◽

...

Keyword(s):

Rational Design ◽

Full Range ◽

Human Motion ◽

Strain Sensors ◽

Gauge Factor ◽

Wearable Electronics ◽

Trade Off ◽

Human Motion Detection ◽

Sensing Applications ◽

Anisotropic Structures

AbstractFlexible multidirectional strain sensors are crucial to accurately determining the complex strain states involved in emerging sensing applications. Although considerable efforts have been made to construct anisotropic structures for improved selective sensing capabilities, existing anisotropic sensors suffer from a trade-off between high sensitivity and high stretchability with acceptable linearity. Here, an ultrasensitive, highly selective multidirectional sensor is developed by rational design of functionally different anisotropic layers. The bilayer sensor consists of an aligned carbon nanotube (CNT) array assembled on top of a periodically wrinkled and cracked CNT–graphene oxide film. The transversely aligned CNT layer bridge the underlying longitudinal microcracks to effectively discourage their propagation even when highly stretched, leading to superior sensitivity with a gauge factor of 287.6 across a broad linear working range of up to 100% strain. The wrinkles generated through a pre-straining/releasing routine in the direction transverse to CNT alignment is responsible for exceptional selectivity of 6.3, to the benefit of accurate detection of loading directions by the multidirectional sensor. This work proposes a unique approach to leveraging the inherent merits of two cross-influential anisotropic structures to resolve the trade-off among sensitivity, selectivity, and stretchability, demonstrating promising applications in full-range, multi-axis human motion detection for wearable electronics and smart robotics.

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Optimum Strain Gauge Application to Bladed Assemblies

Volume 4: Turbo Expo 2002, Parts A and B ◽

10.1115/gt2002-30306 ◽

2002 ◽

Cited By ~ 1

Author(s):

J. Szwedowicz ◽

S. M. Senn ◽

R. S. Abhari

Keyword(s):

Strain Gauge ◽

Element Model ◽

Strain Gauges ◽

Structural Components ◽

Algorithm Optimization ◽

Rotating Blades ◽

Novel Approach ◽

Present Technique ◽

Optimization Function ◽

Rotating Impeller

Optimum placements of the strain gauges assure reliable vibration measurements of structural components such as rotating blades. Within the framework of cyclic vibration theory, a novel approach has been developed for computation of the optimum gauge positions on tuned bladed discs regarding the determined sensitivity, orthogonality, gradient and distance criteria. The utilized genetic algorithm optimization tool allows for an effective numerical search of suitable solutions of the defined optimization function. A rotating impeller disc represented by a cyclic finite element model demonstrates the application of this method. The present technique can be easily applied to other structural components requiring optimal strain gauge instrumentation.

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