Metal Strain Gauges Research Articles

Three-Dimensional Turning Force Sensor Based on a Decagonal Ring Structure: Crosstalk Mitigation Design and Performance Optimization

Abstract Real-time data acquisition using high-precision three-dimensional turning force sensors is crucial for intelligent manufacturing. However, existing sensors face challenges such as low integration levels and poor crosstalk resistance, rendering them inadequate for high-precision measurements. Theoretical analysis has demonstrated that a fully centered decagonal ring structure can effectively mitigate the effects of eccentric loading. This study focuses on designing a fully centered turning force sensor with minimal crosstalk. To achieve a balance between sensitivity and stiffness, multi-objective optimization was conducted using GWO-BP and TOP algorithms, resulting in a twofold increase in the sensitivity of the decagonal ring. The sensor design incorporates metallic strain gauges, instrumentation amplifiers, and peripheral circuits into the ring arms of the decagonal structure. Experimental results show that the sensor’s amplified sensitivities in the Fc, Ff, and Fp directions are 11.78 mV/N, 10.31 mV/N, and 1.78 mV/N, respectively. The first three natural frequencies in an unconstrained state are 2518.5 Hz, 2537.5 Hz, and 4256.4 Hz. The sensor's Fc-Fy crosstalk ranges from 0.18% to 0.88%, with noise limits for the Fc, Ff, and Fp directions of 0.035 N, 0.03 N, and 0.23 N, respectively. Cutting experiments have demonstrated that under varying spindle speeds and cutting depths, the sensor effectively detects surges in cutting force caused by rapid tool retraction, as well as other common faults.

Railroad bridge monitoring using Dragonfly® piezoelectric strain gauge

Structural Health Monitoring (SHM) applied to civil structures such as bridges, high-rise towers, and electricity pylons can help plan their maintenance, detect damages or un-expected events, and extend their remaining operating lifetime. Metallic foil strain gauge and vibrating wire are the historic sensors used to measure strain on civil structures. However, civil structures are designed to undergo little deformation in service (0.1-50 µdef). Both SG and vibrating wire are limited by their resolution around 1 µdef. Moreover, they are known for their DC drift over time, which complexifies long term monitoring. There is therefore a need for more sensitive and less prone to drift sensors in the time domain. Dragonfly new piezoelectric strain gauges, with a resolution three order of magnitude over classic sensors, solve these issues and enable new applications. Dragonfly sensors consist in an extremely thin piezoelectric ceramic packaged in a flexible PCB and pre-wired with a SMA connector. The flexible sensor is glued with cyanoacrylate glue to the object to be studied. This paper presents the implementation of Dragonfly sensors on a railroad bridge. With a single sensor, it has been possible to identify the bridge girder first two resonance using ambient noise, train passage loading for fatigue-life analysis, train passage reproducibility, and pedestrian passage on the walkway. A complete comparison with classic metallic foil strain gauge is detailed.

Strain-Modulated Flexible Bio-Organic/Graphene/PET Sensors Based on DNA-Curcumin Biopolymer.

In recent years, there has been growing interest in the development of metal-free, environmentally friendly, and cost-effective biopolymer-based piezoelectric strain sensors (bio-PSSs) for flexible applications. In this study, we have developed a bio-PSS based on pure deoxyribonucleic acid (DNA) and curcumin materials in a thin-film form and studied its strain-induced current-voltage characteristics based on piezoelectric phenomena. The bio-PSS exhibited flexibility under varying compressive and tensile loads. Notably, the sensor achieved a strain gauge factor of 407 at an applied compressive strain of -0.027%, which is 8.67 times greater than that of traditional metal strain gauges. Furthermore, the flexible bio-PSS demonstrated a rapid response under a compressive strain of -0.08%. Our findings suggest that the proposed flexible bio-PSS holds significant promise as a motion sensor, addressing the demand for environmentally safe, wearable, and flexible strain sensor applications.

Effect of mechanical strain on lateral photovoltaic effect in n‐3C‐SiC/n‐Si hetorjunction Toward mechanical strain sensors capable of photoenergy harvesting

It is beneficial to have sensors capable of harvesting photoenergy in the era of Internet of Things (IoT) and 5 G integrated infrastructure. In this paper, we report the piezo-optoelectronic coupling characteristic of n-type 3C‐SiC/n‐type Si heterostructure and demonstrate it with a mechanical strain sensing device capable of harvesting photoenergy. The device is capable of generating a photovoltage as high as 3.4 mV when illuminated by a laser power as small as 10 μW, i.e. four times higher than similar sensors in previous studies. In addition, the strain sensitivity ΔV/V/ε ratios are 9.94 and 13.11 for tensile and compressive strain, respectively, which are five times better than conventional metal strain gauges. These findings contribute to the overall understanding of the piezo-optoelectronic coupling effect of SiC/Si heterojunction paving the way for the development of multifunctional sensors with light harvesting capabilities.

Inkjet-Printed Multiwalled Carbon Nanotube Dispersion as Wireless Passive Strain Sensor.

In this study, a multiwalled carbon nanotube (MWCNT) dispersion is used as an ink for a single-nozzle inkjet printing system to produce a planar coil that can be used to determine strain wirelessly. The MWCNT dispersion is non-covalently functionalized by dispersing the CNTs in an anionic surfactant, namely sodium dodecyl sulfate (SDS). The fabrication parameters, such as sonication energy and centrifugation time, are optimized to obtain an aqueous suspension suitable for an inkjet printer. Planar coils with different design parameters are printed on a flexible polyethylene terephthalate (PET) polymer substrate. The design parameters include a different number of windings, inner diameter, outer diameter, and deposited layers. The electrical impedance spectroscopy (EIS) analysis is employed to characterize the printed planar coils, and an equivalent electrical circuit model is derived based on the results. Additionally, the radio frequency identification technique is utilized to wirelessly investigate the read-out mechanism of the printed planar MWCNT coils. The complex impedance of the inductively coupled sensor undergoes a shift under strain, allowing for the monitoring of changes in resonance frequency and bandwidth (i.e., amplitude). The proposed wireless strain sensor exhibits a remarkable gauge factor of 22.5, which is nearly 15 times higher than that of the wireless strain sensors based on conventional metallic strain gauges. The high gauge factor of the proposed sensor suggests its high potential in a wide range of applications, such as structural health monitoring, wearable devices, and soft robotics.

Nanoscale strain gauges on flexible polymer substrates

Biological cell force is important for proper cell and tissue function and can be an indicator of disease. Therefore, measuring cell force has potential in disease diagnosis and treatment. However, biological cell force measurement approaches are limited and typically slow due to the analysis of optical images before and after cell application or other methods that have low throughput. This work seeks to overcome this bottleneck by the use of nanoscale strain gauges which can measure cell forces as an electrical signal in real time, as well as being able to be scaled to measure tens of thousands of cells, simultaneously. This paper presents the design, COMSOL simulation, fabrication, as well as electrical and mechanical testing of gold nanometer scale strain gauges embedded in soft polydimethylsiloxane (PDMS) using a sacrificial aluminum layer method. A process flow using an aluminum sacrificial layer is presented, which successfully fabricated gold strain gauges with 100 nm dimensions in soft PDMS polymer and have been used to measure strain applied to the PDMS surface. Compressive strains ranging from 0.4% to 1.7% in the PDMS surface, corresponding to forces of 718 nN to 2.0 μN have been detected with resistance changes of 1%–8%. To the best of our knowledge, these are the smallest metal strain gauges to be made on soft polymers and is a promising new approach for biological cell force measurement.

Quartz crystal based sensor head design and analysis for robot torque sensor application

Background: Background: In recent years, with the gradual development of robot human-computer interaction, robots need to meet the precise control of more complex movements. Torque sensors play an important role. The traditional sensor uses metal strain gauge as the sensing element, which makes the sensor slow in response and low in resolution. In view of the shortcomings of strain gauge sensor, a sensor with cut quartz square as the sensing head is proposed. Methods: In order to study the quartz square sensitive head, COMSOL56 simulation modeling was first used to obtain the stress ratio relationship between the square quartz chip and the circular quartz chip. The formula for calculating the force frequency coefficient of the circular quartz chip was modified based on the ratio coefficient, and the formula for calculating the force frequency coefficient of the square quartz chip was obtained. The feasibility of the formula was verified through practical experiments; Secondly, theoretical simulation and experimental research were conducted on the buckling limit force of quartz chips, and the calculation formula for the buckling limit force during the installation process of quartz chips was revised, laying the foundation for the theoretical design of quartz sensors; Finally, the designed sensitive head is installed on the elastomer structure for verification; In order to collect frequency signals at a sampling rate of 1000Hz, the frequency signal output by the square quartz sensitive head is mixed, filtered, and amplified to form a 3.3V square wave between peaks. The frequency signal is collected by STM32. Conclusion: the test shows that the sensor with square quartz chip as the sensor head has a range of 150Nm, a sensitivity of 350 Hz / Nm, a linearity of 98.14%, a hysteresis of 0.51%, a repeatability of 98.44% and a resolution of 0.02%.

Development of High Dynamic Range Six-Axis Force Sensor with Simple Structure

We propose a six-axis force sensor with a simple structure that can measure small forces while affording a high load capacity. For a robot to perform complex motions in an unknown environment, the force sensor used must exhibit a high resolution and high load rating. Various studies have been conducted to simultaneously satisfy these two requirements. However, the high processing cost due to the complicated sensor structure is problematic. Therefore, we develop a column-type high dynamic range (HDR) six-axis force sensor using two types of strain gauges. The sensor was composed of a drawn pipe to solve structural problems that arise during manufacturing. By attaching strain gauges to the surface of the drawn pipe, the forces and torques in the six axes can be measured. HDR measurement was realizable using a semiconductor strain gauge for small loads and a metallic foil strain gauge for large loads. Based on the simulation results, the rated loads of the sensor were 1400 N in the Fx and Fy directions, 9000 N in the Fz direction, and 120 Nm in the Mx, My, and Mz directions. The performance of the fabricated force sensor was evaluated. The maximum nonlinearity errors of the semiconductor strain gauge and the metallic foil strain gauges were 1.21% and 1.81%, respectively. In addition, when comparing the S/N ratios, the minimum measurable values were 0.035 N and 0.13 N for Fy and Fz, respectively.

SiOC-Based Strain Gauge with Ultrahigh Piezoresistivity at High Temperatures

The nonlinear response of strain gauges at high temperatures has restricted their applications despite their high-precision and real-time measurement capability. This work addresses this limitation by utilizing the easy preparative access and versatility of silicon oxycarbide-based (SiOC) thin films as strain gauges offering outstanding high-temperature robustness and giant piezoresistive response. The sensitivity of the strain gauge is assessed with continuous cyclic loads, tensile and compressive, resulting in gauge factors of ca. 2000–5000. The linearity of the response is preserved up to 700 °C with a shift in the electrical response occurring at temperatures beyond 500 °C, switching the SiOC film from semiconducting to conducting behavior. This change causes a drop in the gauge factor of the SiOC-based thin films; nevertheless, it is still significantly higher than that of metallic and Si-based commercial strain gauges. Notably, the studied thin films can regulate the effect of temperature enabling them to be a highly sensitive device with good reversibility and replicability in high-temperature environments. Furthermore, the electrical shift at 460 °C broadens the application of the SiOC film as a current-limiting device and temperature sensor.

Rotation Grids for Improved Electrical Properties of Inkjet-Printed Strain Gauges.

We report an image data driven approach for inkjet printing (IJP) to improve the electrical properties of printed metallic strain gauges (SGs). The examined SGs contain narrow conducting paths of multiple orientations and therefore suffer from two challenges: 1. The printing direction of inkjet printed conducting paths has an impact on film formation and electrical properties. 2. A loss-free rotation algorithm for IJP image data is lacking. New ways of IJP image data processing are required to compensate for quality-reducing effects. Novel grid types in terms of loss-free rotation algorithms are introduced. For this purpose, a new grid (e.g., 45° tilted) with a different grid constant is placed over a given pixel grid in such a way that all cell centers of the given pixel grid can be transferred to the rotated grid. Via straightening the tilt, the image data is rotated without interpolation and information loss. By applying these methods to measurement gratings of a full bridge with two perpendicular grating orientations, the influence on the manufacturing quality is investigated. It turns out that the electrical detuning of full bridges can be reduced by one order of magnitude compared to state-of-the-art printing by using so-called diagonal rotation grids.

Quartz crystal based sensor head design and analysis for robot torque sensor application

Background: In recent years, with the gradual development of robot human-computer interaction, robots need to meet the precise control of more complex motion. Torque sensors play an important role. The traditional strain gauge sensor uses a metal strain gauge as the sensitive element, which means that the sensor has a slow response, low resolution and can easily be affected by external signal noise. Aiming at these deficiencies of strain gauge sensors, a sensor with cutting quartz square sheet as the sensor head is proposed. Methods: In order to study the application of quartz square sensing head in the sensor, firstly, COMSOL (5.6) simulation modeling is used to obtain the stress relationship between square quartz sheet and circular quartz sheet. Then the calculation formula of the force frequency coefficient of the circular quartz sheet is modified to obtain the calculation formula of the force frequency coefficient of the square quartz sheet, and the feasibility of the formula is verified by practical experiments. Next, the theoretical simulation and experimental research on the buckling limit force of quartz wafer are carried out, and the formula of buckling limit force in the process of quartz wafer installation is modified. Finally, the designed sensitive head is installed on the elastomer structure for verification. The frequency signal is collected by SGS-THOMSON Microelectronics 32 with a sampling rate of 1000Hz. Results: The main performances of the sensor are range 150nm, sensitivity 350Hz / nm, linearity 98.14%, hysteresis 0.51%, repeatability 98.44%, resolution 0.02%. Conclusions: As the sensitive unit of the torque sensor, the designed quartz wafer can obtain high response time and high resolution, solve the problems of low resolution and slow response time of the traditional strain gauge torque sensor, and reduce the use cost of the sensor.

The Strain Sensitivity of Coal Reinforced Smart Concrete by Piezoresistive Effect

The structures are challenged by earthquakes, material degradations and other environmental factors. In order to protect the lives, assets, and for maintenance planning, structural health monitoring (SHM) is important. In SHM applications, strain gages are widely used which have low durability, low sensitivity while they have high cost. To monitor a structure, large number of strain gages have to be used that increases the cost. In this study, seven coal reinforced concrete mixtures with 0, 0.35, 0.5, 0.8, 1, 1.5 and 2 volume % of coal were designed; three cubic samples for each mixture were fabricated. Simultaneous strain and electrical resistance measurement of the samples during the compression test was conducted. A strong linear piezoresistive relationship between strain and electrical resistance change with a correlation coefficient of 0.99 was determined. The concrete mixture having 0.8 volume % coal had the highest strain sensitivity of K=44, which was 22 times the strain sensitivity of commercial metal strain gages while it had a linearity error of LE=6.9% that was low. This mixture with 0.8 volume % coal is a candidate to be smart concrete which can sense its strain. As a contribution to the literature, a phenomenological model for the relationship between gage factor and coal volume % was explained in details. The multifunctional smart concrete will be used as a smart material, which can sense its strain in SHM applications while acting as a load bearing material.

High Dynamic Range 6-Axis Force Sensor Employing a Semiconductor–Metallic Foil Strain Gauge Combination

This letter proposes a force sensor that combines semiconductor strain gauges and metallic foil strain gauges to present force information of a higher dynamic range to robots. The strain gauges have different sensitivities, with semiconductor strain gauge sensitivity being approximately 90-fold than that of the metallic foil strain gauges. Using this difference in sensitivity, large forces and small forces are both detected through the two types of strain gauges and high dynamic range force detection is achieved by combining the output signals of these two. It was confirmed from the SN ratio test that the proposed sensor has a measurement range from 0.005 N to 1000 N, the maximum load. The dynamic range is 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\times 10^5$</tex-math></inline-formula> , extending the dynamic range of the 6-axis force sensor with the highest range in previous studies two-fold.

Laboratory measurements with DAS: A fast and sensitive tool to obtain elastic properties at seismic frequencies

Forced-oscillation stress-strain laboratory measurements are increasingly employed to obtain elastic and viscoelastic properties of rocks at seismic frequencies. Yet these measurements are time-consuming and expensive, due in part to the use of metal or semiconductor strain gauges, which need to be glued to the sample. Such gauges are fragile, have relatively low sensitivity, and measure very local strain only so the measurements can be affected by a slight misalignment of the system assembly and local heterogeneity of the rock. The emergence of fiber-optic distributed acoustic sensing (DAS) technology provides an alternative means of measuring strain. Strain measurements with DAS involve winding an optical fiber around the sample multiple times and connecting it to a DAS recording unit. Pilot experiments performed using this setup on a range of rocks and materials show good agreement with strain gauge measurements. Advantages of DAS over strain gauges include much higher strain sensitivity (down to 10−11) and signal-to-noise ratio (and hence, shorter time required for measurements), larger dynamic range, ability to measure average (rather than local) strain in the sample, and robustness at elevated temperatures. Although the pilot experiments demonstrate the potential of DAS for rock physics measurements, further research and improvement of the proposed methodology are required to obtain independent estimates of Young's modulus and Poisson's ratio and to port the system into a pressure vessel to obtain rock properties under in-situ conditions.

Triple mode and multi-purpose flexible sensor fabrication based on carbon black and thermoplastic polyurethane composite with propolis

This study reports the design, fabrication, and application of strain and tactile sensors molded with Carbon Black (CB)/Thermoplastic Polyurethane (TPU) composite ink into flexible-soft 3D printed TPU substrate. In sensor design, three different geometries, namely Straight Line/Zigzag/Wavy, are produced to investigate the effect on the sensing behavior. 3D printed molds are preferred due to their low cost and simplicity in fabrication. Additionally, propolis, which is antibacterial and has therapeutic properties for wound and fungal diseases, is added to the composite material to benefit its healing and protective properties. The sensing properties of propolis are investigated for its use as mixing and coating materials. According to electrical characterization, the fabricated structures can be used in triple mode as piezoresistive, piezocapacitive, and piezoinductive sensors. The gauge factor (GF) values for sensors using different ratios of materials varies between 3 and 10. Given conventional metallic strain gauges whose GF is typically around 2, the obtained GF values are remarkable. The distribution of the applied stress on the sensor surface is given by simulations. In addition, the characteristic changes of the samples according to the frequency are examined, and equivalent circuits are provided.

Evaporation of Ti/Cr/Ti Multilayer on Flexible Polyimide and Its Application for Strain Sensor.

A flexible Ti/Cr/Ti multilayer strain gauge have been successfully developed based on polyimide substrate. The pure Ti metal strain gauge have shown the hysteresis phenomenon at the relationship between resistance and strain during tensile test. The experimental results of multilayer strain gauge show that adding Cr interlayer can improve the recovery and stability of the sensing electrode. When the interlayer Cr thickness was increased from 0 to 70 nm, the resistance decreased from 27 to 8.8 kΩ. The gauge factor (GF) value also decreased from 4.24 to 2.31 with the increase in the thickness of Cr interlayer from 30 to 70 nm, and the hysteresis phenomenon disappeared gradually. The multilayer Ti/Cr/Ti film has feasible application for strain sensor.

Characterization of a tactile sensor using a small, embedded strain gauge

In recent years, tactile sensors comprising flexible materials have been studied for soft robotics. Several conventional tactile sensors are based on a microchannel filled with liquid metal, for flexibility. In this study, we proposed a soft tactile sensor that is vertically embedded with a liquid metal strain gauge in an elastomer using a narrow wire mold. Despite the narrow and small design, the strain gauge can detect an applied force. In addition, the design has the potential to be arrayed in a dense setting. In this study, we evaluated our proposed tactile sensor with a single strain gauge and confirmed its sensing capability.

Creep adjustment of strain gauges based on granular NiCr-carbon thin films

Abstract. An important property of high-precision mechanical sensors such as force transducers or torque sensors is the so-called creep error. It is defined as the signal deviation over time at a constant load. Since this signal deviation results in a reduced accuracy of the sensor, it is beneficial to minimize the creep error. Many of these sensors consist of a metallic spring element and strain gauges. In order to realize a sensor with a creep error of almost zero, it is necessary to compensate for the creep behavior of the metallic spring element. This can be achieved by creep adjustment of the used strain gauges. Unlike standard metal foil strain gauges with a gauge factor of 2, a type of strain gauges based on sputter-deposited NiCr-carbon thin films on polymer substrates offers the advantage of an improved gauge factor of about 10. However, for this type of strain gauge, creep adjustment by customary methods is not possible. In order to remedy this disadvantage, a thorough creep analysis is carried out. Five major influences on the creep error of force transducers equipped with NiCr-carbon thin-film strain gauges are examined, namely, the material creep of the metallic spring element (1), the creep (relaxation) of the polymer substrate (2), the composition of the thin film (3), the strain transfer to the thin film (4), and the kind of strain field on the surface of the transducer (5). Consequently, we present two applicable methods for creep adjustment of NiCr-carbon thin- film strain gauges. The first method addresses the intrinsic creep behavior of the thin film by a modification of the film composition. With increasing Cr content (at the expense of Ni, the intrinsic negative creep error can be shifted towards zero. The second method is not based on the thin film itself but rather on a modification of the strain transfer from the polyimide carrier to the thin film. This is achieved by controlled cutting of well-defined deep trenches into the polymer substrate via a picosecond laser.

A Simple Model Relating Gauge Factor to Filler Loading in Nanocomposite Strain Sensors.

Conductive nanocomposites are often piezoresistive, displaying significant changes in resistance upon deformation, making them ideal for use as strain and pressure sensors. Such composites typically consist of ductile polymers filled with conductive nanomaterials, such as graphene nanosheets or carbon nanotubes, and can display sensitivities, or gauge factors, which are much higher than those of traditional metal strain gauges. However, their development has been hampered by the absence of physical models that could be used to fit data or to optimize sensor performance. Here we develop a simple model which results in equations for nanocomposite gauge factors as a function of both filler volume fraction and composite conductivity. These equations can be used to fit experimental data, outputting figures of merit, or predict experimental data once certain physical parameters are known. We have found these equations to match experimental data, both measured here and extracted from the literature, extremely well. Importantly, the model shows the response of composite strain sensors to be more complex than previously thought and shows factors other than the effect of strain on the interparticle resistance to be performance limiting.

Characterization of MWCNTs-polystyrene nanocomposite based strain sensor

The usage of nano phase materials for strain sensing applications has attracted attention due to their unique electromechanical properties. The nanocomposite as piezo-resistive films provides an alternative for the realization of strain sensors with high sensitivity than the conventional sensors based on metal and semiconductor strain gauges. In this work, polymer based nano-composite with carbon nanotubes as filler were developed. The multi-walled carbon nanotubes/polystyrene (MWCNTs/PS) nano-composite films were prepared with different wt.% of CNTs using solution mixing method. Field emission scanning electron microscopy technique was carried out to investigate the morphology and dispersion of CNTs in the nano-composite sample. Fourier transform infrared spectroscopy technique was employed to characterize the bonds present in the prepared nano-composite. The electrical response of the composite films was recorded in the form of current-voltage (I-V) characteristics using source meter. The electromechanical response of the nano-composite films with different wt.% of filler CNTs was recorded by applying uni-axial tensile load. The electromechanical responses were then analyzed to obtain gauge factor for the strain sensitivity. The highest gauge factor of 133 was recorded during tensile testing of the nano-composite with 3 wt.% of CNTs fillers.