Linear Strain Sensor Research Articles

Achieving a Wide-Range Linear Piezoresistive Response in Electrowritten Soft-Hard Polymer Blends via Salami-Inspired Heterostructure Design.

Flexible electronics capable of acquiring high-precision signals are in great demand for the development of the internet of things and intelligent artificial. However, it is currently a challenge to simultaneously achieve high signal linearity and sensitivity for stretchable resistive sensors over a wide strain range toward advanced application scenarios requiring high signal accuracy, e.g., sophisticated physiological signal discrimination and displacement measurement. Herein, a film strain sensor, which has an electrical and mechanical dual heterostructure, was fabricated via a direct near-field electrowriting and molecule-guided in situ growth of silver nanoparticles with different concentrations on high-modulus polystyrene domains and low-modulus styrene-butadiene copolymers with a salami-like morphology. Mechanism analyses from both theoretical and experimental investigations reveal that the salami-like heteromodulus microstructure regulates microcrack propagation routes, while the heteroconductivity changes the electron transport paths and amplifies the resistance increase during crack propagation. Therefore, the as-designed strain sensor shows a linear resistive response within ca. 70% strain with a gauge factor of 25, unveiling a simple and scalable strategy for trading off signal linearity and sensitivity over a wide strain range for the fabrication of high-performance linear strain sensors.

Linear Strain Sensors via a Spatial Heteromodulus Tricontinuous Structure Design for High-Resolution Recording of Snoring Breath.

Porous conductive elastomer composites are very attractive for designing flexible and air-permeable mechanical sensors for healthcare, while it is challenging to achieve a linear and sensitive electromechanical response over a wide strain range for high-resolution recording of physiological activities and body motions. Here, a scalable strategy is developed to construct porous elastomer composites with a bamboo-shaped heteromodulus microstructure in the pores for the fabrication of linear stretchable strain sensors. Such a spatial heteromodulus microstructure is fabricated via phase separation and selective location of high-modulus phase during melt compounding of elastomers and thermoplastics, together with green etching of the water-soluble plastic in the tricontinuous elastomer composites. The bamboo-shaped heteromodulus microstructure is constructed on the pore struts via the fracture of a high-modulus polymer self-assembled on the pore surface and relaxation recovery of the elastomer matrix after prestretching, which blocks the propagation of cut-through microcracks upon stretching. The composites with super low resistance after in situ growth of silver nanoparticles sustain up to 110% tensile strain with a linear and sensitive electromechanical response, demonstrating potential applications in discriminating respiration status and monitoring snoring breath. This work unveils a new approach to fabricate high-performance air-permeable strain sensors in a simple and scalable way.

Highly adhesive chitosan/poly(vinyl alcohol) hydrogels via the synergy of phytic acid and boric acid and their application as highly sensitive and widely linear strain sensors.

In recent years, flexible strain sensors have attracted increasing interest, and accurate sensing and comfortable wearables are highly demanded. However, current flexible strain sensors fail to have wide linearity and high sensitivity simultaneously, and their adhesion is insufficient for convenient wear and precise motion monitoring. Herein, chitosan/poly(vinyl alcohol) hydrogels with phytic acid (PA) and boric acid (BA) as crosslinkers (CS/PVA-PA-BA hydrogels) were fabricated. The synergy of phytic acid and boric acid not only improved the mechanical properties of the obtained hydrogels (1070% of fracture strain and 0.83 MPa of fracture stress), but also provided them with outstandingly strong adhesion. Their adhesive strength was up to 527 kPa for a variety of materials, including glass, silica rubber, steel, polytetrafluoroethylene (PTFE), and skin. In addition, the hydrogel-based strain sensor demonstrated high sensitivity (gauge factor = 4.61), a wide linear strain range (up to 1000%, R2 = 0.996), fast response time (90 ms), and good stability. A flexible strain sensor with such high sensitivity and wide linear range simultaneously, to the best of our knowledge, has never been reported before. The development of CS/PVA-PA-BA hydrogels is expected to inspire a novel method for high-adhesive and high-sensing-performance wearable electronics.

Bionic Multifunctional Wide-Range Linear Strain Sensor, Achieving Underwater Motion Monitoring and Weather Condition Monitoring

Bionic Multifunctional Wide-Range Linear Strain Sensor, Achieving Underwater Motion Monitoring and Weather Condition Monitoring

Unidirectional, highly linear strain sensors with thickness-engineered conductive films for precision control of soft machines

By drop-casting conductive inks onto the soft 3D printed surfaces, strain sensors of spatially-varying thickness mimicking the inherent surface undulation of the substrate are fabricated with a gauge factor of 151 over a linear strain range of ε = 97%.

A Study on MoS₂ Nanolayer Coated Etched Fiber Bragg Grating Strain Sensor

In this paper, we report on the comprehensive study on Molybdenum disulfide (MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) nanolayer coated etched Fiber Bragg Grating (eFBG) strain sensor. MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanolayer is coated using Physical Vapor Deposition (PVD) of Molybdenum (Mo) on eFBGs followed by sulfurization of the same in an inert atmosphere at 450° C. Such coating technique provides a direct control over the coating thickness of MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , thereby enabling a study based on the effect of nanolayer coating thickness on the intrinsic strain sensitivity as well as the power of the back reflected Bragg wavelength of eFBG in the 0.78eV spectral region. High uniformity of MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanolayer coating ensures consistent, repeatable and highly linear FBG strain sensors with a correlation coefficient of 0.988 in the range of 0 to 2500 με. A maximum intrinsic strain sensitivity of ~6.65 pm/με with a resolution of ~150 nε have been achieved with optimized MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> coated eFBG sensors. This kind of consistent, highly sensitive and linear strain sensors when incorporated with proper packaging schemes can be particularly useful for applications demanding high sensitivity of FBG sensors such detection of seismic vibrations, underwater acoustic signals, low amplitude accelerations, etc.

An Ultra-Stretchable and Highly Sensitive Photoelectric Effect-Based Strain Sensor: Implementation and Applications

High performance strain sensors have recently attracted considerable attention because of their applications in human motion detection, soft robotics, and human-machine interface. However, it remains some challenges in achieving satisfactory features (e.g., high sensitivity, high stretchable, linearity, and easy fabrication) for soft strain sensors. Inspired by the working principle of the eye's adaptation to different light luminance, this paper presents an ultra-stretchable, highly sensitive and high linear strain sensor based on the photoelectric effect. The sensor has a simple structure which is made of light-emitting diode (LED), photosensitive element, silicone rod, and sensor shell. When the silicone rod is stretched, the light's shielding area becomes larger, causing the increase of light luminous received by the photosensitive element. Hence, the sensitivity of the sensor can be tuned by changing luminance of LED and the amplification factor. Experiments demonstrate that the sensor has a high sensitivity (the maximum gauge factor was 1050), wide strain-sensing range (the max sensing range was up to 800%), high linearity range (from 100% to 300%), good repeatability (decreased by 5.48% over 5000 cycles at the wide tensile strain of 0 - 300%), low drift, and high signal-to-noise ratio (over 60dB). The proposed strain sensor has been applied in the bending detection of the wrist and finger, the recording of the human moving patterns, and the human's pulse counting. The sensor can be further fabricated into a data glove for detecting the human hand movement.

Distributed modular temperature-strain sensor based on optical fiber embedded in laminated composites

A smart structure based on carbon fiber reinforced polymer (CFRP) embedding optical fibers is proposed for distributed sensing in structural health monitoring. The proposed CFRP package provides mechanical protection to the optical fiber, enables temperature-strain discrimination, and also facilitates the sensor's installation to secure reliable measurements. Experimental results verify a linear strain sensor response with temperature compensation, agreeing well with the response of strain gauges and the expected theoretical behavior. The smart structure can be used by gluing it on the surface of the monitored structure or by embedding it as one of the layers used during manufacturing big composite structures.

Linear strain sensor made of multi-walled carbon nanotube/epoxy composite

In this study, a fabrication process was developed to make the multi-walled carbon nanotubes/epoxy (MWCNT/EP) composite films. The electrical-strain behaviour of the films in direct and alternating current circuits were both tested. It is found that the direct current resistance and the dielectric loss tangent of the MWCNT/EP composite films are dependent on the strain and the weight fraction of the carbon nanotubes. In an alternating current circuit, the test frequency affects the impedance and the phase angle of the composite film, but it has nothing to do with the change ratio of the dielectric loss tangent of the film in tension. This phenomenon can be interpreted by a proposed equivalent circuit model. Experiment results show that the change rate of the dielectric loss tangent of the MWCNT/EP sensor is linearly proportional to the strain. The findings obtained in the present study provide a promising method to develop ultrasensitive linear strain gauges.

Gum Sensor: A Stretchable, Wearable, and Foldable Sensor Based on Carbon Nanotube/Chewing Gum Membrane.

Presented in this work is a novel and facile approach to fabricate an elastic, attachable, and cost-efficient carbon nanotube (CNT)-based strain gauge which can be efficiently used as bodily motion sensors. An innovative and unique method is introduced to align CNTs without external excitations or any complicated procedure. In this design, CNTs are aligned and distributed uniformly on the entire chewing gum by multiple stretching and folding technique. The current sensor is demonstrated to be a linear strain sensor for at least strains up to 200% and can detect strains as high as 530% with a high sensitivity ranging from 12 to 25 and high durability. The gum sensor has been used as bodily motion sensors, and outstanding results are achieved; the sensitivity is quite high, capable of tracing slow breathing. Since the gum sensor can be patterned into various forms, it has wide applications in miniaturized sensors and biochips. Interestingly, we revealed that our gum sensor has the ability to monitor humidity changes with high sensitivity and fast resistance response capable of monitoring human breathing.

Elastomeric Ionic Hydrogel Sensor for Large Strains

An elastomeric hydrogel membrane containing dissolved salt is demonstrated to be a linear strain sensor for large strains up to 25%. AC sensing circuitry allows the ionic conductor to function as a sensor without polarization effects. The homogeneous gel is shown to be lacking a relaxation or hysteresis response found in the soft composite piezoresistors that are commonly used for large strain sensing. This allows operation of the sensor with minimal post-processing and increased accuracy during real-time operation. The gauge factor of the gel sensor is shown to be near two, consistent with the observation that the strain sensing of the material is solely derived from the deformation of the bulk. The very low Young's modulus of the gel (~1 kPa) allows deformation of a fabric substrate to be followed without significantly constraining the fabric. A prototype sleeve that uses these sensors for proprioceptive sensing of joint angle motion on a robotic arm is demonstrated as a potential application. Water loss from the hydrogel due to evaporation from the surface is slow. We show that the resulting trend in the impedance of the sensor can be easily corrected by simple signal processing.

Theory of the recoverable linear strain sensor and its application in geomechanics : Azzam, R; Yuen, S Rock Mech Rock EngngV22, N1, Jan-March 1989, P51–63

Theory of the recoverable linear strain sensor and its application in geomechanics : Azzam, R; Yuen, S Rock Mech Rock EngngV22, N1, Jan-March 1989, P51–63

The theory of the recoverable linear strain sensor and its application in geomechanics

After introducing the new linear strain sensors and the theory behind their modus operandi, the paper discusses in general the performance characteristics as well as the potential value of their application in geomechanics. Application features and effects of application environments are then outlined and examples of practical applications are given.