Electromechanical Characterization Research Articles

Mechanical Deformation Effects on Flexible Thin Film Transistors: A Comparison Between 6,13‐Bis(Triisopropylsilylethynyl)Pentacene and N,N′‐Bis‐(2‐Ethylhexyl)‐1,7‐Dicyanoperylene‐3,4:9,10‐bis(Dicarboximide) Derivatives

AbstractIn this work, the investigation of the surface strain‐induced electrical changes in two commonly employed solution‐processable organic semiconductors, i.e., 6,13‐bis(triisopropylsilylethynyl)pentacene (TIPS‐Pentacene) and N,N′‐bis‐(2‐ethylhexyl)−1,7‐dicyanoperylene‐3,4:9,10‐bis(dicarboximide) (N1400), is reported. A detailed electromechanical characterization of two sets of flexible organic field‐effect transistors is performed, clearly demonstrating that both systems are affected by mechanical deformation in terms of electrical performance. However, the N1400 system shows a much more stable and reproducible response, even after continuous mechanical stress. XRD and AFM analysis demonstrate that such difference is mainly related to the changes induced on the two thin film morphology by the applied deformations.

Dielectric Elastomer Generators: Recent Advances in Materials, Electronic Circuits, and Prototype Developments

The ongoing climate crisis requires innovative methods to maximize renewable and sustainable energy resources. There have been advancements in harvesting energy from ambient motions such as wind, ocean waves, and human movements. Dielectric elastomer generators (DEGs) are a promising option for energy harvesting due to their high energy density and compatibility with low‐frequency oscillations. This review provides an in‐depth overview of DEGs, including electroactive materials, electromechanical characterization, electronics for harvesting, interfacing circuits, prototypes, and challenges. DEGs have the potential to play a significant role in decarbonizing energy for both small‐ and large‐scale applications using ambient energy sources.

Shock value: advancing sustainable sensing materials

Shock value: advancing sustainable sensing materials Biomolecular crystals have emerged as exciting new sustainable piezoelectrics. Currently, little research is focused on developing these crystals as reliable, solid-state sensors to integrate into conventional electronic devices due to their water solubility, uncontrolled growth, variable response and electroding difficulties. Pb-FREE is taking on the challenge of accelerating the design, growth, and engineering of these novel piezoelectric materials through high-throughput computational screenings, novel crystal growth procedures, and standardised electromechanical characterisation and packaging.

Dynamic electromechanical characterizations of poly(vinylidene fluoride) based nanocomposite films on ultra‐low modulus polymer substrate

AbstractThis article explores the electromechanical performance of poly(vinylidene fluoride) (PVDF) films with silver nanoplatelets on smooth polydimethylsiloxane (PDMS) substrates. PVDF, a semi‐crystalline polymer, shows piezoelectric properties when processed at low temperatures, making it ideal for energy harvesting and sensors. This research addresses a gap by examining high strain rate and complex electromechanical characteristions of PVDF composites, which are underexplored. Films, fabricated using a non‐vacuum rod coating method, underwent dynamic electromechanical tests (strain rate ~ 2 s−1), including stretching, twisting, combined stretching and twisting, and forced vibrations. Results show the films function up to 17% applied strain with a gage factor of 10.57. In twisting tests, the laminates perform up to 387° in slow twisting (gage factor = 28.34) and 341° in fast twisting (gage factor = 7.65). Combined stretching and twisting tests show performance decreases, with functionality up to 6.24% strain at a twist angle of 330.1°. Vibration tests reveal that increased amplitude reduces performance, with the laminates enduring frequencies between 4.35 and 12.14 Hz. The films also exhibit a linear piezoelectric response, with a maximum open circuit voltage of 37.2 V under an impact load of 1112 N, underscoring the potential of PVDF/Ag nanocomposites for advanced MEMS applications.

Three-dimensional free-standing heterostructures out of MoS2 and rGO with infused PDMS towards electromechanical pressure sensing

Abstract The behavior of two-dimensional (2D) materials constructed as three-dimensional structures is studied to bring such materials one step closer to the real-life application. Lattices structures of gyroid triply periodic minimal surface (TPMS) were fabricated out of 2D materials, namely, molybdenum disulfide (MoS2), and reduced graphene oxide (rGO), forming for the first time free-standing MoS2 (FSM) lattice and free-standing hetero-structural lattice of MoS2 and rGO (FSH) out of TPMS. These 2D materials were also integrated with polydimethylsiloxane (PDMS) elastomer, forming FSM/PDMS and FSH/PDMS composites. Mechanical characterization, including compression and cyclic tests, were conducted on FSM, FSH, and the composites. Additionally, electromechanical characterization was conducted to evaluate the sensing potential of these structures. It is worth noting that the elastic modulus of the 10 unit-cells with either FSM or FSH was higher than the other lattices of the same type. FSH tends to have a higher modulus at 1504.4 kPa in the 10 unit-cells. This modulus is even higher at 3 MPa when PDMS is added to the FSH lattice. Due to the brittle fracture, FSM or FSH lattices follow the layer-by-layer failure mechanism. Samples with PDMS are more stable towards such cyclic tests without noticeable failures or a decrease in elastic modulus. Finally, the 10 unit-cell lattices of FSH/PDMS composite have the highest conductivity at 2.5 mA, and a comparable sensitivity at 0.365 kPa−1 over the range of 0–100 kPa.

An intrinsic electromechanical design method for MXene-based electrodes of ultra-highly sensitive and stable pseudocapacitive pressure device

To achieve the optimal performances of flexible pressure devices, the current approaches typically involve extensive experimental trials. However, such methods lack guidance from theoretical models in a positive fashion, not only introducing unpredictability and uncertainty into results but also potentially limiting the applicability of any achieved advancements to the alternative material systems. Here, an electrical-mechanical design model, combining density functional theory and molecular dynamics simulations, was proposed for calculating the specific capacitance and mechanical strength of various modified MXene films. Based on which, the optimal hybrid film entailed the cross-linking of holey reduced graphene oxide and MXene via cysteamine was prepared. This film, upon electromechanical characterizations, has effectively overcome the issues of MXene self-stacking and brittleness, thus validating the conclusions of theoretical predictions. Subsequently, the proposed film was integrated as electrode into a pseudocapacitive pressure sensor, achieving highly sensitivity (∼143,258 kPa−1) and mechanical stability (with capacitance drift below 1.2 % after 10,000-repeated test). Ultimately, the fabricated sensors were developed into sound collection system and robotic skins, respectively, to achieve recognition of distinctive sounds and stable perception of gravity. The calculation-based approach holds enormous potential for the design of two-dementional materials-based pressure sensors.

Multiscale Fabrication and Characterization of a NEMS Force Sensor

AbstractThis study investigates the fabrication and characterization of an innovative nanoelectromechanical system force sensor that utilizes suspended submicron silicon nanowires for detecting multi‐axis forces in the micro‐newton range. The sensor combines microscale shuttle platforms with nanowire piezoresistors along with retaining springs. Its fabrication involves a rather involved set of Si deep etching, doping, metallization, release, and encapsulation processes on silicon‐on‐insulator wafers. Electromechanical characterization demonstrates sensor reliability under mechanical strains up to the level of 10% as well as gauge factor measurements. Dynamic response analysis confirms a high resonant frequency of 12.34 MHz with a quality factor of 700 in air, closely matching simulation results. Thermal characterization of the sensor reveals a Temperature Coefficient of Resistance of 6.4 × 10⁻⁴ °C⁻¹. Sensor characterization under jet flow reveals its ability to detect strong flows demonstrating a resistance change of as much as 2.02% under sustained gas flow through a nozzle. Sensor integration into the gas flow measurement setup demonstrates its versatility in detecting small forces, paving the way for further exploration of thermomechanical factors. Combined with its miniature footprint, the sensor's electromechanical performance hints at applications in the analysis of velocity gradients in microscale flows including micro/nano diffusers and nozzles in small satellite propulsion.

Laser-Induced Graphene Strain Sensors for Body Movement Monitoring.

To enable the development of artificial intelligence of things, the improvement of the strain sensing mechanisms and optimization of the interconnections are needed. Direct laser writing to obtain laser-induced graphene (LIG) is being studied as a promising technique for producing wearable, lightweight, highly sensitive, and reliable strain sensors. These devices show a higher degree of flexibility and stretchability when transferred to an elastomeric substrate. In this article, we manufactured polydimethylsiloxane (PDMS)-encapsulated LIG piezoresistive strain sensors with a quasi-linear behavior and a gauge factor of 111. The produced LIG was morphologically characterized via Raman spectroscopy and scanning electron microscopy before and after the electromechanical characterization and before and after the LIG transfer to PDMS. The results from these analyses revealed that the integrity of the material after the test was not affected and that the LIG volume in contact with the substrate increased after transfer and encapsulation in PDMS, leading to the improvement of the sensor performance. The sensors' capability for measuring bend angles accurately was demonstrated experimentally, making them useable in a wide range of applications for human body movement monitoring as well as for structural health monitoring. Regarding body monitoring, a PDMS-encapsulated LIG sensor for knee bending angle detection was proposed. This device showed unaffected performance of 1500 cycles under 8% uniaxial deformation and with response times in the range of 1-2 s.

Electromechanical characterization of 3–2 ceramic-air composites

In this study, a type 3–2 ceramic-air composite was designed, and the impact of varying thicknesses on its electromechanical properties was analyzed. Initially, finite element simulation software was employed to model type 3–2 ceramic-air composites of differing thicknesses. This modeling facilitated the determination of resonance and anti-resonance frequencies, calculation of effective electromechanical coupling coefficients, and assessment of frequency discrepancies corresponding to each thickness. Subsequently, type 3–2 ceramic-air composites of various thicknesses were fabricated using the reverse cutting method. The experimental results corroborated the simulation outcomes, demonstrating consistency. In the final analysis, the performance parameters of conventional type 1–3 piezoelectric composites were evaluated alongside those of type 3–2 composites. Findings indicated an improvement of 0.8 in the thickness electromechanical coupling coefficient for type 3–2 composites compared to conventional type 1–3 composites. Consequently, type 3–2 composites show promise for the development of highly sensitive piezoelectric transducers.

Electromechanical and ferroelectric hysteresis in dense and porous PZT-type piezoceramics

In the present study, particular aspects of the large-signal switching properties and electromechanical hysteresis of the lead zirconate titanate (PZT)-type porous piezoceramics were studied in comparison with the dense piezoceramics of the same composition. Large-signal ferroelectric polarization and strain hysteresis loops were recorded at the bipolar electric fields in the range of 0 ÷ 5 kV/mm and in the frequency range of 0.01 ÷ 5 Hz. Measurements and analysis were performed by means of the electromechanical measurement system (STEPHV) and electromechanical response characterization program (STEP), combining large-signal modeling of the mechanical and electrical behavior of ferroelectric materials.

Electromechanical properties of uniaxial polar ionic plastic crystal [(C2H5)4N][FeBrCl3

Abstract Ferroelectric plastic crystals are an emerging class of materials that combine room temperature ferroelectricity and piezoelectricity with a high temperature plastic mesophase prior to melting. These materials offer possibilities for accessing different property parameter spaces from the state-of-the-art metal oxide and polymer ferroelectrics. Tetraethylammonium bromotrichloroferrite, [(C2H5)4N][FeBrCl3], has a unipolar wurtzite-like structure and thus may have potential for small but stable piezoelectric coefficients like the iso-symmetrical AlN. In this study, density functional theory was used to compute elastic compliance, piezoelectric coefficients, and dielectric constant values. Single crystals grown from aqueous solutions were evaluated via single crystal synchrotron x-ray diffraction, impedance spectroscopy and high and weak-field electromechanical characterization. Diffraction studies revealed that the anion tetrahedra orientated preferentially so that the Br− ion had a 30% alignment with the polarization vector. Electromechanical measurements found piezoelectric coefficients in the 5–9 pC N−1 and pm V−1 range. The piezoelectric coefficient (d 33) was most stable with 3.4% variation between 0.4 and 90 Hz and 0.5 and 3 V. Additional piezoelectric stability measurements were made as a function of DC bias field and temperature. Impedance measurements indicate contributions from either intrinsic effects unique to ionic plastic crystals, such as molecular rotation, or the extrinsic effect of electrode interfaces, both of which can play a role in the electromechanical response of the materials. The results show that [(C2H5)4N][FeBrCl3] has potential as a small signal piezoelectric that has a softer elastic moduli than AlN but a stiffer moduli than polyvinylidene fluoride, and thus occupies a unique parameter space.

Chemical modification of lead zirconate titanate piezoceramics through cold-sintering process

This study presents a facile strategy to chemically modify the PZT through the cold-sintering process. The presence of lead oxide phases in the XRD patterns of samples cold-sintered at 290 °C confirms the dissolution of Pb ions from the surface of PZT particles. Post-annealing the samples at 900 °C resulted in a phase pure material with a perovskite structure, wherein the Ba ions had diffused into the lattice of PZT. The post-annealed samples had a multi-faceted grain with equilibrated triple points and a relative density of ∼93%. The electromechanical characterization showed that the d33 of the samples increased with increasing content of Ba in the PZT, reaching a value of 201 ± 80 pm/V. The post-annealed samples displayed ferroelectric switching current behaviors with saturated polarisation loops. The experimental findings reported in this study highlight the potential of the cold-sintering process for chemical modification of lead zirconate titanate electroceramics.

Textile-based strain sensors for fiber-reinforced composites under tension, compression and bending

Abstract This research addresses the challenging task of monitoring the structural integrity of fiber-reinforced composite (FRC) components under complex loading conditions. Ensuring the safety and functionality of these components is critical but economically challenging. Therefore, this study presents an innovative approach using textile-based strain sensors that are cost-effective and structurally compatible with carbon fiber-reinforced plastic (CFRP) components. The investigation includes the systematic electromechanical characterization and comparison of four different sensor materials at the yarn and composite scale in various test scenarios. Cyclic tensile, compression, and bending tests of CFRP specimens are performed and show good reproducibility of sensor signals within the elastic range, with significant agreement observed with applied strain measurement methods, particularly in tensile tests. Although there are minor deviations in compression and bending evaluations, the signals are still meaningful for in-situ detection of complex loading patterns, crack initiation, and structural failure. The study demonstrates that the integration of textile-based sensor yarns allows for continuous structural health monitoring (SHM) of CFRP components under various loading scenarios, including tensile, bending, and especially compressive loads.

Carbon black silicone composite in surgical simulation—A detailed electromechanical characterization

The integration of advanced materials into surgical simulators has revolutionized medical training. In this study, a detailed characterization of carbon black silicone composites specifically designed as soft sensor material in hybrid surgical simulators including a hyper visco plasto elastic model is performed. Carbon black-silicone composites offer unique properties such as flexibility, softness and electrical conductivity, making them ideal for integration into synthetic tissue imitations in simulators. These sensors provide real-time feedback on tissue deformation, improving the realism and evaluation capability of surgical simulations. The comprehensive, closed-form material model enables detailed analysis of the composite’s mechanical and electrical behavior, accounting for viscoelasticity, plasticity and hyperelasticity. The application of this model provides insights into the behavior of the conductive composite in different sensory scenarios, which facilitates the development of more realistic simulators.

Fabrication and Electromechanical Characterization of Silicon Nanomechanical Membrane Flexure MEMS Sensor for Gas Sensing Applications

Fabrication and Electromechanical Characterization of Silicon Nanomechanical Membrane Flexure MEMS Sensor for Gas Sensing Applications

Electro-Mechanical Characterisation and Damage Monitoring by Acoustic Emission of 3D-Printed CB/PLA.

Even though the influence of the printing direction on the mechanical properties of 3D-printed samples by fused filament fabrication is established in the literature, very little is known about mechanical and electrical coupling. In this study, electrically conductive polylactic acid filled with carbon black particles undergoes monotonic and repeated progressive tensile loading to better understand the influence of the printing direction on the electro-mechanical properties of three-dimensional-printed samples. The objective is to analyse the electro-mechanical behaviour of this composite for its potential application as an actuator. The classical laminate theory is also applied to evaluate the relevance of this theory in predicting the mechanical characteristics of this material. In addition, a comprehensive damage analysis is performed using acoustic emission, infrared thermography, scanning electron microscopy, and X-ray microcomputed tomography imaging. Results show that the degradation of the mechanical and electrical properties is highly influenced by the printing direction. The appearance and development of crazes in 0° filaments are highlighted and quantified. The conclusions drawn by this study underline the interest in using longitudinal and unidirectional printing directions to improve the conductive path within the samples. Furthermore, the evolution of the resistance throughout the experiments emphasizes the need to control the implemented voltage in the design of future electro-thermally triggered actuators.

High-Frequency Linear Array (20 MHz) Based on Lead-Free BCTZ Crystal.

Centimeter-sized BaTiO3-based crystals grown by top-seeded solution growth from the BaTiO3-CaTiO3-BaZrO3 system were used to process a high-frequency (HF) lead-free linear array. Piezoelectric plates with (110)pc cut within 1° accuracy were used to manufacture two 1-3 piezo-composites with thicknesses of 270 and [Formula: see text] for resonant frequencies in air of 10 and 30 MHz, respectively. The electromechanical characterization of the BCTZ crystal plates and the 10-MHz piezocomposite yielded the thickness coupling factors of 40% and 50%, respectively. We quantified the electromechanical performance of the second piezocomposite (30 MHz) according to the reduction in the pillar sizes during the fabrication process. The dimensions of the piezocomposite at 30 MHz were sufficient for a 128-element array with a 70- [Formula: see text] element pitch and a 1.5-mm elevation aperture. The transducer stack (backing, matching layers, lens, and electrical components) was tuned with the characteristics of the lead-free materials to deliver optimal bandwidth and sensitivity. The probe was connected to a real-time HF 128-channel echographic system for acoustic characterization (electroacoustic response and radiation pattern) and to acquire high-resolution in vivo images of human skin. The center frequency of the experimental probe was 20 MHz, and the fractional bandwidth at -6 dB was 41%. Skin images were compared against those obtained with a lead-based 20-MHz commercial imaging probe. Despite significant differences in sensitivity between elements, in vivo images obtained with a BCTZ-based probe convincingly demonstrated the potential of integrating this piezoelectric material in an imaging probe.

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Aerosol Jet Printing of Strain Sensors for Soft Robotics

The field of soft robotics is rapidly progressing toward applications including; wearable electronics, prosthetics, and biomedical devices. This is leading to demand for flexible, embedded high‐performance strain sensors to deliver real‐time feedback on the static configurations and dynamic motions of these robotic devices, to ultimately enable the levels of autonomous control and structural monitoring required for intelligent manipulation. Herein, aerosol jet printing (AJP) technology is utilized to generate arbitrary piezoresistive strain sensor layouts on fibrous paper suitable for direct integration into elastomeric soft robots. A custom graphene nanoplatelet ink with a viscosity of around 2.70 cP has been formulated for optimized atomization and patterning of conductive traces via AJP. Single and multilayer printing onto different paper substrates are explored; with the nominal resistance of the printed tracks varying from 272 to 4900 kΩ depending on paper type and number of layers. Maximum gauge factors of 24.2 ± 1.8 and 56.5 ± 4.5 are determined for sensor surfaces under tensile and compression modes, respectively. To demonstrate the possibility for direct integration of this approach for soft robotics, strain sensors are directly printed onto the strain‐limiting layer of a pneumatic soft robotic gripper, to provide continuous feedback of the gripper over curvatures up to 80 m−1.

Soft composite actuators of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene)-based nanofibers and polydimethylsiloxane: Fabrication, electromechanical characterization, and dynamic modeling

Nanofibrous unimorph cantilever beam soft actuators offer remarkable advantages, such as rapid viscoelastic relaxation, low power consumption, and high weight-specific properties. However, the presence of high porosity in the nanofibrous active layer poses a challenge due to its low breakdown voltage, limiting the practical applications of this class of soft actuators. This study proposes an innovative solution to enhance the relative permittivity of the nanofibrous layer by redesigning it as a composite layer. By integrating electrospun aligned nanofibers of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) into a polydimethylsiloxane elastomeric matrix, the composite active layer achieves a notable increase in relative permittivity (10.5 at 100 Hz), surpassing the individual materials' values (2.5 and 2.7 at 100 Hz for the nanofibers and polydimethylsiloxane, respectively). To realize novel soft actuators, the composite active layer is placed between carbon black electrodes, with Kapton® serving as the passive layer. Remarkably, aligning the nanofibers in the transversal direction of the actuator enhances its actuation capabilities significantly. When subjected to a 25 MVm−1 electric field, the tip deflection and blocking force exhibit a ∼400% improvement compared to polydimethylsiloxane-based actuators. To support these findings, a physics-based dynamic model is derived and validated through experimental tests in both static and transient time simulations.