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A comparison between Ecoflex and polydimethylsiloxane (PDMS) substrate: Ecoflex substrate at (a) non-stretched state and (b) stretched state. PDMS substrate at (c) non-stretched state and (d) stretched state.
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In this paper, we proposed a stretchable radio frequency (RF) sensor to detect strain direction and level. The stretchable sensor is composed of two complementary split ring resonators (CSRR) with microfluidic channels. In order to achieve stretchability, liquid metal (eutectic gallium-indium, EGaIn) and Ecoflex substrate are used. Microfluidic cha...
Contexts in source publication
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... Ecoflex is suitable for stretchable applications. Figure 1 shows that an Ecoflex substrate with 1 mm thickness has higher stretchability than a PDMS substrate with 1 mm thickness. Recently, there have been many studies for stretchable applications using Ecoflex [19][20][21]. ...
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... L is stretching length. Figure 10a shows the measured resonant frequencies when the fabricated sensor is stretched along +x and −x direction from −22.86% to +22.86%. When L is increased from 0% to 22.86% along +x direction, the resonant frequency is decreased from 2.03 to 1.78 GHz. ...
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... L is increased from 0% to 22.86% along −x direction, the resonant frequency is decreased from 3.63 to 3.13 GHz. Figure 10b The frequency change (∆f ) is defined as ...
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... L is stretching length. Figure 10a shows the measured resonant frequencies when the fabricated sensor is stretched along +x and −x direction from −22.86% to +22.86%. When L is increased from 0% to 22.86% along +x direction, the resonant frequency is decreased from 2.03 to 1.78 GHz. ...
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... L is increased from 0% to 22.86% along −x direction, the resonant frequency is decreased from 3.63 to 3.13 GHz. Figure 10b,c show the frequency change (∆f ) versus stretching length for CSRR #1 and #2, respectively. The relationship is linear and their fitted curves are y = 11.25x ...
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... 7.175 (MHz/%) and y = 24x + 1.36 (MHz/%), respectively. Figure 10d shows the relative frequency change (∆f /f 0 ) versus strain level from 5.72% to 22.86% for each CSRR. The sensitivity is also indicated as maximum 0.0192 mm −1 . ...
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... sensitivity is also indicated as maximum 0.0192 mm −1 . Figure 10. Experimental characterization of the proposed sensor under tension: (a) resonant frequency versus stretching length along +x and −x direction; (b) frequency change (Δf) when only CSRR #1 is stretched from 2.86% to 22.86%; and (c) frequency change (Δf) when only CSRR #2 is stretched from 2.86% to 22.86%; and (d) relative frequency change (Δf/f0) of CSRR #1 and #2. ...
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Citations
... The EAGS pad model consists of electrodes, PVC sheet (base), silicone layer and PET with PUA (gecko-inspired skin). The dielectric constants of the materials are: ϵ air = 1 [31], ϵ PVC = 4 [32], ϵ PET = 3.5 [33], ϵ PUA = 5.5 [34] and ϵ Ecoflex 00−30 = 2.8 [35]. The heat map shows the electric potential distribution for the EAGS and EA pad models under electrical stimulation with 3 kV. ...
Soft robotic manipulators have been increasingly adopted over the last decade due to their passive conformation to the shapes of objects, which can reduce control complexity. The performance of these grippers can be improved using flexible adhesive skins that increase tactile gripping forces, which is particularly important when grasping delicate objects and flexible substrates that are otherwise difficult to manipulate. In this work, we investigate how passive gecko-inspired fibrillar adhesion can be augmented by actively controlled electroadhesion (EA). The passive gecko-inspired skin (GS) enables adhesion with no power consumption while EA is controlled with an applied voltage. We have shown how the microstructures in a gecko-inspired adhesive skin affect EA by using numerical simulation to quantify how they influence the localized EA field strength. The results show that the microstructures cause a highly non-uniform distribution of electric field strength generate and hence the EA force distribution is inhomogeneous. Overall, it was found that the dielectric properties of the gecko-inspired skin reduce the magnitude of field intensity on the adhesive contact surface by only 2.1% at 3 kV. It is experimentally determined that when compared with GS alone, EA with gecko-inspired skin increases the shear force by 66.8% and the normal force by 53.7% with an applied voltage of 4 kV. It is shown that the gecko skin’s adhesion force is enhanced by increased engagement of the fibrillar microstructure to object surfaces due to EA. The increased contact engagement is experimentally demonstrated using frustrated total internal reflection imaging. This work shows that electroadhesive-enhanced gecko-inspired skin generates a greater adhesive force than the sum of forces from the separate gecko-inspired skin and EA. In this way, electrically controllable and passive adhesion mechanisms can be combined to improve the handling of flexible and delicate objects with smooth or rough surfaces.
... The dielectric permittivity derived from measurement varied between 3.15 and 3.0 at frequencies ranging from 1 GHz to 10 GHz. We used a value of 3 in the simulation, in good agreement with other studies and measurements [19,[33][34][35]. Towards a more realistic case, and to study the effect of inhomogeneous interfaces on the transmission properties of realistic stretchable transmission lines, a second set of simulations (#2 in table 2) was performed in which the metal layer was embedded between the flexible substrate and air, as depicted in figure 5(a). ...
Elastic, bendable and stretchable electronics establish a new and promising area of multi-physics engineering for a variety of applications, e.g. on wearables or in complex-shaped machine parts. While the area of metamorphic electronics has been investigated comprehensively, the behavior at radio frequencies (RFs), especially in the GHz range, is much less well studied. The mechanical deformation of the soft substrates, for instance, due to stretching, changes the geometrical dimensions and the electrical properties of RF transmission lines. This effect could be desirable in some cases, e.g. for smart devices with shape-dependent transmission or radiation characteristics, or undesirable in other cases, e.g. in feed and distribution networks due to the variable electrical lengths and thus phase variations. This contribution describes the results of a systematic study of the broadband RF properties of coplanar transmission lines on Ecoflex® substrates, based on numerical simulations and experimental data. Two types of stretchable transmission line structures were studied: Meander- and circular ring-segmented lines. Modeling and simulation were performed combining a 2D circuit simulation software with electromagnetic full-wave simulations. The experimental part of the work included the fabrication of metamorphic substrates metallized with thin copper layers and systematic measurements of the electrical lengths and phase constants of coplanar waveguides in the frequency range from 1 to 5 GHz based on vector network analysis for different stretching levels. With the given substrate technology, we succeeded in demonstrating stretchability up to a level of 21%, while the theoretical limit is expected at 57%. The meander- and circular-shaped line structures revealed markedly different sensitivities to the stretching level, which was lower for circular structures compared to the meander structures by approximately a factor of three.
... This process took ∼4 h to be finished. Through several treatment cases and studies of the bolus material [12,31], Ecoflex™ 0030 (Smooth On, Inc., Easton, PA, USA) [31][32][33] was selected to construct the patientspecific boluses using 3DP and CNC molds. Mass density of the bolus material was 1.105 g/cm 3 , and its Hounsfield unit was set to 120 [31]. ...
The patient-specific bolus fabricated by a mold-and-cast method using a 3D printer (3DP) and silicon rubber has been adopted in clinical practices. Manufacturing a mold using 3DP, however, can cause time delays due to failures during the 3D printing process. Thereby, we investigated an alternative method of the mold fabrication using computer numerical control (CNC) machine tools. Treatment plans were conducted concerning a keloid scar formed on the ear and nose. The bolus structures were determined in a treatment planning system (TPS), and the molds were fabricated using the same structure file but with 3DP and CNC independently. Boluses were then manufactured using each mold with silicone rubbers. We compared the geometrical difference between the boluses and the planned structure using computed tomography (CT) images of the boluses. In addition, dosimetric differences between the two measurements using each bolus and the differences between the measured and calculated dose from TPS were evaluated using an anthropomorphic head phantom. Geometrically, the CT images of the boluses fabricated by the 3DP mold and the CNC mold showed differences compared to the planned structure within 2.6 mm of Hausdorff distance. The relative dose difference between the measurements using either bolus was within 2.3%. In conclusion, the bolus made by the CNC mold benefits from a stable fabricating process, retaining the performance of the bolus made by the 3DP mold.
... In the past twenty years, the integration of small-resonant metamaterial particles, in the form of split-ring resonators (SRRs) [11] or complementary split-ring resonators (CSRRs) [12,13], in planar microwave transmission lines has led to numerous developments of and enhancements to sensory elements and devices in many applications, including but not limited to radio frequency microwave circuits, and materials' characterization and classification [14][15][16][17]. Complementary SRR can be regarded as a quasi-static resonator when its dimension is electrically small as compared with the operating wavelength of the excitation electromagnetic field. ...
This paper presents for the first time the design of a microwave sensing setup for the potential monitoring and identification of red palm weevil (RPW) gender type. The microwave sensor consists of a planar two-port transmission line (TL) with a single complementary split-ring resonant (CSRR) inclusion etched from the bottom metallic layer. The CSRR sensor is placed on top of a customized non-conductive container. The microwave sensing setup was designed, numerically demonstrated, fabricated and tested experimentally. Simulated results correlate quite well with the experimental data. Moreover, the sensitivity of the CSRR sensor when in close proximity to different RPW genders was evaluated both numerically and experimentally. Based on the measured results from 15 RPW samples with different body sizes, different RPW gender types showed unique microwave signatures. A notable shift in the sensor’s resonance frequency was achieved, where on average a resonant frequency shift of 10% for adult RPWs was achieved, while a 2.4% frequency change was obtained for larvae (young) RPWs. Hence, the proposed microwave sensing setup can be adopted in field trials to examine and differentiate between various RPW genders at various developmental stages.
... In comparison to other substrates like glass and silicon, which lack the flexibility of paper and polydimethylsiloxane (PDMS), paper offers a cost advantage over both. Additionally, while PDMS exhibits good flexibility, it is comparatively more expensive than paper [26,27]. Further comparisons between different substrates are presented in Table 1. ...
Gas, ion, and biological sensors have been widely utilized to detect analytes of great significance to the environment, food, and health. Paper-based sensors, which can be constructed on a low-cost paper substrate through a simple and cost-effective fabrication process, have attracted much interests for development. Moreover, many materials can be employed in designing sensors, such as metal oxides and/or inorganic materials, carbon-based nanomaterials, conductive polymers, and composite materials. Most of these provide a large surface area and pitted structure, along with extraordinary electrical and thermal conductivities, which are capable of improving sensor performance regarding sensitivity and limit of detection. In this review, we surveyed recent advances in different types of paper-based gas, ion, and biological sensors, focusing on how these materials' physical and chemical properties influence the sensor's response. Challenges and future perspectives for paper-based sensors are also discussed below.
... In the past twenty years, the integration of small-resonant metamaterial particles, in the form of split-ring resonators (SRRs) [11] or complementary split-ring resonators (CSRRs) [12], in planar microwave transmission lines have led to numerous developments and enhancement to sensory elements and devices in many applications, including but not limited to radio frequency microwave circuits, materials characterization and classification [14][15][16][17]. Complementary SRR can be regarded as a quasi-static resonator, when its dimension is electrically small as compared with the operating wavelength of the excitation electromagnetic field. ...
This paper presents for the first time the design of a microwave sensing setup for the potential monitoring and identification of red palm weevil (RPW) gender type. The microwave sensor consists of a planar two-port transmission line (TL) with a single complementary split-ring resonant (CSRR) inclusion etched from the bottom metallic layer. The CSRR sensor is placed on top of a customized non-conductive container. The microwave sensing setup has been designed, numerically demonstrated, fabricated and tested experimentally. Simulated results correlate quite well with the experimental data. Moreover, the sensitivity of the CSRR sensor when in close proximity to different RPW gender has been evaluated both numerically and experimentally. Based on the measured results from 15 RPW collected samples with different body sizes, different RPW gender types showed unique microwave signatures. Notable shift to the sensor's resonance frequency has been achieved, where on average a resonant frequency shift of 10% for adult RPWs was achieved, while 2.4% frequency change was obtained for larvae (young) RPWs. Hence, the proposed microwave sensing setup can be adopted in field trials to examine and differentiate between various RPW genders at various development stages.
... [47] Furthermore, there are several work mentioning the triboelectric nanogenerators with PDMS and TPU pairing as triboelectric materials while there is no work that studies the TPU with Ecoflex pairing as triboelectric materials. Besides that, the better stretchability and biocompatibility of Ecoflex as compared to PDMS [48] and cost effectiveness of Ecoflex paved the way to investigate the triboelectric output with this material pair. Figure 1 schematically represents the facile and cost-effective fabrication process of the SER-TENG and its structural arrangement. ...
Triboelectric nanogenerators (TENGs) have demonstrated great promise especially for the realization of self‐powered biomedical sensors. Nevertheless, developing TENG sensors able to detect the broad range of biomechanical movements experienced on the human body is still a challenge. Herein, a unique ridge‐structured device sensitive to wide range of forces is reported (i.e., low‐forced pulse monitoring to high‐forced gait monitoring). The device is composed of thermoplastic polyurethane layer sandwiched between two textured silicon elastomeric layers. Compared to non‐textured surface configurations, the proposed ridged‐structure provides an increased frictional contact area between the triboelectric materials, while also acting as a spacer between the triboelectric materials. The influence of ridge dimensions on the output performance is investigated by mechanical simulations and electromechanical experimental tests. The optimized device shows a maximum peak output power and current densities of 490 mW m⁻² and 1750 µA m⁻², respectively at 30 N and 7 Hz of compressive forces. The proposed device exhibits stable electrical output for 10000 cycles. As a proof of concept, the proposed device is used as wearable sensors for monitoring pulse rate, breath patterns, and gait movements. The study suggests the possibility of utilization of novel‐structured sandwich‐type elastomer ridge‐based TENG in different aspects of biomedical sensing and smart wearable application.
... The dominant conduction mechanisms in the MIS structure can be experimentally deduced. The dielectric film in this sensor is Ecoflex 00-30 and is a silicone-based insulator with a relative permittivity of 2.8 [33]. The main parameters affecting the conduction are the barrier heights of the metal (Cu)-dielectric interface and the effective mass of the conduction carrier [34]. ...
Sensors as a composite film made from reduced graphene oxide (rGO) structures filled with a silicone elastomer are soft and flexible, making them suitable for wearable applications. The sensors exhibit three distinct conducting regions, denoting different conducting mechanisms when pressure is applied. This article aims to elucidate the conduction mechanisms in these sensors made from this composite film. It was deduced that the conducting mechanisms are dominated by Schottky/thermionic emission and Ohmic conduction.
... Nominal capacitances can be approximated to be = as under no force the sensor is essentially like a parallel plate capacitor, with a Ecoflex 00-30 polymer dielectric layer sandwiched between two copper layers ( Fig. 5(a)). The choice of dimensions of the sensor gives a rough initial capacitance of 1 , with = o = 8 * 10 −6 * 2.8 * 8.85 * 10 −12 0.2 * 10 − 3 = 0.99 , with a 2mm×4mm = 8mm 2 area sensor with 0.2mm thick dielectric layer, and the dielectric constant = 2.8 for the chosen Ecoflex 00-30 polymer [40]. However, in order to compute the exact Δ , we also need to compute ( max ), and this requires knowing the displacement caused by force, as well as the capacitance of the deformed sensor, which has a squished polymer layer ( Fig. 5(b)). ...
Any two objects in contact with each other exert a force that could be simply due to gravity or mechanical contact, such as a robotic arm gripping an object or even the contact between two bones at our knee joints. The ability to naturally measure and monitor these contact forces allows a plethora of applications from warehouse management (detect faulty packages based on weights) to robotics (making a robotic arms' grip as sensitive as human skin) and healthcare (knee-implants). It is challenging to design a ubiquitous force sensor that can be used naturally for all these applications. First, the sensor should be small enough to fit in narrow spaces. Next, we don't want to lay cumbersome cables to read the force values from the sensors. Finally, we need to have a battery-free design to meet the in-vivo applications. We develop WiForceSticker, a wireless, battery-free, sticker-like force sensor that can be ubiquitously deployed on any surface, such as all warehouse packages, robotic arms, and knee joints. WiForceSticker first designs a tiny 4~mm~~2~mm~~0.4~mm capacitative sensor design equipped with a 10~mm~~10~mm antenna designed on a flexible PCB substrate. Secondly, it introduces a new mechanism to transduce the force information on ambient RF radiations that can be read by a remotely located reader wirelessly without requiring any battery or active components at the force sensor, by interfacing the sensors with COTS RFID systems. The sensor can detect forces in the range of 0-6~N with sensing accuracy of ~N across multiple testing environments and evaluated with over 10,000 varying force level presses on the sensor. We also showcase two application case studies with our designed sensors, weighing warehouse packages and sensing forces applied by bone joints.
... where stands for the volume fraction of air and for the volume fraction of immaculate Ecoflex, where = 1 and = 2.8 [25]. The compression causes the dielectric layer's pores to gradually close, which lowers the volume percent of air and raises the volume fraction of Eco-flex. ...
Many studies have been conducted to develop electronic skin (e-skin) and flexible wearable textiles which transform into actual “skin”, using different approaches. Moreover, many reports have investigated self-healing materials, multifunctional sensors, etc. This study presents a systematic approach to embroidery pressure sensors dependent on interdigitated capacitors (IDCs), for applications surrounding intelligent wearable devices, robots, and e-skins. The method proposed a broad range of highly sensitive pressure sensors based on porous Ecoflex, carbon nanotubes (CNTs), and interdigitated electrodes. Firstly, characterizations of ICDs embroidering on a cotton fabric using silver conductive thread are evaluated by a precision LCR meter throughout the frequency range from 1 kHz to 300 kHz. The effect of thread density on the performance of embroidered sensors is included. Secondly, the 16451B dielectric test fixture from Keysight is utilized to evaluate the composite samples’ dielectric constant accurately. The effect of frequency on sensor performance was evaluated to consider the influence of the dielectric constant as a function of the capacitance change. This study shows that the lower the frequency, the higher the sensitivity, but at the same time, it also leads to instability in the sensor’s operation. Thirdly, assessing the volume fraction of CNTs on composites’ properties is enclosed. The presence of volume portion CNTs upgrades the bond strength of composites and further develops sensor deformability. Finally, the presented sensor can accomplish excellent performance with an ultra-high sensitivity of 0.24 in low pressure (<25 kPa) as well as a wide detection range from 1 to 1000 kPa, which is appropriate for general tactile pressure rages. In order to achieve high sensor performance, factors such as density, frequency, fabric substrate, and the structure of the dielectric layer need to be carefully evaluated.