Printed Bidirectional Stretch Antenna Sensor

In this study, finite element modelling (FEM) is used to estimate the stresses induced by the package on a high precision silicon resonator. A link between the induced stresses and strains at different temperatures and the shift in the resonance frequency is presented. In order to accentuate the effects of the package on the resonance frequency of the resonators a double clamped beam vibrating in a flexural mode was designed. The resonance frequency can be shifted dramatically by the mechanical stress induced by the package; however, those stresses can be used to compensate the shift in resonance frequency due to the intrinsic temperature dependence of silicon. In order to prove the package design, a full 3D FEM of a O-level package containing a square Lame mode resonator is studied. Modelling results show that this resonator and package design is almost insensitive to the package deformation.

Thermoplastic polyurethane (TPU) is a highly elastic linear polymer composed of soft segments, usually flexible polyester, or polyether. It is widely used in 3D printing technologies, being FFF the most common technique. However, stiffness and hardness values of 3D printed TPU in filament form are higher than would be desirable for some applications, which require softer parts. Therefore, it was seen necessary to find a new methodology for 3D printing soft TPU. In this way, the present study seeks to be the first research study that focuses on the possibility of 3D printing TPU using DIW (Direct Ink Writing) technology with UV light. Firstly, the optimal 3D printing and curing parameters to print soft TPU are determined and then two different TPU formulations are 3D printed. Then, both bulk and 3D printed TPU samples were characterized in terms of shear strength using the Warner-Bratzler shear test and hardness using the Shore hardness test. It was seen that the 3D printed samples showed higher softness than bulk samples compared to TPU filament. Finally, it was concluded that the 3D printing of TPU is challenging due to several points: (1) the viscosity of the TPU; (2) their main issue is their sticky behavior; and (3) the shrinkage which takes place after the thermal treatment and for some applications, it might be a problem. Despite that, TPU appears to be a promising material to be used in different industrial applications.

TPU/CNTs flexible strain sensor with auxetic structure via a novel hybrid manufacturing process of fused deposition modeling 3D printing and ultrasonic cavitation-enabled treatment

The adhesion in 3D-printed composites between dissimilar layers was investigated in response to demand for multimaterial prints. Previously, we reported on the thermal properties for printability of thermoplastic polyurethane (TPU) blends~\cite{harris001}. Here, we report the qualitative and quantitative adhesion properties between commonly-printed materials, acrylonitrile butadiene styrene (ABS) or acrylonitrile styrene acrylate (ASA), and flexible TPU. ASTM D1002/D3164 lap shear adhesion tests were performed to measure the adhesion strength between the acrylonitrile plastics and TPU, finding values of $4.7~\mathrm{MPa}$ between ABS and TPU and $6.4~\mathrm{MPa}$ between ASA and TPU. These values are on the same order of magnitude of reported commercial adhesives, suggesting that multimaterial 3D printing can provide an automated, industrially-relevant alternative to handmade fabrication. SEM images are reported to show the quality of adhesion between materials in the composites. These images expose qualitative differences in the interlayer adhesion between materials in the composites that depend on the \textit{order of printing}. Thermal (DSC and TGA) and rheological characterizations were performed to investigate the processing conditions of the extruded plastics while they are in their melt states. The role of viscosity is shown to have major implications on the adhesion, as materials with lower viscosities displayed improved filling of the interlayer voids and increased strength of adhesion.

Two designs of flexible triboelectric nanogenerators (TENGs) were successfully fabricated in three different configurations. Typically, TENG consists of anode layer, cathode layer, and electrodes. In design D1, configuration C1, the TENG was fabricated by assembling a flexible polyimide as an anode layer (bottom substrate), a flexible polyethylene terephthalate (PET) as a cathode layer (top substrate), copper (Cu) tapes as electrodes and glass as supporting layers for the top and bottom substrates. TENGs with configurations C2 and C3 were assembled by replacing cathode layer, PET, with a flexible thermoplastic polyurethane (TPU) and a flexible fabric, respectively. In design D2, configurations C1, C2 and C3 were assembled using same materials as in design D1, except anode layer, Kapton, was replaced with the polydimethylsiloxane (PDMS) sheet as bottom substrate. Multiple configurations were considered in order to determine the best material combination that would provide better TENG performance. The capability of the TENG in terms of open circuit voltage (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</inf> ) and short circuit current (I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</inf> ) was demonstrated by subjecting it to ~ 5-6 Nm force at 10 Hz operating frequency. A maximum V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</inf> of 22.95 V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-p</inf> , 30.44 V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p-p</inf> , power density of 0.31 μW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , 0.46 μW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> were measured for the first and second designs, respectively. The TENG fabricated using PDMS and fabric exhibited a higher open circuit output.

This study addresses the mechanical behavior of lattice materials based on flexible thermoplastic polyurethane (TPU) with honeycomb and gyroid architecture fabricated by 3D printing. Tensile, compression, and three-point bending tests were chosen as mechanical testing methods. The honeycomb architecture was found to provide higher values of rigidity (by 30%), strength (by 25%), plasticity (by 18%), and energy absorption (by 42%) of the flexible TPU lattice compared to the gyroid architecture. The strain recovery is better in the case of gyroid architecture (residual strain of 46% vs. 31%). TPUs with honeycomb architecture are characterized by anisotropy of mechanical properties in tensile and three-point bending tests. The obtained results are explained by the peculiarities of the lattice structure at meso- and macroscopic level and by the role of the pore space.

Origami has several attractive attributes including deployability and portability which have been extensively adapted in designs of robotic devices. Drawing inspiration from foldable origami structures, this paper presents an engineering design process for fast making deployable modules of soft continuum arms. The process is illustrated with an example which adapts a modified accordion fold pattern to a lightweight deployable module. Kinematic models of the four-sided Accordion fold pattern is explored in terms of mechanism theory. Taking account of both the kinematic model and the materials selection, a 2D flat sheet model of the four-sided Accordion fold pattern is obtained for 3D printing. Following the design process, the deployable module is then fabricated by laminating 3D printed origami skeleton and flexible thermoplastic polyurethane (TPU) coated fabric. Preliminary tests of the prototype shown that the folding motion are enabled mainly by the flexible fabric between the gaps of thick panels of the origami skeleton and matches the kinematic analysis. The proposed approach has advantages of quick scaling dimensions, cost effective and fast fabricating thus allowing adaptive design according to specific demands of various tasks.

Fabric-based pneumatic actuators (FPAs) are extensively employed in the design of lightweight and compliant soft wearable assistive gloves. However, conventional FPAs typically exhibit limited output force, thereby restricting the applications of such gloves. This paper presents the development of a novel honeycomb pneumatic actuator (HPA) constructed using flexible thermoplastic polyurethane (TPU) coating through hot pressing or ultrasonic welding techniques. Compared to the previously utilized double-layer fabric-based pneumatic actuators (DLFPAs), the HPAs yields a remarkable 862% increase in end output force. It can produce a tip force of 13.57 N at a pressure of 150 kPa. The integration of HPAs onto a soft pneumatic glove enables the facilitation of various activities of daily living. A series of trials involving nine patients were conducted to assess the effectiveness of the soft glove. The experimental results indicate that when assisted by the glove, the patients' finger metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints achieved angles of 87.67 ± 19.27° and 64.2 ± 30.66°, respectively. Additionally, the average fingertip force reached 10.16 ± 4.24 N, the average grip force reached 26.04 ± 15.08 N, and the completion rate of daily functions for the patients increased from 39% to 76%. These outcomes demonstrate that the soft glove effectively aids in finger movements and significantly enhances the patients' daily functioning.

Experimental investigation on the effect of concentration on the resonance frequency of lipid coated ultrasonically excited microbubbles

The presence of advanced technologies had brought to the development of acoustic wave sensors. Quartz crystal microbalance (QCM), an acoustic wave sensor has provided a good sensing performance which enables it to be extensively used in numerous fields. The performance of the sensor is related to the material used as the sensing layer for the adsorption of analyte gas to occur. This work focuses on the use of polyisobutylene (PIB) and chitosan biopolymer films as the sensing layer to detect volatile organic compounds (VOCs). Acetone, isopropyl alcohol (IPA) and toluene are the selected VOCs used in this work. A QCM sensor with the corresponding sensing layer is modeled using COMSOL Multiphysics. The performance of the QCM sensor is evaluated in terms of the shift in resonance frequency. Toluene gas with greater molar mass exerted a greater shift in resonance frequency. Chitosan sensing layer exhibits greater sensitivity towards toluene detection compared to PIB sensing layer with a resonance frequency shift of -13 Hz at 1000 ppm and sensitivity of 0.0333 Hz/ppm. In comparison with acetone, and IPA detection, toluene shows a greater shift of resonance frequency of -96 Hz for QCM coated with the chitosan sensing layer. This is because toluene gas has a larger molar mass of 92.14 g/mol compared to acetone and IPA. Thus, this work emphasized the material selection for sensing material is crucial in improving the sensor performance.

We devised a signal-switching mechanism (SSM) based on the transportation of liquid metal droplets (LMDs). This method transmits power selectively to the light-emitting diode (LED) connected with a pair of electrodes, including a transported LMD. When an LMD is transported through a channel between multiple pairs of electrodes, the capacitance of the pair of electrodes decreases. In the SSM, we connected the electrodes with a coil and LEDs and investigated the frequency response of the impedance of the mechanism. As a result, we find the resonant phenomena of the SSM and the shift of the resonant frequency owing to the transportation of the LMD. By applying an alternating voltage, whose frequency corresponded with that of the resonant frequency of the LED-connected SSM, we could selectively transmit power to the LED activated by an LMD. Our equivalent circuit model quantitatively predicts the transmitted power and the shift in the resonant frequency due to the transportation of LMDs. The SSM using LMDs has a promising potential to contribute to soft multiplexers without complex wiring, where they can help integrate not only multiple sensors but also actuators as well.

This paper explores the potential of phase change materials (PCM) for dynamically tuning the frequency response of a dumbbell u-slot defected ground structure (DGS)-based band stop filter. The DGSs are designed using co-planar waveguide (CPW) line structure on top of a barium strontium titanate (Ba0.6Sr0.4TiO3) (BST) thin film. BST film is used as the high-dielectric material for the planar DGS. Lower insertion loss of less than -2 dB below the lower cutoff frequency, and enhanced band-rejection with notch depth of -39.64 dB at 27.75 GHz is achieved by cascading two-unit cells, compared to -12.26 dB rejection with a single-unit cell using BST thin film only. Further tunability is achieved by using a germanium telluride (GeTe) PCM layer. The electrical properties of PCM can be reversibly altered by transitioning between amorphous and crystalline phases. We demonstrate that incorporating a PCM layer into a DGS device allows for significant tuning of the resonance frequency: a shift in resonance frequency from 30.75 GHz to 33 GHz with a frequency shift of 2.25 GHz is achieved, i.e., 7.32% tuning is shown with a single DGS cell. Furthermore, by cascading two DGS cells with PCM, an even wider tuning range is achievable: a shift in resonance frequency from 27 GHz to 30.25 GHz with a frequency shift of 3.25 GHz is achieved, i.e., 12.04% tuning is shown by cascading two DGS cells. The results are validated through simulations and measurements, showcasing excellent agreement.

Additive manufacturing (AM) methods such as fused filament fabrication (FFF) and direct ink writing (DIW) enable the free-form design and printing of complex architectures using a range of materials. Compared with traditional manufacturing technologies, AM methods are highly automated to reduce waste, assembly costs, and processing errors. By combining different AM deposition methods, we can fabricate composite materials with desired spatial arrangements and anisotropies to meet unique design requirements and to produce integrated multi-material components that are not easily manufactured by traditional strategies. To address a wide variety of mechanical performance requirements, developing hybrid AM technologies into a low-cost, fully-automated manufacturing process can realize a number of new types of elastomer composite architectures. In this work, FFF and DIW methods have been combined to fabricate thermoplastic polyurethane (TPU) reinforced silicone composite materials. Several specimens with different silicone and TPU infill patterns have been designed to characterize the mechanical compression responses of these structures. With 40–80% infill percentages of silicone and 20–60% infill percentages of TPU, composites specimens can be designed to get any specified compression response between 600 N and 9000 N. This TPU-reinforced silicone printing technique can be applied for silicone composite architecture design in a wide range of applications that require tunable elastic responses.

On natural frequencies of three-dimensional moonpool of vessels in the fixed and free-floating conditions

There are various approaches to measuring muscle fatigue, including such simple measures as surveys for qualitative data, and measuring power output for quantitative data. Electromyography is consistently used to determine muscle fatigue. However, a quantitative measure of muscle recovery after exercise-induced damage is yet to be defined. The objective of this study is to measure the resonance frequency of a muscle group using a 3D laser vibrometer system and make a correlation with both elastography stiffness measurements, and with recovery of a muscle group based on standard muscle fatigue measurement techniques. Measurement of the resonance frequency of a muscle group has been successfully performed, and there is good reason to believe that the resonance frequency of the muscle group does shift after exercise-induced damage occurs. The main outcome of this study will determine whether the shift in resonance frequency of a muscle group can be used to track recovery after a damage protocol.There are various approaches to measuring muscle fatigue, including such simple measures as surveys for qualitative data, and measuring power output for quantitative data. Electromyography is consistently used to determine muscle fatigue. However, a quantitative measure of muscle recovery after exercise-induced damage is yet to be defined. The objective of this study is to measure the resonance frequency of a muscle group using a 3D laser vibrometer system and make a correlation with both elastography stiffness measurements, and with recovery of a muscle group based on standard muscle fatigue measurement techniques. Measurement of the resonance frequency of a muscle group has been successfully performed, and there is good reason to believe that the resonance frequency of the muscle group does shift after exercise-induced damage occurs. The main outcome of this study will determine whether the shift in resonance frequency of a muscle group can be used to track recovery after a damage protocol.