Abstract
Soft exosuits used for supporting human muscle strength must be lightweight and wearable. Shape memory alloy (SMA) spring-based fabric muscles (SFM) are light and flexible, making them ...suitable for soft and shape-conformable exosuits. However, SFMs have a slow actuation speed owing to the slow cooling rate of the SMA spring. This paper proposes a forced air-cooling fan-integrated fabric muscle (FCFM) that improves the cooling rate by arranging a thin-diameter SMA spring bundle with a high surface-area-to-volume ratio inside a breathable fabric with integrated fans. The relaxation time of an FCFM weighing 30 g and containing a 2.6 g SMA spring bundle, which contains 200 thin springs, was reduced by over 70.2% via forced-air cooling using the integrated fans. A 4 kg weight, which is 1530 times the mass of the SMA spring bundle, was hung from the FCFM and was repeatedly actuated in ten-second cycles. An upper limb assistive soft exosuit with FCFMs was fabricated and worn on a mannequin holding a dumbbell, and the arm extension time after flexion was improved by 4.5 times. Additionally, the assistive performance of the exosuits for repetitive tasks in specific scenarios was evaluated, and the strong potential of the proposed FCFM for soft exosuits was verified.
This study proposes a soft inductive coil spring (SICS) strain sensor that can measure the strain of soft actuators. The SICS sensor, produced by transforming a shape memory alloy (SMA) wire with the ...same materials as that of an SMA spring bundle actuator (SSBA) into a coil spring shape, measures inductance changes according to length changes. This study also proposes a manufacturing method, output characteristics of the SICS sensor applicable to the SSBA among soft actuators, and the structure of the SICS sensor-integrated SSBA (SI-SSBA). In the SI-SSBA, the SMA spring bundle and SICS sensor have structures corresponding to the muscle fiber and spindle of the skeletal muscle, respectively. It is demonstrated that when a robotic arm with one degree of freedom is operated by attaching two SI-SSBAs in an antagonistic structure, the displacement of the SSBA can be measured using the proposed strain sensor. The output characteristics of the SICS sensor for the driving speed of the robotic arm were evaluated, and it was experimentally proven that the strain of the SSBA can be stably measured in water under a temperature change of 54 °C from 36 to 90 °C.
In the field of robotics, sensors are crucial in enabling the interaction between robots and their users. To ensure this interaction, sensors mainly measure the user's strength, and based on this, ...wearable robots are controlled. In this paper, we propose a novel three-axis force/torque sensor for wearable robots that is compact and has a high load capacity. The bolt and nut combination of the proposed sensor is designed to measure high-load weights, and the simple structure of this combination allows the sensor to be compact and light. Additionally, to measure the three-axis force/torque, we design three capacitance-sensing cells. These cells are arranged in parallel to measure the difference in capacitance between the positive and negative electrodes. From the capacitance change measured by these sensing cells, force/torque information is converted through deep neural network calibration. The sensing point can also be confirmed using the geometric and kinematic relation of the sensor. The proposed sensor is manufactured through a simple and inexpensive process using cheap and simply structured components. The performance of the sensor, such as its repeatability and capacity, is evaluated using several experimental setups. In addition, the sensor is applied to a wearable robot to measure the force of an artificial muscle.
Underwater explosion (UNDEX) events involve complex physical phenomena and can be categorized into three stages: initial shock wave propagation, cavitation, and bubble pulsation. This study focuses ...on double UNDEX bubbles, elucidating their highly nonlinear interactions across these stages. Both synchronous and asynchronous explosion cases are examined, with a particular emphasis on assessing the influence of phase change. Employing the 3-D high-fidelity computational framework that incorporates the physics-based cavitation model and non-ideal equations of state for water and explosion gas properties, we conduct validations with field experimental data on single bubbles and extend our analysis to double bubbles. Our principal finding is the interaction between the cavity created by the shock wave and the bubble pulsations. Notably, we discern a significant phase change effect in asynchronous explosion, wherein the vapor cavity region delays the contraction of the previously-generated bubble. This delay is attributed to the low-density region created by the phase change, allowing the bubble to remain expanded for an extended period, thereby enhancing agreement with experimental data. To our knowledge, this study represents the pioneering effort to explore the critical role of phase change in accurately simulating the intricate interactions within double UNDEX scenarios.
•Computational investigations on double UNDEX scenarios with thermodynamic cavitation process and non-ideal EOS.•Interactions between the cavity caused by the shock wave and the bubble pulsations are captured.•Phase change effect is more pronounced in asynchronous explosion.•Low-density cavity region delays the previously-generated bubble’s contraction.•3-D effect induced by the misalignment of gravity and bubble contraction direction.
Upper limb exosuits (ULEs) are wearable robots that can assist arms to lift or support an object. However, heavy wearable equipment often interferes with the free movement of a person's arms, which ...have a wide range of motions. This article presents the design and manufacturing processes for a ULE that does not restrict the range of motion of the person wearing it and that can be folded to a small, palm-sized volume for portability. The light and flexible ULE employs a fabric woven from shape memory alloy (SMA) springs (FWS) as an actuator. The FWS uses SMA springs coiled with microdiameter SMA wires, and it exhibits the soft and flexible characteristics of a fabric. The proposed lightweight ULE weighs 540 g and supports the muscular strength for the bending motion of an elbow. The experimental results indicated that the proposed ULE reduced the muscle activity of subjects by approximately 50-70% when they held a load of up to 10 kg under the condition that their temperature was controlled to be 50 °C or lower. This result suggests that the proposed ULE can be used to provide strength assistance for delivery or construction workers.
During cavitation bubble pulsations, a phase change intensively occurs near the collapsing moment due to high pressure and temperature inside bubbles, accompanying distinctive flow features: the rate ...of evaporation and condensation significantly changes according to the phase change regime. To account for this non-isothermal effect, the high-fidelity computational framework incorporating the physics-based cavitation model and a new fluid property model based on artificial neural network is proposed. The key finding of this study is the interplay between the thermal and inertial effects during multiple pulsations. At the early stages of bubble contraction, the phase change is primarily driven by fluid inertia. However, as the bubble continues to compress, the thermal effect becomes dominant and controls the entire phase change region at each moment of collapse. It is observed that the isothermal model relying on the inertial bubble growth rate only, does not capture this transition of dominance and eventually fails to predict multiple pulsations. The physics-based cavitation model successfully captures the bubble pulsation beyond the second collapse. These findings highlight that explicit consideration of the non-isothermal effect is essential for problems with varying phase change regimes, and a phase change model reflecting this effect is vital for accurate computations.
•High-fidelity multi-phase computational framework ACTFlow_MP is proposed.•New fluid property model based on artificial neural network is constructed for water.•The thermal effect turns out to be dominant at the moment of each bubble collapse.•The physics-based model successfully captured bubble pulsations beyond 2nd period.
•Unconventional flow separation mechanism in a TOP nozzle is computationally investigated.•Upstream jump of shock structure and uncommon flow separation pattern are observed.•Entrained flow reduces ...the flow separation time without changing the shock transition process.
The goal of this work is to numerically investigate the mechanism of flow separation in a thrust-optimized parabolic nozzle during high-altitude testing. Both startup and shutdown processes of the Korea Space Launch Vehicle-II (KSLV-II) third-stage rocket engine are examined by axisymmetric computations. In particular, unconventional transitional process between the two representative separation patterns, free-shock separation (FSS) and restricted-shock separation (RSS) during high-altitude engine testing, is explored. It is observed that the attachment of nozzle flow to the diffuser wall leads to the upstream jump of the shock structure during the FSS-to-RSS transition for the engine startup process. For the engine shutdown process, the straight transition from full-flow to RSS is induced by the large trapped vortex which pushes nozzle flow towards the diffuser wall, and the pressure waves caused by the breakdown of vacuum region leads to the RSS-to-FSS transition. Furthermore, the entrained flow effect on flow separation is investigated. During the engine startup process, the entrained flow stabilizes the flow around the diffuser inlet, thereby inducing a smooth RSS-to-FSS transition. While the entrained flow delays the transition from full-flow to RSS during the engine shutdown process, but this delay eventually promotes the RSS-to-FSS transition. Consequently, the entrained flow significantly reduces the time in which flow separation resides inside the nozzle.
This paper discusses a new 5G-Advanced duplex scheme called sub-band full-duplex (SBFD) and the details of implementing it for 5G TDD spectrum. The SBFD requires an advanced self interference ...cancellation (SIC) which is designed to handle extremely high level of cross link interference. Novel SIC techniques were designed for base stations (BSs) operating on 3.4 GHz with massive MIMO and on 26 GHz with multi-beam capability. By utilizing electromagnetic walls in conjunction with electromagnetic bandgap, an extremely high level of isolation between transmit and receive antennas is achieved. Residual interference is further removed using fractional nonlinear interference estimation in baseband. Two Proofs-of-Concepts (PoCs) have been implemented for feasibility verification. The first PoC was for a massive MIMO BS operating with 32 cross polarized antenna ports on 3.4 GHz and a bandwidth of 100 MHz. The second PoC was for a multi-beam BS with 256 antenna elements operating on 26 GHz and a bandwidth of 400 MHz. It was observed that the self-interference in SBFD can be suppressed in real time to a level of less than 0.7 dB over the RX noise floor for both 3.4 GHz and 26 GHz in an outdoor environment.
Here, we systematically investigate optical behaviors of ruthenium (Ru)-coated nanoporous anodic aluminum oxide (AAO) nanoarchitectures in the visible and near-Infrared (NIR) regions, where they are ...fabricated by an atomic layer deposition (ALD) process. Depending on the Ru thickness and the AAO dimensions, the Ru nanoarchitectures could be completely changed (tubular-type or wire-type Ru nanostructures), and the corresponding optical properties are critically affected. Brilliant structural colors are found from the Ru-coated AAO nanostructures, in which the color display covers the full visible range. Beyond the visible region, we also examine the optical behaviors of Ru-coated AAO nanostructures in the NIR region.
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We demonstrate an infrared broadband metasurface absorber that is suitable for increasing the response speed of a microbolometer by reducing its thermal mass. A large fraction of holes are made in a ...periodic pattern on a thin lossy metal layer characterised with a non-dispersive effective surface impedance. This can be used as a non-resonant metasurface that can be integrated with a Salisbury screen absorber to construct an absorbing membrane for a microbolometer that can significantly reduce the thermal mass while maintaining high infrared broadband absorption in the long wavelength infrared (LWIR) band. The non-dispersive effective surface impedance can be matched to the free space by optimising the surface resistance of the thin lossy metal layer depending on the size of the patterned holes by using a dc approximation method. In experiments a high broadband absorption was maintained even when the fill factor of the absorbing area was reduced to 28% (hole area: 72%), and it was theoretically maintained even when the fill factor of the absorbing area was reduced to 19% (hole area: 81%). Therefore, a metasurface with a non-dispersive effective surface impedance is a promising solution for reducing the thermal mass of infrared microbolometer pixels.
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