Structural effects of asymmetric magnet shape on performance of surface permanent magnet synchronous motors.

This study proposes a novel surface permanent magnet synchronous motor (N-SPMSM) structure, which features asymmetric magnets attached to the rotor surface. The N-SPMSM structure exhibits reduced structural complexity and minimal electromagnetic performance degradation. The properties of N-SPMSM are analyzed by comparing its structural complexity (in terms of the shape) and manufacturing complexity and electromagnetic performance [in terms of the cogging-mutual torque ratio and back-electromotive force (EMF) values], with the corresponding values of a ring-type SPMSM (R-SPMSM) and step-skew-type SPMSM (T-SPMSM). The analysis results demonstrate that N-SPMSM has lower shape complexity than T-SPMSM and lower manufacturing complexity than both R-SPMSM and T-SPMSM. The cogging torque reduction and back-EMF performances of N-SPMSM are similar to that of R-SPMSM and T-SPMSM.

Advances in Male Contraception: When Will the Novel Male Contraception be Available?

Many contraceptive methods have been developed over the years due to high demand. However, female contraceptive pills and devices do not work for all females due to health conditions and side effects. Also, the number of males who want to actively participate in family planning is gradually increasing. However, the only contraceptive options currently available to males are condoms and vasectomy. Therefore, many male contraceptive methods, including medication (hormonal and non-hormonal therapy) and mechanical methods, are under development. Reversibility, safety, persistence, degree of invasion, promptness, and the suppression of anti-sperm antibody formation are essential factors in the development of male contraceptive methods. In this paper, male contraceptive methods under development are reviewed according to those essential factors. Furthermore, the timeline for the availability of a new male contraception is discussed.

Penile Erection Morphometry: The Need for a Novel Approach.

For many males, sexual function holds significant value in determining their quality of life. Despite the importance of male erectile function, no quantitative method to measure it accurately is currently available. Standardized assessment methods such as RigiScan™, International Index of Erectile Function (IIEF-5), and the stamp test are used to evaluate sexual function, but those methods cannot repetitively and quantitatively measure erectile function. Only direct measurement can quantitatively assess the shape of an erect penis. This paper presents the essential requirements for developing an ideal measurement method for penile erection. It also introduces current approaches for diagnosing male sexual function and reviews ongoing research to quantitatively measure erectile function. The paper further summarizes and analyzes the advantages and disadvantages of each method with respect to the essential requirements. Finally, the paper discusses the future direction toward the development of Penile Erection Morphometry.

Aphid-Inspired and Thermally-Actuated Soft Gripper Using 3D Printing Technology.

Herein, a thermo-actuated aphid-inspired dry adhesive (TADA) that offers tunable and reversible adhesion is reported. It is easily fabricated through 3D printing using a polylactic acid (PLA) filament and silicone elastomer, avoiding the use of unfavorable methods for micro- and nanofabrication and unwanted particles for actuation. The tunable adhesive system mimics aphid biology to achieve adhesion switchability. Switching between adhesion states is enabled by the thermo-actuated PLA, which has shape memory properties. Additionally, silicone elastomer enables adherence to flat substrates such as glass, silicon wafers, and acrylic plates. The detachment time of the TADA can be controlled by changing the printing layer height, which is a 3D-printing parameter that results in a short detachment time when the printing layer height is small. The adhesion strength is measured by applying different preloads and varying the size of the adhesive area. The reversibility between the adhesion-on and adhesion-off states, revealing good repeatability with similar adhesion strengths is also demonstrated. The TADA has potential applications in transferring silicon wafers. In addition, it can be printed to fit a flat plate of any shape, enabling it to grip the plate stably.

Ultra-Broad Linear Range and Sensitive Flexible Piezoresistive Sensor Using Reversed Lattice Structure for Wearable Electronics.

Flexible pressure sensors have attracted significant attention owing to their broad applicability in wearable electronics and human-machine interfaces. However, it is still challenging to simultaneously achieve a broad sensing range and high linearity. Here, we present a reversed lattice structure (RLS) piezoresistive sensor obtained through a layer-level engineered additive infill structure via conventional fused deposition modeling three-dimensional (3D) printing. The optimized RLS piezoresistive sensor attained a pressure sensing range (0.03-1630 kPa) with high linearity (coefficient of determination, R2 = 0.998) and sensitivity (1.26 kPa-1) due to the structurally enhanced compressibility and spontaneous transition of dominant sensing mechanism of the sensor. It also exhibited great mechanical/electrical durability and a rapid response/recovery time (170/70 ms). This remarkable performance enables the detection of various human motions over a broad spectrum, from pulse detection to human walking. Finally, a wearable electronic glove was developed to analyze the pressure distribution in various situations, thereby demonstrating its applicability in multipurpose wearable electronics.

3D-printing-assisted fabrication of hierarchically structured biomimetic surfaces with dual-wettability for water harvesting.

Freshwater acquisition methods under various environments are required because water scarcity has intensified worldwide. Furthermore, as water is an essential resource for humans, a freshwater acquisition method that can be utilized even under harsh conditions, such as waterless and polluted water environments, is highly required. In this study, a three-dimensional (3D) printing-assisted hierarchically structured surface with dual-wettability (i.e., surface with both hydrophobic and hydrophilic region) for fog harvesting was developed by mimicking the biological features (i.e., cactus spines and elytra of Namib Desert beetles) that have effective characteristics for fog harvesting. The cactus-shaped surface exhibited self-transportation ability of water droplet, derived from the Laplace pressure gradient. Additionally, microgrooved patterns of the cactus spines were implemented using the staircase effect of 3D printing. Moreover, a partial metal deposition method using wax-based masking was introduced to realize the dual wettability of the elytra of the Namib Desert beetle. Consequently, the proposed surface exhibited the best performance (average weight of 7.85 g for 10 min) for fog harvesting, which was enhanced by the synergetic effect between the Laplace pressure gradient and surface energy gradient. These results support a novel freshwater production system that can be utilized even in harsh conditions, such as waterless and polluted water environments.

3D-printing-assisted flexible pressure sensor with a concentric circle pattern and high sensitivity for health monitoring.

In this study, a flexible pressure sensor is fabricated using polydimethylsiloxane (PDMS) with a concentric circle pattern (CCP) obtained through a fused deposition modeling (FDM)-type three-dimensional (3D) printer and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the active layer. Through layer-by-layer additive manufacturing, the CCP surface is generated from a thin cone model with a rough surface by the FDM-type 3D printer. A novel compression method is employed to convert the cone shape into a planar microstructure above the glass transition temperature of a polylactic acid (PLA) filament. To endow the CCP surface with conductivity, PDMS is used to replicate the compressed PLA, and PEDOT:PSS is coated by drop-casting. The size of the CCP is controlled by changing the printing layer height (PLH), which is one of the 3D printing parameters. The sensitivity increases as the PLH increases, and the pressure sensor with a 0.16 mm PLH exhibits outstanding sensitivity (160 kPa-1), corresponding to a linear pressure range of 0-0.577 kPa with a good linearity of R 2 = 0.978, compared to other PLHs. This pressure sensor exhibits stable and repeatable operation under various pressures and durability under 6.56 kPa for 4000 cycles. Finally, monitoring of various health signals such as those for the wrist pulse, swallowing, and pronunciation of words is demonstrated as an application. These results support the simple fabrication of a highly sensitive, flexible pressure sensor for human health monitoring.

3D-Printing-Assisted Extraluminal Anti-Reflux Diodes for Preventing Vesicoureteral Reflux through Double-J Stents.

This paper presents novel umbrella-shaped flexible devices to prevent vesicoureteral reflux along double-J stents, which is a backward flow of urine from the bladder to the kidney and is a critical issue in patients with urinary stones. The anti-reflux devices were designed to mechanically attach to the stent and were manufactured using three-dimensional (3D) printing and polymer casting methods. Based on the umbrella shapes, four different devices were manufactured, and the anti-reflux efficiency was demonstrated through in vitro experiments using a urination model. Consequently, penta-shaped devices exhibited the best anti-reflux performance (44% decrease in reflux compared to the stent without the device), and maximum efficiency occurred when the device was attached near the bladder-ureter junction. In addition, a disadvantage of 3D printing (i.e., unwanted rough surface) helped the device strongly adhere to the surface of the stent during the insertion operation. Finally, long-term soaking experiments revealed that the fabricated devices were mechanically robust and chemically stable (safe) even being soaked in urine for 4 weeks. The findings of this study support the use of additive manufacturing to make various flexible and biocompatible urological devices to mitigate critical issues in patients with urinary stones.

A biomimetic compound eye lens for photocurrent enhancement at low temperatures.

In this study, an artificial compound eye lens (ACEL) was fabricated using a laser cutting machine and polyvinyl alcohol (PVA) solution. A laser cutter was used to punch micro-sized holes (500 µm diameter-the smallest possible diameter) into an acrylic plate; this punched plate was then placed on the aqueous PVA solution, and the water was evaporated. The plate was used as the mold to obtain a polydimethylsiloxane (PDMS) micro lens array film, which was fixed to a dome-shaped three-dimensional-printed mold for further PDMS curing, and a hemispherical compound eye lens was obtained. Using a gallium nitride (GaN) photodetector, a light detection experiment was performed with the ACEL, bare lens, and no lens by irradiating light at various angles under low temperatures. The photodetector with the ACEL generated a high photocurrent under several conditions. In particular, when the light was irradiated at 0° and below -20 °C, the photocurrent of the GaN sensor with the ACEL increased by 61% and 81% compared with the photocurrent of the GaN sensor with the bare lens and without a lens, respectively. In this study, a sensor for detecting light with ACEL was demonstrated in low-temperature environments, such as indoor refrigerated storages and external conditions in Antarctica and Arctic.

Facile microfabrication of three dimensional-patterned micromixers using additive manufacturing technology.

This study investigates the manufacturing method of oblique patterns in microchannels and the effect of these patterns on mixing performance in microchannels. To fabricate three-dimensional (3D) and oblique patterns in microchannels, 3D printing and replica methods were utilized to mold patterns and microchannels, respectively. The angle and size of the patterns were controlled by the printing angle and resolution, respectively. The mixing efficiency was experimentally characterized, and the mixing principle was analyzed using computational fluid dynamics simulation. The analysis showed that the mixing channel cast from the mold printed with a printing angle of 30° and resolution of 300 µm exhibited the best mixing efficiency with a segregation index of approximately 0.05 at a Reynolds number of 5.4. This was because, as the patterns inside the microchannel were more oblique, "split" and "recombine" behaviors between two fluids were enhanced owing to the geometrical effect. This study supports the use of the 3D printing method to create unique patterns inside microchannels and improve the mixing performance of two laminar flows for various applications such as point-of-care diagnostics, lab-on-a-chip, and chemical synthesis.

Structural effects of 3D printing resolution on the gauge factor of microcrack-based strain gauges for health care monitoring.

Measurements of physiological parameters such as pulse rate, voice, and motion for precise health care monitoring requires highly sensitive sensors. Flexible strain gauges are useful sensors that can be used in human health care devices. In this study, we propose a crack-based strain gauge fabricated by fused deposition modeling (FDM)-based three-dimensional (3D)-printing. The strain gauge combined a 3D-printed thermoplastic polyurethane layer and a platinum layer as the flexible substrate and conductive layer, respectively. Through a layer-by-layer deposition process, self-aligned crack arrays were easily formed along the groove patterns resulting from stress concentration during stretching motions. Strain gauges with a 200-µm printing thickness exhibited the most sensitive performance (~442% increase in gauge factor compared with that of a flat sensor) and the fastest recovery time (~99% decrease in recovery time compared with that of a flat sensor). In addition, 500 cycling tests were conducted to demonstrate the reliability of the sensor. Finally, various applications of the strain gauge as wearable devices used to monitor human health and motion were demonstrated. These results support the facile fabrication of sensitive strain gauges for the development of smart devices by additive manufacturing.

Rapid manufacturing of micro-drilling devices using FFF-type 3D printing technology.

Micro-drilling devices with different blade shapes were fabricated with a rapid and facile manufacturing process using three-dimensional (3D) printing technology. The 3D-printed casting mold was utilized to customize the continuous shape of the blades without the need for expensive manufacturing tools. A computational fluid dynamics simulation was performed to estimate the pressure differences (fluidic resistance) around each rotating device in a flowing stream. Three types of blades (i.e., 45°, 0°, and helical type) were manufactured and compared to a device without blades (i.e., plain type). As a result, the device with the 45° blades exhibited the best drilling performance. At a rotational speed of 1000 rpm, the average drilling depth of the device with the 45° blades to penetrate artificial thrombus for 90 s was 3.64 mm, which was ~ 2.4 times longer than that of helical blades (1.51 mm). This study demonstrates the feasibility of using 3D printing to fabricate microscale drilling devices with sharp blades for various applications, such as in vivo microsurgery and clogged water supply tube maintenance.

Modeling and application of anisotropic hyperelasticity of PDMS polymers with surface patterns obtained by additive manufacturing technology.

Polydimethylsiloxane (PDMS) polymer has been widely used in the biomedical fields because of its bio-compatibility, being used as sensors, medical equipment and tissue implants. The present study aims to synthesize and characterize micro lane-type surface patterns of PDMS polymers and evaluate their effects on mechanical properties for various applications in the bio-engineering field. Fabrication of surface patterns is achieved using fused filament fabrication in additive manufacturing, and the mechanical properties of the polymer specimens with the surface patterns are measured using tensile test. The surface patterns are rotated at different angles and changed into different shapes to change the anisotropic material properties of the PDMS specimens. This is achieved by changing the raster angles and modifying the fused filament paths during the additive manufacturing process. In addition, the application of the printed pattern to medical soft robot is presented. Owing to the anisotropic material properties, in-plane and out-of-plane actuation can be realized by attaching polymer patches with different lane-type surface patterns. The results of this study support the implementation of additive manufacturing for the rapid manufacture of scalable structures with anisotropic material properties for various applications.

Development of topological optimization schemes controlling the trajectories of multiple particles in fluid.

This paper describes the development of a new topology optimization framework that controls, captures, isolates, switches, or separates particles depending on their material properties and initial locations. Controlling the trajectories of particles in laminar fluid has several potential applications. The fluid drag force, which depends on the fluid and particle velocities and the material properties of particles, acts on the surfaces of the particles, thereby affecting the trajectories of the particles whose deformability can be neglected. By changing the drag or inertia force, particles can be controlled and sorted depending on their properties and initial locations. In several engineering applications, the transient motion of particles can be controlled and optimized by changing the velocity of the fluid. This paper presents topology optimization schemes to determine optimal pseudo rigid domains in fluid to control the motion of particles depending on their properties, locations, and geometric constraints. The transient sensitivity analysis of the positions of particles can be derived with respect to the spatial distributed design variables in topology optimization. The current optimization formulations are evaluated for effectiveness based on different conditions. The experimental results indicate that the formulations can determine optimal fluid layouts to control the trajectories of multiple particles.

Microfabricaton of microfluidic check valves using comb-shaped moving plug for suppression of backflow in microchannel.

This study reports on an efficient microscale one-way valve system that combines the physical properties of photopolymerized microstructures and viscoelastic microchannels to rectify flows with low Reynolds numbers. The comb-shaped moving plug in the microchannel prevented backflow in the closed state to ensure that the microchannel remained completely blocked in the closed state, but allowed forward flow in the open state. This microfluidic check valve was microfabricated using the combination of the soft lithography and the releasing methods with the use of a double photoresist layer to create microchannels and free-moving comb-shaped microstructures, respectively. As a result, the microfluidic check valves elicited average high-pressure differences as much as 10.75 kPa between the backward and forward flows at low Reynolds numbers of the order of 0.253, thus demonstrating efficient rectification of microfluids. This study supports the use of rectification systems for the development of biomedical devices, such as drug delivery, micropumps, and lab-on-a-chip, by allowing unidirectional flow.

Impact of thermally dead volume on phonon conduction along silicon nanoladders.

Thermal conduction in complex periodic nanostructures remains a key area of open questions and research, and a particularly provocative and challenging detail is the impact of nanoscale material volumes that do not lie along the optimal line of sight for conduction. Here, we experimentally study thermal transport in silicon nanoladders, which feature two orthogonal heat conduction paths: unobstructed line-of-sight channels in the axial direction and interconnecting bridges between them. The nanoladders feature an array of rectangular holes in a 10 µm long straight beam with a 970 nm wide and 75 nm thick cross-section. We vary the pitch of these holes from 200 nm to 1100 nm to modulate the contribution of bridges to the net transport of heat in the axial direction. The effective thermal conductivity, corresponding to reduced heat flux, decreases from ∼45 W m-1 K-1 to ∼31 W m-1 K-1 with decreasing pitch. By solving the Boltzmann transport equation using phonon mean free paths taken from ab initio calculations, we model thermal transport in the nanoladders, and experimental results show excellent agreement with the predictions to within ∼11%. A combination of experiments and calculations shows that with decreasing pitch, thermal transport in nanoladders approaches the counterpart in a straight beam equivalent to the line-of-sight channels, indicating that the bridges constitute a thermally dead volume. This study suggests that ballistic effects are dictated by the line-of-sight channels, providing key insights into thermal conduction in nanostructured metamaterials.

Improved Dielectric Properties of Polyvinylidene Fluoride Nanocomposite Embedded with Poly(vinylpyrrolidone)-Coated Gold Nanoparticles.

A novel nanocomposite dielectric was developed by embedding polyvinylpyrrolidone (PVP)-encapsulated gold (Au) nanoparticles in the polyvinylidene fluoride (PVDF) polymer matrix. The surface functionalization of Au nanoparticles with PVP facilitates favorable interaction between the particle and polymer phase, enhancing nanoparticle dispersion. To study the effect of entropic interactions on particle dispersion, nanocomposites with two different particle sizes (5 and 20 nm in diameter) were synthesized and characterized. A uniform particle distribution was observed for nanocomposite films consisting of 5 nm Au particles, in contrast to the film with 20 nm particles. The frequency-dependent dielectric permittivity and the loss tangent were studied for the nanocomposite films. These results showed the effectiveness of PVP ligand in controlling the agglomeration of Au particles in the PVDF matrix. Moreover, the study showed the effect of particle concentration on their spatial distribution in the polymer matrix and the dielectric properties of nanocomposite films.

A microfabricated sun sensor using GaN-on-sapphire ultraviolet photodetector arrays.

A miniature sensor for detecting the orientation of incident ultraviolet light was microfabricated using gallium nitride (GaN)-on-sapphire substrates and semi-transparent interdigitated gold electrodes for sun sensing applications. The individual metal-semiconductor-metal photodetector elements were shown to have a stable and repeatable response with a high sensitivity (photocurrent-to-dark current ratio (PDCR) = 2.4 at -1 V bias) and a high responsivity (3200 A/W at -1 V bias) under ultraviolet (365 nm) illumination. The 3 × 3 GaN-on-sapphire ultraviolet photodetector array was integrated with a gold aperture to realize a miniature sun sensor (1.35 mm × 1.35 mm) capable of determining incident light angles with a ±45° field of view. Using a simple comparative figure of merit algorithm, measurement of incident light angles of 0° and 45° was quantitatively and qualitatively (visually) demonstrated by the sun sensor, supporting the use of GaN-based sun sensors for orientation, navigation, and tracking of the sun within the harsh environment of space.

Origin and hysteresis of lithium compositional spatiodynamics within battery primary particles.

The kinetics and uniformity of ion insertion reactions at the solid-liquid interface govern the rate capability and lifetime, respectively, of electrochemical devices such as Li-ion batteries. Using an operando x-ray microscopy platform that maps the dynamics of the Li composition and insertion rate in Li(x)FePO4, we found that nanoscale spatial variations in rate and in composition control the lithiation pathway at the subparticle length scale. Specifically, spatial variations in the insertion rate constant lead to the formation of nonuniform domains, and the composition dependence of the rate constant amplifies nonuniformities during delithiation but suppresses them during lithiation, and moreover stabilizes the solid solution during lithiation. This coupling of lithium composition and surface reaction rates controls the kinetics and uniformity during electrochemical ion insertion.

Simultaneous Thermoelectric Property Measurement and Incoherent Phonon Transport in Holey Silicon.

Block copolymer patterned holey silicon (HS) was successfully integrated into a microdevice for simultaneous measurements of Seebeck coefficient, electrical conductivity, and thermal conductivity of the same HS microribbon. These fully integrated HS microdevices provided excellent platforms for the systematic investigation of thermoelectric transport properties tailored by the dimensions of the periodic hole array, that is, neck and pitch size, and the doping concentrations. Specifically, thermoelectric transport properties of HS with a neck size in the range of 16-34 nm and a fixed pitch size of 60 nm were characterized, and a clear neck size dependency was shown in the doping range of 3.1 × 10(18) to 6.5 × 10(19) cm(-3). At 300 K, thermal conductivity as low as 1.8 ± 0.2 W/mK was found in HS with a neck size of 16 nm, while optimized zT values were shown in HS with a neck size of 24 nm. The controllable effects of holey array dimensions and doping concentrations on HS thermoelectric performance could aid in improving the understanding of the phonon scattering process in a holey structure and also in facilitating the development of silicon-based thermoelectric devices.