Search Results (64)

Droplet microfluidics enables high-throughput, compartmentalized reactions using minimal reagent volumes, but most implementations rely on precision-fabricated chips and external pumping systems that limit portability and accessibility. Here, we present a handheld vibrational droplet generator that repurposes a consumer electric toothbrush and a modified disposable pipette tip to produce nearly monodisperse water-in-oil droplets without microfluidic channels or syringe pumps. The device is powered by the toothbrush’s built-in motor and controlled by a simple 3D-printed adapter and adjustable counterweight that tune the vibration amplitude transmitted to the pipette tip. By varying the aperture of the pipette tip, droplets with diameters from ~100–300 µm were generated at rates of ~100 droplets s⁻¹. Image analysis revealed narrow size distributions with coefficients of variation below 5% in typical operating conditions. We further demonstrate proof-of-concept applications in digital loop-mediated isothermal amplification (LAMP) and microbiological colony-forming unit (CFU) assays. A commercial feline parvovirus (FPV) kit manufactured by Beyotime Biotechnology Co., Ltd. (Shanghai, China), three template concentrations yielded emulsified reaction droplets that remained stable at 65 °C for 45 min and produced distinct fractions of fluorescent-positive droplets, allowing estimation of template concentration via a Poisson model. In a second set of experiments, the device was used as a droplet-based spreader to dispense diluted Escherichia coli suspensions onto LB agar plates, achieving uniform colony distributions across the plate at different dilution factors. The proposed handheld vibrational generator is inexpensive, easy to assemble from off-the-shelf components, and minimizes dead volume and cross-contamination because only the pipette tip contacts the sample. Although the current prototype still exhibits device-to-device variability and moving droplets in open containers complicate real-time imaging, these results indicate that toothbrush-based vibrational actuation can provide a practical and scalable route toward “lab-in-hand” droplet assays in resource-limited or educational settings. Full article

The mechanical limitations of gypsum-based composites necessitate reinforcement strategies to enhance their structural performance. This study investigates the feasibility of integrating 3D-printed polylactic acid (PLA) meshes into gypsum composites through a series of preliminary experiments. Various mesh configurations were tested, including different fiber thicknesses, mesh grid sizes, and single- and double-layer applications. The impact of mesh incorporation on bulk density, ultrasonic pulse velocity (UPV), bending strength, and compressive strength was assessed. The results indicate that the inclusion of PLA meshes had a limited effect on bulk density and led to a slight decrease in UPV values, suggesting increased porosity. Although improvements in mechanical properties were anticipated, most specimens exhibited lower bending and compressive strengths compared to the reference specimen. Among the tested configurations, 2 mm thick meshes demonstrated relatively higher performance, particularly in bending strength, with narrow-mesh aperture yielding better results. However, double-layer mesh applications consistently resulted in lower strength values. These findings highlight the challenges associated with integrating 3D-printed PLA meshes into gypsum composites. While the study provides valuable insights into mesh-based reinforcement, further investigations are required to optimize fiber–matrix interactions and enhance mechanical performance. Future research should explore alternative printing parameters, improved adhesion techniques, and hybrid reinforcement approaches to fully exploit the potential of additive manufacturing in gypsum-based composites. Full article

This paper proposes a mechanically reconfigurable multi-polarization antenna based on a 3D-printed anisotropic dielectric polarizer, offering wide bandwidth, high gain, and extremely low cost. The working mechanism of the dielectric polarizer is analyzed, demonstrating its ability to efficiently convert linear polarization (LP) to circular polarization (CP) over a wide frequency range. Furthermore, the polarizer exhibits subwavelength characteristics. For a given duty cycle, its phase response depends only on the height and is independent of the aperture size. This property enables miniaturized and customized designs of the polarizer’s aperture size. Subsequently, the polarizer is placed above a Ku band waveguide and standard horn antennas. The results show that by rotating the dielectric polarizer and adjusting the positions of the antennas, right-handed CP (RHCP), left-handed CP (LHCP), and dual LP radiation switching can be achieved in the 12.4–18.0 GHz band, verifying the quad-polarization reconfigurability. Additionally, the polarizer significantly enhances the gain of the waveguide antenna by approximately 9.5 dB. Furthermore, due to the low-cost 3D printing material, the manufacturing cost of the polarizer is exceptionally low, making it suitable for applications such as anechoic chamber measurements and wireless communications. Finally, the measurement results further validate the accuracy of the simulations. Full article

This work demonstrates the fabrication of microstructures with formulations containing bio-based prepolymers derived from itaconic acid, commercial reactive diluents, photo initiators, and inhibitors, through two-photon polymerization. Lateral and vertical resolutions within the micron range can be achieved by the adjustment of laser scanning speed and pulse energy, and through the use of microscope objectives with high magnification and numerical aperture. The fabrication throughput can be slightly increased by simultaneously increasing the laser pulse energy and scanning speed, with special care to keep the resolution of the features that can be written via two-photon polymerization. Feasibility for the fabrication of 3D microstructures is demonstrated, through the fabrication of benchmark structures like woodpiles and pyramidal structures. Thus, this work proves that resins based on biobased formulations, originally designed for UV-curing 3D printing, can be adapted for two-photon polymerization, obtaining 3D microstructures with resolutions within the micron range. Full article

This paper introduces a high-resolution 77–81 GHz mmWave Synthetic Aperture Radar (SAR) imaging methodology integrating low-cost hardware with modified radar signal characteristics specifically for NDT applications. The system is optimized to detect minimal defects in materials, including low-reflectivity ones. In contrast to the existing studies, by optimizing key system parameters, including frequency slope, sampling interval, and scanning aperture, high-resolution SAR images are achieved with reduced computational complexity and storage requirements. The experiments demonstrate the effectiveness of the system in detecting optically undetectable minimal surface defects down to 0.4 mm, such as bonded adhesive lines on low-reflectivity materials with 2500 measurement points and sub-millimeter features on metallic targets at a distance of 30 cm. The results show that the proposed system achieves comparable or superior image quality to existing high-cost setups while requiring fewer data points and simpler signal processing. Low-cost, low-complexity, and easy-to-build mmWave SAR imaging is constructed for high-resolution SAR imagery of targets with a focus on detecting defects in low-reflectivity materials. This approach has significant potential for practical NDT applications with a unique emphasis on scalability, cost-effectiveness, and enhanced performance on low-reflectivity materials for industries such as manufacturing, civil engineering, and 3D printing. Full article

We present a MEMS array-based approach for micro-irises called “ring shutter”, utilizing subfield addressing for applications in advanced micro-optics, such as interference microscopy. This experimental study is focused on investigating the homogeneity of electro-mechanical and optical characteristics within and between subfields of a lab demonstrator device. The characterization aims to ensure crosstalk-free and swift optical performance, as demonstrated in a previous study. For this purpose, the transmission in the initial state, actuation voltages, and response dynamics are measured for each electrode and the entire device, and the results are thoroughly compared. The measurements are conducted by expanding an existing optical actuation setup via tailored 3D-printed apertures, to isolate selected rings and zones. Evaluation of measurement data confirms the stable and crosstalk-free operation of the ring shutter. Both angular and radial homogeneity are robust and follow the expectations in the experiment. While transmission, actuation voltage and closing time slightly rise (up to 25%) with increased radial position represented by five discrete ring sections, the characteristics for different angular zones remain nearly constant. Response times are measured below 40 µs, actuation voltages do not exceed 60 V, and the overall transmission of the ring shutter yields 53.6%. Full article

A 2048-element dual-polarized receive (RX) phased array for $Ku$-band (10.7–12.7 GHz) satellite communication (SATCOM) is presented in this paper. The design of the multilayer printed circuit board (PCB) it uses adopts a novel copper paste sintering interconnection technology that allows for more flexibility in the design of vias and can reduce the PCB’s lamination number. This technology is more suitable for manufacturing multilayer and complex PCBs than traditional processes. The array is designed to consist of sixteen 8 × 16 element subarrays, each based on the silicon RX beamformer and multilayer PCB. Dual-polarized antenna elements are arranged in a regular rectangle with a spacing of 0.5 for a wavelength of 12.7 GHz, thus achieving a scanning range of ±70° in all planes. By adjusting the amplitude and phase of two line polarizations with cross-polarization levels better than −25 dB at boresight, the array can generate linear or circular polarization. Moreover, the antenna gain-to-noise temperature is above 12 dB/K ($T_{\mathrm{ant}}$ = 20 K) at boresight. The aperture of the 2048-element RX phased array is 768 × 450 mm. With its low profile, the array is appropriate for usage in $Ku$-band SATCOM terminals. Full article

This study presents a novel methodology for designing a planar broadband wide-scanning dual-polarized array using tightly-coupled dipoles and wide-angle impedance matching. By etching the S-shaped gaps between the dipoles and incorporating shorting vias with defected ground structures, we demonstrated that all radiation elements can be arranged on a single-layer substrate. Additionally, we introduced a thin printed circuit board (PCB) layer with two-dimensional periodic structures for impedance matching at wide scan angles. Leveraging high permittivity and constrained electromagnetic waves, we realized zero-scan blindness within this band. The aperture consisted of only two PCB layers, with a total profile of approximately 0.091λ_low, where λ_low represented the free-space wavelength at 6 GHz. A 3 × 4 dual-polarized array was fabricated and measured to validate the proposed approach. The measured active voltage standing wave ratio for one embedded array element surpassed 2.2 over 6–18 GHz. By enabling the orthogonal dipoles at the edge of the array to be mutually coupled using an additional metal patch, the active S₁₁ for the edge cells exceeded −8.8 dB over 6.9–18 GHz. The measured patterns were in good agreement with simulations over 6–18 GHz, with the array exhibiting good radiation performance over ±60° in the E- and H-planes. Full article

This paper presents a 3D-printed fully dielectric bi-material reflectarray with bandgap characteristics for multi-band applications. To achieve bandgap characteristics, a “1D Bragg reflector” unit cell is used. The latter is a layered structure characterized by a spatial distribution of refractive index that varies periodically along one dimension. By appropriately selecting the dimensions, the bandgap can be shifted to cover the desired frequency bands. To validate this bandgap characteristic, a (121.5 mm × 121.5 mm) with an f/D ratio of 0.5 reflectarray was fabricated. The measured gain at 27 GHz is 27.22 dBi, equivalent to an aperture efficiency of 35.05%, demonstrating good agreement between simulated and measured performances within the frequency range of 26–30 GHz. Additionally, the transparency of the reflectarray was verified by measuring the transmission coefficient, which exhibited a high level of transparency of 0.32 dB at 39 GHz. These features make the proposed reflectarray a good candidate for multi-band frequency applications. Full article

Vertical-cavity surface-emitting lasers (VCSELs) are essential for exhibiting single-transverse-mode output characteristics, which are critical for applications in quantum sensing, optical interconnection, and laser printing. In this study, we achieved stable single-transverse-mode lasing using extended-2λ-cavity with an oxide aperture diameter of 7.08 μm. The device demonstrated a high output power of 6.8 mW and a narrow linewidth of 49.8 MHz at room temperature. Additionally, it maintained stable single-mode emission at 794.8 nm and achieved a side-mode suppression ratio (SMSR) exceeding 40 dB within the temperature range of 25 °C~85 °C, thereby meeting the requirements of ⁸⁷Rb atom quantum sensors. The fabricated device obtained high-power and narrow linewidth single-transverse-mode operation by a monolithic extended cavity without introducing additional processing procedures, which is expected to promote the commercial viability of VCSELs in quantum sensing. Full article

Despite the many potential applications of an accurate indoor positioning system (IPS), no universal, readily available system exists. Much of the IPS research to date has been based on the use of radio transmitters as positioning beacons. Visible light positioning (VLP) instead uses LED lights as beacons. Either cameras or photodiodes (PDs) can be used as VLP receivers, and position estimates are usually based on either the angle of arrival (AOA) or the strength of the received signal. Research on the use of AOA with photodiode receivers has so far been limited by the lack of a suitable compact receiver. The quadrature angular diversity aperture receiver (QADA) can fill this gap. In this paper, we describe a new QADA design that uses only three readily available parts: a quadrant photodiode, a 3D-printed aperture, and a programmable system on a chip (PSoC). Extensive experimental results demonstrate that this design provides accurate AOA estimates within a room-sized test chamber. The flexibility and programmability of the PSoC mean that other sensors can be supported by the same PSoC. This has the potential to allow the AOA estimates from the QADA to be combined with information from other sensors to form future powerful sensor-fusion systems requiring only one beacon. Full article

The paper presents a novel small-footprint varactor diode-based reconfigurable reflectarray (RRA) design and investigates its power reflection efficiency theoretically and experimentally in a real-life indoor environment. The surface is designed to operate at 865.5 MHz and is intended for simultaneous use with other wireless power transfer (WPT) efficiency-improving techniques that have been recently reported in the literature. To the best of the authors’ knowledge, no RRA intended to improve the performance of antenna-based WPT systems operating in the sub-GHz range has been designed and studied both theoretically and experimentally so far. The proposed RRA is a two-layer structure. The top layer contains electronically tunable phase shifters for the local phase control of an incoming electromagnetic wave, while the other one is fully covered by metal to reduce the phase shifter size and RRA’s backscattering. Each phase shifter is a pair of diode-loaded 8-shaped metallic patches. Extensive numerical studies are conducted to ascertain a suitable set of RRA unit cell parameters that ensure both adequate phase agility and reflection uniformity for a given varactor parameter. The RRA design parameter finding procedure followed in this paper comprises several steps. First, the phase and amplitude responses of a virtual infinite double periodic RRA are computed using full-wave solver Ansys HFSS. Once the design parameters are found for a given set of physical constraints, the phase curve of the corresponding finite array is retrieved to estimate the side lobe level due to the finiteness of the RRA aperture. Then, a diode reactance combination is found for several different RRA reflection angles, and the corresponding RRA radiation pattern is computed. The numerical results show that the side lobe level and the deviation of the peak reflected power angles from the desired ones are more sensitive to the reflection coefficient magnitude uniformity than to the phase agility. Furthermore, it is found that for scanning angles less than 50°, satisfactory reflection efficiency can be achieved by using the classical reactance profile synthesis approach employing the generalized geometrical optics (GGO) approximation, which is in accord with the findings of other studies. Additionally, for large reflection angles, an alternative synthesis approach relying on the Floquet mode amplitude optimization is utilized to verify the maximum achievable efficiency of the proposed RRA at large angles. A prototype consisting of 36 elements is fabricated and measured to verify the proposed reflectarray design experimentally. The initial diode voltage combination is found by applying the GGO-based phase profile synthesis method to the experimentally obtained phase curve. Then, the voltage combination is optimized in real time based on power measurement. Finally, the radiation pattern of the prototype is acquired using a pair of identical 4-director printed Yagi antennas with a gain of 9.17 dBi and compared with the simulated. The calculated results are consistent with the measured ones. However, some discrepancies attributed to the adverse effects of biasing lines are observed. Full article

This paper presents an innovative method for fabricating reflectarray antennas using inkjet printing technology on flexible substrates, markedly enhancing integration and manufacturability compared to traditional PCB methods. The technique employs inkjet printing to deposit conductive inks directly onto a flexible polyethylene naphthalate (PEN) substrate, seamlessly integrating feed and reflectarray components without complex assembly processes. This streamlined approach not only reduces manufacturing complexity and costs but also improves mechanical flexibility, making it ideal for applications requiring deployable antennas. The design process includes an origami-inspired folding of the substrate to achieve the desired three-dimensional antenna structures, optimizing the focal length to dimension ratio (F/D) to ensure maximum efficiency and performance. The feed and the reflectarray geometry are optimized for an F/D of 0.6, which achieves high gain and aperture efficiency, demonstrated through detailed simulations and measurements. For normal incidence, the configuration achieves a peak gain of 9.3 dBi and 48% radiation efficiency at 10 GHz; for oblique incidence, it achieves 7.3 dBi and 40% efficiency. The study underscores the significant potential of inkjet-printed antennas in terms of cost-efficiency, precision, and versatility, paving the way for new advancements in antenna technology with a substantial impact on future communication systems. Full article

In this article, we present new design techniques to improve the gain and impedance bandwidth of short backfire antennas. For the gain enhancement procedure, our approach was to flare the rim of the antenna, which simultaneously led to an increase in the impedance bandwidth of the antenna. Parametric studies were carried out to obtain the optimal flaring angle. The peak realized gain was obtained as 17.2 dBi with an impedance bandwidth of 55% (2.4 dB and 28.6% increase in gain and bandwidth, respectively, compared to the unflared antenna). To further enhance the impedance bandwidth, an inductive iris was added to improve impedance matching at the waveguide aperture. We varied the width of the iris to obtain the optimal width that provided the best gain and impedance bandwidth result of 17.1 dBi and 66% (~40% increase compared to the unflared antenna without iris). To experimentally verify the work, prototypes were fabricated and tested. We found good agreement between simulation and measurement. The results of this study indicate that gain and bandwidth can be enhanced through optimized geometrical modification of the SBF structure. Furthermore, our 3D-printed technique demonstrates a mass reduction compared with conventional metallic structures. Full article

We report a fusedly deposited frequency-selective composite (FD-FSCs), fabricated with a dual-nozzle 3D printer using a conductive carbon black (CB) polylactic acid (PLA) composite filament and a pure PLA polymer filament. The square frequency-selective pattern was constructed by the conductive CB/PLA nanocomposite, and the apertures of the pattern were filled with the pure dielectric PLA material, which allows the FD-FSC to maintain one single plane, even under bending, and also affects the resonating frequency due to the characteristic impedance of PLA (ε_r′ ≈ 2.0). The number of the deposition layer and the printing direction were observed to affect electrical conductivity, complex permittivity, and the frequency selectivity of the FD-FSCs. In addition, the FD-FSCs designed for an X-band showed partial transmission around the resonant frequency and was observed to, quite uniformly, transmit microwaves in the decibel level of −2.17~−2.83 dB in the whole X-band, unlike a metallic frequency selective surface with full transmission at the resonance frequency. FD-FSCs embedded radar absorbing structure (RAS) demonstrates an excellent microwave absorption and a wide effective bandwidth. At a thickness of 4.3 mm, the 10 dB bandwidth covered the entire X-band (8.2~12.4 GHz) range of 4.2 GHz. Therefore, the proposed FD-FSCs fabricated by dual-nozzle 3D printing can be an impedance modifier to expand the design space and the application of radar absorbing materials and structures. Full article