Thin Array Research Articles

UV-converted heterogeneous wettability surface for the realization of printed micro-scale conductive circuits

Achieving high precision in the fabrication of electronic circuits through additive manufacturing requires breaking the resolution limit of traditional printing processes. To address this challenge, we have developed a novel approach that involves preparing a heterogeneous wetting surface using a light-sensitive NBE-acrylate resin. By creating differences in surface energy on the substrate, we can limit the spread of the ink and surpass the limitations of conventional processes, achieving a printing resolution of 5 μm. The NBE-acrylate resin can be cross-linked under white LED light illumination (with λ > 400 nm) to yield a hydrophobic surface, which can be converted to a hydrophilic surface by UV light illumination (λ = 254 nm). The photochemical reaction of the NBE-acrylate resin under different light irradiation was confirmed by Fourier transform infrared spectroscopy (FTIR) and atomic force microscope (AFM) microforce measurements. In combination with a photomask, patterned heterogeneous wettability surfaces were prepared, which can be utilized for printing precision electronic circuits. Micrometer-scale printed circuits with a low line-to-space (L/S) of 5/50 and 10/10 μm were successfully achieved by optimizing the ink formulation, which is significantly beyond the printing resolution. In the end, fully printed thin film transistor arrays based on semi-conducting carbon nanotubes were achieved, which showed higher charge carrier mobilities of 1.89–4.31 cm2 s−1 V−1 depending on the channel width, demonstrating the application of this precision printed technique.

Ultrathin, Flexible, and Reusable Silicon Shadow Masks Manipulated via Transfer Printing

Stencil lithography is a facile patterning technique that offers a potential solution to the limitations of conventional photolithography. However, several critical factors such as enhanced pattern resolution, ability to pattern on nonplanar surfaces, and multilayer patterning should further be addressed to extend the applications of stencil lithography. This study presents a novel ultrathin silicon shadow mask which is flexible, reusable, and able to be precisely aligned and manipulated through transfer printing. The small thickness of the silicon shadow mask inherently provides it with the enhanced resolution patterning on both planar and nonplanar surfaces. To highlight these attractive benefits, substrates are patterned with metal deposition as well as by etching in a multilayer configuration. Moreover, it is found that the pattern resolution which is degraded as the shadow mask is repeatedly coated with metal and becomes warped can be restored after the mask cleaning procedure, demonstrating its effective reusability. Finally, as a device‐level application, top contact/bottom gate organic thin film transistor arrays are fabricated on both planar and curved surfaces using the shadow mask. These results show the promise of stencil lithography as a versatile and reliable high resolution patterning method for various applications by exploiting the presented ultrathin silicon shadow mask.

Deep focus light-field camera for handheld 3D intraoral scanning using crosstalk-free solid immersion microlens arrays.

3D in vivo imaging techniques facilitate disease tracking and treatment, but bulky configurations and motion artifacts limit practical clinical applications. Compact light-field cameras with microlens arrays offer a feasible option for rapid volumetric imaging, yet their utilization in clinical practice necessitates an increased depth-of-field for handheld operation. Here, we report deep focus light-field camera (DF-LFC) with crosstalk-free solid immersion microlens arrays (siMLAs), allowing large depth-of-field and high-resolution imaging for handheld 3D intraoral scanning. The siMLAs consist of thin PDMS-coated microlens arrays and a metal-insulator-metal absorber to extend the focal length with low optical crosstalk and specular reflection. The experimental results show that the immersion of MLAs in PDMS increases the focal length by a factor of 2.7 and the transmittance by 5.6%-27%. Unlike conventional MLAs, the siMLAs exhibit exceptionally high f-numbers up to f/6, resulting in a large depth-of-field for light-field imaging. The siMLAs were fully integrated into an intraoral scanner to reconstruct a 3D dental phantom with a distance measurement error of 82 ± 41 μm during handheld operation. The DF-LFC offers a new direction not only for digital dental impressions with high accuracy, simplified workflow, reduced waste, and digital compatibility but also for assorted clinical endoscopy and microscopy.

Electrohydrodynamic Printed Ultra-Micro AgNPs Thin Film Temperature Sensors Array for High-Resolution Sensing.

Current methods for thin film sensors preparation include screen printing, inkjet printing, and MEMS (microelectromechanical systems) techniques. However, their limitations in achieving sub-10 μm line widths hinder high-density sensors array fabrication. Electrohydrodynamic (EHD) printing is a promising alternative due to its ability to print multiple materials and multilayer structures with patterned films less than 10 μm width. In this paper, we innovatively proposed a method using only EHD printing to prepare ultra-micro thin film temperature sensors array. The sensitive layer of the four sensors was compactly integrated within an area measuring 450 μm × 450 μm, featuring a line width of less than 10 μm, and a film thickness ranging from 150 nm to 230 nm. The conductive network of silver nanoparticles exhibited a porosity of 0.86%. After a 17 h temperature-resistance test, significant differences in the performance of the four sensors were observed. Sensor 3 showcased relatively superior performance, boasting a fitted linearity of 0.99994 and a TCR of 937.8 ppm/°C within the temperature range of 20 °C to 120 °C. Moreover, after the 17 h test, a resistance change rate of 0.17% was recorded at 20 °C.

A dilating and embedding scheme for constructing sparse MIMO radar array

AbstractIn this letter, a dilating and embedding scheme for constructing sparse multiple‐input and multiple‐output radar arrays is addressed, which seeks to increase the uniform degrees of freedom (uDOFs) and reduce the mutual coupling effects for a given number of transmitters and receivers (Tx/Rx). According to this scheme, a dilated maximum inter‐element spacing constraint (MISC) array with an embedded thinned coprime array in the collocated MIMO radar for DOA estimation is proposed. Theoretical analysis shows that the proposed array can provide higher uDOFs and is robust in a scenario with heavy levels of mutual coupling. Numerical simulations are conducted to validate its aforementioned advantages in line with the design scheme.

Synthesis of linear thinned array based on improved binary brain storm optimization

In this paper, an improved binary brain storm optimization (ImBBSO) method is presented for pattern synthesis of linear thinned array. To avoid local convergence and obtain the global optimum, on the basic of original binary brain storm optimization (BBSO) algorithm, the designed method mainly modifies three aspects, containing the clustering centers selection, the forced bit transposition mechanism and the survival of population. The interactions of these three operations drive optimization variables to move toward a better direction. During optimization process, the formulated cost function balances the relationship among the number of active elements, the peak sidelobe level and the half power beam width, which are eventually in the best balance state after completing iterations. Besides, the subarray partition strategy is also integrated into the proposed optimization framework with slight amendments, which can be applied to many engineering fields with space restrictions. Finally, several numerical examples demonstrate the effectiveness and applicability of the proposed method compared with other existing results of state-of-the-art methods, whether in benchmarking functions or linear array application.

Linear Antenna Array Sectorized Beam Scanning Approaches Using Element Position Perturbation in the Azimuth Plane.

In this paper, two sector beam scanning approaches (BSAs) based on element position perturbations (EPPs) in the azimuth plane are introduced. In EPP-BSA, the elements' excitations are kept constant and the elements' positions in the direction normal to the array line are changed according to a predetermined EPP pattern. The magnitude and repetition rate of the selected EPP pattern determines the steering angle of the main beam. However, EPP-BSA results in a wide scanning range with a significant increase in the side lobe level (SLL). To mitigate this drawback, a reduction in the SLL of the array pattern is firstly performed using the single convolution/genetic algorithm (SC/GA) technique and then perturbing the elements' positions in the azimuth plane. This combination between SLL reduction and EPP-BSA (SLL/EPP-BSA) results in a smaller scanning range with a relatively constant half power beamwidth (HPBW) and a much lower SLL. In addition, keeping the synthesized excitation coefficients constant without adding progressive phase shifters facilitates the manufacturing process and reduces the cost of the feeding network. Furthermore, a planar antenna array thinning approach is proposed to realize the EPP-BSA. The results are realized using the computer simulation technology (CST) microwave studio software package, which provides users with an optimized modeling environment and results in realizable and realistic designs.

Graphitic nanostructure integrated NiO composites for high-performance lithium-ion batteries

So far, various graphite-Nickel Oxide (NiO) composites have been investigated as anodes for Li-ion batteries. However, developing an ideal composite that overcomes NiO's electrical conductivity limitations remains a significant challenge. The current study presents an in-situ one-step hydrothermal technique for integrating NiO into a 3D peony-like graphitic nanostructure (NiO-GNF), resulting in unique thin nanosheet arrays with porous, conductive channels. Notably, the composites endowed controlled aggregation and restacking of NiO, buffered electrode stress and improved electrical conductivity due to the expanded nature of graphite. In addition, the enlarged interlayer spacing of expanded graphite facilitated an improved Li-ion insertion. Overall, in comparison to pure NiO anodes, the NiO-GNF composite achieved an impressive electrochemical improvement exhibiting a highly reversible discharge capacity of 678.2 mAh/g after 370 cycles at a current density of 0.5 A g−1, corresponding to a capacity retention of 60.7 %. The composite also demonstrated a capacity of 752 mAh/g at a high current density of 1.2 A g−1.

Finite element analysis of transverse size effect on the pyroelectric Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3 –PbTiO3 thin film for infrared array applications

Exploring and revealing the influence of the pyroelectric thin film array element size on its structure and pyroelectric performance is crucial for designing integrated pyroelectric infrared detectors. In this work, the transverse size effect on the piezoelectric, dielectric, and especially the pyroelectric properties for a new-generation relaxor ferroelectric material Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIMNT) was studied by a finite element method. The lateral size-dependent piezoelectric and dielectric properties of the PIMNT thin film indicated that with the decrease in the transverse size, the piezoelectric constant d33 and relative dielectric constant εr increased substantially. The piezoelectric constant d33 and relative dielectric constant εr along ⟨001⟩ and ⟨011⟩ orientation increased faster than those along ⟨111⟩. A critical aspect ratio (in this paper, it was defined as radius/thickness) was found around 1:1 for three directions. We further discovered that the pyroelectric coefficient for PIMNT thin film along the ⟨111⟩ direction (the best crystallographic orientation for pyroelectric performance) decreased from 8.5 × 10−4 to 8.0 × 10−4 C/(m2·K) with the aspect ratio down to 0.01. The variation of the piezoelectric, dielectric, and pyroelectric properties originated from the declamping of the PIMNT thin film from the substrate. This finding gives insight into the transverse size effect on the electrical properties of new-generation relaxor PIMNT thin film and provides a guidance for designing high-performance infrared array detectors.

Multi-element metasurface system for imaging in the near-infrared

Metasurfaces are optically thin 2D arrays of subwavelength scatterers that modify scalar and vector properties of incident electromagnetic fields. Metasurface lenses are of particular interest for imaging applications for their flat form factor, compatibility with CMOS fabrication processes, and potential for correcting aberrations with a small number of elements. We advance this capability by realizing a millimeter-diameter, polarization-independent metalens triplet system with chromatic aberration correction over the wavelength range of 1.30–1.60 μm and monochromatic aberration correction enabling a field of view of 50°.

An Improved Synthesis of Sparse Planar Arrays Using Density-Weighted Method and Chaos Sparrow Search Algorithm

This paper presents an improved approach for the synthesis of sparse planar arrays using density-weighted method and chaos sparrow search algorithm (CSSA) with multiple constraints. The approach consists of two stages and has an efficient way in dealing with multiple constraints, including the array aperture, number of elements, and minimum spacing between adjacent elements. In the first step, a density-weighted method is implemented to generate a thinned array structure by introducing the weighted coefficient based on the distribution function of a uniform full array to the elements, which can reduce the time and improve the efficiency of the optimization of sparse matrices. On the basis of a density-weighted array, tent chaotic mapping is introduced to initialize the population, then sparrow search algorithm (SSA) is used to further optimize the location of each element of the array antenna to search for the global optimal solution. As a consequence, the proposed method exhibits improved flexibility with respect to other analytical techniques, and reduces the computational cost of the optimization algorithm. Numerical validation results demonstrate the effectiveness and reliability of the proposed method, showing that it can achieve better results than existing methods in the design of sparse planar array arrangements.

Broadband Statistically Designed Thinned-Binned Array Antennas

Statistically thinned arrays are obtained by thinning a reference filled array, according to a probabilistic law that is dictated by the reference current. The remaining radiators are still separated by commensurable distances, even if randomly located. Hence, wideband operations are prevented by grating lobes’ occurrence. To overcome the above limitation, a new and simple strategy is presented in this article for randomly deploying the elemental radiators across the array aperture. More in detail, unlike classic thinned arrays, elements surviving the thinning are not positioned on a priori fixed deterministic lattice. Instead, their positions are modeled as random variables, which are determined by exploiting the binned strategy. Numerical examples reveal that the new proposed scheme allows for a considerable enlargement of the frequency band, without incurring in grating lobes’ appearance.

Implementation of Thinned Array Synthesis in Hyperthermia Treatment Planning of 434 MHz Phased Array Breast Applicator Using Genetic Algorithm

Genetic algorithm-based array thinning technique is investigated in this paper to study the performance of our 18-element 434 MHz phased array breast applicator when driven by reduced number of active antennas. Selective power deposition ability was assessed for 18, 15, 12, and 9 active antennas on 25 patient models with varying characteristics. The average hotspot to target quotient of 18-, 15-, 12-, and 9-antenna excitation in 25 patient models was 1.18, 1.09, 1.09, and 1.13, respectively. The average temperature in 50% tumor volume for 18-, 15-, 12-, and 9-antenna excitation was 42.42 °C, 42.48 °C, 42.49 °C, and 42.48 °C, respectively. The temperature induced in tumor and healthy tissues is similar for varying number of active channels. However, the amount of power consumed was 25.2%, 53.9%, 97.9% higher for 15, 12, 9 active antennas compared to the filled array. Antenna array with 12 active elements was chosen as the optimal combination as it provided selective tumor heating with good tradeoff between number of channels and power consumption. The heating ability of the thinned array was assessed for 50% reduction in the number of active antennas on patient derived heterogeneous breast phantoms for five tumor target locations. The good agreement between simulated and measured thermal distributions demonstrate the selective heating ability of our phased array applicator for 50% reduction in hardware resources. The study outcome enables us to realize a cost-effective hyperthermia treatment delivery system.

Interisland-Distance-Mediated Growth of Centimeter-Scale Two-Dimensional Magnetic Fe3O4 Arrays with Unidirectional Domain Orientations.

Two-dimensional (2D) nanosheet arrays with unidirectional orientations are of great significance for synthesizing wafer-scale single crystals. Although great efforts have been devoted, the growth of atomically thin magnetic nanosheet arrays and single crystals is still unaddressed. Here we design an interisland-distance-mediated chemical vapor deposition strategy to synthesize centimeter-scale atomically thin Fe3O4 arrays with unidirectional orientations on mica. The unidirectional alignment of nearly all the Fe3O4 nanosheets is driven by a dual-coupling-guided growth mechanism. The Fe3O4/mica interlayer interaction induces two preferred antiparallel orientations, whereas the interisland interaction of Fe3O4 breaks the energy degeneracy of antiparallel orientations. The room-temperature long-range ferrimagnetic order and thickness-tunable magnetic domain evolution are uncovered in atomically thin Fe3O4. This strategy to tune the orientations of nanosheets through the an interisland interaction can guide the synthesis of other 2D transition-metal oxides, thereby laying a solid foundation for future spintronic device applications at the integration level.

Study of spatial organisation of magnetic field directed gold-pickering-ferrofluid-nanoemulsion in spin coated film

The magnetic field directed self-assembly of the nanoparticles is cheap, fast and easy method to prepare the patterned thin film useful for various applications. However, the dipole-dipole interaction between nanoparticles at the interface generates the rough-edged patterns even at microscale causing the excess optical scattering making it unsuitable for the optical applications. In this work, the magnetic field was applied during the spin coating of the Polyethylene glycol 40S (PEG) capped Gold-Pickering ferrofluid nanoemulsion (PEG-C-GM-FF) dispersed in aqueous Polyvinyl alcohol (PVA) solution with different viscosities. Optimised combination of spinning speed and magnetic field strength was achieved to prepare the film with the straight chains of PEG-C-GM-FF required for the optical applications. It is a quick, cost-effective, non-intrusive and simple method for achieving a thin layered array of chains with tuneable gaps between them. The image analysis revealed that the Full Width Half Maximum (FWHM) representing the PEG-C-GM-FF chain spatial density across the substrate for each aqueous phase viscosity decreases with the increase in the spin speeds at constant magnetic field strength. The FTIR (Fourier Transformed Infrared Spectroscopy) of the patterned thin film showed that the intensity of the 2927 ​cm−1 vibrational band corresponding to CH bond in PVA was seen to be linearly increasing with the spatial density of the PEG-C-GM-FF chains. In comparison to the gold strip patterns printed with the nanolithography technique; the magnetically aligned array of PEG-C-GM-FF showed a potential for preparing photonic antenna suitable for enhancing the optical absorption and detect low concentration analyte.

Thinned array ultrasonic imaging of debonding defects in discontinuous impedance bonded structures

Ballastless track is a typical bonding structure with discontinuous impedance. Under the influence of heavy load, deteriorating environment and other situations, the circumstance of debonding occurs frequently and seriously affects the safety of train operation. In this work, a high-precision array ultrasound fast imaging method is proposed. Based on the propagation path and time of sound wave in the medium obtained by ray tracing method, a theoretical model of sound velocity of discontinuous impedance bonding structure is established when the difference in sound velocity among dielectric layers is taken into account. High degree of freedom sparse array based on real number coding as well as synthetic aperture focusing technology (SAFT) imaging method is used to improve detection efficiency. The results of the experiments carried out on ballast less track structure are shown below. The ray tracing method can accurately calculate the propagation path and propagation time of ultrasonic wave and improve the detection accuracy. The optimized thinned array pattern has narrowed the main lobe width and low side lobe gain, which improves the detection efficiency and sound field directivity. The efficiency of thinned array SAFT imaging method is improved by 30.9% when the imaging error of debonding defects is within ±5%, which provides a theoretical support fordetecting such debonding defects.

IFT and Chebyshev-based planar array thinning for adaptive interference suppression

IFT and Chebyshev-based planar array thinning for adaptive interference suppression

Modulation of ZnO Nanostructure for Efficient Photocatalytic Performance.

Structure has been considered to play an important role in photocatalytic performance of the semiconductors, but the intrinsic factors were rarely revealed. Herein, ZnO nanomaterials in the structures of thin film, nanowire array and nanosheet array were synthesized, and their structural characteristics, optical properties, photocurrent response and photocatalytic efficiency were compared with each other for illustrating the issue. The photoluminescence intensity decreased in the order of nanosheets, thin film and nanowires for improved lifetime of the photoexcited charges. The absorption of the nanosheets and nanowires improved obviously in the visible range with a redshift of the absorption edge than that of the thin film. The nanowires possessed the highest response current of 82.65μA at a response time of 2.0ms in a sensitivity of 87.93 at the light frequency of 1Hz, and gained the largest catalytic efficiency of 2.45μg/cm2h for the methylene blue degradation in UV light. Nevertheless, the improvement of catalytic efficiency of the nanosheets (up to 42.4%) was much larger than that of nanowires (5.7%) and thin film (2.6%) for the Au coating. The analysis revealed that the photocatalytic efficiency of the ZnO nanomaterials was modulated by the structure as it contained different surface area, roughness, defect and doping states, vacancies, polar and non-polar crystalline faces, which would provide structural design of semiconductor nanomaterials for the photoelectric and photocatalytic applications.

Fast design technique for thinned linear array with arbitrary grid spacing in the presence of multi-constraint requirements

Global optimization algorithms can be performed to design thinned arrays with various beamshapes. However, they have intensive computational efforts and are therefore limited to small to medium sized array problems. On the other hand, analytical methods do not suffer from this problem, but usually assume an idealized environment, thereby excluding the influence of a complex electromagnetic environment on thinned array designs caused, e.g., by beam-scanning and interference signals. In this paper, a unified framework of the reconfigurable thinned array antenna system is developed and we propose a fast design technique for thinned linear arrays that is capable of dealing with the aforementioned limitations. It is based on the previously published by means of the modified iterative Chirp-Z transform (MICZT) technique, which is herein extended and generalized for linear array thinning with arbitrary grid spacing in the presence of multi-constraint requirements. More specifically, the fast computation of the scannable array factor for a uniformly illuminated thinned linear array is discussed, and beam-scanning thinned arrays with symmetry configuration are also exploited in this paper. In addition, thinned array designs with null placement will be investigated for rejecting multiple sidelobe interference signals. Several representative numerical examples and comparisons with existing methods are presented to validate the effectiveness and efficiency of the proposed technique.

Knock sensing and imaging from structural bending waves

This paper presents a novel knock imaging technique for human-to-things interfaces. It allows any object to use its own surface as an imaging sensor. The methodology is to sense the structural bending waves caused by the knock and reconstruct the intensity image through the beamforming of the wave signals. To verify this, we prepare a thin piezoelectric sensor array on a square plate. The performances are evaluated by measuring the beam peak, beamwidth, and sidelobe level in the reconstructed image. Finally, a real finger knock test is demonstrated, showing an image reconstruction that the position error is only 3 mm.