Multiple Unit Cells Research Articles

Parametric optimization of selected auxetic structures

Auxetic materials exhibit an interesting, counterintuitive behavior—when subjected to uniaxial tension, they stretch laterally, and when uniaxially compressed, they shrink laterally. In contrast to conventional materials, in auxetics, the value of Poisson’s ratio is negative. Behavior of auxetic materials is an effect of their internal structures. The auxetic effect depends mostly on the geometry of their internal unit cells and not on the properties of the bulk material. This paper presents the results of parametric optimization of selected two-dimensional auxetic unit cells with the aim to identify the geometrical parameters which exhibit the strongest influence on the value of Poisson’s ratio in each unit cell, and to identify geometries which exhibit the strongest auxetic effect. The optimization was conducted through numerical simulation with the use of the finite element method in commercial software. Response surface optimization and multi-objective genetic algorithm (MOGA) were applied. Obtained candidate geometries were verified via additional FEM analyses and confirmed to have improved auxetic effect and reduced equivalent stress. 5 × 5 structures composed of reference and optimized geometries of analyzed unit cells were subjected to similar analyses and it was confirmed that the optimization of singular unit cells caused an improvement of auxetic effect and reduction in equivalent stress in regular structures composed of multiple unit cells.

Investigating the Role of TDP-43 Microvasculopathy on Neurovascular unit Function in the Setting of COVID-19 and Alzheimer’s Disease and Related Dementias

Dysfunction of the blood-brain-barrier and the neurovascular unit, comprised of brain endothelial cells, pericytes, neurons, and glia, has been strongly implicated in the neurological manifestations of SARS-CoV-2 and vascular contributions to cognitive impairment and dementia (VCID) in Alzheimer’s disease (AD). A challenging unanswered question is whether the cognitive and neuropsychiatric disturbances of post-acute neurological sequelae of SARS-CoV-2 (Neuro-PASC) or long COVID are potentially linked to the development of AD. The RNA/DNA-binding protein TDP-43 (transactive response DNA-binding protein of 43 kDa) has been implicated in the pathogenesis of several viral infections and is cleaved by the main SARS-CoV-2 protease Nsp5, leading to neurotoxic TDP-43 fragments in mammalian cells. Aggregates composed of phosphorylated, ubiquitinated TDP-43 are also frequently present in AD. While TDP-43 microvasculopathy has been described in a subset of ADRD cases, its impact on blood-brain barrier integrity and neurovascular unit function is unknown. In this study, we investigated whether TDP-43 microvasculopathy is observed in AD and COVID-19 patient brains. We hypothesized that perivascular TDP-43 induces neurovascular unit dysfunction through cell autonomous and non-autonomous effects of pathologic TDP-43 deposition in astrocytic endfeet processes. To test this, hippocampus and dorsolateral prefrontal cortex (dlPFC) from human AD brains (Braak IV-VI; CERAD definite) and cognitively normal age- and sex-matched controls, with and without comorbid COVID-19, were selected from autopsy cases conducted at Yale between 2014-2018 (non-COVID), and COVID-positive cases conducted between April 2020-present; (n=10-12 per group). Our data from COVID-19 and ADRD human brain samples show a distinctive profile of phosphorylated TDP-43 (pTDP-43) and Tau expression compared to COVID-19 negative AD and control brains. Immunofluorescence analysis of hippocampus and cerebral cortex showed perivascular deposits of pTDP-43 found as threads or aggregates in close proximity to capillaries and vascular basal lamina, labeled with type IV collagen. We also observe a subset of pTDP-43 that colocalizes with neuronal tau, suggesting involvement of multiple neurovascular unit cells. Our data also revealed CD31 (platelet endothelial cell adhesion molecule-1, PECAM-1) positive cells in the microvessels colocalize with pTDP-43. Interestingly, colocalization of PECAM-1 and pTDP-43 positive cells in the perivascular zone suggests transendothelial migration. Atypical pTDP-43 accumulation was also noted in astrocytic endfeet, and astrocytic hypertrophy was identified. Furthermore the blood-brain barrier may be breached, detected by a downregulation or change in the expression and distribution of Claudin-5 in the blood vessels where pTDP-43 is present. Breakdown of these tight junction proteins has been strongly implicated in the neurological manifestations of SARS-CoV-2 and vascular contributions to cognitive impairment and dementia (VCID) in AD. These findings raise the possibility that perivascular pTDP-43 aggregates impair endothelial, neuronal, and/or astrocytic functions in the neurovascular unit, disrupt blood-brain-barrier, and potentially suggest a novel role for TDP-43 induced microvasculopathy in ADRD and COVID-19. This research and the Center for Human Brain Discovery is supported through philanthropic funds and NIH/NINDS R01NS122907 (to PPG). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

X-ray Crystallography Module in MD Simulation Program Amber 2023. Refining the Models of Protein Crystals.

The MD simulation package Amber offers an attractive platform to refine crystallographic structures of proteins: (i) state-of-the-art force fields help to regularize protein coordinates and reconstruct the poorly diffracting elements of the structure, such as flexible loops; (ii) MD simulations restrained by the experimental diffraction data provide an effective strategy to optimize structural models of protein crystals, including explicitly modeled interstitial solvent as well as crystal contacts. Here, we present the new crystallography module xray, released as a part of the Amber 2023 package. This module contains functions to calculate and scale structure factors (including the contributions from bulk solvent), evaluate the maximum-likelihood-type crystallographic potential, and compute its derivative forces. The X-ray functionality of Amber no longer relies on external dependencies so that the full advantage of GPU acceleration can be taken. This makes it possible to refine in a short time hundreds of crystal models, including supercell models comprised of multiple unit cells. The new automated Amber-based refinement procedure leads to an appreciable improvement in Rfree (in some cases, by as much as 0.067) as well as MolProbity scores.

Topology optimization of periodic structures for crash and static load cases using the evolutionary level set method

Assembly complexity and manufacturing costs of engineering structures can be significantly reduced by using periodic mechanical components, which are defined by combining multiple identical unit cells into a global topology. Additionally, the superior energy-absorbing properties of lattice-based periodic structures can potentially enhance the overall performance in crash-related applications. Recent research developments in periodic topology optimization (PTO) have shown its efficacy for tackling new design problems and finding advanced novel structures. However, most of these methods rely on gradient information in the optimization process, which poses difficulties for crash problems where analytical sensitivities are usually not directly applicable. In this paper, we present an effective periodic evolutionary level set method (P-EA-LSM) for the optimization of periodic structures. P-EA-LSM uses a low-dimensional level-set representation based on moving morphable components to parametrize a single unit cell, which is replicated in the design domain according to a predefined pattern. The unit cell is optimized using an evolutionary algorithm and the structural responses are calculated for the entire system. We initially assess the performance of P-EA-LSM using three 2D minimum compliance test cases with varying periodicities. Our results demonstrate that our approach produces solutions comparable to other state-of-the-art methods for PTO while keeping a low dimensionality of the optimization problem. Subsequently, we effectively evaluate the capabilities of P-EA-LSM in a crashworthiness scenario. This particular application highlights the significant potential of the method, which does not rely on analytical sensitivities.

Optimizing graded metamaterials via genetic algorithm to control energy transmission

Optimization of functionally graded metamaterial arrays with a high dimensional and continuous geometric design space is cumbersome and could be accelerated via machine learning tools. Mechanical metamaterials can manipulate acoustic or ultrasonic waves by introducing significant dispersive and attenuative effects near their natural frequency. In this work, functionally graded structures are designed and optimized to combine the energy attenuation performance of multiple unit cells with varying frequency responses and to reduce the interlayer mismatch effects. Optimization through genetic algorithms avoids many local minima related to high dimensionality of the design space, but requires many iterations. A reduced order model (ROM) is applied, which can reproduce the transmission response traditionally calculated with FEM in a fraction of the time. Pairing GA and the ROM together, an array of 6 unit cells (with a total of 18 independent geometric design variables) is optimized to have stop bands with extended width and sharper boundaries. Symmetric functionally graded structures are determined to have optimal geometric configurations. Measured 3D printed features are projected onto the ROM solutions to quantify the effect of printing uncertainty on array performance. Repeatability error of ±20μm is determined to reduce the mean depth of the transmission stop band by a factor of 102 and introduce small shifts in center frequency and band width. Proposed methods to improve the resolution of accessible points in the ROM space, reduce sensitivity to geometric uncertainty, and add design freedom include introducing out-of-plane perforations and varying constituent materials using tunable filled resin systems.

Minimal Molecular Building Blocks for Screening in Quasi-Two-Dimensional Organic-Inorganic Lead Halide Perovskites.

Layered hybrid organic-inorganic lead halide perovskites have intriguing optoelectronic properties, but some of the most interesting perovskite systems, such as defective, disordered, or mixed perovskites, require multiple unit cells to describe and are not accessible within state-of-the-art ab initio theoretical approaches for computing excited states. The principal bottleneck is the calculation of the dielectric matrix, which scales formally as O(N4). We develop here a fully ab initio approximation for the dielectric matrix, known as IPSA-2C, in which we separate the polarizability of the organic/inorganic layers into minimal building blocks, thus circumventing the undesirable power-law scaling. The IPSA-2C method reproduces the quasi-particle band structures and absorption spectra for a series of Ruddlesden-Popper perovskites to high accuracy, by including critical nonlocal effects neglected in simpler models, and sheds light on the complicated interplay of screening between the organic and inorganic sublattices.

Simultaneous Optimization of 1-bit 3-D Coding Meta-Volumes for Both Broadband and Wide Field-of-View Radar Cross-Section Reduction

Coding metasurfaces (CMSs) rely on the proper tiling of two or more kinds of complementary unit cells within an array to enable phase cancellation and corresponding destructive interference thereby reducing the radar cross-section (RCS) of a given scatterer. Typically, these unit cells are planar and inherently limited in their field of view (FoV). This work demonstrates that breaking this traditional unit cell design paradigm in favor of novel 3-D meta-volumes enables both broadband and wide-FoV RCS reduction. Further, this work introduces a modified genetic algorithm (GA) framework for simultaneously tailoring the reflection phase of multiple unit cells to achieve the best composite response. By applying these identical pair-optimization strategies, it is shown that 3-D unit cells outperform their 2-D counterparts of the same lateral size in terms of both the fractional bandwidth (FBW) and FoV. One exemplary 3-D solution purely improves the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H_{\mathrm {x}}$ </tex-math></inline-formula> response with FBW exceeding 75% across a full 70° FoV. A second 3-D solution provides an improved <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E_{\mathrm {x}}$ </tex-math></inline-formula> polarization response with a near 70% FBW at 45° and up to 75% FBW at 70° for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H_{\mathrm {x}}$ </tex-math></inline-formula> polarization at the expense of reduced FBW close to 50% for incidence angles less than 45°.

Experimental research on a novel soil displacement monitoring system based on measurement unit cells (MUCs)

Advanced measurement technology is of great significance to the prevention of geological disasters and engineering construction and simultaneously promotes geotechnical engineering development. This paper reports a novel soil displacement monitoring system based on multiple measurement unit cells. A modularized structure and corresponding positioning algorithm were proposed to monitor the 3D displacement of soil. The monitoring software was developed to dynamically display deformation. Then, a calibration experiment was performed to verify the feasibility of the measurement unit cell. Furthermore, a model experiment adopting X-ray visualization was performed to validate the reliability of the soil displacement monitoring system. It is determined that the proposed soil displacement monitoring system has a mm-level accuracy and satisfies geotechnical engineering requirements.

A Phased Array Antenna with Novel Composite Right/Left-Handed (CRLH) Phase Shifters for Wi-Fi 6 Communication Systems

A linear phased array antenna excited with a novel composite right/left-handed (CRLH) phase shifters structure is proposed. The phase of the conventional CRLH transmission line is controlled with magnetically aligned micron-sized particles embedded inside the unit cell of the CRLH transmission line. The cascading of unit cells produces the desired phase shifts for the main beam scanning of the linear antenna array operating at a 5.5 GHz center frequency for Wi-Fi 6 applications. The proposed phase shifter design has a very low insertion loss (0.5–2 dB), excellent matching characteristics with the antenna array (less than −10 dB) and a small phase error (1–2 degrees). A 1 × 4 linear patch antenna phased array operating at a 5.5 GHz center frequency of the Wi-Fi 6 band is simulated using the Method of Moments (MoM) simulator platform. Then, the array is driven with the proposed novel CRLH phase shifters for the main beam at broadside and the main beam steered at 15- and 30-degree scan angles toward the desired users. For experimental validation, multiple unit cells of the proposed phase shifters are fabricated, and the 1 × 4 patch antenna array is fed with these fabricated unit cells of the phase shifters. The phased array radiation patterns are measured using an in-house fully calibrated anechoic chamber and were compared with simulated phased array patterns. The measured phased array patterns are in good agreement with the simulated patterns. As compared with commercially available phase shifters, the proposed novel CRLH phase shifters do not need external complex biasing circuitry, which is a major advantage in space constraint limitations at the router side of multi-user MIMO-OFDM systems.

Multiscale topology optimization of electromagnetic metamaterials using a high-contrast homogenization method

This study proposes a multiscale topology optimization method for electromagnetic metamaterials using a level set-based topology optimization method that incorporates a high-contrast homogenization method. The high-contrast homogenization method can express wave propagation behavior in metamaterials for various frequencies. It can also capture unusual properties caused by local resonances, which cannot be estimated by conventional homogenization approaches. We formulated multiscale topology optimization problems where objective functions are defined by the macroscopic wave propagation behavior, and microstructures forming a metamaterial are set as design variables. Sensitivity analysis was conducted based on the concepts of shape and topological derivatives. As numerical examples, we offer optimized designs of metamaterials composed of multiple unit cell structures working as a demultiplexer based on negative permeability. The mechanism of the obtained metamaterials is discussed based on homogenized coefficients.

A Wideband mm-Wave Watt-Level Spatial Power-Combined Power Amplifier With 26% PAE in SiGe BiCMOS Technology

We present a wideband watt-level power amplifier (PA) for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Ka$ </tex-math></inline-formula> -band designed and implemented in the 0.25- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> SiGe:C BiCMOS technology. The core of the design is a chip with multiple custom PA unit cells (PA-cells), which are interfaced with a power combiner placed on a laminate. The power combiner is based on a principle of the recently proposed multichannel transition with spatial power combining functionality, where an array of strongly coupled microstrip lines (MLs) interface a single substrate integrated waveguide (SIW). The realized watt-level PA combining four differential cascode PA-cells achieves a saturated output power ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{{\text {sat}}}$ </tex-math></inline-formula> ) of 30.8 dBm with 26.7% power-added efficiency (PAE). The 64-QAM modulation tests confirm the competitive PA performance on multi-Gb/s communication signals. The obtained combination of the high PAE and high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P _{{\text {sat}}}$ </tex-math></inline-formula> over a wide frequency band (30%) is an advantageous property of the proposed solution with respect to the previously published designs. This high performance is the result of using the proposed architecture with low-loss (0.6 dB) and wideband (54%) parallel spatial power combiner. Moreover, the presented joint EM–circuit–thermal optimization allows achieving optimal system-level performance by taking into account various critical multiphysics effects occurring in the combined PA. This article describes the design and performance of the whole integrated structure and its individual components.

A 3D-printed sound-absorbing material based on multiple resonator-like unit cells for low and middle frequencies

A 3D-printed sound-absorbing material based on multiple resonator-like unit cells for low and middle frequencies

Sandwich meta-panel based on grooved corrugation for low-frequency sound absorption

In this work, a novel sandwich meta-panel (SMP) with grooved corrugations is proposed to efficiently attenuate low-frequency sound waves under deep subwavelength thickness (e.g., at 133 Hz). Most innovatively, SMP possesses tremendous mechanical characteristics (e.g., high bending stiffness) simultaneously, stemming from its corrugation core configuration. A theoretical prediction for sound absorption with an explicit expression of effective length is built, as well as a direct numerical simulation model. The theoretical and numerical results coincide well with each other, and demonstrate the SMPs' great capacity of manipulating low-frequency sound waves. Further, the SMPs can be tuned flexibly through altering perforation diameter, channel length and folding number, and multiple diverse unit cells can be coupled to get wide high-absorption bands (e.g., from 203 Hz to 249 Hz). The SMPs pave a new way for coiled-up space metastructures to engineering applications, with simple layout and perspicuous designing guidance.

W-band Scalable 2×2 Phased-Array Transmitter and Receiver Chipsets in SiGe BiCMOS for High Data-Rate Communication

This article presents a pair of W-band phased-array transmitter (TX) and receiver (RX) chipsets in a 0.13- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> SiGe BiCMOS process for high data-rate wireless communication. Both the chips integrate four compact front-end channels in 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 distribution, and the distance between the adjacent RF pads is less than 1.8 mm ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.56\lambda $ </tex-math></inline-formula> at 90 GHz) to fit for the tight antenna array and enable array scaling by tiling multiple unit cells. A 6-bit active phase shifter based on the improved phase-inverting variable gain amplifiers is leveraged to achieve high phase-shift precision and bandwidth concurrently. A noise reduction technique using a parallel inductor to resonate with the parasitic capacitors of the cascode transistors is adopted in the low-noise amplifier design. A novel miniature power combiner, which occupies a much more compact area than the Wilkinson power combiner while delivering great RF performance, is proposed and elaborately analyzed. System-level calibration for local oscillator (LO) leakage and dc-offset suppression is enabled by introducing digitally controlled current sources into the up-conversion and down-conversion mixers. On-wafer measurements for the TX chip exhibit a single-channel IF-to-RF conversion gain (CG) of 26 dB, a competitively high output 1-dB compression point (OP <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {1\,dB}}$ </tex-math></inline-formula> ) of 11 dBm. The RX chip achieves an RF-to-IF CG of 19.5 dB with 9-/14-GHz IF/RF 3-dB bandwidth, a noise figure of 7.7 dB, and an input 1-dB compression point of −28 dBm. The phase-shift characteristics are verified by the TX/RX front-end measurements, achieving a 6-bit phase resolution with minimum rms phase/gain error smaller than 0.83°/0.45 dB and a large phase-shift bandwidth higher than 20 GHz. Preliminary wireless transmission test using a low-cost die-on-printed circuit board (PCB) prototype demonstrates wireless data rates of 1.6 and 0.8 gigabits per second (Gb/s) at distances of 0.4 and 1 m with 256-quadratic-amplitude modulation (QAM) and 16-QAM modulated signals, respectively.

Seismic resonant metamaterials for the protection of an elastic-plastic SDOF system against vertically propagating seismic shear waves (SH) in nonlinear soil

The paper explores the key mechanisms that govern the dynamic interaction between resonant metamaterials (consisting of multiple unit cells embedded in the soil, with horizontally vibrating internal masses) and an existing nonlinear structure on nonlinear soil. Elastic behavior of the soil and of the SDOF system, representing the structure, is also investigated for comparison. The Real-ESSI Simulator is employed to develop in-plane (2D) finite element (FE) models, and an extensive parametric analysis is conducted to evaluate the influence of key parameters on the protective efficiency of resonant metamaterials. Both artificial and real ground motions are used as seismic excitation, vertically propagated through the soil as shear waves (SH), employing the Domain Reduction Method (DRM). Two protective mechanisms are identified. The first mechanism is related to the inertial interaction of the metamaterials with the surrounding soil, namely, it is the out-of-phase resonant oscillation of the internal metamaterial masses with respect to the soil at periods close to the natural period of the structure. The maximum reduction in structural response is achieved when the resonant period of the metamaterials is equal or a bit larger than the effective period of the structure. The second mechanism is related to the kinematic interaction of the metamaterials with the surrounding soil, namely, the presence of empty unit cells (no internal masses) in the soil next to the structure creates a protective “shadow” zone. This kinematic interaction mechanism becomes effective when the wavelength of the incoming seismic waves is comparable to the size of the metamaterials, and at the same time, the period of the waves is close to the natural period of the structure. When both soil and structural nonlinearities are considered, the effect of metamaterials remains always beneficial, and their action is localized, making them practically harmless to neighboring structures.

Extremely Wideband and Omnidirectional RCS Reduction for Wide-Angle Oblique Incidence

In this communication, a novel metasurface with multiple unit cells of different thicknesses based on optimized multielement phase cancellation (OMEPC) is proposed for extremely wideband, omnidirectional, and polarization-independent radar cross section (RCS) reduction under wide-angle oblique incidence. Omnidirectional characteristic refers to the capability of RCS reduction under all azimuth angles ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varphi ^{i}$ </tex-math></inline-formula> ) at certain elevation angles ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta ^{i}$ </tex-math></inline-formula> ). The equivalent circuit model of the square patch unit cell is analyzed under both normal and oblique incidences. Unit cells of multiple thicknesses are adopted to solve the in-phase reflection at certain frequencies. The scattered fields of the proposed multiple-element metasurface under different frequencies, polarizations, and incident angles are jointly optimized and simultaneously suppressed by OMEPC. When the range of incident angles is increased from 0° to 40°, the proposed multiple-element metasurface can achieve the 10 dB specular RCS reduction from 7.34 to 64.85 GHz with a ratio bandwidth of 8.84:1 for both TE and TM polarizations, and the 8 dB RCS reduction bandwidth is approximately 6.76–83.70 GHz. The measurement results are in agreement with the theoretical analysis and simulation results.

Broadband sound absorption using multiple hybrid resonances of acoustic metasurfaces

Achieving broadband sound absorption in low-frequency ranges using thin acoustic materials has been a long-standing and challenging problem in acoustics. When using the existing acoustic materials such as porous and fibrous materials, they are inevitably thick for low-frequency sound absorption. In this study, we propose a thin acoustic metasurface for broadband absorption of low-frequency sound by using hybrid resonances at multiple target frequencies. Supercells of the proposed metasurface are partitioned into multiple unit cells, and each of them is composed of two adjacent subwavelength Helmholtz resonators for perfect sound absorption based on hybrid resonance at each target frequency. When the hybrid resonance is derived, the unit cell exhibits perfect sound absorption at the target frequency with the lower Q-factor than the existing absorbing structures with same thicknesses. To take this advantage, we herein propose design procedures for the proposed supercells to achieve perfect sound absorption based on hybrid resonances at multiple target frequencies. The designed supercells are fabricated by 3D printing apparatus and their absorbing performance is experimentally evaluated in impedance tube. A thin (<λ/11) acoustic metasurface composed of the designed supercells achieves high (>90%) absorption band over broad frequency range, whose relative Q-factor is reduced to about one third compared to the one of the designed unit cell for a single target frequency. This work opens possibilities for practical applications of acoustic metasurfaces in noise mitigation of various mechanical systems (e.g., home appliances and power transformers) in that the target frequencies of supercells are eligible to be customized for each system by using the proposed design procedures.

Profiling the neurovascular unit unveils detrimental effects of osteopontin on the blood–brain barrier in acute ischemic stroke

Blood–brain barrier (BBB) dysfunction, characterized by degradation of BBB junctional proteins and increased permeability, is a crucial pathophysiological feature of acute ischemic stroke. Dysregulation of multiple neurovascular unit (NVU) cell types is involved in BBB breakdown in ischemic stroke that may be further aggravated by reperfusion therapy. Therefore, therapeutic co-targeting of dysregulated NVU cell types in acute ischemic stroke constitutes a promising strategy to preserve BBB function and improve clinical outcome. However, methods for simultaneous isolation of multiple NVU cell types from the same diseased central nervous system (CNS) tissue, crucial for the identification of therapeutic targets in dysregulated NVU cells, are lacking. Here, we present the EPAM-ia method, that facilitates simultaneous isolation and analysis of the major NVU cell types (endothelial cells, pericytes, astrocytes and microglia) for the identification of therapeutic targets in dysregulated NVU cells to improve the BBB function. Applying this method, we obtained a high yield of pure NVU cells from murine ischemic brain tissue, and generated a valuable NVU transcriptome database (https://bioinformatics.mpi-bn.mpg.de/SGD_Stroke). Dissection of the NVU transcriptome revealed Spp1, encoding for osteopontin, to be highly upregulated in all NVU cells 24 h after ischemic stroke. Upregulation of osteopontin was confirmed in stroke patients by immunostaining, which was comparable with that in mice. Therapeutic targeting by subcutaneous injection of an anti-osteopontin antibody post-ischemic stroke in mice resulted in neutralization of osteopontin expression in the NVU cell types investigated. Apart from attenuated glial activation, osteopontin neutralization was associated with BBB preservation along with decreased brain edema and reduced risk for hemorrhagic transformation, resulting in improved neurological outcome and survival. This was supported by BBB-impairing effects of osteopontin in vitro. The clinical significance of these findings is that anti-osteopontin antibody therapy might augment current approved reperfusion therapies in acute ischemic stroke by minimizing deleterious effects of ischemia-induced BBB disruption.

Multi-morphology cellular structure design with smooth transition of geometry and homogenized mechanical properties between adjacent cells

The recent development of additive manufacturing has led to an increased interest in the study of functionally graded cellular structures, which exhibit superior mechanical properties to the conventional uniform structures. However, connectivity is a critical problem that should be addressed, especially when multiple unit cell topologies are incorporated into a structure. In particular, inappropriate connectivity may cause stress concentration at the interfaces, reducing the structure’s lifespan. This paper proposes a method to design multi-morphology cellular structures that ensures smooth transition of geometry and homogenized mechanical properties between adjacent unit cells. The proposed method uses a genetic algorithm to design intermediate unit cells between a base and a target unit cell. Moreover, a customized parametric unit cell representation supports the design process. An implicit modeling method is adopted to synthesize the explicit 3D models. Numerical analyses demonstrate that the proposed method guarantees smooth transitions of geometry at the interfaces, variations in density, and homogeneous mechanical properties. Moreover, experimental characterization resulted in an increase of 78.7% in the elastic modulus and a reduction of 54.9% in the maximum von Mises stress for the structure designed with the proposed method when compared with that created using the conventional non-smoothing technique.

A Scalable, Dual-Band Absorber Surface for Electromagnetic Energy Harvesting and Wireless Power Transfer

We present a dual-band electromagnetic (EM) energy harvesting surface that is designed for absorbing EM energy in the GSM-1800 and Wi-Fi bands. The unit cell of the periodic structure incorporates two bow-tie dipoles and a resistive load demonstrating excellent absorption characteristics with minimal dielectric losses. The unit cell geometry also incorporates channeling traces, which makes it possible to combine multiple cells together and increase the collected power per load. To measure its performance, we designed a full-wave rectifier and integrated it with the absorber surface in three different configurations. Prototypes were fabricated and tested, with measurement results demonstrating the benefit of combining multiple unit cells into one rectifier. We conclude by discussing the feasibility of a scalable energy harvesting concept for low-power-density environments.