Tiled Array Research Articles

A reprogrammable mechanical metamaterial with stable memory.

Metamaterials are designed to realize exotic physical properties through the geometric arrangement of their underlying structural layout1,2. Traditional mechanical metamaterials achieve functionalities such as a target Poisson's ratio3 or shape transformation4-6 through unit-cell optimization7-9, often with spatial heterogeneity10-12. These functionalities are programmed into the layout of the metamaterial in a way that cannot be altered. Although recent efforts have produced means of tuning such properties post-fabrication13-19, they have not demonstrated mechanical reprogrammability analogous to that of digital devices, such as hard disk drives, in which each unit can be written to or read from in real time as required. Here we overcome this challenge by using a design framework for a tileable mechanical metamaterial with stable memory at the unit-cell level. Our design comprises an array of physical binary elements (m-bits), analogous to digital bits, with clearly delineated writing and reading phases. Each m-bit can be independently and reversibly switched between two stable states (acting as memory) using magnetic actuation to move between the equilibria of a bistable shell20-25. Under deformation, each state is associated with a distinctly different mechanical response that is fully elastic and can be reversibly cycled until the system is reprogrammed. Encoding a set of binary instructions onto the tiled array yields markedly different mechanical properties; specifically, the stiffness and strength can be made to range over an order of magnitude. We expect that the stable memory and on-demand reprogrammability of mechanical properties in this design paradigm will facilitate the development of advanced forms of mechanical metamaterials.

A Thinned Irregular Array Synthesis Approach Based on Benders Decomposition

A thinned irregular tiled array synthesis approach is proposed for 5G base station array design. To fit the needs of multiusers, different sizes of vertical tiles with thinned elements ae considered. The tiling configuration and excitations are optimized to achieve high gain, low sidelobes, and wide-angle scanning simultaneously. A mixed integer second-order cone programming (MISOCP) model is obtained from convexity analysis and transformation. Besides, a generalized Benders decomposition algorithm is built to decouple the complex original problem into mixed integer linear programming (MILP) master problems and convex second-order cone programming (SOCP) subproblems, which is used to solve the large-scale problems efficiently. Irregular partition optimization is based on full-wave simulations of regular finite arrays. The joint effects of active VSWR and radiation patterns are considered to reduce the mismatch between element simulations and final performances. Numerical results show that the 5G array synthesized by the proposed approach is superior to those reported by the state-of-the-art methods in terms of both E- and H-plane scans and the number of T/R modules.

Interconnect-Aware Area and Energy Optimization for In-Memory Acceleration of DNNs

State-of-the-art in-memory computing (IMC) architectures employ an array of homogeneous tiles and severely underutilize processing elements (PEs). In this article, the authors propose an area and energy optimization methodology to generate a heterogeneous IMC architecture coupled with an optimized Network-on-Chip (NoC) for deep neural network (DNN) acceleration. – Yiran Chen, Duke University

Antenna isolation method using sub-array structure with soft-surface for Tx/Rx separated FDD hybrid beamforming system

The FDD method is normally used for the stability of the Tx and the Rx links in a fast-varying channel. It is required to physically separate the Tx and Rx arrays for independent Tx and Rx beam control. In this system, it is important to reduce the Tx self-interference (SI) that causes the problem of active element saturation and ADC dynamic range in the Rx beamformer. To suppress Tx SI, we proposed two simple techniques. The first is the general soft-surface which attenuates the surface current flow from the Tx tile array to the Rx array. The second is the sub-array structure of the Rx hybrid beamforming system. Based on the Cauchy–Schwartz inequality, the electrical sum by the sub-array acts as a destructive interference of the complex SI signals, and it can be shown as an additional isolation effect. The proposed idea was validated through measurement.

Spectral DiffuserCam: lensless snapshot hyperspectral imaging with a spectral filter array

Hyperspectral imaging is useful for applications ranging from medical diagnostics to agricultural crop monitoring; however, traditional scanning hyperspectral imagers are prohibitively slow and expensive for widespread adoption. Snapshot techniques exist but are often confined to bulky benchtop setups or have low spatio-spectral resolution. In this paper, we propose a novel, compact, and inexpensive computational camera for snapshot hyperspectral imaging. Our system consists of a tiled spectral filter array placed directly on the image sensor and a diffuser placed close to the sensor. Each point in the world maps to a unique pseudorandom pattern on the spectral filter array, which encodes multiplexed spatio-spectral information. By solving a sparsity-constrained inverse problem, we recover the hyperspectral volume with sub-super-pixel resolution. Our hyperspectral imaging framework is flexible and can be designed with contiguous or non-contiguous spectral filters that can be chosen for a given application. We provide theory for system design, demonstrate a prototype device, and present experimental results with high spatio-spectral resolution.

Graphene gets bent

Graphene gets bent

Maximum BCE synthesis of domino-tiled planar arrays for far-field wireless power transmission

The design of transmitting antenna arrays with a modular aperiodic architecture for far-field wireless power transmission (WPT) is addressed in this work. The synthesis of the subarray layout and of the subarrays weights is carried out to maximize the power transmission efficiency, while guaranteeing the full aperture coverage with simple domino-shaped tiles. Two design methodologies, one enumerative and one optimization-based, customized to the synthesis of small and larger apertures are presented. The best tiled array configuration is obtained through the maximization of the beam collection efficiency (BCE) for a given collection area where the receiving rectenna system is assumed. A set of representative numerical examples, including both ideal and real antenna models, is shown to prove the effectiveness of the proposed architectural solution as well as of the clustering methods. Analyses considering different array dimensions and sizes of the collection area, when scanning the beam off-boresight also along diagonal directions, are given to assess the performance of the proposed solutions.

Highly efficient coherent beam combining of tiled aperture arrays using out-of-phase pattern.

We propose a simple, highly scalable, and very efficient scheme for coherent combining of tiled aperture arrays. The scheme relies on changing the beam phasing paradigm from the commonly used in-phase pattern to the out-of-phase pattern (interleaved 0/π phases in the neighboring channels) and using an additional simple combining stage (a beamsplitter). In a proof-of-concept experiment with a one-dimensional fiber array, we achieved 89% of the power in the main combined beam. In numerical modeling, we found optimal conditions leading to 98% efficiency for an unlimited number of channels and arbitrary small initial aperture fill factors. The scheme is highly resistant to the effect of sub-aperture clipping and suitable for combining ultrashort pulses.

High dynamic range CdTe mixed-mode pixel array detector (MM-PAD) for kilohertz imaging of hard x-rays

A hard x-ray, high-speed, high dynamic range scientific x-ray imager is described. The imager is based on the mixed-mode pixel array detector (MM-PAD) readout chip coupled to a 750 μm thick cadmium telluride (CdTe) sensor. The full imager is a 2 × 3 tiled array of MM-PAD sensor/readout chip hybrids. CdTe improves detection for high energy x-rays as compared to silicon sensors, enabling efficient x-ray imaging to extend to >100 keV . The detector is capable of 1 kHz imaging and in-pixel circuitry has been designed to allow for well depths of greater than 4 × 106 80 keV x-rays. A charge integrating front-end allows for quantitative measurement of high flux x-ray images beyond the capabilities of photon counting detectors. Detector performance is summarized and experimental measurements are presented.

Modular Design of Hexagonal Phased Arrays Through Diamond Tiles

The modular design of planar phased array antennas with hexagonal apertures is addressed by means of innovative diamond-shaped tiling techniques. Both tiling configuration and subarray coefficients are optimized to fit user-defined power-mask constraints on the radiation pattern. Toward this end, suitable surface-tiling mathematical theorems are customized to the problem at hand to guarantee optimal performance in case of low/medium-size arrays, while the computationally hard tiling of large arrays is yielded thanks to an effective integer-coded GA-based exploration of the arising high-cardinality solution spaces. By considering ideal as well as real array models, a set of representative benchmark problems is dealt with to assess the effectiveness of the proposed architectures and tiling strategies. Moreover, comparisons with alternative tiling architectures are also performed to show to the interested readers the advantages and the potentialities of the diamond subarraying of hexagonal apertures.

Fabrication Steps and Thermal Modeling of Three-Dimensional Asynchronous Field Programmable Gate Array (3D-AFPGA) With Through Silicon Via and Copper Pillar Bonding Approach

Abstract This work will specifically detail the development of a processing and fabrication route for a three-dimensional asynchronous field-programmable gate array (3D-AFPGA) design based on an extension of pre-existing two-dimensional-field-programmable gate array (2D-FPGA) tile designs. The periodic nature of FPGAs permits the use of an alternative approach, whereby the design entails splitting the FPGA design along tile borders and inserting through silicon vias (TSVs) at regular spatial intervals. This serves to enable true 3D performance (i.e., full 3D signal routing) while leaving most of the 2D circuit layouts intact. 3D signal buffers are inserted to handle communication between vertical and adjacent neighbors. For this approach, the density of vertical interconnections was shown to be determined by the size of the bond pads used for tier–tier communications and bonding. As a consequence, reducing bond pad dimensions from 25 μm to 15 μm, or 10 μm, bond pads are preferred to increase the connectivity between layers. A 3D-AFPGA mockup test structure was then proposed for completing development and exercising the 3D integration process flows. This mockup test structure consists of a three-tier demonstration vehicle consisting of a chip-to-wafer and a subsequent chip-to-chip bond. Besides, an alternate copper bonding approach using pillars was explored. Although the intended application is for the 3D integration process compatible with the 3D AFPGA design, the test structure was also designed to be generally applicable to various applications for 3D integration. Because of the importance of thermal management of 3D-AFPGA, it is important to predict the temperature distribution and avoid the maximum junction temperature. The numerical thermal modeling for predicting the equivalent thermal conductivity in every layer and the 3D temperature distribution in the 3D-AFPGA are developed and discussed as well.

HREXI calibration facility: mapping out subpixel-level responses from high-resolution cadmium zinc telluride imaging x-ray detectors

The High-Resolution Energetic X-ray Imager (HREXI) cadmium zinc telluride (CZT) detector development program at Harvard is aimed at developing tiled arrays of finely pixelated CZT detectors for use in wide-field coded aperture 3 to 200 keV x-ray telescopes. A pixel size of ∼600 μm has already been achieved in the ProtoEXIST2 (P2) detector plane with CZT readout by the NuSTAR application-specific integrated circuits. This paves the way for even smaller than 300-μm pixels in the next-generation HREXI detectors. We describe a new HREXI calibration facility (HCF) that enables a high-resolution subpixel-level (100 μm) two-dimensional (2D) scan of a 256-cm2 tiled array of 2 × 2 cm2 CZT detectors illuminated by a bright x-ray AmpTek Mini-X tube source at timescales of around a day. HCF is a significant improvement from the previous apparatus used for scanning these detectors, which took ∼3 weeks to complete a one-dimensional (1D) scan of a similar detector plane. Moreover, HCF has the capability to scan a large tiled array of CZT detectors (32 × 32 cm2) at 100-μm resolution in the 10- to 50-keV energy range, which was not possible previously. We describe the design, construction, and implementation of HCF for the calibration of the P2 detector plane.

On-chip biochemical sensor using wide Gaussian beams in silicon waveguide-integrated plasmonic crystal.

An on-chip biochemical sensor based on two-dimensional waveguide-integrated plasmonic crystal formed by a nanogap tile (NGT) array is realized. By using on-chip optical lenses, an ultra-wide collimated Gaussian beam is launched, coupled with surface plasmonic crystals and collected with relatively low additional insertion loss, allowing a large sensing area. The optical field enhancement and stop-band shift of the NGT device for biochemical sensing are numerically and experimentally demonstrated with sensitivity reaching up to ${\sim}{260}\;{\rm nm/RIU}$∼260nm/RIU. Our sensor is demonstrated with monolayer thiol molecules illustrating that it can be functionalized with this class of molecule which is commonly used with bulk surface plasmon resonance sensors.

Homeostatic Plasticity Shapes the Retinal Response to Photoreceptor Degeneration.

Homeostatic plasticity stabilizes input and activity levels during neural development, but whether it can restore connectivity and preserve circuit function during neurodegeneration is unknown. Photoreceptor degeneration is the most common cause of blindness in the industrialized world. Visual deficits are dominated by cone loss, which progresses slowly, leaving a window during which rewiring of second-order neurons (i.e., bipolar cells) could preserve function. Here we establish a transgenic model to induce cone degeneration with precise control and analyze bipolar cell responses and their effects on vision through anatomical reconstructions, invivo electrophysiology, and behavioral assays. In young retinas, we find that three bipolar cell types precisely restore input synapse numbers when 50% of cones degenerate but one does not. Of the three bipolar cell types that rewire, two contact new cones within stable dendritic territories, whereas one expands its dendrite arbors to reach new partners. In mature retinas, only one of four bipolar cell types rewires homeostatically. This steep decline in homeostatic plasticity is accompanied by reduced light responses of bipolar cells and deficits in visual behaviors. By contrast, light responses and behavioral performance are preserved when cones degenerate in young mice. Our results reveal unexpected cell type specificity and a steep maturational decline of homeostatic plasticity. The effect of homeostatic plasticity on functional outcomes identify it as a promising therapeutic target for retinal and other neurodegenerative diseases.

Signal Integrity Design and Analysis of 3-D X-Point Memory Considering Crosstalk and IR Drop for Higher Performance Computing

In this article, we, for the first time, used signal integrity (SI) to design and analyze 3-D X-Point memory, including a phase-change memory (PCM) cell, ovonic threshold switch (OTS) selector, interconnection lines, and peripheral circuits. With the narrow space and the long interconnection lines that come with 20-nm process technology, crosstalk and IR drop can degrade the voltage margin of the memory cell and affect the memory operation. For SI analysis considering crosstalk and IR drop, the unit size of the memory array tile was considered in designing the interconnection lines. Crosstalk and IR drop are analyzed using full 3-D electromagnetic and circuit simulations. To cover practical conditions, the PCM cell and OTS selector are modeled as behavior models using Verilog-A modules, respectively. Also, the word lines (WLs) and bit lines (BLs) of 3-D X-Point memory are modeled to resistance and capacitance by ANSYS Q3D extractor. The core peripheral circuits, such as decoder, sense amplifier, and analog-to-digital converter, are included in the circuit simulation. To verify the proposed design and analysis, a transient simulation was conducted considering crosstalk and IR drop of 3-D X-Point memory. A tradeoff relationship between crosstalk and IR drop in the interconnection designs was verified. Additionally, to suppress crosstalk and reduce IR drop, the new design of the interconnection lines considering the tradeoff between SI issues is proposed. The newly proposed interconnection design shows 30% improvement in the voltage margin considering the IR drop issues and under 10% enhancement of crosstalk noise. It is expected that the SI analysis and design methodologies could be widely applied in other new memory developments.

Capacitive sensing for the detection of tile misalignment in ceramic armor arrays

The capacitive nondestructive technique uses a planar, two- or multi-terminal device to detect dielectric changes in its proximity. The technique has the advantages of being non-contact and requiring single-side access to the inspected test-piece. In this work, it is employed to determine the misalignment of ceramic tiles in two-dimensional array arrangements, as used for armored vehicles. Ceramic materials provide protection against projectile penetration in military and security applications. Tile assemblies are manufactured as protective add-on layers to armored vehicles. To provide effective protection, arrangements of rectangular or hexagonal tiles have to minimize potential misalignment, such as inter-tile gaps and out-of-plane mismatch. In this study, three planar capacitive probes with triangle-shaped terminals are used for the investigation of linear arrays of rectangular alumina tiles. Numerical simulations were employed to understand the probe's design parameters, as well as coupling aspects. It was found that the size of the capacitive probe and the separation between terminals provide a balance between spatial resolution, penetrability, and sensitivity to dielectric changes. Inter-tile gaps down to at least 0.5 mm, as well as out-of-plane tile misalignment as small as 0.25 mm were successfully discriminated.

Code-Domain Multiplexing for Shared IF/LO Interfaces in Millimeter-Wave MIMO Arrays

Millimeter-wave (mm-wave) multi-input-multi-output (MIMO) systems with the digitization of every element enable spatial multiplexing, virtual arrays for radar, and digital beamforming for high mobility scenarios. However, per-element digitization results in a formidable I/O challenge in large-scale tiled MIMO mm-wave arrays. This article analyzes a code-domain approach to multiplex signals from different elements as well as the LO on a single interface. System considerations are presented, and the approach is demonstrated through a 28 GHz four-element MIMO receiver in 65-nm CMOS. Measurements show the feasibility of digital beamforming after de-multiplexing of the baseband signals from the IF/LO interface. Each element in the array achieves 16-dB conversion gain while consuming 60 mA from 1.2 V. The IC occupies 5.75 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in 65-nm CMOS, achieving small size and compatibility with λ/2 × λ/2 antenna spacing due to the absence of phase shifters/combiners required in phased arrays.

Catch that word: interactivity, serendipity and verbal fluency in a word production task

Problem solving outside of the cognitive psychologist’s lab unfolds in an environment rich with bodily gesture and material artefacts. We examine this meshwork of internal mental resources, embodied actions and environmental affordances through the lens of a word production task with letter tiles. Forty participants took part in the study which contrasted performance in a high interactivity condition (where participants were able to move letter tiles at will), a low interactivity condition (where movements were restrained) and a shuffle condition (where participants could not move the tiles but were allowed to randomly rearrange the array). Participants were also video recorded to facilitate coding of behaviour. While aggregate performance measures revealed a marginal impact of interactivity on performance, when the participants’ behaviour was taken into account, interactivity had a consistent and statistically significant beneficial effect. Detailed, exploratory examination of a subsample of participants informed the formulation of additional hypotheses tested across the full sample: the luckiness of the shuffle in that condition significantly predicted the number of words produced and a more efficient strategy was significantly easier to enact in the high interactivity condition. Additionally, two detailed case studies revealed several moments when accidental changes to the letter tile array offered unplanned words reflecting a serendipitous coagency as well as many moments when environmental chance was ignored. These data and observations indicate that interactivity, serendipity, and internal cognitive resources determine problem-solving performance in this task.

Divertor currents during type-I edge-localized modes on the DIII-D tokamak

Measurements of divertor currents on DIII-D lead to new insights in nonlinear edge-localized mode (ELM) dynamics and a possible mechanism to explain their explosive growth. Rapidly oscillating currents flowing into the divertor before a significant increase in divertor heat flux occurs are measured with an array of shunted tiles and characterized. Extrapolation results in total n = 0 currents of 5–10 kA flowing into a concentric circle near the strike point. The detected Fourier harmonics appear consistent with a mix of low-n modes (n < 4) with currents up to 4 kA. A heuristic framework for ELM currents is developed based on thermoelectric origin of the tile currents with flow through regions inside of the nominal separatrix and found consistent with the current measurements. A current flow through the confined plasma leading to increased stochasticity and transport at the plasma edge could provide a mechanism for additional nonlinear growth as sought for in computational ELM simulations. Results also imply that ELM currents may open the possibility to manipulate the ELM character by perturbations through non-axisymmetric divertor bias or tile insulation.

A flexible phased array system with low areal mass density

Phased arrays are multiple antenna systems capable of forming and steering beams electronically using constructive and destructive interference between sources. They are employed extensively in radar and communication systems but are typically rigid, bulky and heavy, which limits their use in compact or portable devices and systems. Here, we report a scalable phased array system that is both lightweight and flexible. The array architecture consists of a self-monitoring complementary metal–oxide–semiconductor-based integrated circuit, which is responsible for generating multiple independent phase- and amplitude-controlled signal channels, combined with flexible and collapsible radiating structures. The modular platform, which can be collapsed, rolled and folded, is capable of operating standalone or as a subarray in a larger-scale flexible phased array system. To illustrate the capabilities of the approach, we created a 4 × 4 flexible phased array tile operating at 9.4–10.4 GHz, with a low areal mass density of 0.1 g cm^(−2). We also created a flexible phased array prototype that is powered by photovoltaic cells and intended for use in a wireless space-based solar power transfer array.