Thin Array Research Articles

Haptic Display Responsive to Touch Driven by Soft Actuator and Soft Sensor

Haptic display transfers the sense of touch by applying forces, vibrations, or motions to the user. This article presents a novel bidirectional haptic display responsive to touch. The device is composed of a flexible tactile sensor and tactile actuator, and the actuator is actuated according to the touch signals from the tactile sensor. The tactile sensor is a thin array of resistive type sensors that covers the top of the soft dielectric elastomer actuator array. The tactile sensor measures the normal forces (0 $-$ 6 $N$ ) and positions of touches and then sends these signals to control the corresponding tactile actuator cells. The tactile actuator works within the frequency range of 0 $-$ 300 Hz, provides up to 520 $\mu \text{m}$ of displacement and, 600 mN of normal force, much greater than the human hand threshold (50 mN). And thus, the device can transfer different feelings to users. In this research, we develop and evaluate a stand-alone bidirectional haptic display. Then, we took the psychophysical test and introduced the master—slave system whereby the master device controls the slave device depending on the master input.

Fabrication of piezoresistive Si nanorod-based pressure sensor arrays: A promising candidate for portable breath monitoring devices

This paper reports on the controlled fabrication of a highly sensitive piezoresistive sensor by using Si nanorod (NR) arrays. An efficient, large-area, scalable strategy was adopted to fabricate the pressure sensors by incorporating chemically etched, high-aspect-ratio, vertical Si NR arrays between two thin Au layers. The piezoresistive properties corresponding to dimension- and position-controlled and randomly etched, closely packed, and thin Si NR arrays were exploited to fabricate the small, portable, and device-compatible pressure sensors. The Si-NR-based piezoresistive sensors exhibited a high sensitivity of 0.49 MPa −1 , thereby demonstrating its superiority over other unconventional piezoresistive nanomaterials such as Si with different configurations of nanostructures. Furthermore, the sensors exhibited a large variation (~45%) in the current at a constant bias voltage of 2 V under a weak applied pressure corresponding to an inert gas flow of 5 sccm. The excellent pressure sensing performance of the piezoresistive Si NRs enabled the efficient detection of changes corresponding to the human breathing pattern. In particular, the key advantages of such pressure sensors is the simple, inexpensive, and scalable fabrication process; high sensitivity with ultra-low-pressure detection; and excellent ambient stability (>several months) with a high durability pertaining to more than 1,000 cycles of pressure loading/unloading. Furthermore, we demonstrated the ability of the pressure sensor to act as a portable human breath sensor to monitor respiratory parameters in a noninvasive and personalized manner. The results can provide direction for the realization of next-generation breath-sensing gadgets and other leading-edge applications in the domain of electronic and healthcare devices. • Chemically etched, dimension- and position-controlled Si nanorod arrays are utilized as pressure sensors. • Piezoresistivity in mesoporous Si nanorod is revealed to achieve a high-pressure sensitivity. • The pressure sensor detects a tiny flow of inert gas efficiently. • Demonstrated the pressure sensor’s ability to act as a portable human breath sensor.

Greyscale lithography-based fabrication of thin polymeric cantilevers for MEMS/NEMS applications

Highly photosensitive epoxy-based polymer SU8 is becoming extensively used for MicroElectro-Mechanical Systems (MEMS) and microfluidic devices not only as a negative photoresist but also as the basic constitutional material because of the easy fabrication of devices with tailored dimensions from µm to mm sizes. Here, we have shown a one-step process for the fabrication of thin cantilever arrays of thickness upto 1-2 µm using MASKLESS GRAYSCALE LITHOGRAPHY (MGL). Microfabricated polymeric disposable cantilevers can be utilized for label-free biochemical sensing with desirable advantages such as high sensitivity due to low Young’s modulus, low cost compared to its Silicon counterpart and ease in reproducible fabrication. Microcantilever arrays of different shapes were fabricated reproducibly by optimizing the process parameters. Arrays of suspended cantilevers can be used for the fabrication of chemical/biochemical sensors as SU-8 is highly resistant to chemicals and biocompatible making it a suitable material for such sensors.

Multiple Mode Couplings in a Waveguide Array for Broadband Near-Zero Dispersion and Supercontinuum Generation

We achieve a broadband near-zero dispersion in a thin silicon nitride waveguide array at near-infrared utilizing the multiple mode couplings. Different orders of modes are coupled at four different wavelengths, generating eight zero dispersion wavelengths (ZDWs). The broadband near-zero dispersion profile within 90 ps/nm/km is achieved, spanning over the spectral range of 1350 $-$ 1900 nm. Using the dispersion engineered waveguide array, an octave-spanning supercontinuum is numerically generated with a pump of 100 fs and 200 pJ. The concept of using multiple mode couplings to obtain broadband near-zero dispersion can be applied to other spectral regimes and material platforms as well, by engineering the structural parameters to shift the positions of the ZDWs.

Metal Halide Perovskite Arrays: From Construction to Optoelectronic Applications

AbstractInorganic semiconductor arrays revolutionize many areas of electronics, optoelectronics with the properties of multifunctionality and large‐scale integration. Metal halide perovskites are emerging as candidates for next‐generation optoelectronic devices due to their excellent optoelectronic properties, ease of processing, and compatibility with flexible substrates. To date, a series of patterning technologies have been applied to perovskites to realize array configurations and nano/microstructured surfaces to further improve device performances. Herein, various construction methods for perovskite crystal or thin film arrays are summarized. The optoelectronic applications of the perovskite arrays are also discussed, in particular, for photodetectors, light‐emitting diodes, lasers, and nanogratings.

Microtubules provide guidance cues for myofibril and sarcomere assembly and growth.

Muscle myofibrils and sarcomeres present exceptional examples of highly ordered cytoskeletal filament arrays, whose distinct spatial organization is an essential aspect of muscle cell functionality. We utilized ultra-structural analysis to investigate the assembly of myofibrils and sarcomeres within developing myotubes of the indirect flight musculature of Drosophila. A temporal sequence composed of three major processes was identified: subdivision of the unorganized cytoplasm of nascent, multi-nucleated myotubes into distinct organelle-rich and filament-rich domains; initial organization of the filament-rich domains into myofibrils harboring nascent sarcomeric units; and finally, maturation of the highly-ordered pattern of sarcomeric thick (myosin-based) and thin (microfilament-based) filament arrays in parallel to myofibril radial growth. Significantly, organized microtubule arrays were present throughout these stages and exhibited dynamic changes in their spatial patterns consistent with instructive roles. Genetic manipulations confirm these notions, and imply specific and critical guidance activities of the microtubule-based cytoskeleton, as well as structural interdependence between the myosin- and actin-based filament arrays. Our observations highlight a surprisingly significant, behind-the-scenes role for microtubules in establishment of myofibril and sarcomere spatial patterns and size, and provide a detailed account of the interplay between major cytoskeletal elements in generating these essential contractile myogenic units.

Adaptive Learning of Probability Density Taper for Large Planar Array Thinning

This article presents a novel optimization algorithm to design a probability density taper for large array thinning. This novel algorithm is based on the iterative Fourier technique (IFT) integrated with an innovative adaptive learning mechanism and denoted as the probability learning IFT (PLIFT) here. With successive forward and backward Fourier transforms, the traditional IFT can be capable of thinning large arrays with high convergence rates, but easily get trapped in local optima. The proposed PLIFT utilizes the probability estimation to describe the elements with possible states of “ON” and “OFF” in a thinned array. A probability model is then adopted to determine the locations of elements in the thinned array featuring minimum sidelobe level. In this PLIFT, on the one hand, the probability model of density taper is learned in optimization process and gradually trained to approach the global optima. With the previous information being honored, the probability model taper proves to be reliable and effective in generating diverse competitive seeds, which, in turn, helps training an optimal probability distribution to best-fit the design goal. Several representative examples of large planar arrays thinning are provided to demonstrate the validity, highlighted global searching ability and increased robustness of the PLIFT.

Synthesizing Beam-Scannable Thinned Massive Antenna Array Utilizing Modified Iterative FFT for Millimeter-Wave Communication

In this letter, a modified iterative fast Fourier transform (MI-FFT) technique is presented to synthesize thinned massive array for 5G millimeter-wave (mm-wave) communications. The periodicity of a scannable array factor for a uniformly spaced planar array is discussed and employed to reduce the complexity of array factor computation. A gradual array thinning strategy is introduced to prevent the iterative procedure from being trapped into an endless loop so that a better solution with lower sidelobe level (SLL) can be found. The beamwidth control is also added in the MI-FFT to control the pattern beamwidth. A thinned 128-element planar array with parasitic patch covered microstrip antenna elements is designed with the frequency band from 25.2 to 31.6 GHz. The 128-element positions are optimally selected from a prescribed larger layout by the proposed method, and consequently the obtained thinned array has a much lower SLL and narrower beamwidth than a conventional fully occupied 128-element array.

Epitaxy from a Periodic Y–O Monolayer: Growth of Single-Crystal Hexagonal YAlO3 Perovskite

The role of an atomic-layer thick periodic Y–O array in inducing the epitaxial growth of single-crystal hexagonal YAlO3 perovskite (H-YAP) films was studied using high-angle annular dark-field and annular bright-field scanning transmission electron microscopy in conjunction with a spherical aberration-corrected probe and in situ reflection high-energy electron diffraction. We observed the Y–O array at the interface of amorphous atomic layer deposition (ALD) sub-nano-laminated (snl) Al2O3/Y2O3 multilayers and GaAs(111)A, with the first film deposition being three cycles of ALD-Y2O3. This thin array was a seed layer for growing the H-YAP from the ALD snl multilayers with 900 °C rapid thermal annealing (RTA). The annealed film only contained H-YAP with an excellent crystallinity and an atomically sharp interface with the substrate. The initial Y–O array became the bottom layer of H-YAP, bonding with Ga, the top layer of GaAs. Using a similar ALD snl multilayer, but with the first film deposition of three ALD-Al2O3 cycles, there was no observation of a periodic atomic array at the interface. RTA of the sample to 900 °C resulted in a non-uniform film, mixing amorphous regions and island-like H-YAP domains. The results indicate that the epitaxial H-YAP was induced from the atomic-layer thick periodic Y–O array, rather than from GaAs(111)A.

A Parylene Neural Probe Array for Multi-Region Deep Brain Recordings.

A Parylene C polymer neural probe array with 64 electrodes purposefully positioned across 8 individual shanks to anatomically match specific regions of the hippocampus was designed, fabricated, characterized, and implemented in vivo for enabling recording in deep brain regions in freely moving rats. Thin film polymer arrays were fabricated using surface micromachining techniques and mechanically braced to prevent buckling during surgical implantation. Importantly, the mechanical bracing technique developed in this work involves a novel biodegradable polymer brace that temporarily reduces shank length and consequently, increases its stiffness during implantation, therefore enabling access to deeper brain regions while preserving a low original cross-sectional area of the shanks. The resulting mechanical properties of braced shanks were evaluated at the benchtop. Arrays were then implemented in vivo in freely moving rats, achieving both acute and chronic recordings from the pyramidal cells in the cornu ammonis (CA) 1 and CA3 regions of the hippocampus which are responsible for memory encoding. This work demonstrated the potential for minimally invasive polymer-based neural probe arrays for multi-region recording in deep brain structures.

Full‐State Synthesis of Electromagnetic Fields using High Efficiency Phase‐Only Metasurfaces

AbstractA metasurface is a thin array of subwavelength elements with designable scattering responses, and metasurface holography is a powerful tool for imaging and field control. The existing metasurface holograms are classified into two types: one is based on phase‐only metasurfaces (including the recently presented vectorial metasurface holography), which has high power efficiency but cannot control the phases of generated fields; while the other is based on phase‐amplitude‐modulated metasurfaces, which can control both field amplitudes and phases in the region of interest (ROI) but has very low efficiency. Here, for the first time, it is proposed to synthesize the field amplitudes and phases in ROI simultaneously and independently by using high‐efficiency phase‐only metasurfaces. All points in ROI may have independent values of field amplitudes and phases, and the requirements for X and Y components may be different in achieving spatially varied polarization states. To this end, an efficient design method based on equivalent electromagnetic model and gradient‐based nonlinear optimization is proposed. Full‐wave simulations and experimental results demonstrate that the phase‐only metasurface designed by the method has 10 times higher efficiency than the phase‐amplitude‐modulated metasurface. This work opens a way to realize more complicated and high‐efficiency metasurface holography.

Anisotropic Metasurface Holography in 3-D Space With High Resolution and Efficiency

Electromagnetic metasurfaces are structured surfaces consisting of a thin array of subwavelength elements with engineered scattering properties, thus providing a promising means of holographic display by controlling the field distributions. However, the existing metasurface holography has limited capabilities in achieving 3-D fields with simultaneous features of high spatial resolution and energy efficiency due to the design methods. In this work, we present a transmissive metasurface to achieve polarization-dependent field distributions in 3-D space with both high resolution and efficiency. In the design, a new method that utilizes dyadic Green's function (DGF) as the rigorous propagator is used. Using the method, the sources and fields are linked directly and can be located on arbitrary 3-D points with the intermediate spaces being equal or unequal. The design is successfully validated by full-wave simulations and experimental measurements. The broadband simulation results indicate that the design has a bandwidth of 0.8 GHz. This work demonstrates a feasible and simple route of field synthesis for real-world applications that require high resolution, high efficiency, and 3-D scenarios.

Beampattern Synthesis via the Constrained Subarray Layout Optimization

This article deals with a joint design of subarray layout vector (LV) and weighted coefficient of radiation element (RE) to achieve desired beampattern for a new array architecture. We first present an architecture of thinned array composed of multiple regular subarrays (ACMRS) and establish corresponding subarray layout and beampattern models. Then, we formulate a new optimization problem aiming to minimize the peak sidelobe level (PSL) and the LV norm under the constraints of power beampattern and subarray layout. The resulting problem is quite challenging to solve due to the highly nonconvex discrete LV and double-sided quadratic constraints. In this respect, we formulate the resultant hybrid optimization problem into a new alternating direction method of multipliers (ADMM) form via introducing a series of auxiliary variables, and propose an approximation algorithm based on ADMM. In each iteration of the proposed ADMM, the tractable and small-sized subproblems are globally or locally solved in parallel. Finally, numerical simulations show that the proposed method can obtain a lower PSL beampattern and a thinner (i.e., fewer REs or subarrays) array while satisfying the given constraints. Furthermore, fullwave simulation also shows that it has good reliability in the application of beampattern synthesis for real array.

Antenna performance enhancement using inter-coupling effect reducing mechanisms

Recently, thinning an antenna has resulted in attractive antenna radiation characteristics enhancement. This performance enhancement using a thin antenna array is achieved because the inter-coupling effects of the array elements are reduced. Though the thinning both reduces the weight of the antenna and enhances the radiation characteristics, iterative algorithms can further enhance the performance and hence, in this research, an optimizer algorithm and inter-coupling reducing mechanisms are applied. The excitation weights of the individual array elements are thinned by turning some of the elements off while some of the elements are turned on. The purpose of the thinning is to enhance the antenna performances like reduced SLL, high directivity, reduced power consumption and flexible radiation pattern. The SLL attenuation mechanism is applied to reduce the SLL in addition to the SLL reduction using the thinning and beamforming. Hence, in this paper, the three techniques (thinning, beamforming and SLL attenuation) are proposed to be integrated to enhance the antenna radiation characteristics. In general, the proposed combined method has resulted in much better SLL reduction, directivity improvement, and power wastage reduction.

Flexible, Conformable Organic Semiconductor Proximity Sensor Array for Electronic Skin

AbstractA flexible and conformal thin film proximity sensor array based on organic semiconductor dinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene (DNTT) is demonstrated, which can be perfectly affixed onto the curved objects such as glass ball, human brain model, and even the deforming human skin. Both spatial position and shape can be registered with fast response when human finger or insulator plastic to be recognized is approaching and removing. This flexible, conformal organic semiconductor sensor array bears merits of low operation voltage (1 V) and ultralow power consumption (0.36 nW), which is ideal for applications of the electronic skin in future wearable electronics.

Hearing Preservation With a New Atraumatic Lateral Wall Electrode.

Many individuals have some residual hearing which should be preserved with cochlear implantation. To achieve this goal electrode arrays must fulfil certain design requirements. A new thin lateral wall electrode array (HiFocus SlimJ) was systematically designed on the basis of μCT studies of human cochlea anatomy. The primary objective of this study was to report on initial retrospective hearing preservation results from a cohort of subjects consecutively implanted with this electrode. Secondary objectives were to report on insertion depth and speech perception results for this new array. Twenty subjects with considerable residual hearing in low frequencies were consecutively implanted with the SlimJ electrode array. The electrode was inserted slowly through the round window and the insertion process was controlled by intracochlear electrocochleography measuring cochlear microphonics through the cochlear implant.Postoperative cone beam computed tomography was conducted and precise scalar location and angular insertion depth was estimated following image fusion with the preoperative images. Low frequency hearing at 1 month postsurgery was preserved within 30 dB HL in 85% of subjects and within 15 dB HL in 50% of subjects. Mean angular insertion depth was 393 degrees (SD 62 degrees) with a range from 294 to 520 degrees. All electrode contacts in all subjects were identified within scala tympani. The SlimJ electrode array is easy to handle for atraumatic insertion through the round window, adjusted insertion depth controlled by electrocochleography measurements, and reliable fixation at the posterior tympanotomy. Hearing preservation rates are encouraging on the short term. We aim to further report on larger data sets and long-term outcomes.

Individually addressable, high-density vertical nanotube Schottky diode crossbar array

Abstract We report on the fabrication of individually addressable, high-density vertical zinc oxide (ZnO) nanotube Schottky diode arrays. The individually addressable nanotube Schottky diode arrays were fabricated by arranging the top and bottom electrodes in a crossbar configuration on a free-standing layer consisting of position-controlled ZnO nanotubes on graphene films. The electrical characteristics of each Schottky diode in the arrays were investigated by measuring current–voltage characteristics. We also investigated the variation in device characteristics within an array by spatially mapping the barrier height of individual devices. Additionally, we further confirmed the excellent flexibility and electrical robustness of the free-standing and thin Schottky diode arrays under extreme bending conditions and over multiple cycles. Moreover, the photoresponses of the nanotube Schottky diode arrays were investigated by measuring their spectral responses and current–voltage characteristics under light illuminations, yielding a maximum photocurrent to dark current ratio of 1400 and responsivity of 106 A/W. We believe that this work provides a general and rational route for developing many other two-terminal one-dimensional nanostructure device arrays for ultra-high density electronic and optoelectronic devices.

Adaptive Interference Suppression of Phase-Only Thinned Arrays via Convex Optimization

For antenna arrays, the conventional beamformer (CB) is perhaps the simplest kind of beamforming techniques with only phase shifters connected to the antenna elements. However, the output signal to interference and noise ratio (SINR) performance is usually quite away from the optimum. Besides, as the number of antenna elements increases, the hardware cost and power consumption are still too high for many applications. In this article, based on the phase-only CB, we propose different ways for thinning this kind of antenna arrays, which can be efficiently solved via common convex-optimization solvers. Specifically, the first-derived phase-only thinned array can largely increase the output SINR with fewer active antenna elements than the CB. The second one can keep the output SINR performance as that of the CB with a significantly smaller number of active antenna elements than that required by the CB. The third criterion is to add an additional constraint on the number of active antenna elements while maximizing the output SINR, which may benefit the hardware planning. Simulation results confirm the feasibilities of these methods, and the above-stated tasks are all fulfilled. Therefore, the proposed phase-only thinned arrays have the flexibility to provide various levels of array performance with reduced hardware resources.

Real-time visualized battery health monitoring sensor with piezoelectric/pyroelectric poly (vinylidene fluoride-trifluoroethylene) and thin film transistor array by in-situ poling

Monitoring the health of lithium-ion batteries is extremely important as it can significantly improve the safety of lithium-ion batteries. In the present work, a novel lithium-ion battery health monitoring sensor array is prepared using piezoelectric/pyroelectric poly(vinylidene fluoride-trifluoroethylene) and a thin-film transistor array by in-situ poling. Compared to the present technology that uses the characteristic parameters such as output voltage or internal resistance to predict the health state of lithium-ion batteries, the prepared sensor array can simultaneously realize the direct and real-time response and location of the dynamical mechanical and thermal damage, and can visualize and locate the quasi-static mechanical damage of the lithium-ion battery during its entire service life. Thus, the novel sensor array may provide sufficient advance warning of battery failure and enable more convenient replacement of damaged batteries, endowing it with immense potential for improving the safety of lithium-ion batteries.

Time-domain simulation of wave propagation across resonant meta-interfaces

Meta-interface models stem from the homogenization, in a low-frequency dynamic regime, of thin heterogeneous layers that are structured to achieve uncommon properties at the macroscopic level. When the layer is composed of a thin periodic array of highly-contrasted inclusions embedded within a homogeneous background medium then the corresponding effective interface model is characterized by jump conditions that, in the harmonic regime, involve some singular frequency-dependent terms. In this context, the article is concerned with the simulation of transient waves across such resonant meta-interfaces and a numerical method is proposed to handle the associated resonant jump conditions. To do so, a set of auxiliary variables is introduced locally along the interface and an augmented system of first-order equations in time accompanied with local-in-time jump conditions is derived. This system is then discretized on a Cartesian grid and solved using a high-order finite-difference scheme while the complexity associated with the geometry of the interface and the jump conditions is handled using an immersed interface method. A set of numerical examples in 1D and 2D is proposed to illustrate and validate the overall numerical approach, and quantitative comparisons with semi-analytical solutions are also provided.