Nicholas X. Fang

Weishu Liu, Xiaogang Zhang, Nicholas X Fang; Ionic thermoelectrics: a soft energy conversion technique, National Science Review, , nwag333, https://doi.org

A new performance index is proposed for ionic thermoelectric materials, to bridge the material properties and energy conversion efficiency in real-world application scenarios.

Ionic thermoelectric (i-TE) materials have demonstrated a high thermopower in harvesting low-grade heat, emerging as superior candidates for self-powered electronics. However, coupling two i-TE effects in n-type materials is scarce, which restricts the development of high-performance systems. Herein, we uncover an overlooked thermogalvanic redox reaction between Cu2+ and Cu+ stabilized by Cl⁻ and quantitatively track the progressive reaction process by operando characterization. In binary polyvinyl alcohol (PVA)-CuCl2 gels, an interactive i-TE coupling effect driven by ion speciation is validated, which exhibits an enhanced thermogalvanic redox as CuCl2 concentrations increase while suppressing the thermodiffusion contribution. By distinguishing and quantifying coordination species, we reveal the impact of [Cu-Cl] speciation on the i-TE effect contributions. Correspondingly, a giant thermopower of −30.6 mV K-1 and a remarkable power density of 0.6 mW m-2 K-2 are achieved, respectively, by tuning ion coordination speciation. The long-term power generation exhibits a reversible and sustainable heat-to-electricity conversion. High output voltage of 3.5 V and power of 22 µW are produced in 16-cell i-TE modules when harvesting 15 K. Our findings reveal an interactive thermo-diffusion/galvanic coupling effect based on coordination chemistry, offering a potential design principle for high-performance i-TE materials. Coupling two ionic thermoelectric effects in n-type materials is scarce, restricting the development of high-performance systems. Here, the authors present an ionic-thermoelectric material with interactive thermo-diffusion/galvanic coupling effect based on coordination chemistry.

The mass law is a cornerstone in predicting sound transmission loss, yet it neglects the constraints of causal dispersion. Current causality-based theories, such as the Rozanov limit, are applicable only to one-port reflective absorbers. Here, we derive a universal sum rule governing causal scattering in acoustic systems, establishing a rigorous analogy to the Baldin sum rule in quantum field theory. This relation reveals that the integral of the extinction cross-section is fundamentally locked by the scatterer's static effective mass and stiffness, which is validated numerically using seminal examples of underwater metamaterials. Furthermore, the proposed sum rule predicts an optimal condition for an anomalously broadened transmission loss bandwidth, as experimentally observed through the spectral shaping effect of an acoustic Fano resonator. Our findings open up an unexplored avenue for enhancing the scattering bandwidth of passive metamaterials.

The mass law is a cornerstone in predicting sound transmission loss, yet it neglects the constraints of causal dispersion. Current causality-based theories, such as the Rozanov limit, are applicable only to one-port reflective absorbers. Here, we derive a universal sum rule governing causal scattering in acoustic systems, establishing a rigorous analogy to the Baldin sum rule in quantum field theory. This relation reveals that the integral of the extinction cross-section is fundamentally locked by the scatterer's static effective mass and stiffness, which is validated numerically using seminal examples of underwater metamaterials. Furthermore, the proposed sum rule predicts an optimal condition for an anomalously broadened transmission loss bandwidth, as experimentally observed through the spectral shaping effect of an acoustic Fano resonator. Our findings open up an unexplored avenue for enhancing the scattering bandwidth of passive metamaterials.

Optical phase imaging is a powerful tool widely used in bioimaging, material characterization, pathology, and nanomanufacturing.Yet, it faces a persistent challenge: the inherent contradiction between resolution and field of view (FOV) in conventional microscope-based systems.To address this limitation, we propose Lateral Line-Scan Computational Phase Imaging (L 2 -CPI), a novel computational phase imaging architecture that enables consecutive phase imaging of moving samples.Our experiments with both transparent and opaque samples demonstrate that L 2 -CPI achieves an equivalent FOV of DL, where D is the camera sensor edge length and L is the motorized stage travel range.This implies that the equivalent FOV of L 2 -CPI in a single measurement can be arbitrarily large, provided the stage travel range L is arbitrarily long.Our work breaks the long-term contradiction between resolution and FOV, establishing a new paradigm for ultra-large-FOV phase imaging in dynamic mode without sacrificing optical resolution.This advancement holds significant potential for applications in bioimaging, material characterization, biosensing

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Causality constraints are known to bind sound absorption to a limit that can only be achieved by optimizing the system bandwidth for a specific material thickness. This limit is defined on the assumption of a one-port system, generally causing duality symmetry to be overlooked. Here, we define a generalized causality constraint of sound absorption by investigating reflection and transmission of a two-port hybrid monopole-dipole resonator. With our theory, we show that the absorption limit is approached by relying on the well-established critical coupling as well as by matching effective compressibility and density. We experimentally show that the designed resonator absorbance follows the duality symmetry condition embodied in the large bandwidth reported, confirming an intrinsic connection between duality symmetry and scattering causality. A comparison with a traditional foam liner and other competitive works further validates our findings. Our results reveal previously untapped absorption potential in broadband acoustic metamaterials. Absorption in one-port passive systems is known to be bound by causality constraints. Here, authors study reflection and transmission of a two-port system to introduce a generalized causality constraint based on duality symmetry. Experimentally, the broadened bandwidth of their meta-absorbers shows the untapped absorption potential of broadband acoustic metamaterials.

Assembly of DNA nanostructures to sub-millimetre scales is expected to have significant potential for applications in materials science and medicine. One approach to control nanostructure growth is through using acoustic waves to create pressure nodes for clustering. Here, we report a facet-based underlying DNA nanostructure architecture with structural and stability characteristics ideal for acoustic patterning. The architecture comprises only 16 canonical DNA oligonucleotides which self-assemble to form a nested cube, inspired by the four-dimensional hypercube known as a "tesseract." Cryogenic electron microscopy (Cryo-EM) and atomic force microscopy (AFM) analysis revealed a fully formed tesseract structure with exceptional stiffness and a melting temperature of 84°C, significantly higher than other unmodified DNA nanostructures. The DNA tesseract nanostructures could be acoustically shaped into wires spanning over 500 µm, observed after deposition onto an interdigitated electrode (IDE). The wires were shown to be electrically conductive, highlighting unique prospects for application. Simplified bottom-up assembly of a small number of oligonucleotides into a relatively complex and structurally stable DNA nanostructure with characteristics ideal for modular assembly holds promise for applications across bioelectronics and other fields.

The primary challenge in creating controllable liquid-based materials lies in managing the structural complexities and multiscale interfaces that govern solid, liquid, and gas phase interactions. Current fabrication methods for liquid-infused surfaces lack topological flexibility, limiting them to planar and simple-patterned structures. Conversely, digitally fabricating slippery architectural materials marks a significant shift towards scalable microprinting of complex, topologically slippery designs. This paper introduces a method for digitally fabricating slippery objects with solid–liquid composite interfaces and geometric design freedom. The slippery architecture has been demonstrated through digital printing of photopolymerization-induced multiphase materials and photoinduced grafting, enabling precise control over structural topologies and slippery properties of infused liquids. This versatile platform facilitates the fabrication of structures at multiple scales, enhancing liquid manipulation, droplet evaporation, and biomedical microfluidic chip design. These methods advance beyond conventional techniques, showcasing the potential of architected slippery surfaces with controlled structural scales. Control of liquid-based materials is important for developing materials based on these, but topological flexibility is limited. Here, the authors report a method for digital fabrication of slippery objects with solid-liquid composite interfaces and geometric design freedom.

Abstract Point‐of‐care diagnostics, in situ monitoring during nanomanufacturing, and in‐line metrology are stimulating demands for portable, ultracompact, and robust optical imaging and metrology systems. In this paper, an on‐chip computational wavefront sensor (OCWS) is proposed and demonstrated by fusing photonic integrated circuits and single‐layer metasurfaces. By simultaneously measuring the optical intensities coupled into the metagratings, OCWS enables the single‐shot acquisition of two orthogonal phase gradient images, from which the wavefront can be computationally reconstructed. Moreover, phase imaging of vortex beams and Gaussian phases is experimentally performed using the OCWS system. This miniaturized system may catalyze diverse applications such as point‐of‐care diagnostics, endoscopy, in situ QPI, and in‐line surface profile measurement.

We investigate the wave characteristics and homogenization theory of soft-matter layered structures in the low-frequency P-wave limit. Using the potential method, we derive a closed-form dispersion relation and identify three distinct wave modes: quasistatic, resonance, and slip. These modes are governed by equivalent interface conditions---namely, a continuous interface for the quasistatic mode, a springlike interface for the resonance mode, and a sliplike interface for the slip mode. Furthermore, we propose a simplified model that captures P-wave characteristics in the high-frequency S-wave regime. Our findings provide a unified framework for wave--structure interactions across solids, liquids, and soft-matter composites, enabling predictive design of metamaterials with programmable wave responses. This study offers insight into the fundamental understanding of layered media and provides direct design principles for applications in acoustic cloaking, vibration damping, and biomedical imaging.

For more than 60 years, it has been widely accepted that the irradiance of the incoming light plays the most critical role in the etching effect of the photoelectrochemical etching process, which is built upon the underlying physics that photo-generated charge carriers catalyze the dissolution of n-type semiconductors. However, in this paper, we report an anomalous physical phenomenon, i.e., the spatially distributed photons with a lateral gradient could drive the lateral distribution of carriers on the surface of semiconductors, which leads to the anomalous etching phenomenon on the surface of undoped semiconductor materials during the PEC etching process. Research shows that parameters such as light intensity, light intensity gradient, and carrier diffusion length are significantly correlated with this process. This discovery provides a potential method of rapid and large-scale 3D nanomanufacturing on semiconductor materials, which holds promise for significant applications in diverse fields such as microelectronics, nanophotonics, microelectromechanical systems (MEMS), and biomedicine. Photoelectrochemical etching relies on light-driven carrier migration to catalyze reactions on semiconductor surfaces. Here, the authors show that lateral photon gradients induce anomalous etching of undoped semiconductor materials.

Abstract Perfect wave absorption across all wavelengths is forbidden by the causality principle. Here we demonstrate an approach that circumvents this fundamental limitation in acoustics by coupling unstable components to achieve zero static modulus. Both heuristic model simulations based on different mechanisms (electromagnetic and mechanical) demonstrate the same ultra-broadband absorption exceeding 95% at all wavelengths greater than 114 times the absorber thickness, with simultaneous efficient reciprocal radiation capabilities. Theoretical analyses reveal that, counter-intuitively, this strategy approaches ideal blackbody behavior as thickness approaches zero. These findings indicate that fundamental physical constraints no longer prevent blackbody realization, leaving only material limitations as the remaining challenge.

Quantum devices exploiting twistronics by stacking two-dimensional materials could enable breakthroughs in computing and sensing beyond the limits of current transistors. Scaling up these devices poses grand challenges for in situ metrology, because existing tools lack the accuracy for characterizing sub-atomic structures. Here we demonstrate a laser-based interferometric method, termed Phase Amplification microscopy (Φ-Amp), which can push the measurement accuracy limit to the femtometer-level and beyond in ambient conditions. We show Φ-Amp amplifies weak phase signals from graphene by over 100 times through devising a phase cavity based on a novel phase-gain theory, enabling real-time, wide-field mapping of atomic layers with picometer-level accuracy. We quantified interlayer spacing differences between AB-stacked and 30-degree-twisted bilayer graphene to be ~ 0.71 Å, a subtle distortion driven by quantum interactions that was previously inaccessible to in situ metrology. We envision Φ-Amp as a transformative tool for both expediting wafer-scale atomic fabrication and advancing research in quantum materials by probing subatomic phenomena.

Liquid manipulation is ubiquitous in nature and engineering, enabling controllable and efficient liquid delivery. Conventional understanding of liquid manipulation relies on inhomogeneous chemical modifications or single-scale structure design. Here, we present how water is directionally navigated and spontaneously reallocated at high efficiency via the cross-scale topology on Tillandsia capitata leaves. These leaves feature transversely curved lanceolate macrostructures decorated by a layer of microtrichomes with varied morphologies. The macrostructure creates a lanceolate effect in the transport direction for fundamental navigation. At the same time, the microtrichomes serve dual functions: constructing a self-wetting superhydrophilic surface to facilitate the water transport speed and implementing water spreading in the opposite direction for autonomous reallocation. We explain the multiscale transport behavior through theoretic analysis and finite element simulations. Our findings demonstrate how cross-scale topographies jointly function in efficient autonomous fluid manipulation, with potential applications such as droplet driving, fog harvesting, and seawater desalination, offering pathways for improving liquid processing efficiency and reducing energy consumption.

The localization and classification of deep-subwavelength objects embedded in dense background nanopatterns in an imaging mode are challenging because of the optical diffraction limit and the weak signal-to-noise ratio and contrast. In this work, we, for the first time, experimentally validated the proposed conjugate structured illumination microscopy (c-SIM), which utilizes optical proximity correction techniques to generate a wide-field, diffraction-limited, and structured illumination field on the sample surface for defect inspection. Our experiments validated that c-SIM could accurately inspect 29 nm wide defects with an enhanced resolution (half of the diffraction barrier) using a 423 nm laser source. Moreover, our investigation demonstrated that different types of 38 nm wide defects could be precisely pinpointed and directly classified from the captured frames in the lateral scanning process, which is attributed to the fact that a conjugate structured light field could induce a high-intensity gradient in the illumination light. This technology may find diverse applications, such as a patterned wafer defect inspection, photomask inspection, material characterization, metamaterial inspection, and nanosensing.

The integration of large language models, combined with pretrained skills, has emerged as a powerful tool for proposing natural language actions that are both feasible and contextually appropriate to perform real-world tasks. In this paper, to further enhance both the feasibility and contextual appropriateness of actions within physical environments, we introduce CORA (Chain Of Robotic Actions), a model that leverages the chain of thought methodology within multimodal foundation models for robust robotic arm manipulation. CORA initiates the task-grounding process through the chain of thought approach, adeptly identifying action chains from high-level hu-man instructions. This method decomposes complex tasks into transparent, intermediate steps, boosting the model's precision and clarity in problem-solving. The chain of thought methodology not only provides a granular and explicit breakdown of the task-solving process but also improves the model's capacity to address complex, multi-step, and implicit instructions with enhanced interpretability. In the subsequent phase, CORA utilizes a multimodal foundation model for world-grounding, assisting the robot in completing the action plan within the physical environment. In a rigorous experimental setup, we evaluate our method in multiple contexts, including simulated and real-world environments. Ablation studies are conducted to evaluate the effectiveness of the Chain of Robotic Action Reasoning strategies in comprehending action chains explicitly and implicitly stated in human instructions. A comparative analysis with existing approaches further substantiates its superior performance. The results conclusively demonstrate the method's effectiveness and efficiency across various components.

Wetting-Induced Process The wetting-induced interconnected reentrant geometry (WING) process enables the large-scale fabrication of multifunctional re-entrant microcavity surfaces, representing a significant technological advancement. Utilizing capillary action in a scalable roll-to-roll printing technique, it produces surfaces with exceptional liquid repellency while maintaining microstructures under external forces. This process offers a cost-effective and high throughput solution for various applications, such as anti-icing, anti-fouling, and particle capture. More details can be found in article number 2411064 by Seok Kim, Young Tae Cho, and co-workers.

Aberration layers (AL) often present significant energy transmission barriers in microwave engineering, electromagnetic waves, and medical ultrasound. However, achieving broadband ultrasonic focusing through aberration layers like the human skull using conventional materials such as metals and elastomers has proven challenging. In this study, we introduce an inverse phase encoding method employing tunable soft metalens to penetrate heterogeneous aberration layers. Through the application of effective-medium theory, we determined the refractive index of micro-tungsten particles in silicone elastomer, closely aligning with experimental findings. The soft metalens allows for transmission across broadband frequencies (50 kHz to 0.4 MHz) through 3D-printed human skull models mimicking aberration layers. In ex vivo transcranial ultrasound tests, we observed a 9.3 dB intensity enhancement at the focal point compared to results obtained using an unfocused transducer. By integrating soft materials, metamaterials, and gradient refractive index, the soft metalens presents future opportunities for advancing next-generation soft devices in deep-brain stimulation, non-destructive evaluation, and high-resolution ultrasound imaging. The authors present a soft metalens (SML) with tungsten-gel composite for ultra-broadband transcranial focus, significantly enhancing intracranial sound pressure and spatial resolution. This breakthrough advances underwater sonar, medical ultrasound imaging, and non-invasive detection for energy transmission.

Owing to their unique structural robustness, interconnected reentrant structures offer multifunctionality for various applications. a scalable multistep roll-to-roll printing method is proposed for fabricating reentrant microcavity surfaces, coined as wetting-induced interconnected reentrant geometry (WING) process. The key to the proposed WING process is a highly reproducible reentrant structure formation controlled by the capillary action during contact between prefabricated microcavity structure and spray-coated ultraviolet-curable resins. It demonstrates the superior liquid repellency of the WING structures, which maintain large contact angles even with low-surface-tension liquids, and their robust capability to retain solid particles and liquids under external forces. In addition, the scalable and continuous fabrication approach addresses the limitations of existing methods, providing a cost-effective and high-throughput solution for creating multifunctional reentrant surfaces for anti-icing, biofouling prevention, and particle capture.

3D Embodied Spatial Reasoning, emphasizing an agent’s interaction with its surroundings for spatial information inference, is adeptly facilitated by the process of Situated Question Answering in 3D Scenes (SQA3D). SQA3D requires an agent to comprehend its position and orientation within a 3D scene based on a textual situation and then utilize this understanding to answer questions about the surrounding environment in that context. Previous methods in this field face substantial challenges, including a dependency on constant retraining on limited datasets, which leads to poor performance in unseen scenarios, limited expandability, and inadequate generalization. To address these challenges, we present a new embodied spatial reasoning paradigm for enhanced SQA3D, fusing the capabilities of foundation models with the chain of thought methodology. This approach is designed to elevate adaptability and scalability in a wide array of 3D environments. A new aspect of our model is the integration of a chain of thought reasoning process, which significantly augments the model’s capability for spatial reasoning and complex query handling in diverse 3D environments. In our structured experiments, we compare our approach against other methods with varying architectures, demonstrating its efficacy in multiple tasks including SQA3D and 3D captioning. We also assess the informativeness contained in the generated answers for complex queries. Ablation studies further delineate the individual contributions of our method to its overall performance. The results consistently affirm our proposed method’s effectiveness and efficiency.

Cardiovascular diseases (CADs) are the number one cause of death worldwide. In addition to preventive measures, which serve as the first line of defense against CADs, monitoring is crucial for timely intervention. Recently, ultrasound particle image velocimetry (echoPIV) using contrast agents has been utilized to monitor blood flow in arteries. This approach provides vector fields of blood flow over time, allowing physicians to identify features such as vortices and stagnation points around plaques or within vascular aneurysms. However, when a plaque is calcified, it casts a shadow in the ultrasound image, impeding the analysis of blood flow. This study reports the design, fabrication, and testing of a meta matching layer (MML) aimed at reducing reflections from a plaque model (aberrating layer) while improving transmission. The results show that the MML decreases reflections (represented by a ratio defined in this paper) by at least 28% and up to 80% over the range of 3–6 MHz; however, attenuation and shadowing remain challenges. Future work will focus on tacking the attenuation effect.

Invisibility cloaks that can suppress wave scattering by objects have attracted a tremendous amount of interest in the past two decades. In comparison to prior methods that were severely limited by narrow bandwidths, here we present a practical strategy to suppress sound scattering across an ultra-broad spectrum by leveraging illusion metamaterials. Consisting of a collection of subwavelength tunnels with precisely crafted internal structures, this illusion metamaterial has the ability to guide acoustic waves around the obstacles and accurately recreate the incoming wavefront on the exit surface. Remarkably, two ultra-broadband illusionary effects are produced, disappearing space and time shift. Sound scatterings are removed at all frequencies below a limit determined by the tunnel width, as confirmed by full-wave simulations and acoustic experiments. Our strategy represents a universal approach to solve the key bottleneck of bandwidth limitation in the field of cloaking in transmission, and establishes a metamaterial platform that enables the long-desired ultra-broadband sound manipulation such as acoustic camouflage and reverberation control, opening up exciting new possibilities in practical applications. Invisibility cloaks have attracted a tremendous amount of interest. Here, the authors present a strategy to realize ultra-broadband disappearing-space and time-shift camouflages by leveraging illusion metamaterials, thereby removing the longstanding bottleneck of limited bandwidth in invisibility.

Due to its high bandwidth, low latency, low power consumption, and compact size, three-dimensional (3D) integration of semiconductor chips holds the promise of boosting the performance of integrated circuit systems. However, the applications of 3D stacked structures are constrained by the surface deformation of each thin layer induced by thermal effects, vibration, gravity, and other environmental stresses. Therefore, ensuring the performance and reliability of 3D stacked structures necessitates the precise measurement of nanoscale deformation in each layer. Furthermore, the spacing between layers in 3D stacked structures using modern microelectronics and packaging technologies is exceedingly small, making it impossible to measure the deformation of all layers. Here, we present a novel optical endoscope that fuses a miniaturized interferometry array, a laser-fabricated microprobe, and a highly efficient profile reconstruction algorithm for the precise measurements of surface deformation across all layers in 3D stacked structures. Our method offers a potentially effective and noninvasive way to address the challenges associated with in-line deformation measurement across all layers in real 3D stacked wafers and chips.

Soft elastomeric composite materials constituting of an elastomeric matrix with dilute concentrations of thin, relatively higher modulus interfacial layers are presented and demonstrated to exhibit enhanced strain energy storage together with a bi‐/multi‐linear elastic behavior and stress mitigation ‐ all with little to no weight penalty. In this study, the governing mechanism for these features is revealed to be the activation of wrinkling of the embedded interfacial layers upon reaching a critical strain, thereby amplifying energy storage in both the matrix and the interfacial layers. Furthermore, the energy storage in the composite is substantially greater than the sum of the energy storage of the isolated material constituents. The new features of the composite material behavior can be tailored by the concentration of the interfacial layers, and the elastic properties of the elastomeric matrix and interfacial layers. The results are demonstrated and validated through analytical derivations, finite‐element analysis, and experiments. The analytical expressions provide the ability to quantitatively design and predict the material performance. These soft‐layered composites point to opportunities for expanding these enhancements to networked interlayers, multifunctional interlayers, and viscoelastic elastomeric matrices for viscous damping together with energy storage.

in Mechanical Engineering from MIT, specializing in the theory and simulation of bacterial dynamics.As a graduate student, she was a

Phase engineering plays a pivotal role in various scientific research and industrial applications including microwaves, optics, and acoustics. However, traditional phase engineering methods lack the flexibility for arbitrary programming due to the absence of digitization. Conversely, while broadband digitization technology holds promise, its utilization in wave engineering has been constrained by narrowband transmission capabilities. In this study, we introduce a novel approach to broadband digital phase encoding spanning frequencies from 50 to 500 kHz. Our methodology is exemplified through the development of an acoustic soft metacollimator with simulations and experiments conducted underwater across different frequency ranges. Our findings demonstrate that the soft metacollimator significantly enhances transmission intensity by 7.7 dB and improves spatial resolution by a factor of 10. Moreover, the soft metacollimator enables novel functionalities such as long-distance energy enhancement and broadband coding properties in underwater acoustics. This pioneering broadband digital phase encoding technique holds promise for advancing next-generation phase engineering and offers versatile applications in biomedical ultrasonics, acoustic communications, and the development of underwater broadband acoustic antennas.

High resolution resistors capable of detecting minuscule currents are vital for advanced sensors, but existing off-shelf models struggle with inconsistent resistance under varying voltages. The underlying physics of this issue is rooted in unstable surface charges and intrinsic inhomogeneity of surface potential caused by spontaneous polarization (SP) in commercial semi-insulating silicon carbide (SiC) devices. In this work, we found that coating SiC surfaces with an ultrathin zinc oxide layer immobilizes the dangling surface charges in place and balances the natural electric field of the material, ensuring stable resistance even at extreme voltages up to 1000 V. The resulting SiC resistor maintains a record-high resistance of one peta-ohm (10^15 Ω) with negligible voltage fluctuations, outperforming conventional options. Additionally, these devices can switch states when exposed to light or heat, making them dual-purpose tools for ultra-sensitive measurements and sensors. This breakthrough combines high stability, scalability for mass production, and multifunctionality, opening doors to next-generation precision technologies in fields like quantum sensing and environmental monitoring.

Artificial skins or flexible pressure sensors that mimic human cutaneous mechanoreceptors transduce tactile stimuli to quantitative electrical signals. Conventional trial-and-error designs for such devices follow a forward structure-to-property routine, which is usually time-consuming and determines one possible solution in one run. Data-driven inverse design can precisely target desired functions while showing far higher productivity, however, it is still absent for flexible pressure sensors because of the difficulties in acquiring a large amount of data. Here, we report a property-to-structure inverse design of flexible pressure sensors, exhibiting a significantly greater efficiency than the conventional routine. We use a reduced-order model that analytically constrains the design scope and an iterative "jumping-selection" method together with a surrogate model that enhances data screening. As an exemplary scenario, hundreds of solutions that overcome the intrinsic signal saturation have been predicted by the inverse method, validating for a variety of material systems. The success in property design on multiple indicators demonstrates that the proposed inverse design is an efficient and powerful tool to target multifarious applications of flexible pressure sensors, which can potentially advance the fields of intelligent robots, advanced healthcare, and human-machine interfaces.

With the advancements in modern imaging techniques, such as MRI, CT imaging, and nuclear medicine, powerful functional imaging modalities have emerged. The human skull, as a barrier for energy transmission, poses significant challenges for the clinical application of transcranial ultrasound. High-intensity focused ultrasound (HIFU), as an effective tool for modern biomedical tumor imaging and treatment, has benefited from the use of structured focusing transducers, which generate axial pressure waves and induce localized thermal effects within tissues, enabling precise destruction of tumor tissue while minimizing damage to surrounding normal tissue. To date, the preclinical optimization design path for transcranial ultrasound focusing lenses remains uncertain due to the complex interaction between the structured piezoelectric transducer’s near-field coherence and the human skull. For achieving arbitrary wavefront shaping and biomedical transcranial monitoring, holographic techniques are fundamental to applications with high-density data storage and spatial control of intricate acoustic fields. The basic of phase-only acoustic hologram is spatial storage the phase profile of the desired wavefront from real human skull in a manner that allows for wavefront reconstruction by near-field interaction when hologram metalens is illuminated with a suitable coherent source. We propose that by introducing the micro-tungsten-based metalens via acoustic hologram, the arbitrary shaped scattering effect from human skull could be eliminated. The static non-resonance-based design is key to achieving ultra-broadband material properties, which differs from the resonant-based effective medium theory such as dynamic homogenization scheme for acoustic metamaterials. The experimental results show that newly-developed tungsten metalens via acoustic hologram performs well over frequency from 100 kHz to 500 kHz and near-field received sound pressure level (SPL) is improved about 9 dB without human skull when introducing the real human skull. Applications show that our designed micro-tungsten-based metalens performs well than traditional curved focus lens.

The comprehension and control of wave propagation and energy transfer within exponential materials remain an open question to multiple research disciplines. Exponential materials, ubiquitous in nature due to gravitational effects, are found in various contexts including the earth's atmosphere, ground soil, and marine sediments. In this work, we propose a universal theory for predicting the electromagnetic scattering spectra of unidirectional exponential materials characterized by inhomogeneous exponential permittivity and/or permeability. The core concept of our approach revolves around the derivation of modified transfer and scattering matrices through the analytical generalization of plane-wave eigenmodes from uniform to exponential materials. This model's universality and precision demonstrate a superior performance when juxtaposed with two widely recognized theories — the small reflection theory and the transfer matrix method. Moreover, our theory enables the analytical exploration of dispersive group/phase velocities instigated by exponential properties. Theoretical predictions are validated through numerical examples, which are used for predicting scattering spectra. To underscore the efficacy of the proposed theory, we first compute the functionality of field modulation (either amplification or attenuation), and secondly, we analytically establish the correlation between the broadband impedance matching effects of exponential materials and spatial inhomogeneity. Based on these findings, we propose an inverse design scheme for crafting planar layered metamaterials with exceptional broadband anti-reflection performance in the microwave band. This holds potential for resolving impedance matching challenges in diverse systems. The insights garnered from this research serve to deepen our understanding of inhomogeneous gradient materials and to improve their efficient modeling and design.

Controlling the quality factor (Q) of a resonant cavity broadbandly is a highly complex task, as it involves dealing with the intricate modal response and the limitations of boundary control degrees of freedom. The resonant behavior of an acoustic cavity often leads to non-uniform decay times of its wave field, making it quite challenging to achieve spatial uniformity. To tackle this issue, we propose a novel approach: designing impedance boundary conditions on the surface of the cavity walls that vary with both frequency and space. This design allows for the generation of a uniform response across a wide frequency range. To implement such boundary conditions, we leverage the capabilities of customizable dispersive acoustic metasurfaces, a technology that has steadily matured in recent years. These metasurfaces consist of integrated multiple resonators, whose collective average response spectrum can be tailored to achieve the optimal form based on the available space and specific requirements. In essence, our efforts focus on utilizing numerous small resonators at the cavity boundary to effectively control and tame the strong resonances of the larger cavity. This abstract physical problem finds a practical application in the control of reverberation time (T<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</inf>) in room acoustics. We will revisit the principles and concepts behind our recent achievement of maintaining a constant reverberation time over a finite frequency band and provide experimental results to validate the effectiveness of our theoretical design. By introducing wideband customizable metamaterials into the realm of room acoustics, our work has the potential to significantly impact various fields, including listening rooms, recording studios, and automotive acoustics. This groundbreaking approach opens up new possibilities for achieving optimal acoustic experience and enhancing the overall auditory experience in these environments.

Spatially exponential distributions of material properties are ubiquitous in many natural and engineered systems, from the vertical distribution of the atmosphere to acoustic horns and anti-reflective coatings. These media seamlessly interface different impedances, enhancing wave transmission and reducing internal reflections. This work advances traditional transfer matrix theory by integrating analytical solutions for acoustic exponential materials, which possess exponential density and/or bulk modulus , offering a more accurate predictive tool and revealing the physical mechanism of broadband anti-reflection for sound propagation in such non-uniform materials. Leveraging this method, we designed an acoustic dipole array that effectively mimics exponential mass distribution. Through experiments with precisely engineered micro-perforated plates, we demonstrate an ultra-low reflection rate of about 0.86% across a wide frequency range from 420 Hz to 10,000 Hz. Our modified transfer matrix approach underpins the design of exponential materials, and our layering strategy for stacking acoustic dipoles suggests a pathway to more functional gradient acoustic metamaterials .

The long-standing paradox between matte appearance and transparency has deprived traditional matte materials of optical transparency. Here, we present a solution to this centuries-old optical conundrum by harnessing the potential of disordered optical metasurfaces. Through the construction of a random array of meta-atoms tailored in asymmetric backgrounds, we have created transparent matte surfaces that maintain clear transparency regardless of the strength of disordered light scattering or their matte appearances. This remarkable property originates in the achievement of highly asymmetric light diffusion, exhibiting substantial diffusion in reflection and negligible diffusion in transmission across the entire visible spectrum. By fabricating macroscopic samples of such metasurfaces through industrial lithography, we have experimentally demonstrated transparent windows camouflaged as traditional matte materials, as well as transparent displays with high clarity, full color, and one-way visibility. Our work introduces an unprecedented frontier of transparent matte materials in optics, offering unprecedented opportunities and applications.

LEAP Group under Dr. John Liu and Emily Welsh from 2020 to 2021, developing augmented reality experiences for nanotechnology education.Her interests include innovating education technology, as well as exploring new applications of computer vision.She hopes to merge her background in mechanical engineering with computer science to create new modes of digital experiences.