A High-Precision Algorithm for DOA Estimation Using a Long-Baseline Array Based on the Hearing Mechanism of the Ormia Ochracea.

Inspired by the Ormia Ochracea hearing mechanism, a new direction of arrival estimation using multiple antenna arrays has been considered in spatially colored noise fields. This parasitoid insect can locate s cricket's position accurately using the small distance between its ears, far beyond the standard array with the same aperture. This phenomenon can be understood as a mechanical coupled structure existing between the Ormia ears. The amplitude and phase differences between the received signals are amplified by the mechanical coupling, which is functionally equivalent to a longer baseline. In this paper, we regard this coupled structure as a multi-input multi-output filter, where coupling exists between each pair of array elements. Then, an iterative direction-finding algorithm based on fourth-order cumulants with fully coupled array is presented. In this manner, the orientation of the mainlobe can direct at the incident angle. Hence, the direction-finding accuracy can be improved in all possible incident angles. We derive the Cramér-Rao lower bound for our proposed algorithm and validate its performance based on simulations. Our proposed DOA estimation algorithm is superior to the existing biologically inspired direction-finding and fourth-order cumulants-based estimation algorithms.

Bioinspired Dynamic Camouflage from Colloidal Nanocrystals Embedded Electrochromics.

Camouflage is often seen in animals, and it presents in both passive and active forms. For instance, the wings of Closterocerus coffeellae exhibit distinct appearances against different backgrounds, while the chameleon actively changes its skin colors to morph into the environment. Herein, we report an artificial skin-like optoelectronic device that enables actively changing appearances and passively morphing into the environment by manipulating light-matter interactions with electrochromic polymers and photonic colloid nanocrystals. To construct the new electrochromic device, highly reflective, yet transmissive photonic nanocrystals are introduced into the gel electrolyte and sandwiched between the layers of electrochromic polymers and ion storage materials. Through voltage-controlled color switching of electrochromic polymers from colored state to bleached state, the degree of light absorbance, transmittance, and reflectance can be finely balanced and precisely modulated with the device. A broad synthesized color gamut and angle-dependent visual effects can be realized on this electronic skin-like device.

Ambient Oxygen-Doped Conjugated Polymer for pH-Activatable Aggregation-Enhanced Photoacoustic Imaging in the Second Near-Infrared Window.

Photoacoustic (PA) probes absorbing in the second near-infrared (NIR-II: 1000-1700 nm) window hold great promise for deep-tissue diagnosis and treatment. Currently, NIR-II PA probes typically involve complex synthesis and surfactant adjuvant for processing and delivery. Furthermore, these NIR-II PA probes are "always-on," leading to inadequate signal-to-background ratio and low specificity. To address these challenges, this study reports a pH-activatable and aggregation-enhanced NIR-II PA probe. Without using any toxic or exotic oxidants, the selected polymer (PPE) is readily doped by oxygen in an ambient environment and simultaneously red-shifts its absorption profile from visible to NIR-II region. By virtue of the carboxyl groups on the side chains, oxygen-doped PPE is readily water-soluble at a physiological pH but tends to aggregate in an acidic environment. The pH-induced aggregation results in a significant PA enhancement and thus allows specific PA imaging of acidic tumor microenvironment in vivo. Our study provides a facile and surfactant-free strategy for achieving water-soluble and pH-responsive NIR-II PA probes, which could be applied for diagnoses of cancer and other diseases associated with changes in pH. It paves the way for the development of new activatable NIR-II imaging probes and also could facilitate the investigation of biological and pathological processes in deep tissue.

Mechanical breathing in organic electrochromics.

The repetitive size change of the electrode over cycles, termed as mechanical breathing, is a crucial issue limiting the quality and lifetime of organic electrochromic devices. The mechanical deformation originates from the electron transport and ion intercalation in the redox active material. The dynamics of the state of charge induces drastic changes of the microstructure and properties of the host, and ultimately leads to structural disintegration at the interfaces. We quantify the breathing strain and the evolution of the mechanical properties of poly(3,4-propylenedioxythiophene) thin films in-situ using customized environmental nanoindentation. Upon oxidation, the film expands nearly 30% in volume, and the elastic modulus and hardness decrease by a factor of two. We perform theoretical modeling to understand thin film delamination from an indium tin oxide (ITO) current collector under cyclic load. We show that toughening the interface with roughened or silica-nanoparticle coated ITO surface significantly improves the cyclic performance.

Multi-Sensor Passive Localization Using Direct Position Determination with Time-Varying Delay.

This paper focuses on passive emitter localization using moving sensors. The increase in observation time is beneficial to improve the localization accuracy, but it could cause deterioration of the relative motion between the emitter and the sensors, especially the nonlinear motion. The common localization algorithms typically have two steps: (1) parameter estimation and (2) position determination, where the parameters are assumed to be constant, and it is not applicable for long observation times. We proposed the time-varying delay-based direct position determination (DPD-TVD) method, regarding the variation in the propagation time delay during the observation time. Using one step, the proposed algorithm can obtain the emitter's position directly from the received signals by calculating the cost function corresponding to the map grid. By better adapting to highly dynamic scenarios, the proposed algorithm can achieve better localization accuracy than that of constant parameters using one-step or two-step procedures, which is demonstrated by the simulation results.

Low-Temperature Thermally Annealed Niobium Oxide Thin Films as a Minimally Color Changing Ion Storage Layer in Solution-Processed Polymer Electrochromic Devices.

The limited availability of solution-processable ion storage materials, both inorganic and organic, hinders the adoption of roll-to-roll manufacturing for polymer electrochromic devices (ECDs). The n-type transition metal oxides are known for their ion storage properties. However, the fabrication methods of their amorphous metal oxide thin films typically involve sputtering, thermal deposition, electrical deposition, or sol-gel deposition followed by high-temperature thermal annealing (>300 °C), thus making them incompatible for low-cost roll-to-roll manufacturing on flexible substrates. In this study, we report the synthesis of amorphous niobium oxide(a-Nb2O5) thin films from sol-gel precursors through the combination of photoactivation and low-temperature thermal annealing (150 °C). Coupled with p-type electrochromic polymers (ECPs), solution-processed a-Nb2O5 thin films were evaluated as a minimally color changing counter electrode (MCC-CE) material for electrochromic devices. We found that ultraviolet ozone (UVO) treated and 150 °C thermally annealed (UVO-150 °C) a-Nb2O5 thin films show excellent electrochemical properties and cycling stability. Notably, a-Nb2O5/ECP-magenta ECD has a high optical contrast of ∼70% and a fast switching time (bleaching and coloring time of 1.6 and 0.5 s for reaching 95% of optical contrast). In addition, the ECD demonstrates a high coloration efficiency of ∼849.5 mC cm-2 and a long cycling stability without a noticeable decay up to 3000 cycles.

Highly Transparent Crosslinkable Radical Copolymer Thin Film as the Ion Storage Layer in Organic Electrochromic Devices.

A highly transparent crosslinkable thin film made of the radical polymer poly(2,2,6,6-tetramethyl-4-piperidinyloxy methacrylate)- co-(4-benzoylphenyl methacrylate) (PTMA- co-BP) has been developed as the ion storage layer in electrochromic devices (ECDs). After photo-crosslinking, the dissolution of PTMA- co-BP in electrolytes was mitigated, which results in an enhanced electrochemical stability compared with the homopolymer PTMA thin film. Moreover, the redox capacity of PTMA- co-BP increased because of the formation of a crosslinked network. By matching the redox capacity of the PTMA- co-BP thin film and bis(alkoxy)-substituted poly(propylenedioxythiophene), the ECD achieved an optical contrast of 72% in a small potential window of 2.55 V (i.e., switching between +1.2 and -1.35 V), and it was cycled up to 1800 cycles. The ECD showed an excellent optical memory as its transmittance decayed by less than 3% in both the colored and bleached states while operating for over 30 min under open-circuit conditions. Use of crosslinkable radical polymers as the transparent ion storage layer opens up a new venue for the fabrication of transmissive-mode organic ECDs.

Tuning of Polyoxopalladate Macroanionic Hydration Shell via Countercation Interaction.

Three types of macroanion-countercation interactions in dilute solution, decided by the strength of electrostatic attraction and the change of hydration shells are reported: minor interaction between macroanions [MO8 Pd12 (SeO3 )8 ]6- (M=Zn2+ or Ni2+ ) and monovalent cations (Na+ , K+ , Rb+ , Cs+ ), leaving their hydration shells intact (solvent-separated ion-pairs); strong binding between macroanions and divalent cations (Sr2+ , Ba2+ ) to form solvent-shared ion-pairs with partial dehydration; very strong electrostatic attraction between macroanions and Y3+ ion with contact ion-pairs formation by severely breaking their original hydration shells and forming new ones. In addition, divalent cations can help the macroanions self-assemble into hollow spherical blackberry structures through counterion-mediated attraction, whereas macroanions with mono- or trivalent cations only stay as discrete ions due to either weak interaction or a small number of bound countercations.

Self-Bleaching Behaviors in Black-to-Transmissive Electrochromic Polymer Thin Films.

Polymer-based electrochromic smart windows are an emerging energy-saving technology. There are several technological hurdles in the development of organic electrochromics. In this article, the self-bleaching behaviors of a black electrochromic polymer (ECP-black) thin film were investigated. We found that the electrochemical break-in process led to a less dense morphology and the increased free volume facilitated ion permeation in the ECP-black thin films. The polarized interface between the polymer thin film and transparent indium-tin-oxide (ITO) electrode made charge transfer accessible, which caused the self-bleaching behaviors. Herein, we proposed two approaches to study and mitigate the self-bleaching phenomenon. First, a densely packed morphology was regenerated by increasing the cathodic polarization time under open-circuit conditions (Voff). The second involved the modification of the electrode (ITO) surface with a partial coverage of the octadecyltrichlorosilane layer. The combination of the two approaches rendered the ECP-black thin film capable of maintaining the colored state for up to 900 s. To extend the scope of our studies, self-bleaching of ECP-magenta and ECP-blue thin films were also tested and suppressed by using these two methods. Additionally, the cycling stability of the ECP-black has been improved from ∼600 cycles to up to 2300 cycles without a noticeable decay of optical contrast.