Boosting Contact Electrification by Amorphous Polyvinyl Alcohol Endowing Improved Contact Adhesion and Electrochemical Capacitance.

Ion conductive hydrogels are relevant components in wearable, biocompatible, and biodegradable electronics. Polyvinyl-alcohol (PVA) homopolymer is often the favored choice for integration into supercapacitors and energy harvesters as in sustainable triboelectric nanogenerators (TENGs). However, to further improve hydrogel-based TENGs, a deeper understanding of the impact of their composition and structure on devices performance is necessary. Here, it is shown how ionic hydrogels based on an amorphous-PVA (a-PVA) allow to fabricate TENGs that outperform the one based on the homopolymer. When used as tribomaterial, the Li-doped a-PVA allows to achieve a twofold higher pressure sensitivity compared to PVA, and to develop a conformable e-skin. When used as an ionic conductor encased in an elastomeric tribomaterial, 100 mW cm-2 average power is obtained, providing 25% power increase compared to PVA. At the origin of such enhancement is the increased softness, stronger adhesive contact, higher ionic mobility (> 3,5-fold increase), and long-term stability achieved with Li-doped a-PVA. These improvements are attributed to the high density of hydroxyl groups and amorphous structure present in the a-PVA, enabling a strong binding to water molecules. This work discloses novel insights on those parameters allowing to develop easy-processable, stable, and highly conductive hydrogels for integration in conformable, soft, and biocompatible TENGs.

A Wireless Sensor Network for Residential Building Energy and Indoor Environmental Quality Monitoring: Design, Instrumentation, Data Analysis and Feedback.

This article outlines the implementation and use of a large wireless instrumentation solution to collect data over a long time period of a few years for three collective residential buildings. The sensor network consists of a variety of 179 sensors deployed in building common areas and in apartments to monitor energy consumption, indoor environmental quality, and local meteorological conditions. The collected data are used and analyzed to assess the building performance in terms of energy consumption and indoor environmental quality following major renovation operations on the buildings. Observations from the collected data show energy consumption of the renovated buildings in agreement with expected energy savings calculated by an engineering office, many different occupancy patterns mainly related to the professional situation of the households, and seasonal variation in window opening rates. The monitoring was also able to detect some deficiencies in the energy management. Indeed, the data reveal the absence of time-of-day-dependent heating load control and higher than expected indoor temperatures because of a lack of occupant awareness on energy savings, thermal comfort, and the new technologies installed during the renovation such as thermostatic valves on the heaters. Lastly, we also provide feedback on the performed sensor network from the experiment design and choice of measured quantities to data communication, through the sensors' technological choices, implementation, calibration, and maintenance.

Tailoring silicon for dew water harvesting panels.

Dew water, mostly ignored until now, can provide clean freshwater resources, just by extracting the atmospheric vapor available in surrounding air. Inspired by silicon-based solar panels, the vapor can be harvested by a concept of water condensing panels. Efficient water harvesting requires not only a considerable yield but also a timely water removal from the surface since the very beginning of condensation to avoid the huge evaporation losses. This translates into strict surface properties, which are difficult to simultaneously realize. Herein, we study various functionalized silicon surfaces, including the so-called Black Silicon, which supports two droplet motion modes-out-of-plane jumping and in-plane sweeping, due to its unique surface morphology, synergistically leading to a pioneering combination of above two required characteristics. According to silicon material's scalability, the proposed silicon-based water panels would benefit from existing infrastructures toward dual functions of energy harvesting in daytime and water harvesting in nighttime.

Employing a MEMS plasma switch for conditioning high-voltage kinetic energy harvesters.

Triboelectric nanogenerators have attracted wide attention due to their promising capabilities of scavenging the ambient environmental mechanical energy. However, efficient energy management of the generated high-voltage for practical low-voltage applications is still under investigation. Autonomous switches are key elements for improving the harvested energy per mechanical cycle, but they are complicated to implement at such voltages higher than several hundreds of volts. This paper proposes a self-sustained and automatic hysteresis plasma switch made from silicon micromachining, and implemented in a two-stage efficient conditioning circuit for powering low-voltage devices using triboelectric nanogenerators. The hysteresis of this microelectromechanical switch is controllable by topological design and the actuation of the switch combines the principles of micro-discharge and electrostatic pulling, without the need of any power-consuming control electronic circuits. The experimental results indicate that the energy harvesting efficiency is improved by two orders of magnitude compared to the conventional full-wave rectifying circuit.

Inductor-Free Output Multiplier for Power Promotion and Management of Triboelectric Nanogenerators toward Self-Powered Systems.

The output voltage of triboelectric nanogenerators (TENGs) is much higher than the overload capacity of most commercial electronics, making it hard to power them directly; so the power-management solution is indispensable. In the meanwhile, it is critical for practical applications to enhance the output performance of the TENG toward its breakdown limit, which is usually ignored before. Here, an inductor-free output multiplier (OM) for power promotion and management of TENGs is proposed, with the breakdown effect considered. This OM, as expanded based on bennet's doubler, is theoretically studied and experimentally demonstrated to significantly enhance the output performance of the TENG within only a few working cycles. The charge output was enhanced by 7.6 times experimentally with the OM. An external capacitor and a switch are applied to realize a high energy extraction ratio of up to 196%, with the average charge output per cycle of ∼3-3.75 µC achieved. This OM circuit with the smart switch is suitable for power promotion of TENGs with variable capacitance and for power management of all TENGs. The OM circuit is demonstrated to ensure the high output performance of TENGs even at a low triboelectric charge density, which is crucial for broad applications of the TENG toward self-powered systems, potentially to be a solution for improving the output performance of TENGs working in harsh environments.

DNA Printing Integrated Multiplexer Driver Microelectronic Mechanical System Head (IDMH) and Microfluidic Flow Estimation.

The system designed in this study involves a three-dimensional (3D) microelectronic mechanical system chip structure using DNA printing technology. We employed diverse diameters and cavity thickness for the heater. DNA beads were placed in this rapid array, and the spray flow rate was assessed. Because DNA cannot be obtained easily, rapidly deploying DNA while estimating the total amount of DNA being sprayed is imperative. DNA printings were collected in a multiplexer driver microelectronic mechanical system head, and microflow estimation was conducted. Flow-3D was used to simulate the internal flow field and flow distribution of the 3D spray room. The simulation was used to calculate the time and pressure required to generate heat bubbles as well as the corresponding mean outlet speed of the fluid. The "outlet speed status" function in Flow-3D was used as a power source for simulating the ejection of fluid by the chip nozzle. The actual chip generation process was measured, and the starting voltage curve was analyzed. Finally, experiments on flow rate were conducted, and the results were discussed. The density of the injection nozzle was 50, the size of the heater was 105 µm × 105 µm, and the size of the injection nozzle hole was 80 µm. The maximum flow rate was limited to approximately 3.5 cc. The maximum flow rate per minute required a power between 3.5 W and 4.5 W. The number of injection nozzles was multiplied by 100. On chips with enlarged injection nozzle density, experiments were conducted under a fixed driving voltage of 25 V. The flow curve obtained from various pulse widths and operating frequencies was observed. The operating frequency was 2 KHz, and the pulse width was 4 µs. At a pulse width of 5 µs and within the power range of 4.3-5.7 W, the monomer was injected at a flow rate of 5.5 cc/min. The results of this study may be applied to estimate the flow rate and the total amount of the ejection liquid of a DNA liquid.

A power supply module for autonomous portable electronics: ultralow-frequency MEMS electrostatic kinetic energy harvester with a comb structure reducing air damping.

A MEMS electrostatic kinetic energy harvester (e-KEH) of about 1 cm2, working at ultralow frequency (1-20 Hz), without any supported additional mass on its mobile electrode, and working even without a vacuum environment is reported. The prototype is especially suitable for environments with abundant low frequency motions such as wearable electronics. The proposed e-KEH consists of a capacitor with a finger-teeth interdigited comb structure. This greatly reduces the air damping effect, and thus the capacitance variation remains important regardless of the presence of air. With the new design, the energy transduced per cycle of excitation is no less than 33 times higher than the classic design within 10-40 Hz/2 g peak, while is 85 times higher at 15 Hz/2 g peak. An enclosed miniature ball combined with non-linear stoppers enables the oscillation of the movable electrode through impact-based frequency up-conversion mechanism, which is also improved by the low air damping. Thanks to this new design, a higher efficiency than the classic gap-closing comb structure is obtained, as a larger range of working frequency (1-180 Hz) in air. A maximum energy conversion of 450 nJ/cycle is obtained with a bias voltage of 45 V and an acceleration of 11 Hz, 3 g peak. Working with a diode AC-DC rectifier, the proposed KEH is able to support up to 3 RFID communications within 16 s while operated at 11 Hz, 3 g peak.

Static and dynamic aspects of black silicon formation.

We present a combination of experimental data and modeling that explains some of the important characteristics of black silicon (BSi) developed in cryogenic reactive ion etching (RIE) processes, including static properties (dependence of resulting topography on process parameters) and dynamic aspects (evolution of topography with process time). We generate a phase diagram predicting the RIE parameter combinations giving rise to different BSi geometries and show that the topographic details of BSi explain the metamaterial characteristics that are responsible for its low reflectivity. In particular, the unique combination of needle and hole features of various heights and depths, which is captured by our model and confirmed by focused ion beam nanotomography, creates a uniquely smooth transition in refractive index. The model also correctly describes dynamical characteristics, such as the dependence of aspect ratio on process time, and the prediction of new etching fronts appearing at topographical saddle points during the incipient stages of BSi development--a phenomenon reported here for the first time.

On the free-space Gaussian beam coupling to droplet optical resonators.

In this paper, light coupling into droplet optical resonators by means of a free-space Gaussian beam (GB) is investigated through numerical simulations and experiments. This method is introduced as an alternative to previously reported methods based on coupling through tapered fibers or prisms. Though applicable to solid-state optical resonators, this method is investigated here in the context of optofluidics for preserving the integrity of the droplet shape and for facilitating the steps of alignment and light coupling. The glycerol droplet under study is supported by a super-hydrophobic surface, which consists of Teflon-coated nanostructured silicon, to provide the advantage of keeping the droplet at a specific location, while maintaining a nearly spherical shape. The effectiveness of this method is tested with millimeter-sized droplets through measurements of their spectral responses. Quality factors Q in excess of 6 × 10(3) have been recorded. An analytical model for the external quality factor associated with this coupling technique has been derived, and the effect of the coupling parameters is demonstrated, allowing discussion about the scaling effects.

Thermal conductivity and thermal boundary resistance of nanostructures.

: We present a fabrication process of low-cost superlattices and simulations related with the heat dissipation on them. The influence of the interfacial roughness on the thermal conductivity of semiconductor/semiconductor superlattices was studied by equilibrium and non-equilibrium molecular dynamics and on the Kapitza resistance of superlattice's interfaces by equilibrium molecular dynamics. The non-equilibrium method was the tool used for the prediction of the Kapitza resistance for a binary semiconductor/metal system. Physical explanations are provided for rationalizing the simulation results. PACS: 68.65.Cd, 66.70.Df, 81.16.-c, 65.80.-g, 31.12.xv.