Sustainable and affordable supply of clean, safe, and adequate water is one of the most challenging issues facing the world. Membrane separation technology is one of the most cost-effective and widely applied technologies for water purification. Polymeric membranes such as cellulose-based (CA) membranes and thin-film composite (TFC) membranes have dominated the industry since 1980. Although further development of polymeric membranes for better performance is laborious, the research findings and sustained progress in inorganic membrane development have grown fast and solve some remaining problems. In addition to conventional ceramic metal oxide membranes, membranes prepared by graphene oxide (GO), carbon nanotubes (CNTs), and mixed matrix materials (MMMs) have attracted enormous attention due to their desirable properties such as tunable pore structure, excellent chemical, mechanical, and thermal tolerance, good salt rejection and/or high water permeability. This review provides insight into synthesis approaches and structural properties of recent reverse osmosis (RO) and nanofiltration (NF) membranes which are used to retain dissolved species such as heavy metals, electrolytes, and inorganic salts in various aqueous solutions. A specific focus has been placed on introducing and comparing water purification performance of different classes of polymeric and ceramic membranes in related water treatment industries. Furthermore, the development challenges and research opportunities of organic and inorganic membranes are discussed and the further perspectives are analyzed.

This paper proposes a piezoelectric energy harvester to supply power for low-consumption devices in intelligent vehicle wheels. The harvester is embedded in the spoke and possesses the ability of self-tuning due to the centrifugal force in the rotational motion. A dynamic model suitable for design is derived through the Euler-Lagrange method and verified by experiments. In order to facilitate the design of the harvester, the concept of design factor is proposed and discussed. The wheel's rotational characteristics is measured by a road test and a harvester is designed for the R16 wheel. An experimental platform with Macro Fiber Composite is built and the output power of 0.61-6.28 mW is achieved at the wheel speeds from 40 to 120 kph on real road test. The results demonstrate that the proposed piezoelectric energy harvester can be applied to establish a wireless self-sufficient intelligent vehicle wheel system.

Dispersive acoustic metamaterials (AMMs) with graded refractive index is promising in acoustic sensing enhancement by providing acoustic rainbow trapping (ART) effect. However, previous solutions to this type of AMMs are based on 2D unit cells that require infinite or very large size in the third dimension; they cannot integrate with conventional acoustic sensors without deteriorating the ability of acoustic wave manipulation. In order to advance their practical applications, this paper proposes an axisymmetric, microphone embedded AMM device with gradient profile as well as gradient plate thickness and gradient gap width along the axis. Both numerical simulations and experiments are performed to examine the ART effect of the proposed AMM device and demonstrate its excellent capacity of acoustic pressure amplification and multi-band acoustic filtering. Deploying a microphone in the gap does not disturb the acoustic field, so the proposed AMM sensor experimentally achieves remarkable acoustic gains over one order of magnitude. Sound waves of different frequencies are picked up by microphones at different gaps, realizing the real-time spatially splitting of the sound spectrum. The proposed AMM provides excellent immunity to broadband noise and a little weak suppression of the single tone noise while significantly amplifying acoustic signals of a given frequency.

This paper proposed a strategy of tracking pipe PIG utilizing Fiber Optic Distributed Vibration Sensor (FODVS) and YOLO object detection algorithm. Phase sensitive Optical Time Domain Reflectometer (φ-OTDR) is employed as the distributed sensor to collect the real field vibration signal generated as a result of the collision between leather bowl and weld joint. The space-time graphs of φ-OTDR are prepared to construct data sets to train a typical YOLOv3 net model. The trained model is proved to be able to accurately capture the invert-V signature in the space-time graph thus revealing the real time position of a PIG. This paper provides a concept-proof preliminary demonstration on the promising combination of FODVS and object detection scheme for pursuing better performance of events recogntion.

The capacitive micro-machined ultrasonic transducer (CMUT) has a good acoustic matching with air. In this paper, a 16-element CMUT array for airborne application is designed and fabricated by SOI wafer bonding process. All the CMUT cells have the same geometric parameters with circular and sealed membrane, which vibrate uniformly for good transmission efficiency. And the thin membrane with small mass is proposed to broaden the bandwidth of CMUT. The sensor array operates at a 215.6 kHz resonance frequency with a large -3dB fractional bandwidth of 15.7% and a good consistency. The selection of the driving parameters (i.e. the DC bias voltage and AC excitation signal) has been analyzed comprehensively, which can be used to optimize the driving strategy of the CMUT for better transmission and reception performance. The CMUT array proposed in this paper has been used to demonstrate a two-dimension non-contact air-coupled imaging by through-transmission mode and pitch-catch mode. The images of two kinds of objects have been reconstructed to exhibit the capability of the CMUT array in air-ultrasonic imaging, suggesting broad applications including 3D imaging, gesture recognition, and other human-machine interactions in air.

Piezoelectric energy harvesting is a promising way to develop self-sufficient systems. Structural design and parameter optimization are key issues to improve the performance in applications. This paper presents a magnetic coupled piezoelectric energy harvester to increase the output and bandwidth. A lumped parameter model considering the static position is established and various modes are simulated. This paper focuses on the “Low frequency repulsion mode”, which is more practical. The experiment platform is built with the Macro Fiber Composite (MFC) material, and the results are consistent with the analytical simulation. The optimization process of some key parameters, such as magnets spacing and flux density, is carried out. The results show that there is a corresponding optimal spacing for each flux density, which is positive correlated. With the optimized parameter design, the system achieves peak electrical power of 3.28 mW under the harmonic excitation of 4 m/s². Compared with the conventional single cantilever harvester, the operated bandwidth is increased by 66.7% and the peak output power is increased by 35.0% in experiment.