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.

SUMMARY: A 2D path following control method for Autonomous Underwater Vehicles (AUVs) based on dynamic circle heading modification (DCHM) is presented. The method makes a dynamic auxiliary circle, whose radius depends on the cross-track error e, to intersect the desired path to get a new expected path point, and then determines a modified expected heading for the AUV. The guidance function is achieved by a direct mapping between e and the heading modification value Ψ_m. Several cases are tested in order to demonstrate the performance of the guidance and control method based on DCHMs for a real AUV. Results show that methods using a convex mapping function between e and Ψ_m based on our new idea can easily achieve a better convergence of path following, and reduce the error between the actual and desired heading angles. We can also customize a discretionary mapping between e and Ψ_m to get better path following performance.

Accurate location of subsea pipelines is a prerequisite for real-time tracking and detailed inspections by underwater robots. The magnetic anomalies generated by ferromagnetic pipelines can be used to locate both exposed and buried pipelines. However, due to the low signal ratio and model inconsistencies under weak and variable ambient magnetization, there is currently no intuitive and reliable pipeline detection method for pipeline tracking. This paper proposes a method capable of immediately and accurately locating pipelines via active magnetization and vertical magnetic measurements. Finite element simulations show that a magnet array can significantly enhance the magnetic anomaly, and that the vertical magnetic component alone can accurately indicate the pipeline’s position, avoiding the inconvenience of magnetic three-component alignment in the field. It is experimentally demonstrated that the magnetic detection signal-to-noise ratio can be significantly increased by 5 dB–20 dB for a Φ219 mm steel pipe using the magnet array, and the maximum lateral positioning error is 0.03 m and much smaller than that without the magnet array.

Underwater acoustic ranging and detection usually require hydrophones to have high sensitivity at narrowband operating frequencies. Different from traditional sensitization methods with the help of new materials and solid/liquid resonance structure, this paper proposes a low-cost, high-sensitivity hydrophone based on a resonant air cavity containing an affordable MEMS microphone inside to sense the focused acoustic waves transmitted from the external water across the solid shell into the air cavity. Both finite element simulations and experiments are carried out to test its acoustic sensing performances. Resonance frequency and directivity of the proposed hydrophone are determined by the air cavity size and the acoustic mode, but is independent of the solid shell, which facilitates the precise designability. The sensitivity of the developed hydrophone at the resonance frequency is up to -157 dB re 1V/μPa calibrated by commercial standard hydrophone TC4013. Finally, several further considerations, improvements and applications on the proposed hydrophone are discussed.