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Abstract Collection and conversion of widespread mechanical energy is one promising way to alleviate environmental pollution and energy crisis. Piezoelectric materials can effectively realise this conversion between mechanical and electrical energies. Here, via near‐field electrospinning, piezoelectric poly(vinylidene fluoride) microfibers were fabricated on flexible polyethylene terephthalate substrate. Bending measurement indicated that open‐circuit voltage response from piezoelectric microfibers was strain dependent but insensitive to bending frequency. The microfiber sensor could detect acoustic signals with sound pressure level between 70 and 120 dB and the recorded acoustic frequency was well consistent with the nominal frequency. Light wind from a low‐power hand fan was also detected by this microfiber sensor. This simply structured and highly flexible piezoelectric microfiber sensor provided a promising and low‐cost fabrication measure for weak mechanical excitation sensing.

In order to analyze the effect of the background flow on the sound prediction of fine-scale turbulence noise, the sound spectra from static and flow environments are compared. It turns out that, the two methods can obtain similar predictions not only at 90 deg to the jet axis but also at mid- and high frequencies in other directions. The discrepancies of predictions from the two environments show that the effect of the jet flow on the sound propagation is related to low frequencies in the downstream and upstream directions. It is noted that there is an obvious advantage of computational efficiency for calculating in static environment, compared with that in flow environment. A good agreement is also observed to some extent between the predictions in static environment and measurements of subsonic to supersonic. It is believed that the predictions in static environment could be an effective method to study the propagation of the sound in jet flow and to predict the fine scale turbulence noise accurately in a way as well. [ABSTRACT FROM AUTHOR]

When sound barriers are installed on both sides of a noise source, degradation in performance is observed. Barriers having negative-phase-gradient surfaces successfully eliminate this drawback by trapping sound energy in between the barriers. In contrast, barriers can also be designed to “dredge” the energy flux out. An extended model considering higher-order diffractions, which resulted from the interplay of the induced surface wave and barrier surface periodicity, is presented. It is found that the sound dredging barriers provide a remarkable enhancement over the trapping ones, and hence have the potential to be widely used in noise control engineering. [ABSTRACT FROM AUTHOR]

The screening effect of a roadside balcony deteriorates considerably due to sound reflection from its ceiling. Nonetheless, this drawback can be eliminated by artificially steering the reflected sound away from the building facade, which is achieved by introducing impedance inhomogeneity to the ceiling surface. This paper presents an elaborated investigation on the effect of the phase gradient of a ceiling surface on screening exterior noise, theoretically and numerically. By balancing its sound-steering capability and performance fluctuation level, such a balcony ceiling may have the potential to be widely used on roadside buildings. [ABSTRACT FROM AUTHOR]

this paper, inhomogeneous boundaries having constant phase gradient are investigated. In principle, such a theoretically proposed boundary is dispersionless. In practice, however, when the boundary is realized by a subwavelength-structured tubes array, the impedance discretization brings about sub-reflections at high frequencies. Moreover, determined by the longest duct in the array, a realized boundary is impractically thick. Therefore, a finite-thickness boundary is further proposed by truncating and periodizing the tubes in the array. In this paper, the theoretical analysis agrees well with the numerical simulations. By appropriately choosing its phase gradient and target frequency, the finitethickness boundaries have potential applications in noise control. [ABSTRACT FROM AUTHOR]

When barriers are placed in parallel on opposite sides of a source, their performance deteriorates markedly. However, barriers made from materials of inhomogeneous impedance eliminate this drawback by altering the behavior of sound as it undergoes multiple reflections between the barriers. In this paper, a theoretical approach is carried out to estimate the performance of the proposed barriers. By combining the ray-tracing method and sound diffraction theory, the existence of different ray paths between the proposed barriers is revealed. Compared to conventional rigid-walled barriers, barriers having inhomogeneous surfaces may have the potential to be widely used in environmental noise control. [ABSTRACT FROM AUTHOR]

Sound barriers are extensively used in environmental noise protection. However, when barriers are placed in parallel on opposite sides of a sound source, their performance deteriorates markedly. This paper describes a barrier made from materials of inhomogeneous impedance which lacks this drawback. The nonuniform impedance affects the way sound undergoes multiple reflections, and in the process traps acoustic energy. A proposed realization of the barrier comprises a closely spaced array of progressively tuned hollow narrow tubes which create a phase gradient. The acoustics of the barrier is theoretically examined and its superiority over conventional barriers is calculated using finite element modeling. Structural parameters of the barrier can be changed to achieve the required sound insertion loss, and the barrier has the potential to be widely used in environmental noise control. [ABSTRACT FROM AUTHOR]