Phononic crystal with free-form waveguiding and broadband attenuation

Waveguiding is highly desirable for multiple applications but is challenging to achieve in wide continuous frequency ranges. In this work, we developed a three-dimensional phononic crystal with broadband waveguiding functionality. Waveguiding is achieved by combining two types of unit cells with different wave scattering features to create an arbitrary-curved defect path. The unit cell design is governed by contradictory requirements to induce narrow- and broad-band wave attenuation along the path and within the phononic medium, respectively. This is achieved by modulating structural parameters to activate Bragg's scattering, local resonances and inertial amplification mechanism and interplay between them. We demonstrated numerically and experimentally the waveguiding with strong wave localization and confinement in additively manufactured three-dimensional structures along straight, angle- and arbitrary-curved paths. This work opens new perspectives for the practical utilization of phononic crystals in ultrasonic sensors, medical devices, and acoustic energy harvesters

Dissipative Dynamics of Polymer Phononic Materials

Phononic materials are artificial composites with unprecedented abilities to control acoustic waves in solids. Their performance is mainly governed by their architecture, determining frequency ranges in which wave propagation is inhibited. However, the dynamics of phononic materials also depends on the mechanical and material properties of their constituents. In the case of viscoelastic constituents, such as most polymers, it is challenging to correctly predict the actual dynamic behavior of real phononic structures. Existing studies on this topic either lack experimental evidence or are limited to specific materials and architectures in restricted frequency ranges. A general framework is developed and employed to characterize the dynamics of polymer phononic materials with different architectures made of both thermoset and thermoplastic polymers, presenting qualitatively different viscoelastic behaviors. Through a comparison of experimental results with numerical predictions, the reliability of commonly used elastic and viscoelastic material models is evaluated in broad frequency ranges. Correlations between viscous effects and the two main band-gap formation mechanisms in phononic materials are revealed, and experimentally verified guidelines on how to correctly predict their dissipative response are proposed in a computationally efficient way. Overall, this work provides comprehensive guidelines for the extension of phononics modeling to applications involving dissipative viscoelastic materials.</p

Ammonia sensing properties of ZnO nanoparticles on flexible substrate

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Lead-free KNN-based thin films obtained by pulsed laser deposition

In this work, 0.96(K0.48Na0.52)0.95Li0.05Nb0.94Sb0.06O3−0.04Ba0.94Ca0.06ZrO3 (KNLNS-BCZ) and 0. 9S(K0.48Na0.52)0.95Li0.05Nb0.95Sb0.05O3−0.02Ba0.5(Bi0.5Na0.5)0.5ZrO3 (KNLNS-BBNZ) ferroelectric thin films were obtained by pulsed laser deposition. The structural, and morphological characteristics were studied to determine the best deposition parameters and analyse the piezoelectric properties. The studied deposition parameters were temperature, laser fluence, oxygen partial pressure and frequency. These parameters impact important characteristics of the thin films like grain morphology, thickness, and roughness. KNLNS-BCZ thin films with pure perovskite structure, homogeneous grain growth, and thickness ≥100 nm were fabricated at 700∘C,2J/cm2,300 mTorr, and frequencies of 5 Hz and 10 Hz. These films presented good ferroelectric behaviour and piezoelectric coefficient d 33eff of 83.80 pm/V and 25.80 pm/V, respectively

Lead-free KNN-based thin films obtained by pulsed laser deposition

In this work, 0.96(K0.48Na0.52)0.95Li0.05Nb0.94Sb0.06O3−0.04Ba0.94Ca0.06ZrO3 (KNLNS-BCZ) and 0. 9S(K0.48Na0.52)0.95Li0.05Nb0.95Sb0.05O3−0.02Ba0.5(Bi0.5Na0.5)0.5ZrO3 (KNLNS-BBNZ) ferroelectric thin films were obtained by pulsed laser deposition. The structural, and morphological characteristics were studied to determine the best deposition parameters and analyse the piezoelectric properties. The studied deposition parameters were temperature, laser fluence, oxygen partial pressure and frequency. These parameters impact important characteristics of the thin films like grain morphology, thickness, and roughness. KNLNS-BCZ thin films with pure perovskite structure, homogeneous grain growth, and thickness ≥100 nm were fabricated at 700∘C,2J/cm2,300 mTorr, and frequencies of 5 Hz and 10 Hz. These films presented good ferroelectric behaviour and piezoelectric coefficient d 33eff of 83.80 pm/V and 25.80 pm/V, respectively