No abstract

No abstract

In this work, we numerically designed and then experimentally verified a metamaterial perfect absorber based on artificial dielectric "atoms". This metamaterial absorber is composed of dielectric ceramic material (SrTiO₃) "atoms" embedded in a background matrix on a metal plate. The dielectric "atoms" couple strongly to the incident electric and magnetic fields at the Mie resonance mode, leading to the narrow perfect absorption band with simulated and experimental absorptivities of 99% and 98.5% at 8.96 GHz, respectively. The designed metamaterial perfect absorber is polarization insensitive and can operate in wide angle incidence.

Lead zirconate titanate (PZT)‐based piezoelectric ceramics are important functional materials for various electromechanical applications, including sensors, actuators, and transducers. High piezoelectric coefficient and mechanical quality factor are essential for the resonant piezoelectric application. However, since these properties are often inversely proportional, simultaneously high performances are hard to achieve, consequently, a wide range of applications are strongly restricted. In the present study, exceptionally well‐balanced performances are achieved in PZT‐based ceramics via innovative defect engineering, which involves multi‐scale coordination among defect dipole, domain‐wall density, and grain boundary. These materials are superior to many state‐of‐the‐art commercial counterparts, which can potentially satisfy high‐end requirements for advanced electromechanical applications, such as energy harvesting, structural health monitoring, robotic sensors, and actuator.

No abstract

A tunable dual-band ferrite-based metamaterial has been investigated by experiments and simulations. The negative permeability is realized around the ferromagnetic resonance (FMR) frequency which can be influenced by the dimension of the ferrites. Due to having two negative permeability frequency regions around the two FMR frequencies, the metamaterials consisting of metallic wires and ferrite rods with different sizes possess two passbands in the transmission spectra. The microwave transmission properties of the ferrite-based metamaterials can be not only tuned by the applied magnetic field, but also adjusted by the dimension of the ferrite rods. A good agreement between experimental and simulated results is demonstrated, which confirms that the tunable dual-band ferrite-based metamaterials can be used for cloaks, antennas and absorbers.

Recently, all-dielectric metasurfaces (AMs) have emerged as a promising platform for high-efficiency devices ranging from the terahertz to optical ranges. However, active and fast tuning of their properties, such as amplitude, phase, and operating frequency, remains challenging. Here, a generic method is proposed for obtaining high-efficiency active AMs from the terahertz to optical ranges by using "hybrid structures" integrated with phase-change materials. Various phase-change mechanisms including metal−insulator phase change, nonvolatile phase change, and ferroelectric phase change are investigated. We first experimentally demonstrate several high-efficiency active AMs operating in the terahertz range based on hybrid structures composed of free-standing silicon microstructures covered with ultrathin phase-change nanofilms (thickness d ≪ λ). We show that both the frequencies and the strength of the Mie resonances can be efficiently tuned, resulting in unprecedented modulation depth. Furthermore, detailed analyses of available phase-change materials and their properties are provided to offer more options for active AMs. Finally, several feasible hybrid structures for active AMs in the optical range are proposed and confirmed numerically. The broad platform built in this work for active manipulation of waves from the terahertz to optical ranges may have numerous potential applications in optical devices including switches, modulators, and sensors.

Magnetoelectric (ME) Ni/PZT/TbFe2 and TbFe2/PZT composites with two semiring structures are prepared. The dependence between ME coupling and magnetostrictive property of the composite is discussed. Because Ni possesses negative magnetostrictive property and TbFe2 shows positive magnetostrictive property, the ME voltage coefficient of Ni/PZT/TbFe2 semiring structure is much larger than that of TbFe2/PZT. In these composites, the ME voltage coefficient increases and the resonance frequency gradually decreases with the increase of the semiring radius, showing that structural parameters are key factors to the composite properties. Due to the strong ME coupling effect, a giant ME voltage coefficient αE = 44.8 V cm−1 Oe−1 is obtained. This approach opens a way for the design of ME composites with giant ME voltage coefficient.