Microwave Absorbing and Energy Storage Materials

Dear Colleagues,

Innovations in tunable microwave elements and energy storage devices often arise from research advances in material chemistry, composite synthesis, and multilayer films that enable new material properties and device functionalities. This Special Issue will include two important types of materials: nonlinear dielectrics and multiferroics.

Nonlinear dielectrics have several characteristics, including high dielectric tunability, large polarizability, and control of phase transitions, which make them unique and of great interest in microwave and capacitor applications. For example, when compared with other devices for energy storage, such as batteries, fuel cells and electrochemical supercapacitors, dielectric capacitors excel in specific power, compactness and cost-effectiveness. As the demand increases for dielectric devices to be made more durable and efficient under high dc-voltage and temperature stress, it becomes crucial to resolve mechanisms of electrical degradation, which lead to increases in leakage current and ultimate breakdown. The mechanisms are usually multifaceted, including both electronic and ionic processes, and involving defects in the bulk phase and at the dielectric interfaces. Many other issues are also important in the field of nonlinear dielectrics, such as (1) new ceramics to improve their energy efficiencies and dielectric strengths while at the same time maintaining their large dielectric constants, (2) ferroelectric films with special domain architectures to delay the polarization saturation, and (3) substrate effects to control the strain field distribution and therefore domain interactions.

Multiferroic composite materials have led to many novel microwave devices, including tunable resonator, phase shifters, and tunable filters, etc. However, it has been challenging in achieving strong magnetoelectric (ME) coupling at microwave frequencies, which is mainly due to the large loss tangent at microwave frequencies from the two constituent phases. Layered composite heterostructures with a magnetic film provide great opportunities for achieving strong ME coupling at microwave frequencies due to minimized charge leakage, large permeability, high self-biased ferromagnetic resonance frequencies and low loss tangents at microwave frequencies associated with magnetic thin films. Most recently, there are many great developments along this direction of research. The field is rapidly advancing into new areas of technologies and discovery.

It is my pleasure to invite you to submit a manuscript for this Special Issue. Full papers, communications, and reviews are all welcome.

Prof. Yuhang Ren
Guest Editor

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