The method for tuning the first phononic band gaps (PGBs) of locally resonant pentamode metamaterials (PMs) is proposed in this paper. Based on the equivalent relationship between the locally resonant mode at the lower edge of the first PBGs and spring-mass system, the approximate relationships between the lower edge of the first PBGs and structure parameters are obtained. The theoretical and numerical results show that the first phononic band gaps of PMs can be tailored between 52 Hz and 548 Hz by a small-sized PMs. In addition, the single mode PBGs of PMs can be expanded by 6.5 times, and the pentamodal characteristics can be improved by 13.7 times.
Single-crystal quartz material is widely applied in the manufacture of resonators and sensors, but it is difficult to process because of its high hardness. A novel way to fabricate single-crystal quartz structures is proposed in this paper; the method includes quartz-on-silicon (QoS) technology and inductively coupled plasma (ICP) etching, which makes it feasible to fabricate complex structures with crystal quartz. The QoS method encompasses the bonding of silicon and quartz, followed by the thinning and polishing of quartz, which can enable the fabrication of an ultra-thin quartz wafer on silicon. In this way, instead of the conventional wet etching with hydrofluoric acid, the quartz layer can be easily etched using the ICP dry-etching method. Then, the structure of the pure quartz material is obtained by removing the silicon wafer. In addition, the silicon layer can be processed into the appropriate structure. This aspect overcomes the difficulty of processing a complex structure of single-crystal quartz with different crystal orientations. Thin single-crystal quartz wafers of Z-cut with a thickness of less than 40 μm were obtained by using this method, and a complex three-dimensional structure with an 80 μm width was also acquired by the ICP etching of the quartz wafer. The method can be applied to make both crystal-oriented quartz-based sensors and actuators, such as quartz resonant accelerometers.
A terahertz spoof surface plasmonic polaritons waveguide with metallic rectangular spiral is proposed in the paper. By analyzing dispersion relation and electric field distribution, it is found that proposed waveguide has lower asymptotic frequency, tighter localized filed with 11.7 times enhancement and more compact size compared with T-grooves waveguide. Based on rectangular-spiral waveguide structure, compact and very-sharp roll-off lowpass filter is investigated and experimentally verified by scaling down frequency to microwave region. The fabricated lowpass filter has high roll-off rate of 566 dB/GHz, ultrahigh figure-of-merit of 43039, and compact size. Therefore, it may be applicable for various compact integrated devices and circuits in THz and microwave frequency ranges.
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