PZT对Ni-Zn铁氧体衰减电磁波能力的影响

研究了Ni-Zn铁氧体与锆钛酸铅PZT复合材料在1～1000MHz范围内对电磁波的衰减情况.结果表明,PZT由于具有铁电性与铁磁性共存特点,在1～1000MHz范围内有较好的吸波能力.在Ni-Zn铁氧体中添加PZT后可提高Ni-Zn铁氧体在100MHz以下频段对电磁波的衰减能力,在>100MHz频段后则降低对电磁波的哀减能力.     

多层复合材料屏蔽电磁波的理论模型

本文从基本的电磁波传播理论出发，考虑了电磁波在屏蔽层中的反射、衰减及多次反射，提出了多怪复合材料屏蔽效能的理论模型和计算公式。公式的应用简便，快捷，适用范围广，可用于不同入射方向的电磁波入射多层复合材料的屏蔽效能计算预测。最后对公式进行验证，计算结果与实验数据基本吻合。     

蜂窝铝-木基复合材料电磁波吸收特性研究

采用时域有限差分(FDTD)方法,对蜂窝铝-木基复合材料的电磁波吸收特性进行了研究。探讨了嵌入蜂窝铝的层数、蜂窝孔径、层间距以及周期尺寸等结构参数对复合材料电磁波吸收特性的影响。结果表明,在1~20 GHz频率范围内,蜂窝铝的嵌入可明显改善其电磁波吸收性能。嵌入的层数越多,复合材料对电磁波的吸收效能越好;在8 mm厚木材中嵌入5层具有单一孔径蜂窝铝时,复合材料的电磁波吸收效果最高可达70%。并且蜂窝孔径越小、层间距越大,复合材料的电磁波吸收性能越好。将具有不同孔径的蜂窝铝有序组合,可以进一步提高复合材料对电磁波的吸收率,最高可达到80%。     

蜂窝铝-木基复合材料电磁波吸收特性研究

采用时域有限差分(FDTD)方法,对蜂窝铝-木基复合材料的电磁波吸收特性进行了研究。探讨了嵌入蜂窝铝的层数、蜂窝孔径、层间距以及周期尺寸等结构参数对复合材料电磁波吸收特性的影响。结果表明,在1~20GHz频率范围内,蜂窝铝的嵌入可明显改善其电磁波吸收性能。嵌入的层数越多,复合材料对电磁波的吸收效能越好;在8mm厚木材中嵌入5层具有单一孔径蜂窝铝时,复合材料的电磁波吸收效果最高可达70%。并且蜂窝孔径越小、层间距越大,复合材料的电磁波吸收性能越好。将具有不同孔径的蜂窝铝有序组合,可以进一步提高复合材料对电磁波的吸收率,最高可达到80%。     

微波透射式振法对复合材料缺陷的检测

本文论据复合材料局部缺陷对电磁波的散射特性,介绍了复合材料内部缺陷的透射式偏振检测法的基本原理,系统设计思想及电路主要部件性能分析并给出了该检测系统对陶瓷材料,碳复合材料内部缺陷的检测结果。     

微波透射式偏振法对复合材料缺陷的检测

本文依据复合材料局部缺陷对电磁波的散射特性,介绍了复合材料内部缺陷检测的透射式偏振检测法的基本原理、系统设计思想及电路主要部件性能分析,并给出了该检测系统对陶瓷材料、碳复合材料内部缺陷的检测结果。     

复合材料的微波透射式偏振检测法的研究

本文依据复合材料局部缺陷对电磁波的散射特性 ,介绍了复合材料内部缺陷检测的透射式偏振检测法的基本原理、系统设计思想及电路主要部件性能分析 ,并给出了该检测系统对陶瓷材料 ,碳复合材料内部缺陷的检测结果。     

含Minkowski活性碳毡电路屏复合材料的吸波性能研究

研究了含Minkowski活性碳毡电路屏复合材料的微波吸收特性,并对电路屏的吸波机理进行了初步的探讨。结果表明,含Minkowski活性碳毡电路屏复合材料的吸波性能与电路屏阵列单元的尺寸密切相关,经合理设计,复合材料在5.3～18GHz频率范围内有-10dB以下的吸收,有效带宽达12.7GHz。复合材料对电磁波的主要吸收机制是电磁波在电路屏和反射板之间的多次反射、衰减。     

PZT／Ni－Zn铁氧体复合材料电磁特性研究

研究了铁电材料ＰＺＴ和铁磁材料Ｎｉ－Ｚｎ铁氧体的复合材料在１～１０００ＭＨｚ频率范围内的电磁特性。结果表明，ＰＺＴ具有铁电与铁磁共存的双重特性。当与Ｎｉ－Ｚｎ铁氧体复合后，其复合磁导率及复合介电常数均具有可调性，由此可优化设计高吸收电磁波能力的新型复合材料。     

PZT／Ni—Zn铁氧体复合材料电磁特性研究

研究了铁电材料ＰＺＴ和铁磁材料Ｎｉ－Ｚｎ铁氧体的复合材料在１￣１０００ＭＨｚ频率范围内的电磁特性。结果表明，ＰＺＴ具有铁电与铁磁共存的双重特性。当与Ｎｉ－Ｚｎ铁氧体复合后，其复合磁导率及复合介电常数均具有可调性，由此可优化设计高吸收电磁波能力的新型复合材料。     

超薄单向纤维增强复合材料低频多模式超声兰姆波定征方法

提出低频多模式超声兰姆波定征方法来估计超薄层状单向纤维增强复合材料的密度、厚度、弹性常数等参数。这里"超薄"的概念是指材料厚度h远小于材料中的声波波长λ,导致在时域上材料前后界面的各次回波信号相互混迭。分析了沿平行和垂直于纤维两个方向上,在超薄层状单向纤维增强复合材料中传播的低频兰姆波色散特性,提出在最小二乘意义下以材料色散曲线为基础的反向算法对材料参数进行了估计。文中分析了影响估计准确性的各种因素,研究了该方法对材料参数的灵敏度及其在误差传递中的意义。结合超声漏兰姆波频域分析方法,并使用超声耦合剂耦合方式和一对中心频率为2MHz的宽带纵波换能器,实验结果证实,该方法能够准确估计h<0.05 λ的单向玻璃纤维增强双酚A型聚砜(PSF)复合材料的材料参数。      

Fabrication of high sensitivity ZnO thin film ultrasonic devices byelectrochemical etch techniques

In this experiment, high quality thin film acoustic devices were constructed utilizing zinc oxide (ZnO) thin film deposition, integrated circuit (IC), and electrochemical etch techniques. The bridge type ZnO thin film ultrasonic devices produced showed acute high frequency response sensitivity, with the high frequency response at 600 KHz attaining -124 dBV μBar. The highest response was near 8 MHz. Sensitivity increased in direct proportion to frequency, indicating that the bridge-type ZnO thin film acoustic devices were suitable for application as ultrasonic wave sensors at high operating frequencies. Further experimentation verified that the bridge-type ZnO thin film acoustic devices fabricated also had ultrasonic signal transmitting capability and signal bidirectional devices having both transmission and reception functions were successfully constructed. Therefore, bridge-type ZnO thin film acoustic devices will continue to be developed in the future due to the reliable control possible over the structural transformations involved; and, since IC fabrication techniques can be readily adopted in the process, the manufacturing of such devices will be greatly assisted     

Dispersion and mirror transmission characteristics of bulk acoustic wave resonators

A heterodyne laser interferometer is used for a detailed study of the acoustic wave fields excited in a 932-MHz solidly mounted ZnO thin-film BAW resonator. The sample is manufactured on a glass substrate, which also allows direct measurement of the vibration fields from the bottom of the acoustic mirror. Vibration fields are measured both on top of the resonator and at the mirror-substrate interface in a frequency range of 350 to 1200 MHz. Plate wave dispersion diagrams are calculated from the experimental data in both cases and the transmission characteristics of the acoustic mirror are determined as a function of both frequency and lateral wave number. The experimental data are compared with 1-D and 2-D simulations to evaluate the validity of the modeling tools commonly used in mirror design. All the major features observed in the 1-D model are identified in the measured dispersion diagrams, and the mirror transmission characteristics predicted for the longitudinal waves, by both the 1-D and the 2-D models, match the measured values well.     

超声纵波换能器用于平测时的测距修正方法研究

研究了超声纵波换能器用于平测时的测距修正方法.首先,根据弹性波理论分析了利用平测布置代替对测布置测量波速时的实际物理意义;然后,分析了两种换能器布置方式的真实传播距离并通过设计混凝土试件切割-测量实验进行了两种布置方式的声时对比;最后,根据实验数据在对测回归直线方程的基础上提出了计算换能器平测布置修正测距的最小二乘法....     

Effect of r.f. sputtering parameters on ZnO films deposited onto GaAs substrates

In order to compensate the piezoelectrical property of GaAs-based material for monolithic integrated acousto-optic circuit applications, a ZnO film with a highly preferred orientation should be deposited. R.f. sputtering was employed to deposit ZnO films with various technological parameters. The optimal conditions to deposit high quality ZnO film onto GaAs-based substrates were deduced and investigated. Low loss surface acoustic wave devices fabricated on ZnO/GaAs wafers were obtained. The total insertion loss measured at a centre frequency of 25.37 MHz was 20 dB.     

手性吸波混凝土研制与展望

综述了混凝土吸波特性的研究现状,指出了传统吸波混凝土的局限,提出了手性吸波混凝土的研制方案,分析了其优点及难点.手性吸波混凝土在改善力学性能的同时改善了吸波性能.     

Deposition of ZnO thin films on SiO2/Si substrate with Al2O3 buffer layer by radio frequency magnetron sputtering for high frequency surface acoustic wave devices

ZnO films with c-axis (0002) orientation have been grown on SiO₂/Si substrates with an Al₂O₃ buffer layer by radio frequency magnetron sputtering. Crystalline structures of the films were investigated by X-ray diffraction, atomic force microscopy and scanning electron microscopy. The center frequency of the surface acoustic wave (SAW) device with a 4.8 μm thick Al₂O₃ buffer layer was measured to be about 408 MHz, which was much higher than that (265 MHz) of ZnO/SiO₂/Si structure and approaches that (435 MHz) of ZnO/sapphire. It is a possible way as an alternative for the sapphire substrate for the high frequency SAW device applications, and is also useful to integrate the semiconductor and high frequency SAW devices on the same Si substrate.     

混凝土中瞬时爆炸波测试技术及分离的实验研究

为稳定测量混凝土中炮孔周围的爆炸波,对应变片和超动态应变测试系统的频响及最优匹配开展了系统研究,得到了应变片相对误差δ与其允许最高频率fmax之间的关系,测试系统的阶跃信号响应上升时间为0.3μs。基于一维应力波原理,提出了用SHPB技术中透射杆上的应力动态标定试件上输出电压的新方法,得到了爆炸冲击波作用下测试系统的频响和时频分布。针对爆炸波微信号传输中的易受干扰问题,采用了电磁屏蔽等抗干扰技术。用该系统对混凝土模型开展了不耦合装药爆炸波测试,成功测得了23μs内在爆炸近中区激起的爆炸波。通过Rihaczek分布,将爆炸波分离为[(2.3～4.5μs),(0～829 kHz)]的爆炸冲击波区、[(4.5～7.2μs),(0～743 kHz)]的应力波区及[(7.2～24.7μs),(0～514 kHz)]的爆生气体膨胀作用区,并就分离各区作用过程做了分析。     

平面爆炸波在半无限混凝土介质中传播与衰减特性的数值分析

采用非线性软件LS-DYNA,混凝土选用JHC模型的基础上,数值模拟了一维应变下爆炸波在半无限混凝土介质中的传播过程,得到了平面爆炸波在混凝土中随时间和空间的衰减规律,以及在爆炸冲击波作用下,脆性介质混凝土形成破碎区和损伤区的演化特性。数值拟合结果表明,在爆炸近区应力波幅值衰减速率快,材料损伤演化和应力波幅值衰减存在着内在的联系。模拟结果对于爆破与防护工程设计均具有一定的参考价值。     

Surface micromachined capacitive ultrasonic transducers

The current state of novel technology, surface microfabricated ultrasonic transducers, is reported. Experiments demonstrating both air and water transmission are presented. Air-coupled longitudinal wave transmission through aluminum is demonstrated, implying a 110 dB dynamic range for transducers at 2.3 MHz in air. Water transmission experiments from 1 to 20 MHz are performed, with a measured 60 dB SNR at 3 MHz. A theoretical model is proposed that agrees well with observed transducer behavior. Most significantly, the model is used to demonstrate that microfabricated ultrasonic transducers constitute an attractive alternative to piezoelectric transducers in many applications.