基于球壳内壁反射的球形换能器自易校准方法

基于球形换能器发射的脉冲球面声波及其在同心球壳内壁的反射,应用机电互易定理,导出了在球面波发射回波声场中,用于校准球形换能器的互易常数。以此为基础,提出一种使用封闭球壳反射器的自易校准方法,通过一次测量即可得到球形换能器的5个基本电声参数。进一步,将自易法校准所得的电压灵敏度换算成平面波声场中定义的标准灵敏度,给出了换算系数。为确定该换算系数,发展了对换能器散射系数进行测量的方法。在25~63 kHz频率范围内,对半径10 mm的球形换能器实施了自易校准。结果表明,测得的电压灵敏度的标准不确定度估计优于0.9 dB。      

合成近场校准基阵的方法研究

本文利用单根的束控线阵来构造一个虚拟近场校准基阵,使换能器能在它的近场直接测量辐射声场特性。通过利用改进的矩阵稳定技术,解决了求解束控线阵的束控系数时最小二乘解的稳定性和实用性问题。借助计算机仿真,研究了特定线阵条件下,合成近场测量基阵（Ｓ－ＮＦＣＡ）的近场空间的平面波均匀性与线阵间的间距、线阵的工作频率之间的关系。并以小球源为阵元合成一虚拟平面ＮＦＣＡ,用它对一平面喇叭换能器的近场测量得到远场指向性,并与远场实测结果比较,得到了相当吻合的结果。     

基于电谐振单元的超介质吸波材料及矩形波导匹配终端应用研究

针对在自由空间中测试超介质吸波材料的高复杂性及高成本特点, 实验研究了4种由电谐振单元构成的超介质吸波材料在X波段(8–12 GHz)矩形波导里的吸波性能. 实验结果表明, 此4种吸波材料在终端短路的矩形波导里显示出与其在自由空间中相似的吸波性能及吸波机理.据此, 进一步研究了基于超介质吸波材料的矩形波导匹配终端应用. 分析结果显示, 此种新型匹配终端具有结构紧凑、工作频段可简单控制、成本低等优点. 通过展宽超介质吸波材料的吸波频段可设计出宽频带的矩形波导匹配终端. 关键词： 电谐振单元 超介质 吸波材料 匹配终端     

Tunable broadband metamaterial absorber consisting of ferrite slabs and a copper wire

A tunable broadband metamaterial absorber is demonstrated at microwave frequencies in this paper.The metamaterial absorber is composed of ferrite slabs with large resonance beamwidths and a copper wire.The theoretical analysis for the effective media parameters is presented to show the mechanism for achieving the perfect absorptivity characteristic.The numerical results of transmission,reflectance,and absorptivity indicate that the metamaterial absorber exhibits a near perfect impedance-match to free space and a high absorptivity of 98.2% for one layer and 99.97% for two layers at 9.9 GHz.The bandwidth with the absorptivity above 90% is about 2.3 GHz.Moreover,the absorption band can be shifted linearly in a wide frequency range by adjusting the magnetic bias.This metamaterial absorber opens a way to prepare perfectly matched layers for engineering applications.     

Metamaterial absorbers realized in an X-band rectangular waveguide

In this paper,we demonstrate six types of metamaterial absorbers(MMAs) by measuring their absorptivities in an X-band(8-12 GHz) rectangular waveguide.Some of the MMAs have been demonstrated previously by using the free space measurement method,and the others are proposed firstly in this paper.The measured results show that all of the six MMAs exhibit high absorptivities above 98%,which have similar absorbing characteristics to those measured in the free space.The numerically obtained surface current densities for each MMA show that the absorbing mechanism is the same as that under the free space conditions.Such a demonstration method is superior to the conventional free space measurement method due to the small-scale test samples required,the simple measure device,and its low cost.Most importantly,the proposed method opens a way to enable MMAs to be used in microwave applications such as matched terminations.     

使用激光测振技术校准水听器灵敏度

介绍了我们利用激光测振技术在 １０～ ２００ ｋＨz频段建立的一套校准水听器灵敏度的测试装置。在该套装置中,通过激光测振仪直接测量声波作用下水介质的质点振速并导出相应的声压量值,然后利用该声压量进行待测水听器灵敏度的校准。由于不存在换能器非线性和非互易性等因素的影响,整套装置的测量不确定度减小到 ０．５ ｄＢ左右,同时该方法还具有操作方便的特点。     

负折射率介质测试装置设计与测试

为深人了解负折射率媒质的奇异传输特性,基于斯涅耳折射原理,设计并加工了一种用于测试X波段((8.2-12.4GHz),以亚铁磁材料为基体,内嵌金属线阵列宏结构的负折射率介质样品折射特性的实验装置.分别测试了楔形石蜡样品和楔形负折射率介质样品在波段的折射特性,对石蜡样品测试结果的分析证明了该折射特性测试装置的有效性,对负...     

电磁超材料中负磁导率对负介电常数的影响

为深入了解电磁超材料中物质间相互作用关系,理论分析了金属导体线阵列宏结构嵌入单负磁导率媒质中时其等效介电常数的变化特性。数值计算和电磁仿真方法相结合,讨论了单负磁导率媒质和单负介电常数媒质的相互作用关系,提出了减小其相互作用的解决方法。仿真结果显示:将金属线阵列直接嵌入到单负磁导率媒质中时,电磁超材料传输特性在整个频段内为传输禁带;将金属线裹附一层绝缘材料后,传输禁带变为传输通带,这表明金属线阵列和单负磁导率媒质之间必须加入一种绝缘材料才能合成双负的电磁超材料。