基于Leach模型的空气耦合超声换能器声阻抗匹配特性研究

压电陶瓷与空气之间的声阻抗差异巨大，导致声波在固-气介质间的能量传输效率低，研究匹配层特性对提升换能器能量传输效率具有重要意义。文章通过Leach模型仿真，研究了空气耦合超声换能器阻抗与瞬态响应，并搭建实验平台进行测试验证。仿真和实验结果表明，增加一层匹配层可将接收信号幅值增大约280%,增加两层匹配层可将接收信号幅值增大约363%。通过采用经声阻抗匹配后的换能器对碳纤维板缺陷进行检测，能明显检测出深度为0.5 mm、直径为1 mm凹槽缺陷的变化，验证了通过等效电路模型研究换能器匹配特性方法的有效性。     

Ultraviolet photoionization in TEA lasers

Measurements of UV photoionization parameters for TEA CO2gas lasers are presented. Electron density and ionization decay times are given as a function of pressure for several gases and gas mixtures. Penetration depth of ionizing radiation in the gases is determined. The effect of selected additives on photoionization is demonstrated. The results show that a significant enhancement in electron density can be achieved. TheX-band microwave interferometer data provide additional insight into the mechanisms involved and further substantiate the effectiveness of the technique in high-powered CO2laser design.     

压电超声无线能量传输通道阻抗特性研究

基于压电晶体沿厚度方向振动的数学模型,用等效电路法分析得到表面镀银的某型压电超声换能器的谐振频率和反谐振频率,与实测结果相符。在考虑耦合层影响条件下,建立了由外部压电换能器-金属壁-内部压电换能器所构成超声无线能量传输通道的等效电路模型,并仿真得到了通道的阻抗特性,与高精度阻抗分析仪实际测得的阻抗进行比较,验证了所建模型的准确性。     

Excitation of an Infinite Microstrip Line With a Vertical Coaxial Feed

An efficient method is presented for the analysis of a vertical coaxial probe excitation of an infinite microstrip line. The novel feature of the method is that it uses a semianalytical Green's function that is derived for current sources in the presence of the infinite microstrip line. Hence, in a method of moments approach, unknown currents need only be placed on the conducting probe feed and not on the infinite strip surface. The method also utilizes an attachment mode at the contact point between the probe and line so that the correct Kirchhoff condition is automatically satisfied. Once the surface current density on the probe is known, the surface current density on the strip conductor can be readily obtained using the Green's function of the background grounded substrate. The method is valid even at high frequency, where simple transmission line theory fails to account for effects such as the continuous-spectrum current that is excited on the line. After validating the method with various commercial software simulation packages, results are presented to study the fundamental behavior of the input impedance, probe current, and current launched on the microstrip line, and to examine the high-frequency behavior of these currents.      

Exact Theory of Interdigital Band-Pass Filters and Related Coupled Band-Pass Structures

An exact theory of interdigital line networks and related coupled structures is presented. The theory of parallel-coupled line arrays is reviewed briefly, and the derivation of exact equivalent circuits from the impedance matrix using modem network synthesis techniques is discussed. A simplified theory of equivalent coupled structures is introduced in order to avoid the lengthy analysis required when using the impedance matrix approach. Equivalent networks for the interdigital line are obtained by inspection, using a transformed capacitance matrix associated with the two-dimensional geometry of the conductors and ground planes. The techniques presented are simple to apply and allow a given transmission response to be obtained in a variety of line configurations. A practical design example and experimental results are given to illustrate the simplicity of the approach, along with general criteria for the design of practical filter networks with optimum transmission characteristics. The paper is directed toward the design of interdigital band-pass filters; however, the techniques presented can be used to analyze and design a much broader class of microwave networks. The relationship of the exact theory to existing approximate theory is discussed.     

Finite-difference time-domain implementation of surface impedanceboundary conditions

Surface impedance boundary conditions can be utilized to avoid using small cells, made necessary by shorter wavelengths in conducting media throughout the solution volume. The standard approach is to approximate the surface impedance over a very small bandwidth by its value at the center frequency, and then use that result in the boundary condition. In this paper, two implementations of the surface impedance boundary condition are presented. One implementation is a constant surface impedance boundary condition and the other is a dispersive surface impedance boundary condition that is applicable over a very large frequency bandwidth and over a large range of conductivities. Frequency domain results are presented in one dimension for two conductivity values and are compared with exact results. Scattering width results from an infinite square cylinder are presented as a two dimensional demonstration     

Experiences with the impedance probe on satellites

A system is presented for measuring the impedance of a dipole antenna on a satellite orbiting in the ionosphere. These impedance variations are used to determine the electron density of the ionosphere. Details of the instrumentation are given. Experimental results from many satellite flights are given in the form of antenna impedance to aid in antenna engineering. Electron density profiles are also presented. The density data show interesting spatial and temporal variations. Discussion is made of the electron density in the vehicle wake.     

Accurate time synchronization of ultrasonic TOF measurements in IEEE 802.15.4 based wireless sensor networks

This paper discusses the problem of accurate time synchronization of wireless sensor networks (WSNs) used in applications in which a physical phenomenon must be monitored through periodical sampling. In some applications incorrect time synchronization can significantly degrade the system precision. This is for example the case of local positioning systems (LPSs) using ultrasonic time of flight (TOF) measurements for pseudorange estimation. The nodes clock drifts and the random variations of the start time used in each measurement are the two main error sources. In this work a Time Division Multiple Access (TDMA) synchronization algorithm is presented to overcome these problems for WSN using the IEEE 802.15.4 standard. The algorithm is able to compensate for the mentioned error sources in an easy and effective way. Experimental results for an implementation of an ultrasonic pseudorange measurement system between wireless nodes show the effectiveness of the proposed algorithm.     

CCC Ⅱ模拟电感的非理想特性分析及应用

提出了利用理想第二代电流控制传输器(CCC II)模拟电感特性的结构。分析了基于CCC II模拟电感的理想电感效应有效范围、主要寄生电容电阻的影响及其补偿方法,给出了模拟电感特性仿真结果。在此基础上,对5阶巴特沃斯(Butterworth)高通滤波器进行综合。电路具有结构简单、集成度高,截止频率连续可调等优点。仿真结果证明了设计的正确性。     

计算多层印刷传输线色散特性的一种简单方法

本文给出计算多层印刷传输线色散特性的一种简单方法，本方法利用ＴＥ波及ＴＭ波的平面结构谱域等效电路，导出二维谱域并矢格林函数，再利用格林函数由积分方程的解给出传输常数，进而求得特性阻抗表示式。用本文方法所得到的数值结果和更复杂的方法所得到的结果非常一致。     

The synthesis of patterns using a series-fed array of annularsector radiating line (ANSERLIN) elements: Low-profile, circularlypolarized radiators

A series-fed, circularly polarized array of annular sector radiating-line elements that operates over a ground plane and has a low profile is presented. Pattern shaping can be achieved through control of the fraction of the incident power that is radiated by each element. This can be accomplished over a wide range by a simple adjustment in the geometry of each element. A synthesis technique is given, and experimental results are presented. The array is demonstrated to have a high return loss (good impedance match) and a low axial ratio     

The estimation of the gradient of a density function, with applications in pattern recognition

Nonparametric density gradient estimation using a generalized kernel approach is investigated. Conditions on the kernel functions are derived to guarantee asymptotic unbiasedness, consistency, and uniform consistency of the estimates. The results are generalized to obtain a simple mcan-shift estimate that can be extended in ak-nearest-neighbor approach. Applications of gradient estimation to pattern recognition are presented using clustering and intrinsic dimensionality problems, with the ultimate goal of providing further understanding of these problems in terms of density gradients.     

多向复合超声换能器有限元分析与试验

超声换能器是微电子封装技术的核心执行元件,为解决传统一维纵振超声换能器键合效率低、键合面不均匀及键合点不牢靠等问题,采用ANSYS仿真软件建立换能器有限元模型进行模态分析及谐响应分析,设计了一种可同时实现轴向纵振、水平弯振及竖直俯仰振动的40 kHz多向复合夹心压电式超声换能器。其中,压电部分由整圆环和可单独激励的1/4圆环陶瓷片组成。利用阻抗分析仪实物测试,得到换能器纵振、弯振及俯仰振动的阻抗 频率特性曲线。结果表明,测试值与仿真值基本一致,且结构性能参数均符合键合要求,验证了该结构的合理性。     

Bandwidth enhancement of inset-microstrip-line-fedequilateral-triangular microstrip antenna

By embedding a pair of properly-bent narrow slots in an equilateral-triangular microstrip patch, broadband operation of microstrip antennas with an inset microstrip-line feed can be achieved. With the proposed antenna design, the impedance bandwidth can be as large as ~3.0 times that of a corresponding simple triangular microstrip antenna. Some simple design rules for the proposed antenna have also been determined experimentally. The design rules and experimental results are presented and discussed     

测量大功率LDMOS晶体管特性的TRL校准方法研究

The impedance and output power measurements of LDMOS transistors are always a problem due to their low impedance and lead widths.An improved thru-reflect-line(TRL) calibration algorithm for measuring the characteristics of L-band high power LDMOS transistors is presented.According to the TRL algorithm,the individual two-port S parameters of each fixture half can be obtained.By de-embedding these S parameters of the test fixture,an accurate calibration can be made.The improved TRL calibration algorithm is successfully utilized to measure the characteristics of an L-band LDMOS transistor with a 90 mm gate width.The impedance of the transistor is obtained,and output power at 1 dB compression point can reach as much as 109.4 W at 1.2 GHz, achieving 1.2 W/mm power density.From the results,it is seen that the presented TRL calibration algorithm works well.     

小型加载短路针微带天线的宽频带特性研究

提出了一种直径较大的加载短路针、低介电常数,厚介质衬底、同轴探针馈电微带天线.对直径较大的同轴探针抵消因其长度引入的电感的原理进行分析;从腔模理论出发,结合叠加原理,提出一种较为简单的分析直径较大同轴探针馈电的加载短路针天线输入阻抗的方法,在宽频带内实现阻抗匹配,达到展宽频带的目的;并给出加载短路针圆形天线的实例,用HFSS仿真的结果与实测结果进行比较,证实了该方法的有效性.     

Microwave modeling of 2-D active grid antenna arrays

A new measurement technique for determining the broadband driving point impedance of large two-dimensional active grid arrays is presented. The active array radiates a plane wave in the broadside direction when all elements are locked in phase. For analysis, the array is reduced to a single unit cell by exploiting the array symmetries. The driving point impedance of the unit cell is determined by using the dielectric waveguide measurement method (DWM). The approximations of the method are discussed, and the method is compared with other measurement techniques. Results are presented for four square arrays: dipole, bow-tie, double-vee and slot array. The measurement method is verified by comparing it to the full-wave theory in the whole range. It is shown that all four antenna arrays can be represented by very simple circuits that use only transmission lines as circuit elements. The bow-tie array is found to represent the best choice for broadband operation     

折叠偶极子天线的设计

射频识别(RFID)应用中的天线设计需考虑的最重要因素是低价位、小剖面和小型化,而为了最大功率传输,天线的输出阻抗必须和其后的芯片的输入阻抗匹配。本文介绍一种新颖的简单结构折叠偶极子天线,所需的输入阻抗能通过选择合适的几何参数轻易获得,这对设计特殊阻抗的天线非常有用。     

An annular-ring microstrip antenna fed by a co-planar feed circuitfor mobile satellite communication use

A new configuration of circularly polarized annular-ring microstrip antenna (ARMSA) fed by a branch-line hybrid coupler placed at the inner part of the ARMSA and its design method using an equivalent circuit are presented. Since the ARMSA has a narrow bandwidth and high-input impedance, a parasitic element placed above the ARMSA is employed for not only obtaining a broadband characteristic, but decreasing the input impedance down to 50 Ω. A hybrid coupler to generate circular polarization, therefore, can be connected to the co-planar space of the ARMSA directly without a large-size matching circuit and a very low profile and simple structure can be achieved. The ARMSA is excited at the TM₂₁ mode to produce a conical pattern, which has a high gain in a low-elevation angle for mobile satellite communications. An effective design method using the equivalent circuit is indicated and, as a result, it is obvious that a broadband characteristic is obtained when each resonant frequency of the ARMSA and parasitic element is identical. Experimental results in the L-band showed satisfactory characteristics for vehicle antennas     

V形微带缝隙天线

提出了一种新颖的V形微带缝隙天线,地板上开一个直角V形缝隙,在V形缝隙的顶角处附加一个小直角三角形补偿隙,通过改变三角形补偿隙面积的大小可以对天线阻抗匹配进行优化,由基片另一侧的箭形微带线终端对缝隙单元馈电。这种天线易于实现宽带特性,设计简单,便于加工。文中给出了天线阻抗和方向图的计算结果,并给出了反射损耗和增益的实验结果。实测结果表明,该天线的阻抗带宽达到了43%,覆盖了1146~1776MHz的频率范围,-10dB阻抗带宽内增益值在4.5~6.5dB之间,平均增益约为5.5dB。