Boundary Conditions and Ohmic Losses in Conducting Wedges

The present work is concerned with the boundary conditions required to calculate the ohmic losses occurring in metallic wedges under the influence of electromagnetic waves which are sinusoidal in time. The validity of the surface impedance condition used in calculating waveguide wall losses is examined carefully, and a "modified" surface impedance condition, which can be applied to wedge problems in which the perfectly conducting solution is known, is developed. A simple waveguide having a circular cross section, a sector of which is occupied by a metal wedge, is used as an example. The tangential magnetic field variations along the surface of the wedge are shown graphically, demonstrating, near the tip of the wedge, a large deviation from the tangential magnetic field of the perfectly conducting solution.     

Losses in Microstrip

Expressions are derived for the conductor loss in microstrip transmission lines. The formulas take into account the finite thickness of the strip conductor and apply to the mixed dielectric system. Good agreement with experimental data is obtained for rutile and alumina substrates.     

Scattering by a perfect electromagnetic conductor (PEMC) plate embedded in lossy medium

In this article, we develop an analytic theory for a perfect electromagnetic conductor (PEMC) plate embedded in lossy medium. The duality transformation introduced by Lindell and Sihvola is applied to study the electromagnetic wave scattering by a PEMC plate. Perfect electric conductor and perfect magnetic conductor are the limiting cases of PEMC media. Here, we study monoscattering by PEMC plate embedded in four different soil models. Numerical results are discussed and compared with the available literature.     

Performance enhancement of PEMC liquid level sensor subjected to environmental temperature variation

In this paper, the performance of a resonant Piezoelectric-excited Millimeter-sized Cantilever (PEMC) used as liquid level sensor has been studied. The sensitivity of this sensor affected by environmental temperature variation is investigated via theoretical and Finite Element Models (FEM). In order to validate this FEM, first, simulation results are compared with the theoretical and experimental ones for a sensor operating at constant room temperature. The simulation results are in a good agreement with experimental ones. Then, proposed theoretical model and FEM are used to study the dynamic behavior of the device when the environmental temperature is changed. The results indicate that although natural frequencies of sensor change due to temperature variation, the resultant shift remains almost the same regardless of specific immersion depths. Also, it can be concluded that temperature variation of about 50 °C affects the liquid level measurement accuracy up to 29 μm which is significant compared to a minimum detectable liquid level change of about 8 μm by this sensor reported previously in literature.     

Losses in GaAs microstrip

Newly measured data for the loss of microstrip on 4 mil GaAs from DC to 40 GHz are presented. These data were taken from transmission measurements of lightly coupled, multiple-half-wave-length resonators. A comparison of the loss data with the predicted losses from three popular CAE (computer-aided engineering) tools is provided. The loss models provided by two out of three software vendors agree fairly well with measured data through 40 GHz. Since the measured loss roughly follows a square-law frequency relationship through 20 GHz, it should be possible to adjust the loss below this frequency and above 1 GHz by modifying the resistivity of the conductor in the simulator     

Losses in tantalum pentoxide waveguides

Thin films of tantalum pentoxide for possible use as waveguides have been prepared by reactive sputtering and by thermal and anodic oxidation of sputtered tantalum films. Measurements have been made of the losses in these films for different guided modes. These results have been analyzed to determine the loss mechanism. The losses do not fit the Rayleigh scattering theory precisely and the deviation is attributed to absorption by impurities at the surface as well as in the bulk. The effects of bulk and surface loss mechanisms have been obtained and causes of these are discussed.     

Losses in fibre laser cavities

A passive cavity ring-down technique has been used to measure the intrinsic losses of a fibre laser cavity. The results show that very low cavity losses can be obtained using conventional mirrors butted to the fibre. Optimum output coupling for a typical cavity intrinsic loss is derived     

Losses in Dielectric Image Lines

The dipole mode in a dielectric rod permits an image system in which half the dielectric and its surrounding field are replaced by a metal sheet. If the field is allowed to extend many wavelengths outside the rod, the resulting line has very low losses. The contribution of the image surface to line loss is calculated, and shown to be generally less than the dielectric loss. Radiation from obstacles along the line is also discussed. Such obstacles in closed single-mode waveguides are useful for matching purposes. Although matching elements are easily constructed for the image line, radiation loss proves difficult to control.     

Excess Losses in H-Plane Loaded Waveguides

The attenuation in a waveguide partially filled with absorbing material can become larger than that of the same waveguide completely filled with that same material. Theoretical and experimental results are presented together with field distributions showing that this excess loss is due to a large concentration of electric field within the lossy dielectric in the partially filled configuration.     

E类放大电路中晶体管的功率损耗

在理想情况下,E类放大电路的效率可以达到100%,因此E类放大电路适用于高功率,高频率电路的设计,但在实际情况下,由于所有的器件都不是理想的。例如,电感、电容中会有寄生电阻的存在,晶体管的饱和电压,饱和电阻以及集电极电流的下降时间不为零,这些因素的存在都会导致E类放大电路的效率降低,但当电路的负载匹配且处于谐振状态,则引起电路功率损耗的主要因素也就是晶体管中的功率损耗。对E类放大电路中由晶体管引起的损耗进行分析,并得出简单的估算方法,并用实验的方法验证。     

Microwave Q Measurements in the Presence of Coupling Losses

In the use of the impedance (Q-circle) method of measuring the cavity Q values, the presence of losses in the coupling network (between the cavity and the available external terminals) is usually neglected. If appreciable losses are present this simplification is not justitied, and its use can lead to significant errors. The losses in any coupling network can be described by means of an equivalent canonical circuit containing a series and a shunt resistor. The losses due to the series element are immediately apparent from the character of the impedance locus when plotted on a Smith Chart and can be corrected for an "apparent" Q value. However, unless the shunt loss can be determined by a separate calibration of the coupling network, the apparent Q value will be ambiguous because the shunt losses occurring in the coupling network are not distinguishable from those in the cavity proper. Methods for using the impedance data for determining the Q values are given on the assumption that the coupling network parameters cm be found. It is also pointed out that due to the presence of coupling losses the loaded and external Q values are no longer uniquely defined, but their meaning depends upon the application of interest. Formulas relating these to the coupling network parameters are given.     

Measurement of Losses in Noise-Matching Networks

The noise contribution of an input-matching network to a low-noise amplifier is equal to the inverse of the network's available gain. The available gain of various networks at 4 GHz was computed from high-accuracy S-parameter measurements. The available gain of a typical tuner was experimentally found to be a strong function of its tuning, which shows that "back-to-back" measurements of two tuners to obtain the loss of each tuner can be inaccurate. Measurement of the available gain of an amplifier's input-matching circuit is shown to give quick insight into its minimum noise contribution before the actual amplifier stage is built.     

Conversion Losses in Schottky-Barrier Diode Mixers in the Submillimeter Region

Conversion Iosses, both intrinsic and parasitic, are calculated for Schottky diode mixers in the submillimeter region, and optimum mixer performance is shown to depend strongly upon operating frequency and upon diode diameter. The implications for high-frequency diode fabrication are discussed, and a comparison is made of the expected performance of GaAs, Si, and InSb Schottky diodes at frequencies up to 5 THz.     

Losses in very large planar waveguides

Planar optical waveguides with linear dimensions exceeding one metre, are readily available as a byproduct of standard glass processing treatments. Measurements of the mode distribution and losses in such guides are reported for two types of float glass. Typically, the layers support one or two modes. Losses were noted to be as low as 0.3 dB/cm. A possible source of error for planar guide losses in conventional samples is discussed.<>     

Losses in small-radius bends in single-mode fibres

Refractive index profiles and mode field radii determine small-radius bending losses in single-mode fibres. Losses in six different types of fibres were measured in bends with radii ranging from 1.25 to 8 mm. The results show that a refractive index depression in the core centre reduces the bending-loss sensitivity.<>     

Losses of Microstrip Lines

This article summarizes state-of-the-art information on losses of single and coupled microstrip lines. Conductor loss, substrate loss (for pure dielectric or magnetic materials), and radiation loss are considered along with the effect of dispersion. Finally, a rough comparison is made between the losses of microstrip and that of several other types of lines used in microwave integrated circuits.     

Transport AC Losses in YBCO Coated Conductors

Modeling and design of superconducting power devices (e.g. fault current limiters), based on second generation HTS tapes, requires accurate evaluation and prediction of AC losses. Transport AC losses measurements have been performed on samples of YBCO coated conductors at 77 K, as a function of current. The results have been compared with the classical analytical model for self field AC losses calculation, taking into account the role of the magnetic substrate.     

Calculation of Power Losses in Thyristor Converters

This paper shows that the power loss in a thyristor and its commutation circuit can be adequately calculated from a detailed knowledge of the current waveforms and the use of a simple model for conducting thyristors and diodes. In some thyristor circuits, device switching losses can be neglected with little loss in accuracy. Snubber losses are included. The analytical technique described is verified.     

微环谐振器的弯曲损耗

通过解弯曲波导的正规模的方法,从理论上分析了微环谐振器的弯曲损耗与微环的直径、宽度和厚度间的对应关系,给出了微环谐振器的弯曲损耗与微环芯和周围介质折射率对比间的关系.将上述的计算结果与保角变换方法的计算结果进行了比较.设计了微环谐振器的特征参数.     

光学薄膜的损耗

对光学薄膜的表面散射、体散射和吸收这三个损耗因素进行系统的分析和计算,并在它们都存在的条件下,计算了光学薄膜的反射率、透过率和损耗率.由于计算程序考虑了各种因素对光学薄膜的影响,所以计算模型和计算方法比一般的方法有更多的普遍性.文中给出11层ZnS/MgF_2反射膜和21层TiO_2/SiO_2反射膜的计算结果.