Microwave fields and applications

Ohne Zusammenfassung     

Microwave heating in the food industry

Food processing has become an important aspect of microwave heating; several technically and some economically successful developments have been reported over the past 10 years. However, the number of microwave installations in the food industry is still very small and not in proportion to the publicity given in many trade journals. The basic theory for the dielectric heating of foods is first reviewed and examples are given of the methods which can be used to analyze heating applications, a valuable complement to empirical testing. Present applications of microwave heating of foods are reviewed. Promising new applications of partial thawing, cooking, and sterilization are discussed in some detail. Some of the reasons for the apparently slow development of these applications are discussed, pointing out the need for better cooperation between manufacturers and users. The opinion is expressed that microwaves will eventually become a standard tool in the food industry for certain processing steps along a continuous production line where very rapid and uniform heating is required. However, it will be necessary, to a much larger extent than in the past, to adapt microwave heating equipment to the processes rather than to adapt the processes to standard microwave systems.     

TCP/IP modeling and validation

We discuss the different issues to be considered when modeling the TCP protocol in a real environment. The discussion is based on measurements we made over the Internet. We show that the Internet is so heterogeneous that a simplistic assumption about TCP congestion control or the network may lead to erroneous results. We outline some of our results in this field, and we present a novel approach For a correct validation of a model for TCP     

Nonlinear modeling and validation of solenoid-controlledpilot-operated servovalves

Solenoid-controlled pilot-operated servovalves are flow control devices widely used to drive high-flow hydraulic actuators in heavy-duty off-highway machinery. In these applications, a spool-operated pilot stage is required to account for large flow force in the main hydraulic valve. Design optimization, performance improvement, and fault diagnosis of such complex two-stage servovalves often require sophisticated analytical models with accurate physical parameters. The paper presents a step-by-step methodology for nonlinear modeling, parameter determination, model validation, and performance evaluation of solenoid-controlled pilot-operated spool valves. The proposed model takes into account such nonlinearities as pilot spool dead band, spool friction, flow coefficient variability, and leakage. This new model is complete in the sense that all nonlinear interactions between various electromechanical elements have been incorporated in a compact yet comprehensive model. The simulation model accepts a command voltage to the solenoids as input and gives the second stage spool displacement as output. To obtain the physical parameters used in the valve model, a systematic approach is proposed based on state measurement and curve-fitting techniques. The identified parameters of an example valve were used in simulations both to validate the nonlinear valve model and also to assess the valve's performance when certain valve parameters change     

Microwave multiplexers for space applications

The channel performance of a satellite payload is largely determined by the frequency response of its input and output multiplexers. This paper provides an insight into some of the requirements for these multiplexers and how they are met. An example of a simplified 12/14 GHz payload with key specification parameters for the multiplexers is given. The electrical design of the multiplexers is described and the mechanical, thermal and high-power aspects of their performance are discussed. State-of-the-art examples are given with typical computed and measured performance characteristics     

Microwave path-loss modeling in urban line-of-sight environments

To model the path-loss characteristics in microwave urban line-of-sight (LOS) propagation, we performed measurements in metropolitan Tokyo at frequencies of 3.35, 8.45, and 15.75 GHz. The actual breakpoint distance was shorter than the theoretical one because of the influence of vehicles, pedestrians, and other objects on the road. This effect has been referred to as effective road height. We found that the breakpoint disappeared when the mobile-antenna height approached the effective road height. Based on these breakpoint characteristics, we propose new upper- and lower-bound formulas for LOS path loss in urban microcellular environments. They will be useful for the system and cell design of fourth-generation multimedia mobile communication systems using microwave bands.     

Microwave noise modeling for InP-InGaAs HBTs

Analytical expressions for the noise parameters of microwave InP double heterojunction bipolar transistors (DHBTs) are presented in this paper. These expressions are derived from an accurate small-signal and noise equivalent-circuit model, which takes into account the influences of the base-collector capacitance and the base resistance distributed nature. Pad capacitances and series inductances are also included. Further simplified expressions for noise parameters in the low-frequency range are given. Good agreement is obtained between measured and calculated results up to 20 GHz for InP-InGaAs DHBTs with a 5/spl times/5 /spl mu/m/sup 2/ emitter area over a wide range of bias points.     

Visual authorization modeling in e-commerce applications

Considers how task-based security models let enterprises control access at the application rather than the operating system level. The Visual Security Administrator (Visa) uses visual languages to represent steps in this authorization process with icons and gestures to support security management by nontechnical users, such as enterprise managers.     

Microwave noise performance and modeling of SiGe-based HFETs

Microwave noise performance of SiGe-based heterostructure field effect transistors (HFETs) is presented. Noise parameters for devices with buried channel fabricated on several virtual substrates are discussed. The impact of such strain relieved buffers on device noise performance is estimated by a proper noise de-embedding technique. Then, the noise properties measured in the 2.5-18-GHz frequency range are compared with those of other technologies. Noise parameters of SiGe HFETs are simulated using Pospieszalski's and Van Der Ziel's noise models. Some detrimental effects like access resistances and self-heating effects that negatively impact the microwave noise behavior are discussed and some alternatives to overwhelm them are proposed.     

Microwave acoustic materials, devices, and applications

This paper surveys applications of acoustic waves in microwave devices. After a general and historical introduction to bulk acoustic waves (BAWs), surface acoustic waves (SAWs), practical wave types, and acoustoelectric transducers, a review is given of technologically important materials for microwave acoustic applications. Following this, we discuss BAW and SAW microwave devices and their technologies. Specifically reviewed are thin-film resonators and filters, transversal filters, and filters for correlative analog signal processing. Finally, an overview of the most important microwave applications is given, along with manufacturing and packaging issues     

Piezo-actuators modeling for smart applications

This paper deals with piezoelectric actuators modeling. The objective is to contribute in piezo-models library construction. Compared to existing models in commercial packages, the proposal model integrate nonlinear effects, especially hysteresis, while not requiring high computing efforts. This will help in the generalization of piezo-actuator usage for smart applications. Our methodology and approaches are clearly justified in the paper.     

无线传播信道回放模型建模方法及应用

介绍了一种确定性无线信道建模方法——回放模型建模方法，该方法以实时高速的实际无线传播环境测量为基础，能精确复制无线环境的传播特征。首先给出回放模型的建模思路以及对无线信道测量方法和测量仪器的要求：然后重点介绍处理实际外场测量数据形成回放模型的主要步骤和方法，并给出一些典型无线环境的测量和数据处理结果；实际测量和应用例子表明回放模型相对统计模型能更加精确的描述典型无线环境的传播特征，从而在WCDMA等无线系统尤其是物理层系统设计和优化过程中发挥重要的作用。     

Microwave SAW bandpass filters for spacecraft applications

Microwave SAW bandpass filters for spacecraft applications are described. Two SAW bandpass filters were designed and fabricated in the 1.5 GHz band using temperature-stable ST-cut quartz substrates. The SAW bandpass filters were then assembled in a SAW filter bank. One unique feature of the SAW filter bank is that a broader band is available merely by adding the outputs of SAW bandpass filters adjacent in the frequency domain. Measured electrical responses as well as results of a transmission experiment show satisfactory performance. Effects of the temperature and aging stability characteristics are investigated based on the measured and calculated responses     

Conceptual modeling of device-independent Web applications

Existing tools for building and deploying complex Web sites are inadequate for dealing with the software production process that involves connecting with underlying logic in a unified and systematic way. As a solution, we propose the OO-H method, an object-oriented software approach that captures relevant properties involved in modeling and implementing Web application interfaces     

Simple MOSFET modeling for digital applications

The charge-control concept provides a common base for the modeling of both the MOSFET and the bipolar transistor in digital applications. The dominating characteristics of common MOSFET digital circuits are contained in simple device models.     

Synergistic modeling and applications of hierarchical fuzzy neuralnetworks

Many common foundations exist between neural networks and fuzzy inference systems in terms of their mathematical models and system structures. This paper explores such a rich synergy and uses it to form the basis for a unifying framework under which fuzzy logic processing and neural networks may be integrated to achieve more robust information processing. It in turn leads to a family of hierarchical fuzzy neural networks (FNNs) which incorporate an adaptive and modular design of neural networks into the basic fuzzy logic systems. Several important models which are critical to the development of the the hierarchical FNN family are studied. We demonstrate how existing unsupervised and supervised learning strategies can be an integral part of a fuzzy processing framework. In addition, hierarchical structures involving both expert modules and class modules are incorporated into the FNNs. Also presented are some promising application examples