13,198 research outputs found
A Measurement System for On-line Estimation of Weed Coverage
No full textThis paper describes two different solutions for the estimation of weed coverage. Both measuring systems discriminate the weed from the ground by means of the color difference between the weed and ground and can be used to on-line control tractor sprayers in order to reduce weedkiller use. The solutions differ with respect to the sensor type: one solution is based on a digital camera and a computer that analyzes the images and determines the weed amount, while the other simpler solution makes use of two photo detectors and an analog processing system. The camera-based solution provides an uncertainty of a few percentage, while the photo detector-based one, though extremely cheap, has an uncertainty of about 5% and suffers from changes in light conditions, which can alter the estimation
Generalized mixed-mode S-parameters
No full textThis paper presents an innovative approach to extend the S-parameter definition to multiport networks having conventional single-ended and differential ports, as is the case for operational amplifiers, transformers and baluns. To give maximum generality to this technique, for example, allowing for complex -parameter reference impedances, the mathematical derivation will be carried out with the most general definition of the -parameters. The presented approach gives the same results already published for circuits with differential ports only when the required simplifications are applied
Physics-based large-signal sensitivity analysis of microwave circuits using technological parametric sensitivity from multidimensional semiconductor device models
No full textThe authors present an efficient approach to evaluate the large-signal (LS) parametric sensitivity of active semiconductor devices under quasi-periodic operation through accurate, multidimensional physics-based models. The proposed technique exploits efficient intermediate mathematical models to perform the link between physics-based analysis and circuit-oriented simulations, and only requires the evaluation of dc and ac small-signal (dc charge) sensitivities under general quasi-static conditions. To illustrate the technique, the authors discuss examples of sensitivity evaluation, statistical analysis, and doping profile optimization of an implanted MESFET to minimize intermodulation which makes use of LS parametric sensitivities under two-tone excitatio
Microwave Measurements Part I: Linear Measurements
No full textAn Overview of the most relevant issues concerning RF and microwave linear measurements is presented. Vector Network Analyzer foremost used instrumentation for this kind of measures is describe
Behavioral modeling of GaN-based power amplifiers: impact of electrothermal feedback on the model accuracy and identification
No full textIn this article, we discuss the accuracy of behavioral models in simulating the intermodulation distortion (IMD) of microwave GaN-based high-power amplifiers in the presence of strong electrothermal (ET) feedback. Exploiting an accurate self-consistent ET model derived from measurements and thermal finite-element method simulations, we show that behavioral models are able to yield accurate results, provided that the model identification is carried out with signals with wide bandwidth and large dynamics
Microwave Measurements. Part II - Nonlinear Measurements
No full textThis paper addresses the problems in microwave non-linear measurements. It discusses techniques to synthesize loads, the most used non-linear measurement techniques, and harmonic load-pulling. An experimental setup for characterizing power amplifiers must be able to measure the complex spectrum of the waves at the amplifier ports as a function of frequency, input power, and source and load termination at the fundamental and harmonic frequencies. The vector network analyzer (VNA) is the core instrument used in the non-linear characterization scenario. The basic idea is to keep the operations of VNA/mixers linear, diverting to them only a small portion of the signal present at the device under test (DUT) ports, therefore keeping unaltered the VNA capabilities already exhibited for small signal measurements
A TCAD approach to the physics-based modeling of frequency conversion and noise in semiconductor devices under large-signal forced operation
No full textRe-engineering the Way Maintenance Data Are Collected and Analysed: The Service Report
No full textManufacturing companies are strongly investing in offerings based on combinations of products and services—known as Product Service Systems (PSS)— for establishing long-lasting relationships with customers under the premise that services can extend the products’ useful life and create additional value. Despite this, it is difficult to deliver services efficiently and effectively. Thus, companies must identify flaws in their service delivery offering and tackle them, with data collection and analysis used as the main leverage for this. In the case of the maintenance service, technicians’ reports constitute the main source of knowledge since they contain information on failure causes, recurrent problems, or optimal strategies for their resolution, and can be used to create the maintenance engineering knowledge necessary to drive improvements. That said, maintenance data collection should be organized in a way that allows proper collection and categorization avoiding blank fields or wrong..
Studio di modelli fisici per la simulazione di effetti di backgate e dispersione a bassa frequenza in GaAs MESFET
No full textIl lavoro di tesi presenta l'implementazione di un modello fisico deriva diffusione a doppio portatore per FET a doppio portatore. Effetti di trappoli e backgate sono inclusi. Il programma fornisce le caratteristiche DC e di piccolo segnale a partire dai parametri fisici di FET per alte frequenz
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