Jose A. Garcia

Bio: Jose A. Garcia is an academic researcher from University of Cantabria. The author has contributed to research in topics: Amplifier & Amorphous solid. The author has an hindex of 13, co-authored 152 publications receiving 819 citations. Previous affiliations of Jose A. Garcia include Escuela Superior Politecnica del Litoral & University of Oviedo.

GaN HEMT Class ${\hbox{E}}^{2}$ Resonant Topologies for UHF DC/DC Power Conversion

Abstract: In this paper, the design and performance of class E2 resonant topologies for dc/dc power conversion at UHFs are considered. Combining the use of RF gallium-nitride HEMT devices, both for the inverter and synchronous rectifier, with high-Q lumped-element terminating networks, peak efficiency values over 70% may be obtained. Control strategies based on carrier bursting, switching frequency modulation, or outphasing are also shown to be feasible. Taking advantage of their improved dynamic response, when compared to low-frequency more traditional switched-mode converters, a class E3 polar transmitter for the EDGE standard has been designed and tested at 770 MHz, offering an average global efficiency over 46% at 4.3 W of output power, through RF-based amplitude and phase constituting branches. Finally, the potential of such a high frequency of operation in terms of power density is explored, absorbing undesired coil parasitics for the original LC series interconnecting network in a 1-GHz design methodology.

Mechanical determination of internal stresses in as-quenched magnetic amorphous metallic ribbons

Abstract: The layer removing method for determining the internal stress distribution through thickness in sheets has been applied to metallic glass ribbons. The internal stresses are obtained from the variation of the radius of curvature of the samples when the layers are removed. The experimental technique used is described here and the results for two ribbons, are presented. A general feature has been observed implying compressive stress near both surfaces (a strong one near the drum surface and a weak one near the air surface), and the central part under tensile stress. This is in agreement with the residual stress distribution shown by other materials after fast cooling procedures.

Magnetic behaviour of non-contacting Ni nanoparticles encapsulated in vertically aligned carbon nanotubes

Abstract: Magnetic properties of carbon nanotubes (CNT) obtained by plasma-enhanced chemical vapour deposition (PECVD) have been studied. The growth of these nanotubes has been activated from Ni catalyst nanoparticles. Samples consist of Ni nanoparticles encapsulated at the tip of vertically aligned multiwalled carbon nanotubes (VACNTs) forming an homogeneous and dense large area monolayer of isolated (non-contacting) nanoparticles. The magnetic characterisation has been performed in the temperature range of 5-300 K with magnetic fields up to 9 T. The results show that the wide size range (30-180 nm) of the particles originates the coexistence of blocked and superparamagnetic particles and leads to the strong ferromagnetic behaviour of the whole assembly. The coercivity decreases monotonically with increasing temperature and the value for the intrinsic coercivity is 225 Oe. The encapsulation of Ni nanoparticles by VACNTs preserves them from aggregation. This makes possible to tune the coercivity by controlling size distribution of particle monolayers. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A Simple and Reliable Synthesis of Superparamagnetic Magnetite Nanoparticles by Thermal Decomposition of Fe(acac)3

Abstract: Magnetic nanoparticles have been largely proposed as means of technological tools due to its value in different fields, especially in biomedicine. Herein, we present a robust, highly reproducible and low-cost method to obtain superparamagnetic magnetite nanoparticles (MNP-II) of about diameter by thermal decomposition of [Fe(acac)3] in a one-pot, two-step method. In the first step, magnetite nanoparticles (MNP-I) of lower size, , with a saturation magnetization ( ) of 65 emu/g and a coercive field ( ) of 1 Oe are obtained. In the second step, those particles MNP-I act as seeds for the final MNP-II which present a saturation magnetization of 70 emu/g and a coercive field of 12 Oe.

A 1 GHz frequency-controlled class E 2 DC/DC converter for efficiently handling wideband signal envelopes

Abstract: In this paper, a 1 GHz class E2 DC/DC converter, implementing a frequency-modulation (FM) control, is proposed for efficiently handling wideband wireless signal envelopes. Properly terminating the inverting and rectifying GaN HEMT devices, a nearly linear output voltage versus switching frequency profile is obtained, with 70% efficiency at a voltage value 5.1 dB below the peak. Incorporating a Voltage Controlled Oscillator (VCO) and a gate-driving amplifier, the large-signal bandwidth (BW) and slew rate have been estimated to be around 20 MHz and 720 V/μSeg, respectively. The FM converter is also shown to offer a good dynamic reproduction of 6.6 dB peak-to-average power ratio (PAPR) 2- and 4-carrier WCDMA envelope signals, with average efficiencies over 60%. Employed as envelope modulator in a pure polar architecture, handling a 5 MHz hole-punched multisine signal, a 6.7 W output power has been obtained with a transmitter efficiency of 56%.

Handbook of Magnetic Materials

Abstract: Preface. Contents of volumes 1-6. 1. Magnetism in ultrathin transition metal films (U. Gradmann). 2. Energy band theory of metallic magnetism in the elements (V.L. Moruzzi, P.M. Marcus). 3. Density functional theory of the ground state magnetic properties of rare earths and actinides (M.S.S. Brooks, B. Johansson). 4. Diluted magnetic semiconductors (J. Kossut, W. Dobrowolski). 5. Magnetic properties of binary rare-earth 3d-transition-metal intermetallic compounds (J.J.M. Franse, R.J. Radwanski). 6. Neutron scattering on heavy fermion and valence fluctuation 4f-systems (M. Loewenhaupt, K.H. Fischer). Author index. Subject index. Materials index.

Making metallic glasses plastic by control of residual stress

Abstract: Metallic glasses, now that many compositions can be made in bulk1,2,3, are of interest for structural applications exploiting their yield stress and yield strain, which are exceptionally high for metallic materials4. Their applicability is limited by their near-zero tensile ductility resulting from work-softening and shear localization. Even though metallic glasses can show extensive local plasticity, macroscopically they can effectively be brittle, and much current research is directed at improving their general plasticity. In conventional engineering materials as diverse as silicate glasses and metallic alloys, we can improve mechanical properties by the controlled introduction of compressive surface stresses5,6,7. Here we demonstrate that we can controllably induce such residual stresses in a bulk metallic glass, and that they improve the mechanical performance, in particular the plasticity, but that the mechanisms underlying the improvements are distinct from those operating in conventional materials.

A comparative overview of microwave and wireless power-amplifier behavioral modeling approaches

Abstract: This paper presents a comparative overview of the most important approaches presented to address the behavioral modeling of microwave and wireless power amplifiers (PAs). Starting from a theoretical framework of recursive and nonrecursive nonlinear filters, it proposes a classification of the various PA behavioral models, discussing their abilities to represent the different effects observed in practical circuits. Using that formal procedure, one explains how it was possible to integrate a wide range of behavioral modeling activities and to show that some of them, which at first glance seemed to be quite different, are, indeed, identical in their modeling capabilities.

Advances in Magnetic Field Sensors

Abstract: The most important milestone in the field of magnetic sensors was when AMR sensors started to replace Hall sensors in many applications where the greater sensitivity of AMRs was an advantage. GMR and SDT sensors finally found applications. We also review the development of miniaturization of fluxgate sensors and refer briefly to SQUIDs, resonant sensors, GMIs, and magnetomechanical sensors.

High Efficiency RF and Microwave Solid State Power Amplifiers

Abstract: Preface. About the Authors. Acknowledgments. 1 Power Amplifier Fundamentals. 1.1 Introduction. 1.2 Definition of Power Amplifier Parameters. 1.3 Distortion Parameters. 1.4 Power Match Condition. 1.5 Class of Operation. 1.6 Overview of Semiconductors for PAs. 1.7 Devices for PA. 1.8 Appendix: Demonstration of Useful Relationships. 1.9 References. 2 Power Amplifier Design. 2.1 Introduction. 2.2 Design Flow. 2.3 Simplified Approaches. 2.4 The Tuned Load Amplifier. 2.5 Sample Design of a Tuned Load PA. 2.6 References. 3 Nonlinear Analysis for Power Amplifiers. 3.1 Introduction. 3.2 Linear vs. Nonlinear Circuits. 3.3 Time Domain Integration. 3.4 Example. 3.5 Solution by Series Expansion. 3.6 The Volterra Series. 3.7 The Fourier Series. 3.8 The Harmonic Balance. 3.9 Envelope Analysis. 3.10 Spectral Balance. 3.11 Large Signal Stability Issue. 3.12 References. 4 Load Pull. 4.1 Introduction. 4.2 Passive Source/Load Pull Measurement Systems. 4.3 Active Source/Load Pull Measurement Systems. 4.4 Measurement Test-sets. 4.5 Advanced Load Pull Measurements. 4.6 Source/Load Pull Characterization. 4.7 Determination of Optimum Load Condition. 4.8 Appendix: Construction of Simplified Load Pull Contours through Linear Simulations. 4.9 References. 5 High Efficiency PA Design Theory. 5.1 Introduction. 5.2 Power Balance in a PA. 5.3 Ideal Approaches. 5.4 High Frequency Harmonic Tuning Approaches. 5.5 High Frequency Third Harmonic Tuned (Class F). 5.6 High Frequency Second Harmonic Tuned. 5.7 High Frequency Second and Third Harmonic Tuned. 5.8 Design by Harmonic Tuning. 5.9 Final Remarks. 5.10 References. 6 Switched Amplifiers. 6.1 Introduction. 6.2 The Ideal Class E Amplifier. 6.3 Class E Behavioural Analysis. 6.4 Low Frequency Class E Amplifier Design. 6.5 Class E Amplifier Design with 50# Duty-cycle. 6.6 Examples of High Frequency Class E Amplifiers. 6.7 Class E vs. Harmonic Tuned. 6.8 Class E Final Remarks. 6.9 Appendix: Demonstration of Useful Relationships. 6.10 References. 7 High Frequency Class F Power Amplifiers. 7.1 Introduction. 7.2 Class F Description Based on Voltage Wave-shaping. 7.3 High Frequency Class F Amplifiers. 7.4 Bias Level Selection. 7.5 Class F Output Matching Network Design. 7.6 Class F Design Examples. 7.7 References. 8 High Frequency Harmonic Tuned Power Amplifiers. 8.1 Introduction. 8.2 Theory of Harmonic Tuned PA Design. 8.3 Input Device Nonlinear Phenomena: Theoretical Analysis. 8.4 Input Device Nonlinear Phenomena: Experimental Results. 8.5 Output Device Nonlinear Phenomena. 8.6 Design of a Second HT Power Amplifier. 8.7 Design of a Second and Third HT Power Amplifier. 8.8 Example of 2nd HT GaN PA. 8.9 Final Remarks. 8.10 References. 9 High Linearity in Efficient Power Amplifiers. 9.1 Introduction. 9.2 Systems Classification. 9.3 Linearity Issue. 9.4 Bias Point Influence on IMD. 9.5 Harmonic Loading Effects on IMD. 9.6 Appendix: Volterra Analysis Example. 9.7 References. 10 Power Combining. 10.1 Introduction. 10.2 Device Scaling Properties. 10.3 Power Budget. 10.4 Power Combiner Classification. 10.5 The T-junction Power Divider. 10.6 Wilkinson Combiner. 10.7 The Quadrature (90 ) Hybrid. 10.8 The 180 Hybrid (Ring Coupler or Rat-race). 10.9 Bus-bar Combiner. 10.10 Other Planar Combiners. 10.11 Corporate Combiners. 10.12 Resonating Planar Combiners. 10.13 Graceful Degradation. 10.14 Matching Properties of Combined PAs. 10.15 Unbalance Issue in Hybrid Combiners. 10.16 Appendix: Basic Properties of Three-port Networks. 10.17 References. 11 The Doherty Power Amplifier. 11.1 Introduction. 11.2 Doherty's Idea. 11.3 The Classical Doherty Configuration. 11.4 The 'AB-C' Doherty Amplifier Analysis. 11.5 Power Splitter Sizing. 11.6 Evaluation of the Gain in a Doherty Amplifier. 11.7 Design Example. 11.8 Advanced Solutions. 11.9 References. Index.