402 results found
Bovtun V, Veljko S, Axelsson A, et al., 2008, Microwave characterization of thin ferroelectric films without electrodes by composite dielectric resonator, 19th International Symposium on Integrated Ferroelectrics, Publisher: TAYLOR & FRANCIS LTD, Pages: 53-61, ISSN: 1058-4587
Centeno A, Breeze JD, Alford NMN, et al., 2008, Measurement of high loss dielectric materials using a resonant technique
This paper will report on a technique that has been developed for the measurement of the dielectric loss of materials which have a relatively high loss tangent. The method used employs a composite resonator that consists of the material under test being placed in the centre of a low loss ceramic ring resonator. The important feature of this configuration is that the electric energy filling factor in the sample is significantly lowered. This has the desirable effect of reducing the contribution to the resonator Q-factor of the sample material which has a high loss compared to the ceramic ring resonator. This enables the measurement of dielectric loss tangents which are significantly larger than those that can be measured using a conventional technique, such as making a cylindrical dielectric resonator of the sample material. In this technique the choice of resonant mode is very important. The electrical energy filling factor must low enough to ensure a measurable Q factor but at the same time high enough to measure a detectable perturbation of the resonance. It is also important to know the electrical filling factor of the ring resonator, which is made of a well characterised ceramic material, and the Q-factor contribution of any conducting surfaces in the resonant structure such as cavity walls. The choice of resonant mode and the effects of the other components in the resonator are obtained by using Finite Difference Time Domain (FDTD) and Mode Matching modelling tools. Measurement of the loss tangent of high resistivity Silicon over temperature has already been carried out with this technique by employing a BZT ring resonator resonating at around 5GHz in the TE01? mode. The results are very promising with loss tangents being measured that are an order of magnitude higher than could be measurable using a more conventional resonant technique. The current focus of this work is the measurement of liquids at microwave and millimetre wavelengths using Alumina resonators
Alford NM, Buslov OY, Keis VN, et al., 2008, Band-Pass Tunable Ferroelectric Filter Based on Uniplanar Dielectric Resonators, 38th European Microwave Conference, Publisher: IEEE, Pages: 740-+
Alford NM, Buslov OY, Keis VN, et al., 2008, Band-Pass Tunable Ferroelectric Filter Based on Uniplanar Dielectric Resonators, European Wireless Technology (EuWiT), Publisher: IEEE, Pages: 282-+
Krupka J, Breeze J, Alford NMN, et al., 2007, Measurements of permittivity and dielectric loss tangent of high resistivity float zone silicon at microwave frequencies
Real part of permittivity and the dielectric loss tangent of float zone high resistivity Silicon were measured at microwave frequencies at temperatures from 10 K up to 380 K employing dielectric resonator technique. The real part of permittivity proved to be frequency independent and the decrease in dielectric loss tangent versus frequency proved to be not entirely proportional to the inverse of frequency. At temperatures below 25 K where all free carriers are frozen-out loss tangents values the order of 10-4 were measured.
Alford N, 2007, Functional films, MATERIALS WORLD, Vol: 15, Pages: 27-29, ISSN: 0967-8638
Valant M, Axelsson A-K, Alford N, 2007, Peculiarities of a solid-state synthesis of multiferroic polycrystalline BiFeO3, CHEMISTRY OF MATERIALS, Vol: 19, Pages: 5431-5436, ISSN: 0897-4756
Breeze J, Krupka J, Alford NM, 2007, Enhanced quality factors in aperiodic reflector resonators, APPLIED PHYSICS LETTERS, Vol: 91, ISSN: 0003-6951
Danylyuk S, Poppe U, Kadlec F, et al., 2007, Broadband microwave-to-terahertz near-field imaging, Pages: 1383-1386, ISSN: 0149-645X
In this paper we present a high performance near-field imaging method suitable for broadband applications. Recent advances in preparing micrometer and submicrometer resolution near-field probes are reported, along with examples of applications of this method both for frequency and time domain measurements. For the latter, pulsed terahertz radiation has been used to probe a broadband (300 GHz-2 THz) spectroscopic response of substances with different dielectric properties. For frequency domain measurements a continuous wave 80 GHz radiation has been applied to metallic, semiconducting, ferroelectric and biological objects. Frequency independent high spatial resolution and high sensitivity have been demonstrated for all measurements. © 2007 IEEE.
Salak AN, Ferreira VM, Vieira LG, et al., 2007, Dielectric relaxation anal microwave loss in the La(Mg1/2Ti1/2)O-3-(Na1/2Bi1/2)TiO3 perovskite ceramics, JOURNAL OF MATERIALS RESEARCH, Vol: 22, Pages: 2676-2684, ISSN: 0884-2914
Petrov PK, Palkar VR, Tagantsev AK, et al., 2007, Dielectric properties characterization of La- and Dy-doped BiFeO3 thin films, JOURNAL OF MATERIALS RESEARCH, Vol: 22, Pages: 2179-2184, ISSN: 0884-2914
Valant M, Axelsson A-K, Zou B, et al., 2007, Oxygen transport during formation and decomposition of AgNbO3 and AgTaO3, JOURNAL OF MATERIALS RESEARCH, Vol: 22, Pages: 1650-1655, ISSN: 0884-2914
Valant M, Axelsson A-K, Zou B, et al., 2007, Strain influence on crystallography of AgNbO3-based thin films, 5th International Romanian Conference on Advanced Materials, Publisher: NATL INST OPTOELECTRONICS, Pages: 1377-1381, ISSN: 1454-4164
Scott DJ, Coveney PV, Kilner JA, et al., 2007, Prediction of the functional properties of ceramic materials from composition using artificial neural networks, Journal of the European Ceramic Society, Vol: 27, Pages: 4425-4435, ISSN: 0955-2219
We describe the development of artificial neural networks (ANN) for the prediction of the properties of ceramic materials. The ceramics studied here include polycrystalline, inorganic, non-metallic materials and are investigated on the basis of their dielectric and ionic properties. Dielectric materials are of interest in telecommunication applications, where they are used in tuning and filtering equipment. Ionic and mixed conductors are the subjects of a concerted effort in the search for new materials that can be incorporated into efficient, clean electrochemical devices of interest in energy production and greenhouse gas reduction applications. Multi-layer perceptron ANNs are trained using the back-propagation algorithm and utilise data obtained from the literature to learn composition–property relationships between the inputs and outputs of the system. The trained networks use compositional information to predict the relative permittivity and oxygen diffusion properties of ceramic materials. The results show that ANNs are able to produce accurate predictions of the properties of these ceramic materials, which can be used to develop materials suitable for use in telecommunication and energy production applications.
ALFORD NEIL M, SALINAS FLORES ENER O, 2007, dsl modem and transformer US2007001794 - 2007-01-04, US2007001794
Anjana PS, Sebastian MT, Axelsson A-K, et al., 2007, Microwave dielectric properties of CeO2-0.5AO-0.5TiO(2) (A = Ca, Mg, Zn, Mn, Co, Ni, W) ceramics, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Vol: 27, Pages: 3445-3452, ISSN: 0955-2219
Pullar RC, Zhang Y, Chen L, et al., 2007, Manufacture and measurement of combinatorial libraries of dielectric ceramics - Part II. Dielectric measurements of Ba1-xSrxTiO3 libraries, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Vol: 27, Pages: 4437-4443, ISSN: 0955-2219
Chien H, Petrov PK, Palkar VR, et al., 2007, Microwave characterisation of La- and Dy- doped BiFeO3 thin films, 16th IEEE International Symposium on Applications of Ferroelectrics, Publisher: IEEE, Pages: 380-+, ISSN: 1099-4734
Pullar RC, Farrah S, Alford NM, 2007, MgWO4, ZnWO4, NiWO4 and CoWO4 microwave dielectric ceramics, 9th Conference and Exhibition of the European-Ceramic-Society, Publisher: ELSEVIER SCI LTD, Pages: 1059-1063, ISSN: 0955-2219
Danylyuk S, Poppe U, Kadlec F, et al., 2007, Broadband microwave-to-terahertz near-field imaging, IEEE/MTT-S International Microwave Symposium, Publisher: IEEE, Pages: 1378-+, ISSN: 0149-645X
Pullar RC, Zhang Y, Chen L, et al., 2007, Manufacture and measurement of combinatorial libraries of dielectric ceramics - Part I: Physical characterisation of Ba1-xSrxTiO3 libraries, International Conference on Electroceramics, Publisher: ELSEVIER SCI LTD, Pages: 3861-3865, ISSN: 0955-2219
Valant M, Axelsson A-K, Alford N, 2007, Review of Ag(Nb, Ta)O-3 as a functional material, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Vol: 27, Pages: 2549-2560, ISSN: 0955-2219
Petrov PK, Palkar VR, Alford NMN, et al., 2006, Microwave responce from La- and Dy- doped BiFeO <inf>3</inf> thin films, Pages: 28-33, ISSN: 0272-9172
The dielectric response of La- and Dy- doped BiFeO 3 thin films to electric- and magnetic fields was measured at microwave frequencies (up to 12GHz) in a temperature range from 25°C to 300°C. Interesting phenomena were observed. Significant oscillations in the C(f) characteristic which were unaffected by the electric field or by elevated temperature but which were dampened by a magnetic field. We also observed 'N'-type I-V characteristics. A possible explanation for this mesoscopic response is the presence of structural features that cause resonance (e.g. grains, grain-boundaries, domains, domain walls etc), with a contribution strong enough to be averaged by the system. The exact origin of these features is unknown at present. © 2007 Materials Research Society.
Centeno A, Breeze JD, Krupkaf J, et al., 2006, Evaluating the properties of dielectric materials for microwave integrated circuits, Pages: 21-26
It is important to be able to accurately evaluate the electrical properties of dielectric materials to enable the accurate design of passive microwave integrated circuit components. This paper reports on research that has been undertaken in this area at London South Bank University. Three measurement techniques are reported. The first is a novel technique for measuring dielectric materials with a large tan δ using a composite resonator. The second is the measurement of the permittivity of ferroelectric thin films using a planar capacitor. The third is the use of an evanescent microwave probe to find the electrical properties at the surface of a sample.
ALFORD NEIL MCNEILL, SALINAS FLORES ENER ORLANDO, 2006, DSL MODEM AND TRANSFORMER EP1719138 2006, EP1719138, US2007001794 -
Krupka J, Breeze J, Centeno A, et al., 2006, Measurements of permittivity, dieletric loss tangent, and resistivity of float-zone silicon at microwave frequencies, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, Vol: 54, Pages: 3995-4001, ISSN: 0018-9480
ALFORD NEIL MCNEILL, 2006, COOLING OF RECEIVE COIL IN MRI SCANNERS, DE60121984D
ALFORD NEIL MCNEILL, PETROV PETER KRASTEV, 2006, TUNABLE OR RE-CONFIGURABLE DIELECTRIC RESONATOR FILTER, WO2006059159
Dunne LJ, Axelsson AK, Alford NM, et al., 2006, Quasi-classical fluctuation-dissipation description of dielectric loss in oxides with implications for quantum information processing, INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Vol: 106, Pages: 986-993, ISSN: 0020-7608
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