Imperial College London

ProfessorNeilAlford

Central FacultyOffice of the Provost

Associate Provost (Academic Planning)
 
 
 
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Contact

 

+44 (0)20 7594 6724n.alford

 
 
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Assistant

 

Miss Catherine Graham +44 (0)20 7594 3330

 
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Location

 

2..05 (in RSM) or 3.09 (in the Faculty Building)Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

404 results found

McN Alford N, Breeze J, Penn SJ, Poole Met al., 2000, Temperature compensated high Q and high thermal conductivity dielectrics for Ku and Ka band communications, IEE Colloquium (Digest), Pages: 25-28, ISSN: 0963-3308

Aluminium oxide is a favourable candidate for use as a dielectric resonator in Ku and Ka band microwave devices especially at high powers due to its very low tanδ ∼2×10 -5 at 10 GHz, modest relative permittivity of 9.8 and high thermal conductivity of 30 W/mK. However, its temperature coefficient of the resonant frequency TCf of -60ppm/K is rather high for practical purpose. The application of a film of titanium oxide which has an opposite sign TCf of +450ppm/K. onto an alumina puck, produces a composite in which the TCf can be tuned to be zero across a large temperature range. The tanδ of the composite at zero TCf is 3.3×10 -5 (Qd =30,000) at-room temperature and 10GHz.

Journal article

Alford NMN, Breeze J, Penn SJ, Poole Met al., 2000, Layered Al2O3-TiO2 composite dielectric resonators with tuneable temperature coefficient for microwave applications, IEE PROCEEDINGS-SCIENCE MEASUREMENT AND TECHNOLOGY, Vol: 147, Pages: 269-273, ISSN: 1350-2344

Journal article

BUTTON TIMOTHY W, ALFORD NEIL MCN, 2000, Method of producing an electromagnetic signal, US6119025

Patent

Breeze J, Penn SJ, Poole M, Alford NMet al., 2000, Layered Al2O3-TiO2 composite dielectric resonators, ELECTRONICS LETTERS, Vol: 36, Pages: 883-884, ISSN: 0013-5194

Journal article

Kovac P, Husek I, Gomory F, Oduleye OO, Pachla W, Diduszko R, Alford NMet al., 2000, Electrical and mechanical properties of Bi-2223/Ag/barrier/Ag composite tapes, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, Vol: 13, Pages: 378-384, ISSN: 0953-2048

Journal article

Alford NM, Wang A, Penn SJ, Poole M, Jones Aet al., 2000, Effect of ceramic binders on microwave dielectric loss of alumina, BRITISH CERAMIC TRANSACTIONS, Vol: 99, Pages: 212-214, ISSN: 0967-9782

Journal article

Templeton A, Wang XR, Penn SJ, Webb SJ, Cohen LF, Alford NMet al., 2000, Microwave dielectric loss of titanium oxide, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Vol: 83, Pages: 95-100, ISSN: 0002-7820

Journal article

ALFORD NEIL MCNEILL, PENN STUART JAMES, 1999, Ceramic composites; resonators, GB2338478

Patent

Penn SJ, Alford NM, Bracanovic D, Esmail AA, Scott V, Button TWet al., 1999, Thick film YBCO receive coils for very low field MRI, 1998 Applied Superconductivity Conference, Publisher: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, Pages: 3070-3073, ISSN: 1051-8223

Conference paper

Oduleye OO, Penn SJ, Alford NM, Le Lay L, Beales Tet al., 1999, Thermal cycling, critical current vs. strain, and finite element modelling of 1, 7, 19 and 37 filament Ag/Bi-Sr-Ca-Cu-O (BSCCO) tapes, 1998 Applied Superconductivity Conference, Publisher: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, Pages: 2621-2624, ISSN: 1051-8223

Conference paper

Hossain AKMA, Cohen LF, Kodenkandeth T, MacManus-Driscoll J, Alford NMet al., 1999, Influence of oxygen vacancies on magnetoresistance properties of bulk La0.67Ca0.33MnO3-delta, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, Vol: 195, Pages: 31-36, ISSN: 0304-8853

Journal article

Akther Hossain AKM, Cohen LF, Damay F, Berenov A, MacManus-Driscoll J, Alford NM, Mathur ND, Blamire MG, Evetts JEet al., 1999, Influence of grain size on magnetoresistance properties of bulk La<inf>0.67</inf>Ca<inf>0.33</inf>MnO<inf>3-δ</inf>, Journal of Magnetism and Magnetic Materials, Vol: 192, Pages: 263-270, ISSN: 0304-8853

The magnetic and magnetoresistive properties of six polycrystalline bulk samples of nominal chemical composition La0.67Ca0.33MnO3-δ and varying grain size (3.3 μm-20.4 μm), were investigated. Although the Curie temperature, Tc, is independent of grain size, the variation of the saturation magnetisation with grain size depends on the magnetic history. At 20 K and 8 T applied field, the magnetisation decreases as the grain size increases. An approximate linear variation of resistivity and magnetoresistivity with grain size allows the use of a simple 1D model to extract the intrinsic grain magnetoresistance for these materials at Tc and to separate the grain and grain boundary resistivity contributions. The relationship between resistivity and magnetisation is discussed. © 1999 Elsevier Science B.V.

Journal article

Hossain AKMA, Cohen LF, Damay F, Berenov A, MacManus-Driscoll J, Alford NM, Mathur ND, Blamire M, Evetts JEet al., 1999, Influence of grain size on magnetoresistance properties of bulk La0.67Ca0.33MnO3-delta, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, Vol: 192, Pages: 263-270, ISSN: 0304-8853

Journal article

Moreno JMC, Guiu F, Meredith M, Reece MJ, Alford NM, Penn SJet al., 1999, Anisotropic and cyclic mechanical properties of piezoelectrics-compression testing, ELECTROCERAMICS VI 98, Publisher: ELSEVIER SCI LTD, Pages: 1321-1324, ISSN: 0955-2219

Conference paper

Xiaoru W, Templeton A, Penn SJ, Alford NMNet al., 1998, Dielectric loss of single crystal and polycrystalline TiO<inf>2</inf>, Pages: 183-188, ISSN: 0272-9172

Dielectric loss of single crystal and polycrystalline TiO2 has been studied. In polycrystalline TiO2 the dielectric loss is determined by both the microstructure and by the oxygen stoichiometry. Experiments have been carried out to determine the influence of both the microstructure (particularly porosity) and the oxygen stoichiometry. The TiO2 powder has been doped with partially stabilised zirconia, an oxygen ion conductor, in order to modify the oxygen stoichiometry. Sintered discs have been examined for loss as a function zirconia doping, pore volume and as a function of temperature. The behaviour of the doped and undoped titania powders is significantly different. Since many microwave dielectric materials contain Ti eg Ba-Ti-O, Ba-Nd-Ti-O, (Ba-RE-Ti-O, RE=Rare Earth), Zr-Sn-Ti-O etc it is essential to understand the role of the titanium, particularly as it can exist in mixed valence states, and the role of oxygen and its influence on the dielectric loss.

Conference paper

Alford NMN, Penn SJ, Templeton A, Wang X, Filhol P, Klein N, Zuccaro C, Gallop JCet al., 1998, Very low loss ceramic dielectric resonator materials, Pages: 189-194, ISSN: 0272-9172

Certain dielectric oxide single crystals display very low loss at microwave frequencies and on cooling the loss is generally observed to drop. In this paper, the loss of polycrystalline ceramics of Al2O3, Ba(Mg1/3Ta2/3)O3(BMT) and Zr0.875Sn0.25Ti0.875O4(ZTS) has been studied. Alumina, Al2O3has been studied as a model material for dielectric loss. Theory predicts that the loss in single crystal sapphire should follow a T5dependence. However at low temperatures the loss is dominated by extrinsic losses due to crystal imperfection, residual dopant atoms, dislocations and other lattice defects and the T5dependence does not hold. In polycrystalline alumina the intrinsic loss is immediately masked by these extrinsic losses, even at room temperature, and a simple T dependence is observed. Results on polycrystalline alumina show that a Q of > 5×104at 10 GHz and at room temperature are possible and Q's well in excess of 105at 10 GHz and 77 K can be achieved.

Conference paper

Ghivelder L, Castillo IA, Alford NM, Tomka GJ, Riedi PC, MacManus-Driscoll J, Hossain AKMA, Cohen LFet al., 1998, Specific heat of La1-xCaxMnO3-delta, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, Vol: 189, Pages: 274-282, ISSN: 0304-8853

Journal article

Oduleye OO, Penn SJ, Alford NM, 1998, The mechanical properties of (Bi-Pb)SrCaCuO, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, Vol: 11, Pages: 858-865, ISSN: 0953-2048

Journal article

Alford NM, Templeton A, Penn SJ, 1998, A simple process for manufacturing barium zirconate crucibles, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, Vol: 11, Pages: 703-703, ISSN: 0953-2048

Journal article

BUTTON TIMOTHY W, ALFORD NEIL, 1998, Method of producing high-temperature superconducting materials

Patent

Alford NMN, Penn SJ, Templeton A, Wang X, Webb SJet al., 1998, Effect of processing on the dielectric properties of ceramic dielectric resonator materials, Workshop on Growth and Processing of Materials for Electronics at Materials Congress 98, Publisher: INST MATERIALS, Pages: 117-123

Conference paper

Oduleye OO, Penn SJ, Alford NM, 1998, Elastic modulus, mode I (opening) fracture toughness and the critical defect size of Bi(Pb)SrCaCuO extruded rods., Workshop on Growth and Processing of Materials for Electronics at Materials Congress 98, Publisher: INST MATERIALS, Pages: 108-116

Conference paper

Alford NMN, Penn SJ, Templeton A, Wang X, Gallop JC, Klein N, Zuccaro C, Filhol Pet al., 1997, Microwave dielectrics, IEE Colloquium (Digest), ISSN: 0963-3308

In the last 20 years the field of microwave communications has seen exceptional growth. It has been estimated that there are over 55,000 new users of cellular communications every day1. This is largely due to the wish of most people for mobility as a key feature of communications. This growth places an enormous burden on the filters to the extent that filters using current technology simply cannot cope with the increased traffic demand. There is a requirement for systems with lower insertion loss, steeper filter skirts, better selectivity and ideally all of these with miniaturisation. In this paper, dielectric resonators are discussed. The interest in dielectric resonators is a direct consequence of the hurdles facing current technology. Dielectric resonators are now being developed with extremely attractive properties as well as the inherent potential for miniaturisation. The key properties are seen to be the dielectric loss (tan δ) the dielectric constant (ε') and the temperature coefficient of the resonant frequency (TCf).

Journal article

Button TW, Smith PA, McN Alford N, Greed RB, Adams MJ, Nicholson BFet al., 1997, HTS cavities for low phase noise oscillator applications, IEEE Transactions on Applied Superconductivity, Vol: 7, Pages: 3064-3066, ISSN: 1051-8223

The origins of phase noise in oscillator systems are reviewed. A simple self-excited 7. 5Ghz oscillator incorporating either a conventional metal cavity resonator or a high temperature superconducting (HTS) cavity has been produced. Comparative measurements made at 77K demonstrate significant improvements in the close-to-carrier noise performance of the oscillator incorporating the HTS cavity; lOdB at a 10kHz offset rising to more than 25dB at a lOHz offset. The unloaded Q of the HTS cavity doubled to >ltf on cooling from 77K to 64K suggesting that further improvements in noise performance could be achieved. © 1997 IEEE.

Journal article

Penn SJ, Alford NMN, Button TW, 1997, High Q dielectric resonators using ybaicuaox thick films and polycrystalline dielectrics, IEEE Transactions on Applied Superconductivity, Vol: 7, Pages: 3500-3503, ISSN: 1051-8223

The combination of high Q dielectric resonators and high temperature superconducting (HTS) films offer many advantages in the area of cellular and satellite communications. The high cost of single crystal dielectrics and HTS thin films may be unattractive in certain applications. Superconducting thick films and polycrystalline ceramic dielectrics offer a high performance low cost alternative to high Q thin film/single crystal dielectric resonators. Results on polycrystalline dielectrics show that g's well in excess of 10s at 10 GHz and 77 K can be achieved in a design made compact by the use of a HTS thick film shield. © 1997 IEEE.

Journal article

Penn S, Alford NMN, Centeno AE, Parker JRet al., 1997, Application of low loss dielectric and high temperature superconducting materials in microwave filters, IEE Colloquium (Digest), ISSN: 0963-3308

Recently cryogenically cooled low loss dielectric materials and high temperature superconducting films have received much attention. This presentation reports on the latest dielectric materials and on the possible electrical designs of electrically small filters using these novel materials. © 1997 The Institution of Electrical Engineers. Printed and published by the IEE.

Journal article

Penn SJ, Alford NMN, Templeton A, Klein N, Gallop JC, Filhol P, Wang Xet al., 1997, Low loss ceramic dielectrics for microwave filters, IEE Colloquium (Digest), ISSN: 0963-3308

Certain dielectric oxide single crystals display very low loss at microwave frequencies. On cooling the loss is generally observed to drop. The Q of sapphire at 10 GHz exceeds 106at low temperatures of around 10K. However, single crystals are expensive and the purpose of this research is to explore inexpensive, sintered polycrystalline alternatives. By very careful attention to purity, processing and microstructure Q values approaching those of single crystals have been achieved. The loss of polycrystalline ceramics of Al2O3, Ba(Mg1/3Ta2/3)O3(BMT) and Zr0.875Sn0.25Ti0.875O4(ZTS) has been studied Alumina, Al2O3has been studied as a model material for dielectric loss. Theory predicts that the loss in single crystal sapphire should follow a T5dependence. However at low temperatures the loss is dominated by extrinsic losses due to crystal imperfection, residual dopant atoms, dislocations and other lattice defects and the T5dependence does not hold. In polycrystalline alumina the intrinsic loss is immediately masked by these extrinsic losses, even at room temperature, and a simple T dependence is observed. Results on polycrystalline alumina show that a Q of > 5×104at 10 GHz and at room temperature are possible and Q's well in excess of 105at 10 GHz and 77 K can be achieved in a design made compact by the use of a HTS thick film shield.

Journal article

Alford NM, Penn SJ, Templeton A, Wang XRet al., 1997, Low loss sintered dielectric resonators with HTS thick films, JOURNAL OF SUPERCONDUCTIVITY, Vol: 10, Pages: 467-472, ISSN: 0896-1107

Journal article

ALFORD NEIL MCNEILL, PENN STUART JAMES, 1997, IMPROVED SINTERED MATERIALS, WO9723430

Patent

Penn SJ, Alford NM, Templeton A, Wang XR, Xu MS, Reece M, Schrapel Ket al., 1997, Effect of porosity and grain size on the microwave dielectric properties of sintered alumina, JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Vol: 80, Pages: 1885-1888, ISSN: 0002-7820

Journal article

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