High Temperature Dielectric Property Measurements - An Insight into Microwave Loss Mechanisms in Engineering Ceramics

1994 ◽  
Vol 347 ◽  
Author(s):  
J. G. P. Binnen ◽  
T. E. Cross ◽  
N. R. Greenacre ◽  
M. Naser-Moghadasi

ABSTRACTIt is now possible, in a number of laboratories worldwide, to make microwave dielectric property measurements at temperatures up to about 1500°C. These measurements have shown that the loss tangent, tanδ, of a wide range of engineering ceramics increases dramatically at elevated temperatures. The interaction between the ceramic material and the impurities present during processing can have a dramatic effect on both the ease with which the material is able to extract energy from the microwave field and on the properties of the final ceramic. While the effect of impurities on the ceramic properties is relatively well understood the effect of impurities on the microwave loss mechanisms at elevated temperatures is not. This paper will review some of the recent work on the high temperature microwave dielectric property measurements performed at Nottingham.

2013 ◽  
Vol 2013 (HITEN) ◽  
pp. 000046-000055
Author(s):  
John R. Fraley ◽  
Edgar Cilio ◽  
Bryon Western

In recent years, high temperature magnetic structures have been developed and used for inductors and transformers in high temperature applications ranging from power electronics to wireless telemetry systems. Research in the high temperature magnetics field has led to the development of more advanced magnetic structures that can enable diverse applications ranging from regulators to amplifiers, with far reaching implications for the high temperature electronics community. Current high temperature electronics have shown potential in lab and rig tests, but high temperature electronics systems suffer from the relatively limited lifetime of the semiconductor devices themselves. The advanced magnetics discussed in this paper can be designed to have extreme lifetime capabilities even at elevated temperatures, and as such can have an immediate impact on the implementation of true field deployable high temperature electronic systems. Aerospace, power generation, and automotive industries may especially benefit from this technology, as significant advances in health monitoring and active engine control will be enabled by these advanced magnetic structures. A theoretical understanding of these advanced magnetic structures is necessary for initial design and feasibility, while the true development and implementation of this technology depends on state of the art high temperature packaging approaches. By combining high temperature, grain-oriented magnetic materials along with high temperature packaging processes, APEI, Inc. has created advanced high temperature magnetic systems that indicate the technology described in this paper is a viable one, with applications across a wide range of high temperature electronics systems.


2006 ◽  
Vol 424 (1-2) ◽  
pp. 388-393 ◽  
Author(s):  
Ryosuke Umemura ◽  
Hirotaka Ogawa ◽  
Atsushi Yokoi ◽  
Hitoshi Ohsato ◽  
Akinori Kan

2007 ◽  
Vol 336-338 ◽  
pp. 307-309 ◽  
Author(s):  
Jun Qi Li ◽  
Fa Luo ◽  
Dong Mei Zhu ◽  
Wan Cheng Zhou

This paper presents the microwave dielectric property of porous silicon nitride ceramics at a frequency of 9360 MHz, which were fabricated by the nitridation of silicon powder. The porous ceramics with different volume fraction of porosity from 18.6% to 56.2% were produced by adding different amount of the pore-forming agent into the initial silicon powder. Microstructural analysis revealed a dense matrix containing large pores and cavities with needle-shaped and flaky β-Si3N4 grains distributing in it. The results showed that the dielectric constant of the ceramics reduces with the porosity increases. With the addition of α-Si3N4 powder in the raw silicon powder, the nitridation rate is raised, and the dielectric constant and the dielectric loss of the ceramics decrease notablely.


Author(s):  
D. Filsinger ◽  
A. Schulz ◽  
S. Wittig ◽  
C. Taut ◽  
H. Klemm ◽  
...  

A further increase of thermal efficiency and a reduction of the exhaust emissions of ground based gas turbines can be achieved by introducing new high temperature resistant materials. Therfore, ceramics are under international development. They offer excellent strengths at room and elevated temperatures. For gas turbine combustor applications, however, these materials have to maintain their advantageous properties under hostile environment. For the assessment and comparison of the oxidation behavior of different nonoxide ceramic materials a test rig was developed at the Institute for Thermal Turbomachinery (ITS), University of Karlsruhe, Germany. The test rig was integrated into the high temperature/ high pressure laboratory. A ceramic model combustion chamber was designed which allowed the exposure of standard four-point flexure specimens to the hot combustion gas flow. Gas temperatures and pressures could be varied in a wide range. Additionally, the partial steam pressure could be adjusted to real combustor conditions. The present paper gives a detailed description of the test rig and presents results of 100 hours endurance tests of ceramic materials at 1400°C. The initial strengths and the strengths after oxidation tests are compared. In addition to this, photographs illustrating the changes of the material’s microstructure are presented.


2019 ◽  
Vol 112 ◽  
pp. 103366 ◽  
Author(s):  
Banu Saçlı ◽  
Cemanur Aydınalp ◽  
Gökhan Cansız ◽  
Sulayman Joof ◽  
Tuba Yilmaz ◽  
...  

2007 ◽  
Vol 22 (10) ◽  
pp. 2676-2684 ◽  
Author(s):  
A.N. Salak ◽  
V.M. Ferreira ◽  
L.G. Vieira ◽  
J.L. Ribeiro ◽  
R.C. Pullar ◽  
...  

Dielectric response of the perovskite ceramics (1–x)La(Mg1/2Ti1/2)O3–x(Na1/2Bi1/2)TiO3 [(1–x)LMT–xNBT] (0 ⩽ x ⩽ 0.6) has been characterized at radio, microwave, and far infrared frequency ranges. Temperature variations of the dielectric permittivity and loss estimated by different methods were compared and analyzed. It was revealed that the low temperature dielectric response of the compositions with x ⩾ 0.2 is frequency-dependent over a wide range (102–109 Hz) below the resonant frequencies of the polar phonon modes. Contributions of different factors (both extrinsic and intrinsic) to the microwave dielectric loss of the ceramics were considered. The dielectric relaxation has been associated with the amount of bismuth in the system. The relaxation in LMT–NBT was considered in the context of similar effects observed in other Bi-containing, A-site disordered oxygen-octahedral compositions.


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