Content uploaded by M. A. S. Silva
Author content
All content in this area was uploaded by M. A. S. Silva on Sep 19, 2015
Content may be subject to copyright.
A preview of the PDF is not available
An alternative method for the measurement of the microwave temperature coefficient of resonant frequency (τf)
Abstract and Figures
In this paper an alternative method for the measurement of the temperature coefficient of resonant frequency (τf), is presented. The traditional method (based on the Courtney method) present some limitations of measuring the values of τf, for samples with high dielectric loss due to their inability to observe clearly the TE011 mode. The alternative experimental setup, to measure the τf value, is based on the variation of the temperature of the dominant mode of a dielectric resonator antenna. The method is quite compatible with the measurement of τf, based on the Courtney method. It presents the advantage that it is less sensitive to the sample loss. In the studied samples, with loss higher than 10−2, the τf were obtained. Samples of known τf were measured in both methods, using the configuration proposed by Courtney and the present study. The alumina (Al2O3) and calcium titanate (CaTiO3) were selected because they have well known values of τf and have low dielectric losses, the bismuth niobate and titanium (Bi3NbTiO9) was chosen because it is not possible to measure its τf by the traditional method due to its high dielectric loss. The obtained results, by measuring, the τf value of CaTiO3 and Al2O3, in this proposed method, present excellent agreement when compared to the traditional Courtney, transmission method. It was also very efficient for measurements of the τf value, of high dielectric loss materials (>10−2), as for the bismuth and titanium niobate (Bi3NbTiO9). The analysis of the temperature coefficient of resonant frequency (τf) in dielectric resonators is an important property for the development of electronic devices. This is because the τf is a fundamental parameter, for the production of new components like filters, oscillators and antennas, with high thermal stability.
Figures - uploaded by M. A. S. Silva
Author content
All figure content in this area was uploaded by M. A. S. Silva
Content may be subject to copyright.
... The dielectric properties in the microwave region were measured using the Hakki-Coleman method by employing the vector network analyzer in Agilent model N5230C. The Silva-Fernandes-Sombra method [27] was employed to obtain the temperature coefficient of resonant frequency (τ f ) for each of the systems evaluated. ...
... Another important parameter for microwave dielectric ceramics is the temperature coefficient of the resonant frequency (τ f ) because this parameter indicates the stability of the ceramic material when subjected to temperature variation. τ f was obtained using the Silva-Fernandes-Sombra method [27]. Table 2 shows that the τ f values were negative for the composites because ZNO and ZTNO have negative τ f values (TiO 2 reacted completely with ZNO to form ZTNO, as shown by the X-ray diffraction results) [24,28]. ...
... Impedance spectroscopy was used to analyze the dielectric properties of the material in the radiofrequency range, where data were obtained through an impedance analyzer (model Solartron 1260) as a function of frequency (1 Hz-1 MHz) in the temperature range of 380-460 • C. Evaluation of the dielectric properties in the Microwave region (MW) was performed by Hakki-Coleman method using the network analyzer of Agilent model N5230A. To determine the temperature coefficient of resonant frequency (τ f ) and so evaluate the thermal stability of materials the Silva-Fernandes-Sombra (SFS) method [15] was employed. The refinement parameters obtained for the synthesized MNO sample were R WP = 5.13 %; χ 2 = 2.05; and R Bragg = 10.07 %, demonstrating that the refinement carried out is adequate. ...
... The thermal stability of the material was determined using the SFS method, 32,33 in which the DRA is fed laterally by an SMA probe coupled to a ceramic oven. The τ f shows the evolution of the resonance frequency with temperature variation and the mode used was HE 11δ , which is easy to detect, even for materials. ...
This work studies the dielectric properties in the microwave region (MW) of the Ba2TiSi2O8 (BTS) ceramic with TiO2 additions and its applications as a dielectric resonator antenna (DRA). In this study, structural characterization through x-ray diffraction (XRD) is performed and the Rietveld refinement is used to confirm the phases formed. Analysis of the morphology of the materials is performed using scanning electron microscopy (SEM). The resonant frequency temperature coefficient (τf) reveals a variation from − 47.0 ppm°C−1 to + 16.5 ppm°C−1. The dielectric properties in the MW region reveal an increase in the dielectric permittivity (εr) and a decrease in the loss tangent (tanδ) of the samples. Numerical simulation shows good fits of the experimental data, with gain and directivity standing out, ranging from 4 dBi to 6 dBi and radiation efficiency below 80%. The results demonstrate that the samples can operate in C-band electronics, Wi-Fi devices, meteorological radar systems, etc.
... Three essential parameters of microwave dielectric ceramics, including; dielectric constant, quality factor, and temperature coefficient of resonant frequency, should be integrated and incorporated to justify new demands [1][2][3][4][5][6]. Many microwave dielectric ceramics with high dielectric constant and high-quality factors, such as CaTiO 3 [7] and Ba 2 Ti 9 O 20 [8], have been developed for different new applications. However, many devices, such as phase shifters, need new materials with low dielectric constant and high quality factor. ...
In this work, the microstructure and microwave dielectric properties of novel MgTiO3-x wt% MgAl2O4 (x = 5, 10, 15, 20) composite ceramics were investigated. MgTiO3 and MgAl2O4 compounds were synthesized by conventional solid-state reaction method and the composites were fabricated by wet mixing, pressing in die and sintering in the temperature range of 1200–1350 oC for 5 h in air. X-ray analysis of the sintered sample proved that no reaction occurred between the two phases during sintering process. The results proved that sinter-ability of MgTiO3 is improved by adding MgAl2O4 second phase up to 10 wt% and for more than it, sintered density of the fabricated composite decreased due to higher refractoriness of MgAl2O4 phase. Dielectric constant of the fabricated composites decreases from around 16.4 to 15 by increasing the amount of secondary phase from 0 to 20 wt% and nearly follow a linear relation in semi logarithmic scale. The temperature coefficient of resonant frequency became more negative by increasing the amount of used MgAl2O4. The quality factors values were determined in the range of 140,000–160,700 GHz, reaching the maximum of 160,700 GHz for the composite includes 10 wt% of MgAl2O4 second phase.
... The values of τ f were calculated over a temperature range from 30 to 80 °C by Silva-Fernandes-Sombra (SFS) method [22]. The dielectric resonator antennas (DRA) measurements were also performed using an Agilent Network Analyzer, Model PNA N5230A. ...
A series of MCuSi4O10 (M = Ca²⁺, Sr²⁺ and Ba²⁺) electroceramics have been prepared by solid-state reaction and sintered at 1150 (CCSO (CaCuSi4O10)), 1100 (SCSO (SrCuSi4O10)), and 1150 °C (BCSO (BaCuSi4O10)). The structure and dielectric properties of the samples were studied by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), impedance spectroscopy at radiofrequency (RF) and dielectric resonator antenna (DRA) at microwaves. The electroceramics presented values of thermo-activated process and activation energy (Ea) between 0.65 and 1.66 eV. In addition, fitting plots showed the equivalent circuit consisting of two parallel (R/CPE) connected in series, which is associated with the grain and grain boundary electrical contributions. The microwave dielectric properties showed dielectric constant (εr) of 3.47, 5.04, and 5.40 and quality factor (Q x f) of 11,350.00, 11,438.60, and 28,983.00 GHz for CCSO, SCSO, and BCSO, respectively. All the samples have a great potential for microwave applications, especially the CCSO- and BCSO-based DRA, due to the near-zero temperature coefficient of resonant frequency (τf) values (− 2.24 and − 7.41 ppm.°C⁻¹, respectively). The preliminary results indicate that MCuSi4O10 electroceramics are satisfactory for use as a commercial antenna for C- and X-band applications.
In this article, the dielectric properties of a Li4Ti5O12 (LTO) ceramic at the radio frequency (RF) and microwave (MW) regions were evaluated. X-ray diffraction showed that LTO was obtained without the presence of spurious and/or secondary phases. Complex impedance spectroscopy (CIS) analysis was conducted, whereas an activation energy (Ea) of 0.88 eV was observed. The temperature capacitance coefficient (TCC) was also calculated and demonstrated that LTO could be employed as a Class 1 ceramic capacitor. In the MW region, LTO presented ε’r = 25.4, tan δ = 5.7 × 10–4, and τf = -14.5 ppmºC−1, values that are interesting for devices that operate in the MW region. Numerical simulation demonstrated values of a realized gain of 4.78 dBi, a bandwidth of 227 MHz, and a radiation efficiency of 98%. Moreover, LTO was evaluated as a temperature sensor operating in the MW region and demonstrated a sensitivity of -0.06 MHz ºC−1. The values presented demonstrate that LTO could be employed in devices that operate in RF and MW regions.
This work presents experimental and numerical investigations of the microwave dielectric properties of the ceramic matrix CaMoO4 (CMO) with the addition of 8, 12, and 20 wt% TiO2, obtained through the solid-state reaction method. X-ray diffraction and Rietveld’s refinement revealed no evidence of secondary phases, indicating no reaction between the CMO and TiO2 phases. The dielectric properties presented an improvement with the addition of TiO2, with the CMO8 sample presenting εr′ = 12.8, tan δ = 7.8 × 10–4, and τf = − 6 ppm°C−1, demonstrating that this material has thermal stability (τf < 0). The ceramic was tested as a dielectric resonator antenna (DRA) and numerical simulation results showed that the materials have a realized gain of 4.40–4.92 dBi, a bandwidth of 741‒1079 MHz, and a radiation efficiency above 86%. The results indicate that CMO‒TiO2 systems could be employed in devices operating in the S-band.
This paper reviews the dielectric properties of Sr2TiSi2O8 (STS) ceramic in the radio frequency (RF) and microwave (MW) regions. X-ray diffraction (XRD) analysis is used to demonstrate that a small secondary phase of SrTiO3 is present in a synthesised STS ceramic. Complex impedance spectroscopy is performed, and the typical permittivity values of ceramic materials are observed. Nyquist diagrams are fitted based on an equivalent circuit using two associations of R-CPE related to the grain and the grain boundary effects. A dependence study of the changes in AC conductivity with frequency at different temperatures demonstrates that the conduction process is thermally activated, and a value of 1.0 eV is obtained for the activation energy. In the MW range, we observe values of εr = 12.7, tan δ = 0.0139 , and τf =-6.1 ppm/°C, indicating interesting properties for applications in devices that operate in the MW region. A numerical simulation is employed to evaluate STS ceramic as a dielectric res-onator antenna, and we observe a reflection coefficient of below-10 dB, a realised gain of 4.6 dBi, a bandwidth of 475 MHz, and a radiation efficiency of around 75%. The properties of the STS matrix presented here indicate that this ceramic would be a suitable candidate for the operation of devices in the C-band, as well as in devices operating in the RF range.
Herein, we report a study on the suitability of the Sr3Mo1‐xWxO6 (0.1 ≤ × ≤ 0.9) solid‐solution system for radio frequency and microwave (MW) applications. The ceramic powders were synthetized via solid‐state reaction at 1423 K for 6 h. X‐ray diffraction and scanning electron microscopy were performed to confirm the double‐perovskite‐type structure and investigate the surface morphology, respectively. Electrical characterization of the system as a function of temperature was performed using impedance spectroscopy. The equivalent circuit with two parallel association resistor‐constant phase element (R‐CPE), connected in series, associated with grain and grain boundary effects was used to adjust the electric response of the solid solutions. Sr3Mo0.9W0.1O6 solid solution exhibited a resonant frequency temperature coefficient (τ f ) value close to zero (8.5 ppm K‐1), showing a great potential for MW applications. This article is protected by copyright. All rights reserved.
The discipline of antenna theory has experienced vast technological changes. In response, Constantine Balanis has updated his classic text, Antenna Theory, offering the most recent look at all the necessary topics. New material includes smart antennas and fractal antennas, along with the latest applications in wireless communications. Multimedia material on an accompanying CD presents PowerPoint viewgraphs of lecture notes, interactive review questions, Java animations and applets, and MATLAB features. Like the previous editions, Antenna Theory, Third Edition meets the needs of electrical engineering and physics students at the senior undergraduate and beginning graduate levels, and those of practicing engineers as well. It is a benchmark text for mastering the latest theory in the subject, and for better understanding the technological applications.
An Instructor's Manual presenting detailed solutions to all the problems in the book is available from the Wiley editorial department.
Focusing on the design of microwave circuits and components, this valuable reference offers professionals and students an introduction to the fundamental concepts necessary for real world design. The author successfully introduces Maxwell's equations, wave propagation, network analysis, and design principles as applied to modern microwave engineering. A considerable amount of material in this book is related to the design of specific microwave circuits and components, for both practical and motivational value. It also presents the analysis and logic behind these designs so that the reader can see and understand the process of applying the fundamental concepts to arrive at useful results. The derivations are well laid out and the majority of each chapter's formulas are displayed in a nice tabular format every few pages. This Third Edition offers greatly expanded coverage with new material on: Noise; Nonlinear effects; RF MEMs; transistor power amplifiers; FET mixers; oscillator phase noise; transistor oscillators and frequency multiplier.
The perovskite-layered ceramics of Bi3NbTiO9 (BNT), also known as Aurivillius phase, was obtained. The process of preparation was investigated by X-ray diffraction method. The synthesis of BNT was carried out according to the solid-state reaction from the conventional mixture of oxides (Bi2O3, TiO2, Nb2O5) within the temperature range TS=400–1200°C. The influence of addition of NaCl on the process of synthesis was also investigated. It was found that above TS=900°C the ratio of the Bi3NbTiO9 phase was almost 90% and the admixture of NaCl decreased the synthesis temperature. Dependence of the amount of the BNT phase in the bulk material versus the temperature of synthesis is given. Evolution of the structural parameters of BNT and NaCl - modified BNT at different synthesis temperatures was shown as well as recording of Raman scattering spectra.
Bi3NbTiO9 (BNT) ceramic materials with the density ratios of 95–97% to the theoretical density were prepared by the conventional mixed-oxide method. The Curie temperature (Tc), 914°C was found to be almost the highest one among those of all the ceramics known to date. The crystal structure of the ceramic was investigated by X-ray diffraction method. Anisometric plate-like crystalline grains were observed, which revealed the layered structure of the material. The temperature dependence of the electrical resistivity was measured. For the first time the dielectric properties of Bi3NbTiO9 in the vicinity of its transition temperature were measured. Finally, the hysteresis (P–E) loop measurement showed a good ferroelectricity in the Bi3NbTiO9 ceramics, and the piezoelectric constant (d33) was found to be 7pC/N.
The obtention of reliable and high performance piezoelectric ceramics for uses at high temperatures is still an open issue in the field of electroceramics. The materials used nowadays for such applications present limitations due to different causes: low piezoelectric coefficients, difficulties in processing that lead to the necessary use of single crystals, high cost of raw materials and more. In this sense, an increasing interest in materials with the so-called Aurivillius-type structure has occurred during recent years, due to their relatively high piezoelectric coefficients and high ferro–paraelectric phase transition temperature. However, some difficulties must be overcome, such as processing for obtaining highly dense ceramics and determining their real piezoelectric behaviour at high temperature. In this work, a review of the processing and properties of ceramics with this structure is shown. Effects of the use of precursors obtained by an alternative route mechanical activation on the microstructure are explained. A complete piezoelectric characterization at working temperatures (>300 °C), barely found in the literature, is also shown. The effects of trapped charges in the dielectric permittivity and in the piezoelectric radial resonance are also discussed.
The intrinsic temperature coefficient of the resonant frequency TCf0, which is defined as the temperature coefficient of a resonant frequency when all the stored energy is confined inside a dielectric rod, is introduced to evaluate the temperature dependences of dielectric materials. The temperature coefficient of the resonant frequency TCf for a dielectric rod resonator can be estimated accurately from the TCf0 value. Actually, for shielded dielectric resonators of three types; parallel plate, image, and MIC types, it is shown that the TCf values can be estimated with the error of ±0.7 ppm/°C from the measured TCf0 value having the experimental error of ±0.5 ppm/°C
Ferroelectric ceramics of (Bi3TiNbO9)x(SrBi2Nb2O9)1−x compositions are proposed in this work for use as high temperature piezoelectrics. Novel compositions with x>0.40 have been processed and studied. This type of compound grows in lamellar crystals, resembling their layered Aurivillius type structure, with the perovskite c-axis perpendicular to the major surfaces, which tend to pile up with the c-axis parallel to the applied pressure when ceramics are obtained by hot pressing. Such texture does not favor the ferro-piezoelectric properties. Isotropic ceramics with low porosity were processed by natural sintering of a mechanochemically activated oxide mixture. Optical microscopy and computer-aided image analysis and measurements were used in the characterization of the ceramic microstructure. Ceramics with transition temperatures in the range of 420°C≲Tt≲900°C can be obtained. Ferro-piezoelectric characterization shows that ceramics with x=0.60 present Tt=700°C, d33=11 pC N−1 and Kt=9.45%, which make them good candidates to be tested as high temperature piezoelectrics.