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In this paper is reported an experimental and numerical investigation of the microwave dielectric properties of Na2Nb4O11 (NN), ceramic matrix added with (0, 2, 5, and 10 wt%) of Bi2O3, obtained through a new procedure based on the solid-state method. The experimental and theoretical characteristics of the resonator like return loss, bandwidth, inp...
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... drying and calcined at 9508C for 3h with heating/cooling rate of 58 min 21 . Table 1 shows the results of samples that were prepared and added with Bi 2 O 3 for different percentages (0, 2, 5 and 10 wt%). The calcined powders were cold pressed into cylindrical pellets of 12 mm diameter and 1.2-1.3 ...
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Citations
... On this basis, it is possible to combine two or more different ceramics to make new materials with improved dielectric properties. Bi 2 O 3 is chosen here due to its interesting dielectric properties (high r , low loss and τ f < 0) [6,[15][16][17]. ...
In this work, the influence of the addition of Bi2O3 on the dielectric properties in the microwave range of BiCu3Ti3FeO12 (BCTFO) ceramic matrix and its potential application as a dielectric resonator antenna are analysed. X-ray diffraction shows that a reaction between BCTFO and Bi2O3 occurs that results in the formation of new crystalline phases. The morphology of the samples is studied by field-emission scanning electron microscopy and demonstrates a dependence of the grain size on the Bi2O3 content. From the Mössbauer spectro-scopic analysis, it is found that the Fe3+ ions replace the Ti4+ in the crystalline structure. The addition of Bi2O3 also reduces the dielectric permittivity (r), dielectric loss (tan δ) and the coefficient of the resonance frequency (τ f) values. Finally, numerical simulations are carried out in order to obtain the antenna parameters and they demonstrate that BCTFO could be a potential candidate for devices operating in the S-band.
... These results suggest its potential use for miniaturization of devices operating in this range, and BCTFO also presented higher relative dielectric permittivity compared to other ceramics [4]. For s f , although the higher positive value indicates BCTFO is thermally unstable, it makes BCTFO a good candidate for formulating new, thermally stable composites with other ceramic oxides, such as NdAlO 3 , LaAlO 3 , PbZrO 3 -CeO 2 [4] and Na 2 Nb 4 O 11 [30], in processes based on Silva et al. [31]. ...
In the present work, an electroceramic of the perovskite family, BiCu3Ti3FeO12 (BCTFO), was synthesized by the solid-state reaction method. The structural study was performed by X-ray diffraction and Mössbauer and Raman spectroscopy. Electric and dielectric properties were analyzed by impedance spectroscopy and the Hakki-Coleman method. Due to the BCTFO is isostructural of the CaCu3Ti4O12 (CCTO), the BCTFO presents as a promissory electroceramic. Mössbauer spectroscopy reveals paramagnetic spectra to BCTFO, with two octahedral sites for iron ions. Regarding dielectric properties, for 1 Hz, BCTFO presents a high relative dielectric permittivity (εr ≈ 1 × 104) and dielectric loss (tan δ > 1) and εr = 230.88, tan δ ≈ 1 × 10–2 in the microwave range. The produced ceramic exhibited a high resonance frequency temperature coefficient (τf) with a value of + 2852 ppm °C−1, making it a candidate for fabrication of the thermostable electroceramic composites with other ceramic matrices with negative τf values improving the thermal stability.
... The Smith chart also shows that the values of the impedances are close to the characteristic impedance value of 50 Ω, that is it can be considered that at respective resonance frequencies, all the antenna can achieve a maximum power transfer among the antenna. The transmission system [44] and the impedance lines obtained by the relation Z = R + jX, representing each antenna studied, are indicated in Table 5. It can be observed in Fig. 7 and Table 5 that all studied antennas have values in X, negative, representing a capacitive reactance for BVO, BVZ25, and BVZ75 [36,41,42], and positive or inductive reactance for BVZ50. ...
This study reports the dielectric and structural characterisation of composites formed by the mixture of a BiVO4 ceramic matrix with ZnO (25, 50, and 75 wt.%) obtained through a solid-state method procedure for applications in the microwave range. X-ray diffraction is used for structural characterisation. The dielectric properties and temperature coefficient of resonant frequency indicate a composition with ZnO close to zero. Dielectric constants varying with ZnO composition (7 to 67) and dielectric loss of ~ 10−2 are measured, and the results confirm that the ZnO can improve the thermal stability of the composites. The composites are analysed as dielectric resonator antenna, where the experimental and theoretical characteristics of the resonator, like return loss, bandwidth, and input impedance, are in good agreement. Experimentally, for the BiVO4 reference sample, bandwidths of 12.5% and 40.82% are found for the addition of 75 wt.% ZnO for a frequency operation of ~ 5.52 GHz.
... The samples were prepared in a metallic mold with uniaxial constant pressure (98 MPa), followed by sintering at 800 ºC for 4h; this temperature was used in all samples, because of the low sintering temperature of BVO, which has the majority concentration in this compound. The organic binder (PVA) was burned out during sintering in the air atmosphere, and it didn't influence the physical properties of the compounds [19]. To minimise air gaps in samples during the electrical measurement, all ceramic cylinders were polished well. ...
... reactance or inductive reactance [19]. ...
... A C C E P T E D ACCEPTED MANUSCRIPT 33 reactance or inductive reactance [19]. ...
This paper investigated the microwave dielectric properties through the Hakki-Coleman method of BiVO4 ceramic matrix, obtained by the solid-state reaction method, using 8, 16, 24 and 32 wt% of CaTiO3. The X-ray diffraction (XRD) was used for the structural characterisation of the crystalline phases present in ceramic before the sinterisation process. The thermal-stability in microwave range was measured in all dielectric samples, and the temperature coefficient of resonant frequency (τf) was found varying from −244.03 ppm °C⁻¹ to −2.7 ppm °C⁻¹. The CaTiO3 addition reduced the value of the dielectric permittivity (ε’) close to 25% of the BiVO4 values, keeping the dielectric loss (tan δ) around 10⁻³. The experimental and numerical simulated values of the dielectric resonator antenna (DRA) results show the agreement of the input impedance, return loss, bandwidth and radiation patterns. Moreover, all antennae features realised gain above 5dBi. In antenna results, the CaTiO3 addition increased the bandwidth, compared to BiVO4 DRA, that presented bandwidth around 34 MHz.
... In this sense, the research with materials of the ferrite type is important in the study of materials with application in the microwave range 2, 3 . Many studies with ferrites are performed with a FRA because they offer important characteristics such as low ohmic loss, low profile, small size, and wide impedance bandwidth when compared to other antennas 4-6 and have many applications as substrate for thin films, magnetic memory, wireless communications devices among other important applications 7, 8 . Many properties of FRA can be studied by knowing their geometric dimensions, which directly influence the resonant 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 frequency, quality factor and dielectric loss 8 . ...
LiFe5O8 (LFO) spinel-like material has been studied for use in ferrite resonator antennas (FRAs). Antenna parameters such as gain and return loss were greatly affected when an external magnetic field was applied to the FRA. The temperature coefficient of the resonant frequency (τf ) for the FRA presented a value of − 482.16 ppm/°C. The magnetic hysteresis results showed that the LFO was a soft ferrite, considering the values of the remanent magnetization (Mr = 5.95 emu g⁻¹), coercive field (0.76 mT), and saturation magnetization (32.15 emu g⁻¹). The magnetodielectric resonator presented a tuning effect in the resonant frequency as a function of the external magnetic field. The antenna bandwidth was also affected by the presence of the magnetic field. LFO is a soft ferrite with applications in microwave circuits, antennas, and devices for operation at microwave frequencies due to its magnetization and demagnetization properties. Impedance study revealed increasing conductivity from room to higher temperature with low activation energy (0.36 eV).
... Ferrimagnetic materials as the hexagonal-type ferrites can combine the magnetic and insulating properties adequate for these types of applications [2,3]. Ferrite structure of the hexagonal-type may present the general chemical formula MFe 12 O 19 , where M site can be divalent ion with high coordination number (CN) equal to 12. The most common hexagonal ferrites are with M ¼ Ba or Sr. ...
... The most common hexagonal ferrites are with M ¼ Ba or Sr. The SrFe 12 O 19 (SFO) is classified as hard magnet [4], high dielectric constant in radiofrequency (ε r > 100) [5] and temperature coeffi- cient of resonant frequency t f ¼ 44.90 ppm C À1 [6]. The SFO is applied in device operation at radiofrequency and microwave range, as radar detection, antennas etc [5,7e11]. ...
The effects of different BiFeO3 (BFO) additions (0, 20, 40, 60 and 80 wt%) on the SrFe12O19 hexaferrite ceramic matrix (SFO) have been studied by Complex Impedance Spectroscopy (CIS), Mössbauer spectroscopy, magnetic hysteresis and X-Ray Diffraction (XRD) analysis. The solid state reaction method was used for the production of the SFO and BFO, the phase formation was confirmed by the XRD and Rietveld refinement, where the obtained fitting presented an effective refinement. The diffractogram for BFO-SFO composites presented all peaks in agreement with the BFO and SFO phases. The thermo-activated process was studied by the CIS and the Arrhenius equation in the composite series of BFO-SFO with SFO presenting higher values of activation energy between the analyzed samples and the frequency and temperature range studied was 1–10 MHz and 160 °C to 300 °C, respectively. The addition of BFO in the SFO ceramic matrix lead to an improvement of the thermal-stability of the composite, where a signal inversion of Temperature Coefficient of Capacitance (TCC), in the composites, was observed. The Nyquist plots showed the presence of a semicircle that was fitted by an equivalent circuit model using R - CPE association, showing the same profile in all samples. The Mössbauer spectrum of the composites demonstrate the typical five Fe³⁺ site for M-type hexagonal ferrites even after the addition of BFO in a ceramic matrix. The addition of BFO in the formation of composites, with SFO, showed interesting results in the radio frequency range and presented magnetic properties that can be explored in applications in the area of telecommunications, medicine and military industry.
This work presents the dielectric properties of YNbO4 (YNO)-TiO2 composites in the microwave range. X-ray diffraction analysis demonstrates that the addition of TiO2 to YNO results in the formation of a Y(Nb0.5Ti0.5)2O6 phase. In the microwave range, the values of permittivity and dielectric loss did not present major changes with the increment of TiO2. Moreover, the addition of TiO2 results in an improvement in the thermal stability of YNO, with YNO63 demonstrating a resonant frequency of -8.96 ppm.ºC⁻¹. We utilised numerical simulations to evaluate the behaviour of these materials as dielectric resonator antennae and it is found that they exhibit a reflection coefficient below -10 dB at the resonant frequency, with a realised gain of 4.94 to 5.76 dBi, a bandwidth of 665 to 1050 MHz and a radiation efficiency above 84%. Our results indicate that YNO-TiO2 composites are interesting candidates for microwave operating devices.
This work presents the dielectric properties of Ba2TiSi2O8 in the Radiofrequency (RF) and Microwave (MW) regions. X-ray diffraction analysis showed that the material was obtained as a single-phase without the presence of spurious phases. Complex impedance spectroscopy demonstrated that there was no significant change of permittivity with temperature, whereas the dielectric loss was less than 1. Nyquist diagrams were modelled through an equivalent circuit using two associations of R-CPE related to the grain and the grain boundary effects. The MW analysis showed ε′r = 11.01 and tan δ = 4.55 × 10–2, values that are close to the results obtained in the RF region. Moreover, the τf value for Ba2TiSi2O8 was equal to − 47 ppm/°C which is close to the values adequate for a microwave device application. The numerical simulation demonstrated the operation of the material as a Dielectric Resonator Antenna (DRA), where a reflection coefficient below − 10 dB, a realised gain of 6.739 dBi, a bandwidth of 452.96 MHz and a radiation efficiency around 100% were observed. The results indicate that Ba2TiSi2O8 would be an interesting candidate in microwave operating devices in the C-band, as well as in devices operating in RF.
This paper reported the dielectric and structural characterization of composites formed by mixture of BiVO4 and TiO2 and applications in microwave range. The composites were formulated by addition of TiO2 (15, 30, 45 and 60 wt %) in BiVO4. X-Ray Diffraction (XRD) was used in structural characterization. The dielectric properties, temperature coefficient of resonant frequency (τf), dielectric permittivity (ε) and dielectric loss (tan δ), were measured and the results confirm that the TiO2 addition improves the thermo-stability of the composites with values varying from −244.03–246.12 ppm.⁰C⁻¹. The dielectric properties varied with TiO2 composition (31<εr < 67) with dielectric loss around 10⁻³ values. These composites were analyzed as Dielectric Resonator Antenna and all samples showed can be applied as antenna (all presented S11 below −10 dB). The numerical studies of these antennas presented good agreement with experimental results in which the bandwidth, return loss and input impedance had small errors.
This paper presents the application of the Li2MgTi3O8 (LMT) ceramic matrix added with small quantities (0 wt.%, 1 wt.%, 3 wt.%, and 5 wt.%) of Bi2O3 for building and studying dielectric resonator antennas (DRA) to operate in microwave frequency bands. A low-cost procedure of manufacturing was applied to produce a material with good dielectric characteristics such as near zero temperature coefficient of resonant frequency (τf) in − 8.37 ppm.°C⁻¹ for LMT added with 3 wt.% Bi2O3, relative permittivity (εr) varying approximately between 19 and 24 and loss tangent (tan δ) varying between 5.41 × 10⁻⁴ and 1.42 × 10⁻³. Antenna prototypes and computational models were built for each compound, showing excellent agreement between measurements and simulations. All prototypes and simulated models have bandwidths (BW) wider than 100 MHz with resonant frequencies near 3.5 GHz. The gains and radiation efficiencies of the simulated antennas remained above 6.3 dBi and 98%, respectively.
