The Experts below are selected from a list of 7302 Experts worldwide ranked by ideXlab platform
J. Krupka - One of the best experts on this subject based on the ideXlab platform.
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measurements of the complex permittivity of low Loss polymers at frequency range from 5 ghz to 50 ghz
2016Co-Authors: J. KrupkaAbstract:Complex permittivity of Polytetrafluoroethylene (PTFE), Polypropylene (PP), Polyethylene (PE) and cross-linked Polystyrene (Rexolite), has been measured at frequency range from 5 GHz to 50 GHz. Measurements have been performed in two cylindrical cavities employing several quasi $\text{TE}_{0 \mathrm{mn}}$ modes excited in samples under test. Measurement uncertainties for the real part of permittivity were $\pm$ 0.5% while for the imaginary part of permittivity in the range from $\pm$ 8% for the lowest Loss materials to $\pm$ 3% for Rexolite. It has been confirmed that the real part of permittivity of all measured polymers is constant in the microwave frequency spectrum to within measurement uncertainties, while the Dielectric Loss Tangent values vary with frequency
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measurements of permittivity Dielectric Loss Tangent and resistivity of float zone silicon at microwave frequencies
2006Co-Authors: J. Krupka, Jonathan Breeze, Neil Mcn. Alford, Thomas Claussen, Anthony Centeno, Leif JensenAbstract:The complex permittivity and resistivity of float-zone high-resistivity silicon were measured at microwave frequencies for temperatures from 10 up to 400 K employing Dielectric-resonator and composite Dielectric-resonator techniques. At temperatures below 25 K, where all free carriers are frozen out, Loss-Tangent values of the order of 2times10-4 were measured, suggesting the existence of hopping conductivity or surface charge carrier conductivity in this temperature range. Use of a composite Dielectric-resonator technique enabled the measurement of materials having higher Dielectric Losses (or lower resistivities) with respect to the Dielectric-resonator technique. The real part of permittivity of silicon proved to be frequency independent. Dielectric Losses of high-resistivity silicon at microwave frequencies are mainly associated with conductivity and their behavior versus temperature can be satisfactory described by dc conductivity models, except at very low temperatures
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complex permittivity measurements of low Loss microwave ceramics employing higher order quasi te 0np modes excited in a cylindrical Dielectric sample
2005Co-Authors: J. Krupka, Weite Huang, Meanjue TungAbstract:Higher order quasi TE0np modes have been used for precise measurements of permittivity and Dielectric Loss Tangent of low-Loss Dielectric ceramics versus frequency in the microwave frequency range. It has been shown that, using this technique, Dielectrics having arbitrary permittivity value and Dielectric Loss Tangent values in the range 10 −6 –10 −2 can be measured with relative uncertainties below 0.5% for real permittivity and below 5% for Dielectric Losses. Several Dielectric materials have been measured including singlecrystal quartz, single-crystal sapphire and the low-Loss microwave ceramics BMT, BZT and BZNT.
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uncertainty of complex permittivity measurements by split post Dielectric resonator technique
2001Co-Authors: J. Krupka, A P Gregory, O C Rochard, R M Clarke, Billy F Riddle, James R BakerjarvisAbstract:Abstract Split-post Dielectric resonators operating at frequencies 1.4–5.5 GHz were used to measure complex permittivity of single crystal standard reference Dielectric materials with well known Dielectric properties previously measured by other techniques. Detailed error analysis of permittivity and Dielectric Loss Tangent measurements has been performed. It was proved both theoretically and experimentally that using split post resonators it is possible to measure permittivity with uncertainty about 0.3% and Dielectric Loss Tangent with resolution 2×10 −5 for well-machined laminar specimens.
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Use of whispering-gallery modes for complex permittivity determinations of ultra-low-Loss Dielectric materials
1999Co-Authors: J. Krupka, K. Derzakowski, A. Abramowicz, M.e. Tobar, R.g. GeyerAbstract:Whispering-gallery modes are used for very accurate permittivity, Dielectric Loss, and temperature coefficient of permittivity measurements for both isotropic and uniaxially anisotropic Dielectric materials. The relationship between resonant frequencies, dimensions of the resonant structure, and permittivity of the sample under test is calculated with a radial mode-matching technique. The relative accuracy of these computations is better then 10/sup -4/. The influence of conductor Losses on Dielectric Loss Tangent determination is treated for both whispering-gallery-mode and TE/sub 01/spl delta//-mode Dielectric-resonator techniques. Two permittivity tensor components of sapphire and their temperature dependence were measured from 4.2 to 300 K. The total uncertainty in permittivity when use is made of whispering-gallery modes was estimated to be less than 0.05%. The uncertainty was limited principally by uncertainty in sample dimensions. Experimental and calculated resonant frequencies of several whispering-gallery modes differed by no more than 0.01%. The Dielectric Loss Tangent of sapphire parallel and perpendicular to its anisotropy axis was calculated to be less than 10/sup -9/ at 4.2 K. The permittivity and Dielectric Loss Tangent of a commercially available low-Loss high-permittivity ceramic material has also been measured at S- and C-band frequencies using a large number of whispering-gallery modes.
Jun Qiu - One of the best experts on this subject based on the ideXlab platform.
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constructing honeycomb conductive rings in graphene foam epoxy resin metacomposites for adjustable negative permittivity low Dielectric Loss Tangent and mechanical enhancement
2020Co-Authors: Ruoyu Zhan, Jun QiuAbstract:Abstract The reduced graphene foam (RGF)/epoxy resin (EP) elastomer composites with adjustable negative permittivity were prepared sequentially through hydrothermal reaction, high-temperature reduction and impregnating processing. The negative permittivity can be achieved by graphene foam owing to the existence of three-dimensional conductive honeycomb rings, and the rise of graphite oxide (GO) content brought in enhancement for negative permittivity. The fundamental principles of Lorentz-like and Drude-type negative permittivity were discussed. The negative permittivity increased significantly as filling multi-walled carbon nanotubes (MWCNTs) with a mass ratio of 2:1 based on the more electrons hopping between the MWCNTs. Low Dielectric Loss Tangent (tan δ ) (close to 1.0 over 600 MHz-1 GHz) was investigated in RGF/EP composites as a result of reducing conductance Loss, interfacial polarization and dipole polarization Loss. Besides, compression strength and compression modulus of the RGF/EP composites also were enhanced with increase of GO content. This work provides an understanding guidance on the mechanism of metamaterials with low Dielectric Loss and high mechanical property.
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graphene polypyrrole nanocomposites with high negative permittivity and low Dielectric Loss Tangent
2019Co-Authors: Ge Qin, Jun QiuAbstract:Abstract Graphene (GNs)/ polypyrrole (PPy) nanocomposites with different content of GNs prepared by in-situ polymerization possess negative permittivity in the range of test frequency. Importantly, the GNs/PPy nanocomposites also have low Dielectric Loss Tangent. ATR and XRD tests showed that no significant change in chemical bond and crystallization is found in GNs/PPy nanocomposites. SEM analysis indicated that GNs/PPy nanocomposites form different morphologies with the increase of GNs content. The negative permittivity of GNs/PPy nanocomposites is mainly caused by the plasmon resonance of the free electrons. The variation of resistivity and negative permittivity are basically consistent, which reflects that the good conductivity of the nanocomposites is attribute to the plasmon resonance of free electrons. The moderate addition of GNs is beneficial to the development of permittivity to a great negative value and decrease the Dielectric Loss Tangent. The negative permittivity is up to −1.226 × 105 and the Dielectric Loss Tangent is reduce to 0.32 in GNs/PPy nanocomposites with 10 wt% GNs content. The negative permittivity and the low Dielectric Loss Tangent in GNs/PPy nanocomposites is achieved in a wider frequency range 1–1000 MHz.
Jie Kong - One of the best experts on this subject based on the ideXlab platform.
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ultralow Dielectric fluoride containing cyanate ester resins with improved mechanical properties and high thermal and dimensional stabilities
2017Co-Authors: Wencai Dong, Lin Tang, Jie Kong, Yusheng Tang, Yongqiang Guo, Sruthi Tadakamalla, Bin Wang, Zhanhu GuoAbstract:In this contribution, we present a new strategy for the fabrication of modified cyanate ester resins combined with ultralow Dielectric properties, improved mechanical properties and high thermal and dimensional stabilities. The fluoride-containing compound 2-((3-(trifluoromethyl)phenoxy)methyl)oxirane (TFMPMO), synthesized from m-(trifluoromethyl)phenol (TFMP) and epichlorohydrin (ECH), was used to modify bisphenol A dicyanate ester (BADCy) resins via copolymerization reaction. The BADCy resin modified with 15 wt% TFMPMO presented ultralow Dielectric constant (e, 2.75) and Dielectric Loss Tangent values (tan δ, 6.7 × 10−3), high mechanical properties (impact strength of 15.4 kJ m−2 and flexural strength of 141.0 MPa), and superior thermal and dimensional stability (THeat-resistance index of 206 °C and coefficient of thermal expansion of 6.4 × 10−5), and it possesses great potential application in radomes and antenna systems of aircraft.
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development of wave transparent light weight composites combined with superior Dielectric performance and desirable thermal stabilities
2017Co-Authors: Wencai Dong, Yusheng Tang, Jie KongAbstract:Abstract In this paper, a novel interfacial compatibilizer of soluble epoxy-terminated poly (p-phenylene-2, 6-benzobisoxazole) precursor (epoxy-prePBO) was synthesized to modify bisphenol A cyanate ester (BADCy) resin via copolymerization. Compared to PBO fibers/BADCy wave-transparent composites, the obtained PBO fibers/epoxy-prePBO modified BADCy (PBO fibers/PBO-co-BADCy) wave-transparent composite with 7 wt% epoxy-prePBO showed ultra-low Dielectric constant (e, 2.68) and Dielectric Loss Tangent (tanδ, 0.0061) values, excellent mechanical properties (flexural strength, 658.5 MPa) and interlaminar shear strength (48.4 MPa), and outstanding thermal stability (THeat-resistance index, 262.9 °C). These properties proved its potential in applications, such as in radomes and antenna system of aircrafts.
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hyperbranched polyborosilazane and boron nitride modified cyanate ester composite with low Dielectric Loss and desirable thermal conductivity
2017Co-Authors: Junwei Gu, Yusheng Tang, Shuang Xu, Qiang Zhuang, Jie KongAbstract:In this paper, we presented a new strategy for fabrication of polymeric composites combined with low Dielectric Loss and desirable thermal conductivity. With the incorporation of hyperbranched polyborosilazane (hb-PBSZ) into bisphenol A cyanate ester (BADCy) matrix, the modified hb-PBSZ/BADCy resin with 4 wt% hb-PBSZ possessed a low Dielectric constant (a) value of 2.37 and relatively low Dielectric Loss Tangent value of 0.008 at 1MHz. Furthermore, by integrating micrometer boron nitride particles (mBN) into hb-PBSZ/BADCy matrix, the mBN/hb-PBSZ/BADCy composites presented relatively low a of 3.09, desirable thermally conductive coefficient (λ of 0.63 W/(m·K)) and thermal diffusivity (α of 0.42 mm2/s) values. It provides an important perspective for designing Dielectric and thermally conductive polymeric composites for electrical packaging and energy storage fields.
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hexagonal boron nitride polymethyl vinyl siloxane rubber Dielectric thermally conductive composites with ideal thermal stabilities
2017Co-Authors: Xudong Meng, Qiang Zhuang, Yusheng Tang, Jie KongAbstract:Abstract Hexagonal boron nitride/polymethyl-vinyl siloxane rubber ( h BN/VMQ) Dielectric thermally conductive composites were fabricated via kneading followed by hot compression method. The thermally conductive coefficient ( λ ), thermal diffusion coefficient ( α ), Dielectric constant ( e ) and Dielectric Loss Tangent (tan δ ) values were all increased with the increasing addition of h BN fillers. When the volume fraction of h BN fillers was 40 vol%, the corresponding λ and α was 1.110 W/m K and 1.174 mm 2 /s, 6 and 9 times than that of pure VMQ matrix, respectively. The corresponding e and tan δ was 3.51 and 0.0054, respectively. Furthermore, the tensile strength and T Heat-resistance index ( T HRI ) values were both maximum with 20 vol% h BN fillers, tensile strength of 3.31 MPa, 12 times than that of pure VMQ matrix (0.28 MPa), and T HRI of 253.8 °C. The obtained h BN/VMQ composites present great potential for packaging in continuous integration and miniaturization of microelectronic devices.
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preparation of poss quartz fibers cyanate ester resins laminated composites
2015Co-Authors: Yusheng Tang, Jie KongAbstract:Quartz fibers (QFs) and two polyhedral oligomeric silsesquioxane (POSS) (epoxy-POSS and hydroxy-POSS) are performed to regulate the Dielectric properties, heat resistance, and mechanical properties of cyanate ester (CE) resins. With the introduction of POSS, the Dielectric constant and Dielectric Loss Tangent values of the POSS/QFs/CE laminated composites are decreased obviously. The heat resistance properties and flexural strength values of the laminated composites are increased, but the interlaminar shear strength values of the laminated composites are decreased slightly. The EP-POSS/QFs/CE laminated composites have relatively better Dielectric, heat resistance, and mechanical properties than those of HO-POSS/QFs/CE laminated composites. POLYM. COMPOS., 36:2017–2021, 2015. © 2014 Society of Plastics Engineer
M.e. Tobar - One of the best experts on this subject based on the ideXlab platform.
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single crystal sapphire resonator at millikelvin temperatures observation of thermal bistability in high q factor whispering gallery modes
2010Co-Authors: Daniel L Creedon, M.e. Tobar, Jeanmichel Le Floch, Yarema Reshitnyk, Tim DutyAbstract:Resonance modes in single crystal sapphire ({alpha}-Al{sub 2}O{sub 3}) exhibit extremely high electrical and mechanical Q factors ({approx_equal}10{sup 9} at 4 K), which are important characteristics for electromechanical experiments at the quantum limit. We report the cool down of a bulk sapphire sample below superfluid liquid-helium temperature (1.6 K) to as low as 25 mK. The electromagnetic properties were characterized at microwave frequencies, and we report the observation of electromagnetically induced thermal bistability in whispering gallery modes due to the material T{sup 3} dependence on thermal conductivity and the ultralow Dielectric Loss Tangent. We identify ''magic temperatures'' between 80 and 2100 mK, the lowest ever measured, at which the onset of bistability is suppressed and the frequency-temperature dependence is annulled. These phenomena at low temperatures make sapphire suitable for quantum metrology and ultrastable clock applications, including the possible realization of the quantum-limited sapphire clock.
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use of whispering gallery modes and quasi rm te _ 0 np modes for broadband characterization of bulk gallium arsenide and gallium phosphide samples
2008Co-Authors: Jerzy Krupka, D Mouneyrac, John G Hartnett, M.e. TobarAbstract:The complex permittivity of bulk crystals of semiinsulating gallium arsenide (GaAs) and gallium phosphide (GaP) were measured over the frequency range from 4 to 30 GHz and at temperatures from 30 up to 300 K employing whispering-gallery-mode (WGM) and quasi-TE0 np-mode Dielectric-resonator techniques. At temperatures about 40 K, Dielectric Loss Tangent values were below 10 -6 for GaAs and below 10 -5 for GaP. The use of several WGMs, as well as TE0 np modes excited in the same test sample enabled a broad frequency range of measurements (one decade). The real part of the permittivity of GaP and GaAs proved to be frequency independent at microwave frequencies. The Dielectric Loss Tangents of GaAs and GaP increase with temperature and frequency.
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Use of whispering-gallery modes for complex permittivity determinations of ultra-low-Loss Dielectric materials
1999Co-Authors: J. Krupka, K. Derzakowski, A. Abramowicz, M.e. Tobar, R.g. GeyerAbstract:Whispering-gallery modes are used for very accurate permittivity, Dielectric Loss, and temperature coefficient of permittivity measurements for both isotropic and uniaxially anisotropic Dielectric materials. The relationship between resonant frequencies, dimensions of the resonant structure, and permittivity of the sample under test is calculated with a radial mode-matching technique. The relative accuracy of these computations is better then 10/sup -4/. The influence of conductor Losses on Dielectric Loss Tangent determination is treated for both whispering-gallery-mode and TE/sub 01/spl delta//-mode Dielectric-resonator techniques. Two permittivity tensor components of sapphire and their temperature dependence were measured from 4.2 to 300 K. The total uncertainty in permittivity when use is made of whispering-gallery modes was estimated to be less than 0.05%. The uncertainty was limited principally by uncertainty in sample dimensions. Experimental and calculated resonant frequencies of several whispering-gallery modes differed by no more than 0.01%. The Dielectric Loss Tangent of sapphire parallel and perpendicular to its anisotropy axis was calculated to be less than 10/sup -9/ at 4.2 K. The permittivity and Dielectric Loss Tangent of a commercially available low-Loss high-permittivity ceramic material has also been measured at S- and C-band frequencies using a large number of whispering-gallery modes.
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Measurement of Dielectric Loss Tangent of alumina at microwave frequencies and room temperature
1994Co-Authors: R.a. Woode, M.e. Tobar, E.n. Ivanov, D.g. BlairAbstract:The use of whispering gallery modes allows the Dielectric Loss Tangent of polycrystalline Al/sub 2/O/sub 3/ (alumina) to be accurately determined at microwave frequencies without the use of a cavity. The Dielectric Loss Tangent of alumina is shown to be strongly variable from sample to sample with a lowest measured value of 4.3*10/sup -5/ observed at 9.0 GHz in a 99.5% alumina sample.
Yongqiang Guo - One of the best experts on this subject based on the ideXlab platform.
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fabrication proposed model and simulation predictions on thermally conductive hybrid cyanate ester composites with boron nitride fillers
2018Co-Authors: Yongqiang Guo, Xiao Zhong, Qiuyu ZhangAbstract:Abstract DCPDCE/BADCy hybrid resin and BN fillers were performed to fabricate the thermally conductive BN/DCPDCE/BADCy composites. When the molar ratio of DCPDCE/BADCy was 0.4/0.6, the Dielectric constant (e) and Dielectric Loss Tangent (tgδ) value of the DCPDCE/BADCy hybrid resin was decreased to 2.92 and 5.08 × 10−3, respectively. Impact and flexural strength was increased to 10.7 kJ/m2 and 100.7 MPa, respectively. And the heat-resistance index (THRI) was 201.6 °C. Furthermore, the thermally conductive coefficient (λ) of the BN/DCPDCE/BADCy composite with 30 wt% BN fillers was improved to 0.64 W/mK, about 3 times in comparison to that of pristine DCPDCE/BADCy hybrid resin. Compared to that of Maxwell and Russell models, our proposed thermally conductive model could predict the experimental λ values more precisely. THRI value was enhanced from 201.6 °C (Pristine DCPDCE/BADCy hybrid resin) to 206.6 °C. Moreover, the BN/DCPDCE/BADCy composite with 10 wt% BN presented the optimal impact strength (11.7 kJ/m2) and flexural strength (108.4 MPa).
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ultralow Dielectric fluoride containing cyanate ester resins with improved mechanical properties and high thermal and dimensional stabilities
2017Co-Authors: Wencai Dong, Lin Tang, Jie Kong, Yusheng Tang, Yongqiang Guo, Sruthi Tadakamalla, Bin Wang, Zhanhu GuoAbstract:In this contribution, we present a new strategy for the fabrication of modified cyanate ester resins combined with ultralow Dielectric properties, improved mechanical properties and high thermal and dimensional stabilities. The fluoride-containing compound 2-((3-(trifluoromethyl)phenoxy)methyl)oxirane (TFMPMO), synthesized from m-(trifluoromethyl)phenol (TFMP) and epichlorohydrin (ECH), was used to modify bisphenol A dicyanate ester (BADCy) resins via copolymerization reaction. The BADCy resin modified with 15 wt% TFMPMO presented ultralow Dielectric constant (e, 2.75) and Dielectric Loss Tangent values (tan δ, 6.7 × 10−3), high mechanical properties (impact strength of 15.4 kJ m−2 and flexural strength of 141.0 MPa), and superior thermal and dimensional stability (THeat-resistance index of 206 °C and coefficient of thermal expansion of 6.4 × 10−5), and it possesses great potential application in radomes and antenna systems of aircraft.
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Dielectric thermally conductive boron nitride polyimide composites with outstanding thermal stabilities via in situ polymerization electrospinning hot press method
2017Co-Authors: Yongqiang Guo, Lidong Tian, Hua Qiu, Qiuyu ZhangAbstract:Abstract Micrometer boron nitride/polyamide acid ( m BN/PAA) compound was firstly fabricated via in -situ polymerization, performed to obtain the m BN/PAA electrospun fibers by electrospinning technology, finally to fabricate the Dielectric thermally conductive m BN/polyimide ( m BN/PI) composites via thermal-imidization followed by hot press method. The obtained m BN/PI composite with 30 wt% m BN presents relatively highly thermally conductive coefficient ( λ ), excellent Dielectric constant ( e ) & Dielectric Loss Tangent (tan δ ), and extremely outstanding thermal stability, λ of 0.696 W/m K, e of 3.77, tan δ of 0.007, T Heat-resistance index ( T HRI ) of 279 °C and glass transition temperature ( T g ) of 240 °C, which presents a great potential for packaging in integration and miniaturization of microelectronic devices.