Broadband complex permittivity measurements of nematic liquid crystals based on cavity perturbation method

Yu, Chengyong; Li, En; Zhang, Zhiyong; Wang, Xiangru; Gao, Chong; Guo, Gaofeng; Zheng, Huinan

doi:10.1080/02678292.2019.1630488

Cited by 13 publications

(3 citation statements)

References 23 publications

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“…For liquid crystal phased array antennas, large dielectric tunability and high quality factor of liquid crystal materials are required. The dielectric properties of the newly developed MW1036 at 19GHz were tested at 25 ºC using the resonant cavity perturbation method [26] and the results are shown in Table 6.…”

Section: The Dielectric Properties Of Mw1036 At 19ghzmentioning

confidence: 99%

P‐12.12: Development and Application of High Birefringence Liquid Crystal Materials

Li¹,

Li²,

Hu³

et al. 2023

Symp Digest of Tech Papers

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The development of new liquid crystal optoelectronic devices, including laser phase modulation, microwave and terahertz devices, requires liquid crystal materials with high birefringence. In this paper, three new molecular design strategies are proposed, including the introduction of olefin chain, lateral fluorine substitution and new ring core. Four new series of isothiocyanate liquid crystal compounds with high birefringence, low melting point and wide nematic temperature range were synthesized. Based on these new liquid crystal compounds, a liquid crystal mixture with nematic temperature range of ‐40~146 ºC and birefringence of 0.42 was developed. At 19 GHz, the new liquid crystal mixture shows excellent dielectric properties, with dielectric anisotropy of 1.28 and dielectric loss of 0.0087. The new liquid crystal mixture also has very low viscoelastic coefficient. The results at 1550nm and 60 ºC show that the response speed can reach 3.6 milliseconds with 2π phase modulation in the reflection mode.

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Section: The Dielectric Properties Of Mw1036 At 19ghzmentioning

confidence: 99%

P‐12.12: Development and Application of High Birefringence Liquid Crystal Materials

Li¹,

Li²,

Hu³

et al. 2023

Symp Digest of Tech Papers

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“…The material intrinsic parameters are the central column mapping the material's ability to react under the excitation of an electromagnetic wave. Thereby, the probe (in transmission or reflection) [7,10,11], free-space (antenna or ellipsometry) [12][13][14], cavity [15][16][17][18], parallel plates capacitor (MIM) [19][20][21], inductive (spiral approach) [22,23], and transmission line (stub, short-circuit, waveguide, etc) [24][25][26]. All these methods are based on the perturbation [27][28][29] of the electromagnetic field lines in the insertion environment of the sample to be characterized.…”

Section: Introductionmentioning

confidence: 99%

Probe with a metallic bowl termination to determine the electric material parameters from variable thicknesses

Bouesse,

Moukanda Mbango

2024

Eng. Res. Express

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This paper discusses a new approach to determining the material electric parameters (dielectric constant and dissipation factor) through a technique based on identical material variation thicknesses. The copper bowl controls the material thicknesses and allows quick and safe measurements to get to the electromagnetic material information. This approach assumes that the discontinuities generated at the probe and bowl are identical and removed through mathematical operations. The material under test (MUT) gap thickness doesn’t exceed one millimeter. Some formulations have been developed to determine the discontinuity condensers and both capacitors of each thickness. Two proposed developments have been given to extract the complex effective and relative permittivities. A mathematical formula has been proposed to ensure the transition from effective to intrinsic parameters, where the MUT thicknesses and the probe’s outer diameter of the inner conductor are considered. A de-embedding operation is necessary, and the method is suitable but not limited to low-k. The coaxial probe is flat terminated, and the experimental validation has been made in the frequency ranges 1 MHz – 2.2 GHz for FR-4 HTG-175 and 1 MHz – 0.8 GHz for Alumina 99.5%. All MUTs are cm2, except their thicknesses. The suggested approach is straightforward in sample insertion, simple in its data acquisition and implementation, and precise in the final parameters' results.

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“…So the depolarization factor must be redefined because the sample length is smaller than the width of the cavity, and especially when the ratio of sample length to cavity width is less than 0.7 [18]. Also, the permeability and permittivity have been measured in earlier studies by placing the specimen at a non-radiating slot in the E-plane of the rectangular cavity [17], [23].…”

Section: Introductionmentioning

confidence: 99%

An Improved Cavity-Perturbation Approach for Simultaneously Measuring the Permittivity and Permeability of Magneto-Dielectric Materials in Sub-6G

Zhang

et al. 2021

IEEE Access

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Magneto-electric materials with low loss have prospective applications in microwave systems as they enable miniaturization and broadband impedance matching. Two example applications are antennas and filters in sub-6G communication systems. Therefore, high-accuracy and wideband testing are critical for magneto-electric materials, whose complex permittivity and permeability are usually dependent on frequency. In this paper, the mutual interference between the electric and magnetic field within magneto-electric material samples was seriously considered. It was found that the results calculated with the original perturbation formula were overestimated when the sample size was not so small or higher-order modes are used, especially when the electric or magnetic field is perpendicular to the material under test. Two methods based on perturbation, namely the iteration method and the multi-state method are proposed to reduce the impact of the mutual interference, which have been proven to be direct and effective through theoretical analysis and experiments. Finally, several rod-shaped specimens processed from several standard dielectric materials (PTFE, fused silica, Al 2 O 3 ) and synthesized magneto-electric materials were measured in a fabricated cavity with a vector network analyzer. Experimental results show that the results obtained by the modified formula are more accurate than those obtained by the original formula, and are in good agreement with the data measured by other methods.INDEX TERMS Magneto-electric materials, complex permittivity and permeability, iteration, multi-state, mutual interference, perturbation.

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Broadband complex permittivity measurements of nematic liquid crystals based on cavity perturbation method

Cited by 13 publications

References 23 publications

P‐12.12: Development and Application of High Birefringence Liquid Crystal Materials

P‐12.12: Development and Application of High Birefringence Liquid Crystal Materials

Probe with a metallic bowl termination to determine the electric material parameters from variable thicknesses

An Improved Cavity-Perturbation Approach for Simultaneously Measuring the Permittivity and Permeability of Magneto-Dielectric Materials in Sub-6G

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