Dr. Senad Bulja, PhD, FIET, SMIEEE https://drbulja.com Wed, 18 Sep 2024 08:03:43 +0000 en-US hourly 1 Finite element analysis of a balanced microstrip line filled with nematic liquid crystal https://drbulja.com/finite-element-analysis-of-a-balanced-microstrip-line-filled-with-nematic-liquid-crystal-361/ https://drbulja.com/finite-element-analysis-of-a-balanced-microstrip-line-filled-with-nematic-liquid-crystal-361/#respond Mon, 13 Feb 2023 06:50:45 +0000 https://drbulja.com/?p=361 The interest in the millimeter-wave band has been renewed recently, driven by the need for short-range high-speed data communications equipment. There is demand for compact and low-cost components, that are mass producible and have low power consumption. It is desirable for these systems to be reconfigurable in order to ensure continuity in data transmission. Nematic Liquid Crystal (LC) materials possess a birefringence that extends into the microwave range. Low voltages can be used to control this birefringence, making these materials an attractive modulation medium in such systems. 

Very few LC mixtures have been characterized at milli-meter wave frequencies. The conventional optical methods are very often impractical due to the need for large cell thicknesses, which lead to oversimplification resulting in inaccurate characterisation. 

 

We take a comprehensive approach in modeling both the liquid crystal orientation and the microwave fields, using a Finite Element Method (FEM) approach on a balanced microstrip line, i.e. the case when the width of the ground plane is the same the width of the strip line. Simulation tools have been developed to aid in the characterization of liquid crystalline materials at millimetre-wave frequencies. Firstly, the steady-state liquid crystal orientation is calculated, switched by a low frequency voltage waveform applied to the electrodes. Secondly, the resulting permittivity distribution is passed to a modal solver that is used to calculate the small signal wave propagation in the line at millimetre-wave frequencies. The finite element method has been used to solve the equations involved. The frequency dependence of the effective permittivity has been calculated as the voltage applied to electrodes is altered.

Fig. 1. Director field with 1V applied, where the director color represents the tilt angle (left) and Director field with 5V applied, where the director color represents the tilt angle (right)
Fig. 1. Director field with 1V applied, where the director color represents the tilt angle (left) and Director field with 5V applied, where the director color represents the tilt angle (right)

 

]]> https://drbulja.com/finite-element-analysis-of-a-balanced-microstrip-line-filled-with-nematic-liquid-crystal-361/feed/ 0 Accurate modelling for the wideband characterisation of nematic liquid crystals for microwave applications https://drbulja.com/accurate-modelling-for-the-wideband-characterisation-of-nematic-liquid-crystals-for-microwave-applications-251/ https://drbulja.com/accurate-modelling-for-the-wideband-characterisation-of-nematic-liquid-crystals-for-microwave-applications-251/#respond Mon, 09 Jan 2023 09:31:56 +0000 https://drbulja.com/?p=251 The interest in the millimeter-wave band has been renewed recently, driven by the need for short-range high-speed data communications equipment. There is demand for compact and low-cost components, that are mass producible and have low power consumption. It is desirable for these systems to be reconfigurable in order to ensure continuity in data transmission. Nematic Liquid Crystal (LC) materials possess a birefringence that extends into the microwave range. Low voltages can be used to control this birefringence, making these materials an attractive modulation medium in such systems. 

Very few LC mixtures have been characterized at milli-meter wave frequencies. The conventional optical methods are very often impractical due to the need for large cell thicknesses, which lead to oversimplification resulting in inaccurate characterisation. 

 

We take a comprehensive approach in modeling both the liquid crystal orientation and the microwave fields, using a Finite Element Method (FEM) approach. The spatial distribution of the permittivity tensor resulting from the minimization of the free energy of the liquid crystal is used to calculate the microwave fields. Characterization is then made possible through the comparison of modeling results and experimental results for simple waveguiding structures. With these modeling tools we are not only able to characterize the liquid crystal better, but they can also be used to design more complicated liquid crystal based components such as filters and couplers.

Fig. 1. Equipotential lines and director field with 5 V applied. Directors are represented by cylinders. Inset displays the lower right-hand electrode edge in more detail.
Fig. 1. Equipotential lines and director field with 5 V applied. Directors are represented by cylinders. Inset displays the lower right-hand electrode edge in more detail.

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