CST Studio Research Articles

Equivalent circuit analysis of a higher order mode coaxial reentrant cavity

An equivalent circuit analysis has been proposed for co-axial reentrant cavities which have been used extensively in Multiple-beam Klystron (MBK). Formulation for the equivalent capacitance and inductance of coaxial reentrant cavities (single and double reentrant cavity) have been obtained and used for the calculation of cavity parameters, i.e. resonant frequency and characteristic shunt impedance. The unloaded quality factor of the cavities has been obtained using Wheeler’s incremental inductance rule. Simulations of coaxial reentrant cavities have been carried out using CST studio and simulation results have been compared with the results obtained from the proposed analysis. A good agreement between the results has been obtained.

Second order triple band waveguide band-pass filter with adjustable centre frequency and 3-dB bandwidth

ABSTRACT This paper presents, a novel and simple resonator structure based second order triple band waveguide band-pass filter with adjustable centre frequency and 3-dB bandwidth. The planar insert consists of a circular shape etched part in which three stubs is placed. Three asymmetrical stub length and width are used to control three resonant frequency and 3-dB bandwidth independently. The insert is placed into the transverse plane of the WR-90 waveguide. To achieve second order band-pass filter response two symmetrical resonators is placed at an optimised distance of 8.99 mm. Simulation and optimisation analysis of the proposed filter is carried-out using CST Studio Suite (v23). To validate the 3D model, planar insert and WR-90 waveguide are fabricated individually and inserted manually. The measured results shows triple band bandpass filter characteristics having centre frequencies f 01 = 8.44 GHz, f 02 = 9.98 GHz and f 03 = 11.51 GHz with 3-dB bandwidth of 0.78, 0.12 and 0.3 GHz. The insertion loss of the measured filter is 0.35, 0.8 and 0.55 dB. The in band return loss of the proposed filter are better than 12 dB.

Transient induced response on cables by lightning electromagnetic pulse with different experimental conditions

The coupling of lightning electromagnetic pulse (LEMP) on cables can generate disruptive surge current and voltage, which may cause damage to devices or systems connected with cables. In this paper, a double toroidal magnetic field, through injection of an 8/20 μs lightning current into a double toroidal coil, is generated to induce indirect effects on nine communication/electrical cables. The impacts of different types and shielding methods of communication cables on induced surge current are evaluated, and the results show that twisted-pair cables with shielding layer have the best shielding effectiveness, with the ability to absorb more energy on the communication cables from LEMP. In addition, the study's findings demonstrate that the induction properties of cables are independent of the number of cores, but related to the shielding layer of cables. Meanwhile, simulation analysis in CST Studio Suite is carried out here, and results are basically similar to experimental results, with the difference attributed to the ignorance of some losses in the simulation environment. Finally, the magnetic field strength at each point of the LEMP is simulated, with some engineering proposals for the actual and simulated experiments.

Metal-free ultrathin terahertz absorber with independently tunable dual narrow bands

Abstract A technique is introduced to precisely control the resonance behaviour of a metal-free graphene-based terahertz absorber by independently tuning dual resonant peaks. The proposed ultrathin absorber features a multilayer configuration, with two isolated resonator layers of patterned graphene on dielectric (SiO2) substrates, and a thin graphite sheet at the bottom serving as a reflector. The stacked arrangement enables independent tunability of the high-absorptivity resonant peaks at 7.33THz and 9.34THz. The structure, with a thickness of just λ/15 of the free-space wavelength, offers a compact design suitable for space-constrained applications. Its symmetrical geometry ensures polarization insensitivity and stable performance for incident angles up to 60°. Simulated results, analysed via CST Studio and validated with an Equivalent Circuit Model (ECM), demonstrate excellent thermal stability. Furthermore, the narrowband response of the proposed absorber improves its sensitivity for refractive index variations induced by biomolecular interactions validating its suitability in biosensing applications. The absorber demonstrates peak absorption across both the resonant frequencies with an analyte optimised at 1.5μm thickness. Sensitivity levels of 1.1THz/RIU and 1.05THz/RIU along with figure-of-merit (FOM) values of 2.11 and 2.23. are recorded for the lower and upper bands, respectively. The absorber offers enhanced selectivity owing to low values of full-width at half maximum (FWHM). High Q-factors of 12.85 and 19.3, confirm its strong potential for refractive index sensing. 

A deep learning approach for non-invasive Alzheimer’s monitoring using microwave radar data

Over 50 million people globally suffer from Alzheimer’s disease (AD), emphasizing the need for efficient, early diagnostic tools. Traditional methods like Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) scans are expensive, bulky, and slow. Microwave-based techniques offer a cost-effective, non-invasive, and portable solution, diverging from conventional neuroimaging practices. This article introduces a deep learning approach for monitoring AD , using realistic numerical brain phantoms to simulate scattered signals via the CST Studio Suite. The obtained data is preprocessed using normalization, standardization, and outlier removal to ensure data integrity. Furthermore, we propose a novel data augmentation technique to enrich the dataset across various AD stages. Our deep learning approach combines Recursive Feature Elimination (RFE) with Principal Component Analysis (PCA) and Autoencoders (AE) for optimal feature selection. Convolution Neural Network (CNN) is combined with Gated Recurrent Unit (GRU), Bidirectional Long Short Term Memory (Bidirectional-LSTM), and Long Short-Term Memory (LSTM) to improve classification performance. The integration of RFE-PCA-AE significantly elevates performance, with the CNN+GRU model achieving an 87% accuracy rate, thus outperforming existing studies.

High-isolation Quad-port MIMO Antenna for 5G Applications

This paper presents a compact, high-isolation MIMO antenna with physical dimensions of 68 × 68 × 0.8 mm, designed for use in 5G applications. The antenna's bandwidth ranges from 3.25 GHz to 4.34 GHz and it offers a gain of 4.3 dBi, making it suitable for applications relying on 5G technology. Several improvements have been introduced to improve its overall efficiency, such as adjustments to the ground plane and integrating apertures in the radiating patch. The alterations referred to above were optimized using the sweep parameter method to ensure that their best configurations are achieved. Furthermore, much attention has been paid to enhance isolation by ensuring all terminals are positioned precisely at 90° angles. The CST Studio Suite was utilized to design and thoroughly simulate the proposed MIMO antenna.

Optimizing Wireless Power Transfer Systems: A Simulation-Based Approach Using CST Studio Suite

In the rapidly evolving field of wireless power transfer (WPT), achieving systems that combine efficiency with reliability is crucial. This paper presents a simulation-based approach using CST Studio Suite to optimize WPT systems for wireless battery chargers in electric bikes. The study fixes the size of both the transmitter and receiver coils, the spacing between turns, and the number of coil turns, with a set distance of 20mm between the transmitter and receiver coils. CST Studio Suite is employed to determine the parameters of resonance capacitors and the optimal switching frequency to enhance WPT efficiency. This powerful simulation tool allows researchers and engineers to design resonance compensation circuits more effectively, optimizing power transfer efficiency. The simulation conducted with CST Studio Suite confirms its effectiveness in designing a WPT system, achieving an impressive peak efficiency of 99.61% at the resonant frequency. The paper demonstrates CST Studio Suite's capability to accurately predict WPT system performance by developing detailed electromagnetic models and fine-tuning simulation parameters to reflect real operating conditions. Iterative simulations resulted in optimized practices, validated by select results that highlight the method's effectiveness and showcase an optimal balance between system complexity and efficiency. These findings provide a strategic framework for future WPT system development, offering practical guidance for researchers and industry professionals aiming to advance WPT technology.

A tunable chiral metasurface useable in terahertz imaging and wavefront shaping

We proposed a tunable chiral metasurface comprising a reflective bottom layer of gold, a dielectric layer of polyimide, and a structural top layer of gold-graphene. Its main properties were studied via numerical simulations conducted using CST Studio Suite. The results indicate that, based on the chiral metasurface, we achieved dual-band circular dichroism of −0.5 and 0.77 at 0.9 THz and 1.06 THz, respectively, and complementary near-field imaging applications were realized by tuning the Fermi level (E f ) of graphene. Subsequently, exploiting the exceptional selective characteristics of circularly polarized waves using a chiral metasurface, eight chiral phase-gradient metasurfaces were constructed by rotating the chiral structure. Moreover, based on the Pancharatnam-Berry phase principle, tunable wavefront shaping applications were further realized, including anomalous reflection, vortex beams, and focusing. In anomalous reflection, the reflection angles for left-circularly polarized (LCP) and right-circularly polarized (RCP) incidences are opposite when adjusting the E f of graphene. For example, when the graphene E f is 0 eV and the LCP wave is incident at 0°, the reflection angle is −18°. Conversely, when the graphene E f is 1 eV and the RCP wave is incident at 0°, the reflection angle is 18°. In the application of vortex beams, by adjusting the E f of graphene, we achieved vortex beams with opposite topological charges under different circularly polarized incidences. In the focusing application, the incident LCP and RCP can achieve focusing and defocusing, respectively. And the graphene E f can dynamically control the focusing efficiency at the incident LCP, increasing it from 13.63% to 44.84%.

Implementation of a Highly Mobile UAVs Direction Finding Complex Using Virtual Magnetic Dipoles

Relevance. In the context of the development of modern broadband communication systems, the task of performing direction finding of signals using highly mobile direction finding systems (UAVs) is becoming especially urgent. They impose restrictions on the size of antenna elements and the distance between them, which leads to an increase in the mathematical error of the bearing. Problem statement. The paper sets the task of considering the possibility of increasing the direction finding accuracy of a highly mobile complex by using virtual magnetic dipole technology. A feature of this method is the minimization of distortions introduced by the carrier body into the characteristics of the measured field. To measure the field characteristics, as well as their partial components, vector antenna elements were used. Goal of the work is to study the characteristics of a radio direction finding complex using virtual magnetic dipole methods in conditions of distortions introduced by the carrier body. As an example, cases of direction finding of differently polarized waves, taking into account the influence of radomes of antenna elements, assessment of the maximum resolution accuracy, as well as noise stability are considered. The finite element method implemented in DS CST Studio Suite 2024 was used in the modeling. Result. During the research, a plane wave with different bearings fell on a UAV with a direction finding complex, which made it possible to carry out the most accurate research. The results of the work also include the creation of a model of a radio direction finding complex, which can be installed on a small UAV, providing high accuracy of wave direction finding in passive mode.The novelty of the method used lies in the application of methods for the formation of virtual magnetic dipoles based on the measured characteristics of the distorted electric field. New to this work are modeling cases that are associated with noise suppression, the influence of antenna element housings, as well as assessment of the maximum resolution accuracy.Practical significance of the work lies in the creation of a model of a radio location system based on vector antenna elements, which are used to measure the characteristics of the electromagnetic field with subsequent direction finding based on the magnetic field.

Numerical simulation and measurements on reduced scale structures of floating production storage and offloading units

Protecting offshore structures against the effects of lightning strikes, sparks, and short circuits is a considerable challenge to designers and deployment engineers once the numerous exposed structures, pieces of equipment, and devices make the behavior of electromagnetic phenomena difficult to predict. Numerical simulations are important tools to predict such behavior. However, due to the uncertainties involved, they should be compared against laboratory results. This paper presents the results of the measurements performed on three scaled models and compares them to those obtained with two different applications, CST Studio Suite and NEC-4. We elaborate hypotheses regarding the differences between laboratory results and those obtained using simulation software. As an application, after validating modeling techniques, the paper discusses the results of induction on cable loops on “gooseneck” chimneys commonly used in ships and floating production storage and offloading units.

Metal reflector-enhanced thermoacoustic imaging as a guidance for puncture biopsy

Puncture biopsy is an important clinical technique to obtain diseased tissue for pathological diagnosis, where imaging guidance is critical. In this paper, we describe a metal reflector-enhanced microwave-induced thermoacoustic imaging (TAI) approach capable of guiding puncture biopsy for detection of breast cancer and joint diseases. Numerical experimentations simulating puncture guidance in breast cancer and knee gout models were first conducted using (CST STUDIO SUITE) (CST) software, and then ex-vivo experiments were performed followed by qualitative observations and semi-quantitative analysis. The results of both the simulations and ex-vivo experiments showed that our reflector-enhanced TAI could image the puncture needle in high resolution with a large depth of [Formula: see text][Formula: see text]cm.

Multipactor analysis of 431 MHz L-shaped inductive output tube cavity

Gridless inductive output tubes (IOTs) offer compact size and high-power amplification at sub-GHz frequencies. Minimizing cavity dimensions in the interest of compactness leads to smaller gaps, which may cause multipactor discharge under high-power operating conditions. The uncontrolled electron growth resulting from multipactor breakdown can lead to undesired effects including surface damage and system failure. This paper performs a parallel-plate multipactor analysis for a high-Q, L-shaped, aluminum, 431 MHz cavity designed for a gridless IOT to be operated in the MW-power regime. The cavity gap is 27 mm, and diameter is 339 mm. Multipactor susceptibility regions are calculated for non-zero emission energy, half-cycle, and non-half-cycle multipactor using a semi-analytic approach and a standard aluminum secondary electron yield (SEY) curve. The analytical results are validated with particle-in-cell simulation in CST Studio. Simulation results show a voltage range of 6.4–19 kV, compared to the analytically calculated values of 8.2 and 18.3 kV for the lower and upper bounds, respectively. Fluorocarbon coating as a means to reduce secondary electron emission is simulated, which shows 46% reduction in peak particle population with an 11.2 nm PTFE coating, with further reduction as coating thickness increases. The results show that the L-shaped cavity is a suitable choice for this IOT design as it does not exhibit single-surface multipactor and will not develop two-surface multipactor at full-power operation.

Rectenna and Patch Microstrip Antenna Proposal for Energy Harvesting in S-band CubeSats

Abstract A proposal of a 2.4 GHz rectenna is presented as a complementary device for the electrical power system (EPS) in CubeSats, with the goal of maintaining its size regulations and providing an extra voltage input to the existing methods, like solar cells and batteries, thus possibly increasing the CubeSat’s durability. The antenna design was done in CST STUDIO SUITE, adjusting different parameters that optimize its performance. There is also an analysis of the rectenna elements, and the equations needed to do it. For the rectifier section of the rectenna, the software ADVANCED DESIGN SYSTEM (ADS) was used, using a band-pass filter and a 3-stage Dickson voltage amplifier. These elements are essential to ensure an optimal and efficient performance of the rectenna that provides an extra voltage source for the subsystems of a nanosatellite.

Semi-Automatic Design of Dual-Band End-Fed Antennas for Digital Antenna Arrays

Introduction. The topic of implementing a dual-band mode of operation for director dipole antennas is represented by a wide range of works, almost all of which are dedicated to studying the properties of a classic dipole. However, the issue of end excitation of radiators for dual-band director antennas remains open. The development of such radiators requires a deep analysis both from the point of view of developing mathematical and electrodynamics models, which corresponds to the tactical and technical requirements of modern digital antenna arrays.Aim. To substantiate a procedure for determining the initial appearance of a dual-band antenna exciter from the standpoint of the systems approach to the design of antenna elements and nodes. This procedure is suitable for a semi-automated design of more complex antenna systems.Materials and methods. As part of the research, the input impedance of a dual-band system consisting of two active radiators and two passive directors was determined using the method of induced electromotive forces (EMF). Models of dual-band director radiators were developed using the CST Studio Suite 2021 full-wave electromagnetic simulation.Results. The results of developing procedures for a semi-automatic design of antennas with a dual-band function of input impedance are presented. Following a comparative analysis, approaches to implementing the printed layout of an antenna comprising standard radio engineering components, which imply serial production, are proposed.Conclusion. The proposed models can be used when designing director, turnstile, and cardioid antennas, as well as antenna arrays. These designs are analogous to antennas based on a classic central excited dipole.

FR2/mmWave, N258 and N261 Bands, 5G Frequency‐Compatible Ultra‐Thin Metamaterial Absorber with Polarization Insensitivity for EMI shielding Applications

AbstractSince adopting 5G technology, a notable rise in the prevalence of electromagnetic (EM) waves in the environment has become a significant concern. To reduce EM interference, broadband metamaterial absorbers offer an alternative solution for protecting devices in defense, communication, and healthcare applications, unlike their narrowband counterparts. This article presents a numerical investigation of an ultra‐thin, polarization‐insensitive metamaterial absorber (MMA) that uses metasurfaces and provides electromagnetic interference (EMI) reduction, covering the FR2/mmWave licensed N258 and N261 bands with an oblique incidence angle of up to 15 degrees. Comprehensive simulations are performed within the CST Studio Suite S2 2023 to examine the absorber's performance. Under normal incidence, the proposed MMA exhibits a wideband absorbency response exceeding 90% within the frequency range of 24.30–28.12 GHz. Moreover, the physical absorption mechanism is explained with electric and magnetic field distributions, including surface current distributions. Confirmation of the lack of mutual interaction among neighboring unit cells is established through testing with 1 × 2 and 2 × 2 arrays. An equivalent circuit model is also developed to confirm the EM simulation findings. The notable features of the proposed MMA make it an exceptional candidate for EM shielding applications, providing EMI reduction and covering the N258 and N261 bands.

Novel numerical analysis of electric fields in the near field of very‐low‐frequency antennas based on the charge simulation method

AbstractVery‐low‐frequency (VLF) transmitting antennas have a crucial influence on the nearby electromagnetic environment. Commercial software packages, such as CST Studio Suite (CST) or Altair FEKO (FEKO), are always utilised to calculate the electric fields of VLF antennas, which consume considerable computing resources and time. The classical method of electric field calculation, the charge simulation method (CSM), is first applied to the calculation of electric field near the VLF transmitting antenna. The distribution characteristics of three‐dimensional electric fields were analysed. The electric field surrounding the antenna exhibited axial symmetry. The highest electric field strength was at the top of the antenna, and as the distance from the antenna increased, the electric field strength exponentially decreased. The comparisons are performed between the results of the CSM and those of commercial software, the average relative errors of CSM on two observation paths are very small, 2.20% and 2.21%, respectively. Meanwhile, the CSM shows considerable advantages in saving calculation resources and improving efficiency. Additionally, the comparison between CSM calculation and the measured data is carried out. The results show that this method can accurately calculate the electric field near VLF transmitting antenna and offer valuable insights and a new solution.

Design of a Wilkinson Power Divider with Harmonic Suppression for Mobile Application

This paper presents a Wilkinson Power Divider (WPD) operating at 6 GHz capable of suppressing unwanted harmonics up to the 3rd harmonic. The design formulas are analysed and presented in detail. Power dividers are widely used in microwave circuit structures. Indeed, this paper outlines the design and simulation of a 1:1 power divider for mobile applications using CST Studio Suite.

Investigation of the radiated emission of honeycomb structured aluminum foam/cellular heatsinks at 1–10 GHz

Metal foams or cellular structures like honeycombs, can also be evaluated according to mechanical, acoustic, thermal, and chemical resistance parameters in terms of functionality. However, it is vital to investigate the performance of these cellular structures' radiated emission (RE), which can be used as PCB heatsinks. In this study, the radiated emission (RE) performance of honeycomb-structured aluminum foam (or cellular) heatsinks (AFH), which can be considered as unidirectional regular foam, is examined in the frequency range of 1–10 GHz as a novelty. Also, the effect of four primary variables (the geometry of AFH, honeycomb hole direction, honeycomb cell size, and honeycomb cell wall thickness) on the RE performance of AFH is investigated. Unlike classical honeycomb production methods, the investment flask mold casting (loss wax) method is preferred due to the complex offset strip geometry of designed honeycombs. The original design offset hexagonal honeycomb structures were successfully produced using this investment casting method with additive manufacturing technologies from molten metal. While all simulations are carried out using CST Studio Suite, the RE performance of the proposed AFHs is measured in a standard 3 m fully anechoic chamber using a reference horn antenna and vector network analyzer (VNA). When the results are examined, the measured and simulated results agree with each other quietly. Regarding RE, structures with a CPI value of 14 are better at low frequencies, while structures with a CPI value of 3.5 are better at high frequencies. Secondly, the honeycomb cell thickness value does not significantly affect EMI performance. Lastly, although there is no significant difference in EMI in the low-frequency region, it is better to use a directional structure with vertical holes in the high-frequency region. As a result, in the design of AFH, the RE performances of the heatsinks and their thermal performance should be considered.

Drone Shaped Fractal Antenna with Defected Ground Structure for RF Energy Harvesting Applications

A proposed multiband drone shaped fractal antenna (Antenna-1) is introduced in this paper that targets the most required frequencies used for radio frequency energy harvesting applications, including WLAN-2.4G, WLAN-5G, WLAN-6G, Mobile DCS1700, Mobile LTE and WIMAX services. A novel fractal shape is designed and combined with a standard square geometrical shape in order to implement the front patch of the antenna. The antenna is simulated with CST Studio Suite software and fabricated on FR-4 substrate. Different antenna stages with parametric study and optimization were implemented to get the best performance from the drone shape fractal antenna. The multiband (Antenna-1) supports six resonate frequencies (1.7155 GHz, 2.424 GHz, 3.36 GHz, 3.789 GHz, 5.843 GHz, 6.886 GHz) with peak gain of (2.83 dBi) at the frequency 2.45 GHz and a maximum bandwidth of (0.4281 GHz) at the frequency 5.8 GHz that make it a suitable antenna for radio frequency energy harvesting applications.

A tunable terahertz chiral metasurface with circular dichroism and Pancharatnam-Berry phase characteristics

A dual-mode reflective chiral metasurfaces, consisting of the photosensitive semiconductors germanium (Ge), vanadium dioxide (VO2), silicon dioxide (SiO2), and gold, is proposed, and the chirality of the metasurfaces is theoretically investigated by using CST Studio suite. The metasurfaces was found to be capable of realizing two modes of operation by adjusting the conductivity of the photosensitive semiconductor germanium with pump light and the conductivity of VO2 by temperature. When Ge is in the dielectric state and VO2 is in the metallic state (Mode I) at 0.791 THz, right CD is 0.904, adjusting the VO2 conductivity can tune the CD in the range 0.1–0.904. When Ge is in the metallic state and VO2 is in the dielectric state (mode II) at 0.841 THz, left CD is 0.91, adjusting Ge conductivity can tune CD in the range 0.06–0.91. By adjusting the geometric parameters of germanium and VO2, the resonance frequency can be tuned. Based on this property, a near-field imaging application has been developed. In addition, based on the Pancharatnam-Berry (PB) phase, the reflection phase distribution of the metasurfaces was designed. By designing different reflection phase distributions, focusing and vortex beam generation were realized.