Double Slot Antenna Research Articles

Effect of the antenna slot numbers and position on the performance of microwave ablation

Microwave ablation (MWA) is a type of thermal ablation used for cancer treatment in interventional radiology. To induce localized tissue heating MWA employs electromagnetic waves within the microwave energy spectrum, which is done by the precisely designed antenna. This study substantially emphasizes the design and performance ameliorating of slot (both single and double) antennae and compares the results with conventional monopole antennae in terms of temperature distribution, specific absorption ratio (SAR), and thermal tissue damage rate. The simulation has been done in COMSOL by solving the Bioheat equation along with Maxwell electromagnetic equations using the finite element method. The simulation results reveal that the double-slot antenna has the most accurate and directional heat dissipation for liver tumors as well as the highest tissue damage rate and SAR. The highest SAR was found to be 3500 ​W/kg and 3350 ​W/kg at the implant depth of 61 ​mm and 63 ​mm for double and single-slot antennae, respectively. In addition, the fastest tissue damage occurred near the upper slot of the double-slot antenna. This study helps to understand the basic design parameters for enhancing single and double-slot antennae performance.

마이크로웨이브 캐비티 모드 전환에 의한 웨이퍼 가열 특성

As a solution to the limitations of semiconductor miniaturization and multilayer technology, Atomic Layer Deposition(ALD) and Atomic Layer Etching(ALE) technologies are attracting attentions. For ALD and ALE process technologies, temperature uniformity is an important factor in determining the film quality of thin films and aspect ratio. Conventionally, an indirect heating method by a buried heater that heats the substrate is used, but the method has a decrease in productivity due to the preheating process. This study introduce a direct wafer heating method using GHz band microwaves to suggest the direction for new heater equipment to solve the problems of the existing method. At atmospheric pressure, the 2.45 GHz microwave is radiated through a double-slot antenna to heat a 12inch silicon wafer. The microwave propagates through the waveguide in TE10 mode and heats the wafer by cavity heating. It was confirmed through simulations and experiments that the wafer can be heated quickly using microwaves and the temperature distribution can be made uniform by the cavity conversion.

Thermal Evaluation of Multi-Antenna Systems Proposed to Treat Bone Tumors: Finite Element Analysis.

Microwave ablation is commonly used in soft tissue tumors, but its application in bone tumors has been barely analyzed. Antennas to treat bone tissue (~3 cm2), has been lately designed. Bone tumors at pathological stage T1 can reach 8 cm wide. An antenna cannot cover it; therefore, our goal is to evaluate the thermal performance of multi-antenna arrays. Linear, triangular, and square configurations of double slot (DS) and monopole (MTM) antennas were evaluated. A parametric study (finite element method), with variations in distance between antennas (ad) and bone thickness (bt) was implemented. Array feasibility was evaluated by SWR, ablated tissue volume, etc. The linear configuration with DS and MTM antennas showed SWR ≤ 1.6 for ad = 1 mm–15 mm and bt = 20 mm–40 mm, and ad = 10 mm–15 mm and bt = 25 mm–40 mm, respectively; the triangular showed SWR ≤ 1.5 for ad = 5 mm–15 mm and bt = 20 mm–40 mm and ad = 10 mm–15 mm and bt = 25 mm–40 mm. The square configuration (DS) generated SWR ≤ 1.5 for ad = 5 mm–20 mm and bt = 20 mm–40 mm, and the MTM, SWR ≤ 1.5 with ad = 10 mm and bt = 25 mm–40 mm. Ablated tissue was 4.65 cm3–10.46 cm3 after 5 min. According to treatment time and array configuration, maximum temperature and ablated tissue is modified. Bone tumors >3 cm3 can be treated by these antenna-arrays.

Analysis of Nonsquare Artificial Dielectric Layers and Application to the Design of Anisotropic Slabs

We present a general analysis to describe non-square artificial dielectric layers (ADLs). Closed-form expressions for the equivalent layer impedance are given for generic plane-wave incidence, assuming that the ADLs have different geometrical parameters in the x- and y-directions. The analytical expressions account for the interaction between layers due to higher-order Floquet modes, thus remain valid for arbitrarily small electrical distance between layers. Such non-square geometries allow the design of artificial anisotropic slabs with azimuth-dependent effective refractive index. As an example for an application, the equivalent model is used to design the superstrate of a double slot antenna, with independent pattern shaping in the two main planes.

Double slot aerosol jet printed antenna for X-band applications

A double slot antenna for X-band applications was designed and aerosol jet printing technology was used to fabricate the prototype with silver nano-ink on a flexible polyimide substrate. We investigated the microwave losses of printed antennas in the range from 100 kHz to 27 GHz, obtained at sintering temperatures of 200 °C and 250 °C. Double slot X-band antennas have been calculated and measured. It was found that an operating bandwidth of the printed antenna is 10% in the region of the central frequency of 10.5 GHz. Thus, the possibility of forming antennas on flexible polymer substrates with high functional characteristics by aerosol jet printing method has been demonstrated.

Double Slot Antenna for Microwave Thermal Ablation to Treat Bone Tumors: Modeling and Experimental Evaluation

According to statistics of the American Cancer Society, the number of young people diagnosed with bone tumors is growing. Surgery and radiotherapy are the common treatments, however they have several side effects which affect the patient’s life. Therefore, a cheaper and less side-effect therapy called thermal ablation has been explored. The goal of this paper is to measure the therapeutic temperatures and the viability of a double slot antenna designed to treat bone tissue by microwave ablation. The antenna (at an operating frequency of 2.45 GHz) was designed, modeled, constructed, and experimentally evaluated. The finite element method was used to predict the antenna performance by means of 2D axisymmetric models. The modeling parameters were used to build the antenna. The experimental evaluation shows that the antenna behavior is repeatable and the standing wave ratio (SWR) was around 1.5–1.8. Temperatures around 60–100 °C were achieved over the bone tissue. The antenna insertion modifies the antenna performance. An insertion lower than 3.5 cm is not recommended because the convection effects modified the tissue temperature. The thermal patterns showed a heat focus near to the slots, which makes it possible for use in the treatment of small tumors.

Computational FEM Model and Phantom Validation of Microwave Ablation for Segmental Microcalcifications in Breasts Using a Coaxial Double-Slot Antenna.

Introduction Cancer is the second leading cause of death worldwide. Breast cancer is the second most common cause of cancer-related mortality, accounting for 11.6% of the total number of deaths. The main treatments for this disease are surgical removal of the tumor, radiotherapy, and chemotherapy. Recently, different minimally invasive technologies have been applied (e.g., emission of electromagnetic waves, thermal and chemical means) to overcome the important side effects of these treatment modalities. The objective of this study was to develop and evaluate a predictive computational model of microwave ablation. Materials and Methods The predictive computational model of microwave ablation was constructed by means of a dual-slot coaxial antenna. The model was compared with an experiment performed using a breast phantom, which emulates the dielectric properties of breast tissue with segmental microcalcifications. The standing wave ratio (SWR) was obtained for both methods to make a comparison and determine the feasibility of applying electromagnetic ablation to premalignant lesions in breasts. Specifically, for the analysis of segmental microcalcifications, a breast phantom with segmental microcalcifications was developed and two computational models were performed under the same conditions (except for blood perfusion, which was excluded in one of the models). Results The SWR was obtained by triplicate experiments in the phantom, and the measurements had a difference of 0.191 between the minimum and maximum SWR values, implying a change of power reflection of 0.8%. The average of the three measurements was compared with the simulation that did not consider blood perfusion. The comparison yielded a change of 0.104, representing a 0.2% change in power reflection. Discussion. Both experimentation in phantom and simulations demonstrated that ablation therapy can be performed using this antenna. However, an additional optimization procedure is warranted to increase the efficiency of the antenna.

Percutaneous Microwave Ablation: Applications for Liver; Recommendations for COVID-19 Patients

Microwave ablation (MWA) is an alternative to surgical resection of solid tumors and plays an essential role in the treatment of malignancies and is widely used for hepatic tumors. This paper reviews all the commercial devices and the most recent noncommercial designs and principles behind them alongside the recent ly reported developments and issues of MWA. The paper also provides microscopic insights on effects of microwave irradiation in the body. Based on our review we conclude that MWA is a safe and effective minimally-invasive method with high ablation completion rates. However, for large tumors the completion rates slightly decrease, and recurrences increase. Thus, for large tumors we suggest using multiple antenna placements. Some comparisons between the two common ablation frequencies 915 MHz and 2.45 GHz have shown inconsistent results mainly due to non-identical conditions. This review suggests that 915 MHz devices are more effective for ablating large tumors and the theory behind MWA effects corroborates this proposition. For small tumors or tumors adjacent to vital organs, however, 2.45 GHz is suggested due to its more localized ablation zone. Among the antenna designs, the double-slot antenna with metallic choke seemed more effective by localizing the radiation around the tip of the antenna and preventing the backward radiation towards the skin. MWA should be considered for COVID-19 patients with hepatic tumors as a fast treatment with a short recovery time. As liver injury is one of the risk factors for COVID-19 patients, liver function tests including ALT and AST, and bilirubin measurements are recommended. Moreover, the patient treated with drugs including remdesivir, tocilizumab, lopinavir, chloroquine and hydroxychloroquine need more intensive monitoring. Considering MWA for all patients is highly suggested during pandemics when the clinical resources are stretched to capacity. Funding: This research was financially supported by the Natural Sciences and Engineering Research Council of Canada and by University of Guelph COVID-19 Research Development and Catalyst Fund.Conflict of Interest: The authors declare that they have no conflict of interest.

Generation of plane spiral orbital angular momentum using circular double-slot Vivaldi antenna array

A novel and feasible solution to generate plane spiral orbital angular momentum (PSOAM) vortex beam is proposed in this paper. The general principle of generating PSOAM in circular antenna array (CAA) is deduced, and verified by the simulation of the dipole CAA. Four double-slot Vivaldi antenna elements connect sequentially and are inserted into a CAA, which makes the proposed antenna easily fabricated and fully miniaturized. Both simulated and measured results show that it can generate PSOAM with l = 3 (l is the mode number of vortex wave) at 5 GHz. The vortex phase of l = 3 is observed, the measured peak gain is 5.7 dB. The VSWR remains below 2 from 4 to 6 GHz, which shows the impedance bandwidth of S11 < −10 dB is more than 40%.

Graphene-based microwave coaxial antenna for microwave ablation: thermal analysis

AbstractIn this study, the problem of backward heating in microwave ablation technique is examined and an electromagnetic solution based on the use of high impedance graphene material is presented for its mitigation. In this context, a one-atom-thick graphene layer is added on the coaxial double slot antenna. In addition to the electromagnetic behavior, thermal effects caused by the graphene-covered antenna are emphasized. The graphene's conductivity being highly dependent on its chemical potential and the relaxation time, a parametric study is performed to determine a range of tolerances within which the graphene-coated antenna outperform a typical graphene-free antenna. The range of values is found to be 0 &lt; μc &lt; 0.5 eV and τ &lt; 0.4 ps, for the chemical potential and the relaxation time, respectively. The backward heating problem being prevented, the ablation region is ensured to be spherical around the tip of the antenna. Effects of the graphene layer to the heat dissipation in the tissue, the necrotic tissue ratio (damage to the cancerous tissue of the caused by electromagnetic energy), and the treatment time using the coaxial double slot antenna were examined. The results show that the heat dissipation is concentrated around the slots (region of cancerous tissue) and a higher necrotic tissue ratio can be achieved with a graphene-covered double slot antenna in a shorter time.

Use of microwave ablation for thermal treatment of solid tumors with different shapes and sizes-A computational approach.

Microwave Ablation (MWA) is one of the most recent developments in the field of thermal therapy. This approach is an effective method for thermal tumor ablation by increasing the temperature above the normal physiological threshold to kill cancer cells with minimum side effects to surrounding organs due to rapid heat dispersive tissues. In the present study, the effects of the shape and size of the tumor on MWA are investigated. To obtain the temperature gradient, coupled bio-heat and electromagnetic equations are solved using a three-dimensional finite element method (FEM). To extract cellular response at different temperatures and times, the three-state mathematical model was employed to achieve the ablation zone size. Results show that treatment of larger tumors is more difficult than that of smaller ones. By doubling the diameter of the tumor, the percentage of dead cancer cells is reduced by 20%. For a spherical tumor smaller than 2 cm, applying 50 W input power compared to 25 W has no significant effects on treatment efficiency and only increases the risk of damage to adjacent tissues. However, for tumors larger than 2 cm, it can increase the ablation zone up to 21%. In the spherical and oblate tumors, the mean percentage of dead cells at 6 GHz is nearly 30% higher than that at 2.45GHz, but for prolate tumors, treatment efficacy is reduced by 10% at a higher frequency. Moreover, the distance between two slots in the coaxial double slot antenna is modified based on the best treatment of prolate tumors. The findings of this study can be used to choose the optimum frequency and the best antenna design according to the shape and size of the tumor.

Planar double-slot antenna integrated into a Nb5N6 microbolometer THz detector.

In this Letter, we propose and demonstrate a new type of planar double-slot antenna for a Nb5N6 microbolometer terahertz (THz) detector. The calculated results show that the planar antenna possessed high coupling efficiency, and the THz signals were obviously focused on the antenna center place. The new planar antenna was integrated with Nb5N6 microbolometer THz detectors using micro-fabrication technology. The measured results showed that the maximum optical voltage responsivity (Ro) of the detectors reached up to 113 V/W at 0.643 THz, and the corresponding noise equivalent power was 44pW/√Hz. In addition, the performance of double-slot antennas applied into array detectors in a tunable Fabry-Perot cavity was investigated. The measured results of the Nb5N6 THz detector remained almost unchanged when the distance between the chip substrate and the copper plate was altered. This indicated that this planar double-slot antenna, which possessed the advantages of high coupling efficiency and easy integration, has great application prospects in a THz detector.

Wideband Epidermal Antenna for Medical Radiometry.

Microwave thermometry is a noninvasive and passive technique for measuring internal body temperature. Wearable compact antennas, matched to the specific body area, are required for this method. We present a new epidermal wideband antenna for medical radiometry. The double asymmetric H-shaped slot antenna was designed to be matched to different parts of the body without fat layers. The slots are fed by a short-circuited microstrip line in order to decrease size and back radiation, thus reducing potential interferences. In this way, contribution to radiometric temperature due to back radiation is lower than 4%, versus the 20% of the volume under investigation, over the whole operating frequency band. The designed prototype was manufactured on a flexible substrate. The antenna is a very small size, to make it comfortable and suitable for being used by patients with different body mass indexes. The double H-shaped antenna shows good wideband matching results from around 1.5 GHz up to 5 GHz, in different body locations such as the neck, foot instep and foot sole.

Design of double-slot antennas for terahertz array detectors in flip chip packaging.

In flip chip packaging, the performance of terahertz (THz) array detectors is directly influenced by the flip chip. In addition, predicting this effect is difficult because the readout circuits in the flip chip are very complex. In this study, to reduce the influence of the flip chip, we design a new type of double-slot antennas for THz array detectors. For comparison, we designed and analyzed dipole antennas with the same period. Numerical simulations showed that the coupling efficiency of the double-slot array antennas at approximately 0.6255 THz does not degrade, if the flip chip structure is changed. However, in the case of dipole array antennas with the same period of 250 µm, coupling efficiency was severely affected by the flip chip structure. These results revealed that double-slot antennas are more applicable to THz array detectors compared with dipole antennas, as they can more effectively reduce the influence of the flip chip. Furthermore, we integrated the double-slot antennas into Nb5N6 THz array detectors using the micro-fabrication technology. Measurement results indicated that double-slot antennas possess the advantages of facile preparation and large-scale integration, which provide great potential for THz array detectors in flip chip packaging.

Modal Analysis of a Circular Slot Monopole Antenna for UWB application

In this study, a wideband double slot antenna is introduced. The proposed monopole antenna is designed using the theory of characteristic mode for slot monopoles. A circular shape is used as the initial design stage, to enhance the bandwidth, two circular slots are employed. Four modes have been excited to gain a physical insight and to find out which mode is dominant. The design and analysis were completed utilizing both the time domain and multilayer solver in CST 2017, without considering the feeding port. An antenna model in UWB frequency is constructed. Experimented and simulated results shows that the proposed planar structure has a wide impedance width with good radiation characteristics.

A Study of a Narrow-Band Receiving System of Cold-Electron Bolometers for the 220 and 240 GHz Channels using an Oscillator Based on the High-Temperature YBCO Superconductor

We present the results of theoretical and experimental studies of the resonant properties of a single cell of a receiving system based on cold-electron bolometers (CEBs) with a double-slot antenna and curved coplanar lines, which is intended for receiving a signal in the range 220–240 GHz with a bandwidth of 5%. The resonant properties of a CEB located on the cryostat plate with a temperature of 0.3 K, are measured using an oscillator based on high-temperature superconductor (HTS) of yttrium barium copper oxide (YBCO), placed inside the same cryostat on a plate with a temperature of 4 K, which allows one to obtain smooth amplitude-frequency characteristics.

Terahertz Source Radiating to Open Space Based on the Superconducting Flux-Flow Oscillator: Development and Characterization

We have elaborated, fabricated, and tested a terahertz source based on the Josephson flux-flow oscillator (FFO) integrated with a transmitting lens antenna. The oscillator was coupled to the on-chip double-slot antenna via microstrip lines, and the chip was mounted on the silicon lens providing the continuous terahertz emission output. The oscillator samples were made of superconductor–insulator–superconductor (SIS) trilayers based on Nb/AlN/NbN, with a gap voltage of about 3.6 mV. The output emission was studied using two independent techniques: a THz spectrometer based on the SIS receiver with a high spectral resolution (better than 0.1 MHz) and an Si bolometer. An operating range of the oscillator of 400–580 GHz and a ratio of detected signal to background signal at the receiver output of up to 55 dB are obtained. In addition, a design for the oscillator with an integrated harmonic mixer for FFO locking is developed and fabricated using Nb/AlO x /Nb trilayers, which is better for FFO operation than Nb/AlN/NbN trilayers at some frequencies due to lower surface losses and hence better spectral properties. The pumping of the mixer by the FFO output power was measured and found to be sufficient for phase locking.

Impact of Antenna Design on the Electric-Field Direction Sensitivity of Zero-Biased Y–Ba–Cu–O Detectors to Ultra-Short THz Pulses

Detectors made from sub-micron-sized bridges of the high-T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconductor Y-Ba-Cu-O have unique properties useful for the detection of THz radiation, namely evidence of a detector response with an additional sensitivity to the direction of the electric field of short THz pulses when used without a transport current in the so-called “zero-bias” regime. In order to examine the influence of the antenna design on the detector response, we have conducted electromagnetic simulations and performed experiments at a synchrotron light source and with a photomixing setup as sources for short THz pulses. In this paper, we evaluate a narrow-band double-slot antenna as well as a broadband log-spiral antenna design.

Design, Simulation and Fabrication of Multiband Antenna using HFSS

Microstrip antennas are popular because of their low profile, light weight and low cost but narrow bandwidth and gain are the main disadvantages of this antenna. In this paper Multiband Octagonal Patch Antenna has been designed by ring slot technique for working in nine different frequencies presented in multi band C-band, X-band, Ku-band, K-band, Ka-band, Q-band and U-bands. Main applications of these bands are used in terrestrial microwave communications. In this research work, the performance of octagonal patch antenna operating at 7 different bands is analyzed. The Design methodology of the proposed research carried in 2 major modules. 1. Design of Single Octagonal Ring Slot antenna, 2. Design of Double Octagonal Ring Slot antenna. In the first design a single octagonal ring slot microstrip patch antenna is developed which resonates at six frequencies of five different frequency bands of C-band, Ku-band, K-band, Q-band and U-bands. In the second design a double octagonal ring slot microstrip patch antenna is developed which resonates at nine frequencies of six different frequency bands of X-band, Ku-band, K-band, Ka-band, Q-band and U-bands. The proposed antenna has been simulated by HFSS and measured by combinational analyzer.

A dual-band cold-electron bolometer with on-chip filters for the 220/240 GHz channels of the LSPE instrument

We are developing multi-chroic double-slot antenna with cold-electron Bolometer (CEB) on-chip filters for the 220/240 GHz interstellar dust monitoring channels of the LSPE–SWIPE experiment. For this goal, we used a narrowband double-slot resonant antenna with CEBs connected by coplanar lines. The simulations show that we have achieved 5% bandwidth for 220 GHz and 5.5% bandwidth for 240 GHz in our numeric modeling for the single cells. A series array of unit cells using double-slot design and coplanar lines with CEBs shows proper frequency selection. Estimations of the noise properties of the CEB arrays in a voltage-biased mode with the SQUID readout show photon-noise limited operation for the optical power load of 6 pW for channel 220 GHz and 20 pW for channel 240 GHz.