Sleeve Antenna Research Articles

In Vivo Microwave-Induced Thermoacoustic Endoscopy for Colorectal Tumor Detection in Deep Tissue.

Optical endoscopy, as one of the common clinical diagnostic modalities, provides irreplaceable advantages in the diagnosis and treatment of internal organs. However, the approach is limited to the characterization of superficial tissues due to the strong optical scattering properties of tissue. In this work, a microwave-induced thermoacoustic (TA) endoscope (MTAE) was developed and evaluated. The MTAE system integrated a homemade monopole sleeve antenna (diameter = 7 mm) for providing homogenized pulsed microwave irradiation to induce a TA signal in the colorectal cavity and a side-viewing focus ultrasonic transducer (diameter = 3 mm) for detecting the TA signal in the ultrasonic spectrum to construct the image. Our MTAE, system combined microwave excitation and acoustic detection; produced images with dielectric contrast and high spatial resolution at several centimeters deep in soft tissues, overcome the current limitations of the imaging depth of optical endoscopy and mechanical wave-based imaging contrast of ultrasound endoscopy, and had the ability to extract complete features for deep location tumors that could be infiltrating and invading adjacent structures. The practical feasibility of the MTAE system was evaluated i n vivo with rabbits having colorectal tumors. The results demonstrated that colorectal tumor progression could be visualized from the changes in electromagnetic parameters of the tissue via MTAE, showing its potential clinical application.

Comparative Analysis of Simulated Signal-to-Noise Ratio in Loop and Sleeve Antennas at 10.5 Tesla for Human Head Imaging

Comparative Analysis of Simulated Signal-to-Noise Ratio in Loop and Sleeve Antennas at 10.5 Tesla for Human Head Imaging

A 32-Channel Sleeve Antenna Receiver Array for Human Head MRI Applications at 10.5 T.

For human brain magnetic resonance imaging (MRI), high channel count ( ≥ 32 ) radiofrequency receiver coil arrays are utilized to achieve maximum signal-to-noise ratio (SNR) and to accelerate parallel imaging techniques. With ultra-high field (UHF) MRI at 7 tesla (T) and higher, dipole antenna arrays have been shown to generate high SNR in the deep regions of the brain, however the array elements exhibit increased electromagnetic coupling with one another, making array construction more difficult with the increasing number of elements. Compared to a classical dipole antenna array, a sleeve antenna array incorporates the coaxial ground into the feed-point, resulting in a modified asymmetric antenna structure with improved intra-element decoupling. Here, we extended our previous 16-channel sleeve transceiver work and developed a 32-channel azimuthally arranged sleeve antenna receive-only array for 10.5 T human brain imaging. We experimentally compared the achievable SNR of the sleeve antenna array at 10.5 T to a more traditional 32-channel loop array bult onto a human head-shaped former. The results obtained with a head shaped phantom clearly demonstrated that peripheral intrinsic SNR can be significantly improved compared to a loop array with the same number of elements- except for the superior part of the phantom where sleeve antenna elements are not located.

Increasing bandwidth of orthogonally polarised omnidirectional antenna composed of halo and sleeve antennas

AbstractIn this study, we developed and investigated a small‐diameter, low‐profile, wideband orthogonal‐polarisation multiple‐input multiple‐output (MIMO) antenna. A polarisation MIMO antenna is a combination of a modified sleeve antenna for vertical polarisation and a halo antenna with four parasitic elements for horizontal polarisation. Four parasitic elements vertically were loaded above and below the halo antenna, and a sleeve antenna with an upper sleeve structure was inserted inside the halo antenna to achieve a low profile, wideband antenna with a small diameter. Simulation and measurement results showed that the proposed antenna achieved a relative bandwidth of 10.1% (|S11| and |S22| ≤ −10 dB). For the lower frequency wavelength (λmin) in the required bandwidth, the diameter and height of the proposed antenna are 0.14λmin and 0.57λmin respectively. Additionally, it is capable of orthogonal‐polarisation isolation of approximately 20 dB within the operating frequency bandwidth.

Modeling of interstitial microwave hyperthermia for hepatic tumors using floating sleeve antenna.

Microwave hyperthermia is a treatment modality that uses microwaves to destroy cancer cells by increasing their temperature to 41-45°C. This study aims to design, model, and simulate a microwave sleeve antenna for hepatic (liver) hyperthermia. A floating sleeve antenna with 0.5 w input power was designed to resonate at 2.45GHz. The antenna was tested in six different 3D liver models. The models were varied from a very simple model without a tumor and blood vessels to complex models that contain realistic tumors and blood vessels. To test the capability of the proposed antenna for heating the interstitial tumors, the size, shape, and location of the tumor were changed. The specific absorption rate (SAR) and temperature were calculated for each model. The tumors' temperature was elevated between 43 and 45°C, while the temperature of the surrounding tissues was below 41°C. The Specific Absorption Rate (SAR) was between 29 and 30W/kg in the tumors and below 24W/Kg in the surrounding tissues. The return loss of the antenna varied from - 45 to - 25dB for the six models. The antenna could heat hepatic tumors with different sizes and locations. The heating process was performed in a short time by using a very low input power compared to all previous studies.

Evaluation of 8-Channel Radiative Antenna Arrays for Human Head Imaging at 10.5 Tesla.

For human head magnetic resonance imaging at 10.5 tesla (T), we built an 8-channel transceiver dipole antenna array and evaluated the influence of coaxial feed cables. The influence of coaxial feed cables was evaluated in simulation and compared against a physically constructed array in terms of transmit magnetic field (B1+) and specific absorption rate (SAR) efficiency. A substantial drop (23.1% in simulation and 20.7% in experiment) in B1+ efficiency was observed with a tight coaxial feed cable setup. For the investigation of the feed location, the center-fed dipole antenna array was compared to two 8-channel end-fed arrays: monopole and sleeve antenna arrays. The simulation results with a phantom indicate that these arrays achieved ~24% higher SAR efficiency compared to the dipole antenna array. For a human head model, we observed 30.8% lower SAR efficiency with the 8-channel monopole antenna array compared to the phantom. Importantly, our simulation with the human model indicates that the sleeve antenna arrays can achieve 23.8% and 21% higher SAR efficiency compared to the dipole and monopole antenna arrays, respectively. Finally, we obtained high-resolution human cadaver images at 10.5 T with the 8-channel sleeve antenna array.

Comparison of 16-Channel Asymmetric Sleeve Antenna and Dipole Antenna Transceiver Arrays at 10.5 Tesla MRI.

Multi-element transmit arrays with low peak 10 g specific absorption rate (SAR) and high SAR efficiency (defined as are essential for ultra-high field (UHF) magnetic resonance imaging (MRI) applications. Recently, the adaptation of dipole antennas used as MRI coil elements in multi-channel arrays has provided the community with a technological solution capable of producing uniform images and low SAR efficiency at these high field strengths. However, human head-sized arrays consisting of dipole elements have a practical limitation to the number of channels that can be used due to radiofrequency (RF) coupling between the antenna elements, as well as, the coaxial cables necessary to connect them. Here we suggest an asymmetric sleeve antenna as an alternative to the dipole antenna. When used in an array as MRI coil elements, the asymmetric sleeve antenna can generate reduced peak 10 g SAR and improved SAR efficiency. To demonstrate the advantages of an array consisting of our suggested design, we compared various performance metrics produced by 16-channel arrays of asymmetric sleeve antennas and dipole antennas with the same dimensions. Comparison data were produced on a phantom in electromagnetic (EM) simulations and verified with experiments at 10.5 Tesla (T). The results produced by the 16-channel asymmetric sleeve antenna array demonstrated 28 % lower peak 10 g SAR and 18.6 % higher SAR efficiency when compared to the 16-channel dipole antenna array.

A new compact and wideband CPW-fed sleeve antenna

AbstractIn this article, a sleeve antenna with a wide impedance bandwidth that consists of a coplanar waveguide line connected to a metallic cylinder is presented. The effect of design parameters on the impedance bandwidth is considered by some simulations. In addition to the wide impedance bandwidth, the omnidirectional pattern, high efficiency, low cost and easy fabrication process, and compact dimensions cause this antenna to be a good choice for some applications at low VHF/UHF frequency bands. Due to the flexible structure of this antenna, it is possible to cover the various frequency bands by changing the parameters of the antenna. In this work a typical model of the proposed antenna for the frequency range of 127 to 586 MHz is fabricated and compared with other previous works. An equivalent circuit model has been proposed to better understand how the antenna works. The proposed antenna has a bandwidth of about 128.7% for a voltage standing wave ratio (VSWR) of less than 3, compact size of 0.274λ × 0.047λ and higher than 90% efficiency.

Design of a 3D Top-Loaded Low-Profile Sleeve Antenna for UAV Applications

In this article, a 3D top-loaded low profile sleeve antenna for unmanned aerial vehicle (UAV) applications is proposed. By loading a 3D disc cone structure on the top of a sleeve antenna, the overall height of the antenna can be significantly reduced compared with the height of a traditional quarter-wavelength monopole antenna. In addition, adding shorted columns between the top plate of the disc cone and the ground can generate a new resonant point at lower frequency, so that the frequency bandwidth can be effectively extended. Finally, in order to further achieve the miniaturization of the antenna, an annular slot ring structure was etched on the upper surface of the top plate. Under the conditions of $S_{11} , the designed antenna with a total size of $160mm\times 160mm\times 26.6mm\,\,(0.44\lambda \times 0.44\lambda \times 0.07\lambda)$ has a wide band covering from 840MHz to 1.69GHz (67.2%), while the height of the proposed antenna is only $0.07\lambda $ (where $\lambda $ is the wavelength of the lowest frequency point). Moreover, omnidirectional radiation performances through the operating band can be achieved for both the measured and simulated results.

SPPs-Shared Dual-Band Antenna With Large Frequency Ratio

The operating frequency of future communication systems will cover both microwave and millimeter-wave (MMW) bands simultaneously. This paper presents a novel design of spoof surface plasmon polaritons (SPPs) structure-shared dual-band antenna with large frequency ratio, which consists of a planar open sleeve monopole antenna operating at S-band and a taper slot antenna (TSA) at K/Ka-band. In this design, the SPPs structure takes important roles in two aspects: it serves as an equivalent-lens to enhance the gain of TSA and a monopole of the planar open sleeve antenna to keep a low profile. To realize high isolation between the two antennas, a substrate integrated waveguide (SIW) and an integrated coaxial line are designed to feed the TSA and the planar open sleeve monopole antenna respectively. The SPPs-shared antenna shows an enhanced endfire gain of 13.09 dBi in the frequency range of 19.32-32.90 GHz and an omnidirectional gain of 1.06-2.92 dBi over the range of 2.23-3.69 GHz, keeping a compact size. The large frequency ratio of 10.8, low profile and the wide operating bands in both lower and upper frequency ranges can meet many wireless communication applications. Reasonable agreement between the measured and simulated results is observed.

The study of the wideband planar sleeve antenna

In this paper, the wideband planar sleeve antenna with two sleeves on the upper side and two sleeves on the bottom side are analyzed numerically. In the previous study, the wideband planar sleeve antenna is used at frequency 3.5 GHz. The purpose of this research is addressed to analyze the wideband planar sleeve antenna in the range frequency of 400-4000 MHz by using WIPL-D EM Simulator by adjusting the antenna parameter. The antenna upper sleeve, lower sleeve, the length of the antenna and the gap between the lower and upper sleeves are adjusted. The result shows that the wideband planar sleeve antenna is achieved. When the length of the upper sleeve is increased, the antenna will work at lower frequency but the return loss slightly reduced, the same effect occurred by increasing the lower sleeve size, but it doesn’t affect at the lower frequency. When the antenna length is increased, the return loss of the antenna is reduced. Furthermore, the distance between the lower and upper sleeve affects the return loss characteristic. This is indicated that by adjusting the length of the antenna parameter, the antenna is applicable for many systems, such as television system and the ISM system.

Dual‐sleeve wideband monopole antenna for shipborne systems in VHF band

A dual-sleeve wideband monopole antenna with loaded plasma cylinders is proposed for shipborne systems in lower very high frequency (VHF) range. The monopole with sleeves, engineered as vertical polarised element, operates at the frequency from 30 to 100 MHz. It performs good radiation ability with low elevation angle in E-plane. The monopole antenna height over feed point is 0.33λ at the lowest band. Plasma cylinder array as reflector is mounted above the monopole to restrain the deformation of patterns. Impedance and pattern measurements are conducted; the VSWR ≤ 2:1 bandwidth of the sleeve antenna is >107%. Unmanned aerial vehicle system is introduced to measure the radiation patterns at 110 MHz. Obtained results confirm that the proposed antenna is a variable candidate for communications with ships and flying vehicles in anti-stealth systems.

Design of Compact Broadband Omni directional Canonical Sleeve Antenna covering 500-3600 MHz

A novel compact broadband Canonical Sleeve Antenna (CSA) covering 500-3600 MHz with omni directional characteristics is presented in this paper. A new method is employed in which the radiating antenna structure is designed as combination of three different canonical structures: hemispherical, conical and cylindrical elements. To accomplish the broad bandwidth with compact size, dipole antenna is designed by using cylindrical sleeve over the hemispherical dipole with conical extensions and cylindrical attachments. Performance characteristics of CSA is simulated and compared with BiConical Antenna (BCA) and other antenna configurations and found to be best antenna configuration with compact form factor. The antenna has height of 111.43 mm and diameter of 116.66 mm. Simulation studies are carried out using CST Microwave Studio. The simulated results are validated by fabricating CSA and evaluating its performance metrics. CSA has 7.2:1 bandwidth with measured VSWR <2.7:1 and Gain varies from 0 to 3.6 dBi. The antenna finds use in wireless communication industry, spectrum monitoring and defence applications.

Coaxially Fed Monopole Antenna With Choke Structure Using Left-Handed Transmission Line

A composite right/left-handed (CRLH) transmission line (TL) is proposed for a choke structure. The dispersion relation of the CRLH TL is designed with the left-handed (LH) branch at around 700 MHz. The proposed CRLH TL is applied to the choke structure. The radiation patterns and current distributions on the outer conductor of the coaxial cable are calculated to verify the operation of the choke structure. The characteristics of a conventional sleeve antenna are calculated and compared with those of the proposed antenna. To verify the simulation results, the proposed antenna is fabricated. The $|S_{11}|$ characteristics, the radiation patterns, and the total antenna efficiency are measured. At 585 MHz, the length of the monopole and the choke structure using LH TL are 0.12 and 0.05 wavelength, respectively.

Design and Development of a Conformal Printed sleeve dipole antenna operating in 800MHz to 3000MHz

In this paper, a conformal loaded printed sleeve dipole antenna operating in 800MHz to 3000MHz frequency band is designed and presented with measured results. The wide band characteristics are achieved using sleeve configuration along with capacitive loading. The proposed antenna has VSWR ≤ 3:1 with good radiation efficiency and omni-directionality. The proposed antenna is designed in CST Microwave StudioTM and fabricated using photolithography technique. As the antennas is printed on 10 mils thick RT Duroid 5880TM substrate. The antenna is flexible and can be conformed to given cylindrical shaped platform. The proposed conformal antenna finds wide applications in avionics and wireless communication systems.

Microwave ablation of ex vivo bovine tissues using a dual slot antenna with a floating metallic sleeve

Purpose: To study the efficiency of a dual slot antenna with a floating metallic sleeve on the ablation of different ex vivo bovine tissues.Materials and methods: COMSOL Multiphysics® version 4.4 (Stockholm, Sweden), which is based on finite element methods (FEM), was used to design and simulate monopole and dual slot with sleeve antennas. Power, specific absorption rate (SAR), temperature and necrosis distributions in the selected tissues were determined using these antennas. Monopole and dual slot with sleeve antennas were designed, simulated, constructed and applied in this study based on a semi-rigid coaxial cable. Ex vivo experiments were performed on liver, lung, muscle and heart of bovine obtained from a public animal slaughter house. The microwave energy was delivered using a 2.45 GHz solid-state microwave generator at 40 W for 3, 5 and 10 min. Aspect ratio, ablation length and ablation diameter were also determined on ablated tissues and compared with simulated results. Student’s t-test was used to compare the statistically significant difference between the performance of the two antennas.Results: The dual slot antenna with sleeve produces localised microwave energy better than the monopole antenna in all ablated tissues using simulation and experimental validation methods. There were significant differences in ablation diameter and aspect ratio between the sleeve antenna and monopole antenna. Additionally, there were no significant differences between the simulation and experimental results.Conclusions: This study demonstrated that the dual slot antenna with sleeve produced larger ablation zones and higher sphericity index in ex vivo bovine tissues with minimal backward heating when compared with the monopole antenna.

FEM simulation of tapered cap floating sleeve antenna for hepatocellular carcinoma therapy

ABSTRACTMalignant liver tumors are the sixth most common and deadly cancer in the world and the third most common cause of cancer mortality. Hepatocellular carcinoma (primary liver cancer) is one of the most common malignancies worldwide with one of the highest mortality rates. Microwave ablation (MWA) is a new, promising, and multidisciplinary technology designed to destroy unhealthy tissue of various natures by radiating electromagnetic waves with microwave antennas. The finite element method (FEM) has been used in the present work to generate the simulated models of tapered cap floating sleeve antenna for validation of its design concepts, because FEM allows modeling of complex geometries that cannot be solved by analytical methods or finite difference models. The performances have been evaluated in terms of objective metrics, ablation zone, antenna matching, power absorption and SAR pattern.

DESIGN OF A WIDEBAND SLEEVE ANTENNA WITH SYMMETRICAL RIDGES

In this letter, a novel sleeve antenna with wideband characteristic is presented for wireless communication applications. By employing a sleeve structure, impedance bandwidth of the antenna is improved through exciting a new resonant point. To obtain an impedance bandwidth enhancement further, four symmetrical ridges are introduced between the sleeve and the main radiator. An excellent wideband impedance bandwidth for VSWR ≤ 2 of 148.45% is achieved, covering the frequency range from 1.04 to 7.03 GHz, and good monopole-like radiation patterns are obtained where the un-roundness in the H-plane is less than 1.49 dB. It is very suitable for recent wireless communication services such as DCS, PCS1900, UMTS, IMT2000, WLAN, WiMAX2350/3500, WiBro, etc.

A NOVEL WIDEBAND SLEEVE ANTENNA WITH CAPACITIVE ANNULUS FOR WIRELESS COMMUNICATION APPLICATIONS

A novel wideband sleeve antenna with capacitive annulus for wireless communication applications is presented in this paper. A sleeve structure is introduced to improve the impedance bandwidth through exciting a new resonate point. By loading capacitive annulus at the center of the sleeve, an impedance bandwidth enhancement is achieved at the upper frequency band. The measured impedance bandwidth for VSWR • 2 about 142.8% ranging from 1.01 to 6.06GHz is achieved, and monopole-like radiation patterns are presented. A prototype has been fabricated and tested, and the experimental results validate the design procedure. It is su-cient for accommodating recent wireless communication services such as DCS1800, PCS1900, IMT2000, WLAN, WiMAX2350/3500, etc.

Focusing system of burst electromagnetic waves for medical applications

Bioelectrics has attracted much attention. Inducing apoptosis in malignant cells using subnanosecond pulses has previously been investigated; these results have encouraged the authors to develop a burst electromagnetic wave focusing system for cancer treatment through the induction of apoptosis to cells. Burst electromagnetic waves are characterized by a high-frequency and narrow band signal over a very short duration. This system consists of a radiating antenna and an ellipsoidal reflector which focuses radiation waves. The ellipsoidal reflector has the characteristic of focusing burst electromagnetic waves radiated from the first focal point to the second focal point, thus enhancing the electric field at the second focal point. This system is immersed in heated water to avoid permittivity mismatch between living tissue and the water in which electromagnetic waves propagate, thus reducing reflection and refraction at the surface of biological tissue. This paper presents experimental and simulated results purposed on narrowing focusing point area. The focusing of burst electromagnetic wave at the second focal point was confirmed by preparing a distribution map of electric fields. The experiment and simulation compared three types of transmitting antenna: sleeve, brown and discone antennas. The discone antenna was found to give the shortest FWHM of the electric field distribution. Attenuation of burst electromagnetic waves by biological tissue was investigated using pig tissue: skin, fat and muscle. Attenuation by muscle was found to be greatest. Thicker tissue was found to lead to greater attenuation.