Antenna Input Power Research Articles

The thermal sensation threshold and its reliability induced by the exposure to 28 GHz millimeter-wave.

The application of 28 GHz millimeter-wave is prevalent owing to the global spread of fifth-generation wireless communication systems. Its thermal effect is a dominant factor which potentially causes pain and tissue damage to the body parts exposed to the millimeter waves. However, the threshold of this thermal sensation, that is, the degree of change in skin temperature from the baseline at which the first subjective response to the thermal effects of the millimeter waves occurs, remains unclear. Here, we investigated the thermal sensation threshold and assessed its reliability when exposed to millimeter waves. Twenty healthy adults were exposed to 28 GHz millimeter-wave on their left middle fingertip at five levels of antenna input power: 0.2, 1.1, 1.6, 2.1, and 3.4 W (incident power density: 27-399 mW/cm2). This measurement session was repeated twice on the same day to evaluate the threshold reliability. The intraclass correlation coefficient (ICC) and Bland-Altman analysis were used as proxies for the relative and absolute reliability, respectively. The number of participants who perceived a sensation during the two sessions at each exposure level was also counted as the perception rate. Mean thermal sensation thresholds were within 0.9°C-1.0°C for the 126-399 mW/cm2 conditions, while that was 0.2°C for the 27 mW/cm2 condition. The ICCs for the threshold at 27 and 126 mW/cm2 were interpreted as poor and fair, respectively, while those at higher exposure levels were moderate to substantial. Apart from a proportional bias in the 191 mW/cm2 condition, there was no fixed bias. All participants perceived a thermal sensation at 399 mW/cm2 in both sessions, and the perception rate gradually decreased with lower exposure levels. Importantly, two-thirds of the participants answered that they felt a thermal sensation in both or one of the sessions at 27 mW/cm2, despite the low-temperature increase. These results suggest that the thermal sensation threshold is around 1.0°C, consistent across exposure levels, while its reliability increases with higher exposure levels. Furthermore, the perception of thermal sensation may be inherently ambiguous owing to the nature of human perception.

Optimal design of aperiodic tri-slot antennas for the conformal ablation of liver tumors using an experimentally validated MWA computer model

ObjectiveThis study aims to demonstrate that the conformal microwave ablation (MWA) of liver tumors could be attained by optimizing the structure of an aperiodic tri-slot coaxial antenna, its insertion depth, and input power. MethodsA computational MWA model with an aperiodic tri-slot coaxial antenna operating at the frequency of 2.45 GHz was built and validated by both an ex vivo and a pilot in vivo experiment with porcine healthy livers. The validated in vivo computational MWA model implemented with a liver tumor was then used as a testbed to investigate the conformal ablation of liver tumors. Five liver tumors in different sizes and shapes were investigated. A genetic algorithm optimization method (NSGA-II) was used to optimize the structure of antenna, insertion depth of antenna, and microwave antenna input power for the conformal ablation of liver tumors. ResultsThe validation results showed that a good agreement in both the spatiotemporal temperature distribution and ablation zone was found between the computer model and the ex vivo experiments at both 45 W, 5 min and 60 W, 3 min treatments and the in vivo experiment at 45 W, 5 min treatment. The optimized simulation results confirmed that five cases of liver tumors in different sizes and shapes can be conformally ablated by optimizing the aperiodic tri-slot coaxial antenna, antenna insertion depth, and microwave antenna input power. ConclusionThis paper demonstrates that the aperiodic tri-slot coaxial antenna can be optimized with the insertion depth and input power for the conformal ablation of liver tumors, regardless the size and shape of liver tumors.

Analysis of the Electrical Performance of Multituned VLF Thirteen-Tower Umbrella Antennas

The concept of multituned thirteen-tower umbrella antenna is developed in this study to address the problem that increasing the power capacity of a single-tuned VLF transmitting antenna leads to a decrease in self-resonance. The calculation method of electrical parameters such as input resistance and radiation efficiency is theoretically analyzed based on the radiation resistance of different antenna units in a thirteen-tower umbrella antenna, and the electrical performance of the single-tuned and multituned thirteen-tower umbrella antennas is simulated and compared with the measured results of the Cutler antenna. Under the same antenna structure parameters and input power, the antenna radiation efficiency of the multituned thirteen-tower umbrella antenna is basically the same as that of the single tuned one. However, the multituned antenna has lower input current and higher self-resonance, which can effectively improve the antenna’s safety and broaden its operating frequency range.

Design and Dosimetric Characterization of a Broadband Exposure Facility for In Vitro Experiments in the Frequency Range 18-40.5 GHz.

A novel exposure facility for exposing cell monolayers to centimeter and millimeter waves (18-40.5 GHz) used by future 5G mobile communication technology and similar applications has been developed. A detailed dosimetric characterization of the apparatus for frequencies of 27 and 40.5 GHz and 60 mm petri dishes, used in a presently ongoing study on human dermal fibroblasts and keratinocytes, was carried out. The exposure facility enables a well-defined, randomized, and blinded application of sham exposure and exposure with selectable values of incident power flux density, and additionally provides the possibility of continuous monitoring of the sample temperature during exposure while it does not require significant deviations from routine in vitro handling procedures, i.e. petri dishes are not required to be placed inside waveguides or TEM cells. Mean specific absorption rate (SAR) values inside the cell monolayer of 115 W/kg (27 GHz) and 160 W/kg (40.5 GHz) per watt antenna input power and corresponding transmitted power density (St ) values at the bottom of the cell monolayer of 65 W/m2 (27 GHz) and 70 W/m2 (40.5 GHz) per watt antenna input power can be achieved, respectively. For reasonable amounts of harvested cells (80% of petri dish bottom area), the variation (max/min) of SAR and St over the cell monolayer remains below 3.7 dB (27 GHz) and 3.0 dB (40.5 GHz), respectively. © 2021 Bioelectromagnetics Society.

In Situ Assessment of 5G NR Massive MIMO Base Station Exposure in a Commercial Network in Bern, Switzerland

This paper describes the assessment of radiofrequency (RF) electromagnetic field (EMF) exposure from fifth generation (5G) new radio (NR) base stations in a commercial NR network in Bern, Switzerland. During the measurement campaign, four base station sites were investigated and the exposure induced by the NR massive multiple-input-multiple-output (MaMIMO) antennas was assessed at 22 positions, at distances from the base station between 30 m and 410 m. The NR base stations operated at 3.6 GHz and used codebook-based beamforming. While the actual field levels without inducing downlink traffic were very low (<0.05 V/m) due to a low traffic load and low antenna input powers of up to 8 W, setting up a maximum downlink traffic stream towards user equipment resulted in a time-averaged exposure level of up to 0.4 V/m, whereas the maximum extrapolated exposure level reached 0.6 V/m. Extrapolated to an antenna input power of 200 W, values of 4.3 V/m and 4.9 V/m, respectively, were obtained, which amount to 0.5–0.6% of the reference level recommended by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). In Bern, it was found that the impact of the NR network on the total environmental RF exposure was very limited; with maximum downlink, it contributed 2% on average. Finally, it was also concluded that extrapolation to the maximum exposure level can be done without prior knowledge of the radiation patterns, directly based on the measurement of the Physical Downlink Shared Channel (PDSCH) resource elements.

Radio frequency susceptibility test of Beidou airborne receiver

The radio frequency susceptibility testing method of RTCA/DO-160G section 20 has been widely utilized to verify the reliability of airborne equipments in civil aviation. However, there are only a few of theory analysis and practical test of Beidou airborne equipment based on the procedure of radio frequency susceptibility test originated from RTCA/DO-160G, the research of radio frequency susceptibility test stemmed from RTCA/DO-160G is aiming at provide theoretical reference and practical bases for civil Beidou airborne receiver. Firstly, a theoretical model of calibration for conducted susceptibility and radiated susceptibility is derived and validated its effectiveness, the derived theoretical model indicate that choosing a suitable injection probe that meets the requirements of standard is much more important than the choose of a high power amplifier, a method for estimating the input power of antenna is also obtained under far field zone. Secondly, an equivalence model based on the susceptibility probability is formulated between the anechoic chamber and reverberation chamber method of radiated susceptibility test, the theory and experimental results show that the model can predict the difference between these two test methods well. Finally, a susceptibility evaluation model is constructed in terms of the needed test signal. The practical minimum radiated susceptibility threshold for continuous wave and pulse modulated signal are 5 V/m and 40 V/m, which indicates the receiver shows a better endurance to pulse interference than continuous wave.

Antenna rectifier using quadrature hybrid coupler for power‐harvesting applications

This article presents the design, simulation, fabrication, and measurement of a compact power-harvesting circuit. A quadrature hybrid coupler is used for this harvesting circuit because of its advantageous matching, high isolation, and lossless characteristic. It properly feeds the bridge rectifier, combining the signals received with two antennas. The bridge rectifier component is a turnout full-wave rectification from a two-wire alternative current input. The measurements found output power to be −25.5 dBm using a 5 KΩ load resistor, at 5 GHz. The transmitter antenna input power level is 7 dBm, at 50 cm distance. Both results of the Friis Equation and the measurements are in agreement. According to the results, the power-harvesting circuit can operate for wireless local area network sensor applications.

Design and Dosimetric Analysis of an Exposure Facility for Investigating Possible Effects of 2.45 GHz Wi-Fi Signals on Human Sleep.

A new head exposure system for double-blind provocation studies investigating possible effects of 2.45 GHz Wi-Fi exposure on human sleep was developed and dosimetrically analyzed. The exposure system includes six simultaneously radiating directional antennas arranged along a circle (radius 0.6 m) around the test subject's head, and enables a virtually uniform head exposure, i.e. without any preferred direction of incidence, during sleep. The system is fully computer-controlled and applies a real wireless local area network (WLAN) signal representing different transmission patterns as expected in real WLAN scenarios, i.e. phases of "beacon only" as well as phases of different data transmission rates. Sham and verum are applied in a double-blind crossover study design and all relevant exposure data, i.e. forward and reverse power at all six antenna inputs, are continuously recorded for quality control. For a total antenna input power (sum of all antennas) of 220 mW, typical specific absorption rate (SAR) in cortical brain regions is approximately 1-2 mW/kg (mass average SAR over respective brain region), which can be seen as a realistic worst-case exposure level in real WLAN scenarios. Taking into account variations of head positions during the experiments, the resulting exposure of different brain regions may deviate from the given average SAR levels up to 10 dB. Peak spatial 10 g average SAR in all brain and all head tissues is between 1.5-3.5 and 10.4-25 mW/kg, respectively. Bioelectromagnetics. © 2020 Bioelectromagnetics Society.

RF Energy Absorption in Human Bodies Due to Wearable Antennas in the 2.4 GHz Frequency Band.

Human exposure to electromagnetic fields produced by two wearable antennas operating in the 2.4 GHz frequency band was assessed by computational tools. Both antennas were designed to be attached to the skin, but they were intended for different applications. The first antenna was designed for off-body applications, i.e. to communicate with a device placed outside the body, while the second antenna model was optimized to communicate with a device located inside the body. The power absorption in human tissues was determined at several locations of adult male and female body models. The maximum specific absorption rate (SAR) value obtained with the off-body antenna was found on the torso of the woman model and was equal to 0.037 W/kg at 2.45 GHz. SAR levels increased significantly for the antenna transmitting inside the body. In this case, SAR values ranged between 0.23 and 0.45 W/kg at the same body location. The power absorbed in different body tissues and total power absorbed in the body were also calculated; the maximum total power absorbed was equal to 5.2 mW for an antenna input power equal to 10 mW. Bioelectromagnetics. 2020;41:73-79 © 2019 Wiley Periodicals, Inc.

A PIC-MCC code RFdinity1d for simulation of discharge initiation by ICRF antenna

Discharges produced and sustained by ion cyclotron range of frequency (ICRF) waves in absence of plasma current will be used on ITER for (ion cyclotron-) wall conditioning (ICWC, eV, ). In this paper, we present the 1D particle-in-cell Monte Carlo collision (PIC-MCC) RFdinity1d for the study the breakdown phase of ICRF discharges, and its dependency on the RF discharge parameters (i) antenna input power Pi, (ii) RF frequency f, (iii) shape of the electric field and (iv) the neutral gas pressure . The code traces the motion of both electrons and ions in a narrow bundle of magnetic field lines close to the antenna straps. The charged particles are accelerated in the parallel direction with respect to the magnetic field BT by two electric fields: (i) the vacuum RF field of the ICRF antenna and (ii) the electrostatic field determined by the solution of Poisson’s equation.The electron density evolution in simulations follows exponential increase, . The ionization rate varies with increasing electron density as different mechanisms become important. The charged particles are affected solely by the antenna RF field at low electron density ( , ). At higher densities, when the electrostatic field is comparable to the antenna RF field , the ionization frequency reaches the maximum. Plasma oscillations propagating toroidally away from the antenna are observed. The simulated energy distributions of ions and electrons at correspond a power-law Kappa energy distribution. This energy distribution was also observed in NPA measurements at ASDEX Upgrade in ICWC experiments.

Optimization of multi-slot coaxial antennas for microwave thermotherapy based on the S11-parameter analysis

The underlying aim of presented article is to determine the optimal location and sizes of the air gaps inside a multi-slot coaxial antenna with 50-ohm feed based on the S11-parameter characteristics of microwave applicator to get the best antenna impedance matching to the treated tissue. The next step is the selection of the limit levels of the antenna input power, for which temperature of the tissue do not exceed known therapeutic elevations for microwave therapies at hyperthermic and ablation temperatures. The proposed approach provides a relatively simple method for optimization of the location and size of slots in the antenna structure. The proper choice of limit values of total antenna input power enables appropriate adjustment of temperature of the target tissue to preserve optimal cancer treatment.

MULTILAYERED BROADBAND ANTENNA FOR COMPACT EMBEDDED IMPLANTABLE MEDICAL DEVICES: DESIGN AND CHARACTERIZATION

Design and characterization of a multilayered compact implantable broadband antenna for wireless biotelemetry applications is presented in this paper. The main features of this novel design are miniaturized size, structure that allows integration of electronic circuits of the implantable medical device inside the antenna, and enhanced bandwidth that mitigates possible frequency detuning caused by heterogeneity of biological tissues. Using electromagnetic simulations based on the finite-difference timedomain method, the antenna geometry was optimized to operate in the 401-406 MHz Medical Device Radio communications service band. The proposed design was simulated implanted in a muscle tissue cuboid phantom and implanted in the arm, head, and chest of a high-resolution whole-body anatomical numerical model of an adult human male. The antenna was fabricated using low-temperature co-fired ceramic technology. Measurements validated simulation results for the antenna implanted in muscle tissue cuboid phantom. The proposed compact antenna, with dimensions of 14mm × 16mm × 2 mm, presented a -10 dB bandwidth of 103 MHz and 92MHz for simulations and measurements, respectively. The proposed antenna allows integration of electronic circuit up to 10mm × 10mm × 0.5 mm. Specific absorption rate distributions, antenna input power, radiation pattern and the transmission channel between the proposed antenna and a half-wavelength dipole were evaluated.

Four Element Wideband Rectangular Dielectric Resonator Antenna Terminated in a Bio-medium

In this paper, a new four element rectangular dielectric resonator antenna (RDRA) for 5.0 GHz WLAN/WiMAX band is proposed. The simulation results for its radiation characteristics and the specific absorption rate (SAR) distribution in a homogenous bio-medium (muscle layer) for different antenna-to-muscle layer spacings are presented at different frequencies in 4.9---5.9 GHz band. The input characteristics of the proposed antenna and a single element RDRA of same size as the element are compared. The effect of changing antenna input power on maximum SAR value is also analyzed. The simulation study has been carried out using CST Microwave Studio software.

Analysis of mobile phone design features affecting radiofrequency power absorbed in a human head phantom

The US FCC mandates the testing of all mobile phones to demonstrate compliance with the rule requiring that the peak spatial SAR does not exceed the limit of 1.6 W/kg averaged over any 1 g of tissue. These test data, measured in phantoms with mobile phones operating at maximum antenna input power, permitted us to evaluate the variation in SARs across mobile phone design factors such as shape and antenna design, communication technology, and test date (over a 7-year period). Descriptive statistical summaries calculated for 850 MHz and 1900 MHz phones and ANOVA were used to evaluate the influence of the foregoing factors on SARs. Service technology accounted for the greatest variability in compliance test SARs that ranged from AMPS (highest) to CDMA, iDEN, TDMA, and GSM (lowest). However, the dominant factor for SARs during use is the time-averaged antenna input power, which may be much less than the maximum power used in testing. This factor is largely defined by the communication system; e.g., the GSM phone average output can be higher than CDMA by a factor of 100. Phone shape, antenna type, and orientation of a phone were found to be significant but only on the order of up to a factor of 2 (3 dB). The SAR in the tilt position was significantly smaller than for touch. The side of the head did not affect SAR levels significantly. Among the remaining factors, external antennae produced greater SARs than internal ones, and brick and clamshell phones produced greater SARs than slide phones. Assuming phone design and usage patterns do not change significantly over time, we have developed a normalization procedure and formula that permits reliable prediction of the relative SAR between various communication systems. This approach can be applied to improve exposure assessment in epidemiological research.

Optimization of Passive Low Power Wireless Electromagnetic Energy Harvesters

This work presents the optimization of antenna captured low power radio frequency (RF) to direct current (DC) power converters using Schottky diodes for powering remote wireless sensors. Linearized models using scattering parameters show that an antenna and a matched diode rectifier can be described as a form of coupled resonator with different individual resonator properties. The analytical models show that the maximum voltage gain of the coupled resonators is mainly related to the antenna, diode and load (remote sensor) resistances at matched conditions or resonance. The analytical models were verified with experimental results. Different passive wireless RF power harvesters offering high selectivity, broadband response and high voltage sensitivity are presented. Measured results show that with an optimal resistance of antenna and diode, it is possible to achieve high RF to DC voltage sensitivity of 0.5 V and efficiency of 20% at −30 dBm antenna input power. Additionally, a wireless harvester (rectenna) is built and tested for receiving range performance.

Design and dosimetric analysis of a 385 MHz TETRA head exposure system for use in human provocation studies

A new head exposure system for double-blind provocation studies investigating possible effects of terrestrial trunked radio (TETRA)-like exposure (385 MHz) on central nervous processes was developed and dosimetrically analyzed. The exposure system allows localized exposure in the temporal brain, similar to the case of operating a TETRA handset at the ear. The system and antenna concept enables exposure during wake and sleep states while an electroencephalogram (EEG) is recorded. The dosimetric assessment and uncertainty analysis yield high efficiency of 14 W/kg per Watt of accepted antenna input power due to an optimized antenna directly worn on the subject's head. Beside sham exposure, high and low exposure at 6 and 1.5 W/kg (in terms of maxSAR10g in the head) were implemented. Double-blind control and monitoring of exposure is enabled by easy-to-use control software. Exposure uncertainty was rigorously evaluated using finite-difference time-domain (FDTD)-based computations, taking into account anatomical differences of the head, the physiological range of the dielectric tissue properties including effects of sweating on the antenna, possible influences of the EEG electrodes and cables, variations in antenna input reflection coefficients, and effects on the specific absorption rate (SAR) distribution due to unavoidable small variations in the antenna position. This analysis yielded a reasonable uncertainty of <±45% (max to min ratio of 4.2 dB) in terms of maxSAR10g in the head and a variability of <±60% (max to min ratio of 6 dB) in terms of mass-averaged SAR in different brain regions, as demonstrated by a brain region-specific absorption analysis.

Boost of plasma current with active magnetic field shaping coils in rotamak discharges

A set of magnetic shaping coils is installed on the Prairie View (PV) rotamak for the study of active plasma shape control in the regimes with and without toroidal field (TF). In the spherical tokamak regime (with TF), plasma current Ip can be boosted by 200% when all five shaping coils (connected in series) are energized. The enhancement of current drive efficiency is mainly attributed to the radial compression and the substantially axial extension of the plasma column; this in turn improves the impedance matching and thus increases antenna input power. In the field-reversed configuration (without TF), plasma current can be boosted by 100% when one middle coil is used; the appearance of radial shift mode limits the achievable value of Ip. The experiments clearly demonstrate that the plasma shape control plays a role in effectively driving plasma current in rotamaks.

Expanded modeling of temperature-dependent dielectric properties for microwave thermal ablation

Microwaves are a promising source for thermal tumor ablation due to their ability to rapidly heat dispersive biological tissues, often to temperatures in excess of 100 °C. At these high temperatures, tissue dielectric properties change rapidly and, thus, so do the characteristics of energy delivery. Precise knowledge of how tissue dielectric properties change during microwave heating promises to facilitate more accurate simulation of device performance and helps optimize device geometry and energy delivery parameters. In this study, we measured the dielectric properties of liver tissue during high-temperature microwave heating. The resulting data were compiled into either a sigmoidal function of temperature or an integration of the time–temperature curve for both relative permittivity and effective conductivity. Coupled electromagnetic–thermal simulations of heating produced by a single monopole antenna using the new models were then compared to simulations with existing linear and static models, and experimental temperatures in liver tissue. The new sigmoidal temperature-dependent model more accurately predicted experimental temperatures when compared to temperature–time integrated or existing models. The mean percent differences between simulated and experimental temperatures over all times were 4.2% for sigmoidal, 10.1% for temperature–time integration, 27.0% for linear and 32.8% for static models at the antenna input power of 50 W. Correcting for tissue contraction improved agreement for powers up to 75 W. The sigmoidal model also predicted substantial changes in heating pattern due to dehydration. We can conclude from these studies that a sigmoidal model of tissue dielectric properties improves prediction of experimental results. More work is needed to refine and generalize this model.

CALCULATION OF WHOLE-BODY SAR FROM A 100 MHZ DIPOLE ANTENNA

This paper presents results of a dosimetry study at an FM broadcasting frequency of 100MHz. The work focused on SAR calculations with high resolution Magnetic Resonance Imaging (MRI)- based full-body models. FDTD computer modeling used a half-wave dipole as the exposure source. Extensive calculations give the variation of SAR with distance and show that whole-body average SAR exhibits a difierent distance dependency from the incident power density. Body size has a signiflcant efiect on SAR. Based on the numerical results, an empirical formula was developed to describe the relationship between antenna input power and distance for the limiting SAR value.

Assessment of the influence of real-world radio station ­antennas

The boom in the use of cellular communications around the world lead to a significant increase in the number of radio base stations (herein referred to as “ERB”) in populated areas. The main objective of this study is to show how the electromagnetic energy spreads out in the environment, and thus verify whether there is compliance with the current le gislation in Brazil by analyzing the propagation characte ristics through computer simulations. In order to quantify the electromagnetic propagation loss it is employed the model COST 231 by Ikegami-Walfisch (European..., 1996). It is also worthy mentioning that real measured data are employed to model the antennas in the ERBs. The influence of various system parameters are assessed and discussed in detail, such as the antenna side lobes, height of the tower in the ERB, antenna inclination angle and input power.