Transmitted Power Density Research Articles

Assessment of Transmitted Power Density in the Planar Multilayer Tissue Model due to Radiation from Dipole Antenna

Recent relevant safety guidelines IEEE-Std C95.1- 2019 and ICNIRP-RF Guidelines 2020 have converged towards 6 GHz as a transition frequency from specific absorption rate (SAR), as basic restriction quantity, to absorbed power density (APD). Namely, the penetration of electromagnetic waves into the human tissue rapidly decreases as frequency increases, therefore, tissue heating can be considered as superficial above 6 GHz. However, besides the APD, an alternative internal dosimetric quantity transmitted power density or TPD is sometimes computed since its relation to SAR is more obvious and is easier to obtain. This paper deals with an analytical/numerical approach to determine TPD in planar multi-layered model of the human tissue exposed to the dipole antenna radiation. Analytical approach deals with assumed sinusoidal current distribution, while numerical approach pertains to the determination of current by solving the corresponding Pocklington integro-differential equation via Galerkin-Bubnov Indirect Boundary Element Method. The novelty presented in this paper with respect to previous work is a multilayer geometry whose effects are considered via the corresponding Fresnel plane wave reflection/transmission approximation. Some illustrative results for current distribution, transmitted field, volume power density (VPD) and TPD at various frequencies and distances of the antenna from the interface are given.

On Optimal Power Allocation in Multibeam Multicast NOMA for Satellite Communication Systems

This paper addresses two key challenges in the multibeam multicast non-orthogonal multiple access (MB-MC-NOMA) scheme and respective beamforming design problems in satellite systems. Achieving the max-min fairness (MMF) and maximum sum-rate among multiple multicast groups of users are jointly considered in a theoretical information framework. It is assumed that each frame contains information of multiple users in multicast transmission. Therefore, contrary to the unicast linear precoding, we have developed the multicast linear precoding with mapping function considering trade-offs to deal with the lack of the spatial degree of freedom. In our proposed scheme, each beamforming vector conveys information to more than one group of users in a NOMA framework, relying on the superposition techniques at the transmitters and successive interference cancellation (SIC) at the receivers. We have derived the capacity rates achievable in each beam, proposing the methods to maximize the minimum rate and weighted sum-rate. Considering the dependency of the broadcasting power and the respective achievable rates, the equivalent channel and water-filling algorithm for the MB-MC-NOMA is developed; as such, the optimal transmit power density for the groups of users within multiple beams are efficiently computed. The extensive simulation results confirm the proposed theoretical findings, providing a considerable boost in both minimum-rate and sum-rate with respect to state-of-the-art multibeam multicast satellite systems.

Numerical Study on the On-Grid Performance of Superconducting Cable Cooperated With R-SFCL

The high temperature superconducting (HTS) cable has shown promising prospects in megacities for the advantages of high transmission power density and low loss. However, when HTS cable is working on grid, various kinds of faults may cause irreversible damage, resulting in the failure of reclosing. In this paper, the resistive superconducting fault current limiter (R-SFCL) is introduced into the power system to cooperate with the HTS cable, so as to reduce the potential damage caused by fault current. Firstly, the equivalent circuit models are established, and then transient response of HTS cables under fault condition is analyzed, the recovery time of HTS tapes are used to define the design of R-SFCL. Finally, the operating reliability of HTS cable has been evaluated and measures about adaptive reclosing times were proposed under different fault currents.

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.

Age-dependence of electromagnetic power and heat deposition in near-surface tissues in emerging 5G bands

With the development of 5th generation (5G) mobile networks people of different ages will be exposed in the upper part of the microwave spectrum. From the perspective of non-ionizing radiation dosimetry, an accurate analysis of age-dependent electromagnetic power deposition and resulting heating is required. In this study, we evaluate the effect of age on exposure at 26 GHz and 60 GHz. A near-surface tissue model illuminated by a plane wave is used to asses the exposure considering both frequency-independent and frequency-dependent limits. The age-related variation of the skin thickness and tissue electromagnetic properties has been considered. Moreover, the blood flow decrease rate has been taken into account to assess the age-dependent heating. Our results demonstrate that the overall variations of the power density, specific absorption rate (SAR) and heating in the near-surface tissues are limited to about 10–15%. These variations are mainly due to the tissue permittivity and blood flow change with age. In contrast to the transmitted power density that increases with age, the peak SAR decreases at both frequencies. The peak steady-state heating increases from 5 to 70 years old by roughly 11% at 26 GHz and 13% at 60 GHz.

The Novel CPW 2.4 GHz Antenna with Parallel Hybrid Electromagnetic Solar for IoT Energy Harvesting and Wireless Sensors

The design and implementation's novelty simultaneously utilizes the antenna's frequency, polarization, and feed structure to maximize the harvested RF energy and become a microstrip communication circuit for wireless sensor or communication systems in IoT devices. In addition, the optimization of the parallel circuit configuration has a voltage doubler model with an integrated parallel system and thin-film solar cells. Implementation of the antenna structure has two-line feeds in one antenna. Usage both feeds have the same function as CPW circular polarization. Another advantage is that there is no miss-configuration when installing the port exchanges when using both output ports simultaneously. The 2-port antenna has an area of 1/2 per port (where accessible wavelengths work well at the 2.4 GHz frequency). It has been shown to achieve a relatively narrow bandwidth of 86.5 percent covering WiFi frequency band networks and IoT communications. It does not require additional filters and analog matching circuits that cause power loss in the transmission process in parallel voltage doubler circuits. Integrating a reflector on the CPW antenna with two ports for placement of thin-film solar cells provides antenna gain of up to 8.2 dB. It provides a wide beam range with directional radiation. Using a multi-stage parallel to increase voltage output and integrated with a thin-film solar cell converter proves efficient in the 2.4 GHz frequency band. When the transmission power density is -16.15 dBm with a tolerance of 0.023, the novel energy harvester configuration circuit can produce an output voltage of 54 mV dc without adding solar cell energy. And Integrated thin-film solar cell a light beam of 300 lux in the radiation beam area of -16.15 dBm, the energy obtained has a value of 1,74467V. It also shows that the implementation of this configuration can produce an optimal dc output voltage in the actual indoor and outdoor ambient settings. The optimization of antenna implementation and the communication process with Multiple signal classifications improves the configuration of antennas that are close to each other and have identical phase outputs. It is instrumental and efficient when applied to IoT devices.

Antenna/Body Coupling in the Near-Field at 60 GHz: Impact on the Absorbed Power Density

Wireless devices, such as smartphones, tablets, and laptops, are intended to be used in the vicinity of the human body. When an antenna is placed close to a lossy medium, near-field interactions may modify the electromagnetic field distribution. Here, we analyze analytically and numerically the impact of antenna/human body interactions on the transmitted power density (TPD) at 60 GHz using a skin-equivalent model. To this end, several scenarios of increasing complexity are considered: plane-wave illumination, equivalent source, and patch antenna arrays. Our results demonstrate that, for all considered scenarios, the presence of the body in the vicinity of a source results in an increase in the average TPD. The local TPD enhancement due to the body presence close to a patch antenna array reaches 95.5% for an adult (dry skin). The variations are higher for wet skin (up to 98.25%) and for children (up to 103.3%). Both absolute value and spatial distribution of TPD are altered by the antenna/body coupling. These results suggest that the exact distribution of TPD cannot be retrieved from measurements of the incident power density in free-space in absence of the body. Therefore, for accurate measurements of the absorbed and epithelial power density (metrics used as the main dosimetric quantities at frequencies > 6 GHz), it is important to perform measurements under conditions where the wireless device under test is perturbed in the same way as by the presence of the human body in realistic use case scenarios.

Limitations of Incident Power Density as a Proxy for Induced Electromagnetic Fields.

The most recent safety guidelines define basic restrictions for electromagnetic field exposure at frequencies more than 6 GHz in terms of spatial- and time-averaged transmitted power density inside the body. To enable easy-to-perform evaluations in situ, the reference levels for the incident power density were derived. In this study, we examined whether compliance with the reference levels always ensures compliance with basic restrictions. This was evaluated at several distances from different antennas (dipole, loop, slot, patch, and helix). Three power density definitions based on integration of the perpendicular real part of the Poynting vector, the real part of its three vector components, and its modulus were compared for averaging areas of λ2 /16, 4 cm2 (below 30 GHz) and 1 cm2 (30 GHz). In the reactive near-field (d < λ/(2π)), the transmitted power density can be underestimated if an antenna operates at the free space exposure limit. This underestimation may exceed 6 dB (4.0 times) and depends on the field source due to different coupling mechanisms. It is frequency-dependent for fixed-size averaging areas (4 and 1 cm2 ). At larger distances, transmission can be larger than the theoretical plane-wave transmission coefficient due to backscattering between the body and field source. Using the modulus of the incident Poynting vector yields the smallest underestimation. © 2020Bioelectromagnetics Society.

Insulation design of ±10kV bipolar coaxial HTS DC cable

The high-temperature superconducting cable has low loss and high current-carrying density, and has extensive research prospects in power system transmission. In recent years, the advantages of DC transmission over long distances have become more and more obvious, and superconducting DC transmission has also become a research hotspot. Bipolar coaxial DC cable has a good economy, compact structure, and greater transmission power density, but also requires higher insulation, so the insulation design is particularly important. In this paper, a 10 kV / 6000 A / 10 m bipolar coaxial superconducting DC cable with a cold insulation structure is considered. In consideration of DC withstand voltage and lightning shock, an insulation design is carried out and a type test is performed. The test results meet the cable insulation requirements.

Spectrum Sensing: Analog (or Partially Analog) CMOS Real-Time Spectrum Sensing Techniques

Congestion of the radio spectrum, caused by licensed primary users and an increasing demand for new devices, has created a need for alternative methods of radio spectrum use in the future. Licensed primary users can be inactive for a specified time, leaving their allocated frequency band unoccupied so that secondary users can then use it. The U.S. Federal Communications Commission (FCC) has allowed unlicensed users to operate under specified circumstances for specific frequency bands. Secondary users cannot interfere with primary users at any time, whether by detecting the presence of primary signals and avoiding the occupied bands or by having a very small transmission power density compared to primary users. Hence, they appear as noise in primary receivers.

Estimating transmitted power density from mobile phone: an epidemiological pilot study with a software modified phone

The aims of this study were to evaluate the weekly and annual cumulative radiofrequency-electromagnetic field (RF-EMF) exposure attributed to mobile phone (MP) use, and assess whether a novel app (Quanta Monitor™) could be employed in a small human sample to characterise the RF-EMF exposures associated with the use of MPs. Ten participants provided their twomonths' daily objective data on their MP exposures (i.e. transmitted and received power densities) attributed to different modes of MP usage such as cellular calls, cellular data and Wi-Fi. The results demonstrated that total transmitted power density (cellular phone calls, data and Wi-Fi surfing) could be many orders of magnitude higher than that from the total received power density. Of the total transmitted power density, cellular data use contributed the largest portion. Our study showed that Quanta Monitor™ could be employed in prospective assessment of exposures to MPs in epidemiological studies.

EXPOSURE ASSESSMENT OF PORTABLE WIRELESS DEVICES ABOVE 6 GHz.

The emerging 5 G wireless devices working at frequencies above 6 GHz are expected to have antenna arrays formed by dipoles, slots, patches or their combination. At lower frequencies, the accepted criteria for exposure compliance is stated in terms of specific absorption rate. IEEE and ICNIRP are adopting epithelial or transmitted power density (PD through body surface) as the dosimetric reference for frequencies above 6 GHz, which entails the measurement of free space PD. Theoretical and numerical results presented in this article show that it is possible to perform meaningful free space PD assessments at half wave (λ/2) distance from arrays and, with the proper instrumentation, as close as λ/(2π). However, if a dissipative body is placed very close (<λ/2π) to the arrays, its reflection and absorption of RF energy can change the electric currents and charges over the antenna. The relevance of such an effect should be further investigated, for instance by means of experimental analysis including measurements of tissue heating when in the presence of a strong reactive near field.

Area-Averaged Transmitted Power Density at Skin Surface as Metric to Estimate Surface Temperature Elevation

In the international guidelines/standards for human protection, the specific absorption rate (SAR) is used as a metric to prevent excessive surface temperature elevation at frequencies up to 3 or 10 GHz. Above that transition frequency, including the frequency region assigned to 5th generation wireless communication systems, an area-averaged incident power density on human body surface is used as the physical quantity to specify the restrictions on human exposure to electromagnetic fields. However, the incident power density is an external physical quantity, resulting in frequency-dependent temperature elevation, which is attributable to frequency-dependent variations in the reflection coefficient at the skin surface and energy penetration depth into tissue. In this paper, we discuss analytically and computationally the effectiveness of the transmitted power density (TPD) at the skin as a new metric to estimate the steady-state skin temperature elevation above the transition frequency. We also consider simplified models for uniform and Gaussian beam patterns and the analytical solutions to the bioheat equation for an one-dimensional model, which are in good agreement with numerical solutions. These show that the TPD provides an excellent estimate of skin temperature elevation through the millimetre-wave band (30-300 GHz) and a reasonable and conservative estimate down to 10 GHz, whereas the SAR is a good metric below 3 GHz. Computational results for the dipole and patch antenna arrays demonstrated that the one-dimensional analysis is conservative metric as compared with the TPD averaged over the area of 4 cm2 (2-cm square). Considering extreme cases, averaging area smaller than 4 cm2 is needed above 30 GHz for beam exposure with small diameters. Finally, we consider the choice of averaging area as related to peak temperature increases for small beams. For extremely small exposure areas, limits on peak power density may be needed.

Numerical Simulation and Cold Test of a Compact 2G HTS Power Cable

Superconductinge power cables offer the advantages of lower loss, lighter weight, and smaller dimensions, in comparison with conventional cables. It is important to developed most compact cable with a small diameter to increase the transmission power density of a cable. Precise analysis should be used to provide optimal cable layout with uniform current distribution among layers. We have developed an electric circuit model of a cable, and two FEM models using a finite-element code ANSYS. The numerical simulations can provide detailed information about the current distribution inside the cable and the optimal parameters from the point of view of current distribution of the cable have been determined. On the base of the models, the compact 2G HTS cable model with three layers in the core and two layers in the shield has been produced and tested. The outer diameter of the cable was as small as ~20 mm that is less than previously 1G and 2G HTS power cables tested. The experiment with the model cable demonstrated that even rather small mistake in the diameter of a layer leads to considerable change of current distribution among layers. This phenomenon was analyzed with the simulation models developed. It was shown that change of a layer diameter as small as the thickness of one tape (~0.1 mm) led to the current distribution change observed. Calculated results qualitatively coincide with the experiments. In addition, ac losses at different frequencies have been measured to compare them with ac loss in previously tested cables with larger diameter.

A Novel Dual-Band, Dual-Polarized, Miniaturized and Low-Profile Base Station Antenna

In this paper, a novel dual-band, dual-polarized, miniaturized and low-profile base station antenna operating in the frequency bands of 820–960 and 1710–2170 MHz is designed. Elements are arranged such that high-frequency elements are embedded in low frequency elements to reduce volume. A baffle is used to reflect the transmitted power density in the forward direction and also improve isolation between elements. Therefore, surrounding isolation baffles and rectangular baffles are appended around high-frequency elements and low-frequency elements, respectively. The diameter of the proposed antenna cover is only 200 mm, which is smaller than the existing antenna diameter of 280 mm. Compared with the other commonly used antennas, the proposed antenna also has some advantages such as concealment and low profile using a tubular form of radome, which can easily integrate the proposed antenna with the surrounding environment. The measured results verify that the proposed antenna meets the stringent design requirements: voltage standing wave ratio (VSWR) is less than 1.3, the isolation is greater than 30 dB, and the pattern parameters also meet telecommunications industry standards.

On Optimal Downlink Coverage in Poisson Cellular Networks with Power Density Constraints

This paper studies downlink coverage maximization for cellular networks in which base station (BS) locations are modeled using a spatial Poisson point process, considering three different coverage models, and under constraints on transmit power, BS density and transmit power density. Firstly, the coverage optimization problem is solved analytically for the first coverage model that focuses on noise-limited communication by ignoring interference and random fading effects. This model provides useful insights into the significance of bounded path loss models to obtain meaningful solutions for this problem. The other two coverage models are based on the users' received signal-to-interference-plus-noise-ratio (\sinr) from their associated BSs. For these models, it is shown that the coverage optimization problem can be reduced to a constrained single dimensional optimization problem without any loss of optimality. The related solutions can be obtained with limited computational complexity by resorting to a numerical search over a compact subset of candidate values. Bounds on the optimum BS density are also provided to further truncate the search space. All results are derived for general bounded path loss models. Specific applications are also illustrated to provide further design insights and to highlight the importance of using bounded path loss models for coverage analysis <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">.</sub>

Energy Transfer by Resonance Coupling

This paper presents the research work focusing on the possibility to transmit power with a high power densitiy and a high efficiency. The applications of power supply require a smaller size, lower weight with a good energy on-board management. This work shows not only the possibility of wireless power transfer, but also the biological effect is taken into account for the safety precaution of human use. The system is described and set up using the resonance coupling effect and impedance adaption for multi-stage conversion. The transmitting power up to 180W is applied at a frequency of 6.78 MHz across a gap in the range between 30 mm to 80 mm. The experimental results show that the maximum efficiency up to 88 % has been achieved. The maximum transmitted power density reaches up to 0.14 W/mm 2 . High power can be transmitted using resonant coupling with high efficiency. Coupling coil characteristics significantly affect wireless power system losses. High power density of the active areas can be in the high range of 0.14 W/mm 2 . Resonance coupling can be applied in short range applications keeping EMC and EMF restrictions. DOI: http://dx.doi.org/10.11591/ijece.v3i5.3938

Spectrum sharing in frequency-selective unlicensed bands: a game theoretic approach

Power allocation is an important issue for spectrum sharing of unlicensed bands, in which multiple unlicensed systems may coexist and operate. Some recent works have been reported on spectrum sharing in frequency-flat FF unlicensed bands. However, there has not been much work on power allocation for spectrum sharing in frequency-selective FS unlicensed bands. For multiple cooperative systems cooperating on FS interference channels ICs, we study an optimal power allocation strategy, which allows the transmission power density to vary within one subcarrier. By showing the duality of FS and parallel FF channels, we can therefore compute the achievable rate region of the proposed strategy when systems cooperate with each other. For non-cooperative scenarios, we construct a game-theoretical framework for multiple selfish systems on FS ICs. This framework enables us to utilize existing protocols designed for FF ICs to FS scenarios. By numerical results, in both cooperative and non-cooperative scenarios, we show that the proposed strategy achieves a larger rate region than a conventional strategy, where the transmission power density on each subcarrier is set equal. Our work can be regarded as an extension of previous works for FF scenarios. Copyright © 2012 John Wiley & Sons, Ltd.

RESONANT TRANSMISSION THROUGH A PAIR OF RIDGE-LOADED CIRCULAR SUB-WAVELENGTH APERTURES

This paper deals with resonant transmission through a pair of ridge-loaded circular sub-wavelength apertures in an inflnite perfect electric conductor (PEC) plane. The efiect of the distance between the two resonant circular sub-wavelength apertures allocated along the ridge direction (\parallel case) and perpendicular to the ridge direction (\collinear case) on the transmission cross section (TCS) is analyzed numerically by using a method of moments (MoM). It is found that the TCS for the parallel case varies more sensitively to the distance than that for the collinearly located case, and the maximum TCS for the parallel case is tripled compared to the TCS value of a single resonant aperture. For the case of maximum TCS in the parallel conflguration, the directivity in the broadside direction is about 8.76 times (= 9:43dB) compared to that for the single resonant aperture. For the purpose of validation, the single resonant aperture and a pair of resonant apertures in the parallel conflguration with a distance for maximum TCS are fabricated on a stainless steel plate with 0.3mm thickness, and their transmission characteristics are measured. Experimental results show that the transmittance, which is a transmitted power density measured at 50cm away from the aperture plane, for the parallel resonant apertures is about 7 times (= 8:43dB) higher than that for the single aperture, which agrees well with the simulation.

Direct sequence spectrum spreading techniques for next generation mobile broadband satellite services

AbstractThe recently approved mobile version of the Digital Video Broadcasting Return Channel via Satellite (DVB‐RCS+M) foresees the use of direct sequence spectrum spreading (DS‐SS) in the forward link. The addition of a spreading mode, on top of the conventional time division signaling structure of the fixed DVB‐S2, allows in fact for the efficient extension of DVB‐S2 to mobile terminals with small aperture antennas operating in Ku (11–14 GHz) and Ka (20–30 GHz) bands. Spectrum spreading has been introduced to augment the received energy without increasing the transmitted power density, which is limited by regulatory constraints, and to enhance the waveform resilience to co‐channel interference. In this paper, we report on the design and assessment of the DS‐SS technique that we carried out for its inclusion in the DVB‐RCS+M standard. In particular, by comparing the physical layer performance of the spread and nonspread modes in the specific DVB‐RCS+M mobile scenarios, we show that the proposed DS‐SS technique has no impact on the DVB‐RCS+M data detection performance, while satisfying the requirements on interference resilience and received energy augmentation. In order to deal with the acquisition issues raised by the introduction of the DS‐SS technique, we then propose and evaluate several synchronization sub‐systems able to deal with the specific impairments of the mobile satellite scenarios, that is, large frequency offsets, phase noise, link obstructions, etc. Finally, a possible implementation of the DS‐SS technique that fully accommodates the reuse of the specific hardware compatible with conventional DVB‐S2 is also reported. Copyright © 2009 John Wiley &amp; Sons, Ltd.