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- Gustafsson, Mats, et al.
(author)
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An optimization approach to multi-dimensional time domain acoustic inverse problems
- 1997
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Reports (other academic/artistic)abstract
- An optimization approach to a multi-dimensional acoustic inverse problem in the time domain is considered. The density and/or the velocity are reconstructed by minimizing an objective functional. By introducing dual functions and using the Gauss divergence theorem, the gradient of the objective functional is found as an explicit expression. The parameters are then reconstructed by an iterative algorithm (the conjugate gradient method). The reconstruction algorithm is tested with noisy data, and these tests indicate that the algorithm is stable and robust. The computation time for the reconstruction is greatly improved when the analytic gradient is used.
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- He, Wang, et al.
(author)
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RF Compliance Study of Temperature Elevation in Human Head Model Around 28 GHz for 5G User Equipment Application : Simulation Analysis
- 2018
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In: IEEE Access. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2169-3536. ; 6
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Journal article (peer-reviewed)abstract
- The crowdedness of current cellular bands and the demand for higher transmission speed prompt the use of the millimeter-wave spectrum for the next-generation mobile communication. In the millimeter-wave frequencies, the dosimetric quantity for human exposure to electromagnetic fields changes from the specific absorption rate to incident power density. In this paper, we used 28-GHz beam-steering patch arrays, a dipole antenna, and plane waves to investigate the temperature elevation in a multi-layer model of human head and its correlation with power density metrics. The power density averaged over one square-centimeter in free space and the peak temperature elevation in tissue at 28 GHz have good correlation. The peak temperature elevation indicated by the power density averaged one square-centimeter also agrees well with the peak temperature elevation induced by the plane waves. The results show that the averaging area of a few square-centimeters may be a good candidate for the spatial-average power density. The findings provide valuable input to the ongoing revision and updating of relevant safety standards and guidelines.
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- Xu, Bo, et al.
(author)
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Effective beam-scanning efficiency of millimeter-wave subarrays for 5G user equipment application
- 2018
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In: IET Conference Publications. - : Institution of Engineering and Technology.
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Conference paper (peer-reviewed)abstract
- The forthcoming 5G communication system is expected to adopt millimeter-wave bands in order to satisfy the ever-growing traffic explosion. The coverage efficiency was proposed in earlier works to evaluate the beam-scanning capability and coverage performance of array antennas implemented in 5G user equipment. However, when multi-subarray configurations are introduced into user equipment, the coverage efficiency fails to reflect the coverage performance of each subarray under the influence of housing. In this paper, we use the effective beam-scanning efficiency to evaluate the coverage performance of a subarray covered by a superstrate. The results provide valuable insight into 5G mobile antenna design.
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- Xu, Bo, et al.
(author)
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Investigation of Planar Near-Field Measurement of Millimeter-Wave Antenna for 5G Application
- 2016
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In: 2016 INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION (ISAP). - : IEEE. - 9784885523137 ; , s. 600-601
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Conference paper (peer-reviewed)abstract
- The requirement of higher data rates and the emergence of new wireless device demands in future 5G communication put millimeter-wave frequencies in focus. To investigate electromagnetic-filed exposure at such frequencies for 5G cellular phone application, a planar near-field antenna measurement system is established. A tapered open-ended rectangular waveguide was used as the probe antenna, and a patch array antenna operating at 28 GHz was used as antenna under test. The distribution of power density above the antenna surface was calculated based on the measured data and the plane wave expansion method.
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- Xu, Bo, et al.
(author)
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Radiation Performance Analysis of 28 GHz Antennas Integrated in 5G Mobile Terminal Housing
- 2018
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In: IEEE Access. - : Institute of Electrical and Electronics Engineers (IEEE). - 2169-3536. ; , s. 48088-48101
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Journal article (peer-reviewed)abstract
- Radiation from printed millimeter-wave antennas integrated in mobile terminals is affected by surface currents on chassis, guided waves trapped in dielectric layers, superstrates, and the user’s hand, making mobile antenna design for 5G communication challenging. In this paper, four canonical types of printed 28 GHz antenna elements are integrated in a 5G mobile terminal mock-up. Different kinds of terminal housing effects are examined separately, and the terminal housing effects are also diagnosed through equivalent currents by using the inverse source technique. To account for the terminal housing effects on a beam-scanning antenna subarray, we propose the effective beam-scanning efficiency to evaluate its coverage performance. This paper presents the detailed analysis, results, and new concepts regarding the terminal housing effects, and thereby provides valuable insight into the practical 5G mobile antenna design and radiation performance characterization.
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