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Xu, Bo
Publications (10 of 15) Show all publications
Xu, B., Zhao, K., Ying, Z., Sjoberg, D., He, W. & He, S. (2019). Analysis of Impacts of Expected RF EMF Exposure Restrictions on Peak EIRP of 5G User Equipment at 28 GHz and 39 GHz Bands. IEEE Access, 7, 20996-21005
Open this publication in new window or tab >>Analysis of Impacts of Expected RF EMF Exposure Restrictions on Peak EIRP of 5G User Equipment at 28 GHz and 39 GHz Bands
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2019 (English)In: IEEE Access, E-ISSN 2169-3536, Vol. 7, p. 20996-21005Article in journal (Refereed) Published
Abstract [en]

Above 6 GHz, radio frequency (RF) electromagnetic field (EMF) exposure from the mobile communication user equipment (UE) should be assessed in terms of incident power density, rather than specific absorption rate as below 6 GHz. Such regulatory RF EMF restrictions will constrain the transmit power of the UE and its peak equivalent isotropically radiated power (EIRP). This paper provides an analysis of the peak EIRP levels of UE containing code-book-based beamforming arrays at 28 GHz and 39 GHz. Different types of antenna elements, incremental element spacing, 4- and 8-element array configurations, and realistic housing integration are considered. The analysis and results show that in realistic housing integration, the 3GPP requirements on minimum peak EIRP can be generally met under the expected RF EMF exposure restrictions.

Place, publisher, year, edition, pages
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2019
Keywords
5G, antenna array, EIRP, RF EMF exposure, incident power density, millimeter wave, user equipment
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-247854 (URN)10.1109/ACCESS.2019.2897271 (DOI)000460554100001 ()2-s2.0-85062913955 (Scopus ID)
Note

QC 20190326

Available from: 2019-03-26 Created: 2019-03-26 Last updated: 2019-05-16Bibliographically approved
Li, Y., Cheng, M., Jungstedt, E., Xu, B., Sun, L. & Berglund, L. (2019). Optically Transparent Wood Substrate for Perovskite Solar Cells. ACS Sustainable Chemistry and Engineering, 7(6), 6061-6067
Open this publication in new window or tab >>Optically Transparent Wood Substrate for Perovskite Solar Cells
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2019 (English)In: ACS Sustainable Chemistry and Engineering, ISSN 2168-0485, Vol. 7, no 6, p. 6061-6067Article in journal (Refereed) Published
Abstract [en]

Transparent wood is a candidate for use as an energy-saving building material due to its low density (ca. 1.2 g/cm(3)), high optical transmittance (over 85% at 1 mm thickness), low thermal conductivity (0.23 W m(-1) K-1), and good load-bearing performance with tough failure behavior (no shattering). High optical transmittance also makes transparent wood a candidate for optoelectronic devices. In this work, for the first time, perovskite solar cells processed at low temperature (<150 degrees C) were successfully assembled directly on transparent wood substrates. A power conversion efficiency up to 16.8% was obtained. The technologies demonstrated may pave the way for integration of solar cells with light transmitting wood building structures for energy-saving purposes.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
Keywords
Biocomposite, Perovskite solar cell, Energy-Efficient, Building material, Transparent wood, Mechanical properties
National Category
Composite Science and Engineering
Identifiers
urn:nbn:se:kth:diva-248333 (URN)10.1021/acssuschemeng.8b06248 (DOI)000461978200051 ()30918764 (PubMedID)2-s2.0-85063061391 (Scopus ID)
Note

QC 20190410

Available from: 2019-04-10 Created: 2019-04-10 Last updated: 2019-04-10Bibliographically approved
Xu, B., Gustafsson, M., Shi, S., Zhao, K., Ying, Z. & He, S. (2019). Radio Frequency Exposure Compliance of Multiple Antennas for Cellular Equipment Based on Semidefinite Relaxation. IEEE transactions on electromagnetic compatibility (Print), 61(2), 327-336
Open this publication in new window or tab >>Radio Frequency Exposure Compliance of Multiple Antennas for Cellular Equipment Based on Semidefinite Relaxation
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2019 (English)In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 61, no 2, p. 327-336Article in journal (Refereed) Published
Abstract [en]

Human exposure to radio frequency (RF) electromagnetic fields should not exceed the exposure limits set by the relevant regulatory guidelines. In this paper, we provide approaches to determine upper bounds of maximum exposure from multiple antennas. When the total transmitted power is fixed, the maximum exposure can be determined by an eigenvalue decomposition. If an individual antenna has additional power constraint, the exposure maximization problem can be relaxed to a semidefinite program. Two case studies are given to demonstrate the approaches to the maximum exposure of cellular equipment using multiple antennas. The methods and the obtained results provide valuable insights into RF compliance procedures of cellular equipment.

Place, publisher, year, edition, pages
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2019
Keywords
5G, cellular equipment, eigenvalue decomposition (EVD), multi-input and multi-output (MIMO), multiple antennas, power density, radio frequency (RF) exposure, semidefinite relaxation (SDR), specific absorption rate (SAR)
National Category
Occupational Health and Environmental Health
Identifiers
urn:nbn:se:kth:diva-244480 (URN)10.1109/TEMC.2018.2832445 (DOI)000457790400002 ()2-s2.0-85047999601 (Scopus ID)
Note

QC 20190320

Available from: 2019-03-20 Created: 2019-03-20 Last updated: 2019-03-20Bibliographically approved
Scialacqua, L., Foged, L. J., Scannavini, A., Herbiniere, F., Mioc, F., Xu, B., . . . Bolin, T. (2018). Advanced measurement post-processing by equivalent currents on small 5G antennas. In: 12th European Conference on Antennas and Propagation (EuCAP 2018): . Paper presented at 12th European Conference on Antennas and Propagation, EuCAP 2018; London; United Kingdom; 9 April 2018 through 13 April 2018. Institution of Engineering and Technology (CP741)
Open this publication in new window or tab >>Advanced measurement post-processing by equivalent currents on small 5G antennas
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2018 (English)In: 12th European Conference on Antennas and Propagation (EuCAP 2018), Institution of Engineering and Technology, 2018, no CP741Conference paper, Published paper (Refereed)
Abstract [en]

Fifth-Generation (5G) mobile communication demands a wide use of multi beam scanning array antennas, providing effective coverage performances at millimeter waves [1-3]. In particular, when the telecommunication channel is characterized by a reduced signal to noise ratio, an omni like radiation pattern could be generated by the beam scanning antenna system. The testing of the AUT (Antenna Under Test), in such conditions, is typically performed with low directive reference antennas. These antennas can suffer of the interaction with the feeding cable. The measurement post-processing by the equivalent currents approach (EQC) [4-7], implemented in the MVG software INSIGHT [8], can be used for diagnostic investigations on this kind of reference antennas and to filter undesired currents on the feeding cable. In this paper the EQC approach is applied, for the first time, on diagnostic and filtering of feeding cable on a measurement of a low directive antenna for 5G tests.

Place, publisher, year, edition, pages
Institution of Engineering and Technology, 2018
Series
IET Conference Publications
Keywords
5G mobile communication, Antenna measurements, Antenna radiation patterns
National Category
Signal Processing
Identifiers
urn:nbn:se:kth:diva-246536 (URN)10.1049/cp.2018.0952 (DOI)2-s2.0-85057309082 (Scopus ID)
Conference
12th European Conference on Antennas and Propagation, EuCAP 2018; London; United Kingdom; 9 April 2018 through 13 April 2018
Note

QC 20190320

Available from: 2019-03-20 Created: 2019-03-20 Last updated: 2019-03-20Bibliographically approved
Xu, B., Scialacqua, L., Scannavini, A., Foged, L. J., Ying, Z., Bolin, T. & He, S. (2018). Antenna diagnosis and power density calculation of 5G millimeter-wave mobile terminal using inverse source technique. In: 12th European Conference on Antennas and Propagation (EuCAP 2018): . Paper presented at 12th European Conference on Antennas and Propagation, EuCAP 2018; London; United Kingdom; 9 April 2018 through 13 April 2018. Institution of Engineering and Technology (CP741)
Open this publication in new window or tab >>Antenna diagnosis and power density calculation of 5G millimeter-wave mobile terminal using inverse source technique
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2018 (English)In: 12th European Conference on Antennas and Propagation (EuCAP 2018), Institution of Engineering and Technology, 2018, no CP741Conference paper, Published paper (Refereed)
Abstract [en]

Millimeter-wave antennas may suffer from stronger effects of surface waves in 5G mobile terminals. In this paper, printed 28 GHz antennas are implemented in a mobile handset mock-up. The influence of surface waves is examined by the reconstructed equivalent currents obtained through the inverse source technique. The obtained equivalent currents are reused for the power density calculation for the purpose of millimeter-wave exposure assessment. The results provide valuable insight into 5G millimeter-wave mobile antenna design and measurement.

Place, publisher, year, edition, pages
Institution of Engineering and Technology, 2018
Series
IET Conference Publications
Keywords
5G, Equivalent currents, Inverse source technique, Millimeter-wave antenna, Power density
National Category
Signal Processing
Identifiers
urn:nbn:se:kth:diva-246537 (URN)10.1049/cp.2018.0713 (DOI)2-s2.0-85057303928 (Scopus ID)
Conference
12th European Conference on Antennas and Propagation, EuCAP 2018; London; United Kingdom; 9 April 2018 through 13 April 2018
Note

QC 20190320

Available from: 2019-03-20 Created: 2019-03-20 Last updated: 2019-03-20Bibliographically approved
Xu, B., Ying, Z., Gustafsson, M. & He, S. (2018). Effective beam-scanning efficiency of millimeter-wave subarrays for 5G user equipment application. In: IET Conference Publications: . Paper presented at 12th European Conference on Antennas and Propagation, EuCAP 2018; London; United Kingdom; 9 April 2018 through 13 April 2018. Institution of Engineering and Technology (CP741)
Open this publication in new window or tab >>Effective beam-scanning efficiency of millimeter-wave subarrays for 5G user equipment application
2018 (English)In: IET Conference Publications, Institution of Engineering and Technology , 2018, no CP741Conference paper, Published paper (Refereed)
Abstract [en]

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.

Place, publisher, year, edition, pages
Institution of Engineering and Technology, 2018
Keywords
5G, Coverage efficiency, Effective beam-scanning efficiency, Millimeter-wave array antenna, Subarray, User equipment
National Category
Communication Systems
Identifiers
urn:nbn:se:kth:diva-246533 (URN)2-s2.0-85057323045 (Scopus ID)
Conference
12th European Conference on Antennas and Propagation, EuCAP 2018; London; United Kingdom; 9 April 2018 through 13 April 2018
Note

QC 20190403

Available from: 2019-04-03 Created: 2019-04-03 Last updated: 2019-04-03Bibliographically approved
Liu, P., Wang, L., Karlsson, K. M., Hao, Y., Gao, J., Xu, B., . . . Kloo, L. (2018). Molecular Engineering of D-pi-A Type of Blue-Colored Dyes for Highly Efficient Solid-State Dye-Sensitized Solar Cells through Co-Sensitization. ACS Applied Materials and Interfaces, 10(42), 35946-35952
Open this publication in new window or tab >>Molecular Engineering of D-pi-A Type of Blue-Colored Dyes for Highly Efficient Solid-State Dye-Sensitized Solar Cells through Co-Sensitization
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2018 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 42, p. 35946-35952Article in journal (Refereed) Published
Abstract [en]

A novel blue-colored organic donor-pi-acceptor sensitizer, the so-called MKA16 dye, has been employed to construct solid-state dye-sensitized solar cells (ssDSSCs). Using 2,2',7-,7'-tetrakis(N,N-di-p-methoxyphenyl-amine) 9,9'-spirobifuorene (Spiro-OMeTAD) as hole-transport material, a good conversion efficiency of 5.8% was recorded for cells based on the MKA16 dye and a high photovoltage of 840 mV in comparison with 5.6% efficiency using the known (Dyenamo Blue) dye. By co-sensitization using the orange-colored D35 dye and MKA16 together, the solid-state solar cells showed an excellent efficiency of 7.5%, with a high photocurrent of 12.41 mA cm(-2) and open-circuit voltage of 850 mV. The results show that the photocurrent of ssDSSCs can be significantly improved by co-sensitization mainly attributed to the wider light absorption range contributing to the photocurrent. In addition, results from photo-induced absorption spectroscopy show that the dye regeneration is efficient in co-sensitized solar cells. The current results possible routes of improving the design of aesthetic and highly efficient ssDSSCs.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2018
Keywords
solid-state dye-sensitized solar cell, blue-colored dye, co-sensitization, molecular engineering, D-pi-A dye
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-239097 (URN)10.1021/acsami.8b11405 (DOI)000448754500028 ()30260625 (PubMedID)2-s2.0-85054957061 (Scopus ID)
Note

QC 20181121

Available from: 2018-11-21 Created: 2018-11-21 Last updated: 2018-11-21Bibliographically approved
Xu, B., Ying, Z., Scialacqua, L., Scannavini, A., Foged, L. J., Bolin, T., . . . Gustafsson, M. (2018). Radiation Performance Analysis of 28 GHz Antennas Integrated in 5G Mobile Terminal Housing. IEEE Access, 6, 48088-48101
Open this publication in new window or tab >>Radiation Performance Analysis of 28 GHz Antennas Integrated in 5G Mobile Terminal Housing
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2018 (English)In: IEEE Access, E-ISSN 2169-3536, Vol. 6, p. 48088-48101Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2018
Keywords
5G, effective beam-scanning efficiency, equivalent current, surface current, millimeter-wave antenna, mobile terminal, guided wave, user equipment, user's hand
National Category
Communication Systems
Identifiers
urn:nbn:se:kth:diva-235906 (URN)10.1109/ACCESS.2018.2867719 (DOI)000445453300001 ()2-s2.0-85052651597 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20181009

Available from: 2018-10-09 Created: 2018-10-09 Last updated: 2018-10-09Bibliographically approved
He, W., Xu, B., Gustafsson, M., Ying, Z. & He, S. (2018). RF Compliance Study of Temperature Elevation in Human Head Model Around 28 GHz for 5G User Equipment Application: Simulation Analysis. IEEE Access, 6
Open this publication in new window or tab >>RF Compliance Study of Temperature Elevation in Human Head Model Around 28 GHz for 5G User Equipment Application: Simulation Analysis
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2018 (English)In: IEEE Access, E-ISSN 2169-3536, Vol. 6Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2018
Keywords
28 GHz, 5G, antenna array, human head, incident power density, millimeter wave, RF compliance, safety guidelines, safety standards, temperature elevation, user equipment
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-224049 (URN)10.1109/ACCESS.2017.2776145 (DOI)000425675300025 ()2-s2.0-85035807157 (Scopus ID)
Note

QC 20180316

Available from: 2018-03-16 Created: 2018-03-16 Last updated: 2018-03-16Bibliographically approved
Xu, B., Gustafsson, M., Shi, S., Ying, Z. & He, S. (2018). Upper Bound Study of 5G RF EMF Exposure. In: 2018 IEEE ANTENNAS AND PROPAGATION SOCIETY INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION & USNC/URSI NATIONAL RADIO SCIENCE MEETING: . Paper presented at IEEE-Antennas-and-Propagation-Society International Symposium on Antennas and Propagation / USNC/URSI National Radio Science Meeting, JUL 08-13, 2018, Boston, MA (pp. 397-398). IEEE
Open this publication in new window or tab >>Upper Bound Study of 5G RF EMF Exposure
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2018 (English)In: 2018 IEEE ANTENNAS AND PROPAGATION SOCIETY INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION & USNC/URSI NATIONAL RADIO SCIENCE MEETING, IEEE , 2018, p. 397-398Conference paper, Published paper (Refereed)
Abstract [en]

Power density emitted by 5G user equipment should not exceed the power density limits set by compliance guidelines. When the amplitude of each port of millimeter-wave array antennas is uniform, the power density maximization problem can be relaxed to a semi-definite program. In this paper, the effect of sampling widths is considered for the maximum power density calculation. The results show that when the sampling distance is less than a half wavelength, the sampling rate should be higher than the Nyquist rate.

Place, publisher, year, edition, pages
IEEE, 2018
Series
IEEE Antennas and Propagation Society International Symposium, ISSN 1522-3965
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-246310 (URN)10.1109/APUSNCURSINRSM.2018.8609310 (DOI)000459711500191 ()2-s2.0-85061915362 (Scopus ID)978-1-5386-7102-3 (ISBN)
Conference
IEEE-Antennas-and-Propagation-Society International Symposium on Antennas and Propagation / USNC/URSI National Radio Science Meeting, JUL 08-13, 2018, Boston, MA
Note

QC 20190319

Available from: 2019-03-19 Created: 2019-03-19 Last updated: 2019-03-19Bibliographically approved
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