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Publications (10 of 596) Show all publications
Liu, Y., Sun, F. & He, S. (2018). Controlling lightwave in Riemann space by merging geometrical optics with transformation optics. Scientific Reports, 8(1), Article ID 514.
Open this publication in new window or tab >>Controlling lightwave in Riemann space by merging geometrical optics with transformation optics
2018 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, no 1, article id 514Article in journal (Refereed) Published
Abstract [en]

In geometrical optical design, we only need to choose a suitable combination of lenses, prims, and mirrors to design an optical path. It is a simple and classic method for engineers. However, people cannot design fantastical optical devices such as invisibility cloaks, optical wormholes, etc. by geometrical optics. Transformation optics has paved the way for these complicated designs. However, controlling the propagation of light by transformation optics is not a direct design process like geometrical optics. In this study, a novel mixed method for optical design is proposed which has both the simplicity of classic geometrical optics and the flexibility of transformation optics. This mixed method overcomes the limitations of classic optical design; at the same time, it gives intuitive guidance for optical design by transformation optics. Three novel optical devices with fantastic functions have been designed using this mixed method, including asymmetrical transmissions, bidirectional focusing, and bidirectional cloaking. These optical devices cannot be implemented by classic optics alone and are also too complicated to be designed by pure transformation optics. Numerical simulations based on both the ray tracing method and full-wave simulation method are carried out to verify the performance of these three optical devices.

Place, publisher, year, edition, pages
Nature Publishing Group, 2018
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-221681 (URN)10.1038/s41598-017-19015-0 (DOI)000419941400001 ()2-s2.0-85040445799 (Scopus ID)
Funder
Swedish Research Council, 2012AA030402
Note

QC 20180122

Available from: 2018-01-22 Created: 2018-01-22 Last updated: 2018-01-29Bibliographically approved
Li, S., Sun, F., An, D. & He, S. (2018). Increasing Efficiency of a Wireless Energy Transfer System by Spatial Translational Transformation. IEEE transactions on power electronics, 33(4), 3325-3332
Open this publication in new window or tab >>Increasing Efficiency of a Wireless Energy Transfer System by Spatial Translational Transformation
2018 (English)In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 33, no 4, p. 3325-3332Article in journal (Refereed) Published
Abstract [en]

A magnetic translational projector (MTP) designed by transformation optics is applied to improve energy transfer efficiency in a wireless power transfer (WPT) system. Our numerical simulation results showtheMTP can greatly enhance energy transfer efficiency (e.g., nearly two orders, compared to the case without our MTP) in the WPT system, which is much larger than that of a previous method (i.e., using magnetic super-lens). A 3-D reduced MTPcomposed of layered isotropicmagnetic materials is designed, whose performance is verified by our 3-D numerical simulation in 10 MHz. The influence of loss in metamaterial on the performance of the proposed MTP is also studied, which shows that the MTP can still enhance energy transfer efficiency when loss exists. Further simulation is also carried out to show that the function of the MTP is not sensitive to large perturbation. Finally, detailed experimental suggestion for implementing the simplified MTP, which is composed of layered medium is given and then verified by our numerical simulation.

Place, publisher, year, edition, pages
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2018
Keyword
Magnetic device, metamaterial, transformation optics, wireless energy transfer
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-222165 (URN)10.1109/TPEL.2017.2703591 (DOI)000422933400050 ()2-s2.0-85040778782 (Scopus ID)
Note

QC 20180205

Available from: 2018-02-05 Created: 2018-02-05 Last updated: 2018-02-05Bibliographically approved
Sun, F. & He, S. (2018). Invisible gateway for both light waves and rays. Optics Express, 26(1), 165-172
Open this publication in new window or tab >>Invisible gateway for both light waves and rays
2018 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, no 1, p. 165-172Article in journal (Refereed) Published
Abstract [en]

Considering that previous invisible gateways (an open entrance that only blocks electromagnetic waves) based on super-scatters designed by transformation optics cannot effectively work for narrow beams and light rays that do not touch negative refractive index material, we explore a new way to realize an improved invisible gateway that can give a good performance for both light waves and rays. In all previous invisible gateways, they require a finite thickness of the wall and the gateway. For the improved invisible gateway proposed in this study, there is no requirement on the thickness of the wall and gateway, i.e. the wall and gateway can be infinitely thin. Our study will go a further step to realize the invisible gateway in fiction.

Place, publisher, year, edition, pages
OPTICAL SOC AMER, 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-221942 (URN)10.1364/OE.26.000165 (DOI)000419549600014 ()29328288 (PubMedID)2-s2.0-85040189274 (Scopus ID)
Note

QC 20180130

Available from: 2018-01-30 Created: 2018-01-30 Last updated: 2018-01-30Bibliographically approved
Li, B., Sun, F. & He, S. (2018). Reducing the dimensions of acoustic devices using anti-acoustic-null media. APPLIED PHYSICS EXPRESS, 11(2), Article ID 024301.
Open this publication in new window or tab >>Reducing the dimensions of acoustic devices using anti-acoustic-null media
2018 (English)In: APPLIED PHYSICS EXPRESS, ISSN 1882-0778, Vol. 11, no 2, article id 024301Article in journal (Refereed) Published
Abstract [en]

An anti-acoustic-null medium (anti-ANM), a special homogeneous medium with anisotropic mass density, is designed by transformation acoustics (TA). Anti-ANM can greatly compress acoustic space along the direction of its main axis, where the size compression ratio is extremely large. This special feature can be utilized to reduce the geometric dimensions of classic acoustic devices. For example, the height of a parabolic acoustic reflector can be greatly reduced. We also design a brass-air structure on the basis of the effective medium theory to materialize the anti-ANM in a broadband frequency range. Numerical simulations verify the performance of the proposed anti-ANM.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-222402 (URN)10.7567/APEX.11.024301 (DOI)000423332300001 ()
Note

QC 20180223

Available from: 2018-02-23 Created: 2018-02-23 Last updated: 2018-02-23Bibliographically 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
Keyword
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
Shi, K., Bao, F. & He, S. (2018). Spectral Control of Near-Field Thermal Radiation With Periodic Cross Resonance Metasurfaces. IEEE Journal of Quantum Electronics, 54(1), Article ID 7000107.
Open this publication in new window or tab >>Spectral Control of Near-Field Thermal Radiation With Periodic Cross Resonance Metasurfaces
2018 (English)In: IEEE Journal of Quantum Electronics, ISSN 0018-9197, E-ISSN 1558-1713, Vol. 54, no 1, article id 7000107Article in journal (Refereed) Published
Abstract [en]

Near-field thermal spectra can be engineered using periodic cross resonance metasurfaces. Structures consisting of single crosses, double crosses, and multiple crosses are proposed to control the spectral heat flux from narrow band to broadband with the Fabry-Perot-cavity-like effect and the interaction between the emitter and receiver. Radiation peaks originating from the cross structures split into two adjacent peaks in the near-field, due to the separate contributions of s- and p-polariton modes. Their frequency can be manipulated by adjusting the length of the crosses. Multiple radiation peaks can be generated by double crosses, and due to the strong coupling of resonance modes, multiple crosses can yield a broadband thermal spectrum ranging from 100-180 THz, with the total heat flux two orders of magnitude above the blackbody limit. The inherent physical mechanisms are illustrated by analyzing the energy transmission coefficients of the cross structures. The features of the radiation peaks and spectra are robust to the change of the gap distance or the temperature, which is advantageous for both the experimental design and fabrication of thermal radiation devices.

Place, publisher, year, edition, pages
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2018
Keyword
Near-field, thermal radiation spectrum, optical resonance, periodic structures
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-222412 (URN)10.1109/JQE.2018.2791639 (DOI)000423191500001 ()2-s2.0-85041112109 (Scopus ID)
Note

QC 20180228

Available from: 2018-02-28 Created: 2018-02-28 Last updated: 2018-02-28Bibliographically approved
Tan, C., Su, X., Zhou, C., Wang, B., Zhan, Q. & He, S. (2017). Acid-assisted hydrothermal synthesis of red fluorescent carbon dots for sensitive detection of Fe(III). RSC Advances, 7(65), 40952-40956
Open this publication in new window or tab >>Acid-assisted hydrothermal synthesis of red fluorescent carbon dots for sensitive detection of Fe(III)
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2017 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 7, no 65, p. 40952-40956Article in journal (Refereed) Published
Abstract [en]

Red-emitting carbon dots (C-dots) were synthesized from p-phenylenediamine (p-PD) aqueous solution with nitric acid (HNO3) assistance by hydrothermal reaction at 200 degrees C for 2 h. p-PD aqueous solution can be transferred to C-dots (or poly(p-PD)) with (or without) the addition of acid. Different acid systems, such as HNO3, H3PO4 and HF, can directly synthesize red-emitting C-dots, and the fluorescence can be enhanced by increasing the strength of acids. N-CDs, 3.46 nm-average-sized C-dots, prepared in dilute HNO3, have a quantum yield of 15.8% with unique, excitation-wavelength independent emission in the red region (600 and 680 nm) and a broad visible excitation band. Carboxyl, ester and hydroxyl groups on the C-dots surface directly lead to red emission. N-CDs have a certain selective specificity for Fe3+ detection and the linear range is 10-300 nmol L-1 with a limit of determination of 1.9 nmol L-1.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2017
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-214912 (URN)10.1039/c7ra06223k (DOI)000409096300033 ()2-s2.0-85028360093 (Scopus ID)
Note

QC 2016-09-27

Available from: 2017-09-27 Created: 2017-09-27 Last updated: 2017-11-29Bibliographically approved
Li, B., Sun, F. & He, S. (2017). Acoustic surface transformation realized by acoustic-null materials using bilayer natural materials. APPLIED PHYSICS EXPRESS, 10(11), Article ID 114001.
Open this publication in new window or tab >>Acoustic surface transformation realized by acoustic-null materials using bilayer natural materials
2017 (English)In: APPLIED PHYSICS EXPRESS, ISSN 1882-0778, Vol. 10, no 11, article id 114001Article in journal (Refereed) Published
Abstract [en]

We propose a general method, known as acoustic surface transformation (AST), to design novel acoustic devices and study the realization of such devices by using naturally available materials in broadband acoustic frequencies. All devices designed by AST only need one anisotropic homogeneous acoustic-null material (ANM). We design the ANM by exploiting natural material-based metal-fluid structures and verify that by numerical simulation. Unlike traditional methods, no complicated mathematical calculations are needed. We only need to design the geometrical shapes of the input and output surfaces of the devices. The proposed method will pave a new road for future acoustic design.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2017
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-217421 (URN)10.7567/APEX.10.114001 (DOI)000413839000001 ()2-s2.0-85039152619 (Scopus ID)
Note

QC 20171117

Available from: 2017-11-17 Created: 2017-11-17 Last updated: 2017-11-17Bibliographically approved
Yang, L., Kou, P., He, N., Dai, H. & He, S. (2017). Anomalous light trapping enhancement in a two-dimensional gold nanobowl array with an amorphous silicon coating. Optics Express, 25(13), 14114-14124
Open this publication in new window or tab >>Anomalous light trapping enhancement in a two-dimensional gold nanobowl array with an amorphous silicon coating
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2017 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 25, no 13, p. 14114-14124Article in journal (Refereed) Published
Abstract [en]

A facile polymethyl methacrylate-assisted turnover-transfer approach is developed to fabricate uniform hexagonal gold nanobowl arrays. The bare array shows inferior light trapping ability compared to its inverted counterpart (a gold nanospherical shell array). Surprisingly, after being coated with a 60-nm thick amorphous silicon film, an anomalous light trapping enhancement is observed with a significantly enhanced average absorption (82%), while for the inverted nanostructure, the light trapping becomes greatly weakened with an average absorption of only 66%. Systematic experimental and theoretical results show that the main reason for the opposite light trapping behaviors lies in the top amorphous silicon coating, which plays an important role in mediating the excitation of surface plasmon polaritons and the electric field distributions in both nanostructures.

Place, publisher, year, edition, pages
Optical Society of America, 2017
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-211008 (URN)000404189800016 ()2-s2.0-85021327644 (Scopus ID)
Note

QC 20170713

Available from: 2017-07-13 Created: 2017-07-13 Last updated: 2017-11-29Bibliographically approved
Zhao, K., Gustafson, C., Liao, Q., Zhang, S., Bolin, T., Ying, Z. & He, S. (2017). Channel Characteristics and User Body Effects in an Outdoor Urban Scenario at 15 and 28 GHz. IEEE Transactions on Antennas and Propagation, 65(12), 6534-6548
Open this publication in new window or tab >>Channel Characteristics and User Body Effects in an Outdoor Urban Scenario at 15 and 28 GHz
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2017 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 65, no 12, p. 6534-6548Article in journal (Refereed) Published
Abstract [en]

The effect of a user's body on channel characteristics for single user downlink transmission in an urban scenario for the fifth generation (5G) systems is investigated with ray-tracing at 15 and 28 GHz. Three different designs of user equipment (UE) antennas are fabricated and integrated into a mobile phone prototype, and their 3-D radiation patterns are measured both with and without a user. The user remains in Cellular Telephone Industries Association (CTIA) standard data mode and talk mode during measurements. The results show that the user's body will cause a strong shadowing loss and generate a large fluctuation on the received signal strength of the UE at both 15 and 28 GHz, which is crucial to channel modeling studies at frequencies above 6 GHz. In addition, the user's body effect on a linear array system in an UE is presented, and the main challenges for the future work are also addressed.

Place, publisher, year, edition, pages
IEEE, 2017
Keyword
5G, array, body effect, channel, millimeter wave (mmWave), mobile phone, user equipment (UE)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-215256 (URN)10.1109/TAP.2017.2740959 (DOI)000417885000031 ()2-s2.0-85028501647 (Scopus ID)
Funder
Swedish Research Council, 621-2011-4620
Note

QC 20171005

Available from: 2017-10-05 Created: 2017-10-05 Last updated: 2018-01-12Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3401-1125

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