Metamaterial research at Aalto University · Metamaterial research at Aalto University Aalto...

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Metamaterial research at Aalto

University

Aalto University

School of Electrical Engineering

Department of Radio Science and Engineering

Sergei Tretyakov and colleagues

Outline

• University, Department, SMARAD Center of Excellence,

research group

• Overview of recent research

– Electromagnetics of complex media

– Invisibility and cloaking

– Isotropic artificial magnetics in the visible

– Some other topics

About myself and my visit to Jena...

Optics and photonics

Jena, Germany

Electromagnetics,

microwave engineering

Espoo, Finland

Aalto University

(former Helsinki University of Technology)

• The oldest and the biggest technical university in Finland – About 15000 students and 250 professors

• School of Electrical Engineering (former faculty of Electronics, Communications, and Automation)

• Department of Radio Science and Engineering – Electromagnetics, circuit theory, microwave to terahertz

techniques (antennas, devices) and measurements, space technology, radio wave propagation, advanced artificial electromagnetic materials

• Research groups lead by professors

About geography

There is no such place called ”Aalto”

• Campuses of the Aalto University are in Espoo and

Helsinki

How it looks like?

Aalto is growing:

SIX Tenure Track PROFESSOR Positions

The School of Electrical Engineering seeks experts in the following fields:

• Electrical engineering, Power and energy, Automatic control, Embedded systems, Smart living environment;

• Radio science and engineering, Radio astronomy, Space science and engineering, Optoelectronics;

• Communications and networking engineering.

The positions are open at all levels from assistant professor to full tenured professor.

Application deadline is September 30, 2012.

The RAD department was established in the beginning of 2008 by integrating four laboratories of TKK (TKK is today Aalto University School of Science and Technology), namely Radio Laboratory, Electromagnetics Laboratory, Circuit Theory Laboratory, and Laboratory of Space Technology, into a single unit.

Personnel:

– 8 professors

– Over 20 other researchers with a doctor degree

– About 30 doctoral students

– Total number of employees about 100

RAD department is involved in SMARAD CoE in research selected by the Academy of Finland for 2002–2007 (as Smart and Novel Radios Research Unit) and 2008–2013 (as Finnish Centre of Excellence in Smart Radios and Wireless Research).

RAD department is also involved in the MilliLab (Millimetre Wave Laboratory of Finland), which has the status of External Laboratory of the European Space Agency (ESA). MilliLab is a joint research institute between Aalto and VTT.

Department of Radio Science and Engineering (RAD)

The Virtual Institute for Artificial Electromagnetic Materials

and Metamaterials (”Metamorphose VI”) is a non-for-

profit international association whose purposes are the

research, the study and the promotion of artificial

electromagnetic materials and metamaterials.

About 20 European universities and institutions are members.

METAMORPHOSE Virtual Institute www.metamorphose-vi.org

6th International Congress

on Advanced Electromagnetic Materials in

Microwaves and Optics

Metamaterials 2012 St. Petersburg, Russia

17-22 September 2012

congress2012.metamorphose-vi.org

Distributed European Doctoral

School on Metamaterials

• Led by Dr. Carsten Rockstuhl, U. Jena

• www.school.metamorphose-eu.org

• METAMORPHOSE Virtual Institute

www.metamorphose-vi.org

The next EUPROMETA school

• Reconfigurable and tunable metamaterials

– September 21-22, 2012, in conjunction with the

Metamaterials'2012 Conference

– St. Petersburg, Russia

Artificial electromagnetic materials and applications

Research group

4 senior researchers (doctoral degree)

4 doctoral students

visitors + undergraduate students

Research group: Main current research

directions

• Artificial materials (metamaterials) with unusual and extreme

electromagnetic properties – engineering materials for applications

• Nano-scale composite materials and artificial surfaces

• New designs of antennas and microwave devices

• New designs for terahertz and optical devices (imaging and sensing, nano-

scale optics...)

• New applications (cloaks, superlenses, solar cells, thermophotovoltaics...)

Classification of electromagnetic

nanostructured materials

Not yet

investigated, but

possible

Metawaveguides1D, linear

nanostructured

optically dense

surfaces without

useful and unusual

electromagnetic

properties

Artificial

impedance surfaces

with long inclusions

or slots

Plasmonic

diffraction grids,

optical band-gap

surfaces and

optical frequency

selective surfaces

Metasurfaces /

metafilms

2D, surface

Bulk nanostructured

materials without

useful and unusual

electromagnetic

properties

Wire media,

multilayer optical

fishnet structures,

alternating solid

plasmonic and

dielectric

nanolayers

Photonic crystals

and quasi-

crystals,

Optically sparse

random

composites

Bulk MTM of small

inclusions

3D, bulk

Optically dense in

one direction, while

either optically

sparse or with

extended inclusions

in other

direction(s)

Optically sparse

(q·a >1)

Optically dense

(q·a<1)

Nanostructures

Not yet

investigated, but

possible

Metawaveguides1D, linear

nanostructured

optically dense

surfaces without

useful and unusual

electromagnetic

properties

Artificial

impedance surfaces

with long inclusions

or slots

Plasmonic

diffraction grids,

optical band-gap

surfaces and

optical frequency

selective surfaces

Metasurfaces /

metafilms

2D, surface

Bulk nanostructured

materials without

useful and unusual

electromagnetic

properties

Wire media,

multilayer optical

fishnet structures,

alternating solid

plasmonic and

dielectric

nanolayers

Photonic crystals

and quasi-

crystals,

Optically sparse

random

composites

Bulk MTM of small

inclusions

3D, bulk

Optically dense in

one direction, while

either optically

sparse or with

extended inclusions

in other

direction(s)

Optically sparse

(q·a >1)

Optically dense

(q·a<1)

Nanostructures

leff=2p/q

Bianisotropic constitutive relations

arbitary,0)j(j :Reciprocal

real,)j(j :Lossless

*TTTT*

(Ari Sihvola)

Classification of bianisotropic materials

Symmetric part:

6 parameters

(RECIPROCAL)

Dielectric crystal

Magnetic medium

Chiral medium

Tellegen (Cr2O3)

Anti-symmetric part

3 parameters

(NON-RECIPROCAL)

Magneto-plasma

Biased

ferrite

Omega medium

Moving medium

(Ari Sihvola)

Material optimized for the purpose?

The ”optimal” spiral The resonant frequency (the total length of the wire) is fixed.

For which shape the particle has the max energy in a given external

field?

I.V. Semchenko, S.A. Khakhomov, and A. L. Samofalov, The Optimal Shape

of a Spiral: Equality of Dielectric,Magnetic and Chiral Properties, NATO

Advanced Research Workshop META’08, Marrakesh, Morocco, May 7-10, 2008.

Optimal metamaterials Chiral media

”Optimal” spiral inclusions: n=0, κ=1 – ”extreme parameter values”

Negative refraction, negative reflection, ”standing spirals”,... S. Tretyakov, I. Nefedov, A. Sihvola, S. Maslovski, C. Simovski, Waves and energy in chiral nihility,

Journal of Electromagnetic Waves and Applications, vol. 17, no. 5, pp. 695-706, 2003.

E. Saenz, I. Semchenko, S. Khakhomov, K. Guven, R. Gonzalo, E. Ozbay, S. Tretyakov,

Modelling of spirals with equal dielectric, magnetic and chiral susceptibilities, Electromagnetics,

vol. 28, pp. 476–493, 2008.

I.V. Semchenko, S.A. Khakhomov and S.A. Tretyakov, Chiral metamaterial with unit negative

refraction index, The European Physical Journal - Applied Physics, vol. 46, no. 3, p. 32607, 2009.

Optimal metamaterials for linear polarization Omega media

Omega coupling is a very general phenomenon

Particle energy (omega particle)

But for evanescent waves the impedance is imaginary

and we can optimize the particle shape to maximize the particle energy.

Bianisotropic materials optimized for strong interactions with

electromagnetic fields

Total absorption in thin bianisotropic layers

Example: Total absorption

in an omega-layer

General approach to design of thin layers for

any desired electromagnetic response

Example: Twist polarizer

Electromagnetic cloaking

• Cloaking: Reduction of an object’s total scattering cross section (SCS)

• Total scattering cross section = ∫ (σ) dΩ

• In the case of infinitely high structures we speak about the

total scattering width: The integration is done over one angle in a plane

Broadband cloaking devices/approaches developed at

Aalto University

• Transmission-line cloak

• Metal-plate cloak

P. Alitalo and S. Tretyakov, “Electromagnetic cloaking with metamaterials,” Materials Today,

vol. 12, no. 3, pp. 22-29, 2009.

P. Alitalo and S. A. Tretyakov, “Broadband electromagnetic cloaking realized with transmission-line and

waveguiding structures,” Proc. IEEE, vol. 99, no. 10, pp. 1646-1659, 2011.

5 6 7 8 9 10 11 12 13 14 150

f [GHz]

tal sca

Transmission-line cloak

• Designed for TE polarization

• HFSS simulations of E-fields at 10 GHz

(complete structure, no homogenization!):

P. Alitalo, et al., “Experimental characterization of a broadband transmission-line cloak in free space,”

IEEE Trans. Antennas Propagat., accepted for publication. (arXiv: 1110.2353)

Metal-plate cloak

5 6 7 8 9 10 11 12 13 14 150

f [GHz]

tal sca

P. Alitalo, et al., “Bistatic scattering characterization of a three-dimensional broadband cloaking

structure,” J. Appl. Phys., vol. 111, p. 034901, 2012.

• Designed for TE polarization

• HFSS simulations of E-fields at 10 GHz

(complete structure, no homogenization!):

Bistatic measurements

• Cloak: metal-plate cloak

• Object to be hidden: metal cylinder (diameter 30mm, height 184mm)

1λ at 10 GHz

Bistatic X-band measurement setup at DLR

• Bistatic measurements can be

carried out in the xy-plane for

angles 22 - 180 deg

• Frequency range: X-band,

specifically, 8.2 GHz – 12.4 GHz

• The measured object is placed

at the origin

Normalized total scattering widths

• Solid lines: HFSS simulations (full integration)

• Dashed lines: HFSS simulations (integration from 22 … 180)

• Dotted lines: measurements (integration from 22 … 180)

Challenge: Isotropic magnetic material in the visible

Another design idea

Silver core – plasmonic electric response

Si shell – Mie magnetic response

Individual polarizabilities

r1 = 30 nm, r2 = 130 nm

Maxwell Garnett

Periodic 3D array

Random 3D array

Effective material parameters:

Plot PER

Plot RAND

Field distributions

λ = 1153 nm λ = 1071 nm

Field distributions

λ = 877 nm λ = 833 nm

Field distributions

λ = 750 nm

Refraction indices

retrieved from all

these pictures

are values

between those

predicted by plots

PER and RAND:

Our interpretation:

Compensation of

radiative losses of

a particle is

incomplete

Arrays of resonant nanoparticles

Regular vs random arrays

Theory

Enhancement of micron-gap

thermophotovoltaic systems

Radiative heat transfer spectral density q’’l across a 1 m gap normalized to the black-body heat transfer density q’’ pl. Blue line – with CNT. Red line – without them. Hot surface - T=300ºK, cold surface - T=0.

Modification of the micron gap between the hot

and photovoltaic surfaces of a thermophotovoltaic

system by inserting Carbon NanoTubes or nanowires.

The interdigital arrangement

1. transforms the gap into an indefinite medium layer

2. prevents the phonon transfer

(which would suppress the photovoltaic operation).

Super-doped n-Si (”cold”)

Super-doped n-Si (’’hot’’)

Light-trapping structures for thin-film solar cells

The results of the simulation of EM fields in a unit cell of the array

of Au nanoantennas illuminated by a normally incident plane wave

at 370 THz. It is seen that the nanoantenna produces hot spots

which are fully located in the spacings between metal

nanoelements and do not heat them. The transmittance through

the photoabsorbing layer averaged over the frequency range is

equal to 0.08: the heating of the substrate is also suppressed.

Without light-trapping

structure but with ARC

With light-trapping

structure

The enhancement of photo-absorption

in the presence of nanoantennas versus

frequency (simulations). Nanoantennas

are far from the plasmon resonance

So-called domino modes help to create

a broadband cavity between

the substrate and the superstrate.

CIGS 110 nm

SiO2 10 nm

silica

240 nm

Flexible

substrate

Flexible

super-

strate

320 nm

Electromagnetic characterization of

metasurfaces

Incidence

surface

r=12 (Q=45o) r=12 (Q=45o)

Substrate-induced biansiotropy

appears when r>>1

An ultra-broadband electromagnetically

indefinite medium formed by aligned carbon

nanotubes

Thank you!

http://users.tkk.fi/~sergei

Metamaterial research at Aalto University · Metamaterial research at Aalto University Aalto...

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