Electromagnetic Metamaterials Dr. Alkim Akyurtlu Center for Electromagnetic Materials and Optical Systems University of Massachusetts Lowell September 19, 2006
Objective Outline Background on Metamaterials Background on Left-handed Metamaterials (LHM) FDTDSimulations of LHM Slab Basics of FDTD Results Simulations of LHM structures Experimental Studies & Applications Summary
Objective Applications Metamaterials Theory/Modeling Synthesis Validation
What are Metamaterials? A composite or structured material that exhibits properties not found in naturally occurring materials or compounds. Left-handed materials have electromagnetic properties that are distinct from any known material, and hence are examples of metamaterials.
Why Create Metamaterials? The electromagnetic response of naturally occurring materials is limited. Metamaterials can extend material properties, while simultaneously providing other advantageous properties (e.g., strength, thermal, conformal) Construct new bulk materials from unit cell blocks engineered to exploit small scale physics Possibility of materials with ideal electromagnetic response over broad frequency ranges, that can be customized, made active, or made tunable.
Material Properties All EM phenomena can be explained by Maxwell s four Equations. ε = permittivity; μ = permeability ε relates to materials ability to transmit an electric field μ - degree of magnetization of a material that responds linearly to a magnetic field Quantities ε and μ are typically positive. When ε and μ are both negative, there are dramatically new properties
Objective Outline Background on Metamaterials Background on Left-handed Metamaterials (LHM) FDTD Simulations of LHM Slab Basics of FDTD Results Simulations of LHM Structures Experimental Studies & Applications Summary
Left-handed Metamaterial ε <0 and μ<0 within same frequency range Also referred to as DNG, BW waves, or NIMs In the propagation of electromagnetic waves, the direction of energy flow is given by a right-hand rule, involving E, H, and S: The propagation, or phase velocity, is usually also determined by a right hand rule: Thus, when ε < 0 and μ < 0, the medium is Left-Handed!
Physics of LHM Conventional Materials ε>0, μ>0 Double-Negative Materials ε<0, μ<0 k k S E H S E H Right-Handed System Left-Handed System
Unique Properties of LHM Light propagates in the opposite direction as energy flows! Reversal of the Doppler shift for radiation Reversal of Cherenkov radiation. Cherenkov radiation is the light emitted when a charged particle passes through a medium, under certain conditions. In a normal material, the emitted light is in the forward direction, while in the Left-handed medium, light is emitted in the reverse direction.
Unique Properties of LHM (cont'd) Reversal of Snell s Law Light that enters a left-handed material from a right-handed medium will undergo refraction, but opposite to that usually observed. Reversal due to negative index-of-refraction As an example, a lens made from LHM that would be converging if made from conventional material, will be diverging, and vice-versa.
Negative Index of Refraction M.C.K. Wiltshire, Science 292: 60-61(2001)
Manufacturing Negative ε and μ Periodic array of conducting elements can behave as an effective medium for EM scattering for λ>d & a Negative ε: J.B. Pendry et al, Phys. Rev. Let. 76, 4773 (1996)
Manufacturing Negative μ Create magnetic resonance with nonmagnetic materials Use split ring resonator to get capacitiveinductive resonance Strong resonance gives negative μ J.B. Pendry et al, IEEE Trans. Microwave Theory Tech. 47, 2075 (1999).
LH Metamaterials
LH Metamaterials
FDTD Simulation of Transmission
Objective Outline Background on Metamaterials Background on Left-handed Metamaterials (LHM) FDTD Simulations of LHM Slab Basics of FDTD Results Simulations of LHM Structures Experimental Studies & Applications Summary
FDTD Scheme H E t E H t
FDTD Scheme E H t = 3Δt/2 t = Δt t = Δt/2 t = 0 Z
Simulation of LHM FDTD was used to study LHM through doublenegative dispersive bulk properties: r 2 s j2 m 2 om Lorentzian model r 2 2 p j c Drude Model
Normal Incidence, DNG Slab, n= -1 FDTD Model
Normal Incidence, DNG Slab, n=-1 FDTD Model
Oblique Incidence, DNG Slab, n=-1 FDTD Model
Objective Outline Background on Metamaterials Background on Left-handed Metamaterials (LHM) FDTD Simulations of LHM Slab Basics of FDTD Results Simulations of LHM Structures Experimental Studies of LHM & Applications Summary
Experimental LHM Work in the Microwave Regime Fabricated MTMs Measurement set-up from STL
Metamaterials in the THz Regime FDTD Simulation Geometry for periodic metamaterials Fabricated double-negative metamaterials in the THz regime Non-planar metamaterials