Characterising Properties and Loss in High Powered Metamaterials

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1 Characterising Properties and Loss in High Powered Metamaterials Aimée Hopper PhD Student Supervisor: R. Seviour International Institute for Accelerator Applications University of Huddersfield (UK)

2 Outline Definition of metamaterial Experimental Setup Results from Analysis New Method for Analysis High Power Materials Conclusions Aimée Hopper - University of Huddersfield - aimee.hopper@hud.ac.uk 2

3 What is a metamaterial? Artificial macroscopic composite with a periodic cellular structure which produces two or more responses not available in nature in response to a specific excitation Walser 2003 REAL negative refractive index. n = n + in = ± εμ Aimée Hopper - University of Huddersfield - aimee.hopper@hud.ac.uk 3

4 Why are they useful? Engineer dispersion relation Normal parabolic dispersion curve only gives point interactions maximise interaction between wave and beam Metamaterials cause an arbitrary phase shift Reduced size/weight of vacuum devices Size independent of λ depends on the macroscopic properties of the structure Aimée Hopper - University of Huddersfield - aimee.hopper@hud.ac.uk Note: v g ω k is only true for non(weakly)-dispersive media 4

5 Material Of Study Characterising one realisation of a metamaterials -> wire + SRR A D Narrow region where both ε and μ are negative Double NeGative (DNG), caused by small resonant bandwidth B C Aimée Hopper - University of Huddersfield - aimee.hopper@hud.ac.uk 5

Need to minimise attenuation -> minimise losses -> need VERY accurate

6 Absorption High Power Issues A The structures used for this analysis are not able to withstand high power B C Building and characterising are DIFFICULT! Need to minimise attenuation -> minimise losses -> need VERY accurate measurements -> n, z, ε, μ Aimée Hopper - University of Huddersfield - aimee.hopper@hud.ac.uk 6 frequency

Data taken using Agilent Technologies E8362B VNA Series Network Analyser Characterise understand attenuation

7 Experimental Setup Parallel plate waveguide used absorbing walls Plane wave achieved by the time wave front reaches the structure. Calibration Important! Data taken using Agilent Technologies E8362B VNA Series Network Analyser Characterise understand attenuation very sensitive measurements takes TIME This particular analysis method is only valid in plane-wave systems Aimée Hopper - University of Huddersfield - aimee.hopper@hud.ac.uk 7

8 Loaded System Empty System Measurements A B Needed to understand what the N.A. was producing Magnitude (Amplitude) of wave, and Phase, recorded C D S 11 = S 11 e iθ S 21 = S 21 e iθ Aimée Hopper - University of Huddersfield - aimee.hopper@hud.ac.uk 8

9 Reproducibility A 6 data sets overlapped, with the graphs showing S 11 and S 21 B S 11 S 11 S 21 S 21 Aimée Hopper - University of Huddersfield - aimee.hopper@hud.ac.uk 9

10 Empty System Loaded System A B C E D 10 10

11 Smith technique α = 1 S S 21 2S 21 n = 1 kd cosh 1 (α) ε and μ Characteristics A B z = 1 + s s 21 1 s s 21 ε = n/z μ = nz Aimée Hopper - University of Huddersfield - aimee.hopper@hud.ac.uk 11

12 New Analysis Method Forward Scattering Sum Rule Real part of forward scattering amplitude related to the total cross section of any scatterer. Absorbed power incident on periodic structure proportional to Im h(k) h k = i2 1 T k A is a Herglotz function (positive real function), A is the cross sectional area of the unit cell T is the co-polarised part of the fundamental mode transmission coefficient. h k b = 4 k S 21,object S 21,empty 1 πkd 1 d d 1 2jd only S 21 of the empty and loaded system required Aimée Hopper - University of Huddersfield - aimee.hopper@hud.ac.uk 12

13 h h [cm] h vs frequency Uncalibrated relative measurements Can see structure in the 10-14GHz range Frequency [Hz] Aimée Hopper - University of Huddersfield - aimee.hopper@hud.ac.uk 13

Non Resonant Metamaterials Existing metamaterials commonly made of resonant circuits inductance and capacitance Resonance in LC circuit produces negative μ, negative ε producable by

14 Non Resonant Metamaterials Existing metamaterials commonly made of resonant circuits inductance and capacitance Resonance in LC circuit produces negative μ, negative ε producable by wire array Need new method for producing negative μ so high power applications can be realised. Superconductors? Aimée Hopper - University of Huddersfield - aimee.hopper@hud.ac.uk 14

15 Conclusions Size of devices determined by wavelength of radiation used large structures! Metamaterial structures engineer dispersion curve define phase change. Used to reduce size, weight and cost of device. Characteristics of structure currently take long time to determine. Determined through sensitive calibration - S 11 and S 21 measurements. Forward Sum Rule determine extinction cross section losses of system Analysis of system with simpler measurements Non-resonant Metamaterials Super Conducting Plates Aimée Hopper - University of Huddersfield - aimee.hopper@hud.ac.uk 15

16 Thank you for listening Any Questions? Aimée Hopper - University of Huddersfield - aimee.hopper@hud.ac.uk 16

Characterising The RF Properties of Metamaterials

Characterising The RF Properties of Metamaterials Aimee Hopper Prof Rebecca Seviour International Institute for Accelerator Applications, University of Huddersfield aimee.hopper@hud.ac.uk 1 Outline Metamaterials?