Sviluppo di pupille Toraldo realizzate con metamateriali Giampaolo Pisano

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1 Sviluppo di pupille Toraldo realizzate con metamateriali Giampaolo Pisano Astronomy Instrumentation Group - Cardiff University Workshop: Super-risoluzione in Radioastronomia: Pupille Toraldo Villa Galileo Firenze, 12/10/2017

2 Summary Mesh technology Mesh based Toraldo Pupils Discussion & Conclusions

3 Mesh technology: Spectral filters Markuvitz (1951), Ulrich (1967) Capacitive Inductive Resonant (Low-pass) (High-pass) (Band-pass) Dielectrically Embedded multi-layer filters

4 QO components: Mesh Filters Space qualified technology Band defining Filters Blocking Filters and Filter Chains Dichroics, Polarisers, Beam dividers 45 cm

Flat Mesh Lens: Inhomogeneous Phase Delays G.

5 Flat Mesh Lens: Inhomogeneous Phase Delays G. Pisano et al. Applied Optics 52,n.11, (2013) Inhomogeneous grids Locally variable grid geometries Multiple transmission lines 54 mm Ø W-Band f/3 lens prototype (1.4mm thick) - Very thin and robust - Very light and low loss - No Anti Reflection Coatings required

6 Flat Mesh Lens: Finite-element modelling 3D full model 2D model (cylindrical simmetry) - Central TL array

7 Flat Mesh Lens: VNA beam tests G. Pisano et al. Applied Optics 52,n.11, (2013) Experimental agreement down to the 4 th side lobes

8 Mesh Half Wave Plates: Embedded design G. Pisano et al. PIER M, 25, p101 (2012) Homogeneous anisotropic grids Lerner geometry W-Band Unit cell =20cm Other devices: QWPs (linear circular)

9 Artificial Magnetic Conductor: Design & realisation G. Pisano et al. Applied Optics (2016) 20cm PEC AMC 100 mm Porous Teflon Copper grids AMC Mirror (Df = 0) - Prototype with both PEC and AMC surfaces Polypropylene PEC Mirror (Df = p) Metal planes

10 Embedded Reflective Half Wave Plate: Development Perfect Electric Conductor Incident wave Magnetic mirror E x Wire-Grid Pol 1 Embedded AMC & PEC Df = p Df = 0 Pol 2 E x E y k i E y Reflected wave E y k r E y E x E x G.Pisano et al. Applied Optics v.55, (2016) - One polarisation sees the PEC (Perfect Electric Conductor) - The orthogonal one sees the AMC (Artificial Magnetic Conductor)

11 Mesh technology: Large diameter device facilities upgrade TRP Large radii HWP development UV exposure box for photolithographic processes - Large diameter mesh-devices: - Production of 50cm devices - Prototyping of 120cm devices Large hot-press oven

12 Summary Mesh technology Mesh based Toraldo Pupils Discussion & Conclusions

$Dielectric ring - Phase shift (p) Cons: - Diffraction from edges - Frequency dependence - Need anti-reflection coating - Ring holding$

13 Toraldo Pupils: Baseline design Dielectric-rings design (3-coronae) Pros: - Easy manufacture Structure: - Metal aperture - Air - Dielectric ring - Phase shift (p) Cons: - Diffraction from edges - Frequency dependence - Need anti-reflection coating - Ring holding structure

14 Flat Mesh Lens: In more detail - Lens consisting of ~ 8000 TLs - Solution of just 1/8 of the surface - Optimisation for max transmission & appropriate differential phase shift Flat lens made with 10 grids (5+5)

15 Metamaterial based Toraldo Pupils: Option 1 Mesh-lens type TP (3-coronae) C C Pros: - Easy manufacture - Requires only 2 filter designs Working principle: - Differential phase-shift from different capacitive filters - Similar to mesh-lens but with flat differential phase requirement C 1 C 2 C 1 Structure: - Metal aperture - Transparent Capacitive grids Phase shift f - Transparent Capacitive grids Phase shift (f + p) Bandwidth Df= Cons: - Narrow bandwidth - Large number of grids required so far (~20)

16 Mesh Half Wave Plates: In more detail M-HWP Differential phase-shift DF= ~75% BW Transmission along C-axis Transmission along L-axis

inductive filters - Square patches vs crossed lines Structure: - Metal - Transparent Capacitive grids Phase shift f -

17 Metamaterial based Toraldo Pupils: Option 2 Mesh-HWP type TP (3-coronae) C L Pros: - Large bandwidths - Only 6 grids required - Requires only 2 filter designs Working principle: - Isotropic grids - Differential phase-shift from capacitive and inductive filters - Square patches vs crossed lines Structure: - Metal - Transparent Capacitive grids Phase shift f - Transparent Inductive grids Phase shift (f + p) C L C Bandwidth Df= Cons: - C and L grids at different heights - Assembly could be tricky

18 Embedded Reflective HWP: In more detail Reflection coefficients & x-pol 20 cm < 1mm thick Differential Phase-Shift ~125% BW

Metamaterial based Toraldo Pupils: Option 3 AMC-type TP (3-coronae)

Only 5 grids Working principle: - Differential phase-shift from PEC

Metal - Perfect Electric Conductor (PEC) Phase shift (f) -

Df=180 20 Cons: - Works in reflection - Off-axis performance

19 Metamaterial based Toraldo Pupils: Option 3 AMC-type TP (3-coronae) AMC PEC Pros: - Easy to manufacture - Extremely large bandwidths - Only 5 grids Working principle: - Differential phase-shift from PEC and AMC surfaces, in principle equal to p AMC PEC AMC Structure: - Metal - Perfect Electric Conductor (PEC) Phase shift (f) - Artificial Magnetic Conductor (AMC) Phase shift (f+p) Bandwidth Df= Cons: - Works in reflection - Off-axis performance slightly dependent on S and P polarisations - Oval shaped PEC would work only at a fixed angle

20 Toraldo Pupils: Simulations 3-coronae Toraldo design (a 1 =1/3, a 2 =2/3, a 3 =1) (k 1 =63.83, k 2 = , k 3 =14.952) 3-coronae solution with arbitrary phases (a 1 =1/3, a 2 =2/3, a 3 =1) (k 1 =63.83, k 2 =-35.82, k 3 =9.41) (f 1 =0, f 2 151, a 3 54 )

21 Metamaterial based Toraldo Pupils: Further options Variable-phase mesh TP Working principle: - Solutions with intermediate phaseshifts (0-p) - Possibility to have different frequency dependences (not necessarily flat) C C L C Pros: - Continuously varying phase gradients - More performant designs? - Higher resolution achievable? Cons: - The number of filter designs is equal to the number of discretised phases Components: - Metal aperture - Continuous, radially varying phase-shift ranging from f (centre) to f+p L

22 Summary Mesh technology Mesh based Toraldo Pupils Discussion & Conclusions

23 Discussion & Conclusions 1/2 We have discussed the idea to use the mesh filters technology to develop metamaterial-based Toraldo Pupils We have identified three options derived from previously developed devices: 1) Mesh-lens type TP 2) Mesh-HWP type TP 3) AMC type TP The three designs offer increasing larger operational bandwidths while becoming less and less difficult to manufacture Although Option 1 seems to be the more straightforward design, it is actually the most difficult to implement Option 2 and 3 could be developed very quickly; the latter would need to operate off-axis in reflection

24 Discussion & Conclusions 2/2 The working principles adopted in option 1 and 2 could be used also to arbitrarily manipulate transmission and phase across the TP surface. This gives the possibility to implement a further option: 4) Variable-phase mesh TP This would allow to design TP with continuously varying phase profiles Option 4 could lead to devices with better performance by relaxing the constraint to have differential phase-shift equal to p between coronae, and for this phase-shift to be flat across the operational frequency band We note that all the designs discussed could be implemented also using alternative technologies

25 Grazie!

A BROADBAND METAL-MESH HALF-WAVE PLATE FOR MILLIMETRE WAVE LINEAR POLARISATION ROTATION

Progress In Electromagnetics Research M, Vol. 25, 101 114, 2012 A BROADBAND METAL-MESH HALF-WAVE PLATE FOR MILLIMETRE WAVE LINEAR POLARISATION ROTATION G. Pisano *, M. W. Ng, V. C. Haynes, and B. Maffei