First test of a photonic band gap structure for ADMX-HF Workshop on - - PowerPoint PPT Presentation

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First test of a photonic band gap structure for ADMX-HF Workshop on - - PowerPoint PPT Presentation

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First test of a photonic band gap structure for ADMX-HF Workshop on Microwave Cavities and Detectors for Axion Research Livermore National Laboratory January 13, 2017 Samantha Lewis Graduate student University of California - Berkeley

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SLIDE 1

First test of a photonic band gap structure for ADMX-HF

Samantha Lewis

Graduate student University of California - Berkeley

Workshop on Microwave Cavities and Detectors for Axion Research Livermore National Laboratory January 13, 2017

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SLIDE 2

Outline

I. Background and motivation II. Prototype design III. Fixed frequency results

  • IV. Discussion and future work
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SLIDE 3

Background and motivation

  • Periodic lattice of metal and/or dielectric rods
  • Open boundary (not enclosed)
  • Bands of frequencies which cannot propagate
  • Desired modes can be isolated using defect in

lattice

Photonic band gap structures

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SLIDE 4

Background and motivation

  • Eliminate mode crossings

– Mode crossings reduce scan rate and make some tuning regions effectively unusable

  • Move to higher frequencies

– Lots of design parameters and flexibility

  • Potential for high Q

Motivation

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SLIDE 5

Simple lattice configurations

Background and motivation

Triangular lattice Square lattice

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SLIDE 6

Band gap maps

Background and motivation

TM modes TE modes Square lattice Triangular lattice

Adapted from: Smirnova, et al., J. Appl. Phys., 2002

Disallowed regions Disallowed region

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SLIDE 7

Prototype design

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SLIDE 8

Lattice parameters

Prototype design

TM010 TM010 TE

TM modes TE modes

  • Densely packed lattice
  • Large rods (quarter inch OD)

for structural stability

  • Defect formed from

removing multiple periods

  • Goal maximum frequency:

roughly 10 GHz

  • Starting length: 10 cm
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SLIDE 9

Tuning

Prototype design

  • Single metal tuning rod in defect
  • Tunes via the same mechanism as existing

cavity (off-axis axle, 180 degree rotation)

  • Roughly 2.2 GHz in tuning total

Note: tuning curve for a slightly different lattice

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SLIDE 10

TM010-like mode in simulation

Prototype design

Maximum tuning position: 9.434 GHz

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SLIDE 11

Prototype design

Spectrum at top tuning position

TM010-like mode No TE modes, two TEM modes found with field probes but not S21

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SLIDE 12

Comparison with cavity

Prototype design

Size of “equivalent” cavity

  • Cylindrical cavity with

the same size tuning rod

  • Volume: roughly 0.2 L
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SLIDE 13

Comparison with cavity

Prototype design

Cavity TM010-like mode

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SLIDE 14

Fixed frequency results

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SLIDE 15

Assembled structure

Fixed frequency results

  • Fixed frequency tests

first, no tuning rod

  • Tuning rod will be

added to the same structure later

  • Made of 7075

aluminum

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SLIDE 16

Simulated vs measured S21

Fixed frequency results

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SLIDE 17

Measurement status

Fixed frequency results

  • Measured Q value was 7,000, vs 17,000 simulated

– Likely somewhat due to haphazard setup: poor connection with antennas – Simulation does not include the holes in the endcaps for access ports and the tuning rod axle – Simulation includes absorber outside the structure which we plan to use – Worst case: poor electrical contact within the structure

  • Frequencies of the three modes were almost exactly as

expected (less than 0.15% difference in all cases)

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SLIDE 18

Discussion and future work

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SLIDE 19

Fixed frequency device

Discussion and future work

  • Narrow down the discrepancy in Q

– Take more thorough measurements – Incorporate all features of the design into the simulation

  • Bead pull measurements

– Verify all three modes are what we expect – Check the flatness of the profile

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SLIDE 20

Tuning measurements

Discussion and future work

  • Fabricate and add the tuning rod

– Requires disassembly and reassembly, allowing for a full cleaning of the structure

  • Bead pull measurements

– Look for unexpected modes – Study the potential TEM mode crossing – Validate full simulations of the tuning curve – Make a complete mode map

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SLIDE 21

Summary

  • Fabricated a fixed frequency PBG to validate our

simulations

  • Tuning rod to be implemented by the end of the

month

  • Extensive study planned to examine the single tuning

rod method

  • Knowledge will be used to investigate other designs,

including higher Q and other frequencies

Discussion and future work

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SLIDE 22

ADMX-HF/X3 Team

Yale University (experiment site)

Steve Lamoreaux, Ling Zhong, Ben Brubaker, Sid Cahn, Kelly Backes

UC Berkeley

Karl van Bibber, Maria Simanovskaia, Samantha Lewis, Jaben Root, Saad Al Kenany, Nicholas Rapidis, Isabella Urdinaran

CU Boulder/JILA

Konrad W. Lehnert, Daniel Palken, William F. Kindel, Maxime Malnou

Lawrence Livermore National Lab

Gianpaolo Carosi, Tim Shokair

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SLIDE 23

Questions?