dispersive effects experimental observation and analysis ...the author uses ie3d to layout the...
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The author uses IE3D to layout the structure and to perform method-of-moments EM simulation.
Experimental Observation and Control of Wave Dispersion
Kyle McLellan, C. Isaac Angert and S.K. Remillard
Hope College Physics Department
Matlab graphs
• Electrons in a Lattice• EM wave in a solid• Sound in elastic media
Dispersive Effects
Acknowledgements
Analysis and Modeling
This material is based upon work supported by the National Science Foundation under NSF-REU Grant No. 0452206
Kronig-Penny potential in the Schrödinger equation
( )( )21221121
22
21
2211 cos)sin()sin(2
)cos()cos( dddkdkkk
kkdkdk +=−− β
(2)
d1 d2 d1+d2≡Lattice Constantλi=wavelength in region “i”
Wave, β=2π/λ
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 152
1
0
1
2R.H.S of Eq. 1
Frequency (GHz)
Left
Han
d S
ide
of E
quat
ion
1
speed wave 2
ii
=== vv
ki
i λπω
+= −
21
1 L.H.S.cos
ddβ
Forbidden
Band
Objective
Experiment Outline
Dispersion Engineering: Impurity States
d1=d2=7 mm
Periodic microwave transmission lines are used to create dispersive effects which mimic thoseassociated with the band theory of solids. Students are equipped with a simple method to construct a crystal lattice using a hobby knife. The measured frequency response is then analyzed with a student-generated code using MatLab and reduced to an experimental dispersion curve.
h
w1
w2
d2d1
εs
ε2,effε1,eff
)/(1212
1
2
1,
i
SSeffi
wh+−++≈ εεε
Periodic variation in εeff produces a periodic impedance mismatch of the wave.
Signal in
S11 ≡ Measured reflection coefficient magnitude and phaseS21 ≡ Measured transmission coefficient magnitude and phase
21
211
2221
211
221
211)(
2
)2()1(1
S
SSSSSe Ljj −−+++−
=+ βα
Propagation constant, solved by inverting this equationAttenuation coefficient (ref. 1)
d1+d2≡Lattice Constant
Band Gap
!Dispersion Constant ⇒≠βω
d
d
β⋅(d1+d2)/2π0 0.1 0.2 0.3 0.4 0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
ω⋅ (d
1+d 2)
/2π c
Brillouin Zone Edge
β 21 dd +π0
(1)
Periodic Transmission Lines
1. Write C-based code to evaluate Equation 1 and to invert Equation 22. Design a periodic transmission line using an EM field simulator3. Fabricate the periodic transmission line4. Measure the transmission and reflection coefficients vs. frequency5. Use the computer program to compute β vs. frequency with Eq. 26. Plot the dispersion relation in the extended or reduced zone scheme7. Attempt some “dispersion engineering” with an impurity
Dispersion Curves 4 Ways
Analytic: Using Equation 1Simulated S-Parameters: Using Equation 2
and T&R coefficients from EM sim.Measured: Using Equation 2 and T&R
coefficients from measurementSim Current Distr: Using λ observed in the
current distribution to find β
b.d2d1
Results
Experiment
This transmission line was fabricated using photolithography.
A corporate sponsor of R&D at Hope CollegeDean of Natural and Applied Science
The dispersive structure is hand-fabricated using an Exacto knife.
T & R parameters of the dispersive structure are measured with a vector network analyzer.
See Reference 2.
References1. W.R. Eisenstadt and Y. Eo, “S-Parameter Based IC Interconnect Transmission Line Characterization,” IEEE Trans. Components, Hybrids and Manufacturing
Technol., 15, no. 4, 483-490 (1992).2. C. Isaac Angert and S.K. Remillard, "Dispersion in One-Dimensional Photonic Band Gap Periodic Transmission Lines," Microwave and Optical Technology
Letters, 51, no. 4, 1010-1013 (2009). 3. E. Yablonovitch, et. al, “Donor and Acceptor Modes in Photonic Band Structure,” Phys. Rev. Lett., 67, no. 24, 3380-3383 (1991).4. Brian C Wadell, Transmission Line Design Handbook, Artech House, Inc, Norwood, MA, 1991, Page 94.5. IE3D EM Design System, Zeland Software Inc, Fremont, CA.6. MATLAB, The MathWorks, Natick, MA.
P type gap state N type gap state
Transmission line equations from Reference 4.Code Written in MATLAB (ref 6).
Method-of-Moments simulation using IE3D (Ref. 5) yields both scattering parameters and surface current distribution.
(A/m)
Matlab is used to invert Equation 2 and to calculate the wave number, β.
has a transcendental solution:
K.-P. potential
ω
β
dispersionless case:
|LHS|<1
Simulated & MeasuredTransmission, α and β
The 400 lines of Matlab code are used to process raw T&R data. Parts of the code are left blank as a programming exercise.
p-Silicon (IV)doped with Al (III)
n-Silicon (IV)doped with As (V)
Reduced interstitial spacing simulates p-type dopingIncreased interstitial spacing simulates n-type doping
Reference 3
Copper tape
Paper design layout
L