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REFRACTION EXPERIMENTS IN WAVEGUIDE ENVIRONMENTS

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REFRACTION EXPERIMENTS IN WAVEGUIDE ENVIRONMENTS

指導教授 吳瑞北

學生 許宗堯

- Review : resonator, negative refraction
- Measurement technique
- The axially symmetric SRR, the omega SRR, and the S ring
- Solid-state structure

- Waveguide miniaturization---subwavelength resonator
- The phase delay of the forward-wave can be completely compensated by the phase advance of backward-wave.

- DNG metamaterial has negative refraction
ENG DNG MNG DPS

- For normally incident wave
- n2 is real, wave number is also real
- n2 is pure imaginary, wave number is also pure imaginary → the wave is strongly attenuated inside the slab

- For obliquely incident wave
- Boundary condition :
- kx1 = kx2

- dispersion relation

- Boundary condition :

DNG

uniaxial MNG

- Many variations of rings and rods have been devised to achieve negative permittivities and permeabilities
- Various geometries….
- driving criteria:
- increase the bandwidth, reduce the losses, yield stable and repeatable results in measurements

- driving criteria:
- Main ring used now : the edge-coupled SRR, the broadside SRR , the axially symmetric SRR, the omega SRR ,and the S ring.

- all the rings exhibit a frequency dispersive permittivity response, in addition to the required frequency-dispersive permeability response
- However, the interesting region of permittivity response where negative values are achieved is usually much higher in frequency than the region where the permeability is negative, making this effect not usable

- Transmission level can be measured without many difficulties.
- The first step to perform transmission measurements on metamaterials is to obtain a proper incident beam
- an approximated plane wave can be created by eliminating the interference from the external environment as much as possible

- slab aperture D = 5 cm
- Frequency : around 10GHz
- Far-field limit = =17 cm
- Distance >17 cm

- The position of the sample is a result of a trade-off between incidence and reception
- far enough:
- the wave front exiting the waveguide coupler has enough space to flatten out and to approach a plane-wave front while it has to be far enough from the reception to minimize all near-field effects

- close enough
- the tapering effect of the absorbers cannot be avoided, and neither can the Gaussian far-field distribution due to the aperture source

- the axially symmetric SRR, the omega SRR, and the S ring

- Set of specific dimensions resonant and plasma frequencies
- fmo ≈ 8 GHz,fmp ≈ 9 GHz, and fep ≈ 11 GHz

- These frequencies are directly related to the thicknesses of the metallizations, the gaps, and other geometric parameters in the design of the SRR

- a stand alone peak between 8.2 and 8.7 GHz at a refraction angle of about −30◦

- peform both negative values of permittivities and permeabilities
- Transmission band is between 12GHz to 13.2GHz

- the refracted beam is seen to bend at an angle of about -27◦corresponding to an effective index of refraction of about −1.7
- It should also be mentioned that the losses of the prism at 12.6 GHz are smaller than 14 dB, which is acceptable

- S ring does not require the addition of a rod to exhibit a negative permittivity at similar frequencies to where it exhibits a negative permeability
- The second important feature of this ring is that its shape can be easily modified to achieve desired frequency responses

dash line: permittivity

solid line: permeability

- A major drawback in most metamaterials realized to date is the losses that they exhibit
- Various causes have been identified as a possible origin of losses, one of them being mismatch
- Another major drawback of most of the current implementations of negative metamaterials is their mechanical fragility

- A way that appears to avoid both drawbacks is to realize a solid-state metamaterial
- mechanical standpoint
- it is less fragile

- electromagnetic standpoint
- it exhibits less mismatched boundaries

- The insertion losses : we have measured the transmission power with and without the metamaterial sample
- Without the metamaterials samples, the corresponding value at 8.85 GHz is −9.8 dBm
- return loss at the incident interface is less than 5 dB
the original solid-state structure