Does the wavelength the unique criteria to choose the size of unit cells in metamaterial regime ? particularly for microwave applications.
every cell has it's own frequency-related and spatial electromagnetic properties. So, when you need a smaller cell, you are still limited by these factors changes. then, there is a coupling between small cell components, which you usually try avoiding, until know how to use it for your benefit.
A metamaterial should look "smooth" at a scale of a wavelength, so needs something like 5 or more periods per wavelength.
The size of any meta-material has to be less than the objective frequency of operation, for instance If your design frequency is 30 GHz, in free-space the wavelength will be 10 mm, so the size should be very less than 10 mm, in order for the cell to act like a meta-material. You can built numerous type of meta-material structure, based on your application criteria. Depending on the application, you need to define the B.C accordingly.
Yes, the size of the cell in metamaterial depends entirely on the wavelength, which is mentioned in references as is less than a quarter of the wavelength
The size of the cell in metamaterial should be less than a 1/10 of the wavelength
Conference Paper Metamaterials on antenna solutions
Conference Paper Parametric Synthesis of 3D Structure of SRR Element of the M...
Instead of asking the physical dimension, it would be more accurate to know the electrical length of the unit cell. We have to use the trial error method always for a certain limiting error. For example, if Lamda/10 does not give correct results in FDM or FDTD, etc numerical technique, we refine the mesh. if we get the results within lamda/5 meshing, we use it. We dont go for lamda / 10 mesh-size
The length (electrical) of the unit cell depends on the area of applications.
1. if we are using within it (metamaterial) in a metallic waveguide, much smaller (than the conventional substrate based metamaterial) unit cell is required. The final results depend on the bending of electric/magnetic fields and its total length (electric/magnetic).
2. Similarly, if we are designing the metamaterial using a substrate, please, use the trial error method to generate a suitable electric length to achieve the results. With my limited knowledge, it is found from the published research articles, if we are working upto 18 or 20 GHz, the physical dimensions of the unit cell is approximately 7-10mm depending on application. Form example, at 18GHz, lamda = 16.67mm. Lamda / 4 = 4.17mm.
But, the physical dimension is 7.5mm X 7.5mm or 10mm X 10mm.
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