# Mode Profile Shaping in Wire Media: Towards An Experimental Verification
## 5 Conclusions and Future Work  
We have presented evidence that it should be possible to reproduce the field profile shaping results of [3] in an experimentally realisable system. The system consists of a finite number of wires, a single period long, inside a metal cavity, and despite the many potential difficulties introduced by the cavity, simulations still show that we can modify the profile of the longitudinal electric field at will. Further, the shaped mode that we intend to excite should be sufficiently distinct from other \begin{table}
\begin{tabular}{l l l l l l l l l l} \hline Mode Number & 82 & 83 & 84 & 85 & 86 & 87 & 88 & 89 & **90** \\ \hline Freq (GHz) & 12.088 & 12.098 & 12.158 & 12.159 & 12.175 & 12.250 & 12.274 & 12.388 & **12.430** \\ \hline Type & Long & Long & Long & Trans & Long & Trans & Trans & **Our Mode** \\ \hline Mode Number & 91 & 92 & 93 & 94 & 95 & 96 & 97 & 98 & 99 \\ \hline Freq (GHz) & 12.433 & 12.460 & 12.539 & 12.556 & 12.565 & 12.577 & 12.583 & 12.723 & 12.831 \\ \hline Type & Trans & Trans & Long & Long & Long & Long & Trans & Long & Trans \\ \hline \end{tabular}
\end{table} 
Table 1: Modes of the modulated wire media in a cavity that are nearby to our chosen longitudinal mode (index ‘90, shown in bold). They are categorized into either transverse (‘Trans’) or longitudinal modes (‘Long’). This depends on the field pattern of the electric field. The electric field in the longitudinal modes is principally parallel to the wires as in Figure 8 whereas in the transverse modes it is perpendicular to the wires, Figure 14.  
Figure 14: An example showing the electric field vectors on a slice in the \((x,y)\) plane perpendicular to the wires. Most of the field modes near our desired longitudinal modes are of this transverse type, and should not be excited by a carefully designed (longitudinal) excitation field. The dimensions of the waveguide are the same as in Figure 8.  
nearby modes to allow the effect to be observed in practise. Nevertheless, more work is needed to improve this separation, either by identifying better methods of frequency isolation or by exploiting the properties of the nearby modes. Despite these promising predictions, there are other practical challenges that need to be overcome. We know that wires with a relative permittivity of \(\epsilon=50\) can be produced from a composite blend of _TiO_ particles and plasticiser, but thin wires with radii between 0.5 mm and 0.7 mm may be impractical to work with, even via controlled extrusion. If such manufacturing constraints cannot be overcome, we can easily redesign the system to use a larger cavity, work at a lower frequency, and need lower permittivity wires. Of course such adjustment will need to be led by the actual experimental design and lessons learned during its implementation and testing. Beyond the challenges involved in construction of the field profile shaping apparatus, there is also the question of what is the best method for exciting the longitudinal modes, and what the best way to measure them. One approach would be to load a sample of our wire array media into a section of a larger waveguide. In this way the naturally occurring longitudinal wave of the bare waveguide could couple naturally to the longitudinal (and shaped) wave in the loaded section, with minimal effect on the unwanted - but nearby in frequency - transverse modes. For measurement, a probe attached to a spectrum analyser can be used to map the internal field profile, or, alternatively, a perturbation bead-pull approach could be used. In summary, we believe our simulations provide sufficient evidence that our field profile shaping method will work in practise; justifying our intent to proceed with designing and building an experiment to verify this. Nevertheless, the frequency domain simulations done here could still be extended upon - notably we would like to move forward to time domain simulation to provide more information, such as to how the field profile will build up in the wire array media when the excitation field is turned on.