Design for DRF-DSRR Basing on SDSRR

Figure 4.6: Schematic layout for DRF-DSRR basing on SDSRR. Each lager DSRR consists of 40 small DSRRs. The lattice constant a is set to be 60mm while the lattice constant of small ones is 4mm. The linewidth of small DSRRs is still 0.655mm.

The overall design of DRF-DSRR basing on SDSRR is presented in Fig. 4.6 as the details of a single unit have been shown in Fig. 4.3 (a). It has been fully considered through the limitation of experiment equipments and fabrication techniques. Due to the restriction of network analyzer, frequency exceeding 20GHz is not acceptable.

Hence it is impossible to manufacture small DSRRs with lattice constant less than 4mm. On the other hand, the resonant frequency of large DSRRs should not be smaller than 1GHz because it will be extremely inconvenient to build up the setup and to measure. Therefore, two frequency regions around 1GHz and 15GHz, which make a compromise of facilities limitation, are chosen as the investigated spectrums.

Their corresponding ratio, 15GHz to 1GHz, is 15.

As shown in Fig. 4.6, each large DSRR is composed by 40 small ones whose lattice constant is 4mm. Meanwhile, the lattice constant a of large DSRR is 60mm which is just 15 times of that of small ones. Since the value of lattice constant times resonant frequency should be constant, then it is very reasonable that the lattice constant of large DSRRs is 60mm by setting 1GHz as the desired resonant frequency

In the following experiment verification, two different frequency ranges will be measured around 1GHz and 15GHz. The higher and lower parts of spectrum are for smaller and larger DSRRs respectively. With 4x4 units of large DSRRs, as shown in Fig. 4.6, the higher spectrum will be observed first. Another sample contains 16x12 units of large DSRRs is measured around 1GHz in the end. The experiment setup has already been shown in Fig. 3.6 except that the horn antennas are replaced by two standard gain horns whose operating frequency are about 1GHz (Rozendal Asociates, RA3150-1; operating frequency range is from 800MHz to 1200 MHz). Furthermore, the distance between antennas and the center of sample changes from 30cm to 300cm.

After separate measurement, a special measurement combines two distinct frequency area will be discovered if there are indeed some physical responses for large DSRRs.

4.2.3 Experiment Verification

High Frequency Response

Figure 4.7: Transmission spectrum of DRF-DSRR basing on SDSRR. There are three different angles in the diagram. The response of 0 degree incident is presented by clear triangles; the result of 45 and 90 degree incident are shown by bold solid line and clear circles respectively.

Again, free space activity is presented in Fig. 4.7 as the reference, and the responses of DRF-DSRR basing on SDSRRs are under investigated as well. Obvious absorption occurs around 10GHz and 14GHz at incident angle of 90 degree. In contrast to the case of original DSRRs where only one resonant frequency is observed, the DRF-DSRR basing on SDRRs pattern at 90 degree indicates double resonant frequency. The transmission drops extending from 9GHz to 11GHz and 13GHz to 15GHz hold the value over than 10dB, comparing with the reference power.

Peak absorption value appears at 13.85GHz, and the difference between it and reference power exceeds 20dB. As Fig. 4.7 shown, the physical reactions of 0 and 45 degree incident almost overlap with the reference power, which implies that external microwaves do not sense the existence of DRF-DSRR pattern at all under such as a incident condition. It also provides an indirect evidence for proving that the power drop is indeed caused by negative permeability.

Another illustration of DRF-DSRR basing on SDSRR is depicted in Fig. 4.8. It notes that the absorption is very sensitive to misalignment; a slight change of rotation angle will affect the position of resonant frequency and the strength of absorption.

The characteristic of angle sensitivity only allows absorption exhibiting from 80 to 100 degree incident. Meanwhile, this trait is similar to that of other ring structures such as SRRs and DSRRs except for the double resonant frequency regions.

In fact, the property of double resonant frequency region for this DRF-DSRR pattern is due to the fractal-like scheme. In Fig. 4.6, the fractal-like design produces a lot of removal space hence the small DSRRs do not compose a complete square layout anymore. The discontinuous small DSRRs model generates the potential for incident magnetic field sensing lattice constant other than 5mm, thus dual absorptions can be detected in observed spectrum. The reason why double resonant frequency displays can be described specifically from the prospect of large DSRRs. For the linewidth of every large DSRR in Fig. 4.6, there are two rows of small DSRRs simultaneously. If each large DSRR is divided into a 4x4 areas geometrically, then it can be viewed as a complete DSRR whose linewidth is 6.62mm. Hence it is very rational for a second resonant frequency appearing.

Figure 4.8: Transmission spectrum of DRF-DSRR basing on SDSRR showing the sensitivity of rotation angle. The response of 80 and 90 degree are illustrated as bold solid line and clear circles respectively.

In summary, the final results of experiment data in the range of X-band have successfully introduced the possibility for accomplishing DRF-DSRR pattern through fractal-like SDSRRs. One of the double resonant frequencies has been observed and its physical explanation has been explored. Next step, the low frequency response of large DSRR awaits further investigations.

Low Frequency Response

In the experiment for low frequency response, the pattern comprises of 16x12 large DSRR cells is placed parallel to the propagating direction of the incident microwaves, where the magnetic field penetrates all metallic structures. The measured transmission scattering parameter S21 for this sample at lower band is depicted in Fig.

4.9. Again, the activity of free space without any sample in the middle of two horn antennas is denoted by solid squares while the response of DRF-DSRR is labeled by clear triangles. Apparently, the curves of free reference and that of DRF-DSRR pattern do not have significant dissimilarity. The maximum difference is extremely small if the absorption about several decades at higher band is taken as the standard.

The difference, merely 0.82dB, might be taken as inevitable noise fluctuation of whole system instead of any meaningful physical reaction.

Figure 4.9: Transmission characteristics of DRF-DSRR pattern around 1GHz when the propagating direction is parallel to the PCB. Solid squares denotes the response of free space, and clear triangles indicates the reactivity of a 16x12 large DRF-DSRR array whose lattice constant set to be 60mm.