R MUTHU RATTINA SUBASH
Research Scholar - Department of Engineering Design
Indian Institute of Technology Madras
1. Design of Single Antenna Applicator
The design of single antenna applicator is complete. Three antenna's were designed (2 Rigid and 1 paper like flexible) operating at 434MHz and 168MHz, which have shown excellent characteristics compared to the antenna's present at the same operating frequency available in the literature. The results obtained in the simulation are given as figures below. Currently metamaterial based approach is used to design a section of lens which will be integrated to the antenna to improve the performance even better, which is expected to be completed by Jan 2021.
The figure 1 below shows the model used for simulation for designing of the antenna in HFSS.
Figure 1. Simulation model used for designing antenna in HFSS
1.1 Simulation results of rigid antenna applicator operating 433MHz ISM band
Figure 2.1. Side view of the Designed antenna Figure 3.1. Variation of SAR inside the muscle
Figure 4.1. Normalised iso SAR contours at 5mm depth in muscle Figure 5.1. Normalised iso SAR contours at 15mm depth in muscle
Figure 6.1. Variation of SAR in lateral direction at 5mm depth in muslce Figure 7.1. Variation of SAR in lateral direction at 5mm depth in mucle
Figure 8.1. Shift in the resonance with change in water bolus height Figure 9.1. Shift in the resonance with change in permittivity of load
1.2 Simultion results of paper like flexible antenna operating at 433 MHz ISM band
Figure 2.2. Side view of the Designed antenna Figure 3.2. Variation of SAR inside the muscle
Figure 4.2. Normalised iso SAR contours at 5mm depth in muscle Figure 5.2. Normalised iso SAR contours at 15mm depth in muscle
Figure 6.2. Variation of SAR in lateral direction at 5mm depth in muslce Figure 7.2. Variation of SAR in lateral direction at 5mm depth in mucle
Description of figures
Figure 2.1, Figure 2.2 -
Figure 3.1,Figure 3.2-
Figure 4.1,figure 4.2 -
Figure 5.1,Figure 5.2 -
Figure 8.1,Figure 9.1-
Similar observations and results follow for the 168MHz applicator also. Currently reconfigurable structures are being designed, which when placed in front of antenna will could futher improve the penetration depth which can be used to deliver heating to higher depth inside the muscle. The final design of the antenna would include this reconfigurable structure with which the antenna will be tested on phantoms for validation. This work is expected to be complete by Feb 2022.
Shows the side view of the designed antenna. Figure 2.1 shows the semi rigid antenna which has a substrate thickness of 1.28mm backed by plexigless of thickness 0.1mm. The antenna woud support large bend radius and hence can be used to treat surface which are uniform. On the other hand, the antenna shown in figure 2.2 has a thickness of 0.23mm developed on a highly flexible substrate which can have any bend radius. The flexibility is upto the extent that it can be rolled. This antenna would be highly helpful in conforming over the body surface which can be placed on the surface like head, neck, hips, breast and etc. It would be suitable to treat any region on the body providing uniform with power loss and hence will be highly efficient.
Both these figures show the variation of SAR with depth inside the muscle. The SAR dictates the amount of heating that is taking place inside the muscle. Hence more linear the curve is, better the penetration depth. In order to have penetration depth to be higher, the electromagnetic fields must have components only in tagential directions to the muscle. It is because the tangential components are continuous across dielectric boundary and hence losses at interface is minimum. Whereas, the normal components will have discontinuity at the dielectric interface. The amount of tangential field present in this current design is 94% which is the highest among the current literature, because of which the penetration depth is also increased by 39%. compared to best in literature. The table I below compares all the parameters of the designed antenna with the latest literature. This design as such could be used to locally advanced tumours extending to more than 1 cm depth inside the muscle.
These show the normalised iso- SAR contours at 5mm depth inside the muscle. The observation from these results signify the area covered for heating by antenna (Effective field size - EFS). The area covered is dependent mostly on the size of the antenna. But in this work, the size of the antenna is miniaturized to a great extent using novel techniques but EFS is also very good and equivalent to antenna's with large aperture.
These show the normalised iso- SAR contours at 15mm depth inside the muscle. The observations from these follow the same as from figure 4.1& figure 4.2 given above.
Figure 8.1 shows the shift in the resonance observed with respect to change in the water bolus height. Since these applicators would use a floppy water bolus, the size of the water bolus may increase or decrease based on the locations on the body where the applicator is placed, amount of force given over the applicator and etc. Hence the antenna must be robust enough to handle these changes and radiate efficiently. The plots show the return loss of antenna vs the frequency where the antenna resonates, it can be observed that the antenna is robust to changes for variety of thickness of waterbolus.
Figure 9.1 shows the shift in the resonance observed with respect to change in the relative permittivity of muscle. Every individual will definitely have different relative permittivity which also varies with locations in body. The antenna's performace was tested for variation of permittivity with +50% to -50% change. From the plots we can observe that the antenna's resonance frequency doesn't change and hence provides stable and robust performance.
