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Dual Frequency Long Shape Bowtie Antenna for Microwave Hyperthermia at 915 Mhz and 2450 Mhz

Hanalde Andre

Siteba Polytechnic of Health

Electromedic Division

Padang, Indonesia

hanalde.andre@

Abstract— Microwave hyperthermia radiation is used clinically to heat tissue situated deep in the body and minimize the coincidental rise in skin temperature seen with other forms of therapeutic heating. Long shape bowtie hyperthermia antenna at dual frequency 915 MHz and 2450 MHz is described in this paper. The side angle parameter is used to for dual frequency resonant. Calculation and simulation has been cover up to get specific antenna. Simulation shows the antenna with flare angle of 150 degree and side angle of 10 degree suitable for dual frequency. Simulation used finite element method (FEM).

Keywords— Long Shape Bowtie Antena; Microwave; Hyperthermia; Dual Frequency; Finite Element Method (FEM)

Introduction

Antennas and other EM applicators similar to those used for hyperthermia, particularly capacitive and inductive applicators, have been used for diathermy. EM applicators can produce deeper heating than methods that simply heat the body surface and rely on thermal conduction to carry the heat to the deeper tissues. Similar applicators have also been used to rewarm hypothermic patients.

Hyperthermia is the elevation of tissue temperatures to 40-45 °C and is mainly applied as a cancer therapy in combination with other treatment modalities, such as radiotherapy or chemotherapy. It took a long time before the potential of hyperthermia was demonstrated in randomized studies. Basically, the aim is to achieve an elevated homogeneous temperature distribution within the target volume and no heating of the surrounding tissue.[1-3] Hyperthermia induced by microwave diathermy into tissue can stimulate repair processes, increase drug activity, allow more efficient relief from pain, help in the removal of toxic wastes, increase tendon extensibility and reduce muscle and joint stiffness. Moreover, hyperthermia induces hyperthermia, improves local tissue drainage, increases metabolic rate and induces alterations in the cell membrane.

Frequencies historically used in the rehabilitation were 2450, 915, 434, (with surface cooling) and 27.12 MHz [4]. These frequencies differ because of the peculiar range of depth in which they can generate heat inside tissues. The efficacy of an electromagnetic wave device is strictly related to the ability of the heating device to achieve a certain temperature at the target site[5-7].

Development research on microwave antennas for medical applications has been done to hyperthermia for medical treatments. Antennas applied to elevate the temperature of cancer tissues are located inside or outside of the patient’s body, and the types of antennas depend on the location. For instance, waveguide or low-profile antennas are externally positioned, and monopole or dipole antennas transformed from a coaxial cable are designed for internal use at hyperthermia applicator.[8]

As one of ultra wide band antennas, bowtie antennas fed by coaxial line, coplanar waveguide and strip line, have many advantages, such as low profile, ultra wide impedance band, high radiation efficiency and easy to manufacture etc. They are used in many domains due to the advantages mentioned above, such as ground penetrating radar, pulse antennas and medical application. The clinic equipment of microwave hyperthermia has a simple structure and, convenient to operate. Microwave hyperthermia has less complications and little side effect. So it has extensive application prospects for researcher.

In this paper, long shape bowtie antenna will be discussed for microwave hyperthermia application using finite element method (FEM). Basically this antenna adopted bowtie antenna parameter. In section 2 will study about long bowtie antenna design. Simulated result and analyses will be discussed in section 3. Side angle and flare angle in long shape bowtie antenna will be considered in this design.

LONG SHAPE BOWTIE ANTENNA

The antenna characteristic is strongly influenced by the geometric form. The most fundamental thing in designing an antenna is the wavelength of the desired frequency. Parameters is used in long shape bowtie antenna is a flare angle, side angle, round corners and gap distance. All of these parameters will affect the length of the antenna to get characteristic purpose. The shape of the bowtie antenna long shape can be seen in Fig. 1.

[pic]

Fig. 1. Long Shape Bowtie Antenna

Simulations conducted on the influence of parameters and flare angle side angle. Method finite element method is used to see the result of the influence of these two parameters. Antenna using FR4 epoxy substrate with a material with a material thickness of 1.6 mm. The substrate has a length of 120 mm and a width of 70 mm. dielectric constant of the substrate is 4.4. antenna has a length of 108 mm. The long wavelength based on the desired frequency of 915 MHz. Finite Element Method is used for the simulation. Antenna placed on radiation area with length is 250 mm, its suitable for the lowest frequency 915 MHz.

[pic]

(a) (b) (c)

Fig. 2. Flare Angle

[pic]

Fig. 3. Simulation Results Return Loss |S11| Vs. Frequency

[Flare Angle Long Shape Bowtie Comparison]

The simulation results obtained using different values ​​of flare angle can be seen in Fig. 2. Great value flare angle used in the simulation is 90 degrees, 120 degrees and 150 degrees. Return loss values ​​obtained from the three values ​​of the angle of flare shows bahawa the greater the value of flare angle influence on the antenna characteristics at high frequencies. At the antenna with a flare angle value of 150 degrees to 120 degrees and has two resonances at low frequencies and high frequencies while for values ​​flare angle of 90 degrees has only one resonance. The difference of the value of high-frequency characteristics of flare angle of 120 degrees and 150 degrees, a shift in the resonance frequency. Value of the resonant frequency with a flare angle of 150 degrees is slightly lower than the value of the resonant frequency of flare agle 120 degrees.

[pic]

(a) (b) (c)

Fig. 4. Side Angle

Side angle is an additional parameter that differentiates the long shape with a bowtie antenna bowtie antenna. Simulations conducted on three forms of the antenna with different values ​​side angle as can be seen in Fig. 4. Simulation results show the effect on the value side angle antenna characteristics at high frequencies as can be seen in Fig. 5. Value side angle of 10 degrees has the characteristics of high frequency better than the other forms. For the low frequency of characteristics can be seen there was a slight shift in the resonance frequency becomes higher towards the increase of the value of side angle.

[pic]

Fig. 5. Simulation Results Return Loss |S11| Vs. Frequency

[Side Angle Long Shape Bowtie Comparison]

Characteristics of long bowtie antenna shape has two resonant frequencies. This can be be proved from the results of simulations that have been carried out. This antenna has a resonance at low frequency and high frequency. Research was conducted to obtain antenna as therapeutic apparatus hyperthermia applicator at the frequency of 915 Mhz and 2450 Mhz. To see frequency characteristics of the antenna at the frequencies used parameters reutrn loss (RL). This parameter may view the better than the characteristics of the antenna VSWR parameters. In table 1 we can see the value of the parameter RL flare angle and side angle that has been simulated at a frequency of 915 MHz and 2450 MHz. of the value obtained in accordance with the shape of the antenna characteristics for hyperthermia therapy device is the value of a flare angle of 150 degrees and the value side angle of 10 degrees.

Table 1. Simulation Result Return Loss in 915 MHz and 2450 Mhz

(variation flare angle and side angle long shape bowtie antenna)

|Antenna Parameter |Return Loss [RL] |

| |915 MHz |2450 Mhz |

|Flare Angle | | |

|90 Degree |-13.8161 |-3.1261 |

|120 Degree |-16.3864 |-7.5353 |

|150 Degree |-18.0334 |-15.1285 |

|Side Angle | | |

|10 Degree |-18.0334 |-15.1285 |

|20 Degree |-17.2404 |-9.4930 |

|30 Degree |-14.8988 |-7.2288 |

Simulated Result And Analyses

This section will discuss the comparison between the simulation results for long shape bowtie antenna with bowtie antenna. In Fig. 6 it can be seen geometry of the bowtie antenna.

[pic]

Fig. 6. Bowtie Antenna

Bowtie antenna used in the simulation has a length of 108 mm. This value is obtained from the calculation and simulation of the desired lowest frequency of 915 MHz. Value flare angle of 60 degrees is used in accordance with the research that has been done to obtain the optimal frequency response of the bowtie antenna.

long shape bowtie antenna using the antenna length equal to the length of the antenna is used in a bowtie antenna. Value flare angle and side angle used is 150 degrees and 10 degrees. This value is obtained from calculations and simulations that have been carried out in the previous section. shape long parameter values ​​bowtie antenna can be seen in Table 2. From the values ​​obtained from long bowtie antenna shape as can be seen in Fig. 7.

Tabel 2. Parameter Long Shape Bowtie Antenna

|Parameter |Value |

|Length antenna |108 mm |

|Flare angle |150 degree |

|Length Flare Angle |8 mm |

|Side Angle |10 degree |

|Length Side Angle |40 mm |

|Length Round Corner |6 mm |

|Gap Distance |8 mm |

[pic]

Fig. 7. Long Shape Bowtie Antenna

. Based on the antenna surface area owned, long sahape bowtie antenna has a surface area greater than the bowtie antenna. Bowtie antenna has a surface area of 2438.88 mm2 and long shape bowtie antenna has a surface area of 3429.08 mm2. However, with a larger surface obtained two frequencies on long shape bowtie antenna. It is necessary in this study to be used in hyperthermia therapy alata. In Fig. 8 it can be seen the simulation results for the second antenna frequency characteristics. From the simulation results it can be seen long shape bowtie antenna has two adjustments are in resonance while the bowtie antenna has only one resonance frequency.

[pic]Fig. 8. Simulation Results Return Loss |S11| Vs. Frequency

[Bowtie and Long Shape Bowtie Antenna]

Table 3. Simulation Result Return Loss in 915 MHz and 2450 Mhz

(Bowtie antenna and long shape bowtie antenna)

|Antenna |Return Loss [dB] |

| |915 MHz |2450 MHz |

|Bowtie |-10.6595 |-2.4024 |

|Long Bowtie |-16.6295 |-18.2697 |

Return loss characteristics of the antenna can be used to look at the performance of the antenna. The smaller the value of the return loss the better owned power antenna radiation produced. High return loss can also cause heat generated from power loss. It is very harmful because hyperthermia tool used very close to the patient's body. In table 3 it can be seen retun value loss of the second antenna at a frequency of 915 MHz and 2450 MHz. simulation results show the value of the return loss of long shape bowtie antenna is smaller than -10 dB for both frequencies. -10 dB threshold value is used to indicate 90% power radiated by the antenna.

[pic]

Fig. 9. Simulation Results VSWR

[Bowtie and Long Shape Bowtie Antenna]

Another characteristic to look at the performance of the antenna is VSWR. In Fig. 9 can be seen VSWR characteristics of the frequency to the second antenna. The simulation results show the VSWR of the long shape bowtie antenna better than bowtie antenna. There is little shift in the lowest resonance frequency of long shape with a bowtie antenna bowtie antenna. In Table 4 it can be seen both antenna VSWR values ​​at a frequency of 915 MHz and 2450 MHz.

Table 4. Simulation Result VSWR in 915 MHz and 2450 Mhz

(Bowtie antenna and long shape bowtie antenna)

|Antenna |VSWR |

| |915 MHz |2450 MHz |

|Bowtie |1.8293 |7.2770 |

|Long Bowtie |1.3458 |1.2780 |

[pic]

Fig. 10. Simulation Magnitude Impedance

[Bowtie and Long Shape Bowtie]

The simulation results show the long shape bow tie antenna has an impedance values ​​are close to the line impedance is 50 ohms used. In Fig. 8 it can be seen the simulation results magnitude impedance for both the antenna. Compatibility with the antenna impedance transmission line affects the amount of radiation generated power antenna. The closer to the line impedance of the antenna, the greater the power generated antenna radiation. This is commonly referred to as impedance matching. In Table 5 it can be seen the value of both the antenna impedance at the frequency of 915 MHz and 2450 MHz.

Table 5. Simulation Result Magnitude Impedance in 915 MHz and 2450 Mhz

(Bowtie antenna and long shape bowtie antenna)

|Antenna |Mag. Impedance [Ω] |

| |915 MHz |2450 MHz |

|Bowtie |57.0423 |339.3099 |

|Long Bowtie |47.4868 |51.3574 |

Conclusion

The long shape bowtie hyperthermia antenna was discussed for dual frequency at 915 MHz and 2450 MHz. return loss of antenna at 915 MHz is -16.6295 and at 2450 MHz is -18.2697. Antenna using flare angle of 150 degrees and side angle of 10 degrees. Simulation results show the antenna better than bowtie antenna at the dual frequency for VSWR and magnitude impedance. VSWR antenna at 915 MHz is 1.3458 and at 2450 MHz is 1.2780 MHz, for magnitude impedance antenna at 915 MHz is 47.4868 ohm and at 2450 MHz is 51.3574 ohm. In the further, antenna measurements were taken using a network analyzer.

References

1] P. Wust, B. Hildebrandt, Sreenivasa G., B. Rau, J. Gellermann, H. Riess, R. Felix, P. M. Schlag, “Hyperthermia in combined treatment of cancer,” The Lancet Oncology,3(8), pp. 487–497, 2002.

2] M. H. Falk, R. D. Issels, “Hyperthermia in oncology,” International Journal of Hyperthermia, 17(1), pp. 1–18, 2001.

3] Vrba, J., Oppl, L.. “Prospective Applications of Microwaves in Medicine”. Microwave Techniques. COMITE 2008. 2008 , pp: 1 – 4

4] Du Yong-Xing, Xi Xiao-li and Guo Wei, “The Design and Simulation of Two-Armed Spiral Antenna for Microwave Hyperthermia”, 5th International Conference on Bioinformatics and Biomedical Engineering, (iCBBE), pp. 1-4, May 2011

5] K.Y. Yazdandoost, K. Sato, “Long Rectangular Microstrip Antenna for Interstitial Microwave Hyperthermia”, 32nd European Microwave Conference, pp. 1-4, Sept 2002.

6] M. Converse, Bond, J. Essex, B.D. Veen, S.C. Hagness, “A computational study of ultra-wideband versus narrowband microwave hyperthermia for breast cancer treatment” IEEE Transactions on Microwave Theory and Techniques, Vol. 54 , Issue: 5, pp. 2169-2180, May 2006

7] O. Isik, E. Korkmaz, S. Kara, M.A. Nassor, B. Turetken, “Development of a hyperthermia applicator with compact microstrip antennas”, IEEE Antennas and Propagation Society International Symposium (APSURSI), pp. 1-2, July 2012

8] Du Yong-Xing, Qin Ling, Xi Xiao-li, “The Analysis and Simulation of Microstrip Spiral Antenna for Microwave Hyperthermia”, 3rd International Conference on Bioinformatics and Biomedical Engineering, ICBBE, pp. 1-4, June 2009.

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