Research On Biological Effects Of Terahertz Radiation

In recent years, Bio-electromagnetics is an interdisciplinary of electro-magneticfield theory and biomedical science, gradually emerging in recent years. It mainlyfocuses on the research of life organization associated with electric, magnetic andelectromagnetic effect. It can be applied to medical detection, diagnosis and treatment.With the gradual in-depth study on the electromagnetic spectrum as well as thecontinuous development of high technology, THz radiation has gradually become one ofscientists’ research focuses. THz wave possesses unique advantages. It is non-ionizingand has low photon energy, so it does not cause harmful photoionization in biologicaltissues. Moreover, THz wave presents a strong absorbent to polar molecules (especiallywater molecule). Therefore, the research of characteristics of biological tissue underTHz region has a great research significance and broad application prospect, especiallyTerahertz Pulse Imaging (TPI) technology’s great application potential innon-destructive diagnosis of cancerous tissue.Based on the above application background, the research in this paper mainlycontains two parts: the first part is the design of THz antenna with high gainperformance based on meta-material; the second part is the research of THz wave effecton biological tissues.In the first part of research, this paper presents to add meta-material, an artificialnegative refractive index material, into the THz antenna’s substrate. At a certainfrequency, the meta-material structure’s refractive index can be0, which leads tovertical refraction. Taking advantage of this characteristic can gather theelectromagnetic waves radiated from antenna, so as to realize high directivity and highgain performance. Based on the above idea, after the brief introduction ofmeta-material’s theoretical foundation, firstly we designed a typical square SRRresonant ring structure and its several transformational structures in this paper, andanalyzed the effects of their structural characteristics on the negative refractive. Then,these meta-materials’ structures are respectively embedded into the designed THzantenna’s substrate and made simulations. Simulation results show that, withcomparison to the reference THz antenna with no meta-material, the new antennas’ withmeta-material structures’ gains are greatly increased and their side-lobe levels areobviously decreased. Finally, this paper also gives the theoretical explanation of whymeta-materals can improve antenna’s gain performance.The second part of this paper is to research the biological tissues’ characteristicsunder THz region. Firstly, this paper introduces the Finite Difference Time DomainMethod (FDTD), which is the most widely used electromagnetic field numericalcalculation method in bio-electromagnetics, and briefly summarizes the basic knowledge of bio-electromagnetic. In the study of THz effect on biological tissues, weuse double Debye model theory to analyze the variation rules of dispersive media’sdielectric constant with frequency under THz range and deduce its correspondingexpressions in FDTD method. Considering the double Debye model’s practicalapplications, we study the refractive index and absorption coefficient, two parameters oftransmission characteristics of three kinds of polar materials: water, methanol and skin.Similarly, the transmission characteristic of human’s healthy skin and BCC cancer tissue.The significant difference in refractive index and absorption coefficient between the twotissues provides sufficient support for the TPI technology’s application in cancerdetection of biomedical field. What’s more, take human’s healthy skin as an example,we further discuss the dependence of double Debye model’s parameters on the media’srefractive index and absorption coefficient, helping us understand how these parametersinfluence THz wave’s propagation. In the last, a simple skin model with BCC embeddedis modeled and the SAR is calculated. According to the planar distribution and verticaldistribution, we can observe an obvious boundary between the healthy skin and BCC,which implys the great possibilitiy of applying THz in cancer diagnosis.