tailieunhanh - Radio Frequency Identification Fundamentals and Applications, Design Methods and Solutions Part 8

Tham khảo tài liệu 'radio frequency identification fundamentals and applications, design methods and solutions part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | RFID Tag Antennas Mountable on Metallic Platforms 167 n X E1 - E2 0 2-1 n D1 - d2 0 2-2 n X H1 - H Js 2-3 n B1 - b2 0 2-4 where n is the unit normal vector to the boundary directed from medium 2 to medium 1 E is the electric field intensity V m D is the electric flux density C m2 H is the magnetic field intensity A m B is the magnetic flux density W m2 ps is the surface charge density C m Js is the surface current density A m2 By using above boundary conditions we can also find the electromagnetic boundary conditions for the cases of PEC Perfect Electric Conductor . Boundary conditions at the PEC interface Fig. Boundary conditions at the interface of PEC If medium 2 is a PEC with infinite conductivity all field components must be zero inside of the PEC. Then we can express the boundary conditions at the interface as follows n X E1 0 or Eit 0 2-5 n D1 Ps or D1n Ps 2-6 n X Hi Js or Hit Js 2-7 n B1 0 or Bin 0 2-8 It is noticed that there are no tangential components of the electric field on a PEC boundary and there are only normal components of the electric field for oscillation. On the other hand there are no normal components of the magnetic field on a PEC boundary. There are only tangential components of the magnetic field. In addition normal incident waves are totally reflected from the interface because the skin depth of the PEC is zero. Therefore the amplitude of incident wave and reflected wave are the same but their phases are 1800 168 Radio Frequency Identification Fundamentals and Applications Design Methods and Solutions different. In other words while the total of the incident and reflected electric fields at the PEC boundary will be zero the total magnetic field tangential component will be doubled at the PEC boundary surface. 3. Effects of metallic platforms on RFID tag antenna Since RFID systems frequently apply near the metallic environment the effect of metallic platforms should be considered in designing the tag antenna. As mentioned in the .