| The development of the Internet of Things(IoT,the Internet of Things)has further promoted the rapid development of radio frequency identification technology(RFID,Radio Frequency Identification Technology).The application of RFID technology has spread all over of our lives.Because RFID tags have many advantages,such as long reading distance,non-line of sight reading,automatic identification and tracking,etc.However,RFID tags still cannot be widely accepted in the field of low-priced goods that require trillions of tags,because of the constraints of tag costs.The drawback hinders the further development of the IoT.The cost of the tag mainly depends on the cost of the tag chip,and it is impossible to reduce the cost of the tag by considering the material and process of the chip.It has been an urgent need to solve the problem of reducing the tag cost.Some researchers proposed the concept of chipless tag to reduce the cost of chipped tag.The chipless tag has two major categories:the time domain based and the frequency domain based.The time domain based chipless tag falls into two types,i.e.,surface acoustic wave(SAW,Surface Acoustic Wave)and delayed transmission line.The first one uses pulse modulation coding with the capacity of 256 bits,but the cost of SAW itself is close to the chipped tag and requires the submicron etching process.The cost of the second one is close to the barcode,but the coding capacity is too low to be applied to practical projects.The frequency domain based chipless tag can be encoded by the position of the resonant frequency,which has wide bandwidth and high coding capacity.At present,the studies of the frequency domain based chipless tag mainly focus on developing chipless tag structures and printable chipless tags that can replace bar codes.Some work about the frequency domain based chipless tag have been studied in this paper.Firstly,starting from the resonant characteristics of various resonators,the structure and coding mode of resonators are discussed,and the working types of chipless tags are especially studied.Two kinds of retransmitted chipless tags based on frequency domain work are proposed,which are L-shaped microstrip coupled resonator chipless tag and complementary split ring resonator(CSRR,Complementary Split Ring Resonator)coupling microstrip line chipless tag.Two kinds of self-resonant chipless tags based on frequency domain are also proposed,which are multi I-shaped slot resonator chipless tag and rectangular slot ring resonator embedding chipless tag respcetively.The main work are as follows:1.Using the coupling theory,a high-Q L-shaped microstrip band-rejection resonator and a high-Q CSRR band-rejection resonator are used as the chipless tag resonating units.They are respectively coupled with the main transmission microstrip line to form two kinds of the retransmission chipless tags.The high-Q band-rejection resonators will change the ultra wideband(UWB,Ultra Wideband)uniform spectrum on the main transmission line.The coding information in resonant circuits will form the ultra-wideband spectral features.The coding capacity is increased by hybrid coding with frequency position and amplitude modulation.In order to reduce the area of the tag,the L-shaped microstrip coupling resonator chipless tag is deformed into an L-shape open-stub line,so the tag area is reduced by 61.7%.Then,some typical L-shaped chipless tag are produced and tested with a communication distance of 10 cm,a coding density of 1.67bits/cm~2 and a coding capacity of 3.56 bits/GHz.Another retransmitted chipless tag is designed by using the high-Q CSRR resonator,and a stepped microstrip UWB antenna with slots on microstrip patch on both sides is designed as transceiving antenna for this tag to reduce the area of chipless tag.Finally,the CSRR chipless tag is tested with a communication distance of 30 cm,a coding density of 0.63 bits/cm~2 and a coding capacity of 5.5 bits/GHz.2.A chipless tag based on an I-shaped slot resonator is proposed.The coding information of the I-shaped slot resonators is loaded into the radar cross section(RCS,Radar Cross Section)spectrum feature which is backscattered to the reader.The L-shaped microstrip band-rejection resonators and the CSRR band-rejection resonators constituted the chipless tag have the second-harmonic interference of the lowest resonant frequency,which limits the frequency-domain coding range.The retransmission chipless tag requires two transceiving orthogonal UWB antennas,so the area of chipless tag is increased.In addition,the UWB transceiving orthogonal antennas of tag must be aligned with the transceiving orthogonal antennas of the reader.For these unfavorable factors,a chipless tag based on the self-resonant I-shaped slot is proposed,which removes the two orthogonal UWB antennas to reduce the area of the tag.The I-shaped slot resonator has no second harmonic,which increases codeable frequency bandwidth.Finally,the 4-bit and 12-bit tags are produced for testing and the test results are good agree with the simulation results.The coding density reaches 1.58 bits/cm~2,and the coding capacity is 3bits/GHz.The reader uses a high-gain horn antenna and the communication distance reaches 20cm.3.The multi-rectangular slot ring embedded chipless tag is proposed and studied.Although the I-shaped slot resonator increases the bandwidth of the available code,it is also interfered by the third harmonic,and the incident direction of the electric field must be perpendicular to the I-shaped slot.These problems are well solved by the embedded rectangular slot ring.We proposed a chipless tag based on a rectangular slot ring resonator without second,third,or fourth harmonics,and further expands the bandwidth available for encoding.Where the deviation from the normal direction is not more than 30 degree,the direction of the excited electric field of the incident wave is not limited.Moreover,the area of the chipless tag is reduced by using the rectangular slot ring embedded method.The area of the 12-bit coded chipless tag is only 35 mm×35 mm.The code density is 0.98 bits/cm~2 and the code capacity is 1.9 bits/GHz.High-gain horn antenna is used for testing,and the communication distance reaches 50 cm. |
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