Surface-acoustic wave radio frequency identification system- design for tags

• Main Authors: Chung-Hau Huang, 黃重浩
• Other Authors: Watson Kuo
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/qfrkx9

碩士 === 國立中興大學 === 物理學系所 === 101 === Radio frequency identification (RFID) system is to use wireless communication to transfer data from a tag for identification and tracking. Unlike conventional IC tags, surface acoustic wave(SAW) tags can be applied as fully passive tags in a RFID system. Here we report a work on SAW RFID tags focus on the 2.45GHz communication frequency. The electromagnetic waves were received and transmitted via panel antenna array, fabricated on ceramics/glass composite circuit board. The radiation pattern of a panel antenna is directive, appropriate for point-to-point transmission. SAW tags were made on 128°Y-X cut lithium niobate (LiNbO3) substrate, which is a well-known piezoelectric material. The incident electromagnetic waves, received by the antenna were transduced to Rayleigh waves on the substrate surface. As propagating on the surface, these Rayleigh waves may be reflected by reflectors. We applied pulse position coding scheme for identification: by tracing the time delay from the reflectors, one can identify the tag. Here we reported two methods to measure our tags. One is the time domain results converted from frequency domain data by inverse Fourier transform. The other is time domain directed measured by homodyne method. The panel antenna array has a frequency of 2.4GHz, a return loss of -27dB, and a gain of 11 dBi. The SAW chip has a frequency of 2.51GHz, a return loss of -15dB. With a metallization of 25%, the reflectors have transmittance of 0.76 and reflectance of 0.24. All reflection pluses could be discerned for a tag coded by 1001110101 both by inverse Fourier transform method and by homodyne method.