| Summary: | 碩士 === 南台科技大學 === 電機工程系 === 101 === In recent years, wireless products have been widely used in our lives. Automatic Meter Reading (AMR) system, which is the main topic discussed in this thesis, is an important wireless application. AMR system uses wireless transmission technique to reduce manpower in meter-reading and monitor the user's water consumption by software. In many developed countries, water meter box and its lid are made of plastic or concrete, which has less interference for developing wireless meter reading. The results make the AMR more applicable. In Taiwan, on the other hand, townhouse users place water meters inside a iron box located on the front door. Mansion or apartment users install water meters on the top floor with stainless steel cover to protect them. The commercially available antennas used for AMR will be interfered and seriously reduced radiation efficiency by the metal lid. Therefore, the main topic of this thesis is to design antennas for applying in iron water meter box and wireless meter reading system.
This thesis will design two different antennas for wireless meter reading system and using the frequency band in ZigBee 2.4 GHz. The ZigBee system is placed in a plastic box with size 73 × 45 × 24 mm3 and installed on the water meter by an aluminum ring-shaped frame. The two antennas are designed with directivity for radiating toward the water meter lid, which has advantage of longer reception distance. The design of antenna type 1 is adopted Moxon antenna with size 34.4 × 23 × 1.6 mm3, which matches the ZigBee module size of 43 × 33 × 1 mm3. The substrate material of the antenna is fiberglass board (FR4) with permittivity of r = 4.4. To test the system’s functions, antenna type 1, ZigBee module, and Alkaline -battery are integrated into a plastic box, which is inside the iron meter box and next to the water meter. The design of antenna type 2 is slot antenna, which will use the iron lid as part of the antenna. The design concept is to truncate a slot on the iron lid and place the slot antenna beneath the iron lid. The slot antenna has a dimensions of 160 × 156 × 0.4 mm3 and uses fiberglass board (FR4) with permittivity of r = 4.4 as the substrate material. ZigBee module and Alkaline -battery are placed into plastic box and installed next to the water meter. Because the iron lid is too thick to manufacture, this thesis uses FR4 board and copper plate to replace the iron lid.
Owing to environmental effects of water meter iron box, the resonant frequency of antenna type 1 is shifted out of the application band in 2.4 GHz. At the same time, the antenna impedance in meter box is changed steeply. Therefore, the antenna figure is sharpened in order to slow down its change. After proper tuning the antenna’s impedance matching, the resonance reallocates to 2.4 GHz for antenna type 1 placing inside the water meter box. The measured results of S11 and gain obtained in the air are -24 dB and 5.4 dBi, respectively. In addition, the measured S11, which is obtained inside the iron meter box and covered with iron lid, is -16 dB. In experimental measurement, antenna type 1 together with ZigBee system reaches the transmission distance of 45 meter in the air and that of 8 meter inside the iron meter box. To increase the impedance bandwidth of antenna type 2 (Slot antenna), bowtie-shaped structure is adopted in the upper board and end of slot. In addition, the antenna type 2 proposes two different materials for upper boar. As FR4 substrate is used in the upper board, the measured S11 and gain obtained in the air are -24 dB and 8.1 dBi, respectively. As upper board substrate is changed to copper plate, the measured S11 at 2.38 and 2.48 GHz are -12 and -14 dB, respectively. Furthermore, the measured gain is 7.3 dBi. The results verify that antenna type 2 with two kinds of materials of upper board can be applied in ZigBee 2.4 GHz. In experimental measurement, antenna type 2 together with ZigBee system reaches the transmission distance of 60 meter in the air and that of 11 meter inside the iron meter box.
Finally, the ZigBee system proposed in this thesis is set up in an open environment with various kinds of interferences to access a meter-reading. The measured results confirmed that the proposed antennas (type 1 and type 2) perform good functionality and correctly read the data transmitted from the water meter inside a iron box.
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