The Design of Micro-antenna and Broadband Antenna on Biomedical and Homecare Application

• Main Authors: Bo-MingJeng, 鄭博銘
• Other Authors: Ching-Hsing Luo
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/63277325867131491223

博士 === 國立成功大學 === 電機工程學系碩博士班 === 101 === Implementing wireless biotelemetry systems in home care has received widespread attention recently. The purpose of this technology is to enable patients with chronic diseases to receive home care or care close to home. In particular, numerous recent studies have examined integrating contact lenses and wireless biotelemetry systems. This application offers long-term monitoring and control advantages for patients with chronic eye disease. However, previous studies have indicated that a narrow bandwidth is a disadvantage; the device is easily affected by the eye environment because antennas embedded in the contact lenses are loop antennas and the resonant wavelengths of traditional loop antennas are full wavelengths. Therefore, zero current points might occur on the surface of the lenses and the device covers only one frequency. Consequently, the number of antennas necessary for the system equals the number of frequencies in dual or multi-frequency operations. However, because contact lenses have limited space, antenna design is difficult and the number of usable frequencies is constrained, thereby restricting system development. The primary purpose of this study was to propose an innovative broadband open-loop micro-antenna that allows multi-band operations within contact lenses, and to integrate homecare environments and wireless biomedical telemetry systems. A handheld device (i.e., digital tablet) was adopted to receive physiological signals transmitted by contact lenses. One antenna was a Digital Video Broadcasting – Terrestrial (DVB-T) antenna that received wireless TV signals, thereby allowing the handheld device to function as an entertainment platform. The other antenna was an ultra-wideband (UWB) antenna that could transmit a substantial amount of physiological signals or other health care information to family members, care centers, or medical centers. Broadband open-loop micro-antenna embedded in contact lenses combined with DBV-T antenna and UWB antenna could facilitate the development of biomedical and home care systems. To address the discussed deficiency of traditional loop antenna, this study proposed an 11-μm-thick innovative broadband open-loop antenna with a 5-mm radius. The proposed antenna was produced using microelectromechanical systems (MEMS) and gold (Au) on polydimethysiloxane (PDMS) medium, and was subsequently embedded into contact lenses. The key of the proposed design was breaking the circuit at the zero current point of a traditional loop antenna, thereby reducing the resonant wavelength to only a quarter. This not only moved the first resonant mode toward lower frequencies, but it also formed a broadband by combining with the second and third resonant modes. To further investigate the influences of ocular environments on the broadband open-loop micro-antenna, pig eyes were adopted as an alternative for human eyes for simulation and practical measurement. A traditional UWB antenna has a large coverage frequency band, which is likely to interfere with any proximal systems operating at an identical frequency. To address this deficiency and to avoid interfering with the frequency bands required by the wireless ocular physiological monitoring system, the UWB antenna must be equipped with band notch characteristic. In this study, the design of UWB antennas with band notch characteristic adopted quarter-wave metal plates and short-circuited antennas to induce mutually cancelling reverse currents between the two materials. In addition, the anti-interference ability of the system can be further increased if the antennas are attached to ground slots to act as a dual-band notch characteristic. Commercial DVB-T antennas on the market are over-sized for operating at low frequencies. Therefore, this study embedded DVB-T antennas into handheld devices. Combining the proposed open-loop technique with a foldable monopole antenna, the new antenna can be fully integrated into a handheld device that is 160 mm 70 mm. The proposed innovative broadband open-loop micro-antenna covers the 1.7–9.7 GHz frequency band (140%, return loss 10 dB), and possesses lower resonant frequencies without having to increase the size of the antenna size. Moreover, the antenna gain can be increased to -15 dBi. The radiation pattern of this antenna shows directivity, which could reduce the amount of radiation absorbed by human eyes. In this study, pig eyes substituted for human eyes for measurement. The permittivity of the pig eye tissues was compared to that of human eyes reported by the literature. The measurement results indicated that pig eyes had a permittivity similar to that of human eyes. Additionally, the experiment results in a real-world environment showed that the broadband open-loop micro-antenna displayed satisfactory radiation characteristics within the coverage frequency range, and effectively reduced frequency drift that was caused by specific environmental factors. The proposed UWB antenna within the handheld device, which was responsible for data transmissions, covered a maximum frequency band of 2.5–16.8 GHz (220%, VSWR ≦ 2). This frequency band exhibited omnidirectional radiation patterns that did not interfere with the 2.4 and 5.8 GHz frequency bands (VSWR ≧ 6) used by the wireless dual-band ocular physiological monitoring system. The proposed embedded DVB-T antenna not only accommodates the limited size of handheld devices, but it also covers the operating frequency of digital TV (470–860 MHz). The gain measured approximately 2.8 dBi, and the antenna radiation efficiency reached 87%. The innovative broadband open-loop micro-antenna proposed in this study can be embedded in contact lenses for operations at multiple frequencies. This antenna simultaneously meets numerous needs, such as wireless powering and physiological data transmissions. After the physiological signals have been transmitted for analysis from the embedded broadband open-loop micro-antenna to the handheld device, users can send the analyzed data via the UWB antenna to hospitals or care centers for health management. Furthermore, the proposed embeddable DVB-T antenna can be integrated with data analysis and management systems, thereby functioning as a mobile multimedia platform enabling biomedical health care. Experiments conducted in this study verified that the proposed three antennas exhibited satisfactory radiation characteristics. These antennas can be integrated with system circuits to implement ocular physiological monitoring systems and home care networks, and contribute to improving the ease of medical care provided in the patient’s home.