EEE12 NANYANG RESEARCH PROGRAMME WATER RECTENNA Dinesh Valavan NUS High School of Mathematics and Shen Zhongxiang Science School of Electrical and Electronic Tan Hui Yang Engineering Dunman High ABSTRACT allowed DRAs to become the center of interest for antenna applications. Liquid dielectrics can Water antennas are a new type of antenna be used to build a DRA due to their high which has attracted increasing attention in permittivity and low loss [2]. recent years. They show potential as promising alternatives to traditional antennas for various Liquid antennas are a type of antenna that applications. This project aims to present a transmits and receives signals using fluids. study into water-based liquid antennas as Water antennas, as a special form of liquid reconfigurable wideband and multiband antennas, have gained considerable attention antennas used in modern communication for a variety of reasons. Firstly, conformability. It systems, aiming at gaining a better is possible to achieve any antenna shape or understanding of water-based liquid antennas design due to the nature of the liquid. Secondly, from the liquids used in the antenna designs. In both physical and chemical reconfigurability [2]. this paper, innovative water antenna designs Changing the height and width of the liquid with different shapes are presented. The stream and its chemical makeup will efficiently achievable performance of water antennas adjust the resonance frequency and bandwidth designed for multiple bandwidths, compactness of the antenna [2]. Thirdly, its low cost. and low profile are illustrated. The results Compared to more expensive liquid metals, demonstrate that water antennas are promising such as mercury, liquid dielectrics are candidates that can be utilized in modern inexpensive and readily available. Fourthly, it is communications systems, or more specifically, transparent and eco-friendly. And lastly, it has a be able to resonate at WiFi frequencies and high permittivity which allows it to make smartphone frequencies. antennas more compact. These factors allow water to be an excellent choice for designing 1. INTRODUCTION reconfigurable antennas. A rectenna is a special type of antenna that can A dielectric resonator antenna (DRA) is transform microwave energy into useful direct an antenna that usually transmits and receives current (DC). Rectennas are used in the signals above 300 MHz. Antennas are transmission of wireless microwave power. The reciprocal, meaning that their transmission, or density of ambient wireless power is growing radiation, capabilities is equivalent to their with the explosive and rapid growth of wireless reception capabilities. Their high radiation technology as there are an increasing number of efficiency, compact size, and good match to electromagnetic power sources, such as cellular most commonly used transmission lines [2] has EEE12 mobile base stations, digital TV towers, and Wi- where TE is transverse electric, TM is Fi routers. In order to replace the battery and transverse magnetic, and Xnp and X’np denote save maintenance costs [1], the notion of using the roots of the Bessel radio frequency (RF) energy to power low-power functions of the first kind and electronic devices has gained immense of the first order derivatives popularity in recent years. Using rectifying respectively [3]. The impact of antenna (rectenna) technologies, wireless the geometrical parameters of energy harvesting is a feasible solution for a cylindrical DRA (radius a converting ambient RF power to usable DC and height h) as well as the power [1]. relative dielectric constant (휀r) and the relative permeability 2. AIM (μr) on the resonant frequency is investigated. Using the The objective of this project is to design an equations, it was found that Figure 1: Model of innovative water antenna that will be able to Cylindrical Water DRA a cylindrical water DRA with receive signals at 1.8 GHz and 2.4 GHz. a radius of 1.05 cm and a height of 2.52 cm were ideal for a resonant frequency of 2.4 GHz, 3. METHODOLOGY when using pure water with a dielectric constant of 78.57 and relative permeability of 0.9999. I. Design of DRA (Dielectric Resonator Antenna) ii) Rectangular DRA Dielectric Resonator Antenna (DRA) of different Fig. 2 shows the three-dimensional view of a dimensions and shape have varying radiation rectangular DRA. An advantage of using performance. Our team decided on 3 main rectangular DRA is that it offers more flexibility in shapes: a) Monopole Cylindrical DRA design; b) design compared to cylindrical DRA due to three Rectangular DRA design; c) Conical Cylindrical independent geometrical dimensions; length, DRA design. The size of the DRA is proportional breadth and height [3]. The dielectric waveguide 휆0 푐 model is used to , with 휆0 = being the free-space √휀푟 푓0 to analyze the wavelength at the resonant frequency f0 and rectangular where εr denotes the relative permittivity of the DRA. The material forming the radiating structure [3]. resonant frequency is i) Monopole Cylindrical DRA calculated by means of the The resonant frequency of the modes supported following by a cylindrical DRA can be calculated using the equations [3]: following equations [3]: 푐 푋 2 (2푚 + 1)휋 2 √ 푛푝 푓푇퐸푛푝푚 = ( ) + ( ) 2휋√휀푟휇푟 푎 2ℎ Figure 2: Model of Rectangular Water DRA 푐 푋′ 2 (2푚 + 1)휋 2 √ 푛푝 푓푇푀푛푝푚 = ( ) + ( ) 2휋√휀푟휇푟 푎 2ℎ EEE12 푐 2 2 2 푓0 = √푘푥 + 푘푦 + 푘푧 2휋√휀푟 휋 푘 = 푥 푎 휋 푘 = 푧 2푏 2 푘 푑 = 푡푎푛ℎ ( 푦0) 푘푦 푘푦 2 2 푘푦0 = √푘푥 + 푘푧 where a, b, and d denote the geometrical dimensions of breath, height and length respectively and 휀r is the relative dielectric constant of the material forming the resonator, Figure 4: Cross-section view of which is 78.57 in the case of pure water. Using Conical Cylindrical Water DRA the equation, the dimensions of the rectangular DRA that works at a resonant frequency of 2.4 GHz were a = 4.51 cm, b = 3.32 cm and d = II. Design of Rectifier 3.76 cm. The rectifier is composed of a voltage doubler iii) Conical Cylindrical DRA and a resistive load, as shown in Fig. 5. A single-stage standard full-wave voltage doubler Figure 3 shows is considered as the best option for RF to DC the three- rectification, considering the simple design and dimensional high performance. It has more potential for view of a conical power processing than a half wave rectifier. cylindrical DRA. Assume that the input AC signal is sinusoidal. The shape of The negative half cycle of the signal is rectified this DRA is by the shunt diode D1 and the energy is retained unique and in C1. The positive half cycle is rectified by the there has not series diode D2 and the energy is retained in C2 been much [1]. During the next period, the energy in C1 is research done removed. At last, the energy from both C1 and about it. Thus, C2 will be discharged to the load resistor R. we decided to Figure 3: Three-dimensional view of Conical Cylindrical Water DRA experiment with the shape to test the feasibility of it in creating wide-band and multi-band water antennas. The height and radius of this DRA is first arbitrarily decided to be 8.00 cm (height), 1.00 cm (lower conical radius) and 0.50 cm (upper conical radius) respectively to allow sufficient depth to achieve our desired resonant frequency. Figure 5: Rectifying Circuit diagram The diodes D1 and D2 we used are BAT54,215 due to its low forward voltage of 800 mV. C1 and EEE12 C2 are electrolytic capacitors with a voltage of lumped port (Port 1) is placed at the waveguide 10 V and a capacitance of 470 microfarads. R1 opening to excite the antenna; h) water medium is a red LED. The whole rectifier is placed on a - pure water as well as saline water with relative Rogers RT/duroid ro3003 substrate with a permittivity of 81.0 is used to observe changes dielectric constant of 3.00 and a thickness of in radiation performance. 0.76 mm, with copper of 1.40 mm thickness on it. The layout of the rectifier is shown in Fig. 6. The simulation produces 2 types of results we want: 1) Graph of reflection coefficient against frequency (S11 graph); 2) Plot of directivity of antenna. The S11 parameter represents how much power is reflected from the antenna, and thus is referred to as the reflection coefficient, or also called return loss. If S11 = 0 dB, then all the power is reflected from the antenna and nothing is radiated. When S11 = -10 dB, if 3 dB of power is delivered to the antenna, -7 dB is the reflected power. The remainder of the power is delivered to the antenna. This accepted power is either radiated or absorbed as loss within the antenna [4]. In short, the lower the value of reflection coefficient, the less power is reflected, and more power is being radiated by the antenna. Only Fig 6: Layout of rectifier. (L1 = 88.00 mm, L2 = 111.30 mm, L3 = 10.00 mm, L4 = 68.00 mm, L5 = 2.50 mm, L6 = 43.20 S11 values at or below -10 dB are capable at mm, L7 = 36.50 mm, L8 = 33.30 mm, L9 = 4.10 mm, L10 = radiating, as anything above -10 dB would mean 6.50 mm, L11 = 1.50 mm, L12 = 8.00 mm, L13 = 4.00 mm, L14 = 31.00 mm, L15 = 1.20 mm, L16 = 12.00 mm) that S11 is close to 0 dB and most of the power is reflected. For the directivity plot, it measures the degree to which the radiation emitted is III. Simulation of DRA Designs concentrated in a single direction.