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Note for Advanced Digital Signal Processing - ADSP by Sanaullah Khan

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Defence Science Journal, Vol. 68, No. 6, November 2018, pp. 566-571, DOI : 10.14429/dsj.68.12669  2018, DESIDOC Internet of Things Controlled Reconfigurable Antenna for RF Harvesting V. Arun* and L.R. Karl Marx# Department of Electronics and Communication Engineering, Anna University Regional Campus, Madurai - 625 019, India Department of Electronics and Communication Engineering, Thiagarajar College of Engineering, Madurai - 625 019, India * E-mail: arunece@autmdu.ac.in * # ABSTRACT Internet of Things (IoT) controlled a reconfigurable antenna with PIN diode switch for modern wireless communication is designed and implemented. Direct contact of biasing network with the antenna is eliminated and the switching unit is manipulated through IoT method. The proposed antenna has ring structures, in which the outer ring connects the inner ring structure through a PIN diode switch. The dimension of the proposed antenna is reported as 50 mm × 50 mm and its prototype has been made-up on epoxy-Fr4 substrate with 1.6 mm thickness. This antenna setup is made to reconfigurable in four bands (4.5 GHz, 3.5 GHz, 2.4 GHz, and 1.8 GHz) through switching provided by IoT device (NodeMCU). The antenna has a good return loss greater than -10dB.In switching state 2 the antenna has a return loss of -30 dB peak is attained at 3.4 GHz of operating frequency. Similarly the gain response of antenna is good in its operating bands of all switching states and obtained a maximum gain of 2.7 dB in 3.5 GHz. Bidirectional radiation pattern is obtained in all switching states of the antenna. Keywords: Reconfigurable antenna; Internet of Things antenna; PIN diode switching antenna; Frequency reconfiguration; RF Harvesting Nomenclature Area of the ring structure Antenna frequency FR4substrate thickness Relative permittivity Resonant frequency a F h ε r fr 1. INTRODUCTION Modern communication devices are supported by more than one service and are extensively must for today’s communication1. Reconfigurable antenna is a perfect entrant to meet such demand in today’s communication. Reconfigurable antennas are categories based on: Polarisation reconfigurable2, pattern reconfigurable3, and frequency reconfigurable4. This reconfigurability is achieved by altering the physical structure of the antenna that is by connecting or disconnecting the radiating elements of antenna structure5. Various switching techniques are employed for reconfiguration that are provided by devices such as PIN diode, varactor diode, MEMS switched and photoconductive switches6. Reconfigurable antenna design with PIN diode and varactor diode requires external cable connection to provide DC bias to the lumped elements7. Though the MEMS switches provides high isolation between the lumped elements and DC biasing circuitry, the switching speed is very low compared to other switching mechanism8. Micro-controller switching mechanism makes more time efficient without any human hindrance. The reconfigurability Received : 05 February 2018, Revised : 06 September 2018 Accepted : 10 October 2018, Online published : 31 October 2018 566 of the Antenna can be controlled by programming the microcontroller9. The RF Energy harvesting using the reconfigurable antenna is an uptrend research area. In addition to that energy harvesting this micro controller programmed antenna can auto fit to the remote location for the RF Energy harvesting persistence5,10. Dual tone RF harvesting antenna is discussed; it harvests in GSM and UMTSb and. But it’s bulky in size due to Yagi antenna array11. In these existing techniques the controlling of antenna and switching should done with a manual connectivity to micro-controller. The IoT controlled Reconfigurable antenna eliminates the human assistance and function the antenna switching. This paper presents the NodeMCU (ESP8266) as a device to achieve the IoT controlled reconfigurable antenna. Also it is employed as a switching element in the PIN Diode. 2. DESIGN PROCEDURE OF RING ANTENNA The basic shapes of microstrip patch antennas are found to be rectangular15, triangular and circular. Among these circular/ annular ring shape antenna is analysed and found to be simple and better with respect to multiband frequency operation and in placement of feed point16. The Antenna has simple monopole ring structure that is fed by microstrip feed line technique with length of 11 mm and width 4 mm. It consists of three layers: The upper radiation patch, the inner substrate that is made up of epoxy-FR4 material of thickness 1.6 mm and the bottom ground plane. The upper and bottom layer of antenna is made up of copper material of thickness 0.04 mm. The inner and outer diameter of the first ring is 34 mm and 38 mm and the

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Arun & Marx : Internet of Things Controlled Reconfigurable Antenna for RF Harvesting second ring is 22 mm and 26 mm, respectively. Both the rings are connected in the upper side with a square patch of 4 mm × 4 mm. The antenna ground is taken to be 50 mm × 50 mm to allow radiation above and below the substrate is described in the Table 1. Table 1. Details of length and width of the antenna Ring antenna (Parameters) Dimension (mm) Patch length 50 Patch width 50 Outer ring diameter 38 Inner ring diameter 26 Centre patch diameter 10 Feed length 11 Feed width 4 Ground plane length 50 Ground plane width 50 FR4 Substrate thickness 1.6 The prototype model testing is made with Vector Network Analyser (VNA) of 0 - 18 GHz. The equivalent circuit of the ring antenna will consist of lumped values of ground, PIN diode and radiating element of ring patch structure. This combined element of ring shaped antenna consists of parallel and series combination of RLC elements. At ON state of this antenna’s reconfigurable switching process the capacitance of respective PIN diodes (D1, D2) are getting cancelled. 3. IoT SWITCHING Switching for this antenna is provided by PIN Diode which is controlled by NodeMCU unit as like the micro-controller switching device3. The block diagram for IoT based switching of Ring Antenna with the help of PIN Diode switches is shown in the Fig. 3. The NodeMCU switches the Diodes D1 and D2 as per the software programmed in it. The Biasing voltage from the NodeMCU can switch on and off the D1 and D2 PIN diodes. Based on the diode switching of The antenna is designed with the help of circular patch antenna dimension equation as follows12. a= F= F 1  2h   Π F    2 ln  1 +  + 1.7726   Πε F   2h     r  8.791*109 f r ε (1) (2) r where a is area of the ring structure and F is antenna frequency. The substrate FR4 thickness and relative permitivity is denoted as h and ε correspondingly. After r including the fringing effect of the circular patch antenna, the effective radius (ae) of the patch antenna is derived from the Eqn. (3) as follows, 1    2 2h   Π a  a = 1 + ln   + 1.7726   e Πε a   2h     r (3) With the assistance of Eqn. (3) the resonant frequency (fr) of the antenna is derived as per the Eqn. (4) 1.8412ν 0 (4) = f r 110 2Πa ε e r ( ) (b) (a) Figure 1. Antenna layout: (a) Top view and (b) Bottom view (all dimensions are in mm). (a) (b) Figure 2. Prototype design of ring antenna with PIN diodes D1 and D2 (a) Front view (b) Back view. The outer ring patch is connected to the inner ring patch with PIN diode D1 and the inner ring is in contact with the center circular patch with PIN Diode D2. Here in this proposed work SOD323 PIN diodes are used, which provides switching to the reconfigurable antenna. The antenna is simulated using HFSS simulator tool and the switching is provided using Lumped RLC boundary. The detail layout structure of antenna is as shown in the Fig. 1. Figure 3. Block diagram of IoT based reconfigurable ring antenna. 567

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Def. SCI. J., Vol. 68, No. 6, november 2018 ON and OFF, the flow of RF signal through the Ring Antenna is varied and the different band of operating frequencies can be achieved. The NodeMCU unit itself consists of WiFi based connectivity with the Internet. This combined reconfigurable antenna and NodeMCU unit control, change of program and monitor through World Wide Web. The prototype model of PIN diode embedded Reconfigurable Ring shaped antenna is connected with the IoT device (NodeMCU) is as shown in above Fig. 4. Frequency (GHz) (a) Figure 4. IoT device connected with the ring antenna. 4. RESULTS AND DISCUSSION The proposed IoT-based reconfigurable antenna is designed and validated using HFSS software. In the experimental measurement PIN diodes used as a switching element and the Prototype antenna results are obtained with VNA. When the D1 and D2 is in off state the antenna operates in the frequency band of 2 GHz to 5 GHz and suitably providing peak response (fp) in 4.5 GHz frequency range, this is considered as a state ‘0’ of the antenna and the results are as shown in the Fig. 5(a). In the state ‘1’, the D1 is in on condition while the D2 is remains off condition, and the obtained frequency range of 2 GHz to 3.7 GHz and concentrates on 3.5 GHz band is as shown in Fig. 5(b). As shown in the Fig. 6(a) the return loss results for stage 3, where the diodes D1 and D2 is in OFF and ON conditions respectively. Here in this state the operating frequency ranges from 1.8 GHz to 3.4 GHz, and it focuses the 2.4 GHz Band. In state 4 both the diodes are in ON condition and the results as shown in Fig. 6(b). In this state the frequency ranges from 1 GHz to 3.7 GHz and it concentrates on the 1.8 GHz band. There is a discrepancy between simulated and measurement results due to switch installation and measuring environment. The comparison table for the four switching states diode’s condition, its working/ resonant frequency range and bandwidth for the appropriate states of the antenna is as given in Table 2. The radiation pattern in E-plane (i.e. X-Z plane represented in brown colour) and the radiation pattern in H-plane (i.e. Y-Z plane represented in red colour) at 2.4 GHz in OFF state and 3.2 GHz and 4.5 GHz in ON state is revealed in the Figs. 7(a), 7(b) and 7(c). The radiation pattern remains same for all the 568 Frequency (GHz) (b) Figure 5. Measured and simulated return loss: (a) state 1 and (b) state 2. Frequency (GHz) (a) Frequency (GHz) (b) Figure 6. Measured and simulated return loss: (a) state 3 and (b) state 4.

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Arun & Marx : Internet of Things Controlled Reconfigurable Antenna for RF Harvesting (a) (c) (b) Figure 7. Radiation pattern: (a) state 1, (b) state 3, and (c) state 4. Table 2. Comparison of Four switching states 0, 0 (state 1) OFF OFF 2-5 (fp = 4.5) 3 0, 1 (state 2) OFF ON 2 - 3.7 (fp = 3.5) 1.7 1, 0 (state 3) ON OFF 1.8 - 3.4 (fp = 2.4) 1.6 1, 1 (state 4) ON ON 1 - 3.7 (fp = 1.8) 2.7 gain (dB) Antenna PIN Diode Working/ resonant Bandwidth switching states D1 frequency (GHz) (GHz) D2 reconfigured frequencies and bidirectional radiation pattern is obtained in the all switching states of antenna. The following Fig. 8 shows the cumulative gain plot of the proposed antenna’s four switching states. It is inferred that the antenna presents a positive gain in operating frequency bands all the states. In state 1, the maximum gain of 2.5 dB is obtained at the frequency of 4.5 GHz. Similarly, in the state 2 and state 3, a gain of 2.7 dB and 1.9 dB is obtained at 3.5 GHz and 2.4 GHz, respectively. Where, in 4th state a peak gain of 1.6 dB at 1.8 GHz and a moderate gain of 0.7 dB at 3.5 GHz is obtained. The obtained gain values for the four switching states of the antenna are as given in Table 3. Where, the Fig. 9 shows the current distribution in antenna switching from state 1 to state 4. In switching state 3 (D1-ON; D2-OFF), the majority of the current flow is distributed in the lower side of the circular ring patch antenna. In state 4 (D1-ON; D2-ON) the current in concentrated both in the outer and inner ring of the antenna. Table 3. Maximum gain obtained at each switching state Switching states Peak gain State 1 2.5 dB at 4.5 GHz State 2 2.7 dB at 3.5 GHz State 3 1.9 dB at 2.4 GHz State 4 1.6 dB at 1.8 GHz Due to the variation in current distribution different frequency reconfiguration is obtained. Frequency (GHz) Figure 8. Measured gain plot of the antenna. Figure 9. Current distribution :(a) state 1,(b) state 2,(c) state 3, and (d) state 4. 5. RF ENERGY HARVESTING This Novel experimental setup is made as shown in the Fig. 10 (a) to scavenge the various ranges of ambient RF energy and can act as a permanent energy harvesting resource for the low power VLSI devices. Compared to the existing harvesting technologies, this 569

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