Wireless power transfer in metal pipes is a promising alternative to tethered exploration robots, with strong potential to enable longer operating times. Here we present experimental results, including rectification efficiency, for a prototype gas pipe inspection robot with wireless power receiver functionality

Doychinov, V

Kaddouh, B

Malik, B

Mills, G

Robertson, ID

Somjit, N

White Rose Research Online

This is an author produced version of Wireless Power Transfer for Gas Pipe Inspection Robots.White Rose Research Online URL for this paper:http://eprints.whiterose.ac.uk/126378/Proceedings Paper:Doychinov, V orcid.org/0000-0001-6730-0057, Kaddouh, B, Mills, G et al. (3 more authors)(Accepted: 2017) Wireless Power Transfer for Gas Pipe Inspection Robots. In: To be confirmed. The UK-RAS Network Conference on Robotics and Autonomous Systems: robots working for and among us, 12 Dec 2017 . (In Press) This is an author produced version of a paper presented at The UK-RAS Network Conference on Robotics and Autonomous Systems: robots working for and among us.promoting access toWhite Rose research paperseprints@whiterose.ac.ukhttp://eprints.whiterose.ac.uk/Wireless Power Transfer forGas Pipe Inspection RobotsViktor Doychinov∗, Bilal Kaddouh∗, George Mills∗, Bilal Malik∗, Nutapong Somjit∗, Ian D Robertson∗∗Robotics at Leeds, University of Leeds, Leeds, United KingdomAbstractWireless power transfer in metal pipes is a promising alternative to tethered exploration robots, withstrong potential to enable longer operating times. Here we present experimental results, including rectificationefficiency, for a prototype gas pipe inspection robot with wireless power receiver functionality.Index TermsWireless Power Transfer, Gas Pipe, Remote Inspection, Autonomous Systems, RoboticsI. INTRODUCTIONThe use of high-power electromagnetic (EM) waves for Wireless Power Transmission (WPT) has beenstudied since the late 19th century [1], with arguably one of the most famous demonstrators being the”Microwave Powered Helicopter” by W. C. Brown [2]. The two main modalities investigated by the researchcommunity are near-field non-radiative power transfer, such as magnetic, inductive, and capacitive coupling;and far-field power transfer through highly directional antennas [3], [4].The near-field methods have successfully been adopted in commercial products for efficient charging ofconsumer electronics. With the increased popularity of Electric Vehicles (EV) concepts have been proposedfor their continuous charging via capacitive coupling systems [5]. The main disadvantage of the near-field method of power transfer is the short maximum operating distance, which is on the order just a fewcentimetres [6]. On the other hand, far-field systems suffer from large propagation losses through atmosphericattenuation and absorption, limiting the amount of power that can be delivered to a receiver [7]. Furthermore,regulations on transmitted power in the Industrial, Scientific, and Medical (ISM) bands further limit thepotential deployments of such systems to low-powered Internet-of-Things sensors [8]–[10].Recently, another mode of WPT has been proposed, and that is WPT in shielded metal pipes, which canpotentially deliver higher power, on the order of several Watts, at distances up to tens of metres [11]. Thisis enabled by considering the pipes as circular waveguides, which support low-loss EM propagation [12].This in turn opens up exciting opportunities for remote powering and charging of pipe inspection robots,eliminating the need for a tethered power connection.In this paper, we present experimental results of WPT to a small robot, designed to fit in and inspect25.4 mm diameter gas pipes. Details of the robot prototype are given, as well as measurements of theelectromagnetic propagation environment within the pipe used for these tests. Finally, a short discussion onthe WPT module performance is included.II. SCENARIO DESCRIPTION AND ROBOT PROTOTYPEA photograph showing the experimental setup is given in Fig. 1a. The pipe used is a decommissioned 2metre long cast iron pipe. A Keysight E8267D Vector Signal Generator is used to provide the EM signal,which can then be coupled to the pipe through a standard gain horn antenna, as shown in Fig. 1d.(a) Main experimental setup(b) Top side of prototype robot(c) Bottom side of prototype robot (d) RF source setupFig. 1: Pipe measurement setup, including prototype robot and method of supplying RF power.(a) Photograph ofthe inside surface12 14 16 18 26 28 30 32 34-25-20-15-10-50Power Transmission (dB)Frequency (GHz) Intrinsic Pipe TSA OutputPower Loss Inside the Gas Pipe(b) Electromagnetic propagation loss0.1k 1k 10k 100k 1000k 10000k0510152025Efficiency (%)DC Load Resistance (Ohm) 12 GHz 14 GHz 15 GHzRectifier Efficiency at 19 dBm RF Power(c) Rectifier efficiencyFig. 2: Overview of the electromagnetic performance of the measurement setup.In this scenario, the aim is to deliver as much power as possible when the robot is at the far end of thepipe, with input RF power limited by the capabilities of the E8267D.The details of the robot prototype are presented in Fig. 1b and Fig. 1c. The body of the robot is 3Dprinted as a whole using a Stratasys Objet1000 Multi-Material 3D printer, and houses the MCU (PololuBaby Orangutan), a single brushed DC motor, backup batteries (2 x 3.7 V 100 mAh LiPo), as well as anight-vision camera. The robot also includes the WPT module, which is discussed in Section III.III. PIPE PROPAGATION MEASUREMENTS AND WPT MODULEAs mentioned earlier, metal pipes act as circular waveguides from an EM propagation point of view.The lowest cut-off frequency, i.e. the frequency below which propagation in the waveguide cannot occur,is an important parameter of any waveguide, and is dependent on its diameter. For the pipe used in thisexperiment, this was found to be 6.922 GHz [13].Furthermore, the assumption for low loss is dependent on the surface roughness of the inside of the pipebeing low [14]. In the case of the cast iron pipe used in this paper, this was found to not be the case, asillustrated by Fig. 2a. The propagation loss inside the pipe was then measured using a Keysight N5247PNA-X, resulting in Fig. 2b. Loss results are shown both for the pipe on its own, as well as a compositeloss when a Tapered Slot Antenna (TSA) [15] is used at the receiver end. The frequency ranges for whichdata is presented correspond to those for which horn antennas were available at the time of the experiments.Once the total propagation losses are known, and the RF input power level can be calculated, an RF-to-DC rectifier can be designed. It has been shown that the efficiency of a rectifier is a function of inputpower level, frequency, input impedance, and DC load resistance [16]. It is also dependent on the type ofsemiconductor element used, i.e. a diode or a transistor, as well as overall circuit topology [7], [16].For the WPT receiver used with the prototype robot, an 8-stage voltage doubler topology was thusselected, using commercially available low-barrier Schottky diodes (Avago HSMS-286C). The circuit wasimplemented on a low-loss PTFE substrate (Duroid 5880), with a TSA used to couple the incoming EMenergy to the rectifier. The output of the rectifier can then be connected to a voltage regulator and a batterycharging circuit, although physical space might become an issue. Details of the rectifier circuit are includedin Fig. 1b and Fig. 1c.The rectifier, as well as the TSA, were designed with dual-band operation in mind, with the bands beingKu-band (12 GHz – 18 GHz) and Ka-band (26.5 GHz – 40 GHz). Rectification efficiency, defined asη = PDC/PRF , was found to be better for lower frequencies, with best performance (23%, 18 mW PDC)obtained at a frequency of 12 GHz and 19 dBm of RF power at the input of the rectifier. A comparisonbetween several frequencies in the Ku-band for different DC load resistances is presented in Fig. 2c.IV. CONCLUSIONExperimental results on EM propagation in a metal pipe, as well as WPT for powering and chargingof a prototype robot have been presented and discussed. We have successfully demonstrated RF-to-DCrectification with up to 23% efficiency at the end of a 2 metre long gas pipe, which can be used to extendthe operating lifetime of an autonomous inspection robot.ACKNOWLEDGMENTThis work was supported by EPSRC Grants EP/N005686/1 and EP/N010523/1. The authors are thankfulto the staff at the EPSRC National Facility for Innovative Robotic Systems for their fabrication work.REFERENCES[1] N. Shinohara, Wireless power transfer via radiowaves. Wiley, 2013.[2] W. C. Brown, “The Microwave Powered Helicopter,” The Journal of Microwave Power & Electromagnetic Energy, vol. 1,no. 1, 1966.[3] N. Borges Carvalho, A. Georgiadis, A. Costanzo, H. Rogier, A. Collado, J. A. Garcia, S. Lucyszyn, P. Mezzanotte,J. Kracek, D. Masotti, A. J. S. Boaventura, M. de las Nieves Ruiz Lavin, M. Pinuela, D. C. Yates, P. D.Mitcheson, M. Mazanek, and V. Pankrac, “Wireless Power Transmission: R&amp;amp;D Activities Within Europe,”IEEE Transactions on Microwave Theory and Techniques, vol. 62, no. 4, pp. 1031–1045, 4 2014. [Online]. Available:http://ieeexplore.ieee.org/document/6734736/[4] Cost Action IC1301 Team, “Europe and the Future for WPT : European Contributions to Wireless Power Transfer Technology,”IEEE Microwave Magazine, vol. 18, no. 4, pp. 56–87, 6 2017. [Online]. Available: http://ieeexplore.ieee.org/document/7920430/[5] H. Zhang, F. Lu, H. Hofmann, W. Liu, and C. C. Mi, “A Four-Plate Compact Capacitive Coupler Design and LCL-CompensatedTopology for Capacitive Power Transfer in Electric Vehicle Charging Application,” IEEE Transactions on Power Electronics,vol. 31, no. 12, pp. 8541–8551, 2016.[6] J. Dai and D. C. Ludois, “A Survey of Wireless Power Transfer and a Critical Comparison of Inductive and CapacitiveCoupling for Small Gap Applications,” IEEE Transactions on Power Electronics, vol. 30, no. 11, pp. 6017–6029, 2015.[7] Z. Popovic, “Cut the Cord: Low-Power Far-Field Wireless Powering,” IEEE Microwave Magazine, vol. 14, no. 2, pp. 55–62,2013.[8] Ofcom, “UK Interface Requirement 2005,” 2006. [Online]. Available: http://stakeholders.ofcom.org.uk/spectrum/technical/interface-requirements/[9] ——, “UK Interface Requirement 2006,” 2006. [Online]. Available: http://stakeholders.ofcom.org.uk/spectrum/technical/interface-requirements/[10] ——, “UK Interface Requirement 2007,” 2007. [Online]. Available: http://stakeholders.ofcom.org.uk/spectrum/technical/interface-requirements/[11] ITU-R, “SM.2392-0 Applications of wireless power transmission via radio frequency beam,” Geneva, Tech. Rep., 2016.[Online]. Available: http://www.itu.int/pub/R-REP-SM.2392-2016[12] D. M. Pozar, Microwave engineering, 4th ed. Wiley, 2012.[13] N. Marcuvitz and Institution of Electrical Engineers., Waveguide handbook. P. Peregrinus on behalf of the Institution ofElectrical Engineers, 1986.[14] K. Chang, Encyclopedia of RF and microwave engineering. John Wiley, 2005.[15] J. L. Volakis, Antenna engineering handbook, 4th ed. McGraw-Hill, 2007.[16] C. R. Valenta and G. D. Durgin, “Harvesting Wireless Power: Survey of Energy-Harvester Conversion Efficiency in Far-Field,Wireless Power Transfer Systems,” IEEE Microwave Magazine, vol. 15, no. 4, pp. 108–120, 2014.

Wireless Power Transfer for Gas Pipe Inspection Robots

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Wireless Power Transfer for Gas Pipe Inspection Robots

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