UK-RAS CONFERENCE: 'ROBOTS WORKING FOR & AMONG US' PROCEEDINGS (2017) Power Transfer for Gas Pipe Inspection Robots Viktor Doychinov∗, Bilal Kaddouh∗, George Mills∗, Bilal Malik∗, Nutapong Somjit∗, Ian D Robertson ∗ at Leeds, University of Leeds, Leeds, United Kingdom

ABSTRACT

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.

Index Terms Wireless Power Transfer, Gas Pipe, Remote Inspection, Autonomous Systems, Robotics

I. INTRODUCTION Recently, another mode of WPT has been The use of high-power electromagnetic (EM) proposed, and that is WPT in shielded metal waves for Wireless Power Transmission pipes, which can potentially deliver higher (WPT) has been studied since the late 19th power, on the order of several Watts, at century [1], with arguably one of the most distances up to tens of metres [11]. This is famous demonstrators being the ” enabled by considering the pipes as circular Powered Helicopter” by W. C. Brown [2]. , which support low-loss EM The two main modalities investigated by the propagation [12]. This in turn opens up research community are near-field non- exciting opportunities for remote powering radiative power transfer, such as magnetic, and charging of pipe inspection robots, inductive, and capacitive coupling; and far- eliminating the need for a tethered power field power transfer through highly connection. directional antennas [3], [4]. In this paper, we present experimental results The near-field methods have successfully of WPT to a small robot, designed to fit in been adopted in commercial products for and inspect 25.4 mm diameter gas pipes. efficient charging of consumer electronics. Details of the robot prototype are given, as With the increased popularity of Electric well as measurements of the electromagnetic Vehicles (EV) concepts have been proposed propagation environment within the pipe for their continuous charging via capacitive used for these tests. Finally, a short coupling systems [5]. The main disadvantage discussion on the WPT module performance of the near-field method of power transfer is is included. the short maximum operating distance, which is on the order just a few centimetres [6]. On II. SCENARIO DESCRIPTION the other hand, far-field systems suffer from AND ROBOT PROTOTYPE large propagation losses through atmospheric A photograph showing the experimental attenuation and absorption, limiting the setup is given in Fig. 1a. The pipe used is a amount of power that can be delivered to a decommissioned 2 metre long cast iron pipe. receiver [7]. Furthermore, regulations on A Keysight E8267D Vector Signal Generator transmitted power in the Industrial, is used to provide the EM signal, which can Scientific, and Medical (ISM) bands further then be coupled to the pipe through a limit the potential deployments of such standard gain horn , as shown in Fig. systems to low-powered Internet-of-Things 1d. sensors [8]–[10].

80 UK-RAS CONFERENCE: 'ROBOTS WORKING FOR & AMONG US' PROCEEDINGS (2017)

Fig. 2: Overview of the electromagnetic performance of the measurement setup.

In this scenario, the aim is to deliver as much of the cast iron pipe used in this paper, this power as possible when the robot is at the far was found to not be the case, as illustrated by end of the pipe, with input RF power limited Fig. 2a. The propagation loss inside the pipe by the capabilities of the E8267D. was then measured using a Keysight N5247 The details of the robot prototype are PNA-X, resulting in Fig. 2b. Loss results are presented in Fig. 1b and Fig. 1c. The body of shown both for the pipe on its own, as well as the robot is 3D printed as a whole using a a composite loss when a Tapered Slot Stratasys Objet1000 Multi-Material 3D Antenna (TSA) [15] is used at the receiver printer, and houses the MCU (Pololu Baby end. The frequency ranges for which data is Orangutan), a single brushed DC motor, presented correspond to those for which horn backup batteries (2 x 3.7 V 100 mAh LiPo), antennas were available at the time of the as well as a night-vision camera. The robot experiments. Once the total propagation also includes the WPT module, which is losses are known, and the RF input power discussed in Section III. level can be calculated, an RF- to-DC rectifier can be designed. It has been shown III. PIPE PROPAGATION that the efficiency of a rectifier is a function MEASUREMENTS AND WPT of input power level, frequency, input MODULE impedance, and DC load resistance [16]. It is As mentioned earlier, metal pipes act as also dependent on the type of semiconductor circular waveguides from an EM propagation element used, i.e. a diode or a transistor, as point of view. The lowest cut-off frequency, well as overall circuit topology [7], [16]. For i.e. the frequency below which propagation the WPT receiver used with the prototype in the cannot occur, is an robot, an 8-stage doubler topology important parameter of any waveguide, and was thus selected, using commercially is dependent on its diameter. For the pipe available low-barrier Schottky diodes (Avago used in this experiment, this was found to be HSMS-286C). The circuit was implemented 6.922 GHz [13]. on a low-loss PTFE substrate (Duroid 5880), with a TSA used to couple the incoming EM Furthermore, the assumption for low loss is energy to the rectifier. The output of the dependent on the surface roughness of the rectifier can then be connected to a voltage inside of the pipe being low [14]. In the case regulator and a battery charging circuit,

81 UK-RAS CONFERENCE: 'ROBOTS WORKING FOR & AMONG US' PROCEEDINGS (2017) although physical space might become an comparison between several frequencies in issue. Details of the rectifier circuit are the Ku-band for different DC load included in Fig. 1b and Fig. 1c. resistances is presented in Fig. 2c.

The rectifier, as well as the TSA, were I.V. CONCLUSION designed with dual-band operation in mind, Experimental results on EM propagation in a with the bands being Ku-band (12 GHz – metal pipe, as well as WPT for powering and 18 GHz) and Ka-band (26.5 GHz – 40 charginG of a prototype robot have been GHz). Rectification efficiency, defined as η presented and discussed. We have = PDC /PRF , was found to be better for successfully demonstrated RF-to-DC lower frequencies, with best performance rectification with up to 23% efficiency at the (23%, 18 mW PDC ) obtained at a end of a 2 metre long gas pipe, which can be frequency of 12 GHz and 19 dBm of RF used to extend the operating lifetime of an power at the input of the rectifier. A autonomous inspection robot.

ACKNOWLEDGMENT This work was supported by EPSRC Grants EP/N005686/1 and EP/N010523/1. The authors are thankful to the staff at the EPSRC National Facility for Innovative Robotic Systems for their fabrication work.

REFERENCES 1. Shinohara, Wireless power transfer via IEEE Transactions on Power Electronics, radiowaves. Wiley, 2013. vol. 30, no. 11, pp. 6017–6029, 2015. 2. W. C. Brown, “The Microwave Powered 9. Z. Popovic, “Cut the Cord: Low-Power Far- Helicopter,” The Journal of Microwave Field Wireless Powering,” IEEE Microwave Power & Electromagnetic Energy, vol. 1, Magazine, vol. 14, no. 2, pp. 55–62, 2013. no. 1, 1966. 10. Ofcom, “UK Interface Requirement 2005,” 3. Borges Carvalho, A. Georgiadis, A. 2006. [Online]. Available: Costanzo, H. Rogier, A. Collado, J. A. http://stakeholders.ofcom.org.uk/spectrum/te Garcia, S. Lucyszyn, P. Mezzanotte, chnical/ interface-requirements/ 4. J. Kracek, D. Masotti, A. J. S. 11. ——, “UK Interface Requirement 2006,” Boaventura, M. de las Nieves Ruiz Lavin, 2006. [Online]. Available: M. Pinuela, D. C. Yates, P. D. http://stakeholders.ofcom.org.uk/spectrum/te Mitcheson, M. Mazanek, and V. Pankrac, chnical/ interface-requirements/ “Wireless Power Transmission: 12. ——, “UK Interface Requirement 2007,” R&D Activities Within Europe,” 2007. [Online]. Available: IEEE Transactions on Microwave Theory http://stakeholders.ofcom.org.uk/spectrum/te and Techniques, vol. 62, no. 4, pp. 1031– chnical/ interface-requirements/ 1045, 4 2014. [Online]. Available: 13. ITU-R, “SM.2392-0 Applications of wireless http://ieeexplore.ieee.org/document/6734736/ power transmission via radio frequency 5. Cost Action IC1301 Team, “Europe and the beam,” Geneva, Tech. Rep., 2016. [Online]. Future for WPT : European Contributions to Available: http://www.itu.int/pub/R-REP- Wireless Power Transfer Technology,” SM.2392-2016 6. IEEE Microwave Magazine, vol. 18, no. 4, 14. M. Pozar, Microwave , 4th ed. pp. 56–87, 6 2017. [Online]. Available: Wiley, 2012. http://ieeexplore.ieee.org/document/7920430/ 15. N. Marcuvitz and Institution of Electrical 7. H. Zhang, F. Lu, H. Hofmann, W. Liu, and C. . Waveguide handbook. P. Peregrinus on behalf of the Institution of Electrical Engineers, 1986. C. Mi, “A Four-Plate Compact Capacitive 16. K. Chang, Encyclopedia of RF and Coupler Design and LCL-Compensated microwave engineering. John Wiley, 2005. Topology for Capacitive Power Transfer in 17. J. L. Volakis, Antenna engineering Electric Vehicle Charging Application,” handbook, 4th ed. McGraw-Hill, 2007. IEEE Transactions on Power Electronics, 18. R. Valenta and G. D. Durgin, “Harvesting vol. 31, no. 12, pp. 8541–8551, 2016. Wireless Power: Survey of Energy-Harvester 8. J. Dai and D. C. Ludois, “A Survey of Conversion Efficiency in Far-Field, Wireless Wireless Power Transfer and a Critical Power Transfer Systems,” IEEE Microwave Comparison of Inductive and Capacitive Magazine, vol. 15, no. 4, pp. 108–120, Coupling for Small Gap Applications,” 2014.

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