A feasibility study on the use of magnetic inductance to charge wireless sensor nodes

Abstract

A Wireless Sensor Network (WSN) is a group of sensors which are used to monitor or detect phenomena. These sensors are capable of transferring sensed data wirelessly. Power supply is a key issue in a WSN. The lifetime of the WSN node’s batteries is limited, thereby limiting the effective lifetime of the node. There is need for ways to recharge batteries wirelessly. Magnetic inductive power transfer might provide an alternative way of recharging WSN nodes, rather than with energy scavenging techniques. This research investigates the use of magnetic inductive power transfer techniques in WSNs. A system used to recharge a WSN node is limited in terms of minimum efficiency, size, and separation distance between the coils. In order to maximise efficiency for small coil sizes, this research focuses on resonant, mid-range power transfer in the near-field region. A new coil type, the hybrid coil, is proposed and the theory to calculate its parameters is presented. A total of four coil types are investigated and compared with each other theoretically and experimentally. The effects of various parameter tolerances are investigated, including the effect of non-resonant operation, the effect of increasing the primary coil size and the effect of misaligned coil centres. The results show that magnetic inductive power transfer is not yet efficient enough to make it a viable option for use in WSNs. In addition, the results show that the hybrid coil proposed in this dissertation outperforms any of the other coil types. AFRIKAANS : ‘n Draadloos Sensornetwerk (DSN) wat gebruik word om verskynsels te monitor en op te spoor. Hierdie sensors is in staat daartoe om waargenome data sonder enige fisiese verbinding oor te dra. Kragtoevoer is ‘n kern vraagstuk in ‘n DSNe. Die leeftyd van ‘n DSN nodus se battery is beperk en beperk dus die effektiewe leeftyd van die DSN nodus self. Daar is ‘n behoefte vir maniere om die batterye draadloos te herlaai. Magneties induktiewe kragoorplasing kan moontlik ‘n alternatiewe manier wees om DSN nodusse te herlaai, eerder as met energie opgaar tegnieke. Hierdie navorsing ondersoek die gebruik van magneties induktiewe kragoorplasing in DSNe. ‘n Stelsel wat gebruik word om ‘n DSN nodus te herlaai is beperk in terme van minimum effektiwiteit, grootte en die afstand tussen die spoele. Om die effektiwiteit van klein spoele te maksimeer fokus hierdie navorsing op resonante, medium afstand, kragoorplasing in die naby-veld omgewing. ‘n Nuwe tipe spoel, die saamgestelde spoel, word voorgestel en die toerie om die spoel se parameters te bepaal word gegee. ‘n Totaal van vier spoel tipes word ondersoek en teoreties en eksperimenteel met mekaar vergelyk.