Physical insight into electromagnetic kinetic energy transducers and appropriate energy conditioning for enhanced micro energy harvesting

Abstract

Abstract. This paper proposes a new method for modeling electromagnetic kinetic energy transducers and gives analytical expressions that enable the design of efficient energy conditioning circuitry. The introduced transducer modeling approach achieves high accuracy without requiring a large set of parameters. The presented transducer characterization allows physical insight into fully assembled and packaged transducers in order to extract the required transducer model parameters without knowledge of the individual components. Moreover, the electromagnetic coupling, the parasitic damping, and the optimal load can be modeled with a dependence on the external excitation. Precise co-simulation with CMOS integrated energy conditioning circuitry is possible implementing this model in a circuit simulator. IntroductionKinetic micro energy harvesting enables the use of ambient vibrations in order to supply low power electronic systems such as wireless sensor nodes [1,2]. In order to guarantee autonomous and reliable system operation, the ambient energy extraction has to be optimized. Therefore, a well-designed kinetic energy harvesting system composed of a kinetic micro power transducer and an efficient energy conditioning such as active rectification is needed (Figure 1).Efficient system design requires an accurate transducer model and precise definitions of the optimal operation conditions of the entire system. In order to design an efficient energy harvester highly accurate transducer modeling is mandatory and a large set of model parameters is needed [3,4]. These parameters are difficult to extract from a fabricated harvester without deep transducer design knowledge which usually applies to circuit designers. However, for the design of efficient energy conditioning circuits a reduced parameter set is sufficient that describes the optimum transducer operation precisely. Harvester disassembly allows to extract this set [5].A fully packaged small-scaled electromagnetic kinetic energy transducer prototyped by the HSG-IMIT (Figure 1) is characterized and modeled accurately in this work without disassembly. Moreover, definitions are proposed that detail the optimum operation of energy conditioning based on ultra-low power CMOS integrated active rectification with low voltage drop [6].

A Comparison of Methods to Measure the Coupling Coefficient of Electromagnetic Vibration Energy Harvesters

“…This can be used to predict the optimum load resistance depending on the vibration strength. The mechanical damping increases with stronger vibration amplitudes [24,25], and therefore the optimum load decreases with the amplitude by Equation (5). Determining the optimum load for the full range of vibration amplitudes would take On average, the experimentally determined coupling coefficients deviate by about 3% from the simulated value K sim .…”