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Compared to many other energy harvesting schemes, harvesting energy from magnetic fields offers potential advantages for energy extraction and sensing. A magnetic energy harvester provides great flexibility for sensors and monitoring applications for condition-based monitoring of electromagnetic actuators, including vibration and thermal monitoring. A core must be managed or operated with carefully timed saturation to ensure maximum power extraction, a complex problem given the nonlinear saturation characteristics of a magnetic core [1]. This paper presents a simulator-friendly "circuit model" for a magnetic core, and uses this model to design and demonstrate several power electronic circuit solutions for harvesting energy. The circuit model has an excellent accuracy to represent the core regardless of the level of saturation. The design techniques to enhance power harvest are proposed, and verified through simulation and experiments, substantially boosting the amount of power harvest.

Purpose It is difficult to assess airway obstruction using spirometry in adult asthmatic patients with preserved lung function. Impulse oscillometry (IOS) can detect not only airway resistance but also reactance. Therefore, IOS may be useful in assessing pulmonary function in such patients. We investigated the applicability of IOS for asthma patients with preserved lung function. Methods Between 2015 and 2018, 1,248 adult asthmatic patients suspected of having asthma who visited the Allergy and Asthma Center of Severance Hospital underwent both spirometry and IOS. Consequently, 784 patients had asthma, 111 had chronic obstructive lung disease (COPD) or asthma-COPD overlap, and 7 had parenchymal lung disease. The remaining 346 patients had chronic cough without underlying lung or airway disease. Among the 784 asthmatic patients, 191 with decreased lung function (predicted forced expiratory volume in 1 second [FEV1] < 80%) were excluded. Propensity score matching was performed to adjust baseline characteristics between 346 non-asthmatic and 593 asthmatic patients with preserved lung function. Subsequently, we compared the spirometry and IOS parameters between the 329 asthmatic and 329 non-asthmatic patients. Results Multiple logistic regression analysis showed that the area of reactance (AX) was associated with asthma with preserved lung function. In receiver operating characteristic (ROC) curve analysis, the area under the curve (AUC) of AX (AUC = 0.6823) for asthma was not significantly different from that of FEV1 (AUC = 0.6758). However, the AUC of a combination of AX and FEV1 (AUC = 0.7437) for asthma was significantly higher than that of FEV1 alone. The cutoff value of AX was 0.51 kPa/L in univariate ROC analysis. Conclusions AX is associated with adult asthma with preserved lung function. Performing spirometry together with IOS is more beneficial than performing spirometry alone for diagnosing asthma in adult patients with preserved lung function.

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