The inefficiency in converting low frequency vibration (6~240？Hz) to electrical energy remains a key issue for miniaturized vibration energy harvesting devices. To address this subject, this paper reports on the novel, three-dimensional micro-fabrication of spring elements within such devices, in order to achieve resonances and maximum energy conversion within these common frequencies. The process, known as projection microstereolithography, is exploited to fabricate polymer-based springs direct from computer-aided designs using digital masks and ultraviolet-curable resins. Using this process, a micro-spring structure is fabricated consisting of a two-by-two array of three-dimensional, constant-pitch helical coils made from 1,6-hexanediol diacrylate. Integrating the spring structure into an electromagnetic device, with a magnetic load mass of 1.236 grams, the resonance is measured at 61？Hz, which is within 2% of the theoretical model. The device provides a maximum normalized power output of 9.14？μW/G ( ？ms？2) and an open circuit normalized voltage output of 621？mV/G. To the best of the authors knowledge, notable features of this work include the lowest Young’s modulus (530？MPa), density (1.011？g/cm3), and “largest feature size” (3.4？mm) for a spring element in a vibration energy harvesting device with sub-100？Hz resonance. 1. Introduction The need for miniaturized, multifunctional electromechanical structures and material systems with the capability to harvest energy from the environment has grown significantly in recent years in response to the proliferation of portable electronic devices and wireless sensors [1–4]. At the present time, batteries are the primary power source for these portable devices. Unfortunately, batteries suffer from a limited lifetime requiring periodic recharging or replacement [5]. Thus, harvesting energy from the environment offers an autonomous means to recharge or directly power conventionally battery-operated devices. In evaluating the available energy harvesting technologies, solar cells are the most mature. However, their dependence on sunlight restricts the locations where solar cells can be effective. In contrast, environmental vibration is a particularly attractive energy source because of its abundance in nearly all environments, spanning a wide frequency range [6]. This has led to the research field known as vibration energy harvesting (VEH), which explores using different principles of transduction to convert available vibration energy into electricity [7–11]. In attempting to miniaturize VEH devices, a major issue
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