A low resonance frequency piezoelectric energy harvesting using a hybrid uid diaphragm (HFD) is presented. This paper describes the design, fabrication and measurement of such device for harvesting energy from environmental vibrations. The HFD consists in an incompressible uid conned between two thin piezoelectric membranes. The output voltage and power of the PVDF HFD are studied based on experimental and simulation results. Compared with conventional vibration harvester, this proposed solution is very simple and suitable for miniaturization and integration. 1 Introduction An increasing interest in wireless sensors networks has been growing up over recent years. The implementation of communicating sensors networks in industrial application, transport or buildings oers possible improvements : productivity gains, reliability and energy performance are feasible by the exploitation of the extensive collected information (temperature, humidity, electric consumption ...). With the rapid advancement of low-power wireless sensor nodes and MEMS technology, microscale energy harvesting has attracted worldwide research interests for powering [1]. Vibration-based energy harvesting has been exploited using transduction mechanisms including piezoelectric, electromagnetic and electrostatic [2, 3]. In order to extract the maximum power from the environment, the resonant frequency of a linear harvesting device has to match the dominant frequency of the excitation. Indeed frequencies of ambient available vibration sources are relatively low (normally less than 200 Hz) [4]. As a result, many vibration-based piezoelectric energy harvesters of centimeter scale have been demonstrated to operate at low frequencies [5]. This paper reports the modelling, fabrication and testing of a new piezoelec-tric uid-membrane structure for vibration energy harvesting. Compared to classical cantilever architectures, this approach takes advantage of the mechanical stretch of circular diaphragms. However, when miniaturized, they present high resonance frequency [6] and it hinders their direct use. The concept of hybrid uid diaphragm (HFD) consists in an incompressible uid conned between two thin piezoelectric membranes, it allows the realization of low resonance frequency membranes. Moreover, Pressure uctuation harvesting [7] can be especially targeted. 2 Piezoelectric HFD concept We propose here, an innovative architecture for vibration energy harvesters. Fig.1 describes the geometry as well as the main geometrical parameters of the structure. The incompressible uid is used as an inertial mass which allows a drastic reduction of the resonance frequency to eectively harvest ambient vibrations. The height of the structure can be easily tunned to provide