An important limitation in the classical energy harvesters based on cantilever beam structure is its monodirectional
sensibility. The external excitation must generate an orthogonal acceleration from the beam plane to induced flexural
deformation. If the direction of the excitation deviates from this privileged direction, the harvester output power is drastically
reduced. This point is obviously very restrictive in the case of an arbitrary excitation direction induced for example by human
body movements or vehicles vibrations.
In order to overcome this issue of the conventional resonant cantilever configuration with seismic mass, a multidirectional
harvester is introduced here by the authors. The multidirectional ability relies on the exploitation of 3 degenerate structural
vibration modes where each of them is induced by the corresponding component of the acceleration vector. This specific
structure has been already used for 3 axis accelerometers but the approach is here totally revisited because the final
functional goal is different. This paper presents the principle and the design considerations of such multidirectional
piezoelectric energy harvester.
A finite element model has been used for the harvester optimisation. It has been shown that the seismic mass is a relevant
parameter for the modes tuning because the resonant frequency of the 1st exploited flexural mode directly depends on the
mass whereas the resonance frequency of the 2nd flexural mode depends on its moment of inertia.
A simplified centimetric prototype limited to a two orthogonal direction sensibility has permitted to valid the theoretical
For biomedical microanalysis systems requiring implementation of optical signal generation and detection, we propose a package of VHDL-AMS functions to allow co-simulations of optical path, opto-electronic elements and associated electronics. This package contains a set of functions, which may be used for functional description of parts of microanalysis systems. An overview of simulation techniques shows that VHDL-AMS allows continuous-time simulation of polychromatic optical signals needed by the wavelength shifting nature of fluorescence. Indeed, directivity of optic path is well managed by VHDL-AMS using directional ports. By design, optical signals are easily simulated together with associated command and processing electronic circuits. Inspired by RF simulation techniques, the proposed description of polychromatic optical signals lies on a discretization of spectra. This format allows each optic band to be processed independently by models. The array data structure available in VHDL-AMS provides a compact form to device descriptions and to optical signal connexions. Fluorescence is modelled with absorbance and emission spectra, and optical couplings are described using results of geometric-optic analysis. A “spectral plug-in” has been developed, to be connected to output-power models of LASER-LED reported in the literature. Furthermore, a physical model of the CMOS Buried Double Junction (BDJ) detector has been described. Models of optic and electronic parts include a modulated LASER source, fibre optic, fluorochrom, BDJ detector and Constant Voltage Threshold (CVT) analogue-to-digital signal conversion. The system-level simulations, with Variable-Time Synchronous Detection (VTSD) are performed using the “Advanced-MS” environment. The validity domain of this approach as well as limitations of the available VHDL-AMS simulators (especially in terms of convergence and simulation time) are discussed.
For sensitive fluorescence detection requiring weak signal recovery, we propose a novel digital synchronous detection method. It is based on a voltage/time duality concept which, compared to a conventional approach, consists of transformation of constant sampling rate with voltage measurement into variable-time sampling with constant threshold voltage. This Variable-Time Synchronous Detection (VTSD) method ensures a constant SNR over a large dynamic range, with optimised measuring rate. It can be implemented without any precise analogue-to-digital converter. A CMOS photodetection system with implementation of this VTSD method together with charge amplification is designed and tested. The results confirm its ability to recover photocurrent signals at femto-Ampers levels.