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Cantilever beam MEMS piezoelectric accelerometers are the simplest and most widely used accelerometer structure. This paper discusses the design of a piezoelectric accelerometer exclusively for SHM applications. While such accelerometers need to operate at a lower frequency range, they also need to possess high sensitivity and low noise floor. The availability of a simple model for deflection, charge, and voltage sensitivities will make the accelerometer design procedure less cumbersome. However, a review of the open literature suggests that such a model has not yet been proposed. In addition, previous works either depended on FEM analysis or only reported on the fabrication and characterization of piezoelectric accelerometers. Hence, this paper presents, for the first time, a simple analytical model developed for the deflection, induced voltage, and charge sensitivity of a cantilever beam piezoelectric accelerometer.The model is then verified using FEM analysis for a range of different cases. Further, the model was validated by comparing the induced voltages of an accelerometer estimated using this model with experimental voltages measured in the accelerometer after fabrication. Subsequently, the design of an accelerometer is demonstrated for SHM applications using the analytical model developed in this work. The designed accelerometer has 60 mV/g voltage sensitivity and 2.4 pC/g charge sensitivity, which are relatively high values compared to those of the piezoresistive and capacitive accelerometers for SHM applications reported earlier.

Wireless Structural Health Monitoring (WSHM) is a less expensive but efficient mode of health monitoring. However, it needs frequent change of batteries since remote WSHM consumes large power. The best scientific solution to this problem is to employ energy harvesters integrated along with the vibration sensors in the same substrate so that the battery is recharged by the energy harvested during vibrations caused by the passing vehicles in bridges. In this work, an attempt has been made to design an energy harvester and a micro accelerometer integrated chip. Civil structures have low natural frequencies and therefore low bandwidth design is adopted to maximize the harvested energy and accelerometer sensitivity. The other special feature of the proposed design is its ability to provide further increase in energy harvesting by the parallel operation of an array of energy harvesters with closely spaced natural frequencies. The studies show that the natural frequencies of the harvesters should be less than that of the structure in healthy condition. Simulation studies conducted on these devices show that it is possible to harvest a maximum power of 2.283 mW/g. The integrated micro accelerometer is also capable of giving a sensitivity of 27.67 V/g with appreciable improvement in other performance indices.

Focused research efforts on enhancing the sensitivity of piezoresistive MEMS pressure sensors have been made in the past. Most of these techniques applied to enhance sensitivity have depended on manipulating the geometries of the diaphragm, selection of the diaphragm material and improving the piezoresistive properties. Piezoresistors change their resistance linearly proportional to the bending stresses induced in the diaphragm on application of the pressure. Therefore the successful design of a high sensitivity piezoresistive pressure sensor totally depends on the efficiency with which the induced stresses are harvested in the transduction process. Introduced is an innovative way to harvest the maximum stresses. The dual Wheatstone bridge implemented with eight piezoresistors effectively converts the XX and YY plane stresses into electrical voltage to double the sensitivity. The simulation experiment results show that the sensitivity of the 91.72 µV/V/kPa with ensured linearity over 0-14 kPa using a 5 µm-thick diaphragm with a single bridge can now be achieved by employing a 7 µm-thick diaphragm with double Wheatstone bridges but with excellent linearity extended over 0-54 kPa. Almost the same trend is seen between the 3 and the 5 µm-thick diaphragms. Thus, this technique paves the way for achieving large voltage sensitivity bundled with a high level of linearity over a wide pressure range by using thick diaphragms.

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