Monitoring of stresses and strains in a structure is important to detect problems during the design or the service cycle of the structure. Piezoresistive sensing rosettes are considered a reliable method for stress and strain monitoring. While few efforts have been focused towards developing a 3D stress/strain sensing rosette, most of the currently developed piezoresistive rosettes extract only in-plane stress/strain components. In this paper, a new approach for building a stress sensing rosette capable of extracting the six stress components and the temperature is presented and its feasibility is verified both analytically and experimentally. The current approach is based on varying the doping concentration of the sensing elements and utilizing the unique behavior of the shear piezoresistive coefficient ( 44 ) in n-Si.

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A single-polarity (n-type) piezoresistive sensing chip for three-dimensional (3D) stress sensing has been microfabricated and fully calibrated. The sensing chip, which is capable of extracting the six stress components, is prototyped using bulk microfabrication techniques on a (1 1 1) crystalline silicon. A full calibration procedure employing uniaxial, thermal and hydrostatic loading has been conducted. The calibration results confirm the feasibility of our proposed technique of using single-polarity (n-type) sensing elements to develop 3D stress sensors. Preliminary testing results are presented to demonstrate the operation of our developed sensing chip.

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A new piezoresistive stress-sensing rosette is developed to extract the components of the three-dimensional (3D) stress tensor using single-polarity (n-type) piezoresistors. This paper presents the testing of a micro-fabricated sensing chip utilizing the developed single-polarity rosette. The testing is conducted using a four-point bending of a chip-on-beam to induce five controlled stress components, which are analyzed both numerically and experimentally. Numerical analysis using finite element analysis is conducted to study the levels of the induced stress components at three rosette-sites and the levels of the stress field non-uniformities, and to simulate the extracted stress components from the sensing rosette. The experimental analysis applied tensile and compressive loads over three rosette-sites at different load increments. The experimentally extracted stress components show good linearity with the applied load and values close to the numerical model.