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Introduction: Although many piezoelectric micromachined ultrasonic transducers (pMUTs) with different structures have been presented and fabricated for photoacoustic imaging (PAI), most of them are lack of systemic analysis and optimizations of design parameters. It is of important to explore the internal physical mechanisms and corresponding cause-effect relationships of the receive performance of pMUTs with different structures. The purpose of this study is to present a novel numerical method for an efficient design of the AlN-based pMUT for application in PAI system. Methods: A planar and two curved (dome-shaped and concave) structures of pMUTs based on aluminum nitride (AlN) were modeled numerically in this study. For each pMUT, the performance of receive sensitivity was simulated systemically using the finite elements analysis (FEA). Moreover, the physical parameters of three structureswere analyzed in detail, such as the radius of curvature, the height of SiO2, the height of AlN and the height of polyimide. Results: The obtained results show that the receive performance of three structures in water or air could be ordered as: the dome-shaped > the concave > the planar. Further, several valuable findings of this study would be used to design pMUTs so as to achieve better receive performance, such as: (a) for an optimum radius of curvature almost exists for any curved pMUT, (b) a thinner supporting layer means a better receive performance, (c) the piezoelectric layer in three structures have an optimum thickness, and (d) the height of polyimide affects little the receive performance in all structures. Conclusions: For a pMUT-based ultrasound sensor in photoacoustic imaging (PAI), the dome-shaped pMUT has a better receive sensitivity than that of the planar structure and the concave structure, whose physical parameters combining the work frequency could be optimized efficiently with a numerical method.
A numerical study and simulation of breast imaging in the early detection of tumors using the photoacoustic (PA) phenomenon are presented. There have been various reports on the simulation of the PA phenomenon in the breast, which are not in the real dimensions of the tissue. Furthermore, the different layers of the breast have not been considered. Therefore, it has not been possible to rely on the values and characteristics of the resulting data and to compare it with the actual state. Here, the real dimensions of the breast at three-dimensional and different constituent layers have been considered. After reviewing simulation methods and software for different stages of the PA phenomenon, a single suitable platform, which is commercially available finite element software (COMSOL), has been selected for simulating. The optical, thermal, elastic, and acoustic characteristics of different layers of breast and tumor at radiated laser wavelength (800 nm) were accurately calculated or obtained from a reliable source. Finally, by defining an array of 32 ultrasonic sensors on the breast cup at the defined arcs of the 2D slices, the PA waves can be collected and transmitted to MATLAB software to reconstruct the images. We can study the resulting PA wave and its changes in more detail using our scenarios.
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