Browsing by Author "Zhang, G."
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Item Open Access FEM-based analysis on sensing out-of-plane displacements of low-order Lamb wave modes by CMUTs(AIP Publishing LLC, 2022-11-23) Lu, W.; Zhang, S.; Wang, R.; Yang, Y.; Zhang, G.; Zhang, W.; Xu, B.; Yılmaz, MehmetIt is well known that acoustic emission (AE) signals, generated by external impacts or damages such as crack initiation, mainly propagate in the form of Lamb waves in plate-like structures. In this work, MEMS-based resonant capacitive micro-machined ultrasonic transducers (CMUTs), which are designed for sensing out-of-plane displacements, have been verified by finite element method (FEM) modeling and theoretical analysis for their feasibility of detecting low-order Lamb waves (A0 and S0). First, combining the propagation theory of Lamb waves and the “spring-mass-damper” model of CMUTs, the out-of-plane sensing mechanism has been explained, together with the analytical expression of sensitivity. Then, simulations based on FEM have been carried out to show that the designed CMUTs are sensitive to out-of-plane displacements, while extremely insensitive to in-plane displacements. Meanwhile, a transient analysis has found the potential abilities of CMUTs for sensing A0 and S0 lamb waves. Besides, the sensing characteristics of CMUTs have also been investigated, including the influence of squeezed-film damping, the amplitude of the input signal, the cell number, and cell space. Finally, the ball drop impact is simulated to show the potential of identifying the location of the AE source by CMUTs. Our studies reveal the out-of-plane sensing behaviors of CMUTs for Lamb waves and may have the potential in promoting the miniaturization and integration of AE sensors.Item Open Access In-plane-sensing analysis of comb-like capacitive micro-machined ultrasonic transducers (cmuts) using analytical small-signal model and fem(Institute of Electrical and Electronics Engineers, 2023-04-18) Zhang, S.; Lu, W.; Yang, Y.; Wang, R.; Zhang, G.; Xu, B.; Yılmaz, Metin; Zhang, W.In this work, capacitive micro-machined ultrasonic transducers (CMUTs) were developed into comb-like shapes to make these comb-like shaped structures work for sensing in-plane vibrations of ultrasonic guided waves. On this basis, an analytical small-signal model, which is mainly a combination of the forced vibration theory and the simplified parallel-plate capacitor model, was proposed to satisfy the requirements of theoretical design. Through the proposed model, the in-plane-sensing behaviors of a comb-like CMUT cell can be predicted, including vibrating velocity, output current, and sensitivity. Compared with the results calculated from the finite element method (FEM) simulation, it was found that the static state and the frequency-domain results of the analytical small-signal model agree well with those of FEM simulations if the used first natural frequencies of these two methods are identical. Considering the fringing field capacitance could further improve the accuracy of the analytical small-signal model. At last, influences of some external parameters, i.e., dc bias voltage, air damping, and input in-plane displacement, on the sensitivity of a comb-like CMUT cell were discussed by the analytical small-signal model and FEM simulation. Relevant results reveal the way to design a comb-like CMUT and indicate the conditions when the analytical small-signal model is accurate. Our work develops the theory on the in-plane-sensing comb-like CMUT and is expected to be combined with the theory on the previous out-of-plane-sensing CMUT to realize 3-D-CMUT for sensing 3-D guided waves.Item Open Access Magnetostimulation limits in magnetic particle imaging(IEEE, 2013) Sarıtaş, Emine Ülkü; Goodwill, P.; Zhang, G.; Conolly, S.For magnetic particle imaging (MPI), specific absorption rate (SAR) and more critically magnetostimulation (i.e., dB/dt) safety limits will determine the optimal scan parameters, such as the drive field strength and frequency. These parameters will impact the scanning speed, field-of-view (FOV) and signal-to-noise ratio in MPI. Understanding the potential safety hazards of the drive field is critical for scaling MPI for human use. In this work, we demonstrate that magnetostimulation is the primary magnetic safety consideration in MPI, and we describe the first human-subject magnetostimulation threshold experiments for MPI using homogeneous coils. Our experiments, performed on the arm and leg, indicate that magnetostimulation thresholds monotonically decrease with increasing frequency. Additionally, we show for the first time that a strong inverse correlation exists between the threshold and the body part size. The chronaxie time, on the other hand, did not vary with body part size. We conclude with an estimation of the magnetostimulation thresholds for a full-body MPI scanner: a mean asymptotic threshold of 14.3 mT-pp (peak-to-peak) with a mean chronaxie time of 289 μs, which correspond to a magnetostimulation threshold of about 15 mT-pp for frequencies between 25 and 50 kHz. These findings will have a great impact on the optimization of MPI parameters, especially in determining the number of partial FOVs required to cover a region of interest.