90 Z. Zhao et al. to reduce metal content; however, the copper stator remains the same. By replacing the stator with a plastic equivalent, the PRM should have a higher degree of MRI compatibility. We extend our previous work in [10] by using a high-speed camera to view the start-up and initial settling behavior of a plastic piezoelectric motor stator component. The results show rotatory motion in the second mode of operation for the stator and demonstrate its potential in the construction of an MRI compatible PRM. 12.2 Methodology The dimensional drawing of the plastic stator is shown in Fig. 12.1a. The plastic stator outside diameter is 30 mm and its height is 5.53 mm. A PZT-5H 30 mm (outside diameter) ×20 mm (inside diameter) ×0.5 mm (height) copper-plated ring (EBL Products, USA) was chemically etched to form the electrode pattern shown in Fig. 12.1b previously validated in [10]. To create the electrode geometry, a mask of the electrode pattern was printed and toner transferred onto the ring. Green toner reactive foil was used as the second mask to increase resolution of the transformed pattern as shown in [11, 12]. The pattern was subsequently etched using a Ferric Chloride solution. Figure 12.1c shows the etched ring bonded to a custom plastic stator manufactured from Ultem 1000 thermoplastic polyetherimide (PEI) using Loctite 3888 conductive epoxy. Four 90◦-shifted sine waves were used to excite the crystal. The stator assembly with bonded piezo ring was secured onto a fixture designed to be mounted to an optical table. By using a variation of the high-speed digital holographic (HDH) system presented in [13, 14], out-of-plane displacement and rotatory motion at the surface of the plastic stator can be observed. Figure 12.2 shows the HDH system setup for stator imaging using a 532 nm 30 mW laser (BWN-532-20E, B&W TEK INC, USA). The laser beam was split into beam A and beamB. BeamAwas reflected by a mirror fixed to a piezo microactuator powered by a piezo controller (MDT694A, Thorlabs, USA). The reflected beam was focused into a fiber through a 20/0.40 lens. Beam B was reflected by a mirror and passed through a 60/0.85 lens to create a wavefront that was shown on the piezo stator. The resultant scattered wavefront was picked up by a 150 mm telecentric lens (Computar, USA) and reflected on a wedge. Beam A left the optical fiber and was shown on the other side of the same wedge. The combined beam was observed by a high-speed camera (FASTCAM SA-Z, Photron, USA) operating at 67 k frame per second (fps). An automated phase correlation calibration algorithm, applied in post-processing, that specifies the sampled image frames with the desired shift in interference phase during each high-speed phase ramp was designed. The system synchronized the PRM excitation phase and strobe phase by triggering automatically to reduce the frequency mismatch problem. To collect more holographic images in each cycle and better image view in each frame, low excitation frequency (the second mode) and voltage were operated. Fig. 12.1 (a) Dimensional drawings of the custom-designed and fabricated plastic stator. Outside diameter is 30 mm, and overall height is 5.53mm. (b) Orthogonal view of underside of stator with wires coming out. (c) Electrode patterning of piezoelectric. Blue is sine, and red is cosine
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