This paper presents the design and evaluation of magnetoelastic sensors intended for wireless monitoring of tissue accumulation in peripheral artery stents. The sensors are fabricated from 28 μm thick foils of magnetoelastic 2826MB Metglas TM , an amorphous Ni-Fe alloy. The sensor layer consists of a frame and an active resonator portion. The frame consists of 150 μm wide struts that are patterned in the same wishbone array pattern as a 12 mm × 1.46 mm Elgiloy stent cell. The active portion is a 10 mm long symmetric leaf shape and is anchored to the frame at mid length. The active portion nests within the stent cell, with a uniform gap separating the two. A gold-indium eutectic bonding process is used to bond Metglas TM and Elgiloy foils, which are subsequently patterned to form bi-layer resonators. The response of the sensor to viscosity changes and mass loading that precede and accompany artery occlusion is tested in vitro. The typical sensitivity to viscosity of the fundamental, longitudinal resonant frequency at 361 kHz is 427 ppm cP −1 over a 1.1-8.6 cP range. The sensitivity to mass loading is typically between 63000 and 65000 ppm mg −1 with the resonant frequency showing a reduction of 8.1% for an applied mass that is 15% of the unloaded mass of the sensor. This is in good agreement with the theoretical response.

This paper reports on the evaluation of a high resolution micro ultrasonic machining (HR-μUSM) process suitable for post fabrication trimming of complex 3D microstructures made from fused silica. Unlike conventional USM, the HR-μUSM process aims for low machining rates, providing high resolution and high surface quality. The machining rate is reduced by keeping the micro-tool tip at a fixed distance from the workpiece and vibrating it at a small amplitude. The surface roughness is improved by an appropriate selection of abrasive particles. Fluidic modeling is performed to study interaction among the vibrating micro-tool tip, workpiece, and the slurry. Using 304 stainless steel (SS304) tool tips of 50 μm diameter, the machining performance of the HR-μUSM process is characterized on flat fused silica substrates. The depths and surface finish of machined features are evaluated as functions of slurry concentrations, separation between the micro-tool and workpiece, and machining time. Under the selected conditions, the HR-μUSM process achieves machining rates as low as 10 nm s −1 averaged over the first minute of machining of a flat virgin sample. This corresponds to a mass removal rate of ≈20 ng min −1. The average surface roughness, S a , achieved is as low as 30 nm. Analytical and numerical modeling are used to explain the typical profile of the machined features as well as machining rates. The process is used to demonstrate trimming of hemispherical 3D shells made of fused silica.

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This paper presents the design and characterization of a high resolution micro ultrasonic machining (HR-µUSM) process suitable for post-fabrication trimming of 3-D microstructures made from fused silica and other materials. The process targets low machining rates, high resolution, and high surface quality. On flat fused silica substrates, the process achieves machining rates ≤10 nm/sec averaged over 1 minute. The average surface roughness (S a ) achieved is ≤30 nm. The process is successfully demonstrated for trimming hemispherical 3-D microstructures made from fused silica.

This letter reports on the evaluation of an unconventional approach to microultrasonic machining in which the workpiece is vibrated while the tool remains static. The vibration of the workpiece, and not the tool, alleviates the accumulation and the agglomeration of the slurry particles and debris between the machined features. This approach is appealing for batch mode pattern transfer of closely packed features into ceramics and glass. However, the question of how the workpiece vibration will cause selective machining of features on the opposing tool surface has not been addressed. In this effort, fluidic modeling is performed to study slurry flow due to workpiece vibration. The modeling reveals a higher slurry velocity (2.20-2.46 m/s) in the target machining regions confined by the proximity of the tool tips and a lower velocity (0.16-0.50 m/s) elsewhere. To demonstrate and characterize the resulting machining ability, arrayed tools made from stainless steel #304 with feature sizes ranging from 5-50 µm were used on flat workpieces of fused silica. At 20-kHz vibration frequency and 12-µm tool-to-workpiece separation, the average machining rates ranged from 6-90 nm/s for workpiece vibration amplitudes ranging from 1-5 µm. The average surface roughness, S a , was 40-65 nm. The tool wear, i.e., the ratio of the tool height worn to the machined depth, was <4%.[2014-0216]