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In-situ SEM analysis tool for stretchable metal-elastomer-laminate-membranes for flexible sensors
(2023)
Feasibility of Parylene C for encapsulating piezoelectric actuators in active medical implants
(2023)
Parylene C is well-known as an encapsulation material for medical implants. Within the approach of miniaturization and automatization of a bone distractor, piezoelectric actuators were encapsulated with Parylene C. The stretchability of the polymer was investigated with respect to the encapsulation functionality of piezoelectric chips. We determined a linear yield strain of 1% of approximately 12-μm-thick Parylene C foil. Parylene C encapsulation withstands the mechanical stress of a minimum of 5×105 duty cycles by continuous actuation. The experiments demonstrate that elongation of the encapsulation on piezoelectric actuators and thus the elongation of Parylene C up to 0.8 mm are feasible.
The charge response of a force applied to piezoelectric stack actuators was characterized in the range of 0 N – 20 N for application in piezoelectric self-sensing. Results show linear behavior between ap-plied force and collected charge for both actuators tested in this study. One actuator exhibits a 3.55 times higher sensitivity slope than the other related to its larger capacitance. An error analysis reveals a reduction of relative error in charge measurement with rising forces applied to the actuators.
In this work, we characterise a flexural mechanical amplifier, which is used for the realisation of a miniaturised piezoelectric inchworm motor designed for large force (some N) and stroke (tens of mm) operation as it is required e.g., for medical implants. The characterisation is based on high precision optical displacement measurements and a force self-sensing approach. An optically measured displacement of 292 nm in lateral direction and 910 nm in vertical direction of the flexural mechanical amplifier has been obtained, corresponding to a deflection attenuation factor of 3.1. Piezoelectric self-sensing of force was used to determine a force amplification factor of 3.43 from the mechanical oval structure.
Investigations to improve the adhesion between the PECVD coated silicon carbide thin films and monocrystalline (110) silicon wafer substrate is reported. The surface treatment of silicon wafer is realized by roughening the wafer surface by wet etching in 1.8M potassium hydroxide solution at 50°C with ultrasonic agitation. The average surface roughness of the silicon wafer was increased from 2.9 nm for polished wafer to a range between 32 nm to 250 nm by wet etching for a duration of 10 minutes to 55 minutes, respectively. The adhesion between the PECVD coated silicon carbide thin films (ca. 300 nm thickness) and the silicon wafers with varying surface roughness was characterized by means of scanning scratch test. The critical load initially increased from 153 mN to 169 mN on increasing the average surface roughness from 2.9 nm to 33 nm, respectively. While with further increase in average surface roughness adversely in-fluenced the adhesion indicated by a gradual decrement in the critical load to 124 mN for the maximum investigated average surface roughness of 250 nm.
Microfabricated 2D inductive eddy-current transducers operating in a reflection differential transmitter-receiver mode are presented for the micro nondestructive detection of micro grinding burn. 2D spiral circular microcoils are employed as excitation coils, while an innovatively conceptualized “interconnected split-D” type differential microcoil is used as a sensing coil. Finite element modelling using COMSOL revealed the efficacy of proposed concept in non-destructive testing of small grinding burn having a width of 100 µm. The induced sensing coil voltage changed as a function of presence of grinding burn, with successful recording of the signal for the investigated lift-off range of 250 µm - 1000 µm for 100 kHz to 1 MHz driving frequencies of excitation coil. Experimental validation showed a 94% increase in the induced voltage of the sensing coil in presence of grinding burn on increasing the driving frequency of excitation coil from 100 kHz to 1 MHz. Thereby, revealing the superficial nature of the grinding burn defect, and showing the efficacy of the proposed concept for the non-destructive testing of grinding burn.