Refine
Year of publication
Document type
- Conference Proceeding (130)
- Article (peer-reviewed) (66)
- Report (34)
- Contribution to a Periodical (13)
- Other (9)
- Part of a Book (5)
- Book (2)
Language
- English (165)
- German (93)
- Multiple languages (1)
Keywords
- CD-ROM (28)
- Porous silicon (15)
- Poster (11)
- Patent (9)
- MEMS (6)
- MOEMS (6)
- Silicon (5)
- FEM simulation (3)
- Needles (3)
- Photonic crystal (3)
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.
The influence of bath hydrodynamics on the resultant micromechanical properties of electrodeposited nickel-cobalt alloy system is investigated. The bath hydrodynamics realized by magnetic stirring is simulated using COMSOL Multiphysics and a region of minimum variation in velocity within the electrolytic cell is determined and validated experimentally. Nickel-cobalt alloy and nickel coating samples are deposited galvanostatically (50 mA/cm2) with varying bath velocity (0 to 42 cm/s). The surface morphology of samples gradually changed from granular (fractal dimension 2.97) to more planar (fractal dimension 2.15) growth type, and the according average roughness decreased from 207.5 nm to 11 nm on increasing the electrolyte velocity from 0 to 42 cm/s for nickel-cobalt alloys; a similar trend was also found in the case of nickel coatings. The calculated grain size from the X-ray diffractograms decreased from 31 nm to 12 nm and from 69 nm to 26 nm as function of increasing velocity (up to 42 cm/s) for nickel-cobalt and nickel coatings, respectively. Consecutively, the measured Vickers microhardness values increased by 43% (i.e., from 393 HV0.01 to 692 HV0.01) and by 33% (i.e., from 255 HV0.01 to 381 HV0.01) for nickel-cobalt and nickel coatings, respectively, which fits well with the Hall–Petch relation.
The approach of using current transients to model the nucleation rate as reported in the seminal work of Scharifker and Mostany is limited to electrodeposition system without bath hydrodynamics (BHD). Therefore, in this work in situ electroanalytical approach is proposed to unveil the influence of BHD on the nucleation kinetics of electrochemically deposited Nickel-Cobalt alloy system (eNiCo). Using the Hydrodynamic linear sweep voltammetry (HLSV) technique, the limiting current density as a function of BHD is computed, wherein it increased (for eNiCo alloys) from 186 mA/cm² to 222.6 mA/cm² on increasing BHD from 0 to 42 cm/s, respectively. Consecutively, the diffusion layer thickness is found to decrease from 19 µm to ca. 15.8 µm on increasing BHD from 0 to 42 cm/s, respectively. Additionally, from Nyquist plots recorded using the Galvanostatic Electrochemical Impedance Spectroscopy (GEIS), the charge transfer coefficient (Rct), exchange current density (io) and double layer capacitance (Cdl) as a function of BHD is computed. It is found that Rct decreased and io, Cdl increased as function of BHD. Thereby, indicating the enhancement in the charge transfer on the cathode surface and reduction in the thickness of the diffusion layer. Hence, with the use of BHD, it is possible to control the growth kinetics, therefore enabling the deposition of tailor-made materials possessing specific required properties.
A sensor fusion concept integrating the optical and microfabricated eddy-current sensor for the non-destructive testing of the grinding burn is reported. For evaluation, reference grinding burn with varying degrees are fabricated on 42CrMo4 tool steel cylinder. The complementary sensing nature of the proposed sensors for the non-destructive testing of the grinding burn is successfully achieved, wherein both the superficial and an in-depth quantitative profile information of the grinding zone is recorded. The electrical output (voltage) of the optical sensor, which is sensitive to the optical surface quality, dropped only by 20 % for moderate degree of grinding burn and by ca. 50 % for stronger degree of grinding burn (i.e. by exclusively considering the superficial surface morphology of the grinding burn). Moreover, a direct correlation among the average surface roughness of the grinding burn, the degree of grinding burn and the optical sensor’s output voltage was observed. The superficial and in-depth information of the grinding burn was recorded using a microfabricated eddy-current sensor (planar microcoil with circular spiral geometry with 20 turns) by measuring the impedance change as function of the driving frequency. The depth of penetration of induced eddy-current in the used 42CrMo4 workpiece (with a sensor to workpiece distance of 700 µm) varied from 223 µm to 7 µm on increasing the frequency of the driving current from 1kHz to 10 MHz, respectively. A very interesting nature of the grinding burn was observed with two distinct zones within the grinding zone, namely, the superficial zone (starting from the workpiece surface to 15 µm in grinding zone) and a submerged zone (>15 µm within the grinding zone). The impedance of the microcoils changed by ca. 8 % and 4 % for the superficial and submerged zone for regions with stronger degree of grinding burn at a frequency of 10 MHz and 2.5MHz, respectively. Furthermore, a correlation between the microhardness of the grinding burn and the impedance change is also observed.
Optimization of Microfabricated 2D Planar Spiral Microcoils for the Micro NDT of Grinding Burn
(2020)
In situ Qualitätsbeurteilung von Schleifprozessen mittels Mikrosystemtechnik basierter Sensorfusion
(2020)
Real time In-Situ Quality Monitoring of Grinding Process using Microtechnology based Sensor Fusion
(2020)
Flexible piezoresistive PDMS metal-thin-film sensor-concept for stiffness evaluation of soft tissues
(2019)
Semi-rigid ring-shaped electrode dielectric electroactive polymer membrane as buckling actuator
(2019)
Influence of current density on the adhesion of seedless electrodeposited copper layers on silicon
(2019)
Smart Energy: Miniaturisierte Energieversorung für autarke mikroelektronische und Mikro-Systeme
(2009)
Skalierbare Verbindungstechnik mittels anpassbarer nanoskaliger Verbindungsstrukturen (NanoBond)
(2009)
Mikrosystemtechnik: Mikrotechnische hergestelltes aktiv-optisches System für Fokussieraufgaben
(2005)
Sensorik: Porous Silicon Based Humidity Sensor with Interdigital Electrodes and Internal Heaters
(2002)
Aktorik: Nanomotor
(2000)
Movement giver
(2001)
Bewegungsgeber
(2000)
Bewegungsgeber
(2001)