With the ongoing miniaturization of surgical instruments, the ability to apply large forces on tissues for resection becomes challenging and the risk of buckling becomes more real. In an effort to allow for high force application in slender instruments, in this study, we have investigated using a hydraulic pressure wave (COMSOL model) and developed an innovative 5F cardiac catheter (L = 1,000 mm) that allows for applying high forces up to 9.0 ± 0.2 N on target tissues without buckling. The catheter uses high-speed pressure waves to transfer high-force impulses through a slender flexible shaft consisted of a flat wire coil, a double braid, and a nylon outer coating. The handle allows for single-handed operation of the catheter with easy adjusting of the input impulse characteristic, including frequency (1–10 Hz), time and number of strokes using a solenoid actuator, and easy connection of an off-the-shelf inflator for catheter filling. In a proof-of-principle experiment, we illustrated that the Wave catheter was able to penetrate a phantom model of a coronary Chronic Total Occlusion (CTO) manufactured out of hydroxyapatite and gelatin. It was found that the time until puncture decreased from 80 ± 5.4 s to 7.8 ± 0.4 s, for a stroke frequency of 1–10 Hz, respectively. The number of strikes until puncture was approximately constant at 80 ± 5.4, 76.7 ± 2.6, and 77.7 ± 3.9 for the different stroke frequencies. With the development of the Wave catheter, first steps have been made toward high force application through slender shafts.@en

The objective of this research is to demonstrate the capability of a long stroke linear ferrofluid (FF) stage. This stage is a passive alternative to existing linear aerostatic stages and can be used in low loaded CNC devices, pick and place machines, microscopy or scanner applications. To compete with aerostatic stages the bearing must be repeatable and achieve sufficient stiffness for the application. The effects of ferrofluid trail formation are countered with the use of a ferrofluid reservoir located on the mover. To increase stiffness a specially designed magnet configuration is used. A linear guidance was built with outer dimensions of 180x600x80 mm (WxLxH), a mover of 1.8 kg without actuator and payload having a 430 mm stroke. The load capacity of the stage was measured to be 120 N, with a stiffness of 0.4 N/μm. The maximum height delta after a stroke with 1 kg payload and a mover velocity of 0.25 m/s was measured to be less than ±3μm, and with 1.75 kg payload and a velocity of 0.5 m/s the height delta was within ±7μm. Using a rheometer, it was shown that the effects of evaporation in ferrofluid can be reversed, within certain limits of mass loss, by adding carrier fluid. The damping is shown to be a function of payload and velocity and was measured to be between 2 and 4 N⋅s/m for velocities between 0.2 and 0.5 m/s. In comparison to a linear aerostatic stage it can be concluded that while the linear ferrofluid stage is outperformed in stiffness and out-of-plane repeatability, the ferrofluid stage does not require a continuous supply of air and has lower fabrication tolerances due to the higher fly height. Thus, the linear ferrofluid stage is a cost-effective alternative to a linear aerostatic stage when the stiffness and straightness are of less importance.

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The novel contribution of this research is insight into the influence of different parameters in the magnet configurations on the load and stiffness of a ferrofluid pressure bearing. It is shown that magnets with a small cross-section magnetized alternatively up and downwards combine a high load capacity and moderate stiffness while being low on material cost and complexity. The configuration where magnets are placed alternatively in left and right direction magnetized inter spaced with iron yields the highest load capacity and stiffness, albeit at the cost of weight and complexity. It is shown that an increase in the number of magnets is beneficial for the stiffness in both magnetization configurations, as is an increase in remanent flux density of the magnet. A metal bottom plate made of iron reduces the necessary height of the magnet in the up-down magnetization configuration. The model was validated using a bearing pad arranged in the up-down configuration. The force-displacement curve of this pad was measured in a load frame, using the APG 513 ​A ferrofluid from Ferrotec. A load capacity of 1.75 ​N/cm² was achieved, this exceeds previous pressure bearing implementations and performs comparable or better than implementations of single seal ferrofluid pocket bearings. These results show that the ferrofluid pressure bearing is a passive alternative in motion systems where the designer otherwise would have needed to use an active bearing.

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This paper presents a comparison on resonance energy harvester power output in the real world versus three benchmark experiments containing elements measured in the real-world vibration. An one degree of freedom electromagnetic energy harvester is built and tested in various lab experiments using an electrodynamic shaker; a sinusoidal frequency sweep, power spectrum matching noise and real-world waveform replication. Comparing to the real-world power output, the frequency sweep indicated a 50% underestimation, the power spectrum matching noise experiment resulted in a 50% overestimation and the field wave replication remained within 7% error. Results indicate the essence of vibration energy harvester performance testing on real-world vibrations, to obtain an accurate performance indication.@en

A major challenge during minimally invasive surgery is transfer of high forces through small, flexible instruments, such as needles and catheters, because of their low buckling resistance. In this study, we determined the feasibility of using a Newton's Cradle-inspired catheter (patented) to transfer high-force impulses. Exerting a high-force impulse on the tissue increases the critical buckling load and can prevent buckling. The system comprised an input plunger onto which the impulse is given, a (flexible) shaft filled with Ø2 mm stainless steel balls, and an output plunger to transfer the impulse to the target tissue. In the proof-of-principle experiment, the effect on efficiency of clearance (0.1, 0.2, and 0.3 mm), length (100, 200, and 300 mm), shaft type (rigid vs. flexible), curve angle (0, 45, 90, 135, and 180°), and curve radius (20, 40, 60, and 100 mm) was determined. The catheter delivered forces of 6 N without buckling. The average impulse efficiency of the system was 35%, which can be further increased by optimizing the design. This technology is promising for high-force delivery in miniature medical devices during minimally invasive surgery.@en

Ferrofluid pocket bearings are a type of bearing that are able to carry a load using an air pocket encapsulated by a ferrofluid seal. Previously designed ferrofluid bearings show the great potential of the stick-slip-free and low viscous friction bearings, however until now the load capacity is limited. In this article a method is presented to increase the load capacity in a simple and cost effective way by the addition of ferromagnetic material around the magnet. First, a mathematical model of the bearing is presented and is validated by experiments using an axially magnetized ring magnet surrounded by two steel rings. The model is used to optimize the dimensions of the added ferromagnetic material for maximum load capacity. Depending on the fly height, the load capacity has been increased by a factor three to four by the addition of steel rings to the ferrofluid pocket bearing configuration.

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Ferrofluid pocket bearings are interesting for fast and precise positioning systems thank to the absence of stick-slip, the low viscous friction and their cost-effective nature. However, the characteristics of the bearing change due to over(de)compression since air escapes out of the enclosed pocket. This article presents an experimentally validated model that includes the air mass inside the pocket in the calculation of the equilibrium position of the ferrofluid bearing. Moreover, a simple and efficient way to obtain the operational range of the bearing is presented and a sensitivity analysis was performed. The sensitivity analysis showed that ferrofluid pocket bearings are always self-aligning and that the tilt stiffness increases when the fly height decreases or the tilt angle increases.@en

High-precision positioning often requires high speed and high resolution displacement measurements in order to compensate for the small vibrations of critical components. The displacement sensor must be precise and stable over a long period of time to avoid expensive recalibration. This requires tight mounting tolerances, which are especially difficult to meet in inaccessible environments. The proposed sensor system is based on a capacitive sensor and consists of three subsystems: 1) a mechanical ``zoom-in'' system that performs self-alignment of the capacitive sensor electrode in order to reduce the mounting tolerances of the sensor; 2) a real-time capacitance-to-digital converter that employs an internal reference and electrical zoom-in technique to effectively reduce the dynamic range of the measured capacitance, thus improving the power efficiency; and 3) a self-calibration circuit that periodically calibrates the internal references to eliminate their drift. In previous publications, the three subsystems have been introduced. This paper shows how the different subsystems can be integrated to achieve optimal performance and presents new repeatability and stability measurement results. The overall system demonstrates a displacement measurement resolution of 65 pm (in terms of capacitance 65 aF) for a measurement time of 20 μs. Furthermore, the thermal drift of the sensor is within 6 ppm/K, owing to the self-calibration circuit. In measurement mode, the system consumes less than 16 mW.@en

Ferrofluid bearings have recently been successfully implemented in precise positioning systems. This article gives an overview of systems built in the Department of Precision and Microsystems Engineering at Delft University of Technology in the Netherlands. Most applications are in microscope stages, where high accuracy is important while stroke and speed attain only moderate levels. Furthermore, some basic theory is provided on ferrofluid bearings that can help engineers incorporate ferrofluid bearings in their designs.@en

Crossing highly calcified occlusions is technically challenging mainly due to guidewire buckling. In an effort to prevent buckling, a catheter that uses a dynamic impulse load is proposed. The proposed Wave catheter consists of an input plunger to generate an impulse at the handle, a hydraulic pressure wave confined within a ∅2 mm catheter to transfer the impulse towards the tip, and an output plunger to transfer the impulse to the occlusion. To determine the feasibility of this catheter, an experiment was performed in which the input and output impulses were recorded as a function of the catheter type, curvature, and plunger travel distance. Additionally, the system was tested on artificial CTO models to determine the clinical validity. The catheter has illustrated the ability to safely transfer high-force impulses of up to 43 N (1.5 N required) with only minimum catheter type and no curvature dependency, allowing for delivering high-force impulses through tortuous vasculature and under any angle. Furthermore, the catheter was able to penetrate the artificial CTO models within 1 strike.@en

A ferrofluid pocket bearings is a type of hydrostatic bearing that uses a ferrofluid seal to encapsulate a pocket of air to carry a load. Their properties, combining a high stiffness with low (viscous) friction and absence of stick-slip, make them interesting for applications that require fast and high precision positioning. Knowledge on the exact performance of these types of bearings is up to now not available. This article presents a method to model the load carrying capacity and normal stiffness characteristics of this type of bearings. Required for this is the geometry of the bearing, the shape of the magnetic field and the magnetization strength of the fluid. This method is experimentally validated and is shown to be correct for describing the load and stiffness characteristics of any fixed shape of ferrofluid pocket bearing.

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Ferrofluid bearings have been demonstrated to be very interesting for precision positioning systems. The friction of these bearings is free of stick-slip which results in an increase of precision. More knowledge on the friction behaviour of these bearings is important for there application in precision positioning systems. This paper demonstrates that the friction of a ferrofluid bearing can be modelled by a viscous damper model and provides a basic model to predict the friction behaviour of a bearing design. The model consists of a summation of a Couette flow with a Poiseuille flow such that there is no net fluid transport under the bearing pads. The model is experimentally validated on a six degrees of freedom stage using ferrofluid bearings. A stiffness in the form of a closed-loop control gain is introduced in the system to create a resonance peak at the desired frequency. The damping coefficient can be identified from the peak height of the resonance, since the peak height is the ratio of total energy to dissipated energy in the system. The results show that the newly derived model can be used to make an estimate of the damping coefficient for small(∼1mm) stroke translations. Furthermore, the model shows that the load capacity of a ferrofluid pocket bearing is affected during sliding.

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A cost-effective position measurement system based on optical mouse sensors is presented in this work. The system is intended to be used in a planar positioning stage for microscopy applications and as such, has strict resolution, accuracy, repeatability, and sensitivity requirements. Three techniques which improve the measurement system's performance in the context of these requirements are proposed; namely, an optical magnification of the image projected onto the mouse sensor, a periodic homing procedure to reset the error buildup, and a compensation of the undesired dynamics caused by filters implemented in the mouse sensor chip.

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A demonstrator adaptive optics-system with a thermally actuated active mirror (AM) is presented to pre-study feasibility of sub-nm wavefront control in extreme ultraviolet (EUV) lithography. The AM is thermally actuated by selective heating using a spatial controllable heat source. Four different methods have been implemented to control the deformation of the AM. First thermal feedforward using estimated state feedback (ESF), second thermal feedback using proportional integral (PI) control, third their combination and fourth deformation feedback using PI control. To support ESF, a thermo-elastic finite element model is employed that describes the thermal deformation of the AM. ESF shows satisfying performance with a time constant of 10 s and a residual error of 0.7 nm. Thermal feedback shows large fluctuations of 12 nm for spherical aberrations of due to feedback of noise from the thermal camera. By applying deformation feedback the RMS-error is reduced to a satisfying 0.25 nm. This study shows that deformation control of this AM can be realised using thermal feedforward and deformation feedback to meet the requirements for EUV lithography.@en

Due to the absorption of extreme ultraviolet (EUV) light in the projection optical system of an EUV lithography machine, its mirrors thermally deform resulting in wavefront errors (WFEs) that deteriorate the imaging process. In order to compensate and correct for these mirror deformations, this paper proposes an adaptive optics (AO) system that uses an active mirror (AM) to counteract these WFEs. For this purpose, a list of system and mirror requirements is composed as well as a list of design choices, which motivate the AM design. In order to asses the specifications of this AM, finite element method (FEM) and experimental analyses are carried out to obtain and validate the general properties of the AM. For assessing linearity, the formal definition of linearity is used and verified in the experimental set-up. The instrument transfer function (ITF) is obtained by actuating the AM with different spatial frequencies fx and measuring the deformation amplitude. The AM is proven to be linear given a linear coefficient of thermal expansion (CTE) and the ITF shows a trend for both the time constant and the amplitude of the deformation. By using the ITF it is shown that the characteristics of the AM is suitable for an AO system for EUV lithography.@en

In EUV lithography, the absorption of EUV light causes wavefront distortion that deteriorates the imaging process. An adaptive optics system has been developed [“Adaptive optics to counteract thermal aberrations,” Ph.D. thesis (TU Delft, 2013)] to correct for this distortion using an active mirror (AM). This AM is thermally actuated by absorbing an irradiance profile exposed by a projector onto the AM. Due to thermal conductivity and bimorph-like deformation of the AM, the relation between actuation profile and actuated shape is not trivial. Therefore, this Letter describes how actuation profiles are obtained to generate Zernike shapes. These actuation profiles have been obtained by a finite-element-based optimization procedure. Furthermore, these actuation profiles are exposed to the AM, and the resulting deformations are measured. This Letter shows actuated Zernike shapes with purities higher than 0.9 for most actuation profiles. In addition, superimposed actuation profiles resulted in superimposed Zernike shapes, showing linearity needed to apply modal wavefront correction. Therefore, this approach can be used to obtain actuation profiles for this AM concept, which can be used for highly precise wavefront correction.@en