Bart Raeymaekers

Manipulation of diamond nanoparticles using bulk acoustic waves

We investigate the manipulation of 5 nm diamond nanoparticles in a user-defined pattern on a substrate using the acoustic radiation force associated with a bulk acoustic standing wave. Both concentric and rectangular patterns are studied and the experimental results are compared with theoretical predictions. The effect of drag force acting on a nanoparticle is evaluated and limits for particle speed and particle size that can be moved by acoustic radiation force are determined. We found good agreement between our experimental results and existing theoretical models and demonstrate that nanosized particles can be manipulated effectively by means of bulk wave acoustic radiation force.

The Effect of Texture Shape on the Load-Carrying Capacity of Gas-Lubricated Parallel Slider Bearings

Surface texturing is used to increase hydrodynamic pressure and reduce friction and wear between gas-lubricated parallel sliding surfaces. The shape, geometry, and density of the patterned microtexture features (“dimples”) play a key role in the tribological performance of the textured slider bearings. The objective of this paper is to compare the load-carrying capacity of commonly used dimple shapes for gas-lubricated textured parallel slider bearings. Six different texture shapes are considered, including spherical, ellipsoidal, circular, elliptical, triangular, and chevron-shaped dimples. The pressure distribution and load-carrying capacity generated by different texture shapes are simulated using the compressible Reynolds equation over a domain containing a column of ten dimples. The texture geometry and density are optimized in terms of maximum load-carrying capacity for each individual dimple shape, as a function of operating parameters such as relative velocity and spacing between the two sliding surfaces. The maximum load-carrying capacity of each individual texture shape—with optimized geometry and density—is then compared relative to each other. It is concluded that the ellipsoidal shape results in the highest load-carrying capacity, and the optimal geometry and density are found to be almost independent of the operating conditions.

Fretting Wear Between a Hollow Sphere and Flat Surface

Wear particles in a hard disk drive may cause the head/disk interface to fail. We have experimentally investigated wear particle generation resulting from fretting wear between the dimple on the suspension and the gimbal spring. We have found that increasing the normal load as well as using a low friction coating reduces the formation of wear particles.

The Effect of Determining Topography Parameters on Analyzing Elastic Contact Between Isotropic Rough Surfaces

Elastic contact between two computer-generated isotropic rough surfaces is studied. First the surface topography parameters, including the asperity density, mean summit radius, and standard deviation of asperity heights of the equivalent rough surface, are determined using an 8-nearest neighbor summit identification scheme. Second, many cross-sections of the equivalent rough surface are traced and their individual topography parameters are determined from their corresponding spectral moments. The topography parameters are also obtained from the average spectral moments of all cross-sections. The asperity density is found to be the main difference between the summit identification scheme and the spectral moments method. The contact parameters, such as the number of contacting asperities, real area of contact, and contact load for any given separation between the equivalent rough surface and a rigid flat, are calculated by summing the contributions of all the contacting asperities using the summit identification model. These contact parameters are also obtained with the Greenwood-Williamson (GW) model using the topography parameters from each individual cross-section and from the average spectral moments of all crosssections. Three different surfaces characterized by a different autocorrelation length, and three different sampling intervals were used to study how the method to determine topography parameters affects the resulting contact parameters.

Continuous and unconstrained manipulation of micro-particles using phase-control of bulk acoustic waves

A method of unconstrained and continuous manipulation of micro-particles in a fluid using bulk acoustic waves is theoretically derived and experimentally demonstrated. The method is based on phase-control of standing pressure waves created by two opposing transducers. Reflections are taken into account, removing the need for complex experiments. The operating domain of this method is characterized and compared to existing techniques. In contrast to methods based on linearly adjusting the phase difference between opposing transducers, it is shown that by independently controlling the phase of each transducer, particles can be manipulated in an unconstrained manner over multiple wavelengths.

Lateral Motion of an Axially Moving Tape on a Cylindrical Guide Surface

The lateral motion of a tape moving axially over a cylindrical guide surface is investigated. The effects of lateral bending stiffness and friction force are studied and the attenuation of lateral tape motion as a function of the guide radius and friction coefficient is determined. Good agreement between numerical predictions and experimental results is observed.

Measurement and Sources of Lateral Tape Motion: A Review

The sources of lateral tape motion in a tape drive are reviewed. Currently used measurement methods and models for lateral tape motion are analyzed and compared. The effect of roller run-out, tape edge contact, and tape tension transients on lateral tape motion is discussed. A dual stage actuator tape head is investigated to improve track-following capability and increase the track density on a magnetic tape.

Deformation of Ultra-Thin Diamond-Like Carbon Coatings Under Combined Loading on a Magnetic Recording Head

Ultra-thin diamond-like carbon (DLC) coatings are used in precision engineering applications, such as magnetic storage devices, to protect intricate structures from wear and corrosion. A DLC coating typically consists of hard amorphous carbon in combination with an interlayer such as silicon (Si), to improve adhesion to the substrate material. Deformation and delamination of these coatings, even in part, could expose the substrate material and compromise its integrity and functionality. We have implemented a molecular dynamics model to quantify the strength of the interface between an ultra-thin tetrahedral amorphous carbon coating, a Si layer, and a permalloy (NiFe) substrate, under combined normal and tangential loading that mimics accidental contact between the recording head and the disk of a hard drive. We have evaluated the effect of the thickness of the different coating layers on deformation and interfacial strength of the coating during combined loading. The results indicate that deformation occurs primarily in the Si layer, and at the interface between the Ni–Si and the Si–C layers. Permanent separation of the Si and ta-C layers is observed, which gradually increases with multiple combined loading cycles. We find that increasing the Si and carbon layer thickness strengthens the DLC coating. However, increasing the carbon layer thickness has a larger effect on coating strength than increasing the Si layer thickness.

The load-carrying capacity and friction coefficient of incompressible textured parallel slider bearings with surface roughness inside the texture features

Surface texturing is used to increase hydrodynamic pressure and reduce friction and wear between parallel sliding surfaces in a variety of applications. The shape, geometry, and density of the patterned microtexture features play a key role in the tribological performance of such textured slider bearings. Lubrication models are used to predict the load-carrying capacity, friction coefficient, and volume flow rate of textured bearings, assuming a smooth surface and ideal shape of the texture features. However, experimental evidence shows that manufacturing techniques such as laser surface texturing only approach the ideal shape of the texture features. Moreover, the manufacturing process typically creates roughness inside the texture features. In this paper, we numerically evaluate the effect of roughness inside the texture features on the load-carrying capacity, friction coefficient, and volume flow rate of the textured parallel slider bearing. We consider the cases of sinusoidal roughness and isotropic random roughness with Gaussian distribution of surface heights and find that the effect of roughness inside the texture features on the bearing load-carrying capacity and friction coefficient increases with increasing roughness height and increasing wavelength of the roughness. In addition, the effect of sinusoidal roughness is larger than the effect of isotropic random roughness with Gaussian distribution of surface heights. We also find that the roughness inside the texture features has negligible impact on the volume flow rate of the textured bearing.

Dynamic behavior of microscale particles controlled by standing bulk acoustic waves

We analyze the dynamic behavior of a spherical microparticle submerged in a fluid medium, driven to the node of a standing bulk acoustic wave created by two opposing transducers. We derive the dynamics of the fluid-particle system taking into account the acoustic radiation force and the time-dependent and time-independent drag force acting on the particle. Using this dynamic model, we characterize the transient and steady-state behavior of the fluid-particle system as a function of the particle and fluid properties and the transducer operating parameters. The results show that the settling time and percent overshoot of the particle trajectory are dependent on the ratio of the acoustic radiation force and time-independent damping force. In addition, we show that the particle oscillates around the node of the standing wave with an amplitude that depends on the ratio of the time-dependent drag forces and the particle inertia.