Microsystem Technologies

Mechanical properties of rotors supported by fluid dynamic bearings (FDBs) cannot be directly measured because most of the mechanical properties of FDBs become active only when the rotors are in revolutionary motion. A typical example is the measurement of mechanical stiffness of the rotors that are used for hard disk drives. A popular measurement method so-called pitch modes requires the rotor to be loaded with disks and rotated at a particular revolutionary speed to maintain a certain mechanical stiffness for the pitch mode measurement. Although the measured pitch modes could represent the mechanical stiffness of the rotors, this approach is rather ad hoc. In this article an attempt is made for eliminating the dummy loads and the mechanical contacts by using hydrodynamic force induced excitations. Applying a compressed airstream to a rotating FDB that generates radial shift of the rotor, the proposed method determines mechanical stiffness of the rotor by relating the air pressure and the radial displacement. A whole design process including numerical validation and component calibration is explained and a series of hardware verification testing is also performed.

 Thermal microheaters as used for example in thermal ink print heads contain a variety of materials, the heater itself is commonly based on refractory metals. Here, a novel concept based on diamond as a multifunctional material is proposed and demonstrated. In this concept, diamond serves as an insulating substrate, a metal-like heater and as a temperature sensor. Superheating of water could be achieved after 7.5 μs heating of a 60×60 μm element. Bubble nucleation was visualized using a high speed stroboscopic technique. The influence of the diamond thermal properties and geometry on the thermal response were investigated by dynamic 3D-simulations.

For assessing the quality of the joining area as well as researching the influence of joining parameters in combination with different materials, the principal stress components of sinter-joined micro valves were analysed. Transmission experiments have been conducted at the high-energy material science (HEMS) beamline P07 at PETRA III, DESY. Due to the dimensions of the samples, a high spatial resolution of the measurements was required. Of special interest was the distribution of residual stress in the joining area of the valves, which demanded a depth resolved measurement using a conical slit. Strains were deduced from the obtained Debye–Scherrer rings of the {200}, {211}, and {220}-planes of the α/α′-phase involving reference measurements on non-sintered powder of the specimen materials. The grain statistics have been improved by integrating over slices of the diffraction rings and by calculating a mean lattice parameter taking into account all lattice planes. From the strain data, the hydrostatic and the deviatoric stress were calculated for the three dimensional stress state.

In this paper, effect of surface, including its elasticity, residual stress and density is investigated on the nano-beam stiffness and mass analytically. To this aim, the governing equation of the nano-beam dynamic behavior is extracted utilizing Gurtin–Murdoch’s theory and Euler–Bernoulli hypothesis which incorporates the surface effects. Effect of surface parameters on nano-beam lumped mass and stiffness is investigated parametrically and necessary conditions for hardening and softening behavior are presented based on the surface stress and elasticity for both clamped–clamped and clamped-free nano-beams. The performed analysis revealed that surface may have different effects on similar nano-beams with only different boundary conditions. The obtained results in this paper can be utilized in analysis and design of nano-systems.

This paper presents a simple method to produce microfluidic channels in soda-lime glasses with the aspect ratio >0.5 utilizing a modified wet etching protocol. A low-cost positive photoresist (PR) layer is used as the etching mask for the wet etching process. Prior to the PR and primer coating procedure, a UV activation process is adopted for enhancing the binding strength of the hexamethyldisilazane primer layer and the glass substrate, resulting in an better adhesion for the PR layer. A fast etching recipe is also developed by increasing the acidity and the temperature of the buffered oxide (BOE) etchant. Since the photoresist etching mask does not peel during the etching process shortly, the structure of the etching mask forms a barrier and results in a different diffusion rate for the etchant inside the etched trench structure. A slower etching rate for the glass is observed at the undercut region such that the proposed anisotropic etching pattern can be achieved. Results show that the etching rate of the modified glass etching process is as high as 7.7 μm/min which is much faster than that of pure BOE etchant (0.96 μm/min). Sealed microfluidic channel with the aspect ratio of around 0.62 is produced with the developed method. The method developed in the present study provides a rapid and efficient way to produce microfluidic channels with higher aspect ratio.

In this work, a mathematical model of three layers system represents how the external thermal shock passing through the three layers of the head: skin, bone, and brain. In this model, we will take into account the internal heat source generated within the human head from the chemical reactions of the tissue and the lag-time to study the response time of the tissue takes due to the perturbation. The materials parameters of the head for an adult and a child have been used to studying and comparing the two cases. Laplace transforms have been used and the inversions have been calculated numerically. We studied the thermal distribute through the human head with different values of time, depth, relaxation time, the frequency of power transmission, and power density. It was shown that all that parameters have significant effects on the human head and the thermal distribution is more harmful to the child than the adult.