The maximum amount of repulsive force applied to the surface plays a very important role in damage of tip or sample in Atomic Force Microscopy(AFM). So far, many investigations have focused on peak repulsive forces in tapping mode AFM in steady state conditions. However, it is known that AFM could be more damaging in transient conditions. In high-speed scanning, and in presence of 3D nano structures (such as FinFET), the changes in topography appear in time intervals shorter than the response time of the cantilever. In this case, the tip may crush into the sample by exerting much higher forces than for the same cantilever-sample distance in steady state situations. In this study the effects of steep upward steps in topography on the tip-sample interactions have been investigated, and it has been found that the order(s) of magnitude higher forces can be applied. The information on the worst case scenario obtained by this method can be used for selection of operation parameters and probe design to minimize damage in high-speed imaging. The numerically obtained results have been verified with the previous works in steady state regime. Based on this investigation the maximum safe scanning speed has been obtained for a case study.
In this paper, we illustrate and study the opportunities of resonant ring type structures as wing actuation
mechanisms for a flapping wing Micro Air Vehicle (MAV). Various design alternatives are presented and studied
based on computational and physical models.
Insects provide an excellent source of inspiration for the development of the wing actuation mechanisms
for flapping wing MAVs. The insect thorax is a structure which in essence provides a mechanism to couple
the wing muscles to the wings while offering weight reduction through application of resonance, using tailored
elasticity. The resonant properties of the thorax are a very effective way to reducing the power expenditure
of wing movement. The wing movement itself is fairly complex and is guided by a set of control muscles and
thoracic structures which are present in proximity of the wing root.
The development of flapping wing MAVs requires a move away from classical structures and actuators. The
use of gears and rotational electric motors is hard to justify at the small scale. Resonant structures provide
a large design freedom whilst also providing various options for actuation. The move away from deterministic
mechanisms offers possibilities for mass reduction.
This paper presents an overview of a new type of thermal
micro-actuators using thermally expandable polymers with embedded skeletons. Embedding a stiff skeleton enhances the actuation capability of the thermally expandable polymer. Consequently, the skeleton-reinforced polymers feature a large maximum actuation stress
(often above 100 MPa) and a moderate maximum strain (often above 1%) besides a faster thermal response. In addition, the present composite design has room for performance improvement by tuning the volume fraction of the polymeric expander or selecting a proper expander material. Furthermore, the micro-actuators can be taylored for different motion characteristics, using various skeleton shapes. Finally, we discussed the possible applications using the present actuators.
Submicron cantilever structures have been demonstrated to be extremely versatile sensors and have potential applications
in physics, chemistry and biology. The basic principle in submicron cantilever sensors is the measurement of the
resonance frequency shift due to the added mass of the molecules bound to the cantilever surface.
This paper presents a theoretical model to predict the resonance frequency shift due to molecular adsorption on
submicron cantilevers. The influence of the mechanical properties of the adsorbed molecules bound to the upper and
lower surface on the resonance frequency has been studied. For various materials, the ratio between the thicknesses of
the adsorbed layer and the cantilever where either stiffness or added mass is dominant will be determined. The critical
ratio (which contribution of effect cancel each others) between the thickness of the adsorbed layer and the cantilever and
ratio between stiffness and density of adsorbed layer and cantilever have been determined. The calculations show the
added mass and stiffness how contribute to the resonant behavior. This model gives insight into the decoupling of both
opposite effects and is expected to be useful for the optimal design of resonators with high sensitivity to molecular
adsorption based on either stiffness or mass effects.
One area that can make use of the miniature size of present day micro electromechanical systems (MEMS) is that of the medical field of minimally invasive interventions. These procedures, used for both diagnosis and treatment, use catheters that are advanced through the blood vessels deep into the body, without the need for surgery. However, once inside the body, the doctor performing the procedure is completely reliant on the information the catheter(s) can provide in addition to the projection imaging of a fluoroscope. A good range of sensors for catheters is required for a proper diagnosis. To this end, miniature sensors are being developed to be fitted to catheters and guide wires. As the accurate positioning of these instruments is problematic, it is necessary to combine several sensors on the same guide wire or catheter to measure several parameters in the same location. This however, brings many special problems to the design of the sensors, such as small size, low power consumption, bio-compatibility of materials, robust design for patient safety, a limited number of connections, packaging, etc. This paper will go into both the advantages and design problems of micromachined sensors and actuators in catheters and guide wires. As an example, a multi parameter blood sensor, measuring flow velocity, pressure and oxygen saturation, will be discussed.
The small size and possible low cost of micromachined sensors make them attractive for some medical applications. Minimally invasive therapy aims to reduce the damage done to healthy tissue by reaching the affected area through existing pathways through the body. However, information is scarce as direct view or touch is lacking. Small sensors are needed on catheters inside the blood vessels to gather the data such as blood pressure and flow. To this end a combined pressure and flow sensor is fabricated in an epi-poly process that uses a 4 micrometer thick polysilicon membrane grown during epitaxial growth, to form the diaphragm of the pressure sensor and the thermal insulation of the thermal flow sensor. Using RIE etching of holes through the membrane, sacrificial etching and closing of the etch holes by oxide depositions, a closed reference chamber is formed for an absolute pressure sensor. The process is compatible with standard bipolar electronics to enable integration of signal conditioning, multiplexing, etc. Measurements of the two sensors show that fabrication of flow and pressure sensors using epi-micromachining is possible and that the sensors have the required measurement range, but drift necessitates calibration before use.
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