K. Sumangala

Nondestructive Evaluation of Prestressed Concrete Beams using an Artificial Neural Network (ANN) Approach

An artificial neural network (ANN) based approach for the assessment of damage in prestressed concrete (PSC) beams using its present stiffness and natural frequency as the test inputs to the ANN has been proposed. The details of the extensive experimental programme designed and executed in this study to induce the known extent of damage in the PSC beams by a method that resembles natural damage processing techniques and to generate the training and test data for the ANN used to model damage levels have been presented. It has been demonstrated that it is possible to assess the damage with reasonable accuracy by the ANN learning by a back propagation algorithm and stiffness and natural frequency as test inputs. The efficiency of this damage assessment algorithm has been studied by testing this ANN with the test data available in the literature. The results indicate that this approach can be used as a cost effective and simple structural health monitoring tool for PSC beams since this procedure needs only limited nondestructive static and dynamic measurements on the structure under study.

Low Actuation Voltage RF MEMS Switch Using Varying Section Composite Fixed-Fixed Beam

The present authors have earlier reported the employment of varying section fixed-fixed beam for achieving lower pull-in voltage with marginal fall in restoring force. Reducing Young’s modulus also reduces the pull-in voltage but with lesser degree of reduction in restoring force. Composite beams are ideal alternatives to achieve decreased Young’s modulus. Hence new varying section composite fixed-fixed beam type RF MEMS switch has been proposed. The main advantage of this RF MEMS switch is that lower pull-in voltages can be achieved with marginal fall in stiction immunity. Spring constant of the proposed switch has been obtained using simulation studies and it has been shown that the spring constant and therefore the pull-in voltage ( ) can be considerably reduced with the proposed switch. Simulation studies conducted on the proposed switch clearly demonstrate that the pull-in voltage can be reduced by 31.17% when compared to the varying section monolayer polysilicon fixed-fixed beam. Further this approach enables the designer to have more freedom to design lower pull-in voltage switches with improved stiction immunity.

A new procedure for damage assessment of prestressed concrete beams using artificial neural network

A damage assessment procedure has been developed using artificial neural network (ANN) for prestressed concrete beams. The methodology had been formulated using the results obtained from an experimental study conducted in the laboratory. Prestressed concrete (PSC) rectangular beams were cast, and pitting corrosion was introduced in the prestressing wires and was allowed to be snapped using accelerated corrosion process. Both static and dynamic tests were conducted to study the behaviour of perfect and damaged beams. The measured output from both static and dynamic tests was taken as input to train the neural network. Back propagation network was chosen for this purpose, which was written using the programming package MATLAB. The trained network was tested using separate test data obtained from the tests. A damage assessment procedure was developed using the trained network, it was validated using the data available in literature, and the outcome is presented in this paper.

Design of Stictionfree - Lower Pull in Voltage RF MEMS Switch Using Varying Section Cantilever Beam

A new varying section cantilever beam type RF MEMS switch has been proposed. The main advantage of this switch is that it is inherently stiction free and therefore enhances design flexibility. An analytical model developed using unit load approach for the spring constant of the proposed switch has been presented and it has been shown that the spring constant and therefore the pull in voltage (Vpi) can be considerably reduced with the proposed switch. Simulation studies conducted on two groups of devices clearly demonstrate that the pull in voltage can be reduced by 26% with ten sections. Comparision of the pull in voltage obtained in the simulation studies for devices with the theoretically estimated Vpi shows that the spring constant model presented in this paper accurately estimates the spring constant. The results of analytical studies also demonstrate that the new proposed cantilever beam can considerably reduce the pull in voltage.

Effect of aspect ratio on the ladder type triangle micro channels employed micro cooling systems

Effective heat transfer in micro cooling systems for VLSI circuits requires large substrate area that is in contact with the flowing liquid and availability of large mass of fluid to carry away the heat. Such heat sinks formed with a collection of parallel ladder type micro channels with triangular cross section extends wall area, provides moderate heat transfer coefficient thus achieving lesser thermal resistances at less pumping power as reported earlier. In this work, the authors have studied the performance of four groups of such devices having five height-to-width ratios using COMSOL multiphysics. The performance-indicating parameters of such heat sinks show that high performance heat sinking can be achieved when the height-to-width ratio is high. It is indeed an interesting finding because this gives larger freedom in the design and it is possible to design the micro coolers with least pumping power and thermal resistance.