Browsing by Author "Rao, Venkatesh K.P."

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Analysis of vibration based windmill coupled micromachined energy harvester
(Vibroengineering Procedia, 2019-11) Rao, Venkatesh K.P.
The present work exploits the centripetal, Coriolis and Euler forces generated in a rotating windmill. The MEMS device is placed on the blade of a windmill to harvest the energy. Modal analysis is carried out to optimize the dimensions of the structure to match the desired conditions. The real time response of the structure and the voltage generated in the piezoelectric layer are evaluated using transient analysis. It was noticed that Euler and Coriolis forces have a significant contribution in the initial time when the wind turbine accelerates from rest. The later portion is dominated by the Coriolis and Euler forces, and in some instances they cancel out each other. However, there is always a steady contribution from the centripetal force which is proportional to the magnitude of angular velocity of the wind turbine.
Atomistic analysis of the effect of cholesterol on cancerous membrane protein system: unfolding and associated resistance stresses under strain
(Taylor & Francis, 2023-05) Rao, Venkatesh K.P.; Belgamwar, Sachin U.
The low-cholesterol cancerous environment can affect the biophysical behaviour of transmembrane proteins. It is difficult to experiment and measure the dynamics of membrane protein systems when cholesterol concentration is decreasing. In this work, atomistic approach is adopted to investigate the transmembrane protein behaviour during lipid-bilayer separation under strain at different cholesterol concentrations. Finding shows that the decreasing cholesterol across membrane protein system leads to an increase in area-per-lipid and average tilt angle by 6.4% and 62.6%, respectively with decreased order parameter. This observation indicates that the decreased cholesterol concentration in a cancerous environment hinders the bonding and compactness of membrane protein system. Stretching and unfolding of protein were observed during bilayer separation and the resistance stresses decreased by 68.01% for decreasing cholesterol. The cholesterol molecules observed to be bonded with proteins. The investigation revealed that the cholesterol is an important constituent of membrane that impedes the diffusion and resist the detachment of protein at high concentration. Thereby, the transmembrane proteins can retain end terminals positions across the membrane and resist functional failure. This study showed that decreased cholesterol concentration causes significant changes in the biophysical behaviour of the membrane protein system that could trigger the mechanosensitivity of transmembrane proteins under mechanical perturbation.
Atomistic approach to analyse transportation of water nanodroplet through a vibrating nanochannel: scope in bio-NEMS applications
(Taylor & Francis, 2022-03) Belgamwar, Sachin U.; Rao, Venkatesh K.P.
Vibrating nanochannels are gaining interest in the fields of bio nano electromechanical systems (bio-NEMS) owing to their acoustic streaming ability (as a tail of nano-swimmers) and drug transportation mechanism. However, it is challenging to articulate such a mechanism experimentally. In this paper, molecular dynamic simulations are carried out to study the effect of the wall vibrations on the forced transportation of a water nanodroplet through a vibrating nanochannel. Here, the motion of water molecules was governed by modified Lennard–Jones (LJ) potential with an initial hydrophobic solid–liquid interface between the walls of nanochannel and water molecules. The density distribution of water molecules was spread towards the nanochannel walls for high vibration (2 (Å) amplitude and 60 GHz frequencies). The average resistance force increased 95.2% for high configuration wall vibrations, showing an increase of 13.96 pN, compared to 7.15 pN for low configuration wall vibrations (0.5 (Å) amplitude and 15 GHz frequency). This work may have significant implications for the application in the fields such as targeted drug delivery, enhanced oil recovery, nanofluidics and inkjet printing.
Capturing higher modes of vibration of micromachined resonators
(IOP, 2009) Rao, Venkatesh K.P.
MEMS resonators have potential applications in the areas of RF-MEMS, clock oscillators, ultrasound transducers, etc. The important characteristics of a resonator are its resonant frequency and Q-factor (a measure of damping). Usually large damping in macro structures makes it difficult to excite and measure their higher modes. In contrast, MEMS resonators seem amenable to excitation in higher modes. In this paper, 28 modes of vibration of an electrothermal actuator are experimentally captured–perhaps the highest number of modes experimentally captured so far. We verify these modes with FEM simulations and report that all the measured frequencies are within 5% of theoretically predicted values.
Classification of diaphysis based on the mechanical response of femur bone
(Vibroengineering Procedia, 2019-11) Rao, Venkatesh K.P.
This work deal with the biomechanical analysis of the Captum Collum Diaphysis (CCD) femur bone. The femur is the largest bone in the upper leg. The angle between femur neck and femur shaft of the femora is a parameter in determining the CCD or FSA angle. 126 ° is the usual angle for a healthy adult and variation in this angle leads to the CCD. This angle in the femur bone helps in determining the knock knee and bow leggedness orthopaedic disease. This angle impacts on the distribution of stress and deflection in the femur bone during the daily activities. Computational Multi-Scale analysis has been done for homogenized properties of femur bone. A Numerical simulation has been made for the biomechanical analysis of CCD femur bone using Finite Element Method. There is significant impact of stress distribution and deflection over the femur bone in case of change in optimum CCD angle (coxa norma) and also leads to change the natural frequency of the bone. Predicted results shows the above mentioned disease behaviour over the healthy bone. The study of these deformity and their results are of clinical importance in musculoseketal behaviour of the human femur bone.
Coupled Field Analysis of Hemispherical Resonator Gyroscope
(International Journal of Vehicle Structures & Systems, 2022) Rao, Venkatesh K.P.
This work deals with the electromechanical analysis of the Hemispherical Resonator Gyroscope (HRG). The HRG is a type of Coriolis vibratory gyroscope (CVG), which uses Coriolis force to measure the input angular rate. For any CVG drive and sense mode, frequencies play a critical role, which decides the sensitivity and bandwidth of a sensor. In this study, we carry out modal analysis to evaluate the natural frequencies and corresponding mode shapes of an HRG. As HRG is an electromechanical structure, the device is driven at resonance in the drive direction, and the Coriolis force leads to motion in the sense direction. In this study, we present the piezoelectric based HRG; coupled field simulations are carried out to evaluate the performance characteristics of a sensor
Coupled field simulation of mems tuning fork gyroscope
(Springer, 2025-06) Rao, Venkatesh K.P.
The use of Microelectromechanical Systems (MEMS) based sensors has become increasingly popular due to the growing demand for miniaturization in electronics. Though developing these sensors may require multiple iterations on smaller samples, Finite Element Method (FEM) based simulations offer a viable solution by enabling the optimization of design parameters to a significant degree. A FEM based simulation methodology has been designed in this paper to incorporate electromechanical coupling in an electrostatically actuated tuning fork gyroscope using COMSOL Multiphysics. The simulation results have been compared with analytical values and an existing simulation example that combines numerical and analytical approaches. The obtained sense mode displacement values predicted by the model lie within 5% of the analytically predicted values and the values predicted by the simulation example.
Design and Analysis of General Purpose MEMS Accelerometer
(KTH, 2007) Rao, Venkatesh K.P.
Inertial sensors including accelerometers and gyroscopes play an important role in vibration sensing, health monitoring, automotive applications etc. Here we design, fabricate and characterize the set of accelerometers with natural frequencies varying from 8 to 18 kHz. The design is compatible with PolyMUMPs process and has an ease of integrability with the electronic circuits. The operating voltage of the sensor is less than 3.5 V and both the structural and electrode layers are in polysilicon. The user is given an option of choosing the accelerometer in terms of sensitivity and the working range of g (acceleration due to gravity) based on the need of the application. Analytical, Numerical and experimental studies are carried out to determine the sensitivity, frequency range, maximum measurable acceleration and the pull-in voltage of each device. Effect of residual stress on the static and dynamic response characteristics of the accelerometer has been explored and the effect of same on its sensitivity.
Design and Analysis of Single Drive Tri-Axis MEMS Gyroscope
(Springer, 2022-11) Rao, Venkatesh K.P.
MEMS based single and dual-axis gyroscopes have been widely explored for potential application in automotive, space, defense, and consumer electronics sectors. Tri-axis gyroscopes based on MEMS, however, have been sparsely studied. This work presents a novel design for tri-axis MEMS gyroscope and an analytical model to obtain the natural frequencies in drive and sense modes. These frequency values have been compared with the numerically obtained frequencies using Finite Element Analysis (FEA). The analytical results lie within 10% of their numerically obtained values. The frequency matching process involves many iterations of geometric dimensions if the end application requires minor design changes. The proposed analytical model will make the design customization easy as the frequencies of each mode will be expressed as a function of critical geometrical parameters saving multiple numerical runs required for design optimization.
Design and characterization of in-plane MEMS yaw rate sensor
(Springer, 2009-10) Rao, Venkatesh K.P.
In this paper, we present the design and characterization of a vibratory yaw rate MEMS sensor that uses in-plane motion for both actuation and sensing. The design criterion for the rate sensor is based on a high sensitivity and low bandwidth. The required sensitivity of the yawrate sensor is attained by using the inplane motion in which the dominant damping mechanism is the fluid loss due to slide film damping i.e. two–three orders of magnitude less than the squeeze-film damping in other rate sensors with out-of-plane motion. The low bandwidth is achieved by matching the drive and the sense mode frequencies. Based on these factors, the yaw rate sensor is designed and finally realized using surface micromachining. The inplane motion of the sensor is experimentally characterized to determine the sense and the drive mode frequencies, and corresponding damping ratios. It is found that the experimental results match well with the numerical and the analytical models with less than 5% error in frequencies measurements. The measured quality factor of the sensor is approximately 467, which is two orders of magnitude higher than that for a similar rate sensor with out-of-plane sense direction.
Design and fabrication of single drive tri-axis MEMS gyroscope
(Elsevier, 2024-03) Rao, Venkatesh K.P.
Gyroscopes are sensors that measure the angular rate of an rotating object along one or more coordinate axis. For measuring angular rate along all three axes, usually three different single axis gyroscopes are used. Three sensor systems imply more space and power requirements which are precious commodities in microelectronics. Single-drive tri axis gyroscopes overcome this issue. Owing to their design complications, they have not been explored to the scale of the single axis gyroscopes. In this paper we present a novel design of single drive tri-axis MEMS gyroscope with detail explanation of its working principle. Since gyroscopes are resonant sensors, the natural frequencies of drive and sense modes are expected to be as close to each other as possible to ensure maximum sensitivity. These frequencies depend on the structural dimensions of the design. A design optimization procedure using Finite Element Method (FEM) based parametric modal analysis has been suggested in order to achieve mode matching. An equivalent analytical model is also presented for drive mode and all three sense modes. The optimized design is fabricated using modified silicon on glass bulk micromachining technique. The natural frequencies in drive and sense modes of as fabricated devices were measured and compared with the numerical and analytical values, The experimental values of frequencies are well within 16% of the numerical values. A design upgrade has been suggested to further reduce this error value.
Design and Simulation of Tactical Grade Capacitive Based MEMS Vibratory Ring Gyroscope
(IEEE, 2023) Rao, Venkatesh K.P.
MEMS Vibratory Ring Gyroscopes (VRGs) are highly sensitive owing to their in-plane symmetric structure that ensures mode matching. We present a VRG with Comb drive actuation that offers linearity in drive mode, and variable gap capacitive detection in sense mode provides a high-scale factor. The numerical analysis of the VRG is undertaken at atmospheric pressure. High linearity is observed between sense mode movement and change in capacitance, indicative of scale factor stability. It offers an operating range of more than 100 degrees per second (dps) and resolution of 0.002 dps. The VRG has been designed to suit the tactical grade mobility requirements of platform stabilization, robotics, and unmanned aerial vehicles.
Development of Non-Destructive Dynamic Characterization Technique for MMCs: Predictions of Mechanical Properties for Al@Al2O3 Composites
(MDPI, 2023-07) Belgamwar, Sachin U.; Rao, Venkatesh K.P.
In the past several decades, many destructive and non-destructive testing techniques have been developed to evaluate the characteristics of metal matrix composites (MMCs). This research aims to calculate the mechanical properties of the Al@Al2O3 composites by varying alumina nanoparticles (Al2O3 NPs) content using a non-invasive, position sensing detector (PSD) unit-based optical method. The composite was prepared by a powder metallurgy technique, and its characterization was conducted using SEM and XRD to understand its surface morphology and microstructure. The natural frequency and Young’s modulus of the composite were estimated experimentally. Young’s modulus was calculated using this natural frequency. The proposed study shows that Young’s modulus of the composite increases with an increase in Al2O3 NPs content in the composition, irrespective of the testing method. Along with this, natural frequency also increases with the increase in the Al2O3 NPs content. Evaluated properties were compared with the numerical modeling using COMSOL Multiphysics. The experimental and numerical results are equivalent and within the margin of error. This study illustrates the development of an experimental approach for evaluating the mechanical properties of a composite material. This experimental approach can be used whenever sample dimension and space are constrained to evaluate the mechanical behavior of nanomaterials and nanocomposites.
Effect of external electric potential on the mechanical resonance of MEMS cantilever resonator
(IOP, 2022-08) Rao, Venkatesh K.P.
This work presents an analytical model to predict the natural frequency of electrostatically actuated micromachined cantilever beam under the application of DC voltage. The analytical modelling uses an energy based method with a sinusoidal vibration assumption. The electric field between the cantilever electrodes is assumed to be vertical and fringing field effects are neglected. The behaviour of natural frequency and a closed-form expression for pull-in voltage are evaluated. The electrostatic spring softening effect of DC bias on the resonant natural frequency is studied in particular. Results are compared with simulation in ANSYS.
Effect of metal coating and residual stress on the resonant frequency of MEMS resonators
(Springer, 2009-10) Rao, Venkatesh K.P.
MEMS resonators are designed for a fixed resonant frequency. Therefore, any shift in the resonant frequency of the final fabricated structure can be a denting factor for its suitability towards a desired application. There are numerous factors which alter the designed resonant frequency of the fabricated resonator such as the metal layer deposited on top of the beam and the residual stresses present in the fabricated structure. While the metal coating, which acts as electrode, increases the stiffness and the effective mass of the composite structure, the residual stress increases or decreases the net stiffness if it is a tensile or compressive type respectively. In this paper, we investigate both these cases by taking two different structures, namely, the micro cantilever beam with gold layer deposited on its top surface and the MEMS gyroscope with residual stresses. First, we carry out experiments to characterize both these structures to find their resonant frequencies. Later, we analytically model those effects and compare them with the experimentally obtained values. Finally, it is found that the analytical models give an error of less than 10% with respect to the experimental results in both the cases.
Electrothermally tunable MEMS filters
(SPIE, 2014-03) Rao, Venkatesh K.P.
MEMS resonators have potential application in the area of frequency selective devices (e.g., gyroscopes, mass sensors, etc.). In this paper, design of electro thermally tunable resonators is presented. SOIMUMPs process is used to fabricate resonators with springs (beams) and a central mass. When voltage is applied, due to joule heating, temperature of the conducting beams goes up. This results in increase of electrical resistance due to mobility degradation. Due to increase in the temperature, springs start softening and therefore the fundamental frequency decreases. So for a given structure, one can modify the original fundamental frequency by changing the applied voltage. Coupled thermal effects result in non-uniform heating. It is observed from measurements and simulations that some parts of the beam become very hot and therefore soften more. Consequently, at higher voltages, the structure (equivalent to a single resonator) behaves like coupled resonators and exhibits peak splitting. In this mode, the given resonator can be used as a band rejection filter. This process is reversible and repeatable. For the designed structure, it is experimentally shown that by varying the voltage from 1 to 16V, the resonant frequency could be changed by 28%.
Engineering a light-driven cyanine based molecular rotor to enhance the sensitivity towards a viscous medium
(RSC, 2021) Rao, Venkatesh K.P.
This article describes the enhanced sensitivity to a viscous medium by a molecular rotor based fluorophore (RBF), TPSI I. The TPSI I molecule is designed in such a way that it consists of a rotor and a fluorophore with a π-rich bridge between them. TPSI I is a light-responsive material in solution as well as in the solid state. The structural design of the molecule allows flexible rotation and photo-induced cis–trans isomerization both in the solid state as well as in solution. These combined attributes of TPSI I are responsible for the ultrasensitive viscosity response of the new material, which was verified through the Förster–Hoffmann equation. According to this equation, the derived ‘x’ value is 1.02 (x is related to the sensitivity) which is the highest among the contemporary reports for RBFs. The facts were evidenced both by experimental as well as theoretical data. The ultrasensitivity towards viscosity was further analyzed in in vitro studies by detecting the subtle changes in the alteration of intracellular viscosity in normal and cancerous cells. An alteration of intracellular viscosity in cells treated with viscosity modulators was also confirmed using a previously well-established viscosity measurement technique, dynamic measurement through the piezoelectric patch. Our research offers a detailed mechanism to improve viscosity sensors and an efficient probe for detecting minute changes in intracellular viscosity.
Experimental And Numerical Studies on Mechanical Resonance of Piezoelectric Hemispherical Resonator Gyroscope
(IEEE, 2021) Rao, Venkatesh K.P.
The Hemispherical Resonator Gyroscope (HRG) is a low-noise, high-performance angular rate sensor, or rotation sensor with a small footprint. A thin, solid-state hemispherical shell is used to fabricate the HRG, which is anchored by a thick stem. In the present study a mesoscale model of HRG was fabricated. The fabricated device is tested using a noncontact approach to measure its natural frequencies and drive and sense directions. Finite element analysis was carried out using commercial software COMSOL multiphysics to validate the experimentally obtained frequencies of the gyroscope. Numerically obtained drive and sense mode frequencies were found to be within 8% of the measured values.
Extraction of Modal Parameters of Micromachined Resonators in Higher Modes
(Springer, 2014-01) Rao, Venkatesh K.P.
In this paper, a micro machined resonator is fabricated using SOI MUMPs process. A total of 50 out-of-plane mode shapes and their corresponding modal parameters (resonant frequency and damping) are extracted. With the applied voltage, due to joule heating, natural frequency (f n ) and Quality (Q) factor change. This can be effectively used for tuning the resonator. A detailed modal analysis is carried out using an FEM simulator to compute the modal parameters across all the modes and results are within 5% of the data measured using a Laser Vibrometer. Q is estimated using the half-power point approach for the first 42 modes. It is also observed that Q goes up by a factor > 2 for modes beyond 27, as only a portion of the structure contributes to modal displacement. At higher voltages, thermal softening is observed due to local heating which results in structure behaving like a coupled resonator. Under these conditions, peak splitting is observed. This structure can be used in different sensor and actuator applications depending on the mode of operation.
Fertilizer monitoring using micromachined cantilever
(Agricultural Science & Technology, 2019-09) Rao, Venkatesh K.P.
In this study, we will create a grid of micro electro-mechanical (MEMS) sensors, which will measure the contents of soil, especially urea. This will inform the farmers about the condition of soil in real time, and thus allowing them to know how much fertilizer they need to add. MEMS sensor is placed in the soil to measure the soil content by chemical reaction with the fertilizers; its accuracy can be improved if these sensors are placed on multiple points, i.e., they are placed in a grid. In the present study, we designed micro-cantilever based gas detectors, to detect ammonia present in the fertilizers. Several designs were proposed to find the best fit for this purpose. Numerical studies have been carried out on the proposed designs, to evaluate the displacement sensitivity and the voltage developed in the piezoelectric layer, and the triangular cantilever was found to be the most sensitive cantilever for that purpose