G. K. Ananthasuresh | Indian Institute of Science (original) (raw)

Papers by G. K. Ananthasuresh

Journal of Mechanical Design, 2002

Single Degree-of-freedom Coupled Serial Chain (SDCSC) mechanisms form a novel class of modular an... more Single Degree-of-freedom Coupled Serial Chain (SDCSC) mechanisms form a novel class of modular and compact mechanisms with a single degree-of-freedom, suitable for a number of manipulation tasks. Such SDCSC mechanisms take advantage of the hardware constraints between the articulations of a serial-chain linkage, created using gear-trains or belt/pulley drives, to guide the end-effector motions and forces. In this paper, we examine the dimensional synthesis of such SDCSC mechanisms to perform desired planar manipulation tasks, taking into account task specifications on both end-effector motions and forces. Our solution approach combines precision point synthesis with optimization to realize optimal mechanisms, which satisfy the design specifications exactly at the selected precision points and approximate them in the least-squares sense elsewhere along a specified trajectory. The designed mechanisms can guide a rigid body through several positions while supporting arbitrarily specifi...

Volume 1B: 25th Biennial Mechanisms Conference

We address the synthesis of serial chain spatial mechanisms with revolute joints in which the rot... more We address the synthesis of serial chain spatial mechanisms with revolute joints in which the rotations about the joints are coupled via cables and pulleys. Such coupled serial chain mechanisms offer a middle ground between the more versatile and compact serial chains and the simpler closed chains by combining some of the advantages of both types of systems. In particular, we focus on the synthesis of single degree-of-freedom, coupled serial chains with two revolute joints. We derive precision point synthesis equations for two precision points by combining the loop closure equations with the necessary geometric constraints in terms of the unknown mechanism parameters. This system of equations can now be solved linearly for the link vectors after a suitable selection of free choices. We optimize over the free choices to generate an end effector trajectory that closely approximates a desired end effector trajectory for motion generation and path following applications.

an interactive map-based technique for de- signing compliant mechanisms that meet the require- me... more an interactive map-based technique for de- signing compliant mechanisms that meet the require- ments of a practical application. Our map juxtaposes user-specifications with the attributes of real compliant mechanisms stored in a database so that not only the practical feasibility of specifications can be discerned quickly but also modifications can be done intuitively to the existing compliant mechanisms. The upper and lower bounds on the specification variables entered by a user are used to show a part of the feasible region on a 2D map. The basis to draw the feas- ible region is the spring-leverage (SL) model, which is used to characterize the kinematic and elastic behavior of single-input-single-output compliant mechanisms for the purpose of static analysis. The SL model consists of three constants: (i) the input spring stiffness, (ii) the out- put spring stiffness, and (iii) the inherent geometric am- plification factor. The three constants are computed a priori for the complian...

Widely spread across and deeply entrenched in many engineering and some science disciplines, Micr... more Widely spread across and deeply entrenched in many engineering and some science disciplines, Microelectromechanical Systems (MEMS) is a mature field today. Moving mechanical elements are the distinguishing features of MEMS, which have earned their own place among the ubiquitous microelectronic devices. This is in part due to clever mechanical designs that defined this field. A few good MEMS designs are reviewed in this chapter, and this opportunity is used to highlight the traits (the signs) that make a design good, and also to examine the roles of intuition (the art) and systematic synthesis (the science) in obtaining good designs. Attention is paid to how MEMS designs have overcome the constraints of essentially planar microfabrication and unlikely mechanical materials such as silicon. It is noted that some MEMS designs are borrowed from other disciplines but many have been developed anew to meet the stringent demands on functionality, performance, and microfabrication. Also inclu...

2017 International Conference on Manipulation, Automation and Robotics at Small Scales (MARSS), 2017

(We describe the fabrication, characterization and operation of a microfabricated, overhanging mi... more (We describe the fabrication, characterization and operation of a microfabricated, overhanging micromachined SU-8 device that can stretch and compress individual cells. This compliant device is composed of folded beams with a single actuation point. Upon actuation with a glass micropipette attached to an XYZ positioner, it can apply varying deformation to multiple cells simultaneously. The applied force is computed using the measured displacement of the compliant device. Cell-attachment is achieved by simply adding a suspension of cells on the device. The stiffness of the device was designed such that cells can deform the beams they are attached to. Measuring this deformation in the absence of actuation allows for quantifying the forces exerted by the cells with a resolution of 0.18 μΝ.)

A click-clack tin-lid mechanism analyzed in this paper has the feature to be switched between its... more A click-clack tin-lid mechanism analyzed in this paper has the feature to be switched between its two stable states by applying forces along different lines of action, generally at two different points, called ports here. A mechanism such as this has an inherent mechanical advantage because the magnitude of the actuation force at one port is different from that at the other port. The 3D circular click-clack tin-lid mechanism is modified to design a planar fully-compliant two-port bistable mechanism. An analytical kinetoelastic model and finite element analysis are used to explain the energy behavior of the mechanism and gain insights in using it in practice. The mechanism is implemented to design a sit-to-stand easy chair where a small force applied on the armrest can gently propel and ease the occupant rising from it. Further, a static balancing spring is combined with the two-port bistable mechanism to enable adjustment for different weights of the occupant.

2018 IEEE 13th Annual International Conference on Nano/Micro Engineered and Molecular Systems (NEMS)

We report a novel microfluidic platform to measure the stiffness of a single cell by evaluating i... more We report a novel microfluidic platform to measure the stiffness of a single cell by evaluating its deformability index through the time information embedded in the electrical impedance data of the cell transit. The deformability index and transit time are two parameters that quantify the stiffness of a single cell passing through a constriction. Conventionally, the deformability index has been measured optically using a highspeed camera, which is expensive, bulky, time-consuming, and thus limits the portability and ease of mechanodiagnostics. Furthermore, the transit time of cell passage is prone to inadvertent flow rate fluctuations. We use Electrical Impedance Spectroscopy combined with a microfluidic channel integrated with an array of coplanar electrodes to evaluate the deformability index of the biological cells. Additionally, measurements of cell impedance during cell transit provides a multi-modal electromechanical signature of individual cells that can be correlated to their health or disease states. The portable and noninvasive method of mechano-phenotyping cell population would make electro-mechanodiagnostics possible.

Micro-Electro-Mechanical Systems (MEMS)

Magnetically actuated diaphragm pumps were fabricated with low temperature co-fired ceramic (LTCC... more Magnetically actuated diaphragm pumps were fabricated with low temperature co-fired ceramic (LTCC) tapes and Kapton polyimide film. The pumps consisted of a chamber machined in a LTCC substrate. The chamber was covered either on one or both sides with Kapton diaphragms on which copper coils were patterned. The diaphragms were actuated by passing electric current through the coils in the presence of permanent magnets. Passive Kapton flap valves were used to direct fluid flow into and out of the chamber. The first design consisted of a single, circular diaphragm pump. In the second design, two circular diaphragms were used. The two diaphragms are deflected into and out of the pressure chamber simultaneously. Flow rates of up to 7 mL/min were measured. The static response of a circular diaphragm subjected to magnetic forces was computed using the finite element method (FEM). The effect of the copper coils on diaphragm stiffness was accounted for. The design parameters (the number of wi...

Volume 1B: 25th Biennial Mechanisms Conference

The physical insight used in formulating a multi-criteria optimization problem for the synthesis ... more The physical insight used in formulating a multi-criteria optimization problem for the synthesis of compliant mechanisms, is quickly lost if mathematical programming techniques (SLP, SQP etc.) are used to determine the optimal solution. As opposed to the previous works that relied upon mathematical programming search techniques to find the optimum solution, in this paper we present an alternative method of solution called the optimality criteria method. Optimality criteria methods have proven to be effective in structural optimization problems with a large number of variables, and very few constraints as is the case in the topology synthesis of compliant mechanisms. The important new results of this paper include: (i) the derivation of a physically insightful optimal property of compliant mechanisms which states that the ratio of the mutual potential energy density and the strain energy density is uniform throughout the continuum (ii) the development of the optimality criteria metho...

Structural and Multidisciplinary Optimization

We present a multi-phase design parameterization to obtain optimized heterogeneous lattice struct... more We present a multi-phase design parameterization to obtain optimized heterogeneous lattice structures. The 3D domain is discretized into a cubical grid wherein each cube has eight distinct unit cell types or phases. When all phases are present, the domain resembles a densely connected ground structure. The crosssection area of beam segments in lattice units, modelled using Timoshenko beam theory, are the design variables. All beam segments in a particular lattice phase have the same area of cross-section to keep the number of design variables low. The optimization problem is formulated for stiff structures and is solved using the optimality criteria algorithm. We present a case study to show the superiority of topology-optimized heterogeneous structures over uniform lattices of a single phase. In order to interpret the phase composition, we perform four basic load tests on single phases, namely, tension or compression, shear, bending, and torsion. The phases are ranked based on the stiffness corresponding to individual loading conditions. The results show that in the optimized structure, the local internal load configuration drives the selection of phases. We also note that micropolar elasticity captures the bulk behaviour of heterogeneous lattice structures, and helps not only to interpret the optimality of phases but also to improve the computational efficiency of the proposed optimization technique.

Journal of Micromechanics and Microengineering

Lack of reliability of radio-frequency microelectromechanical systems (RF MEMS) switches has inhi... more Lack of reliability of radio-frequency microelectromechanical systems (RF MEMS) switches has inhibited their commercial success. Dielectric stiction/breakdown and mechanical shock due to high actuation voltage are common impediments in capacitive MEMS switches. In this work, we report low-actuation voltage RF MEMS switch and its reliability test. Experimental characterization of fabricated devices demonstrate that proposed MEMS switch topology needs very low voltage (4.8 V) for actuation. The mechanical resonant frequency, f 0 , quality factor, Q, and switching time are measured to be 8.35 kHz, 1.2, and 33 microsecond, respectively. These MEMS switches have high reliability in terms of switching cycles. Measurements are performed using pulse waveform of magnitude of 6 V under hot-switching condition. Temperature measurement results confirm that the reported switch topology has good thermal stability. The robustness in terms of the measured pull-in voltage shows a variation of 0.08 V °C −1. Lifetime measurement results after 10 million switching cycles demonstrate insignificant change in the RF performance without any failure. Experimental results show that low voltage improves the lifetime. Low insertion loss (less than 0.6 dB) and improved isolation (above 40 dB) in the frequency range up to 60 GHz have been reported. Measured RF characteristics in the frequency range from 10 MHz to 60 GHz support that these MEMS switches are favorable choice for mm-wave 5G applications.

Morphology of the nucleus is an important regulator of gene-expression. Nuclear morphology is in ... more Morphology of the nucleus is an important regulator of gene-expression. Nuclear morphology is in turn a function of the forces acting on it and the mechanical properties of the nuclear envelope. Here, we present a two-parameter, non-dimensional mechanical model of the nucleus that reveals a relationship among nuclear shape parameters such as projected area, surface area and volume. Our model fits the morphology of individual nuclei and predicts the ratio between forces and modulus in each nucleus. We analyzed the changes in nuclear morphology of liver cells due to Hepatitis C Virus (HCV) infection using this model. The model predicted a decrease in the elastic modulus of the nuclear envelope and an increase in the pre-tension in cortical actin as the causes for the change in nuclear morphology. These predictions were validated biomechanically by showing that liver cells expressing HCV proteins possessed enhanced cellular stiffness and reduced nuclear stiffness. Concomitantly, cells ...

Mechanics of Advanced Materials and Structures

Abstract We present a distributed compliant mechanism, which acts like a transmission between a f... more Abstract We present a distributed compliant mechanism, which acts like a transmission between a flapping wing of a micro air vehicle and a laminated piezoelectric actuator. The piezoelectric bimorph actuator is connected in cantilever configuration with the compliant mechanism at its free end. The mechanism takes translational deflection at its input from the piezoelectric actuator to provide angular deflection at its output, which causes flapping. We used spring-level model and topology optimization to obtain the design of the mechanism. The design of the mechanism has been finalized by analyzing the design considering beam model with geometric nonlinearity. The final mechanism is a planar structure of 1 mm thickness and 40 mm ×24 mm in-plane footprint. The input stiffness of the compliant mechanism is 711 N/m and the output torsional stiffness is 0.014 Nm/rad. The compliant mechanism is tested with a piezoelectric bimorph actuator. The mechanism takes ±1 mm deflection with ±0.2 N block force at 30 Hz as an input and produces ±6° flap angle at 30 Hz as an output. The first fundamental frequency of the mechanism is 391 Hz, which is almost 13 times greater than our assumed wing flapping frequency 30 Hz. The final mechanism is prototyped with a 3D printer using VeroWhitePlus RGD835 material and tested with a piezoelectric bimorph actuator using a bench-top experimental set-up.

Volume 8: 31st Mechanisms and Robotics Conference, Parts A and B, 2007

ABSTRACT

Volume 2: 32nd Mechanisms and Robotics Conference, Parts A and B, 2008

ABSTRACT

2015 2nd International Symposium on Physics and Technology of Sensors (ISPTS), 2015

The Dual-Probe Heat-Pulse technique has been widely used for in-situ moisture sensing. In the hea... more The Dual-Probe Heat-Pulse technique has been widely used for in-situ moisture sensing. In the heater probe described in our earlier work the power consumption was 350 mW-the lowest in this category of sensors. In this paper, by employing a material selection method, we further improve the performance of the sensor by employing Parylene-coated nichrome wire and different packaging methods. The power consumption is reduced to 165 mW with a temperature rise between 1 K to 6.2 K degrees in 34% wet and dry red soils, respectively. A variant of the nichrome sensor was one that employed a ceramic tube with four longitudinal holes that eliminated the need for Parylene coating. The sensor was verified in agar agar solution and calibrated with 1200 kg/m2 red field soil. The compact packaging of the nichrome heater allowed us to provide a heat distribution of 3267 J/m on the probe surface which is two times more than the earlier attempts.

BioResearch Open Access, 2015

We present a perfusion culture system with miniature bioreactors and peristaltic pumps. The biore... more We present a perfusion culture system with miniature bioreactors and peristaltic pumps. The bioreactors are designed for perfusion, live-cell imaging studies, easy incorporation of microfabricated scaffolds, and convenience of operation in standard cell culture techniques. By combining with miniature peristaltic pumps-one for each bioreactor to avoid cross-contamination and to maintain desired flow rate in each-we have made a culture system that facilitates perfusion culture inside standard incubators. This scalable system can support multiple parallel perfusion experiments. The major components are fabricated by three-dimensional printing using VeroWhite, which we show to be amenable to ex vivo cell culture. Furthermore, the components of the system can be reused, thus making it economical. We validate the system and illustrate its versatility by culturing primary rat hepatocytes, live imaging the growth of mouse fibroblasts (NIH 3T3) on microfabricated ringscaffolds inserted into the bioreactor, performing perfusion culture of breast cancer cells (MCF7), and highmagnification imaging of hepatocarcinoma cells (HuH7).

Mechanisms and Machine Science, 2011

ABSTRACT Micromachines is a mature field today, although it is usually known by other names in va... more ABSTRACT Micromachines is a mature field today, although it is usually known by other names in various parts of the world. We briefly review the genesis of this field and how mechanisms researchers became involved. The successes of the field are many and have led to creation of a number of commercial products. This success is partly due to mechanisms research but more significantly due to rapid developments in microfabrication technology. We discuss the influence of the limitations of microfabrication techniques on the mechanisms used in this field. Interestingly, the strategies that were developed for overcoming these limitations have extended the scope of mechanisms and machines and are influencing technologies beyond the realm of micromachines. Many challenges lie ahead and multi-disciplinary approaches combined with mechanisms techniques will prove to be beneficial in the coming years.

Journal of Mechanical Design, 2002

Single Degree-of-freedom Coupled Serial Chain (SDCSC) mechanisms form a novel class of modular an... more Single Degree-of-freedom Coupled Serial Chain (SDCSC) mechanisms form a novel class of modular and compact mechanisms with a single degree-of-freedom, suitable for a number of manipulation tasks. Such SDCSC mechanisms take advantage of the hardware constraints between the articulations of a serial-chain linkage, created using gear-trains or belt/pulley drives, to guide the end-effector motions and forces. In this paper, we examine the dimensional synthesis of such SDCSC mechanisms to perform desired planar manipulation tasks, taking into account task specifications on both end-effector motions and forces. Our solution approach combines precision point synthesis with optimization to realize optimal mechanisms, which satisfy the design specifications exactly at the selected precision points and approximate them in the least-squares sense elsewhere along a specified trajectory. The designed mechanisms can guide a rigid body through several positions while supporting arbitrarily specifi...

Volume 1B: 25th Biennial Mechanisms Conference

We address the synthesis of serial chain spatial mechanisms with revolute joints in which the rot... more We address the synthesis of serial chain spatial mechanisms with revolute joints in which the rotations about the joints are coupled via cables and pulleys. Such coupled serial chain mechanisms offer a middle ground between the more versatile and compact serial chains and the simpler closed chains by combining some of the advantages of both types of systems. In particular, we focus on the synthesis of single degree-of-freedom, coupled serial chains with two revolute joints. We derive precision point synthesis equations for two precision points by combining the loop closure equations with the necessary geometric constraints in terms of the unknown mechanism parameters. This system of equations can now be solved linearly for the link vectors after a suitable selection of free choices. We optimize over the free choices to generate an end effector trajectory that closely approximates a desired end effector trajectory for motion generation and path following applications.

an interactive map-based technique for de- signing compliant mechanisms that meet the require- me... more an interactive map-based technique for de- signing compliant mechanisms that meet the require- ments of a practical application. Our map juxtaposes user-specifications with the attributes of real compliant mechanisms stored in a database so that not only the practical feasibility of specifications can be discerned quickly but also modifications can be done intuitively to the existing compliant mechanisms. The upper and lower bounds on the specification variables entered by a user are used to show a part of the feasible region on a 2D map. The basis to draw the feas- ible region is the spring-leverage (SL) model, which is used to characterize the kinematic and elastic behavior of single-input-single-output compliant mechanisms for the purpose of static analysis. The SL model consists of three constants: (i) the input spring stiffness, (ii) the out- put spring stiffness, and (iii) the inherent geometric am- plification factor. The three constants are computed a priori for the complian...

Widely spread across and deeply entrenched in many engineering and some science disciplines, Micr... more Widely spread across and deeply entrenched in many engineering and some science disciplines, Microelectromechanical Systems (MEMS) is a mature field today. Moving mechanical elements are the distinguishing features of MEMS, which have earned their own place among the ubiquitous microelectronic devices. This is in part due to clever mechanical designs that defined this field. A few good MEMS designs are reviewed in this chapter, and this opportunity is used to highlight the traits (the signs) that make a design good, and also to examine the roles of intuition (the art) and systematic synthesis (the science) in obtaining good designs. Attention is paid to how MEMS designs have overcome the constraints of essentially planar microfabrication and unlikely mechanical materials such as silicon. It is noted that some MEMS designs are borrowed from other disciplines but many have been developed anew to meet the stringent demands on functionality, performance, and microfabrication. Also inclu...

2017 International Conference on Manipulation, Automation and Robotics at Small Scales (MARSS), 2017

(We describe the fabrication, characterization and operation of a microfabricated, overhanging mi... more (We describe the fabrication, characterization and operation of a microfabricated, overhanging micromachined SU-8 device that can stretch and compress individual cells. This compliant device is composed of folded beams with a single actuation point. Upon actuation with a glass micropipette attached to an XYZ positioner, it can apply varying deformation to multiple cells simultaneously. The applied force is computed using the measured displacement of the compliant device. Cell-attachment is achieved by simply adding a suspension of cells on the device. The stiffness of the device was designed such that cells can deform the beams they are attached to. Measuring this deformation in the absence of actuation allows for quantifying the forces exerted by the cells with a resolution of 0.18 μΝ.)

A click-clack tin-lid mechanism analyzed in this paper has the feature to be switched between its... more A click-clack tin-lid mechanism analyzed in this paper has the feature to be switched between its two stable states by applying forces along different lines of action, generally at two different points, called ports here. A mechanism such as this has an inherent mechanical advantage because the magnitude of the actuation force at one port is different from that at the other port. The 3D circular click-clack tin-lid mechanism is modified to design a planar fully-compliant two-port bistable mechanism. An analytical kinetoelastic model and finite element analysis are used to explain the energy behavior of the mechanism and gain insights in using it in practice. The mechanism is implemented to design a sit-to-stand easy chair where a small force applied on the armrest can gently propel and ease the occupant rising from it. Further, a static balancing spring is combined with the two-port bistable mechanism to enable adjustment for different weights of the occupant.

2018 IEEE 13th Annual International Conference on Nano/Micro Engineered and Molecular Systems (NEMS)

We report a novel microfluidic platform to measure the stiffness of a single cell by evaluating i... more We report a novel microfluidic platform to measure the stiffness of a single cell by evaluating its deformability index through the time information embedded in the electrical impedance data of the cell transit. The deformability index and transit time are two parameters that quantify the stiffness of a single cell passing through a constriction. Conventionally, the deformability index has been measured optically using a highspeed camera, which is expensive, bulky, time-consuming, and thus limits the portability and ease of mechanodiagnostics. Furthermore, the transit time of cell passage is prone to inadvertent flow rate fluctuations. We use Electrical Impedance Spectroscopy combined with a microfluidic channel integrated with an array of coplanar electrodes to evaluate the deformability index of the biological cells. Additionally, measurements of cell impedance during cell transit provides a multi-modal electromechanical signature of individual cells that can be correlated to their health or disease states. The portable and noninvasive method of mechano-phenotyping cell population would make electro-mechanodiagnostics possible.

Micro-Electro-Mechanical Systems (MEMS)

Magnetically actuated diaphragm pumps were fabricated with low temperature co-fired ceramic (LTCC... more Magnetically actuated diaphragm pumps were fabricated with low temperature co-fired ceramic (LTCC) tapes and Kapton polyimide film. The pumps consisted of a chamber machined in a LTCC substrate. The chamber was covered either on one or both sides with Kapton diaphragms on which copper coils were patterned. The diaphragms were actuated by passing electric current through the coils in the presence of permanent magnets. Passive Kapton flap valves were used to direct fluid flow into and out of the chamber. The first design consisted of a single, circular diaphragm pump. In the second design, two circular diaphragms were used. The two diaphragms are deflected into and out of the pressure chamber simultaneously. Flow rates of up to 7 mL/min were measured. The static response of a circular diaphragm subjected to magnetic forces was computed using the finite element method (FEM). The effect of the copper coils on diaphragm stiffness was accounted for. The design parameters (the number of wi...

Volume 1B: 25th Biennial Mechanisms Conference

The physical insight used in formulating a multi-criteria optimization problem for the synthesis ... more The physical insight used in formulating a multi-criteria optimization problem for the synthesis of compliant mechanisms, is quickly lost if mathematical programming techniques (SLP, SQP etc.) are used to determine the optimal solution. As opposed to the previous works that relied upon mathematical programming search techniques to find the optimum solution, in this paper we present an alternative method of solution called the optimality criteria method. Optimality criteria methods have proven to be effective in structural optimization problems with a large number of variables, and very few constraints as is the case in the topology synthesis of compliant mechanisms. The important new results of this paper include: (i) the derivation of a physically insightful optimal property of compliant mechanisms which states that the ratio of the mutual potential energy density and the strain energy density is uniform throughout the continuum (ii) the development of the optimality criteria metho...

Structural and Multidisciplinary Optimization

We present a multi-phase design parameterization to obtain optimized heterogeneous lattice struct... more We present a multi-phase design parameterization to obtain optimized heterogeneous lattice structures. The 3D domain is discretized into a cubical grid wherein each cube has eight distinct unit cell types or phases. When all phases are present, the domain resembles a densely connected ground structure. The crosssection area of beam segments in lattice units, modelled using Timoshenko beam theory, are the design variables. All beam segments in a particular lattice phase have the same area of cross-section to keep the number of design variables low. The optimization problem is formulated for stiff structures and is solved using the optimality criteria algorithm. We present a case study to show the superiority of topology-optimized heterogeneous structures over uniform lattices of a single phase. In order to interpret the phase composition, we perform four basic load tests on single phases, namely, tension or compression, shear, bending, and torsion. The phases are ranked based on the stiffness corresponding to individual loading conditions. The results show that in the optimized structure, the local internal load configuration drives the selection of phases. We also note that micropolar elasticity captures the bulk behaviour of heterogeneous lattice structures, and helps not only to interpret the optimality of phases but also to improve the computational efficiency of the proposed optimization technique.

Journal of Micromechanics and Microengineering

Lack of reliability of radio-frequency microelectromechanical systems (RF MEMS) switches has inhi... more Lack of reliability of radio-frequency microelectromechanical systems (RF MEMS) switches has inhibited their commercial success. Dielectric stiction/breakdown and mechanical shock due to high actuation voltage are common impediments in capacitive MEMS switches. In this work, we report low-actuation voltage RF MEMS switch and its reliability test. Experimental characterization of fabricated devices demonstrate that proposed MEMS switch topology needs very low voltage (4.8 V) for actuation. The mechanical resonant frequency, f 0 , quality factor, Q, and switching time are measured to be 8.35 kHz, 1.2, and 33 microsecond, respectively. These MEMS switches have high reliability in terms of switching cycles. Measurements are performed using pulse waveform of magnitude of 6 V under hot-switching condition. Temperature measurement results confirm that the reported switch topology has good thermal stability. The robustness in terms of the measured pull-in voltage shows a variation of 0.08 V °C −1. Lifetime measurement results after 10 million switching cycles demonstrate insignificant change in the RF performance without any failure. Experimental results show that low voltage improves the lifetime. Low insertion loss (less than 0.6 dB) and improved isolation (above 40 dB) in the frequency range up to 60 GHz have been reported. Measured RF characteristics in the frequency range from 10 MHz to 60 GHz support that these MEMS switches are favorable choice for mm-wave 5G applications.

Morphology of the nucleus is an important regulator of gene-expression. Nuclear morphology is in ... more Morphology of the nucleus is an important regulator of gene-expression. Nuclear morphology is in turn a function of the forces acting on it and the mechanical properties of the nuclear envelope. Here, we present a two-parameter, non-dimensional mechanical model of the nucleus that reveals a relationship among nuclear shape parameters such as projected area, surface area and volume. Our model fits the morphology of individual nuclei and predicts the ratio between forces and modulus in each nucleus. We analyzed the changes in nuclear morphology of liver cells due to Hepatitis C Virus (HCV) infection using this model. The model predicted a decrease in the elastic modulus of the nuclear envelope and an increase in the pre-tension in cortical actin as the causes for the change in nuclear morphology. These predictions were validated biomechanically by showing that liver cells expressing HCV proteins possessed enhanced cellular stiffness and reduced nuclear stiffness. Concomitantly, cells ...

Mechanics of Advanced Materials and Structures

Abstract We present a distributed compliant mechanism, which acts like a transmission between a f... more Abstract We present a distributed compliant mechanism, which acts like a transmission between a flapping wing of a micro air vehicle and a laminated piezoelectric actuator. The piezoelectric bimorph actuator is connected in cantilever configuration with the compliant mechanism at its free end. The mechanism takes translational deflection at its input from the piezoelectric actuator to provide angular deflection at its output, which causes flapping. We used spring-level model and topology optimization to obtain the design of the mechanism. The design of the mechanism has been finalized by analyzing the design considering beam model with geometric nonlinearity. The final mechanism is a planar structure of 1 mm thickness and 40 mm ×24 mm in-plane footprint. The input stiffness of the compliant mechanism is 711 N/m and the output torsional stiffness is 0.014 Nm/rad. The compliant mechanism is tested with a piezoelectric bimorph actuator. The mechanism takes ±1 mm deflection with ±0.2 N block force at 30 Hz as an input and produces ±6° flap angle at 30 Hz as an output. The first fundamental frequency of the mechanism is 391 Hz, which is almost 13 times greater than our assumed wing flapping frequency 30 Hz. The final mechanism is prototyped with a 3D printer using VeroWhitePlus RGD835 material and tested with a piezoelectric bimorph actuator using a bench-top experimental set-up.

Volume 8: 31st Mechanisms and Robotics Conference, Parts A and B, 2007

ABSTRACT

Volume 2: 32nd Mechanisms and Robotics Conference, Parts A and B, 2008

ABSTRACT

2015 2nd International Symposium on Physics and Technology of Sensors (ISPTS), 2015

The Dual-Probe Heat-Pulse technique has been widely used for in-situ moisture sensing. In the hea... more The Dual-Probe Heat-Pulse technique has been widely used for in-situ moisture sensing. In the heater probe described in our earlier work the power consumption was 350 mW-the lowest in this category of sensors. In this paper, by employing a material selection method, we further improve the performance of the sensor by employing Parylene-coated nichrome wire and different packaging methods. The power consumption is reduced to 165 mW with a temperature rise between 1 K to 6.2 K degrees in 34% wet and dry red soils, respectively. A variant of the nichrome sensor was one that employed a ceramic tube with four longitudinal holes that eliminated the need for Parylene coating. The sensor was verified in agar agar solution and calibrated with 1200 kg/m2 red field soil. The compact packaging of the nichrome heater allowed us to provide a heat distribution of 3267 J/m on the probe surface which is two times more than the earlier attempts.

BioResearch Open Access, 2015

We present a perfusion culture system with miniature bioreactors and peristaltic pumps. The biore... more We present a perfusion culture system with miniature bioreactors and peristaltic pumps. The bioreactors are designed for perfusion, live-cell imaging studies, easy incorporation of microfabricated scaffolds, and convenience of operation in standard cell culture techniques. By combining with miniature peristaltic pumps-one for each bioreactor to avoid cross-contamination and to maintain desired flow rate in each-we have made a culture system that facilitates perfusion culture inside standard incubators. This scalable system can support multiple parallel perfusion experiments. The major components are fabricated by three-dimensional printing using VeroWhite, which we show to be amenable to ex vivo cell culture. Furthermore, the components of the system can be reused, thus making it economical. We validate the system and illustrate its versatility by culturing primary rat hepatocytes, live imaging the growth of mouse fibroblasts (NIH 3T3) on microfabricated ringscaffolds inserted into the bioreactor, performing perfusion culture of breast cancer cells (MCF7), and highmagnification imaging of hepatocarcinoma cells (HuH7).

Mechanisms and Machine Science, 2011

ABSTRACT Micromachines is a mature field today, although it is usually known by other names in va... more ABSTRACT Micromachines is a mature field today, although it is usually known by other names in various parts of the world. We briefly review the genesis of this field and how mechanisms researchers became involved. The successes of the field are many and have led to creation of a number of commercial products. This success is partly due to mechanisms research but more significantly due to rapid developments in microfabrication technology. We discuss the influence of the limitations of microfabrication techniques on the mechanisms used in this field. Interestingly, the strategies that were developed for overcoming these limitations have extended the scope of mechanisms and machines and are influencing technologies beyond the realm of micromachines. Many challenges lie ahead and multi-disciplinary approaches combined with mechanisms techniques will prove to be beneficial in the coming years.