Karthik Visvanathan

3D-soule: A fabrication process for large scale integration and micromachining of spherical structures

This paper reports a method for integrating and micromachining spherical structures made from materials such as fused quartz that are not amenable to melting or reflow. The 3D-SOULE process combines batch-mode micro ultrasonic machining (µUSM), lapping, and micro electro-discharge machining (µEDM) for creating spherical structures. Micro electro discharge machining is used for creating the stainless steel tool, which is then used for µUSM of the glass spheres. Stainless steel 440 which provides tool wear <5% is used for µUSM. A machining rate of 24 µm/sec is achieved for fabrication of concave and mushroom-shaped spherical structures from 1 mm-diameter glass spheres.

Propulsion and steering of a floating mini-robot based on Marangoni flow actuation

This paper discusses the propulsion and steering of a floating mini-robot based on thermal Marangoni flow. The normal component of the surface tension force keeps the robot floating on the liquid surface, while the localized heating of liquid surface results in tangential Marangoni flows which propel the robot. Lift force modeling shows that six legs of 1 cm long and 300 µm in diameter generate a lift force of 7.56 mN. Simulations suggest that a propulsion force of 0.638 mN per leg can be generated for a heater temperature of 60°C. Preliminary experiments using a 2×1.5cm2 H-shaped structure demonstrate that a velocity of 4.4 mm/sec and a rotational velocity of 0.2 rad/sec can be achieved.

Microheaters based on ultrasonic actuation of piezoceramic elements

This paper describes the use of micromachined lead zirconate titanate (PZT) piezoceramic elements for heat generation by ultrasonic energy dissipated within the elements and surrounding media. Simulations based on three-dimensional finite-element models suggest that circular disk-shaped elements provide superior steady-state temperature rise for a given cross-sectional area, volume of the PZT element and drive voltage. Experimental validation is performed using PZT-5A heaters of 3.2 mm diameter and 0.191 mm thickness. Single-element heaters and dual-element stacks are evaluated. Although the steady-state temperature generated by these heaters reaches the maximum value at the frequency of maximum electromechanical conductance, the heating effectiveness is maximized at the frequency of maximum electromechanical impedance. Stacked PZT heaters provide 3.5 times the temperature rise and 3 times greater heating effectiveness than single elements. Furthermore, the heaters attain the maximum heating effectiveness when bonded to highly damping and non-conducting substrates. A maximum temperature of 120 ◦ C is achieved at 160 mW input power. Experiments are performed using porcine tissue samples to show the feasibility of using PZT heaters in tissue cauterization. A PZT heater probe brands a porcine tissue in 2‐3 s with 10 VRMS drive voltage. The interface temperature is ≈150 ◦ C. (Some figures in this article are in colour only in the electronic version)

Biopsy needle tract cauterization using an embedded array of piezoceramic microheaters

This paper presents the use of an array of piezoceramic microheaters embedded in a biopsy needle for tract cauterization. Circular PZT-5A heaters of 200 µm diameter and 70–80 µm thickness are embedded in the wall of a 20-gauge stainless steel needle. Finite element modeling suggests that a PZT array with no gap between the elements to be the most suitable design. The temperature profile generated is measured at two resonance modes: the radial mode (10.3 MHz) and the thickness mode (22.3 MHz). The needle surface exceeds the minimum target temperature rise of 33°C for applied voltages of 17 VRMS and 14 VRMS for radial and thickness mode, respectively. The corresponding input powers are 236 mW and 325 mW, respectively. The tissue cauterization extends 1–1.25 mm beyond the perimeter of needle.

Locomotion response of airborne, ambulatory and aquatic insects to thermal stimulation using piezoceramic microheaters

This paper reports the locomotion response of airborne, ambulatory and aquatic insects to thermal stimulation. A finite element model has been developed to predict the variation of insect‐stimulator interface temperature with input power. Piezothermal stimulators have been fabricated from lead zirconate titanate (PZT) using a batch mode micro ultrasonic machining process. Typical sizes range from 200 μm to 3.2 mm. For PZT stimulators, the temperature and thermal efficiency reach the maximum value around the resonance frequency which is typically in the range of 650 kHz to 47 MHz. Experiments have been conducted on green June beetles (GJBs), Madagascar hissing roaches and green diving beetles (GDBs) in order to show the versatility of the proposed technique. The stimulators have been implanted near the antennae of the GJBs and on either side of the thorax of the Madagascar hissing roaches and GDBs, respectively. In all cases, the insects move away from the direction of the actuated stimulator. The left and right turns are statistically similar. Thermal stimulation achieves an overall success rate of 78.7%, 92.8% and 61.6% in GJBs, roaches and GDBs, respectively. On average, thermal stimulation results in an angle turn of about 13.7 ◦ ‐16.2 ◦ on GJBs, 30 ◦ ‐45 ◦ on the roaches and 30 ◦ ‐50 ◦ on GDBs. The corresponding average input power is 360, 330 and 100 mW for GJBs, roach and GDBs, respectively. Scaling limits of the PZT stimulators for operating these stimulators are also discussed. (Some figures in this article are in colour only in the electronic version)

Ultrasonic microheaters using piezo-ceramics for cauterization and other applications

This paper presents the use of piezoelectric ultrasonic microheaters for cauterization of biological tissues for tumor ablation and hemostasis. Ultrasonic heaters using PZT-5A ceramic of 3.2 mm diameter and 191 µm thickness were used in the experiments. A finite element model was developed to predict the heat generated by these microheaters. The ultrasonic heaters attained maximum temperature and thermal efficiency at frequency corresponding to maximum conductance and maximum impedance respectively. The thermal efficiency at each resonance frequency (0.5–3 MHz) was proportional to effective coupling factor (0.25–0.5) at that mode. The thermal efficiency is 930°C/W for biological tissue. Stacked heaters provide about three times higher efficiency. Branding of porcine tissue using the proposed device is also discussed.

Control of locomotion in ambulatory and airborne insects using implanted thermal microstimulators

This paper describes the use of implanted microthermal stimulators for locomotion control of ambulatory and airborne insects. In the long term, this research is intended to support micro autonomous vehicles. Experiments were performed using both resistive (nickel), and piezoelectrically driven ultrasonic (PZT-5A) thermal stimulators on green june beetles (GJB) (Cotinis nitida) and Madagascar hissing roaches (Gromphadorhina Portentosa). Ultrasonic heating was 2x more power efficient, requiring 330–360 mW of input power to achieve the 43°C pulses necessary for stimulation. Both stimulators demonstrated the feasibility of locomotion control with a success rate of 80% on GJB and 93.5% on the roaches. The microthermal stimulation resulted in average turn angles of 15–18° and 30–45° on GJB and roaches, respectively. Left and right turns were statistically similar.