Rajesh Duggirala
Cornell University
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Publication
Featured researches published by Rajesh Duggirala.
Applied Physics Letters | 2008
Rajesh Duggirala; Hui Li; Amit Lal
We demonstrate a 5.1% energy conversion efficiency Ni63 radioisotope power generator by integrating silicon betavoltaic converters with radioisotope actuated reciprocating piezoelectric unimorph cantilever converters. The electromechanical energy converter efficiently utilizes both the kinetic energy and the electrical charge of the 0.94μW β radiation from a 9mCi Ni63 thin film source to generate maximum (1) continuous betavoltaic electrical power output of 22nW and (2) pulsed piezoelectric electrical power output of 750μW at 0.07% duty cycle. The electromechanical converters can be potentially used to realize 100year lifetime power sources for powering periodic sampling remote wireless sensor microsystems.
TRANSDUCERS 2007 - 2007 International Solid-State Sensors, Actuators and Microsystems Conference | 2007
Rajesh Duggirala; S. Tin; A. Lai
We report on the first demonstration of high efficiency 3D silicon betavoltaics, microtextured with deep reactive ion etched (DRIE) trenches, for potential application in 5 year lifetime 5 mW / cc Promethium -147 powered microbatteries. Prototype 3D silicon betavoltaics were designed and microfabricated in a 2-mask self-aligned process, and characterized using accelerated electron beams in a scanning electron microscope to yield 1.02 % conversion efficiency @ 30 kV acceleration voltage.
IEEE\/ASME Journal of Microelectromechanical Systems | 2008
Rajesh Duggirala; Ronald G. Polcawich; Madan Dubey; Amit Lal
A radioisotope power generator with a potential lifetime of decades is demonstrated by employing a 100.3-year half-lifetime 63Ni radioisotope thin-film source to electrostatically actuate and cause reciprocation in a microfabricated piezoelectric unimorph cantilever. The radioisotope direct-charged electrostatic actuation of the piezoelectric unimorph cantilever results in the conversion of radiation energy into mechanical energy stored in the strained unimorph cantilever. The gradual accumulation of the actuation charges leads to the pull-in of the unimorph cantilever into the radioisotope thin-film, and the resulting discharge leads to vibrations in the unimorph cantilever. During the vibrations, the stored mechanical energy is converted into electrical energy by the piezoelectric thin-film. The generator was realized by using both microfabricated lead zirconate titanate oxide-silicon (PZT-Si) and aluminum nitride-silicon (AIN-Si) unimorph cantilevers. The radioisotope direct-charged electrostatic actuation of the AIN-Si unimorph cantilevers by a 2.9-mCi 63Ni thin-film radiating 0.3 muW led to charge-discharge-vibrate cycles that resulted in the generation of 0.25% duty cycle 12.95-muW power pulses (across an optimal load impedance of 521 kOmega) at an overall energy conversion efficiency of 3.97%. These electrical power pulses can potentially be useful for periodically sampling sensor microsystems.
Applied Physics Letters | 2007
Mvs Chandrashekhar; Rajesh Duggirala; Michael G. Spencer; Amit Lal
The change in open-circuit voltage of a 4H SiC p-n diode betavoltaic cell in response to temperature was used to sense temperature. A linear sensitivity of 2.7mV∕K was obtained from 24to86°C. This was achieved with only 2.5μCi of active nickel-63 as the β source, giving a short circuit current of 21pA, a low-enough activity for civilian applications. The measured sensitivity of 2.7mV∕K was lower than the 5.5mV∕K predicted from the theory. The 28GΩ shunt resistance of the betavoltaic cell was used to explain the lower sensitivity.
internaltional ultrasonics symposium | 2004
Rajesh Duggirala; Hui Li; Amit Lal
We present a radioactively powered acoustic transmitter for application in wireless sensor nodes. The acoustic transmitter integrates a piezoelectric acoustic transducer with a self-reciprocating radioisotope powered piezoelectric micropower generator for long-life (tens of years) autonomous operation. The radiated /spl beta/-particles from the radioisotope are used to direct charge an air-gap capacitor structure, formed by the collector plate at the tip of a piezoelectric unimorph cantilever beam and the thin-film radioisotope source plate placed directly underneath the collector. The resulting electrostatic forces draw the collector plate towards the source. The collector plate eventually makes contact with the source discharging the air-gap capacitor and releasing the cantilever. The sudden release excites the unimorph mechanical impulse response, causing the cantilever to oscillate. The mechanical vibrations induce charges in the piezoelectric section of the monomorph, which are used to drive the acoustic transmitter. The stored mechanical energy is first converted into electrical energy by the piezoelectric unimorph and then into radiated acoustic energy in the external piezoelectric speaker. Eventually, the vibrations decay and a new cycle begins for the self-reciprocating actuator. At the end of every reciprocation cycle, acoustic transmission at the design frequency of 170 Hz can be sensed using a high sensitivity (-34 dB 1 V/1 Pa) microphone placed as far as 5 cm from the speaker.
international conference on micro electro mechanical systems | 2006
Rajesh Duggirala; Ronald G. Polcawich; E. Zakar; Madan Dubey; H. Li; Amit Lal
We present a microfabricated die-scale Radioisotope-powered Piezoelectric µ -power Generator (RPG) with nuclear to electrical conversion efficiency as high as 3.7%. The generator employs direct charging to convert radiated β-particle kinetic energy into stored electromechanical energy in a piezoelectric unimorph, and piezoelectricity to convert the stored mechanical energy into extractable electrical energy. The generator goes through a charge-discharge-vibrate cycle, integrating the energy collected during the charging phase. This enables high power output (1.13 µ W peak across a 90 kΩ load impedance) for a short time (10 s) during the vibration cycle, even with radioactive film emitting only 100 nW of continuous power.
IEEE\/ASME Journal of Microelectromechanical Systems | 2005
Rajesh Duggirala; Amit Lal
A low-voltage, low-power microvalve for compact battery-powered portable microfluidic platforms is designed, fabricated and experimentally characterized. The microvalve employs laser-machined piezoelectric unimorphs mechanically linked to surface micromachined nickel structures anchored on corrugated Si/sub x/N/sub y/-Parylene composite membrane tethers. The Parylene layer also serves as a compliant sealing layer on the valve seat for reducing the leakage in the off state. A mechanical linking process to connect the bulk piezoelectric unimorphs to micromachined diaphragms in a self-aligned manner has been developed. The design enables large strokes (2.45 /spl mu/m) at low-actuation voltages (10 V) consuming a comparatively low switching energy (678 nJ). The dependence of the measured flow rates on the modulated clearance over the orifice was found to be in good agreement with the theory of laminar flow in the low (1-100) Reynolds number regime. The microvalve was experimentally characterized for both gas and liquid flows. For example, at 10 V unimorph actuation, a gas flow rate of 420 /spl mu/L/min at a differential pressure of 9.66 kPa was measured. The off-state leakage rate for 0 V actuation is estimated to be 10-20 /spl mu/L/min. Typical flow rates with pulse width modulated (PWM) actuation with 50% duty cycle at 20 V/sub pp/ (1 kHz) were measured to be 770 /spl mu/L/min at 6.9 kPa for gases and 2.77 /spl mu/L/min at 4.71 kPa for liquids.
Archive | 2010
Rajesh Duggirala; Amit Lal; Shankar Radhakrishnan
Radioactivity and Radioisotopes.- Radioisotope Thin Films for Microsystems.- Radioisotope Micropower Generation: Microfabricated Reciprocating Electro-Mechanical Power Generators.- Radioisotope Micropower Generation: Integrated Radioisotope Actuated Electro-Mechanical Power Generators.- Radioisotope Micropower Generation: 3D Silicon Electronvoltaics.- Radioisotope Direct Charging: Autonomous Wireless Sensors.- Radioisotope Decay Rate Based Counting Clock.
international conference on micro electro mechanical systems | 2008
S. Tin; Rajesh Duggirala; Ronald G. Polcawich; Madan Dubey; Amit Lal
We demonstrate a self-powered tunable wireless RF transmitter by utilizing discharge events in nickel-63 radioisotope actuated reciprocating AIN-Si unimorph microcantilevers. The nickel-63 thin-film discharge by the reciprocating microcantilevers results in periodic generation of 264 MHz wireless signals detectable up to 3.6 meters (limited by room size). Furthermore, the wireless RF signal frequency can be tuned by as much as 3.44 MHz by varying stressing the unimorph by applied voltage bias across the A1N thin-film. This frequency tunability can be used to realize self-powered wireless RF sensors beacons to convey information between wireless sensor and RFID nodes. The resulting self-powered wireless sensors can function autonomously for decades enabling long-term monitoring of structural and environmental health in remote places.
ieee sensors | 2007
Mvs Chandrashekhar; Rajesh Duggirala; A. Lai; Michael G. Spencer
The change in open-circuit voltage of a 4 H SiC pn diode betavoltaic cell in response to temperature was used to sense temperature. A linear sensitivity of 2.7 mV/K was obtained from 24degC to 86degC. This was achieved with only 2.5 muCi of active Ni-63 as the beta-source, giving a short circuit current of 21 pA, low-enough an activity for civilian applications. The measured sensitivity of 2.7 mV/K was lower than the 5.5 mV/K predicted from theory. The 28 GOmega shunt resistance of the betavoltaic cell was used to explain the lower sensitivity. Despite the lower sensitivity than predicted by theory, this work represents a significant improvement over metal thermocouples which typically give <0.1 mV/K.