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Operation principle of the previously demonstrated radioisotope fueled electromechanical power generator.
(a) Schematic of the betavoltaic IREMPG. The IREMPG is placed in a vacuum chamber to minimize charge leakages from the radioisotope thin film source due to build up of . In this work, both the piezoelectric unimorph cantilever and nickel foils were clamped between ceramic blocks mounted on motion feedthroughs inside a test vacuum chamber. (b) Photograph of a prototype betavoltaic integrated piezoelectric unimorph cantilever, fabricated by epoxy bonding a laser cut PZT-5H (lead zirconate titanate oxide ceramic from Piezo Systems Inc.) sheet to the base of a laser cut copper beam and adhesively bonding four silicon diode chips (Advanced Photonix Inc.) at the tip of the copper beam via a 1 cm × 4 cm double sided adhesive copper tape (3M). Leads from the betavoltaic were wire bonded to solder pads on the piezoelectric unimorph cantilever. The lead wires were too thin to be clearly visible in the photograph. Therefore, curves were hand drawn over them for illustration.
Plot of (a) measured betavoltaic power output with and (b) calculated variation in radioisotope thin film source voltage during reciprocation at (i) , (ii) , (iii) , and (iv) . The calculations were done by first reducing the IREMPG to a one dimensional electromechanical equivalent, deriving the state equations describing the radioisotope actuation dynamics with radioisotope charge gap , and unimorph cantilever tip velocity as the state variables, and solving the nonlinear state equations through a block-diagram model implemented in the Simulink environment of MATLAB. The resistivity of the vacuum in the air gap was assumed to be , and the measured value of parasitic capacitance between the source and vacuum chamber of was used for the calculations.
Plot of measured (a) IREMPG pulsed voltage output across the piezoelectric and (b) bias generated across a capacitor by using the rectified for and .
Plot of measured variation in (a) average betavoltaic and maximum unimorph pulsed power outputs and , respectively, and (b) (iii) betavoltaic, (ii) unimorph, and (i) overall IREMPG energy conversion efficiencies , , and , respectively, with initial gap when and . Here, and .
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