Spectral control development for thermophotovoltaics
Gallium Antimonide (GaSb) infrared photovoltaic cells are light weight whereas batteries are heavy. The specific energy in a hydrocarbon fuel is high at 12,900 W-hr per kg but a lithium ion rechargeable battery has a specific energy of only 145 W-hr per kg. A 10% efficient portable lightweight thermophotovoltaic (TPV) cylindrical generator when compared with a battery can have 6.5 times higher specific energy, operates 7 times longer, and be quickly refueled. The key is the 10% efficiency goal. This efficiency goal depends on matching the spectrum from a combustion heated ceramic IR emitter to the response band of the IR PV cell. Herein, spectral measurements are presented for a propane burner and ceramic IR emitter assembly surrounded by a fused silica glass envelope. The cylindrical IR ceramic emitter consists of an array of NiO doped MgO rods or slats. The Ni ion emission line is centered at 1.6 microns and it matches the GaSb IR response band extending out to 1.8 microns. The ceramic IR emitter is combustion heated to approximately 1200 C. The fuel and air combustion efficiency and hot gas coupling efficiency to the IR emitter are also important parameters.
Spectral filtering of sub-bandgap radiation using all-dielectric gratings for thermophotovoltaic applications
Abstract. Filtering of the sub-band spectral radiation is an attractive technique to overcome the lower efficiencies of direct conversion thermophotovoltaic technology. The poor performance of these systems is due to the relatively small portion of the incident energy being above the bandgap of photovoltaic cell. To effectively filter the majority of the sub-bandgap radiation and re-employ it as regenerative heat, a viable solution is to design an efficient spectrally selective filter ideally matched to the photovoltaic cell’s bandgap. Here, we have explored a high contrast amorphous silicon grating on a quartz substrate. Quartz due to its inherent nature inhibits transmission of sub-band gap radiation in the infrared (IR) region (>4.75  μm), whereas gratings further filter radiation above 1.8  μm suitable for GaSb photovoltaic cell. The optimized filter is fabricated using direct write laser lithography, and optical characterization result shows that 72% of incident radiation in unconvertible region (>1.80  μm) is filtered and recycled. Further, the thermal characterization results of IR filter carried out using a ceramic heater has shown the drop in effective temperature from 1074.9 to 813.2 K in above bandgap region. This suppressed radiation has contributed to an absolute increase in source body temperature by 16.0 K resulting in increase in the above bandgap radiation available for thermophotovoltaic conversion. The proposed spectral filtering design can be tailored to solar cells of any bandgap and is scalable for employment in various thermophotovoltaic applications.
A new power measuring circuit using a bridge-connected magnetic circuit and another magnetic core
The authors describe the operating characteristics of an oscillating circuit using a bridge-connected magnetic circuit and another magnetic core. A square-shape output voltage is obtained in the oscillating circuit. The pulsewidth in positive and negative half cycles of output voltage changes with the current of the U-form core windings and with the signal voltage applied to the exciting windings. The mean value of the output voltage varies in proportion to the product of the current and the signal voltage. Utilizing this feature, an application of the oscillating circuit to a novel power measuring circuit of simple construction is presented. >