Glen C. King

Microwave power for smart material actuators

The concept of microwave-driven smart material actuators was envisioned and developed as the best option to alleviate the complexity and weight associated with a hard-wire-networked power and control system for smart actuator arrays. The patch rectenna array was initially designed for high current output, but has undergone further development for high voltage output devices used in shape control applications. Test results show that more than 200 V of output were obtained from a 6 × 6 array at a far-field exposure (1.8 m away) with an X-band input power of 18 W. The 6 × 6 array patch rectenna was designed to theoretically generate voltages up to 540 V, but practically it has generated voltages in the range between 200 and 300 V. Testing was also performed with a thin layer composite unimorph ferroelectric driver and sensor and electro-active paper as smart actuators attached to the 6 × 6 array. Flexible dipole rectenna arrays built on thin-film-based flexible membranes are most applicable for NASAs various missions, such as microwave-driven shape controls for aircraft morphing and large, ultra-lightweight space structures. An array of dipole rectennas was designed for high voltage output by densely populating Schottky barrier diodes to drive piezoelectric or electrostrictive actuators. The dipole rectenna array will eventually be integrated with a power allocation and distribution logic circuit and microbatteries for storage of excessive power. The roadmap for the development of wireless power drivers based on the rectenna array for shape control requires the development of new membrane materials with proper dielectric constants that are suitable for dipole rectenna arrays.

Cobalt oxide hollow nanoparticles derived by bio-templating

We present here the first fabrication of hollow cobalt oxide nanoparticles produced by a protein-regulated site-specific reconstitution process in aqueous solution and describe the metal growth mechanism in the ferritin interior.

Miniaturization of a Fresnel spectrometer

The core optical parts of an ultra-small spectrometer with less than 1 mm diameter were constructed using Fresnel diffraction. The fabricated spectrometer grating has a diameter of 750 µm and a focal length of 2.4 mm at 533 nm wavelength. The micro-spectrometer was built with a simple negative zone plate that has an opaque center with an ecliptic shadow to remove the zero-order direct beam to the aperture slit. Unlike conventional approaches, detailed optical calculation indicates that the ideal spectral resolution and resolving power in the Fresnel regime do not depend on the miniaturized sizes but only on the total number of rings. We calculated the 2D and 3D photon distributions around the aperture slit and confirmed that improved micro-spectrometers below 1 mm in diameter can be built with Fresnel diffraction. The comparison between mathematical simulation and measured data demonstrates the theoretical resolution, measured performance, misalignment effect, and improvement for the ultra-small Fresnel spectrometer. We suggest the utilization of an array of Fresnel spectrometers for tunable multi-spectral imaging in the ultra-violet range.

Power budget analysis for high altitude airships

The High Altitude Airship (HAA) has various potential applications and mission scenarios that require onboard energy harvesting and power distribution systems. The energy source considered for the HAAs power budget is solar photon energy that allows the use of either photovoltaic (PV) cells or advanced thermoelectric (ATE) converters. Both PV cells and an ATE system utilizing high performance thermoelectric materials were briefly compared to identify the advantages of ATE for HAA applications in this study. The ATE can generate a higher quantity of harvested energy than PV cells by utilizing the cascaded efficiency of a three-staged ATE in a tandem mode configuration. Assuming that each stage of ATE material has the figure of merit of 5, the cascaded efficiency of a three-staged ATE system approaches the overall conversion efficiency greater than 60%. Based on this estimated efficiency, the configuration of a HAA and the power utility modules are defined.

Ultrasonication of Bismuth Telluride Nanocrystals Fabricated by Solvothermal Method

The objective of this study is to evaluate the effect of ultrasonication on bismuth telluride nanocrystals prepared by solvothermal method. In this study, a low dimensional nanocrystal of bismuth telluride (Bi2Te3) was synthesized by a solvothermal process in an autoclave at 180°C and 200 psi. During the solvothermal reaction, organic surfactants effectively prevented unwanted aggregation of nanocrystals in a selected solvent while controlling the shape of the nanocrystal. The atomic ratio of bismuth and tellurium was determined by energy dispersive spectroscopy (EDS). The cavitational energy created by the ultrasonic probe was varied by the ultrasonication process time, while power amplitude remained constant. The nanocrystal size and its size distribution were measured by field emission scanning electron microscopy (FESEM) and a dynamic light scattering system. When the ultrasonication time increased, the average size of bismuth telluride nanocrystal gradually increased due to the direct collision of nanocrystals. The polydispersity of the nanocrystals showed a minimum when the ultrasonication was applied for 5 min.

Power Technology for Application-Specific Scenarios of High Altitude Airships

The High Altitude Airship (HAA) has various potential applications and mission scenarios that require onboard energy harvesting and power distribution systems. The energy source considered for HAAs is solar photon energy that allows the use of either photovoltaic (PV) cells or advanced thermoelectric (ATE) converters. Both PV cells and an ATE system were briefly compared to identify the advantages of ATE for HAA applications in this study. Utilizing the estimated high efficiency of a three-staged ATE in a tandem mode, the ATE generates a higher quantity of harvested energy than PV cells for mission scenarios. When the ATE performance figure of merit of 5 is considered, the cascaded efficiency of a three-staged ATE system approaches an overall efficiency greater than 60%. Based on this estimated efficiency, the configuration of a HAA and the power utility modules are defined.

Thermoelectric Performance Enhancement by Surrounding Crystalline Semiconductors with Metallic Nanoparticles

5NASA Langley Research Center, Hampton, VA 23682 Direct conversion of thermal energy to electricity by thermoelectric (TE) devices may play a key role in future energy production and utilization. However, relatively poor performance of current TE materials has slowed development of new energy conversion applications. Recent reports have shown that the dimensionless Figure of Merit, ZT, for TE devices can be increased beyond the state-of-the-art level by nanoscale structuring of materials to reduce their thermal conductivity. New morphologically designed TE materials have been fabricated at the NASA Langley Research Center, and their characterization is underway. These newly designed materials are based on semiconductor crystal grains whose surfaces are surrounded by metallic nanoparticles. The nanoscale particles are used to tailor the thermal and electrical conduction properties for TE applications by altering the phonon and electron transport pathways. A sample of bismuth telluride decorated with metallic nanoparticles showed less thermal conductivity and twice the electrical conductivity at room temperature as compared to pure Bi2Te 3. Apparently, electrons cross easily between semiconductor crystal grains via the intervening metallic nanoparticle bridges, but phonons are scattered at the interfacing gaps. Hence, if the interfacing gap is larger than the mean free path of the phonon, thermal energy transmission from one grain to others is reduced. Here we describe the design and analysis of these new materials that offer substantial improvements in thermoelectric performance.

Rectenna performance under a 200-W amplifier microwave

The concept of microwave driven smart material actuators is envisioned as the best option to alleviate the complexity associated with hard wired control circuitry for applications such as membrane actuators, insect-like flying objects, or micro-aero-vehicles. Accordingly, rectenna technology was adopted to convert power from microwave to DC and run actuator devices. Previous experimental results showed that 230 VDC output was obtained from a 6 x 6 rectenna array at a far-field exposure (1.8 meters away) with an x-band input power of 20 watts. This result showed the feasibility of using microwaves to power feed and control smart actuators. We have tested a 6 x 6 JPL array patch rectenna which was designed to generate theoretical voltages up to 540 volts. The test result indicated that the performance degradation of Shottky barrier diodes on the rectenna array caused the output voltage to drop. Thus, an estimation of output voltage was made to show the performance beyond the previous measurement by extrapolating and correlating the measured data with a 200 W TWT amplifier in a reverse process. The estimated peak output voltage was 515 volts. In this experiment, due to the degradation of the rectenna performance, we had to measure the output performance based on comparison of the previous result of the rectenna output of a 20W amplifier with the output from the 200 W amplifier. For the real applications, the degradation of Schottky diodes will be a critical issue to be resolved in the fabrication process.

Fabrication of cell structures for bionanobattery

The concept of a bio-nanobattery is based on ferritin, an iron storage protein that naturally exists in most biological systems. Biomineralization allows ferritins to reconstitute iron core with various metallic cores. When the ferritin half cells are integrated into a complete battery system, the fabrication of well-organized ferritin arrays is necessary and very important to enhance the overall battery performance, improving the battery power density, the power discharge rate, the compactness of battery size, etc. In this work, a spin self-assembly (SA) method was used for producing a thin-film array structure of ferritins. The spin SA deposition was repeated until two bilayers of cationized and native ferritins or 4 alternating ferritin layers were achieved. High-resolution field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and variable angle spectroscopic ellipsometry (VASE) were used to characterize the multilayered ferritin arrays. The thickness of ferritin multilayer increased linearly as the spin SA deposition was repeated. The spin SA deposition method produced well-organized, uniform, and flat ferritin layers in a much shorter period of time, compared with Langmuir-Blodgett or dipping deposition methods. Such enhancement can be attributed to a strong electrostatic attraction that holds the ferritin layer on the substrate during the spin-coating process while hydrodynamic drag and centrifugal forces remove loosely-bound ferritins.

Development of a Bio-nanobattery for Distributed Power Storage Systems

Currently available power storage systems, such as those used to supply power to microelectronic devices, typically consist of a single centralized canister and a series of wires to supply electrical power to where it is needed in a circuit. As the size of electrical circuits and components become smaller, there exists a need for a distributed power system to reduce Joule heating, wiring, and to allow autonomous operation of the various functions performed by the circuit. Our research is being conducted to develop a bio-nanobattery using ferritins reconstituted with both an iron core (Fe-ferritin) and a cobalt core (Co-ferritin). Both Co-ferritin and Fe-ferritin were synthesized and characterized as candidates for the bio-nanobattery. The reducing capability was determined as well as the half-cell electrical potentials, indicating an electrical output of nearly 0.5 V for the battery cell. Ferritins having other metallic cores are also being investigated, in order to increase the overall electrical output. Two dimensional ferritin arrays were also produced on various substrates, demonstrating the necessary building blocks for the bio-nanobattery. The bio-nanobattery will play a key role in moving to a distributed power storage system for electronic applications.