Taysir H. Nayfeh

Spatially selective electrochemical deposition of composite films of metal and luminescent Si nanoparticles

We report on a procedure for selective deposition of Si nanoparticles using an electrochemical process. A conducting substrate is immersed in alcohol in which the particles are suspended. Biasing the substrate positively relative to a platinum electrode draws the Si particles to the substrate. Thin particle coatings on metal, foil, or silicon substrates are demonstrated. Fluorescent spectroscopy shows that the deposited particles retain the high luminescence efficiency and spectral distribution characteristic of the dispersed state. The process is used to deposit composite thin films of metal and Si nanoparticles. Dielectric masking allowed selective area deposition. These processes have implications for flat panel or flexible particle-based displays.

Calibrated method for ultrasonic on-line monitoring of gradual wear during turning operations

Abstract On-line tool condition monitoring is essential for modern machining systems, especially in the case of precision and unmanned machining. Knowledge of the condition and the expected life of the tool are very important inputs for determining the optimal machining parameters. Previous efforts have indicated that ultrasonic gaging methods can be used to directly measure in-process gradual tool wear during turning operations. Good correlation was shown between the level of gradual wear and the ultrasonic signals. However, the correlation was tool dependent. This was mainly attributed to variations in the tool materials and inconsistent coupling of the transducer to the tools. This paper describes a robust method for on-line gradual wear monitoring using normalized ultrasonic signals. A consistent calibration mark, cut in the lower comer of the tool nose, is used to generate a calibration echo. The calibration echo is affected by the same variations as that of the gradual wear and is used to normalize the nose and flank echoes. Experiments under various cutting conditions showed that the gradual wear measurements can be made tool independent by normalizing the measurements with the calibration mark. In addition, the variations in the signals which were previously reported are also eliminated.

Optical frequency optimization of a high intensity laser power beaming system utilizing VMJ photovoltaic cells

An effective form of wireless power transmission (WPT) has been developed to enable extended mission durations, increased coverage and added capabilities for both space and terrestrial applications that may benefit from optically delivered electrical energy. The high intensity laser power beaming (HILPB) system enables long range optical ‘refueling’ of electric platforms such as micro unmanned aerial vehicles (MUAV), airships, robotic exploration missions and spacecraft platforms. To further advance the HILPB technology, the focus of this investigation is to determine the optimal laser wavelength to be used with the HILPB receiver, which utilizes vertical multi-junction (VMJ) photovoltaic cells. Frequency optimization of the laser system is necessary in order to maximize the conversion efficiency at continuous high intensities, and thus increase the delivered power density of the HILPB system. Initial spectral characterizations of the device performed at the NASA Glenn Research Center (GRC) indicate the approximate range of peak optical-to-electrical conversion efficiencies, but these data sets represent transient conditions under lower levels of illumination. Extending these results to high levels of steady state illumination, with attention given to the compatibility of available commercial off-the-shelf semiconductor laser sources and atmospheric transmission constraints is the primary focus of this paper. Experimental hardware results utilizing high power continuous wave (CW) semiconductor lasers at four different operational frequencies near the indicated band gap of the photovoltaic VMJ cells are presented and discussed. In addition, the highest receiver power density achieved to date is demonstrated using a single photovoltaic VMJ cell, which provided an exceptionally high electrical output of 13.6 W/cm2 at an optical-to-electrical conversion efficiency of 24 %. These results are very promising and scalable, as a potential 1.0 m2 HILPB receiver of similar construction would be able to generate 136 kW of electrical power under similar conditions.

An integrated ultrasonic sensor for monitoring gradual wear on-line during turning operations

Abstract The condition of the tool and the cutting process are essential inputs to any productivity improvements through process optimization in conventional and unmanned machining. Tool replacement and tool wear compensation strategies, which are based on prior experience and/or tool history are, in general, under performing. Currently, the methods of tool condition monitoring are either time consuming, as in the case of off-line direct measurements of the tool, or are modestly successful, as in the case of the on-line indirect measurements, such as forces or acoustic emissions. This in part is due to the lack of suitable sensors and/or exact dynamic model, which relate the indirect measurements to the actual tool condition. This paper describes a promising ultrasonic method for on-line direct measurement of gradual wear in turning operations. An integrated (transmit and receive) single ultrasonic transducer operating at a frequency of 10 MHz is placed in contact with the tool. The change in the amount of the reflected energy from the nose and the flanks of the tool can be related to the level of gradual wear and the mechanical integrity of the tool. The experimental results show that under laboratory conditions, a correlation exists between the ultrasonic measurement and gradual wear and that it is tool dependent.

Comparison of square and radial geometries for high intensity laser power beaming receivers

In an effort to further advance a realizable form of wireless power transmission (WPT), high intensity laser power beaming (HILPB) has been developed for both space and terrestrial applications. Unique optical-to-electrical receivers are employed with near infrared (IR-A) continuous-wave (CW) semiconductor lasers to experimentally investigate the HILPB system. In this paper, parasitic feedback, uneven illumination and the implications of receiver array geometries are considered and experimental hardware results for HILPB are presented. The TEM00 Gaussian energy profile of the laser beam presents a challenge to the effectiveness of the receiver to perform efficient photoelectric conversion, due to the resulting non-uniform illumination of the photovoltaic cell arrays. In this investigation, the geometry of the receiver is considered as a technique to tailor the receiver design to accommodate the Gaussian beam profile, and in doing so it is demonstrated that such a methodology is successful in generating bulk receiver output power levels reaching 25 W from 7.2 cm2 of photovoltaic cells. These results are scalable, and may be realized by implementing receiver arraying and utilizing higher power source lasers to achieve a 1.0 m2 receiver capable of generating over 30 kW of electrical power. This type of system would enable long range optical ‘refueling’ of electric platforms, such as MUAVs, airships, robotic exploration missions and provide power to spacecraft platforms which may utilize it to drive electric means of propulsion. In addition, a smaller HILPB receiver aperture size could be utilized to establish a robust optical communications link within environments containing high levels of background radiance, to achieve high signal to noise ratios.