Electrostatically driven synthetic microjet arrays as a propulsion method for micro flight

A propulsion system based on acoustic streaming generated by Helmholtz resonators is presented. High frequency (>60 kHz) electrostatically driven micromachined Helmholtz resonators constitute the basic unit of the system. Microjets produced at the exit of these resonators can be combined to form a distributed propulsion system. A high yield (>85%) fabrication process is introduced for fabrication of individual as well as arrays of resonators. The fabrication results for ten different designs are presented. About 1000 resonators of similar design cover the surface of a 4-in. wafer, effectively converting it to a distributed propulsion system. A number of characterization methods such as monitoring the harmonics of the drive current, laser interferometry, hot-wire anemometry, acoustic spectrum measurement and video particle imaging are used to determine the structural and fluidic behavior of different resonator designs. Collapse and recovery times of the diaphragm in the electrostatic actuator of the resonator are characterized and reduced to less than 10 μs by optimizing the perforation design. The occurrence of acoustic streaming in the micron-scale is verified via video particle imaging. The jet streams produced with pulse drive at low frequencies (~1 kHz) are spatially profiled and jet velocities exceeding 1 m/s are measured at the exit of the resonators. It has been verified that the resonance frequencies of the device at 50 and 175 kHz can be closely predicted by modeling.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47854/1/542_2005_Article_600.pd

Computer Aided Design of Radiofrequency and Microwave Circuits

Radiofrequency and microwave CAD computer programs enabling for signal and yield analysis and circuit optimization have been developed. Program is used both in circuit design and student education

Extended law of corresponding states for percolation threshold of short-range attractive spheres

The percolation threshold (PT) for colloidal system refers to the point at which particles aggregate to form an infinite cluster that spans the suspension 1. It is widely assumed that the percolation transition should follow the concept of scaling, and recent numerical studies 2-5 have shown that the wrapping probability of percolation can be described by the universal scaling functions, which enables the estimation of PTs for different types of system

Some biological actions of PEG-conjugated RNase A oligomers

Previously we have shown that monomeric RNase A has no significant biological activity, whereas its oligomers (dimer to tetramer) prepared by lyophilizing from 50% acetic acid solutions, show remarkable aspermatogenic and antitumor activities. Furthermore, conjugates prepared by chemical binding of native RNase A to polyethylene glycol (PEG) have shown a significant aspermatogenic and antitumor activities. In this work we show that the chemical conjugation of PEG to the RNase A C-dimer, and to the two RNase A trimers (NC-trimer and C-trimer) decreases the aspermatogenic activity of the oligomers while increasing their inhibitory activity on the growth of the human UB900518 amelanotic melanoma transplanted in athymic nude mice. Moreover, the PEG-conjugated RNase A oligomers are devoid, like the free oligomers, of any embryotoxic activity