VHF helicopter antennas that incorporate the airframe and reducerotor modulation

Antennas at VHF frequencies mounted to small (with respect to wavelength) helicopter platforms are usually limited to whip and loop antennas. Antenna placement and rotor position can drastically change antenna performance due to induced currents on the platform. This work illustrates deliberate antenna-platform interactions that cause induced currents to reinforce and improve the radiating system performance. Additionally, rotor modulation effects can be simultaneously limited. This is accomplished by using oppositely placed loop antennas at a location on the airframe that is nominally one wavelength in circumference. The resulting broadcast pattern admits low cross-polarization radiation and low copolarized rotor modulation, but is not uniform. The dipole moment of the loops dictates this nonuniformity. Double-loop antennas are used to create a more uniform broadcast pattern without sacrificing the desired low cross-polarized radiation and low copolarized rotor modulation     

The role of optimum dielectric saturation in the reversible combination of oxygen with heme Fe2+ and the tuning of paramagnetic-diamagnetic switching

The paramagnetic-diamagnetic switching mechanism of hemoglobin, triggered by oxygen binding, is studied by a formalism involving an expression of work necessary to polarize the dielectric in Landau form. The “tuning” of the mechanism, or determination of occurrence of the switching in response to a certain input energy, is brought about by dielectric saturation of the medium. The relation between the effect of dielectric saturation of the medium and the effect of application of a constant (nonordering) magnetic field indicates charge transfer between the central Fe²⁺ ion and the porphyrin ring during switching.     

Solder joint reliability of a polymer reinforced wafer level package

Wafer level packages (WLPs) have demonstrated a very clear cost-advantage vs traditional wire-bond technologies, especially for small components that have a high number of dice and I/O per wafer. Ultra CSP^® is a WLP developed by the Kulicke & Soffa Flip Chip Division (formally Flip Chip Technologies). Typical products utilizing the Ultra chip scale package (CSP) have 5×5 or less area arrays at 0.5 mm pitch. This relatively small array has been limited by the inherent solder joint reliability of WLPs. A much larger subset of higher I/O IC’s could benefit from WLPs provided that standard reliability requirements are achieved without the use of underfill.A new polymer reinforcement technology, “Polymer Collar WLP™”, has been developed by K&S Flip Chip Division. Polymer Collar WLP utilizes a polymer reinforcement structure surrounding the solder joint and it has demonstrated more than 50% increase in solder joint life in thermal cycling tests. The most attractive feature of the Polymer Collar WLP process is its simplicity. A simple replacement of the standard solder flux with Polymer Collar material during the solder attach process is all that is required. This simplicity makes Polymer Collar the most cost-effective solution for adding a polymer reinforcement structure to the solder joint. Other methods in use today require additional complex and costly manufacturing steps.This Polymer Collar WLP is expected to widen the WLP market to include larger arrays where the Ultra CSP did not have suitable solder joint reliability.     

Status of device-qualified GaAs substrate technology for GaAsintegrated circuits

A review is presented of the current technical status of large-diameter GaAs crystal growth, the effects of residual impurities, stoichiometric defects and crystalline imperfections on the electrical properties of undoped semi-insulating GaAs, and the effectiveness of Group III and V isovalent, lattice-hardening dopants in yielding dislocation-free, semi-insulating GaAs crystals. Factors related to crystal growth, postgrowth annealing, and the preparation of ultraflat, damage-free GaAs wafers, which can significantly improve the performance and yields of directly implanted devices and monolithic circuits are discussed     

Avalanche breakdown and the probabilistic nature of laser-induced damage

This paper discusses the probabilistic nature of the damaging interaction between light and matter. It is shown that when one recognizes that there is some probability to induce damage at any level of optical irradiation, then the reported irreproducible damage-resistance properties of many useful materials can be understood. This point of view also explains why some optical components may be safely irradiated many times before damage occurs, though no other change in the material can be detected prior to the observation of damage. Experimental data showing the probability for surface damage as a function of power density are presented for several materials. The dependence of damage probability on optical field strength is similar to that of the dc ionization coefficients for semiconductors and gases on the applied field. This observation is discussed and it is suggested that a form of avalanche breakdown might be the cause of laser-induced damage.     

On vibrating strings and information theory

The problem addressed in concreto is the relation of information provided by vibrating strings to that provided by systems describable with equations of one degree of freedom. Whereas the mathematical physics of vibrating strings is based on the wave equation—a second-order differential equation of at least two degrees of freedom—a quantum model of information theory has only been considered for a mechanical system of one degree of freedom.