Textile Applications of Adjustable-Frequency Drives with Digital Ratio Control

The application of digital techniques to program and to process the input signals to adjustable-frequency inverters for the control of rugged ac motors is becoming widespread. It was perhaps inevitable that digital signal control would eventually be combined with the inherently digital adjustable-frequency power inverter to produce systems having high overall line speed accuracy, adjustable ``digital gearing' between sections, locked-in-step acceleration from creep to run speed, and in-train digital jogging. A short introduction to adjustable-frequency motor control is given, and the use of digital techniques for controlling adjustable-frequency inverters to produce digital speed systems is described. Early applications of the first solid-state inverters to synthetic fiber spinning and their continued use is described. Specific current applications of digitally controlled adjustable-frequency speed systems are discussed, and potential applications that demonstrate how the capabilities of such systems can be used to provide economic solutions to many textile industry drive problems are reviewed.     

一种导模共振窄带宽的平顶滤波器设计

鉴于导模共振滤波器具有高峰值反射率、低旁带反射、窄带以及带宽可控等优良特性,采用亚波长光栅的导模共振效应设计了一种平顶滤波器.通过将亚波长光栅与类法布里-珀罗腔结合使用,实现了窄带宽平顶滤波的效果.基于严格耦合波分析方法和等效介质理论,使用FDTD软件对光栅衍射效率进行了仿真分析.仿真结果表明,平顶滤波器在1130 n...     

A planar version of a 4.0 GHz reactively steered adaptive array

-A planar (two-dimensional) reactively steered adaptive array (RESAA) including a single active microstrip element and eight closely coupled parasitic microstrip elements has been designed and tested. Steering of a null toward a single incident jammer is accomplished by adaptive control of reactive terminations on the parasitic elements using a guided random search algorithm. The planar array can steer a null in both the elevation and azimuth directions with a depth of 30 dB.     

Hydrothermal synthesis of various carbonate containing calcium hydroxyapatites

Carbonate containing hydroxyapatites were prepared hydrothermally between 2000 and 20,000 psi and 250 and 900°C using H₂O or CO₂ pressure. On the basis of IR, x-ray and chemical investigations it is shown that under these conditions the CO₃ triangle can replace both the OH group and PO₄ tetrahedron in the apatite structure. Replacement is possible either in only one of these positions or also combined. The extent of the solid solubility, however, is still unknown.     

Simulation study of reactively steered adaptive arrays

A reactively steered adaptive array has a single driven element with closely coupled parasitic elements. Adjustable reactive terminations on the parasitic elements are the adaptively controlled variables. The results of a simulation study show that the best element spacing is approximately 0.2?, that the optimum array size is seven elements, and that this seven-element array can steer three nulls.     

Carrier mobilities in surface inversion layers on high purity germanium

The surface layer mobilities of electrons and holes in high purity (|N_D?N_A|<10¹¹cm^?3) Ge were measured. It was found that the mobility is often considerably smaller at the surface than in the bulk.     

A survey of possible passive antenna applications ofhigh-temperature superconductors

A survey of possible applications of high-temperature superconductors (HTSs) to antennas and antenna feed networks is presented. The frequency range considered is 1 MHz for 100 GHz. Three antenna application areas seem appropriate for HTS material: electrically small antennas and their matching networks; feed and matching networks for compact arrays with enhanced directive gain (superdirective arrays); and feed networks for millimeter-wave arrays. Preliminary experimental results are presented on YBaCuO and TlBaCaCuO 500 MHz half-loop antennas that show an increase in radiation efficiency (compared with a copper antenna at the same temperature) by a factor of 5 for the HTS antennas     

Charge Collection in Surface Channels on High-Purity Ge Detectors

Studies with collimated low energy ?-ray beams show that for ?-ray interactions within a "dead layer" of thickness about 1 mm at the surface of a Ge detector, the pulse height distribution is characteristic of single carrier collection. Independent measurements of the charge transport parameters also show that the majority carriers in the surface channel do not contribute to the charge pulse.     

Reactively steered adaptive array using microstrip patch elements at 4 GHz

A reactively steered adaptive array (RESAA) has one element connected by a transmission line to a receiver and a number of closely spaced parasitic elements, each of which is terminated by an adjustable reactive load. The pattern is formed by control of the reactive loads. Experimental results and the theory are presented for a RESAA consisting of five microstrip rectangular patch elements resonant at 4.0 GHz. Using steepest descent control of the reactive loads in a power inversion mode (no reference), we find that a null with a depth of 30 dB (relative to the pattern maximum) and an angular width of about25degcan be steered towards an interferer. Typically, about 40 steps (iterations) are needed for forming the null. With the slow power meter and general purpose minicomputer that served as the controller, adaptation times of several seconds are required; extrapolation to a dedicated microprocessor controller predicts adaptation times of several milliseconds. Operation in a mode using a reference signal demonstrates that the pattern can be shaped to steer a null toward interference and a lobe towards a desired signal. The nulling bandwidth is approximately 40 MHz with this array. The advantages of a RESAA, as compared With a conventional adaptive array, include the elimination of the mixers and other hardware needed to perform the complex weighting of the output of each element at an intermediate frequency, and better pattern control for closely spaced elements. These advantages are obtained at the expense of a more complicated control algorithm.