Analysis of two-port magnetoelastic delay lines as pulse-compression filters

A critical review is given of the properties of magnetoelastic delay lines, employing yttrium iron garnet (YIG) and having physically distinct input and output ports. Attention is directed to two configurations involving the materials YIG and yttrium alumium garnet (YAG), namely the YAG(nλB/4)-YIG-YAG(n/4) employing YAG quarter-wave plates λB/4, and the YIG-YAG-YIG structures. These offer the highest isolation between input and output ports coupled with the lowest insertion loss for magnetoelastic waves, under specified conditions of microwave frequency and delay. The transfer functions through the YAG material are derived in each configuration for the cases of 1) imperfect matching between the acoustic characteristic impedances of YIG and YAG, with perfect optical bonding, and 2) imperfect optical bonding. Conventional matched filter theory is used to evaluate the time response of each magnetoelastic delay line, linear variation of delay with frequency, to a linearly frequency-modulated pulse. It is established that the configuration employing quarter-wave plates gives desirable weighting of the main pulse. However, a spurious echo of unacceptable level exists, which is delayed approximately by an acoustic round trip in the nλB/4 plate, when a reasonable bandwidth is employed. Analysis shows that this difficulty does not arise for the YIG-YAG-YIG configuration. However, an external weighting network is required for range sidelobe reduction.     

Recent developments in magnetic levitation

New developments in magnetic levitation by tuned circuits are described. Suspension of relatively large weights at low frequencies is now possible. The system is extremely simple and therefore reliable. Owing to the high reliability and cylindrical symmetry, the levitation is suitable for magnetic bearings.     

Recent developments in power transistors

Power transistors capable of providing five watts output are now in production. Because these units are relatively non-linear in their characteristics, large signal graphical analysis of their behavior is necessary. To facilitate this, the static characteristics of the grounded base, grounded emitter, and grounded collector circuits are presented for several temperatures. Since power transistors are seldom driven with a high impedance source, the input voltages must be known as well as the input currents. These characteristics are drawn to indicate both simultaneously on one chart. The power that must be removed from the junction of these transistors requires that the mounting for the transistor be thermally adequate to remove the heat without allowing the temperature of the Junction to exceed its critical value. The temperature power relationship is discussed and the theoretical size requirements for a heat dissipator are shown for free air convection and forced convection.     

Recent developments in feedback communication

The use of a noiseless feedback communication channel to improve both digital and analog transmission is discussed. The feedback channel is used in an iterative signaling procedure called center-of-gravity feedback. Suboptimum schemes having a less severe-feedback requirement are also treated.     

Recent developments in light-emitting-diode technology

This paper describes recent trends in LED technology. Emphasis is placed on the LED materials and device-fabrication technologies that have resulted in larger and brighter LED displays with a variety of colors, and on the monolithic red-emitting LED displays that are commonly employed as watch and calculator displays.     

Recent developments in micromachined silicon

This paper provides a review, directed at scientists and engineers concerned with microsystems technology, of advances in microelectromechanical systems (MEMS). The emphasis is on silicon technology, where the electrical properties of the material are exploited in circuitry and the mechanical properties are used in sensor and microstructure applications. Developments in surface micromachining are discussed, and applications in sensors, microelectronic devices, vacuum microanalysis systems, microfluidics, and optoelectronic subsystems are reviewed. Some emerging technologies are assessed and promising new research directions are identified     

Recent dark-trace tube developments

Dark-trace tubes or skiatrons have certain advantages over bright display tubes which make their use desirable for information displays. These advantages are the ability to integrate visually, to store information, and daylight and sunlight viewing. Since World War II, at the time the 4AP10 was used, several of the basic disadvantages have been corrected in part, such as erase time, writing speed, contrast and color. Several experimental tube types have been evolved and others are under development. Some radical improvements in one or more of the limiting characteristics have been achieved. These were accomplished in several ways, including low heat capacity screens, conductive film techniques, different screen compositions, special electron optics, and other techniques. The characteristics and limitations are summarized for different tube types together with several suggestions for possible further research and development in the field. The equipment design factors peculiar to these tubes, such as stringent voltage requirements, sweep failure protection, beam current limiting circuitry, and other items are discussed to aid preliminary equipment designers in the use of these tubes.     

Parasitic-compensated switched-capacitor delay lines

Describes a systematic approach to the design of passive parasitic-compensated switched capacitor (SC) delay lines employing well known SC branches. Such delay lines are important building blocks for the implementation of high frequency FIR SC decimators and interpolators with high selectivity amplitude responses     

Microwave solid-state delay lines

The low-loss propagation of microwave phonons at room temperature in certain single crystals makes practical the construction of microwave acoustic delay (MAD) lines. The properties of these solid-state units are discussed and compared to those of more conventional microwave delay devices. Various possible applications of solid-state lines are suggested and the present status of these units is reviewed. The dispersive properties of magnetoelastic and magnetostatic wave propagation are also outlined and practical considerations governing their use are discussed. Microwave acoustic delay devices not only offer size and weight advantages over conventional microwave delay lines, but also offer improved performance and in many cases lower cost than the conventional units.     

Surface-wave long delay lines

Recent results obtained with helical surface-acoustic-wave (SAW) delay lines of large time delay and bandwidth are described. Both unguided and guided propagation are involved, with time delays up to one millisecond and bandwidths up to 65 MHz being observed. Fiber delay lines of both capillary and cladded types are also discussed. The potential for future application of SAW delay lines of large time-bandwidth product to high-speed signal-and data-processing systems is considered.     

Continuously variable delay lines

Two types of nonlinear delay line employing variable-capacitance diodes are described. The delays of both lines vary from 9 ns to 15 ns. The pulse risetimes of the two types of lines are considered.     

Solid-state microwave delay lines

Solid-state delay lines operating at microwave frequencies can provide many advantages over conventional delay techniques. These devices use sound waves or magnetic spin waves to obtain fixed, variable, or dispersive behavior. The size and weight of electromagnetic delay lines, together with inherent high cable loss, are avoided with solid-state units. Pulse compression filters with bandwidths of several hundred MHz have been constructed, and the future promises even greater capabilities.     

Fibre-optic variable delay lines

A technique is presented for fabricating large numbers of evanescently coupled taps on a single-mode fibre. An output fibre can be adjusted between any of the taps, resulting in a discretely variable delay. The concept was demonstrated with a 7 tap device which had a 2.5 ns delay between taps and a tap uniformity of ± 1.6 dB. A technique for making continuously variable delay lines is presented.     

Wrap-around surface-wave delay lines

Acoustic-surface-wave beams at 100 MHz have been circulated in multiple transits around the periphery of small lithiumniobate samples. A time delay of 22 ?s per round-trip transit with propagation loss of 5.75 dB per round-trip transit has been observed. This has potential application to delay lines of very long delay using a helical path between input and output transducers, and to delay lines having lower insertion loss and triple-transit signals than conventional lines.     

Acoustic-surface-wave disk delay lines

Information can be stored serially in an acoustic beam wrapping about the closed surface of a circular thin disk. Beamguiding may be secured by exploiting a natural interaction between edge curvature and crystal anisotropy. Observations at 41 MHz, on Y-cut and ST-cut disks, demonstrate the feasibility of building isopaustic low-spurious level (57-dB) long 250-µs) disk delay lines.     

Acoustic-surface-wave disc delay lines

An acoustic-surface-wave beam, launched along the chord of a disc, will fold compactly into an extended delay path. The rounded edges of the disc act as geodesic lenses. Beam-guiding can be obtained by repetitive focusing at the edge. A 96 ?s 41 MHz prototype disc delay line is described.     

应用激光化学的发展近况

本文报导了近年来激光在化学中期应用取得进展的一些成功实例，并提出了激光化学在今后十年内一些看来很有前途的应用领域。请如激光分离同位素，激光提纯化学品，激光热解合成超细粉末材料，激光在分析化学中的应用，激光催化，激光化学沉积及重要化学药品的合成等。由所取得的成果可以予期，应用激光化学将会有一个美好的前景。     

Recent developments in silicon optoelectronic devices

Due to the rapid growth of the internet and multi-media communication networks, there are urgent needs and tremendous commercial values in the development of optoelectronics integrated circuits (OEICs). This work reviews the recent developments and the prospect of silicon-based integrated optoelectronic circuits (Si-OEICs). The technological aspects of porous silicon and oxynitride devices for integrated optoelectronic applications are discussed. Some optoelectronic devices being realized with these technologies are described. Recent achievements indicate that the present constraints for using Si-based materials in optoelectronics are mainly technological rather than physical. Once these technological difficulties are resolved, the realization and applications of Si-OEICs will grow rapidly.