Transmission Line Mechanical

The Electric Power Research Institute has been sponsoring a program to test the ability of structural analysis computer software to predict the behavior of large transmission towers, whose design poses problems not unlike a three-dimensional space-frame roof. A full-size giant tower has been constructed at the Transmission Line Mechanical Research Facility in Haslet, Texas, and the actual structure can be subjected to carefully controlled loads as the reaction of its various members is recorded. The results of such real-world tests were compared with computer predictions of the tower s behavior, and the computer software did not fare too well. 

Cost rules out almost all alternative materials for long-distance pipe lines it is much cheaper to build and protect a mild steel pipe than to use stainless steel instead - even though no protection is then needed. The only competing material is a polymer, which is completely immune to wet corrosion of this kind. City gas mains are now being replaced by polymeric ones but for large diameter transmission lines, the mechanical strength of steel makes it the preferred choice. 

Energy is converted from electrical energy into mechanical energy using the power from electrical transmission lines. 

A major degradation mechanism of modules is the decrease in fill factor. This is caused by an increase in the diode quality factor of the cells making up the module and by an increase in series resistance. The former is related more to the absorber and heterojunction properties and less to the ZnO properties. The series resistance increases because the conductivity of the ZnO drops and because the interconnects are deteriorating. Wennerberg et al. have assessed the individual contributions to increased series resistance [50]. Klaer et al. [52,53] have described a transmission-line test structure that allows to separate the contributions of contact and sheet resistance, respectively. The test structure is prepared by the same scribing techniques as those used in module manufacturing. 

In the case of viscoelastic loaded QCM two approaches have been followed one methodology is to treat the device as an acoustic transmission line with one driven piezo-electric quartz layer and one or more surface mechanical load (TLM) [50, 51]. A simpler approach is to use a lumped-element model (LEM) that represents mechanical inter-actions by their equivalent electrical BVD circuit components [52, 53]. 

The finite thickness of a film on the resonator surface makes the calculation of the mechanical impedance at the surface analogous to that of an appropriately terminated transmission line [41]. Noting the correspondence between stress and voltage and between particle velocity and current, the stress-firee upper film surface is analogous to a short-circuited electrical transmission line. From this analogy, the input impedance seen at the resonator/film interface is [40]... 

Many familiar heal transfer application. involve natural convection as the primary mechanism of heat transfer. Some examples are cooling of electronic equipment such as power transistors, TVs, and DVDs heat transfer from electric baseboard heaters or steam radiators heat transfer from the refrigeration coils and power transmission lines and heat transfer from the bodies of animals and human beings. Natural convection in gases is usually accompanied by radiation of comparable magnitude except for low-emissivity surfaces. 

It is well known that the behavior of electrical transmission lines can be represented in terms of distributed passive elements. As we mentioned at the beginning of this chapter, there exists an analogy between the electrical and mechanical behavior of the systems. Returning to the Maxwell model, one has... 

We can generalize the analogy by considering the viscoelastic materials as a continuum where the theory of transmission lines can be applied. In this way, a continuous distribution of passive elements such as springs and dash-pots can be used to model the viscoelastic behavior of materials. Thus the relevant equations for a mechanical transmission line can be written following the same patterns as those in electrical transmission lines. By representing the impedance and admittance per unit of length by g and j respectively, one has... 

In the schematic shown in Figure 4.2.10, the RF path is visible between the two signal sources (RF ports) used for extracting the S parameters, and is composed of a length of microstrip transmission line from each port connected to a model for a series-switch plate . Driven by the 6 mechanical wires at each side, which control its position, the switch plate is internally modeled as an equivalent circuit including transmission line, frequency-dependent resistance, and variable capacitance between the conductor on the plate and the underlap of the ends of the microstrip lines separated by the gap for the switch isolation. As with the beams, this model is defined by a complete set of parameters, such as the dimensions and material properties. Parameters can be adjusted quickly to achieve the desired RF performance for different closing states of the electromechanical structure. 

Consider the generalized closed-loop system shown in Figure 13.1b. For each of its four components (process, measuring device, controller mechanism, and final control element) we can write the corresponding transfer function relating its output to its inputs. In particular, if we neglect the dynamics of the transmission lines, we have ... 

The MMW region of the electromagnetic spectrum is characterised by quasi-optical electronic components for generation, transmission and detection. MMW sources and detectors are typically semiconductor devices with transmission lines of open tube rectangular waveguide, or coaxial cable at frequencies below 30 GHz. The cables are rather lossy and waveguide is the favoured transmission line for any other than the shortest links or where dielectric loss is less critical than mechanical flexibility, e.g. connecting to a frequency counter. 

Gunn devices belong to a group called transferred electron oscillators and are the ones most often encountered in MMW spectrometry, as they offer the lowest noise figure. They rely on a bulk property of gallium arsenide and indium phosphide when a DC voltage is applied across the end contacts of the n-type material. As the voltage is increased, the current initially increases linearly and then starts to oscillate, with a period closely related to the transit time of the carriers between the contacts across the bulk material. The device is housed in a cavity coupled to a transmission line and is used as a source of MMW radiation, the frequency of which can be tuned mechanically and electronically. 

A widely used practice is to apply a sinusoidal frequency modulation (FM) to the MMW source. This too produces an amplitude modulation of the transmitted signal. Any fi equency dependent component in the MMW transmission line, whether it be a sample, a cavity or a reflecting component, will show similar behaviour. It is important to minimise those spurii by careful construction and attention to mechanical matching of components such as coaxial connectors and waveguide flanges. 

With further technical improvements, such as faster data transmission lines, the prototype may make it possible to display images of line drawings, not just chemical structures, from STN International files. Images would include spectral data, chemical apparatus, graphs, charts, mechanical drawings, and other line drawings. 

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