Task
1. A durable, efficient and effective infrastructure system is fundamental to economic prosperity, social justice, political stability and quality of human life. There is, however, massive and growing evidence that the current infrastructure systems, even in the most developed countries, are deteriorating or cannot satisfy the basic requirements.
In addition, construction industry is nowadays facing new challenges, such as sustainability arising from global worming. Surprisingly, infrastructure crisis occurs in spite of the tremendous advances that have been made in last years. Specifically, in the field of concrete construction, it is possible to achieve higher strength and larger ductility both in tension and compression, to tailor eco‐ friendly composites, to increase the robustness against accidental events, etc. Nevertheless, all these properties of concrete, which mainly involve mechanical aspects, are separately investigated and, therefore, not entirely applicable in real constructions.
A new holistic approach, focusing on strength, ductility, durability, and environmental sustainability has been introduced in the field of concrete materials. The aim is to develop a large number of tailor‐made and innovative cement‐based composites. They can be used in a wide range of applications, not only in new constructions, but also in the regeneration and reconstruction of existing infrastructures. Thus, it comes as no surprise to introduce, for instance, the so‐ called eco‐mechanical indexes (ECOMEX) in place of the classical life cycle assessment of concrete structures.
2. In electromagnetism, a dielectric (or dielectric material) is an electrical insulator that can be polarized by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the material as they do in an electrical conductor, but instead only slightly shift from their average equilibrium positions, causing dielectric polarization.
Because of dielectric polarization, positive charges are displaced in the direction of the field and negative charges shift in the direction opposite to the field (for example, if the field is moving parallel to the positive x axis, the negative charges will shift in the negative x direction).
This creates an internal electric field that reduces the overall field within the dielectric itself.[1] If a dielectric is composed of weakly bonded molecules, those molecules not only become polarized, but also reorient so that their symmetry axes align to the field. Although the term insulator implies low electrical conduction, dielectric typically means materials with a high polarizability. The latter is expressed by a number called the relative permittivity.
The term insulator is generally used to indicate electrical obstruction while the term dielectric is used to indicate the energy storing capacity of the material (by means of polarization). A common example of a dielectric is the electrically insulating material between the metallic plates of a capacitor. The polarization of the dielectric by the applied electric field increases the capacitor’s surface charge for the given electric field strength.
Frequency has a most important influence on dielectric properties, in a way similar to its influence on dynamic mechanical properties. Owing to their inertia, and to restraints in the structure, the dipoles take a certain time to reverse direction. This is characterised as their relaxation time. At low frequency, the dipoles line up in the field, reverse direction when the field reverses, and so contribute to a high permittivity.
At high frequencies, the dipoles will not follow the changes at all, and there will be no contribution to the permittivity. At intermediate, transitional frequencies the reversals of field take place at intervals comparable to the relaxation time, the response of the dipoles is sluggish, which gives a phase difference between voltage and current, and energy is dissipated due to internal friction. Different types of dipole will have different relaxation times, so that, as the frequency is raised, the permittivity drops in steps and the dielectric loss peaks.
When the theory is worked out exactly, it is found that the maximum in ε″ occurs at the same frequency as the maximum rate of decrease of ε′; the maximum of cos ϕ is displaced to a slightly higher frequency.The general behaviour is illustrated by the results for water and ice. At low frequencies, the dipolar water molecules line up in the field, to give a relative permittivity of about 80. At higher frequencies, the permittivity drops in a step, and there is a maximum in the power factor.
For ice, (Fig. 21.7), in which the considerable restraints in the structure limit the movement of the dipoles, this occurs at about 10 kHz; but, for liquid water, in which the molecules are less restrained, the permittivity remains constant up to about 1 GHz, and then drops rapidly and passes half its low-frequency value at about 20 GHz. Above these frequencies, there will still be electronic polarisation, but at high enough frequencies this will cease, and there will be a further decrease in permittivity.
3. Moisture content inside concrete structures can be studied from the data of their interactions with microwaves. This interaction can be revealed in the form of a unique signal spectrum called as reflection coefficient (S11) and transmission coefficient (S21) [33]. Permittivity and conductivity of water percentages will vary the measurement quantities of signal spectrum. Permittivity is a measurement of the dielectric medium response to the applied microwaves through the changing of its electric field.
It depends on the material’s ability to polarize in response to the applied field. This theory can be applied to detect moisture in concrete structures because water generally has high value of dielectric constant ~81 [34]. Dielectric constant and dielectric loss of material is the two key parameters to define permittivity.
i.Dielectric constant (ε′)
Defined as a quantity measuring the ability of a material to store electrical energy in an electric field. The changing moisture content of concrete will vary the dielectric constant due to the polarization of water inside the concrete sample.
ii.Dielectric loss (ε″)
Defined as loss of electromagnetic energy propagating inside the concrete structure due to the rotation and oscillation between the water molecules thus resulting in friction.
Changes of moisture content inside the concrete structure will alter its permittivity and yielding a unique spectrum when it comes in contact with microwave [35]. Hence, this technology is suitable and fits well to evaluate the moisture content inside the concrete
4. Vector Network Analyzers are used to test component specifications and verify design simulations to make sure systems and their components work properly together. Today, the term “network analyzer”, is used to describe tools for a variety of “networks”. For instance, most people today have a cellular or mobile phone that runs on a 3G or 4G network. In addition, most of our homes, offices and commercial venues all have Wi-Fi, or wireless LAN “networks”.
Furthermore, many computers and servers are setup in “networks” that are all linked together to the cloud. For each of these “networks”, there exists a certain network analyzer tool used to verify performance, map coverage zones and identify problem areas. From mobile phone networks, to Wi-Fi networks, to computer networks and the to the cloud, all of the most common technological networks of today were made possible using the Vector Network Analyzer that was first invented over 60 years ago.
R&D engineers and manufacturing test engineers commonly use VNAs at various stages of product development. Component designers need to verify the performance of their components such as amplifiers, filters, antennas, cables, mixers, etc.The system designer needs to verify their component specs to ensure that the system performance they’re counting on meets their subsystem and system specifications.
Manufacturing lines use Vector Network Analyzers to make sure that all products meet specifications before they’re shipped out for use by their customers. In some cases, Vector Network Analyzers are even used in field operations to verify and troubleshoot deployed RF and microwave systems. A Vector Network Analyzer contains both a source, used to generate a known stimulus signal, and a set of receivers, used to determine changes to this stimulus caused by the device-under-test or DUT.
The stimulus signal is injected into the DUT and the Vector Network Analyzer measures both the signal that’s reflected from the input side, as well as the signal that passes through to the output side of the DUT. The Vector Network Analyzer receivers measure the resulting signals and compare them to the known stimulus signal.
The measured results are then processed by either an internal or external PC and sent to a display. Vector Network Analyzer’s perform two types of measurements – transmission and reflection. Transmission measurements pass the Vector Network Analyzer stimulus signal through the device under test, which is then measured by the Vector Network Analyzer receivers on the other side.
The most common transmission S-parameter measurements are S21 and S12 (Sxy for greater than 2-ports). Swept power measurements are a form of transmission measurement. Some other examples of transmission measurements include gain, insertion loss/ phase, electrical length/delay and group delay. Comparatively, reflection measurements measure the part of the VNA stimulus signal that is incident upon the DUT, but does not pass through it. Instead, the reflection measurement measures the signal that travels back towards the source due to reflections. The most common reflection S-parameter measurements are S11 and S22.