Acoustic emission analysis of prestressed concrete structures

This thesis examines the role of Acoustic Emission (AE) as a non-destructive testing (NDT) technique for prestressed and reinforced concrete structures. The work focuses on the development of experimental techniques and data analysis methods for the detection, location and assessment of AE from prestressed and reinforced concrete specimens. This thesis reveals that AE can be used to detect the onset of corrosion activity in wire in the interface between prestressed concrete and mortar as found in prestressed concrete pipes. Furthermore, this technique can be used to locate the corrosion activity on different size prestressed concrete samples. By correlation between three parameters of classical AE analysis techniques (traditional parameters), damage can be detected and located whilst the corrosion area, macro crack and crack propagation can be identified. However, it cannot classify the crack type. Different damage modes, including corrosion activity, micro/macro cracking formation, crack propagation and wire failure generate different types of AE signals with varying amplitudes and absolute energy emitted. A novel analysis approach has been used on composite materials (concrete, mortar and steel) to evaluate differing crack types by a combination of the classical acoustic emission analysis technique and advanced analysis Rise time / Amplitude (RA) and Average Frequency (AF), results proved the effectiveness of the developed techniques for damage detection and classification crack types. The relationship between RA value and AF value can be used to determine the crack area and classify it as either tensile crack type, other type (shear movement) or no crack. The results of the research have demonstrated that the AE technique is valid in larger scale monitoring and hence the potential for monitoring real structures such as prestressed concrete pipes. Use of Kernel Density Estimation Function (KDEF) provides improved visualisation of the data to represent clearly the RA/AF values. Key Words: Acoustic Emission, Corrosion, Reinforced Concrete, Prestressed Concrete, Micro and Macro Concrete Cracks, Crack classification, Source Location, Damage Assessment, Monitoring

Beam Steering of Time Modulated Antenna Arrays Using Particle Swarm Optimization

yesIn this paper, a simple switching process is employed to steer the beam of a vertically polarised circular antenna array. This is a simple method, in which the difference resulting from the induced currents when the radiating/loaded element is connected/disconnected from the ground plane. A time modulated switching process is applied through particle swarm optimisation.Electronics and Telecommunication

A survey on RF and microwave doherty power amplifier for mobile handset applications

This survey addresses the cutting-edge load modulation microwave and radio frequency power amplifiers for next-generation wireless communication standards. The basic operational principle of the Doherty amplifier and its defective behavior that has been originated by transistor characteristics will be presented. Moreover, advance design architectures for enhancing the Doherty power amplifier’s performance in terms of higher efficiency and wider bandwidth characteristics, as well as the compact design techniques of Doherty amplifier that meets the requirements of legacy 5G handset applications, will be discussed.Agencia Estatal de Investigación | Ref. TEC2017-88242-C3-2-RFundação para a Ciência e a Tecnologia | Ref. UIDP/50008/201

Slotted Printed Monopole UWB Antennas with Tuneable Rejection Bands for WLAN/WiMAX and X-Band Coexistence

YesFour versions of the compact hexagonal-shaped monopole printed antennas for UWB applications are presented. The first proposed antenna has an impedance bandwidth of 127.48 % (3.1 GHz to 14 GHz), which satisfies the bandwidth for ultra-wideband communication systems. To reduce the foreseen co-channel interference with WLAN (5.2GHz) and X-Band systems (10GHz), the second and third antennas type were generated by embedding hexagonal slot on the top of the radiating patch. The integration of the half and full hexagonal slots created notched bands that potentially filtered out the sources of interference, but were static in nature. Therefore, a fourth antenna type with tuneable-notched bands was designed by adding a varactor diode at an appropriate location within the slot. The fourth antenna type is a dual-notch that was electronically and simultaneously tuned from 3.2GHz to 5.1GHz and from 7.25GHz up to 9.9GHz by varying the bias voltages across the varactor. The prototypes of the four antenna versions were successfully fabricated and tested. The measured results have good agreement with the simulated results.This work is carried out under the grant of the Fundacão para a Ciência e a Tecnologia (FCT - Portugal), with the reference number: SFRH / BPD / 95110 / 201

Compact Microstrip Antenna Design for Microwave Imaging

YesAn ultra-wideband microstrip antenna design is considered with respect to applications in breast cancer detection. The underlying design concept is based on ground penetrating radar (GPR). Simulated and measured prototype performance show excellent performance in the input impedance and radiation pattern over the target range from 4 GHz to 8 GHz. The 4 GHz to 8GHz frequency band for microwave imaging perform better in comparison with other microwave frequencies. The antenna also shows a reasonable uniform radiation performance in the broadside direction which contributes to the reduction of clutter levels, thus aiding the reconstruction quality of the final image

Frequency and Pattern Reconfigurable Antenna for Emerging Wireless Communication Systems

A printed and minimal size antenna having the functionality of frequency shifting as well as pattern reconfigurability is presented in this work. The antenna proposed in this work consists of three switches. Switch 1 is a lumped switch that controls the operating bands of the antenna. Switch 2 and Switch 3 controls the beam switching of the antenna. When the Switch 1 is ON, the proposed antenna operates at 3.1 GHz and 6.8 GHz, covering the 2.5–4.2 GHz and 6.2–7.4 GHz bands, respectively. When Switch 1 is OFF, the antenna operates only at 3.1 GHz covering the 2.5–4.2 GHz band. The desired beam from the antenna can be obtained by adjusting the ON and OFF states of Switches 2 and 3. Unique beams can be obtained by different combination of ON and OFF states of the Switches 2 and 3. A gain greater than 3.7 dBi is obtained for all four cases

A Capacitively loaded Antenna for use in Mobile Handsets

YesA tuneable slotted patch antenna design is presented and verified for use in the DCS, PCS and UMTS bands. The tuning circuit consists of two varactor diodes with some passive components, and is integrated fully with the r radiator patch, with the varactors occupying different locations over the slot. The tuning does not require any further modification to the patch or feed geometry. Good agreement is observed between the predicted and observed impedance bandwidth, return loss, gain and radiation pattern, throughout the range 1.70 GHz-2.05 GHz

Analysis of the Combinatory Effect of Uniaxial Electrical and Magnetic Anisotropy on the Input Impedance and Mutual Coupling of a Printed Dipole Antenna

The main objective of this work is to investigate the combinatory effects of both uniaxial magnetic and electrical anisotropies on the input impedance, resonant length and the mutual coupling between two dipoles printed on an anisotropic grounded substrate. Three different configurations: broadside, collinear and echelon are considered for the coupling investigation. The study is based on the numerical solution of the integral equation using the method of moments through the mathematical derivation of the appropriate Green's functions in the spectral domain. In order to validate the computing method and evaluated Matlab? calculation code, numerical results are compared with available literature treating particular cases of uniaxial electrical anisotropy; good agreements are observed. New results of dipole structures printed on uniaxial magnetic anisotropic substrates are presented and discussed, with the investigation of the combined electrical and magnetic anisotropies effect on the input impedance and mutual coupling for different geometrical configurations. The combined uniaxial (electric and magnetic) anisotropies provide additional degrees of freedom for the input impedance control and coupling reduction

The Compact Design of Dual-band and Wideband Planar Inverted F-L-antennas for WLAN and UWB Applications

yesTwo miniature low profile PIFLA antennas with a compact volume size of 30mm × 15mm × 8mm has presented in this paper. By applying the magnetic wall concept a reduced size dual-band and a wideband half PIFLAs for WLAN (2.4GHz/5.2GHz) and UWB applications are achieved. The dual-band antenna shows a relative bandwidth of 12% and 10.2% at ISM2400 and IEEE802.11a frequency bands respectively for input return loss less than 10dB. By carefully tuning the geometry parameters of the dual-band proposed antenna, the two resonant frequencies can be merged to form a wide bandwidth characteristic, to cover 3000MHz to 5400 MHz bandwidth (57%) for a similar input return loss that is fully covering the lower band UWB (3.1-4.8GHz) spectrum. The experimental and simulated return losses on a small finite ground plane of size 30mm × 15mm show good agreement. The computed and measured radiation patterns are shown to fully characterize the performance of the proposed two antennas.MSCR