A quad-band microstrip bandpass filter (BPF) based on stub-loaded resonators (SLRs) with improved skirt selectivity is presented. A single metallic via hole in microstrip is utilised to introduce a compact inductive source-load coupling, with which two pairs of SLRs generate eight controllable transmission zeros at each side of all the quadruple passbands. As an example, a quad-band BPF with measured centre frequencies of 1.88, 2.55, 3.55 and 5.15 GHz as well as insertion losses of 1.53, 1.64, 1.79 and 2.55 dB, and respective fractional bandwidths of 4.38, 3.84, 3.44 and 2.9% is designed and fabricated. The measured response shows a good concordance with the simulated one.
The electro-mechanical (E/M) impedance-based method is one important and effective method in damage detection. The basic concept of the impedance method is to monitor the variations in the structural mechanical impedance spectrum caused by damage in the structure. Comparing the impedance spectrum to a baseline measurement of the undamaged structure, the real part of the E/M impedance reflects the state of structural health in the local area, therefore, the structural damage can be localized, a local-area self-sensing method is implemented. In this paper, an aluminium plate mounted on an electromagnetic shaker is used to detect growing fatigue damage using the impedance method. The growing damage is documented by an increase of the indicators. For the case of a static artificial damage the concept is also demonstrated to an Airbus A320 fuselage part using 9 self-sensing elements on the stringers.
During this decade, piezoelectric elements are explored and applied successfully in SHM, which has positioned them as an enabling technology for damage assessment. When permanently bonded to the structure, they provide the bi-directional energy conversion, which is used in impedance-based SHM. In this method, the variations of the structure’s impedance are monitored by piezoelectric elements. However, before experiments are performed, it is important to position correctly the piezoelectric elements on the structure. Therefore, the capability of piezoelectric actuators is explored under the aspect of sensor position. This work presents the investigation of sensing ability of surface-bonded piezoelectric element using numerical simulation and experiment. The results of numerical and experimental investigation are shown in this paper, which illuminates the model in the aluminium plate could be used to predict the state of it. In the experimental investigation, it also shows the factors which influence strongly the capability of sensor detection. Dealing with high frequency excitation, calculation requires a very dense finite element mesh, hence, the spectral element method (SEM) is chosen as model-based method, which is much more efficient than classical FEM. The structure, self-sensing elements as well as damage are modelled, from which the spectra of E/M impedance is computed. It gives the theoretical basis for the experiment design. The numerical results are verified and validated by experimental investigation. With such a numerical tool, the efficiency of the E/M impedance method can be clearly improved with respect to the determination of suitable piezoelectric element locations.
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