R. de Oliveira

Dielectric permittivity and loss of CaCu3Ti4O12 (CCTO) substrates for microwave devices and antennas

The solid state procedure was used to produce bulk ceramics of CCTO (CaCu3Ti4O12). The samples of the CCTO ceramic were studied by X-ray powder diffraction, infrared and Raman scattering spectroscopy. The infrared and Raman scattering spectroscopy confirm the formation of the CCTO phase as seen by X-ray diffraction analysis. For one experimental procedure one uses an organic binder in the process of shaping the samples. In the second procedure the samples were prepared without the presence of the organic phase. For the second situation, we had higher dielectric constant (ɛr=7370) with high loss (D=0.2) at 1 KHz. For the first procedure one has the lower dielectric constant (ɛr=1530) and lower loss (D=0.11) at 1 KHz. Simple rectangular antenna prototypes were also designed on substrate samples (C1, C2, P1 and P2). For the antennas (with P2, C1 and C2 as substrates), the bandwidth (BW) is 90 MHz (around 3%). The antenna with P1 substrate presented a surprisingly high BW of 270 MHz that corresponds to a 10% bandwidth. In the microwave range one observes that higher values of the ɛr in the range of 3 GHz antennas is also presented by the P1 sample (ɛr=41.6), and the lowest one was presented by P2 (ɛr=33.7). Sample P1 also presents the highest value for the loss (Q−1) which is around 0.1 compared to the other samples which is around 0.03. Therefore, these measurements confirm the potential use for small high dielectric planar antennas. These materials are also attractive for capacitor applications and certainly for microelectronics, and microwave devices (e.g., cell mobile phones), where the miniaturization of the devices is crucial.

A NDT assessment of fracture mechanics properties of fiber reinforced polymer concrete

An acoustic emission (AE) methodology has been used to measure the fracture toughness and associated energy using three point bending tests, according to the Two Parameter Model (TPM). The aim of this article is to identify how acoustic emission can measure the damage of polymer concrete and compare the fracture mechanics characteristics with concrete specimens. Polyester and epoxy resins were considered and glass fibers were used as reinforcement for the epoxy polymer concrete.

Modelling of fibre Bragg grating sensor plates

In this paper is presented the design of a composite sensor plate, based on fibre Bragg grating (FBG) sensors, to be used as alternative to the conventional electric strain gages. The use of such composite sensor plate will permit to profit of FBG sensors advantages compared to conventional electrical strain gages increasing its safety considering that they are commonly simply surface mounted in structure using adhesives.