Review on X-ray detectors based on scintillators and CMOS technology

This article describes the theoretical basis, design and implementation of X-ray microdetectors based on scintillating materials and CMOS technology. The working principle of such microdetectors consists in the absorption of X-rays by scintillators, which produce visible light. The visible light is then detected and converted into electric signals by means of photodetectors. In order to understand such detectors, several issues related to its implementation are presented in this article, namely: Production of X-rays and interaction between them and matter - the first step necessary to the detection of X-rays is that they must be absorbed by some material, in this case by a scintillator; Radiation detectors - there are several types of detectors, namely: pn junctions, photoconductors, based on thermal effects and scintillators; Fabrication of scintillator arrays - after the X-ray radiation is absorbed by a scintillator, this material emits visible light whose intensity is proportional to the total energy of the absorbed X-rays; Optical interfaces between scintillators and photodetectors - the visible light generated by scintillators must arrive to the photodetectors, so, it is necessary to have an interface between the scintillators and the photodetectors that ideally does not introduce losses; Photodetectors and interface electronics - the visible light is absorbed by the photodetectors and converted into electrical signals, which are finally converted into digital images by means of interface electronics. The article presents some promising patents on X-ray detectors based on scintillators and CMOS technology.Fundação para a Ciência e a Tecnologia (FCT) - Bolsa SFRH/BSAB/1014/201

Simple versus cooperative relaxations in complex correlated systems

A method for investigating the nature of thermally activated relaxations in terms of their cooperative character is tested in both polymer and low molecular weight crystal systems. This approach is based on analysis of the activation entropy in order to describe thermally activated relaxations. The betaine arsenate/phosphate mixed system of low molecular weight crystals was selected for investigation because pure compounds of this system show ferro-/antiferroelectric phase transitions and the mixed crystals undergo different kinds of relaxation processes involving both dipole-dipole and dipole-lattice interactions. The polymer chosen was a side chain liquid-crystalline polysiloxane, which shows the beta -relaxation characteristic of disordered systems and amorphous materials. The cooperative versus local character of the relaxations is described in terms of "complex'' and ''simple'' relaxations based on calculations of the activation entropies. The initial assumptions of the theory, as well as the resulting equations, were found to be applicable to the systems studied

Magnetic field into multifunctional materials: magnetorheological, magnetostrictive and magnetocaloric

Society is facing serious challenges towards achieving highly efficient utilization of materials and devices. Magnetoactive lightweight materials, such as magnetorheological, magnetostrictive and magnetocaloric materials are attracting increasing interest once they allow a high number of applications such as energy generation, conversion, storage, sensing and actuation, as well as in the biomedical field. In this chapter, the latest research and development in multifunctional lightweight magnetorheological, magnetostrictive and magnetocaloric materials is summarized and discussed in the scope of different application areas. Furthermore, it will be also illustrated the unique functions of inorganic nanomaterials to improve performance of organic materials, as well as combination of the functions of nanomaterials into a device. Final remarks and future perspectives allow to look into a “magnetoactive crystal ball” aiming to foresee what will/should happen in this fascinating research field.The authors thank the FCT- Fundação para a Ciência e Tecnologia- for financial support in the framework of the Strategic Funding UID/FIS/04650/2019 and under project PTDC/BTM-MAT/28237/2017 and PTDC/EMD-EMD/28159/2017. P. Martins thanks FCT for the contract under the Stimulus of Scientific Employment, Individual Support – 2017 Call (CEECIND/03975/2017). The authors acknowledge funding by the Spanish Ministry of Economy and Competitiveness (MINECO) through the project MAT2016-76039-C4-3-R (AEI/FEDER, UE) and from the Basque Government Industry and Education Department under the ELKARTEK, HAZITEK and PIBA (PIBA-2018- 06) programs, respectively. Funding from the European Union’s Horizon 2020 Programme for Research, ICT-02-2018 - Grant agreement no. 824339 – WEARPLEX is also acknowledged

Characterization of poled and non-poled β-PVDF films using thermal analysis techniques

ß-poly(vinylidene fluoride)—ß-PVDF—exhibits ferroelectric properties due to the special arrangement of the chain units in the crystalline phase. The ferroelectric phase can be optimised by poling the original stretched film, that tends to align the randomly organised crystallites against the applied field. In this work, polarised and non-polarised ß-PVDF from the same batch are characterised by mechanical tests and a series of thermal analysis techniques, including DMA, TMA and DSC. The films exhibit mechanical anisotropy, and in the longitudinal direction the poled film presents larger mechanical properties, due to the higher structural organisation. Poled and non-poled show similar crystallinity levels but the melting temperature probed by DSC is higher for the non-poled film; for both films the melting peak exhibits a complex shape, indicating a heterogeneous crystalline organization. Two relaxation processes were found (ß and alpha_c) by dynamic mechanical analysis (DMA). The ß process, attributed to segmental motions in the amorphous phase, appears at the same temperature in both directions, but its intensity was found to be higher for the films tested in the longitudinal direction. For a given direction, the poled films exhibit lower peaks, due to the more organised amorphous structure. At higher temperature, the alpha_c-relaxationwas related to the contraction of the films in the longitudinal direction during heating, recorded by thermal mechanical analysis (TMA). The onset of molecular mobility within the crystalline phase allows for cooperative diffusion processes in the amorphous phase, generating the randomisation of the initially oriented structure.Fundação para a Ciência e Tecnologia (FCT) - Programa Operacional "Ciência, Tecnologia, Inovação" (POCTI) - POCTI/CTM/33501/99

Processo para produção de filamentos poliméricos piezoeléctricos

A presente invenção consiste num processo para obtenção, em linha e em contínuo, de filamentos têxteis de secção variável que incluem um núcleo composto por: eléctrodos(1) revestidos por dieléctrico piezoactivo(2), que por sua vez está revestido por outro eléctrodo(3) e por uma camada isolante eléctrica(4). Adicionalmente, podem ainda ser acrescentada(s) camada(s) destinada(s) a proporcionar ao filamento uma maior estabilidade estrutural, protecção mecânica, características de toque diferentes do filamento nu ou a possibilidade de ser tingido. O processo de fabrico destes filamentos é baseado em métodos convencionais de co-extrusão nos quais são incorporados novos passos, mais concretamente o estiramento a temperatura controlada que possibilitam a obtenção da fase cristalina adequada do polímero piezoeléctrico e a polarização eléctrica do mesmo e o sistema de recirculação para activação do filamento com propriedades piezoeléctricas por polarização. O filamento piezoeléctrico apresenta propriedades mecânicas que tornam possível a sua integração completa em produtos têxteis, através de processos têxteis convencionais, permitindo a sua utilização como sensor ou actuador mecânico.Fundação para a Ciência e a Tecnologia (FCT

Paraelectric-antiferroelectric phase coexistence in the deuteron glass Rb-0.5(ND4)(0.5)D2AsO4

Neutron diffraction was used to study the paraelectric (PE) to antiferroelectric (AFE) phase transition in a deuteron glass crystal Rb-0.5(ND4)(0.5)D(2)ASO(4) (DRADA-50). Coexistence of AFE and PE phases was proven in a temperature range 7-12 K wide.National Science Foundation (NST) - Grant DMR-9520251

Dielectric relaxation in pure and irradiated TGSP crystals

Low frequency dielectric measurements in triglycine sulpho-phosphate (TGSP) and gamma-irradiated TGSP crystals were carried out around the ferroelectric to paraelectric phase transition. The dispersion found in the ferroelectric phase cannot be explained only by a Debye equation with a single relaxation time. The ratio of the Curie constants in the para- and ferroelectric phase (C-p/C-f) for the irradiated TGSP samples show that the crystal is partially clamped. The deviations from the typical single relaxation behaviour are more pronounced in irradiated samples clearly indicating the contribution of defects in addition to the impurities to the dynamics of the syste

Antiferroelectric ADP doping in ferroelectric TGS crystals

Crystal growth, morphology, hysteresis and dielectric measurements on 20 mol% ammonium dihydrogen phosphate (ADP)doped triglycine sulphate (TGS) crystals are reported. Crystals grew with morphology similar to phosphoric acid-doped TGS (TGSP). Inhomogeneous incorporation of dopants gives rise to a distribution in coercive fields in the different growth sectors. The incorporated dopant hinders polarization switching, which results in the increase in coercive field. No internal bias field is created by the dopant and the phase transition observed is similar to pure TGSP. The Curie point shifts to a lower temperature with increasing dopant concentration in the growth sectors. Significant changes in the activation energies of annealed specimen were identified.Universidade do Minho. Instituto de Materiais(IMAT)

Effect of the acoustic impedance in ultrasonic emitter transducers using digital modulations

In an underwater environment it is difficult to implement solutions for wireless communications. The existing technologies using electromagnetic waves or lasers are not very efficient due to the large attenuation in the aquatic environment. Ultrasound reveals a lower attenuation, and thus has been used in underwater long-distance communications. The much slower speed of acoustic propagation in water (about 1500 m/s) compared with that of electromagnetic and optical waves, is another limiting factor for efficient communication and networking. For high data-rates and real-time applications it is necessary to use frequencies in the MHz range, allowing communication distances of hundreds of meters with a delay of milliseconds. To achieve this goal, it is necessary to develop ultrasound transducers able to work at high frequencies and wideband, with suitable responses to digital modulations. This work shows how the acoustic impedance influences the performance of an ultrasonic emitter transducer when digital modulations are used and operating at frequencies between 100 kHz and 1 MHz. The study includes a Finite Element Method (FEM) and a MATLAB/Simulink simulation with an experimental validation to evaluate two types of piezoelectric materials: one based on ceramics (high acoustic impedance) with a resonance design and the other based in polymer (low acoustic impedance) designed to optimize the performance when digital modulations are used. The transducers performance for Binary Amplitude Shift Keying (BASK), On-Off Keying (OOK), Binary Phase Shift Keying (BPSK) and Binary Frequency Shift Keying (BFSK) modulations with a 1 MHz carrier at 125 kbps baud rate are compared.This work was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST-C/FIS/UI607/2011 and project PTDC/CTM-NAN/112574/2009. M. S. Martins thanks the FCT for the grant SFRH/BD/60713/2009

Separation of the pyro- and piezoelectric response of electroactive polymers for sensor applications

One of the main problems for the use of ferroelectric materials for sensor applications, especially for tactile sensors, is the separation of the pyro- and piezoelectric responseproduced by temperature and pressure changes, respectively. We present two different approaches to achieve this goal. The first approach is based on the study of the signal in the frequency domain and uses a signal processing to separate the piezoelectric response from the pyroelectric one. The second approach is based on a double layer configuration of electroactive polymers. In this case, the piezoelectric response is equal in each layer, whereas, the pyroelectric response dominates in the layer exposed to the temperature variations. The pyro- and piezoelectric responses are separated by estimating the difference between the signals of two layers and the signal from one of the layers, correspondingly.Fundação para a Ciência e a Tecnologia (FCT) - Grants POCTI/CTM/33501/99, POCI/CTM/59425/2004.Measurement Specialties Inc