Assessment of material properties of gallium orthophosphate piezoelectric elements for development of phased array probes for continuous operation at 580 degrees C

In this paper, the thickness extension mode gallium orthophosphate single crystal elements were characterised using the impedance analyser. Impedance characteristics of piezoelectric elements were investigated at temperatures from 25°C up to 580°C at first and then at a constant temperature of 580°C for a period of 25 days. The resonant and anti-resonant frequencies extracted from the impedance characteristics, capacitance (measured at 1 kHz), density and dimensions of the gallium orthophosphate elements were used to calculate electromechanical, piezoelectric and elastic properties of these elements at high temperatures as a function of time. The tested gallium orthophosphate elements proved to possess very stable efficiency and sensing capability when subjected to high temperature. The results are very encouraging for proceeding with development of phased array probes using gallium orthophosphate, for inspection and condition monitoring of high temperature pipelines in power plants at a temperature up to 580°C

Development of phased array probes to operate in time-of-flight diffraction configuration to continuously monitor defect growth in thermal power plants

A high temperature (HT) structural health monitoring system for pipes that utilises phased array (PA) probes in time-of-flight diffraction (TOFD) configuration to continuously monitor the defect growth over time is being developed, so that when the defect reaches a critical size the plant can be shut down and maintenance can take place before failure. The numerical models for PA/TOFD inspection technique in either symmetric or asymmetric pitch-catch configuration were developed using the CIVA simulation platform. The probe characteristics were selected and the ultrasonic beam profile was predicted for different points in the volume of interest i.e. the weld and the heat affected zone (HAZ). The probes positions and interspacing between the probes in emission and reception were also selected in order to achieve maximum inspection coverage. The PA probes use piezoelectric elements for generation and reception of ultrasound beam. Single crystal gallium orthophosphate (GaPO4) has been selected for impedance analysis as a candidate for application in the PA probes operating at HT. Impedance characteristics of GAPO4 elements were investigated up to 580°C and together with measured capacitance (at 1 kHz), density and dimensions of the GAPO4 elements used to calculate material properties of these elements at HT as a function of time. The calculated material properties were used to evaluate the developed PA on TOFD technique at HT using COMSOL simulation package. The simulated and experimental results are encouraging for proceeding with development of PA/TOFD probes using GaPO4, for inspection and condition monitoring of HT pipelines in power plants at temperatures up to 580°C.European Commission through the FP7 Programme (FP7-SME-2013-1) under the grant agreement no. 605267, iKnowHow Informatics, CeramTec, InnoTecUK, Brunel University, Enkon, Vermon, Tecnitest Ingenieros and INETEC

Hemodynamic effect of atrioventricular and interventricular dyssynchrony in patients with biventricular pacing: Implications for the pacemaker syndrome

Background/Objectives: Pacemaker syndrome was mainly described as the sequel of atrioventricular (AV) dyssynchrony. The role of interventricular (VV) dyssynchrony has not been studied yet. The aims of this study were to noninvasively assess the hemodynamic effects of different ventricular pacing sites with and without AV and VV dyssynchrony and to observe the patients for clinical symptoms of the pacemaker syndrome during the AV sequential and ventricular-only pacing modes. Materials and Methods: Between March 2009 and February 2010, 40 patients (28 men; mean age, 61 ± 15 years) with biventricular (BiV) device were enrolled. Mean systolic and diastolic blood pressures (BP) of 5 beats were measured 5 minutes after each mode change using fingertip plethysmography. The patients were also observed for the occurrence of symptoms suggestive of the pacemaker syndrome, including dyspnea, palpitations, dizziness, presyncope, and syncope. Results: There was no difference in mean systolic BP among different ventricular-only pacing modes (all P = NS). However, mean systolic BP was significantly higher in AV sequential biventricular pacing (DDD-BiV) compared with ventricular-only pacing modes (all P0.05). Conclusions: The present study showed that the non-AV sequential BiV and LV pacing may have no significant benefit compared with RV pacing in terms of systolic blood pressure. However, there was marked hemodynamic improvement following mode change to AV sequential BiV pacing. This study may have important implications for pathogenesis of pacemaker syndrome

High temperature gallium orthophosphate transducers for NDT and monitoring purposes in nuclear power plants

There is a need for ultrasonic transducers to operate at temperatures up to 580°C for NDT and monitoring purposes in nuclear power plants. One of the key aspects of designing such transducers using high temperature (HT) piezoelectric single crystal material gallium orthophosphate - GaPO4 has been studied: ultrasonic performance of this piezoelectric material at HT as a function of time. An experimental setup was used where two thickness extension mode GaPO4 plates operating at frequency of 2.17 MHz were bonded to a carbon steel block using HT silver adhesive and these were placed in an electric furnace. HT wiring led from the piezoelectric plates through an opening in the furnace outside to an ultrasonic testing device. The ultrasonic measurements show that GaPO4 works as a functional ultrasonic transducer generating and receiving ultrasound at the temperature of 580°C for 13 consecutive days when HT corrosion of carbon steel block occurred leading to failure of the experiment. From the aspect of HT operation of this piezoelectric material, the results are very encouraging for proceeding with development of ultrasonic transducers using GaPO4 for application in nuclear power plants

High temperature gallium orthophosphate transducers for NDT

A transducer has been manufactured leading towards development of an ultrasonic system to operate up to 580°C for non-destructive testing (NDT) and monitoring in power plants. The manufactured transducer has a simple design based on the piezoelectric single crystal gallium orthophosphate (GaPO4) which allows ultrasonic measurements to be performed up to considerably high temperature (HT) levels required in this study. Usually a critical aspect when performing HT ultrasonic NDT– acoustic coupling to the test-material, has been resolved using a commercially available HT silver adhesive which provides permanent installation of the transducer on the structure to be tested. This also means that for future application in an industrial environment drilling and/or machining intervention requirements will be reduced significantly. Finally, the GaPO4 transducer’s sensitivity (f=3.5 MHz) has been successfully tested through measurements on a steel block containing an artificial defect with known geometry (side-drilled hole (SDH) with d=0.8 mm) up to the target temperature of 580°C keeping the defect’s signal-to-noise ratio (SNR) above 6 dB which is high enough for NDT practice