High Temperature Transducers Research Articles

Ultrasonic Monitoring of Nozzle and Cavity during Injection Moulding

Ultrasonic techniques are recognised as powerful sources of process information. Transducers are applied directly, are non-invasive, yet interrogate the entire melt cross-section, while data are available real-time. During injection moulding, two zones are considered: nozzle and cavity. In the nozzle, ultrasonic velocity measurement provides temperature and pressure information. Mean temperatures not observed by other techniques are detected. Previous extrusion based experience is used to address issues of high temperature transducer operation. In the cavity, changes in reflection coefficient and ultrasonic velocity provide information on mould filling and part cooling. Various mould geometries are monitored using a number of ultrasonic transducers.

Dielectric and Piezoelectric Properties of High Curie Temperature Single Crystals in the Pb(Yb1/2Nb1/2)O3–xPbTiO3 Solid Solution Series

Piezoelectric single crystals in the (1-x)Pb(Yb1/2Nb1/2)O3–xPbTiO3 (PYN–xPT) solid solution series were grown by a conventional high temperature solution method using PbO flux. The Curie temperature for compositions grown near the morphotropic phase boundary (x=0.5) was in the range from 300 to 400°C due to compositional variations and the addition of 1 mol% Ba2+, added for perovskite stability. With increasing PT content, the dielectric properties continuously changed from relaxor to normal ferroelectric behavior in the range of 0.2< x <0.8. The coercive field (Ec) for rhombohedral crystals near the MPB was 10–15 kV/cm, increasing to 20 kV/cm for the tetragonal crystals. The remnant polarization (Pr) also increased with the increasing of PT content from 0.9 µC/cm2 (x=0.2) to 42 µC/cm2 (x=0.53). The piezoelectric coefficient (d33) of PYN–xPT single crystals increased with increasing PT content in the rhombohedral phase, being ∼2500 pC/N near the MPB composition (x=0.46), and decreasing to ∼1200 pC/N for the tetragonal phase crystals. These excellent piezoelectric properties together with the high Curie temperature make PYN–xPT single crystals promising candidates for the applications of high temperature and high performance actuators and transducers.

Crystal growth and electrical properties of Pb(Yb 1/2Nb 1/2)O 3–PbTiO 3 perovskite single crystals

Pb(Yb 1/2Nb 1/2)O 3–PbTiO 3 (PYNT) single crystals were firstly grown using the high temperature solution method. Based on X-ray powder diffraction and thermal behavior of polycrystalline material, issues of perovskite instability were revealed. Barium additions were used to aid in the stabilization of the perovskite rhombohedral phase. The Curie temperature of PYNT (60/40) was found to vary from 244°C to 268°C, the characteristic of relaxor ferroelectric with the temperature of dielectric maximum increasing with increasing frequencies. Electrical properties of PYNT (60/40) investigated along 〈0 0 1〉, 〈0 1 1〉, and 〈1 1 1〉 pseudo-cubic directions, revealed remnant polarizations (Pr) of 26.5, 27.6 and 41.6 μC/cm 2, respectively, while the coercive fields ( E c) were 10.1, 9.4, and 11.5 kV/cm. The piezoelectric coefficient ( d 33) of 〈0 0 1〉 oriented samples was found to be ∼1200 pC/N, with a strain reaching 0.54% at 100 kV/cm. The large piezoelectric coefficient, coercive field, and high T c (>250°C) make PYNT single crystals promising candidates for high temperature and high performance solid-state actuators and transducers.

Phase diagram and physical properties of the sodium niobate-lithium niobate-cadmium niobate three-component system

The phase diagram of the (Na,Li,Cd0.5)NbO3 ternary system is refined. The electrical properties of solid solutions over a broad range of the component concentrations were studied. The compositions promising for high-temperature transducers were obtained.

Characterizing aluminum sintering using in-situ NDE

Considerable attention has been given to the use of nondestructive evaluation techniques to reduce the costs associated with the manufacture of powder-metallurgy components. One such technology that is being developed at the U.S Department of Energy’s Ames Laboratory is an in-situ noncontact technique to characterize sintering. The method consists of a high-temperature electromagnetic acoustic transducer to measure the amplitude and velocity of an ultrasonic tone burst traveling through a sample during sintering. Results from the in-situ noncontact nondestructive evaluation measurements indicate that real-time in-situ monitoring of sintering is attainable.

Fabrication and Properties of PbNb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;6&lt;/sub&gt; Ceramics for High-Temperature Transducer

Fabrication and Properties of PbNb&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;6&lt;/sub&gt; Ceramics for High-Temperature Transducer

Ultrasound: A Virtual Instrument Approach for Monitoring of Polymer Melt Variables

Non-invasive ultrasound measurements are not currently widely used, due to limitations in high temperature transducer technology and signal processing. These have been addressed in the ultrasound program in our laboratory, where high frequency sampling using our own high temperature probes is now available. The need for high frequency sampling of the ultrasound signal to resolve measurements of transit time (and amplitude) to the required accuracy requires handling of large amounts of data, and in the case of actual polymer processing such as extrusion, data processing needs to be real time. A computer controlled system for the acquisition of such data is described here, with examples of the sensitivity of the measurements to a range of polymer melt process variables, including polymer composition and fillers, for extrusion and injection moulding processing.

Ultrasonic transducers for high temperature applications

There is an increasing demand ultrasonic transducers to work at high temperatures. Transducers operating in the range from 400 to 1000/spl deg/C are being applied in the power, process, automotive and aeroengine industries, as well as in materials research. To date, the majority of high temperature transducer designs have been based on adaptations of conventional single and dual-element probes for nondestructive testing (NDT). Such designs are outlined. It is noted, however, that the attempt to construct high temperature versions of conventional transducers has led to overcomplicated, expensive structures. In particular, they are modelled on probes used for scanning at ambient temperatures, although scanning is unlikely to be possible at high temperatures. An alternative approach is therefore described, based on the monolithic ultrasonic array structure. This offers not only lower transducer costs, but also full electronic control of the ultrasonic beam angle and emission point, thus facilitating inspection of a region within a test component using only one or two devices in fixed positions. Typical results demonstrating the beam-steering performance of the array, as well as those from B-scan time-of-flight testing, are presented. It is concluded that the problems of transducer development for ultrasonic, high-temperature NDT are not yet completely solved, and that further effort is required in the key areas of materials science and transducer structure. Moreover, a simple design with the minimum of bond lines is most likely to succeed on the grounds of cost and reliability.

Robotic diagnostic device using high-temperature piezoelectric transducers

An apparatus is described for remote inspection of the state of metal in nuclear power plant equipment. The high-temperature piezoelectric transducers used in the instrument section of the apparatus are described, and their technical specifications are given. Alternative ways of using the apparatus to monitor various industrial testpieces are discussed. The article is taken from a paper presented at the Scientific-Practical Conference on Piezoelectric Drivers and Sensors, held January 14–15, 1993, in the city of Obninsk.

PmP118. Piezoelectric ceramics for high-temperature transducers

Abstract The ferroelectrics of the Aurivillius family having TC >700°C are investigated from the point of view of their application as high-temperature transducers. The value of piezoelectric modulus d33 and its stability are the basic parameters determining the range of application.

Development of high-temperature biaxial-strain transducer for use to 1033°K (1400°F)

This study involved the development and evaluation of a high-temperature biaxial-strain transducer for measurement of strains up to 5 percent at temperatures approaching 1033°K (1400°F). The design requirements for transducer were established by specifications prepared by the Pressure Vessel Research Committee (PVRC) of the Welding Research Council. These specifications reflect the needs of the national laboratories and private industry as they relate to safety and structural-behavior studies of nuclear and advanced fossil-fuel systems, including piping, piping components, heat exchangers, and other pressure equipment.

Fluctuating surface pressure measurements on USB wing:Two types of transducers

Measurement of noise levels in the vicinity of a jet exhaust, such as is desired on surfaces of propulsive lift devices, requires high-temperature transducers that will withstand intense low-frequency flow buffeting, yet will be sensitive to lower-pressure loads at high frequencies. For flight test installation in an aircraft assembly. such as the USB YC-14 prototype, rugged transducer integrity and attachment are critical for periodic installation and removal, and for flight exposure occurring in a test program of several months duration. Two transducer types used in such previous test environments were Kulite and Photocon units. These two transducers systems were compared by pairing three wing surface locations in a NASA Langley JT15D upper surface blowing (USB) static test. This USB static arrangement was an inverted simulation of the overwing section of a small airplane used in Langley wind tunnel USB experiments. In addition to transducer comparisons, the experience of measuring full-scale surface-fluctuating pressures of attached flow and jet interaction noise in the nearfield was desired. Some of the noise sources and characteristics of overwing nozzles and Jet interaction are discussed.

A Reliable High Temperature Transducer for Engine Vibration Measurement

EARLY in 1963, a project was initiated in co‐operation with an European airline with a purpose of starting development work for a new transducer for engine vibration monitoring. The low reliability of former pickups motivated this development work. In the course of the development, modern engine design requirements raised the need for the high temperature stability of these transducers. The development work was, therefore, based on the necessity to produce a vibration transducer with extreme high reliability, good interchangeability tolerance and useable up to approximately 600 deg. C. in practical flight operation. With regard to these requirements, a suitable technical approach seemed to be the use of the piezoelectric transducer technique, because seismic acceleration pickups working on the piezoelectric principle do not use moving parts, whereas displacement and velocity pickups, used so far, have at least one moving part, i.e. the inertial mass. Also the requirement for high temperature stability could be met by using modern crystal technology. The following chapters will expound some mechanical and crystallographic considerations in connection with such transducers, and furthermore describe some devices which are now being used in practical flight operation. Today, the concept of a piezoelectric, high temperature accelerometer with 2‐pole signal output has been commonly adopted in industrial production of transducers for airborne vibration monitoring.

Analysis of Two High-Temperature Liquid Metal Pressure Measuring Systems

A design approach to a high-temperature pressure transducer system for use in closed cycle liquid metal facilities utilizes the displacement of a diaphragm member by the liquid metal pressure. The displacement is then monitored by a suitable transduction device whose output indicates the pressure. A main problem area involves the pertinent characteristics of the transducer. This paper presents the analyses of two transduction system approaches based on (1) thermionic and (2) variable impedance phenomena.