Thickness measurements were made on steel pipe at high temperatures using a non-contact watercooled EMAT (electromagnetic acoustic transducer) and also a laser-EMAT system where a portable Nd:YAG laser with a fibre optic cable was used to generate ultrasound on a sample, and a water-cooled coil-wound EMAT used to detect ultrasound. The set-up was designed so that the laser was fired through a hole in the centre of the EMAT, and a low pass 5 MHz filter employed to reduce the plasma noise. Back wall reflections were clearly visible at temperatures up to 900 °C on stainless and ferromagnetic low carbon steel, enabling wall thickness to be measured, taking into account thermal expansion of the sample. The water-cooled EMAT system can measure wall thickness on ferromagnetic low carbon steel at temperatures up to the Curie point; here, ultrasound generation is dependent on the magnetic state of the steel.

High temperature thickness measurements of stainless steel and low carbon steel using electromagnetic acoustic transducers

We report an evolution of an all-digital ultrasonic pulse technique for measurements of elastic constants of solids. An unambiguous analytical procedure is described for determining the correct time delay of echoes without any need for actual echo overlap. We also provide a simple procedure for making corrections for transducer-bond-induced phase shifts. The precision of a measurement made with this system at ambient temperature exceeds one part in 107 without the use of mixers, gates, time delays, and other complications normally associated with such measurements.

http://absimage.aps.org/image/MAR06/MWS_MAR06-2005-000667.pdf

Digital ultrasonic pulse-echo overlap system and algorithm for unambiguous determination of pulse transit time

Acousto-optic effects are demonstrated in polymer dispersed liquid crystal (PDLC) films, showing promise for applications in ultrasound sensing. The PDLC films are used to image two displacement profiles of air-coupled flexural transducers' resonant modes at 295 kHz and 730 kHz. Results are confirmed using laser vibrometry. The regions on the transducers with the largest displacements are clearly imaged by the PDLC films, with the resolution agreeing well with laser vibrometry scanning. Imaging takes significantly less time than a scanning system (switching time of a few seconds, as compared to 8 h for laser vibrometry). Heating effects are carefully monitored using thermal imaging and are found not to be the main cause of PDLC clearing.

/pdf/ultrasound-sensing-using-the-acousto-optic-effect-in-polymer-1cy3lgvr1a.pdf

Ultrasound sensing using the acousto-optic effect in polymer dispersed liquid crystals

The Curie temperature of Pb(Zr,Ti)O3/Pb(Zr,Ti)O3 (PZT/PZT) sol–gel composites was investigated empirically in order to determine the maximum operation temperature of PZT/PZT ultrasonic transducers. A PZT/PZT film was fabricated on a stainless steel substrate and the piezoelectric constant d33 and ultrasonic response were measured after 1 h heating at a specified temperature in a furnace in order to investigate the Curie temperature indirectly. It was found that the Curie temperature of PZT/PZT was between 770 and 870 K. Second, real-time monitoring of the capacitance at various temperatures was attempted in order to measure the Curie temperature directly. A PZT/PZT film was fabricated on a stainless steel substrate and the sample was placed in a furnace and then heated from RT to 870 K. Peaks in the capacitance appeared around 670 and 820 K; thus, it was concluded that a Curie temperature shift of PZT/PZT occurred around 820 K, which was 250 K higher than that of PZT powder made from the bulk material. The high-temperature ultrasonic performance was also monitored and clear reflected echoes were clearly observed at ~724 K.

https://iopscience.iop.org/article/10.7567/JJAP.54.07HB04/pdf

Curie temperature and high temperature behavior of Pb(Zr,Ti)O 3 /Pb(Zr,Ti)O 3 sol-gel composites

The speed and attenuation of ultrasound propagation can be used to determine material properties and identify phase transitions. Standard ultrasonic contact techniques are not always convenient due to the necessity of using couplant; however, recently reliable non-contact ultrasonic techniques involving electromagnetic generation and detection of ultrasound with electromagnetic acoustic transducers (EMATs) have been developed for use on electrically conducting and/or magnetic materials. We present a detailed study of magnetic phase transitions in a single crystal sample of Gd64Sc36 magnetic alloy using contact and non-contact ultrasonic techniques for two orientations of external magnetic field. Phase diagrams are constructed based on measurements of elastic constant C33, the attenuation and the efficiency of generation when using an EMAT. The EMATs are shown to provide additional information related to the magnetic phase transitions in the studied sample, and results identify a conical helix phase in Gd64Sc36 in the magnetic field orientation .

/pdf/magnetic-phase-transitions-in-gd-64-sc-36-studied-using-non-54x1xxrpsr.pdf

Magnetic phase transitions in Gd 64 Sc 36 studied using non-contact ultrasonics

Ultrasonic testing using contacting transducers such as quartz or PZT is well established. However, standard measurement techniques used require physical contact of the sample and ultrasonic transducer and some sort of couplant between the two. With this configuration there is a possibility of damaging the sample, transducer or bond during testing, thermal cycling, or removal of the transducer. We present results taken using recent advances in non-contact methods of ultrasound generation and detection using electromagnetic acoustic transducers (EMATs), which offer some significant benefits over contact ultrasonic techniques. Circumventing the need for couplant removes the possibility of contaminating the system, which is an issue for some material property measurements, and allows easier measurements over a wider range of temperatures. An automated data analysis system has been developed which allows the velocity of sound in the sample, and hence the elastic constants, to be determined to a high accuracy. This technique is illustrated using measurements of the alloy Gd64Sc36.

Non-contact Ultrasonic Measurements of the Elastic Constants of Magnetic Materials

The use of ultrasound for measuring elastic constants and phase transitions is well established. Standard measurements use piezoelectric transducers requiring couplant and contact with the sample. Recently, non-destructive testing (NDT) has seen an increase in the use of non-contact ultrasonic techniques, for example electromagnetic acoustic transducers (EMATs) and laser ultrasound, due to their many benefits. For measurements of single crystals over a range of temperatures non-contact techniques could also bring many benefits. These techniques do not require couplant, and hence do not suffer from breaking of the bond between transducer and sample during thermal cycling, and will potentially lead to a simpler and more adaptable measurement system with lower risk of sample damage. We present recent work adapting EMAT advances from NDT to measurements of single crystals at cryogenic temperatures and illustrate this with measurements of magnetic phase transitions in Gd64Sc36 using both contact and non-contact transducers. We discuss the measurement techniques implemented to overcome noise problems, and a digital pulse-echo-overlap technique, using data analysis in the frequency domain to measure the velocity.

/pdf/measuring-elastic-constants-using-non-contact-ultrasonic-9aq5v3k6cf.pdf

Measuring elastic constants using non-contact ultrasonic techniques

The MAESTRO instrument is a recent development that enables sensitive, spatially located, microbial detection using deep UV spectroscopy at a standoff distance up to 5m. This capability stems from prior deep UV fluorescence/Raman standoff instruments for point chemical, biological, and explosives analysis, as well as from planetary science in the form of the SHERLOC instrument on the Mars 2020/Perseverance Rover, a deep UV fluorescence/Raman mapping robotic arm-mounted instrument looking for signs of life on Mars. The MAESTRO instrument leverages these detection capabilities to enable microbial detection on environmental/natural surfaces with high-speed mapping rates with map areas <1m2 . This talk will discuss the fundamentals of the methodology for detection, the achieved sensitivity, and the analytical approach used to detect and differentiate microbial hazards from the background.

MAESTRO: high speed, wide field microbial detection using deep uv spectroscopy

http://iopscience.iop.org/article/10.1088/1742-6596/286/1/012050/pdf

Non-contact ultrasonic measurements of the elastic constants of magnetic materials

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