The applicability of laser ultrasonics for the determination of grain size and phase composition in steels under different temperatures was investigated. This was done by obtaining the velocity and attenuation of propagating ultrasonic waves in a simulated steel medium. Samples of ferrite and austenite with varying microstructures were modelled and simulated with the finite difference method, as were samples with varying ratios of austenite and martensite. The temperature of the medium was taken into account as an essential parameter, since both velocity and attenuation are temperature dependent. Results of the velocity and attenuation analysis showed that the use of the wave propagation velocity is not feasible for determination of grain size or phase composition due to a high sensitivity to temperature and sample thickness. The frequency-dependent ultrasonic wave attenuation was less sensitive to the variation of temperature and sample thickness. It can be concluded that accurate knowledge of the temperature is essential for obtaining a correct grain size or phase ratio estimation: a temperature accuracy of 100 °C yields a grain size accuracy in the order of a micrometer using the attenuation. Similarly, a temperature accuracy of 70 °C leads to a phase ratio estimation accuracy of 10%.

Ultrasound based mid-air haptic feedback devices can produce tactile sensations at any time and position without restricting human motion. This is useful for augmented and virtual reality, feedback buttons and virtual user interfaces. The haptic feedback mechanism is caused by acoustic radiation force and streaming. Typical solutions to induce haptic feedback reported in literature use arrays made up of ‘standard’ single element transducers and are heavy, rigid and bulky. A novel alternative uses printed polymer transducers (PPTs), which consist of piezomembranes created using a printing process. PPTs are light, fully flexible, have a thickness < 0.25 mm and can easily be integrated in curved surfaces. However, as the piezoelectric charge coefficients of P(VDF-TrFE) are lower than those of regular PZT5A/H, higher excitation Voltages are needed to achieve the sound pressures required for haptic feedback. In this work we report on the development of flexible large-area arrays based on PPTs for mid-air haptic feedback. Simulations and experimental results of test membranes and a 300+ membrane annular array prototype are presented. Extrapolating the results of the aforementioned array, the full size array is expected to produce radiation forces an order of magnitude above the tactile threshold reported in literature.

A sufficiently high spatial sampling is critical for high quality imaging. If the sampling criterion is not met, artifacts appear in the image generally referred to as grating lobes. Probes with a large aperture provide a large field of view, which allows for more efficient inspection. On the other hand this leads to an increase in the number of element to obey the sampling criterion. We have developed a method that reconstructs sparsely sampled data without assuming anything about the medium. The reconstruction method involves an iterative scheme using wave field extrapolation. After the reconstruction an aliasing free dataset is obtained which can be imaged properly. Aliased and non-aliased datasets were modeled based on point diffractors and reflectors with an increasing width. The datasets were imaged using a mapping in the wavenumber-frequency domain. Up to a factor four of under-sampling can be tolerated, providing the same image quality as a properly sampled dataset.

Corrosion is one of the industries major issues regarding the integrity of assets. Currently inspections are conducted at regular intervals to ensure a sufficient integrity level of these assets. Cost reduction while maintaining a high level of reliability and safety of installations is a major challenge. There are many situations where the actual defect location is not accessible, e.g., a pipe support or a partially buried pipe. In case of bottom of the line corrosion, i.e., a single corrosion pit, a simpler approach may be followed. Guided waves are propagated around the circumference of a pipe. In case of wall loss, the phase of the signal changes which is used to estimate the local wall thickness profile. A special EMAT sensor has been developed, which works in a pit-catch configuration at the 12 o’clock position using highly dispersive guided waves. In order to improve the sensitivity, an inversion in performed on multiple orders of circumferential passes. Experimental results are presented on different pipes containing artificial and real defects.

Composite materials are becoming more popular in the aerospace industry, because of their physical properties. In quality assurance and in-service inspection, there is a need for fast, non-contact, high-quality, non-destructive inspection techniques. The most common approach is to perform the inspection using water-coupled high-frequency transducers. Full wavefield techniques are promising to replace the conventional inspection approach. However, these are currently performed by a laser vibrometer setup, which has drawbacks. As an alternative, a low-cost micro-electro-mechanical system (MEMS) sensor array and dedicated processing scheme are presented enabling fast inspection of large samples. This inspection approach uses a piezoelectric actuator to excite the composite or metallic part with Lamb waves. An array of MEMS sensors records the energy that radiates into the surrounding air. A dedicated processing scheme will translate the measured wavefield into a thickness map of the inspected part. For composite parts, the material’s anisotropy needs to be taken into account for accurate thickness mapping. In principle, all relevant defects show up as local thickness reductions. The results in this paper are obtained with a MEMS-sensor array of 128 elements capable of detecting ultrasound up to 250 kHz at a typical stand-off distance of 100 mm. Defects up to 6 mm in diameter could be detected in thick panels, and defects as small as 2.5 mm could be detected in thin panels. A full-size fuselage experiment shows that the method is also suited for fast inspection of large inspection areas.

Both in design and production of nanoparticles and nanocomposites it is of vital importance to have information about their size and concentration. During the formation of nanoparticles, real-time monitoring of particle size and concentration during bottom-up synthesis in liquids allows for a detailed study of nucleation and growth. This provides valuable insights into the formation of nanoparticles that can be used for process optimization and scale up. In the production of nanoparticles, real-time monitoring enables intervention to minimize the number of off-spec batches. In this paper we will qualify an ultrasound nanoparticle sizer (UNPS) as a real-time monitor for the growth of nanoparticles (or sub-micro particles) in the 100 nm–1 µm range. Nanoparticles affect the speed and attenuation of ultrasonic waves in the dispersion. The size of the change depends, amongst other things, on the size and concentration of the nanoparticles. This dependency is used in the UNPS method. The qualification of the UNPS was undertaken in two successful experiments. The first experiment consisted of static measurements on commercially available silica particles, and the second experiment was real-time monitoring of the size and concentration during the growth of silica nanoparticles in Stöber synthesis in a water–alcohol mixture starting from the molecular precursor tetraethyl orthosilicate. The results of the UNPS were verified by measurements of a dynamic light scattering device and a transmission electron microscope.