Nanoparticles are applied in an increasing number of products (e.g. medicine, food and cosmetics). There is a need to real-time monitor the growth of nanoparticles during production inside the chemical reactor. However, standard particle sizing methods such as dynamic light scattering (DLS) and transmission electron microscopy (TEM) cannot do this. A suitable candidate may be ultrasonic transmission spectroscopy (UTS). Here, the sound speed and attenuation are measured of a dispersion and a physics based model is inverted and fitted to the measurements. The measurements have to be done with great accuracy: e.g. one should be able to measure frequency dependent variations in the speed of sound smaller than 0.05%. The measurements also have to be carried out fast enough compared to the time scale of the reaction. Moreover, the inversion has to be able to deal with the changing properties of the solvent during particle formation. Here, we report on the new ultrasound nanoparticle sizer (UNPS) that has these abilities and therefore could successfully monitor the size and concentration growth of nanoparticles during a reaction inside a reactor in real-time.

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Spatial resolution in medical ultrasound images is a key component in image quality and an important factor for clinical diagnosis. In early systems, the lateral resolution was optimal in the focus but rapidly decreased outside the focal region. Improvements have been found in, e.g., dynamic-receive beamforming, in which the entire image is focused in receive, but this requires complex processing of element data and is not applicable for mechanical scanning of single-element images. This paper exploits the concept of two-stage beamforming based on virtual source-receivers, which reduces the front-end computational load while maintaining a similar data rate and frame rate compared to dynamic-receive beamforming. We introduce frequency-wavenumber domain data processing to obtain fast second-stage data processing while having similarly high lateral resolution as dynamic-receive beamforming and processing in time-space domain. The technique is very suitable in combination with emerging technologies such as application-specific integrated circuits (ASICs), hand-held devices, and wireless data transfer. The suggested method consists of three steps. In the first step, single-focused RF line data are shifted in time to relocate the focal point to a new origin t' = 0, z' = 0. This new origin is considered as an array of virtual source/receiver pairs, as has been suggested previously in literature. In the second step, the dataset is efficiently processed in the wavenumber-frequency domain to form an image that is in focus throughout its entire depth. In the third step, the data shift is undone to obtain a correct depth axis in the image. The method has been tested first with a single-element scanning system and second in a tissue-mimicking phantom using a linear array. In both setups, the method resulted in a -6-dB lateral point spread function (PSF) which was constant over the entire depth range, and similar to dynamic-receive beamforming and synthetic aperture sequential be@en