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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Sensing and Imaging".

Deadline for manuscript submissions: closed (21 October 2021) | Viewed by 49450

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Special Issue Editors

Dr. Jorge Camacho

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Instituto de Tecnologías Físicas y de la Información (ITEFI), Spanish National Research Council (CSIC), 28006 Madrid, Spain
Interests: ultrasound imaging for medical and industrial applications; beamforming methods and hardware implementation; real-time ultrasound image processing
Special Issues, Collections and Topics in MDPI journals

Dr. Linas Svilainis

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Guest Editor

Depertment of Electronics Engineering, Kaunas University of Technology, K. Donelaičio g. 73, 44249 Kaunas, Lithuania
Interests: ultrasound electronics; spread spectrum signals; time of flight estimation; signal processing
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Dr. Tomás Gómez Álvarez-Arenas

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Guest Editor

Instituto de Tecnologías Físicas y de la Información (ITEFI), Spanish National Research Council (CSIC), 28006 Madrid, Spain
Interests: piezoelectric transducers; piezoelectric materials; composite materials; ultrasound propagation; materials characterization; inverse problem solution; complex optimization
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Ultrasound imaging is one the most extended diagnostic techniques in medicine, and one of the most demanded tools for non-destructive evaluation in industry. Although it is a well established technique, scientific and technical advances keep pushing the field beyond its frontiers, not only with regard to image quality and frame rate, but also with new applications and imaging modalities. It is, indeed, an amazing research field, which involves topics varying from materials science for transducers manufacturing and wave propagation physics to high-end analog and digital electronics and signal and image processing algorithms.

This Special Issue is open to new research and review papers in any of these fields, including, but not limited to:

New materials for ultrasound transducers
Transducer design for NDT and medical applications
Physical acoustics
Analog and digital ultrasound electronics
New beamforming methods and imaging modalities
New NDT and medical ultrasound applications
Ultrasonic image processing and AI techniques.

We highly appreciate your contribution to this Special Issue, in which we hope to give a comprehensive overview of recent advances in all fields of ultrasonic imaging.

Dr. Jorge Camacho
Dr. Linas Svilainis
Dr. Tomás Gómez Álvarez-Arenas
Guest Editors

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Keywords

ultrasound imaging
ultrasound beamforming
ultrasound transducers
ultrasound applications
ultrasound electronics
echograpy
non-destructive evaluation
artificial intelligence
image processing

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Published Papers (14 papers)

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Editorial

Jump to: Research, Review

7 pages, 227 KiB

Open AccessEditorial

Ultrasonic Imaging and Sensors

by Jorge Camacho, Linas Svilainis and Tomás Gómez Álvarez-Arenas

Sensors 2022, 22(20), 7911; https://doi.org/10.3390/s22207911 - 18 Oct 2022

Cited by 2 | Viewed by 3552

Abstract

Ultrasound imaging is a wide research field, covering areas from wave propagation physics, sensors and front-end electronics to image reconstruction algorithms and software [...] Full article

(This article belongs to the Special Issue Ultrasonic Imaging and Sensors)

Research

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21 pages, 3675 KiB

Open AccessArticle

Design of 2D Planar Sparse Binned Arrays Based on the Coarray Analysis

by Óscar Martínez-Graullera, Júlio Cesar Eduardo de Souza, Montserrat Parrilla Romero and Ricardo Tokio Higuti

Sensors 2021, 21(23), 8018; https://doi.org/10.3390/s21238018 - 30 Nov 2021

Cited by 7 | Viewed by 1795

Abstract

The analysis of the beampattern is the base of sparse arrays design process. However, in the case of bidimensional arrays, this analysis has a high computational cost, turning the design process into a long and complex task. If the imaging system development is considered a holistic process, the aperture is a sampling grid that must be considered in the spatial domain through the coarray structure. Here, we propose to guide the aperture design process using statistical parameters of the distribution of the weights in the coarray. We have studied three designs of sparse matrix binned arrays with different sparseness degrees. Our results prove that there is a relationship between these parameters and the beampattern, which is valuable and improves the array design process. The proposed methodology reduces the computational cost up to 58 times with respect to the conventional fitness function based on the beampattern analysis. Full article

(This article belongs to the Special Issue Ultrasonic Imaging and Sensors)

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20 pages, 12046 KiB

Open AccessArticle

Design of Ultrasonic Synthetic Aperture Imaging Systems Based on a Non-Grid 2D Sparse Array

by Júlio Cesar Eduardo de Souza, Montserrat Parrilla Romero, Ricardo Tokio Higuti and Óscar Martínez-Graullera

Sensors 2021, 21(23), 8001; https://doi.org/10.3390/s21238001 - 30 Nov 2021

Cited by 4 | Viewed by 2704

Abstract

This work provides a guide to design ultrasonic synthetic aperture systems for non-grid two-dimensional sparse arrays such as spirals or annular segmented arrays. It presents an algorithm that identifies which elements have a more significant impact on the beampattern characteristics and uses this information to reduce the number of signals, the number of emitters and the number of parallel receiver channels involved in the beamforming process. Consequently, we can optimise the 3D synthetic aperture ultrasonic imaging system for a specific sparse array, reducing the computational cost, the hardware requirements and the system complexity. Simulations using a Fermat spiral array and experimental data based on an annular segmented array with 64 elements are used to assess this algorithm. Full article

(This article belongs to the Special Issue Ultrasonic Imaging and Sensors)

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19 pages, 3154 KiB

Open AccessArticle

Random Fourier Features-Based Deep Learning Improvement with Class Activation Interpretability for Nerve Structure Segmentation

by Cristian Alfonso Jimenez-Castaño, Andrés Marino Álvarez-Meza, Oscar David Aguirre-Ospina, David Augusto Cárdenas-Peña and Álvaro Angel Orozco-Gutiérrez

Sensors 2021, 21(22), 7741; https://doi.org/10.3390/s21227741 - 20 Nov 2021

Cited by 13 | Viewed by 4086

Abstract

Peripheral nerve blocking (PNB) is a standard procedure to support regional anesthesia. Still, correct localization of the nerve’s structure is needed to avoid adverse effects; thereby, ultrasound images are used as an aid approach. In addition, image-based automatic nerve segmentation from deep learning methods has been proposed to mitigate attenuation and speckle noise ultrasonography issues. Notwithstanding, complex architectures highlight the region of interest lacking suitable data interpretability concerning the learned features from raw instances. Here, a kernel-based deep learning enhancement is introduced for nerve structure segmentation. In a nutshell, a random Fourier features-based approach was utilized to complement three well-known semantic segmentation architectures, e.g., fully convolutional network, U-net, and ResUnet. Moreover, two ultrasound image datasets for PNB were tested. Obtained results show that our kernel-based approach provides a better generalization capability from image segmentation-based assessments on different nerve structures. Further, for data interpretability, a semantic segmentation extension of the GradCam++ for class-activation mapping was used to reveal relevant learned features separating between nerve and background. Thus, our proposal favors both straightforward (shallow) and complex architectures (deeper neural networks). Full article

(This article belongs to the Special Issue Ultrasonic Imaging and Sensors)

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25 pages, 12451 KiB

Open AccessArticle

Modeling Pulsed High-Power Spikes in Tunable HV Capacitive Drivers of Piezoelectric Wideband Transducers to Improve Dynamic Range and SNR for Ultrasonic Imaging and NDE

by Antonio Ramos, Abelardo Ruiz and Enrique Riera

Sensors 2021, 21(21), 7178; https://doi.org/10.3390/s21217178 - 28 Oct 2021

Cited by 3 | Viewed by 2342

Abstract

The signal-to-noise ratios (SNR) of ultrasonic imaging and non-destructive evaluation (NDE) applications can be greatly improved by driving each piezoelectric transducer (single or in array) with tuned HV capacitive-discharge drivers. These can deliver spikes with kW pulsed power at PRF ≈ 5000 spikes/s, achieving levels higher even than in CW high-power ultrasound: up to 5 kW_pp. These conclusions are reached here by applying a new strategy proposed for the accurate modeling of own-design re-configurable HV capacitive drivers. To obtain such rigorous spike modeling, the real effects of very high levels of pulsed intensities (3–10 A) and voltages (300–700 V) were computed. Unexpected phenomena were found: intense brief pulses of driving power and probe emitted force, as well as nonlinearities in semiconductors, though their catalog data include only linear ranges. Fortunately, our piezoelectric and circuital devices working in such an intense regime have not shown serious heating problems, since the finally consumed “average” power is rather small. Intensity, power, and voltage, driving wideband transducers from our capacitive drivers, are researched here in order to drastically improve (∆ >> 40 dB) their ultrasonic “net dynamic range available” (NDRA), achieving emitted forces > 240 Newtons_pp and receiving ultrasonic signals of up to 76–205 V_pp. These measurements of ultrasonic pulsed voltages, received in NDE and Imaging, are approximately 10,000 larger than those usual today. Thus, NDRA ranges were optimized for three laboratory capacitive drivers (with six commercial transducers), which were successfully applied in the aircraft industry for imaging landing flaps in Boeing wings, despite suffering acoustic losses > 120 dB. Full article

(This article belongs to the Special Issue Ultrasonic Imaging and Sensors)

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15 pages, 4494 KiB

Open AccessArticle

Development of Low-Frequency Phased Array for Imaging Defects in Concrete Structures

by Yoshikazu Ohara, Kosuke Kikuchi, Toshihiro Tsuji and Tsuyoshi Mihara

Sensors 2021, 21(21), 7012; https://doi.org/10.3390/s21217012 - 22 Oct 2021

Cited by 11 | Viewed by 3241

Abstract

The nondestructive inspection of concrete structures is indispensable for ensuring the safety and reliability of aging infrastructures. Ultrasonic waves having a frequency of tens of kHz are frequently used to reduce the scattering attenuation due to coarse aggregates. Such low frequencies enable the measurement of the thickness of concrete structures and detection of layer-type defects, such as delamination, whereas it causes a lack of sensitivity to crack-type defects. In this paper, to realize the ultrasonic phased array (PA) imaging of crack-type defects, we fabricated a low-frequency (LF) array transducer with a center frequency of hundreds of kHz. To avoid the crosstalk between piezoelectric elements and dampen the vibration of each element, we adopted soft lead zirconate titanate (soft PZT) with a low mechanical quality factor. Subsequently, we optimized the geometry of each piezoelectric element using a finite element method to generate a short pulse. After validating the design in a fundamental experiment using a single-element transducer, we fabricated a 32-element array transducer with a center frequency of 350 kHz. To show the imaging capability of the LF array transducer, we applied it to a concrete specimen with a delamination. As a result, the PA with the LF array transducer clearly visualized the delamination, which could not be visualized using the PA with a 2.5 MHz array transducer. Furthermore, we applied it to a more challenging defect, a slit, which is sometimes used to simulate crack-type defects. As a result, the PA with the LF array transducer clearly visualized a slit of 1 mm width and 40 mm height in a concrete specimen. Thus, we demonstrated the usefulness of the LF array transducer for inspecting crack-type defects. Full article

(This article belongs to the Special Issue Ultrasonic Imaging and Sensors)

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17 pages, 6205 KiB

Open AccessArticle

Plane Wave Imaging through Interfaces

by Guillermo Cosarinsky, Jorge Fernandez-Cruza and Jorge Camacho

Sensors 2021, 21(15), 4967; https://doi.org/10.3390/s21154967 - 21 Jul 2021

Cited by 7 | Viewed by 2975

Abstract

Plane Wave Imaging (PWI) has been recently proposed for fast ultrasound inspections in the Non-Destructive-Testing (NDT) field. By using a single (or a reduced number) of plane wave emissions and parallel beamforming in reception, frame rates of hundreds to thousands of images per second can be achieved without significant image quality losses with regard to the Total Focusing Method (TFM) or Phased Array (PA). This work addresses the problem of applying PWI in the presence of arbitrarily shaped interfaces, which is a common problem in NDT. First, the mathematical formulation for generating a plane wave inside a component of arbitrary geometry is given, and the characteristics of the resultant acoustic field are analyzed by simulation, showing plane wavefronts with non-uniform amplitude. Then, an imaging strategy is proposed, accounting for this amplitude effect. Finally, the proposed method is experimentally validated, and its application limits are discussed. Full article

(This article belongs to the Special Issue Ultrasonic Imaging and Sensors)

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16 pages, 6620 KiB

Open AccessArticle

A Novel Defect Estimation Approach in Wind Turbine Blades Based on Phase Velocity Variation of Ultrasonic Guided Waves

by Renaldas Raišutis, Kumar Anubhav Tiwari, Egidijus Žukauskas, Olgirdas Tumšys and Lina Draudvilienė

Sensors 2021, 21(14), 4879; https://doi.org/10.3390/s21144879 - 17 Jul 2021

Cited by 11 | Viewed by 2896

Abstract

The reliability of the wind turbine blade (WTB) evaluation using a new criterion is presented in the work. Variation of the ultrasonic guided waves (UGW) phase velocity is proposed to be used as a new criterion for defect detection. Based on an intermediate value between the maximum and minimum values, the calculation of the phase velocity threshold is used for defect detection, location and sizing. The operation of the proposed technique is verified using simulation and experimental studies. The artificially milled defect having a diameter of 81 mm on the segment of WTB is used for verification of the proposed technique. After the application of the proposed evaluation technique for analysis of the simulated B-scan image, the coordinates of defect edges have been estimated with relative errors of 3.7% and 3%, respectively. The size of the defect was estimated with a relative error of 2.7%. In the case of an experimentally measured B-scan image, the coordinates of defect edges have been estimated with relative errors of 12.5% and 3.9%, respectively. The size of the defect was estimated with a relative error of 10%. The comparative results obtained by modelling and experiment show the suitability of the proposed new criterion to be used for the defect detection tasks solving. Full article

(This article belongs to the Special Issue Ultrasonic Imaging and Sensors)

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16 pages, 10461 KiB

Open AccessArticle

Deep-Learning-Driven Full-Waveform Inversion for Ultrasound Breast Imaging

by Thomas Robins, Jorge Camacho, Oscar Calderon Agudo, Joaquin L. Herraiz and Lluís Guasch

Sensors 2021, 21(13), 4570; https://doi.org/10.3390/s21134570 - 3 Jul 2021

Cited by 18 | Viewed by 4652

Abstract

Ultrasound breast imaging is a promising alternative to conventional mammography because it does not expose women to harmful ionising radiation and it can successfully image dense breast tissue. However, conventional ultrasound imaging only provides morphological information with limited diagnostic value. Ultrasound computed tomography (USCT) uses energy in both transmission and reflection when imaging the breast to provide more diagnostically relevant quantitative tissue properties, but it is often based on time-of-flight tomography or similar ray approximations of the wave equation, resulting in reconstructed images with low resolution. Full-waveform inversion (FWI) is based on a more accurate approximation of wave-propagation phenomena and can consequently produce very high resolution images using frequencies below 1 megahertz. These low frequencies, however, are not available in most USCT acquisition systems, as they use transducers with central frequencies well above those required in FWI. To circumvent this problem, we designed, trained, and implemented a two-dimensional convolutional neural network to artificially generate missing low frequencies in USCT data. Our results show that FWI reconstructions using experiment data after the application of the proposed method successfully converged, showing good agreement with X-ray CT and reflection ultrasound-tomography images. Full article

(This article belongs to the Special Issue Ultrasonic Imaging and Sensors)

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13 pages, 2302 KiB

Open AccessCommunication

Lateral Abdominal Muscles Shear Modulus and Thickness Measurements under Controlled Ultrasound Probe Compression by External Force Sensor: A Comparison and Reliability Study

by Grzegorz Mikołajowski, Małgorzata Pałac, Tomasz Wolny and Paweł Linek

Sensors 2021, 21(12), 4036; https://doi.org/10.3390/s21124036 - 11 Jun 2021

Cited by 7 | Viewed by 2599

Abstract

The aim of this study was to perform a reliability and agreement analysis and to compare lateral abdominal muscles (LAMs) thickness and elasticity results obtained by an experienced operator, by a non-experienced operator, and in an ultrasound imaging probe compression controlled (PCC) condition with minimal force necessary to obtain a proper ultrasound image. The sample consisted of 39 adolescents. An Aixplorer ultrasound scanner was used to evaluate the LAM. The probe in PCC condition was positioned in a prepared probe holder coupled with a pressure sensor. The LAM thickness and elasticity measurements were significantly (p < 0.05) different in the ultrasound PCC condition, compared to results obtained by both examiners. The abdominal oblique external and internal muscle thickness measurements were underestimated and all LAM shear moduli were overestimated during measurements without controlling the probe compression by an external sensor. The intra-class correlation coefficient was excellent in all conditions, but the smallest detectable differences were approximately 43–60% lower during the measurements collected in PCC condition. Differences in LAM measurements between PCC and ‘on-hand’ conditions may be clinically irrelevant when the force applied by the probe is consciously controlled by the examiner. However, during ultrasound measurements of the LAM morphology, the potential under/over estimation should always be considered when measurements are performed without controlling probe compression by an external sensor. Full article

(This article belongs to the Special Issue Ultrasonic Imaging and Sensors)

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20 pages, 8820 KiB

Open AccessArticle

Occluded Grape Cluster Detection and Vine Canopy Visualisation Using an Ultrasonic Phased Array

by Baden Parr, Mathew Legg, Stuart Bradley and Fakhrul Alam

Sensors 2021, 21(6), 2182; https://doi.org/10.3390/s21062182 - 20 Mar 2021

Cited by 7 | Viewed by 2892

Abstract

Grape yield estimation has traditionally been performed using manual techniques. However, these tend to be labour intensive and can be inaccurate. Computer vision techniques have therefore been developed for automated grape yield estimation. However, errors occur when grapes are occluded by leaves, other bunches, etc. Synthetic aperture radar has been investigated to allow imaging through leaves to detect occluded grapes. However, such equipment can be expensive. This paper investigates the potential for using ultrasound to image through leaves and identify occluded grapes. A highly directional low frequency ultrasonic array composed of ultrasonic air-coupled transducers and microphones is used to image grapes through leaves. A fan is used to help differentiate between ultrasonic reflections from grapes and leaves. Improved resolution and detail are achieved with chirp excitation waveforms and near-field focusing of the array. The overestimation in grape volume estimation using ultrasound reduced from 222% to 112% compared to the 3D scan obtained using photogrammetry or from 56% to 2.5% compared to a convex hull of this 3D scan. This also has the added benefit of producing more accurate canopy volume estimations which are important for common precision viticulture management processes such as variable rate applications. Full article

(This article belongs to the Special Issue Ultrasonic Imaging and Sensors)

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19 pages, 4321 KiB

Open AccessArticle

High Resolution, High Contrast Beamformer Using Minimum Variance and Plane Wave Nonlinear Compounding with Low Complexity

by Xin Yan, Yanxing Qi, Yinmeng Wang and Yuanyuan Wang

Sensors 2021, 21(2), 394; https://doi.org/10.3390/s21020394 - 8 Jan 2021

Cited by 8 | Viewed by 2723

Abstract

The plane wave compounding (PWC) is a promising modality to improve the imaging quality and maintain the high frame rate for ultrafast ultrasound imaging. In this paper, a novel beamforming method is proposed to achieve higher resolution and contrast with low complexity. A minimum variance (MV) weight calculated by the partial generalized sidelobe canceler is adopted to beamform the receiving array signals. The dimension reduction technique is introduced to project the data into lower dimensional space, which also contributes to a large subarray length. Estimation of multi-wave receiving covariance matrix is performed and then utilized to determine only one weight. Afterwards, a fast second-order reformulation of the delay multiply and sum (DMAS) is developed as nonlinear compounding to composite the beamforming output of multiple transmissions. Simulations, phantom, in vivo, and robustness experiments were carried out to evaluate the performance of the proposed method. Compared with the delay and sum (DAS) beamformer, the proposed method achieved 86.3% narrower main lobe width and 112% higher contrast ratio in simulations. The robustness to the channel noise of the proposed method is effectively enhanced at the same time. Furthermore, it maintains a linear computational complexity, which means that it has the potential to be implemented for real-time response. Full article

(This article belongs to the Special Issue Ultrasonic Imaging and Sensors)

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15 pages, 8347 KiB

Open AccessArticle

Air-Coupled Ultrasonic Probe Integrity Test Using a Focused Transducer with Similar Frequency and Limited Aperture for Contrast Enhancement

by Linas Svilainis, Andrius Chaziachmetovas, Darius Kybartas and Tomas Gomez Alvarez-Arenas

Sensors 2020, 20(24), 7196; https://doi.org/10.3390/s20247196 - 16 Dec 2020

Cited by 8 | Viewed by 3036

Abstract

Air-coupled ultrasonic probes require a special design approach and handling due to the significant mismatch to the air. Outer matching layers have to be soft so can be easily damaged and excitation voltages might cause the degradation of electrodes or bonding between the layers. Integrity inspection is desired during design, manufacturing, and exploitation. Spatial distribution of a transduction efficiency over piezoelement surface is proposed as a convenient means for the air-coupled probe integrity inspection. Focused transducer of similar center frequency is used to scan the surface of the inspected probe. However, such approach creates a challenge, i.e., area of the scanning beam is much smaller than the total receiving area of the inspected probe, therefore, contrast and imaging resolution are significantly degraded. Masking aperture made from cardboard and felt, placed at the focal point was proposed as solution. Far-range sidelobes were suppressed down to the noise floor (−50 dB) and the near-range sidelobes were reduced down to −17 dB. The proposed modification allows to use a similar frequency focused transducer. Probe integrity inspection can be carried out at significantly enhanced contrast and lateral resolution. Natural and artificial defects can be detected by the use of the proposed method. Full article

(This article belongs to the Special Issue Ultrasonic Imaging and Sensors)

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Review

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22 pages, 2769 KiB

Open AccessReview

Ultrasound Sensors for Process Monitoring in Injection Moulding

by Mandana Kariminejad, David Tormey, Saif Huq, Jim Morrison and Marion McAfee

Sensors 2021, 21(15), 5193; https://doi.org/10.3390/s21155193 - 31 Jul 2021

Cited by 18 | Viewed by 7516

Abstract

Injection moulding is an extremely important industrial process, being one of the most commonly-used plastic formation techniques. However, the industry faces many current challenges associated with demands for greater product customisation, higher precision and, most urgently, a shift towards more sustainable materials and processing. Accurate real-time sensing of the material and part properties during processing is key to achieving rapid process optimisation and set-up, reducing down-times, and reducing waste material and energy in the production of defective products. While most commercial processes rely on point measurements of pressure and temperature, ultrasound transducers represent a non-invasive and non-destructive source of rich information on the mould, the cavity and the polymer melt, and its morphology, which affect critical quality parameters such as shrinkage and warpage. In this paper the relationship between polymer properties and the propagation of ultrasonic waves is described and the application of ultrasound measurements in injection moulding is evaluated. The principles and operation of both conventional and high temperature ultrasound transducers (HTUTs) are reviewed together with their impact on improving the efficiency of the injection moulding process. The benefits and challenges associated with the recent development of sol-gel methods for HTUT fabrication are described together with a synopsis of further research and development needed to ensure a greater industrial uptake of ultrasonic sensing in injection moulding. Full article

(This article belongs to the Special Issue Ultrasonic Imaging and Sensors)

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