Ultrasonic transducers are widely used in gas flow metering due to their high accuracy and absence of moving parts. However, designing high-performance transducers often requires extensive prototyping and time-consuming trial-and-error. This study presents a simulation-driven design approach that combines a full factorial design of experiments (DOEs) with finite element analysis to streamline and optimize transducer development. A total of 208 transducer configurations were simulated using finite element software (OnScale), varying three key parameters: matching layer material (MLM), matching layer thickness (MLT), and the presence of a light backing layer (BL). The active element was an 8 mm diameter, 1 mm thick PIC255 piezoelectric disk operating in radial mode at 238 kHz. The design objectives were to maximize acoustic pressure while minimizing pulse duration (PD), both of which are critical for gas flow measurement resolution. The optimal configuration identified was 1 mm gray matching layer (ML) (rho = 681.6 kg/m(3)) combined with a 5 mm RTV 664 BL. Multivariate analysis showed that MLT was the most influential parameter for both amplitude (58.49%) and PD (59.44%). Its interaction with material type and backing configuration also had a significant impact on performance. Experimental validation confirmed the simulation trends, yielding a measured peak voltage of 5.87 & times; 10(-4) V and a PD of 2.61 & times; 10(-4) s, compared to simulated values of 6.54 & times; 10(-4) V and 3.31 & times; 10(-4) s. This corresponds to errors of 10.24% in amplitude and 26.82% in PD. Overall, the proposed approach reduces reliance on physical prototyping while providing reliable performance prediction, offering a practical and scalable method for ultrasonic transducer optimization in gas sensing applications.

The ability to create cell-laden fluidic models that mimic the geometries and physical properties of vascularized tissue would be extremely beneficial to the study of disease etiologies and future therapies, including in the case of cancer where there is increasing interest in studying alterations to the microvasculature. Engineered systems can present significant advantages over animal studies, alleviating challenges associated with variable complexity and control. Three-dimensional (3D)-printable tissue-mimicking hydrogels can offer an alternative, where control of the biophysical properties of the materials can be achieved. Hydrogel-based systems that can recreate complex 3D structures and channels with diameters <500 mu m are challenging to produce. We present a noncytotoxic photo-responsive hydrogel that supports 3D printing of complex 3D structures with microchannels down to 150 mu m in diameter. Fine tuning of the 3D-printing process has allowed the production of complex structures, where for demonstration purposes we present a helical channel with diameters between 250 and 370 mu m around a central channel of 150 mu m in diameter in materials with mechanical and acoustic properties that closely replicate those of tissue. The ability to control and accurately reproduce the complex features of the microvasculature has value across a wide range of biomedical applications, especially when the materials involved accurately mimic the physical properties of tissue. An approach that is additionally cell compatible provides a unique setup that can be exploited to study aspects of biomedical research with an unprecedented level of accuracy.

This paper evaluates the benefits of using ultrasonic guided waves for the mapping of a structure, when implemented on a mobile magnetic robotic platform. It considers the specific problem of mapping geometric features using the guided ultrasonic waves, which enables the localisation of edges and/or the welded joints. Shear Horizontal (SH) guided waves generated by ElectroMagnetic Acoustic Transducers (EMATs) are used for mapping steel samples with a nominal thickness of 10 mm. A Bayesian mapping technique (Occupancy grid mapping) was used to map the boundaries of an irregular sample in a pseudo-pulse-echo mode. The principle is demonstrated in both simulation and laboratory-based experiments. It is shown that the proposed mapping algorithm successfully estimates the position of a sample's edges. Experimentally, a range accuracy of < 1.7 mm (1 sigma) was achieved on a 1 x 2 m sample using miniaturised EMATs operating at a wavelength of 22 mm.

The development of 3D-printed sensors and actuators from piezocomposite materials has increased in recent years due to the ease of production, low-cost and improved functionality additive manufacturing provides. The piezocomposite material developed in this work has the potential to be used as a functional material in stereolithographic additive manufacturing by combining the optical, viscoelastic properties of NOA 65 and the piezoelectric properties of Barium Titanate. The new (0–3) piezocomposite material consists of Norland Optical Adhesive 65 (NOA 65) as the polymer matrix and Barium Titanate (BaTiO 3 ) with particles sizes (100 nm, 200 nm and 500 nm) as the dielectric filler. We synthesized thin film samples of the (0–3) piezocomposite with 60% w/w BaTiO 3 using solution mixing and spin coating method to produce samples with layer thickness of 100 µm. Fourier-transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM) techniques were used to analyze the microstructure of the piezocomposite to determine the effect of different particles sizes of BaTiO 3 on the structural and mechanical properties of the composite. The longitudinal piezoelectric coefficient d 33 was also measured using the laser vibrometer technique. Both single point scans and full surface scans were carried out to obtain the average piezoelectric coefficient d 33 of the composite material. The results of the SEM confirmed the (0–3) structure of the piezocomposite material with isolated BaTiO 3 nanoparticles. It further showed the uniform distribution of the BaTiO 3 nanoparticles across each of the samples. FTIR analysis showed that the filler nanoparticles had no effect on the native structure of the polymer matrix. The longitudinal piezoelectric coefficient d 33 of the piezocomposite material was observed to increase with increasing BaTiO 3 particle sizes, while the indentation modulus of the composite investigated using the method of Oliver and Pharr was observed to decrease with an increase in particle size. Results from the single point scans showed the composite with BaTiO 3 particle size 100 nm, 200 nm and 500 nm having an average d 3 3 of 2.1 pm/V, 3.0 pm/V and 3.9 pm/V while the average d 33 obtained from the full surface scan of 1430 scan points showed 1.4 pm/V, 6.1 pm/V, 7.2 pm/V.

Systemically circulating microbubbles are used as contrast agents to aid both drug targeting and delivery using ultrasound. Exploiting their acoustic behaviour in small diameter vessels is critical for both applications, but the highly controlled experiments required to support this are not possible in vivo and challenging in vitro. Experimental platforms with small diameter channels (below 200 microns) are not readily available nor able to represent vascular geometries, leaving the existence and extent of microbubble-microvessel interactions incompletely defined. In this work we present a 3D-printed microchannel platform using tissue-mimicking hydrogels featuring radii down to 75 microns. We demonstrate application to study microbubble behaviour via acoustic backscatter under controlled environments in physiologically-relevant conditions.

Interest into consumer applications of high power ultrasound is growing and investigation into the development of transducers for this application is necessary. This paper conducts a primary evaluation on alternative small-scale transducer designs for potential application as cavitation generators in portable ultrasonic devices for cleaning applications. Simulation of the pressure field produced by concave cymbal, convex cymbal and uni-ring-morph transducers are compared with disc and ring only transducers. The potential to increase the active cavitation area through alternative transducer drive signals is also investigated. High power ultrasound production from a piezoelectric disc with simultaneous dual frequency drive has been investigated through simulation and experimentation. Implementation of the Rayleigh-Sommerfeld integral is used to estimate the pressure fields from the disc transducer with both dual and single frequency sonication. Experimentation has been carried out using acoustic emission measurements and aluminium foil erosion experiments to evaluate the cavitation behaviour when dual frequency ultrasound is applied. The results indicate an increase in the number and size range of cavitation bubbles as well as improved foil erosion when dual frequency drive signals containing specially selected frequencies are used.

The application of ultrasound to crystallization processes is a well-established technique employed to control the initiation of nucleation and therefore to achieve control over the crystal size and size distribution. In the context of Apfel's golden rules of cavitation: "Know thy liquid," "Know thy sound field" and "Know when something happens," the third rule has been satisfied. However, in order to link the applied ultrasonic energy to the enhanced process parameters, it is important to characterize the sound field and cavitation activity in the crystallization solvent. In order to better understand and design sono-crystallization experiments in the context of pharmaceutical manufacturing, measurements of acoustic emissions, broadband integrated voltage and focused beam reflectance measurements (FBRM) have been carried out in five typical crystallization solvents and water at a fundamental frequency of 40 kHz. The approaches taken have been to detect and measure cavitation activity as a function of ultrasonic power, allowing a comparison across the solvents.

A 32-element, 5MHz linear array, incorporating PMN-PT 1-3 piezo-polymer composite, has been designed using finite element (FE) modelling. The Elasto-Electric material properties of the PMN-PT samples were characterized and evaluated within the FE model to ensure accurate corroboration. The array configuration and performance were then investigated, including array microstructure, and steering and focusing ability. The matching and backing material selection, array sensitivity and bandwidth were assessed using pulse echo responses. Imaging performance was then undertaken, employing full matrix capture and total focusing method. For performance comparison, a reference array comprising of conventional PZT5H ceramic was also investigated, following the same design criteria. The piezocrystal device provides a bandwidth of 87% and a sensitivity-bandwidth product improvement of 160% when compared to the reference PZT5H based array.

Naturally occurring resonating systems utilize structures containing a range of length scales to produce a broad operating bandwidth. It has previously been reported that a piezoelectric composite transducer based on a fractal geometry, which thereby introduces components with varying length scales, results in a wider operational bandwidth and a higher sensitivity. In this paper, the work is now extended to an ultrasonic array device using a Cantor Set (CS) fractal geometry. The behavior of this fractal array is explored using both finite element (FE) modeling and experimentation, including comparison with a conventional 2-2 linear array. The FE simulated pulse-echo responses correlate well with the experimental data, which indicates that the CS fractal array elements possessed a wider-6 dB bandwidth (57.3 % against 49.4 0/0), and a higher sensitivity, (11.4 mV against 8.9 mV peak-to-peak voltage) compared with a conventional 2-2 design. In addition, an improved crosstalk reduction is achieved by the CS fractal array. Images of a wire-water phantom produced by the two arrays using the total focusing method (TFM) and full matrix capturing (FMC) data shows that the CS fractal array outperforms the conventional 2-2 array in terms of image resolution and signal strength. Finally, another advanced fractal geometry comprising orthogonal CS fractal geometries, known as the Cantor Tartan (CT) is investigated to further enhance the bandwidth performance of the array, where a -6 dB pulse-echo bandwidth of 68.1 % can be predicted using FE modeling.

Wider operational bandwidth is an important requirement of an ultrasound transducer across many applications. In nature, it can be observed that several hearing organs possess a broad operating bandwidth by having a varying length scales structure. Moreover, conventional 1-3 piezoelectric composite transducers have been widely recognized for their wider bandwidth over their piezoelectric ceramic counterparts. In this paper, a novel 1-3 piezoelectric composite design using a fractal geometry, known as the Sierpinski Gasket (SG), is proposed in order to explore the potential of further extending the operational bandwidth and sensitivity of the transducer. Two equivalent 1-3 piezocomposite designs are compared to this end, one with a conventional periodic parallelepiped-shaped pillar structure and one with the SG fractal geometry, both theoretically, using a finite-element analysis package, and experimentally. The transmit voltage response and open-circuit voltage response are used to illustrate bandwidth improvement from the fractal composite design. Following the simulation results, a 580-kHz single-element transducer, utilizing the proposed SG fractal microstructure, is fabricated using a pillar placement methodology. The performance of the prototyped device is characterized and compared with a conventional 1-3 composite design, as well as with a commercial ultrasound transducer. In the one-way transmission mode, a bandwidth improvement of 27.2% and sensitivity enhancement of 3.8 dB can be found with the SG fractal design compared to an equivalent conventional composite design and up 105.1% bandwidth improvement when compared to the commercial transducer. In the one-way reception mode, the bandwidth improvement for the SG fractal design is 2.5% and 32.9% when compared to the conventional and commercial transducers, respectively.

Sono-crystallisation has been used to enhance crystalline product quality particularly in terms of purity, particle size and size distribution. In this work, the effect of impurities and ultrasound on crystallisation processes (nucleation temperature, yield) and crystal properties (crystal size distribution determined by Focused Beam Reflectance Measurement (FBRM), crystal habit, filtration rate and impurity content in the crystal product by Liquid Chromatography-Mass Spectroscopy (LC-MS)) were investigated in bulk suspension crystallisation experiments with and without the use of ultrasound. The results demonstrate that ultrasonic intervention has a significant effect on both crystallisation and product crystal properties. It increases the nucleation rate resulting in smaller particles and a narrower Particle Size Distribution (PSD), the yield has been shown to be increase as has the product purity. The effect of ultrasound is to reduce the level acetanilide impurity incorporated during growth from a 2 mol% solution of the selected impurity from 0.85 mol% to 0.35 mol% and likewise ultrasound reduces the uptake of metacetamol from 1.88 mol% to 1.52 mol%.

We have previously demonstrated product purity enhancement during the crystallization of paracetamol in a low intensity ultrasound field. In order to elucidate the underlying mechanisms of sonocrystallization, the applied ultrasonic interventions were characterized by measurements of cavitation bubble number, size and size distribution with a Mettler FBRM probe. Ultrasonic intensity measurements were conducted using a needle hydrophone. The solvents selected for study; water, ethanol and isoamyl alcohol show significant differences in behavior. This data provides an insight into the relationship between solvent properties and cavitation bubble activity under the same applied ultrasonic energy. Substantially more cavitation bubbles form in the organic solvents compared with water, this is consistent with the lower surface tension and higher vapor pressure of the organic solvents. The difference in bubble size distributions between ethanol and isoamyl alcohol is significant. In ethanol most bubbles remain below 30μm whereas in isoamyl alcohol they tend towards 1mm in size. Detection, quantification and measurement of cavitation bubbles in crystallization solvents contributes further evidence that acoustic cavitation is a key component in sonocrystallization. The industrial driver is to incorporate this understanding into both pharmaceutical process and equipment design to improve the product quality, reduce waste and improve access to medicines.

Transcranial Doppler Ultrasound (TCD) is one of the techniques that have been used for stroke diagnosis. This paper compares the potential of three aperiodic sparse array configurations: random array; sunflower spiral array; and log spiral array for application to TCD. To cover the full temporal window, a 30mm diameter circular aperture is selected, with a 2MHz operating frequency to match current TCD instrumentation. A 2D model developed in MATLAB simulates the far field directivity function by applying the 2D FFT on an array's aperture function. Two evaluation criteria, Peak Side-lobe Level (PSL) and Integrated Side-lobe Ratio (ISLR), are used to assess the performance of each array configuration. Simulation results demonstrate that a compromise between PSL and ISLR is required to select a suitable transducer configuration for fabrication and further evaluation. These evaluation results demonstrate that the log spiral array configuration has desirably low PSL relative to the others, while the sunflower spiral array performs better in terms of ISLR. Considering this design evaluation, a prototype array based on a log spiral layout has been manufactured. Characterization of the prototype array show that it performs as predicted.

The resonance frequency of an active element in a piezoelectric ultrasonic transducer is dependent on its length scale. Inspired by natural occurring auditory systems, incorporation of elements with varying length scales in the piezoelectric transducer design can result in a wider operational bandwidth. In this paper, a mathematical algorithm was developed first to define the feature of a fractal geometry called the Cantor Set (CS), then a series of parameter sweep simulations are performed to design a CS fractal array transducer and a conventional array transducer and optimize their performance. The behaviors of these two array transducers were explored theoretically, using finite element modeling and experimentally using the scanning laser vibrometry. The FE simulation results and experimental results correlate well with each other, which indicates an approximate 30% operating bandwidth enhancement and a 5 dB side lobe reduction can be achieved by the CS fractal array compared to the conventional linear array design.

This paper describes the acoustic properties of a range of epoxy resins prepared by photocuring that are suitable for application in piezoelectric ultrasonic transducer matching layers. Materials, based on blends of digylcidyl ether of Bisphenol A and 1,4-cyclohexanedimethanol diglycidyl ether, are described. Furthermore, in order to vary the elastic character of the base resin, samples containing polymer microspheres or barium sulphate particles are also described. The acoustic properties of the materials are determined by a liquid coupled through transmission methodology, capable of determining the velocity and attenuation of longitudinal and shear waves propagating in an isotropic layer. Measured acoustic properties are reported which demonstrate materials with specific acoustic impedance varying in the range 0.88 6.25 MRayls. In the samples comprising blends of resin types, a linear variation in the acoustic velocities and density was observed. In the barium sulphate filled samples, acoustic impedance showed an approximately linear variation with composition, reflecting the dominance of the density variation. While such variations can be predicted by simple mixing laws, relaxation and scattering effects influence the attenuation in both the blended and filled resins. These phenomena are discussed with reference to dynamic mechanical thermal analysis and differential scanning calorimetry of the samples.  Author to whom correspondence should be addressed Richard O'Leary, Centre for Ultrasonic Engineering, University of Strathclyde, 204 George Street, Glasgow, G1 1XW r.oleary@eee.strath.ac.uk

Shear wave inspection is generated from mode conversion of longitudinal waves, using a selected, angled wedge positioned between the transducer and the test specimen. However, in certain scenarios where access is restricted the combination of the transducer and the wedge can be too cumbersome for in situ deployment. In this work, a low profile, linear ultrasound array transducer is proposed to generate shear waves via direct coupling to the component surface precluding the requirement for a wedge. The array transducer was designed using finite element modelling, and a prototyped array was manufactured with 32 elements and operating frequency at ∼2MHz. Preliminary imaging results has shown the shear wave beam generated can be operated at high angles up to 80°.

Advances in manufacturing techniques and materials have led to an increase in the demand for reliable and robust inspection techniques to maintain safety critical features. The application of modelling methods to develop and evaluate inspections is becoming an essential tool for the NDE community. Current analytical methods are inadequate for simulation of arbitrary components and heterogeneous materials, such as anisotropic welds or composite structures. Finite element analysis software (FEA), such as PZFlex, can provide the ability to simulate the inspection of these arrangements, providing the ability to economically prototype and evaluate improved NDE methods. FEA is often seen as computationally expensive for ultrasound problems however, advances in computing power have made it a more viable tool. This paper aims to illustrate the capability of appropriate FEA to produce accurate simulations of ultrasonic array inspections – minimizing the requirement for expensive test-piece fabrication. Validation is afforded via corroboration of the FE derived and experimentally generated data sets for a test-block comprising 1D and 2D defects. The modelling approach is extended to consider the more troublesome aspects of heterogeneous materials where defect dimensions can be of the same length scale as the grain structure. The model is used to facilitate the implementation of new ultrasonic array inspection methods for such materials. This is exemplified by considering the simulation of ultrasonic NDE in a weld structure in order to assess new approaches to imaging such structures.