Low-frequency Ultrasonication Research Articles

Valorization of palm oil mill effluent via enhanced oil recovery as an alternative feedstock for biodiesel production.

Residual oil from palm oil mill effluent (POME) can be valorized into value-added products like biofuel. However, the complex structure in POME limits the full recovery of intracellular lipids. To address this challenge, low-frequency ultrasonication was used as a pre-treatment prior to oil recovery to improve the yield by liberating the entrapped oil via the cell disruption technique. This study focused on optimizing the ultrasound conditions (i.e., ultrasonication amplitude, ultrasonication duration, and probe immersion depth) to maximize the improvement of oil recovery yield using response surface methodology. The optimized conditions were 30.074% ultrasonication amplitude, 0.167 min ultrasonication duration, and 2 cm probe immersion depth. This resulted in an additional 42.50% improvement in oil recovery yield over non-ultrasonicated POME, which is in close agreement with the model prediction. Additionally, a cost-benefit analysis was incorporated to determine the feasibility of ultrasonication for enhancing oil recovery. The study also explored the synthesis of biodiesel from POME-recovered oil and characterized the fuel attributes according to American Society for Testing and Materials- and European Standards-prescribed procedures. The attributes of biodiesel produced from POME-recovered oil are comparable to those of palm-based biodiesel in Malaysia, demonstrating its potential as an alternative source for biodiesel production.

Sonication as a pre-processing step to alter acid whey generation during Greek yoghurt manufacture.

We investigated sonication as a pre-processing step to reduce acid whey generation during Greek yoghurt manufacture. The generation of a large amount of acid whey during the production of Greek yoghurt is an ongoing problem in the dairy industry and many studies are currently focusing on reducing it. We focused on the use of ultrasonication as a novel approach to minimize the casein fraction in the acid whey stream and simultaneously improve the gel properties. Ultrasound applied before the fermentation modified the structural properties and bonding behaviours of milk proteins, and enhanced the retention of casein in the yoghurt gel after the fermentation and straining steps. Therefore, the use of low-frequency ultrasonication as a pre-processing step may have the potential to provide significant economic benefits to the Greek yoghurt manufacturing process. Moreover, it improved the nutritional and physicochemical properties compared to regular Greek yoghurts.

Ultrasonic modulated rice bran protein concentrate: Induced effects on morphological, functional, rheological, and thermal characteristics

The effect of low frequency (20 kHz) ultrasonication at varying amplitude (20%, 30%, 40% for 30 min) on the morphological, functional, rheological, and thermal characteristics of rice bran protein concentrate (RBPC) from three different rice varieties: Pusa Basmati- 1509, 1121 and Sugandha were undertaken for the study. Scanning Electron Microscopy images showed that sonication treatment changed the microstructure of RBPC as some pores appeared on the smooth particles surface and more disordered structures compared to the untreated sample. Sonication treatment decreased mean particle size, D[4,3] from 89.77 μm (untreated) to 64.34 μm (20% amplitude), and increased surface hydrophobicity significantly (p < 0.05), from 1.34 ± 0.0080 (untreated) to 1.65 ± 0.0081 (20% amplitude) of 1121 RBPC variety. The FTIR analysis showed that sonication treatment altered RPBC secondary structure as β sheets, and random coils increased while reducing α-helix and β-turns. Sonication treatment at a lower amplitude of 20% made RBPCs brighter in color as lightness, redness, and yellowness values increased. The results showed that sonication treatment has improved the foaming capacity (FC), foaming stability (FS), and oil binding capacity (OBC) of all RBPC varieties. The FC increased significantly from 34.10 ± 0.27 (untreated) to 50.13 ± 0.98 (30% amplitude), FS (60 min) from 21.19 ± 0.63 (untreated) to 44.20 ± 0.26 (30% amplitude), and OBC from 1.42 ± 0.05 (untreated) to 1.61 ± 0.01 (30% amplitude) of 1509 RBPC variety, respectively (p < 0.05). Furthermore, water binding capacity and emulsion activity were reduced for all RBPC varieties after sonication, while solubility and digestibility improved for the 1121 variety, whereas reduced for the 1509 and Sugandha RBPC varieties. Frequency sweep analysis showed that sonication treatment reduced both the storage modulus and loss modulus of RBPC dispersions. Moreover, protein gel linkages transformed from non-covalent to covalently cross-link with increasing % amplitude for the 1121 RBPC variety. Ultrasonication at a lower 20% amplitude, first decreased the denaturation temperature (Tp) of 1121 RBPC variety from 72.5 °C to 63 °C, then increased it to 77.3 °C at higher 40% amplitude. In conclusion, under the conditions investigated in this study, sonication treatment has the potential to modify the foaming and oil-binding properties of RBPCs.

Ultrasonication Induced Alterations in Physicochemical and Functional Properties of Myosin.

Several reports have indicated that ultrasonication can change the solubility of muscle proteins and improves the functional properties of meat and isolated muscle proteins. Moreover, available literature suggests that ultrasonication can significantly improve the gelling properties of muscle proteins. The present study was carried out to investigate the effect of low-frequency ultrasonication on the secondary structure of myosin and the impact of these structural changes on solubility and gelling ability. Myosin from breast muscles (Pectoralis major) of broiler chicken was extracted and exposed to low-frequency ultrasonication for 30 min. Four aliquots collected at the interval of 5, 10, 20, and 30 min were analysed for change in ATPase activity, sulfhydryl content, surface hydrophobicity, alpha-helicity. The possible impact of these changes on heat-induced gelation was observed through electron micrographs. Ultrasonication reduced the enzymatic activity of myosin and increased the reactive sulfhydryl content. Decreased α-helicity and increased intrinsic fluorescence displayed significant structural changes at the secondary and tertiary levels. Myosin aggregation, as indicated by electron micrographs, showed a marked decrease. The microstructure of myosin gels displayed a distinct correlation with ultrasonication-induced structural changes. Furthermore, improved microstructure led to a significant increase in the water retention capacity of myosin gels. In conclusion, ultrasonication of myosin caused a marked change in structure at the tertiary and secondary levels. Structural changes apparently confined within the globular head region and rod portion of myosin were displayed by reduced enzymatic activity and improved gelation/solubility. Results of our study convincingly showed that ultrasonication improved the microstructure of myosin gels resulting in increased WHC.

Sonochemical decoration of palladium on graphene carpet for electrochemical methanol oxidation

• Decoration of palladium nanoparticles on graphene carpets (Pd/rGO) via low-frequency ultrasonication. • Investigate Pd/rGO as an electrocatalyst towards methanol oxidation. • Pd/rGO shows a higher activity of 51.68 mA cm −2 than commercial Pd/C catalyst. • Pd/rGO shows better stability not only in the initial state but also after the 3600 s. Fuel cells can be considered an effective and sustainable energy source to overcome the upcoming energy crisis. Among other fuel cells, Direct Methanol Fuel Cell (DMFC) attained great attention due to ease in storage and transportation along with the high volumetric energy density of methanol. The application of nanomaterials with unique morphologies and properties towards electrochemical methanol oxidation are being intensively studied to improve efficiency. Noble metals and their composites are generally considered the best candidates as electrode materials for methanol oxidation. In this work, a green strategy for the decoration of palladium nanoparticles on graphene carpets (Pd/rGO) has been proposed using glucose as a reducing and stabilizing agent through the aid of ultrasonication. As prepared material was properly analyzed with suitable analytical instruments. The electrochemical performance of the composite was investigated as an electrocatalyst towards methanol oxidation using Cyclic Voltammetry (CV) and Chronoamperometry (CA) techniques. A comparative study of the electrocatalytic activity towards methanol oxidation was carried out among as-prepared Pd/rGO, palladium nanoparticles (Pd NPs), and commercially available palladium on carbon (Pd/C) catalysts Among other samples, Pd/rGO shows a higher activity of 51.68 mA cm −2 during the electrooxidation of methanol than the individual and the commercial. Further, the long-term assessment also shows Pd/rGO has better stability not only in the initial state but also after the 3600 s.

Effect of Low-Frequency Ultrasonication on Red Wine Astringency

ABSTRACT Wine tastes better with age because of a complex chemical reaction among sugars, acids, and phenolic compounds. This study investigates if applying ultrasonic waves to wine would significantly reduce its perceived astringency levels. Ultrasonic (US) waves were applied to samples of a young Cabernet Sauvignon using a 24 kHz ultrasonic processor and sonotrode probe by varying time,, and amplitude at three levels. To objectively assess the relationship between the US waves and astringency, physical and chemical analysis was carried out that confirmed the underlying assumptions. While the pH of the treated samples decreased slightly, there was no change in color (Hunter CIE Color L*a*b*). Total Phenolic Content (TPC), Total Anthocyanin Content (TAC), and Tannin Concentration (TC) were significantly different (p ≤ .05) among all samples, indicating the impact of sonication on astringency causing components. Additionally, Fourier Transform Near Infrared (FT-NIR) spectroscopy confirmed that there were notable changes in the spectra, attributed to tannins, of wine after the application of sonication in comparison to untreated wine samples. The perception of astringent flavor was evaluated by (i) expert wine tasters and (ii) untrained panelists (n = 60) who were able to clearly distinguish between treated and untreated samples (p ≤ .05) and preferred sonicated samples (180 sec, 100% amplitude) over the control samples, supporting the hypothesis that sonication reduces the astringency of red wine.

Syntheses of flower and tube-like MoSe2 nanostructures for ultrafast piezocatalytic degradation of organic dyes on cotton fabrics

The synthesis of few-layered transition metal dichalcogenides (TMDCs) with abundant exposure of the active site, viz., is an important key to achieve excellent dye degradation performance. Here, we have reported synthesis and ultrafast dye degradation performance of flowers-like MoSe2 nanostructure (FMN) with ~230 nm in diameter and its transformation to tube-like MoSe2 microstructure (~1 μm in length) by tuning the solvothermal reaction time. The piezoelectric devices are developed using the FMNs delivers the highest open-circuit voltage of ~ 2.12 V, which is ~21 times higher than that of the developed device with the tube-like MoSe2 microstructure. The piezoelectric property of the synthesized samples has been judiciously utilized further for ultrafast degradation of organic dyes within 60–120 s only under the low-frequency (40 kHz) ultrasonication vibration in the dark. The estimated dye degradation efficiencies of the FMNs-based piezocatalyst are found to be ∼86% and 85% for degradation of Rhodamine B (RhB) and methylene blue (MB) dye within the 60 s, respectively. Also, the FMN has exhibited an excellent piezocatalytic dye degradation capability for RhB-MB dye mixture and dye loaded on a cotton fabric with an efficiency of ~98% (60 s) and 84% (120 s), respectively. The piezocatalytic dye degradation mechanism of FMNs has also been explained theoretically.

Low-frequency ultrasonication modulates the impact of annealing on physicochemical and functional properties of rice flour

Ultrasonication (US) is a green technology used to physically modify flours to increase their industrial range of applicability. The aim of this work was to study the combined effect that dual US and annealing (ANN) treatments have on starch and protein structure of rice flour, at 20, 40, 50 and 60 °C. Results showed clear modifications of functional, thermal and pasting properties of flours, as well as rheological properties of gels made from them. US + ANN led to generation of small-size particles, which markedly increased the swelling power and starch damage. X-Ray Diffraction and FTIR indicated that starch crystallinity and protein secondary structure was affected by the shear forces of cavitation. The combination of US + ANN improved the crystalline structure arrangement within the starch granules, causing narrowing of the gelatinization temperature range (ΔT). Pasting viscosities were significantly decreased by ultrasonication, following an increasing trend with increasing temperature, while pasting temperature was increased, agreeing in the achievement of a thermodynamically more stable structure. The rheological properties indicated a reduction of the elastic (G′) and viscous (G″) moduli after ultrasonication, as well as lower values of tan (δ), reflecting a higher predominance of elastic modulus versus viscous one than the non-sonicated flours. The rice flour's properties were found to be highly sensitive to the applied treatment conditions, showing a synergetic effect when sonicating at the highest studied temperature.

Propagation of Low Frequency Ultrasonic Guided Waves Through Welded Lap Joint

Propagation of Low Frequency Ultrasonic Guided Waves Through Welded Lap Joint

The influence of combined low-strength ultrasonics and micro-aerobic pretreatment process on methane generation and sludge digestion: Lipase enzyme, microbial activation, and energy yield

Low-frequency ultrasonics is a potential technology to reduce the hydrolysis phase period in anaerobic digestion process. In this study, theinfluence of combined low frequency ultrasonics and micro-aerobic (MA) pretreatment on sewage sludge solubilization, enzyme activity and anaerobic digestion were assessed. Initially, the effect of ultrasonic density (0.012, 0.014, 0.016, 0.018, 0.1, 0.12 and 0.14 W/mL) and irradiation time (1, 3, 5, 8, 9, 10 and 12 min) of 20 kHz frequency waves were investigated. Accordingly, the effect of micro-aerobic pretreatment (Air flow rate (AFR) = 0.1, 0.2, 0.3 and 0.5 VVM) within 20, 30, 40.48 and 60 h were examined. In addition, the effect of combined pretreatment on COD solubilization, lipase enzyme activation, ATP, percentage of live bacteria and methane gas production during the anaerobic process were examined. The results showed that the highest lipase activity (14.9 Umol/mL) was obtained under the effect of ultrasonic density of 0.1 W/ml within 9 min. The highest solubilization (65%) was observed under optimal micro-aerobic conditions: AFR = 0.2 (VVM) and micro-aerobic time: 40 h. Combined ultrasonic and micro-aerobic (US + MA) pretreatment increases the solubilization (70%), microbial activity (2080%) and lipase enzymatic activity (129%) compared to individual pretreatment. The Biogas production during anaerobic digestion pretreated with combined methods increased by 193% compared to the control, while the elevated values of biogas production in reactors pretreated by ultrasonic and micro-aerobic pretreatment alone were observed to be 101% and 165%, respectively. The net energy in reactor with the combined pre-treatment methods was calculated to be 1.26 kWh, while this value for control, pretreated ultrasonic and micro-aerobic reactors were obtained to be 0.56, 0.67 and 1.2 kWh, respectively.

Low-frequency ultrasound assisted synthesis of an aqueous aluminium hydroxide decorated graphitic carbon nitride nanowires based hybrid nanofluid for the photocatalytic H2 production from Methylene blue dye

An aqueous Aluminium Hydroxide [Al(OH)3] decorated Graphitic Carbon Nitride [g-C3N4] nanowires based hybrid nanofluid has been fabricated using the two-step method. Where, both the nanoparticles are synthesized separately and dispersed throughout the base fluid with the aid of ultrasonic cavitation technique. The hybrid nanofluid photocatalytic performance has been compared with Al(OH)3 – (g-C3N4) hybrid photocatalyst. After the preparation, the hybrid nanofluid and nanoparticles properties are systematically characterized. The FESEM results confirmed the effectiveness of the low frequency (30 kHz) ultrasonication in coating the Al(OH)3 nanoparticle on to the g-C3N4 surface. The larger BET specific surface area (80.45 m2/g) and the lower bandgap energy (2.35 eV) assured the enhanced photocatalytic H2 production from the degradation of Methylene Blue dye. Moreover, the obtained 0.5 vol% Al(OH)3–(g-C3N4)/H2O hybrid nanofluid produced about 6 times higher H2 than that of Al(OH)3 – (g-C3N4) hybrid photocatalyst. Even after 4 cycles, the hybrid nanofluid showed only 1% decrement in the photocatalytic performance. This study of replacing photocatalyst with the hybrid nanofluid delivers a sustainable route to harvest the H2 from photocatalytic degradation of the industrial pollutants in the presence of visible light.

Development of Sensor Devices Using Piezoelectric Vibration in Low Frequency Ultrasonic Region

Development of Sensor Devices Using Piezoelectric Vibration in Low Frequency Ultrasonic Region

Use of Ultrasound and Ultraviolet Radiation in Hybrid Methods for Water Disinfection

Hybrid photochemical methods are considered for water disinfection in which treatment with ultraviolet (UV) and ultrasonic (US) radiations are combined (US/UV) and applied consecutively or simultaneously; the use of catalysts is also included. The literature survey shows that inactivation of pathogenic microorganisms in aquatic media by high-frequency US (>100 kHz) has not been studied adequately, whereas only low-frequency (<100 kHz) US and low-pressure mercury vapor lamps (254 nm) were used in hybrid US/UV methods. Irradiation with high-frequency US generates reactive oxygen species (primarily hydroxyl radicals) in greater proportions, and a synergistic effect is observed when UV irradiation is included in treatment. Therefore, the use of high-frequency US and mercury-free UV sources in hybrid oxidizing systems, including those based on Fenton-like processes, is promising for intensifying disinfection processes and improving their effectiveness.

The role of breadfruit OSA starch and surfactant in stabilizing high-oil-load emulsions using high-pressure homogenization and low-frequency ultrasonication

This study aimed to investigate the role of modified breadfruit starch in the presence of Tween 80 for stabilizing the oil-in-water emulsions. An ultra turrax homogenizer was used to produce coarse emulsions, followed by high-pressure homogenization (HPH) or low-frequency ultrasonication (LFU) for fine emulsions. The breadfruit starch was chemically modified using octenyl succinic anhydride (OSA) to produce modified breadfruit OSA starch (BOSA). The dispersed phase was a mixture of palm and lemon oil in a 9:1 ratio. Two BOSA (1% and 2%), three oil concentrations (10%, 25%, and 40%) and Tween 80 (1% of the total amount of oil) were examined based on the emulsion stability. The Fourier transform infrared spectroscopy (FTIR) indicated that starch modification was successful (Degree of Substitution-DS, 0.0241). The most stable coarse emulsions contained 40% oil and 2% BOSA starch. The same formula produced fine emulsions that remained stable for over 42 days, regardless of the homogenization method. BOSA starch and Tween 80 exhibit a mixed stabilization effect on the oil-in-water emulsions. HPH produced more uniformly sized emulsion droplets when compared with those produced using LFU.

Challenges Associated with Byproducts Valorization-Comparison Study of Safety Parameters of Ultrasonicated and Fermented Plant-Based Byproducts.

In order to promote the efficient use of byproducts from the production of plant-based beverages, which still contain a large amount of nutritional and functional compounds, microbiological and chemical safety characteristics should be evaluated and, if needed, improved. Many challenges are associated with byproducts valorization, and the most important ones, which should be taken into account at the further steps of valorization, are biological and chemical safety. For safety improving, several technological treatments (biological, physical etc.) can be used. In this study, the influence of low-frequency ultrasonication (US) and fermentation with Lactobacillus casei LUHS210 strain, as physical and biotechnological treatments, on the safety characteristics of the byproducts (BYs) from the processing of rice, soy, almond, coconut, and oat drinks was compared. Ultrasonication, as well as fermentation, effectively improved the microbiological safety of BYs. Ultrasonication and fermentation reduced the concentration of deoxynivalenol, on average, by 24% only in soy BYs. After fermentation, 15-acetyldeoxynivalenol was formed in all samples (<12 µg kg−1), except for soy BYs. The lowest total biogenic amines content was found in fermented rice BYs and ultrasonicated coconut BYs. When comparing untreated and fermented BYs, significant changes in macro- and micro-elements content were found. Ultrasonication at 37 kHz did not significantly influence the concentrations of macro- and micro-elements, while fermentation affected most of the essential micro-elements. Consequently, while ultrasonication and fermentation can enhance the safety of BYs, the specific effects must be taken into account on biogenic amines, mycotoxins, and micro and macro elements.

Fabrication of ultrasound-mediated tunable graphene oxide nanoscrolls.

In this work, a cost-effective and facile method was adopted for the fabrication of graphene oxide nanoscrolls (GONS) by low frequency (20kHz) ultrasonication with tunable dimensions. The graphene oxide (GO) was synthesized by modified Hummer's method using synthetic graphite as a base material. Later, GO suspension (0.05gL-1) were made using methanol as solvent and subjected to different ultrasonication conditions. It was found that GO sheets curls themselves into nanoscrolls by overcoming the energy barrier for scrolling with the help of bubble cavitation energy provided by ultrasonication. Also, the effect of ultrasonication power (100-150W) for irradiation time (0.5-3h) over the GONS dimensions were investigated. The spiral wounded GONS structures were shown using electron microscopy. Raman Spectroscopy, Thin-film X-Ray Diffraction, Energy Dispersive X-Ray, FT Infrared Spectroscopic analysis were also done to endorse GONS formation. Factors affecting GONS formation such as sonication power and solvent selection were studied as scrolling of GO sheets are strongly dependent on sonication parameters and solvent characteristics. It was found that GONS length varies inversely with irradiation time for identical power density. Also, a solvent with relatively large Hansen solubility parameter, lower dipole movement and less negative value of zeta potential support GONS formation of longer length. Raman analysis overlays the rapid oxygen-defect site cleavage mechanism. The obtained GONS unlocks further developments in various engineering applications like adsorption, drug delivery and filtration membrane.

Ex Vivo Assessment of Cortical Bone Properties Using Low-Frequency Ultrasonic Guided Waves.

The early diagnosis of osteoporosis through bone quality assessment is a major public health challenge. Research in axial transmission using ultrasonic guided waves has shown the method to be sensitive to the geometrical and mechanical properties of the cortical layer in long bones. However, because of the asymmetric nature of cortical bone, the introduction of a more elaborate numerical model than the analytical plate and cylinder models, as well as its inversion, continues to be challenging. The aim of this article is, therefore, to implement a bone-like geometry using semianalytical finite-element (SAFE) modeling to perform the inverse characterization of ex vivo radii at low frequencies (< 60 kHz). Five cadaveric radiuses were taken from donors aged between 53 and 88 and tested using a typical axial transmission configuration at the middle of the diaphysis. The dispersion curves of the propagating modes were measured experimentally and then systematically compared with the solutions obtained with the SAFE method. For each sample, four parameters were estimated using a parameter identification procedure: 1) the bulk density; 2) the thickness; 3) the outer diameter; and 4) a shape factor (SF). The results showed a moderate agreement between the predicted bulk density and the average voxel value calculated from X-ray computed tomography images. Furthermore, a good agreement was observed between the geometrical parameters (thickness, outer diameter, and SF) and the reference images.

Characterization of the physical, microbiological, and chemical properties of sonicated raw bovine milk

Innovative processing technologies, such as ultrasonication, can change the properties of milk, allowing for the improvement or development of dairy foods. Yet taking bench-scale equipment to pilot plant scale has been challenging. Raw milk, standardized to 3% fat and warmed to inlet temperatures of 42 or 54°C, was exposed to continuous, high-intensity, low-frequency ultrasonication (16/20 kHz, 1.36 kW/pass) at flow rates of 0.15, 0.30, and 0.45 L/min that resulted in resident times within the reaction cell of 6, 3, and 2 min per pass, respectively. Multiple passes (3, 5, and 7, respectively) were required to obtain a total exposure time of 14 to 18 min. Evaluation of fat droplet sizes, enzyme coagulation properties, and microstructure of milk and milk gels, as well as determining compositional and lipid properties, were conducted to determine the potential of the ultrasound system to effectively modify milk. Laser scanning particle sizing and confocal microscopy showed that the largest droplets (2.26 ± 0.13 µm) found in raw milk were selectively reduced in size with a concomitant increase in the number of submicron droplets (0.37 ± 0.06 µm), which occurred sooner when exposed to shorter bursts of ultrasonication (0.45 L/min flow rates) and at an inlet temperature of 54°C. Ultrasound processing with milk entering at 42°C resulted in faster gelling times and firmer curds at 30 min; however, extended processing at inlet temperature of 54°C reduced curd firmness and lengthened coagulation time. This showed that ultrasonication altered protein-protein and protein-lipid interactions, thus the strength of the enzyme-set curds. Scanning electron microscopy revealed a denser curd matrix with less continuous and more irregular shaped and clustered strands, whereas transmission electron microscopy showed submicron lipid droplets embedded within the protein strands of the curd matrix. Processing at inlet temperature of 54°C with flow rates of 0.30 and 0.45 L/min also reduced the total aerobic bacterial count by more than 1 log cfu/mL, and the number of psychrophiles below the limit of detection (10 cfu/mL) for this study. Ultrasonication exposures of 14 to 18 min had minimal effect on the milk composition, fatty acid profiles, and lipid heat capacity and enthalpy. The findings show that this continuous ultrasound system, which is conducive to commercial scale-up, modifies the physical and functional properties of milk under the parameters used in this study and has potential use in dairy processing.

Characterization and Design Improvement of a Thickness-Shear Lead Zirconate Titanate Transducer for Low Frequency Ultrasonic Guided Wave Applications.

Thickness-shear transducers for guided wave testing have been used in industry for over two decades and much research has been conducted to improve the resolution and sensitivity. Due to a geometric feature of the current state-of-the art transducer, there is an out-of-plane component in the propagation direction of the fundamental shear horizontal mode which complicates the signal interpretation. In such case, complex signal processing techniques need to be used for mode discrimination to assess the structural health with higher precision. Therefore, it is important to revise the transducer design to eliminate the out-of-plane components in the propagation direction of fundamental shear horizontal mode. This will enhance the mode purity of fundamental shear horizontal mode for its application in guided wave inspection. A numerical investigation has been conducted on a 3 mm thick 2 m circular steel plate to understand the behaviour and the characteristics of the state-of-the-art thickness-shear transducer. Based on the results, it is noted that the redesigning the electrode arrangement will suppress the out-of-plane components on the propagation direction of the fundamental shear horizontal mode. With the aid of this information current state-of-the-art transducers were redesigned and tested in laboratory conditions using the 3D Laser Doppler Vibrometer. This information will aid future transducer designers improve the resolution of thickness-shear transducers for guided wave applications and reduce the weight and cost of transducer array by eliminating the need of additional transducers to suppress spurious modes.

A Systematic Review to Compare the Effect of Low-frequency Ultrasonic Versus Nonsurgical Sharp Debridement on the Healing Rate of Chronic Diabetes-related Foot Ulcers

A systematic review was conducted to determine the effectiveness of nonsurgical sharp debridement (NSSD) versus low-frequency ultrasonic debridement (LFUD) for diabetes-related foot ulceration in adults. Published studies (earliest date available to April 2017) comparing healing outcomes of LFUD- and NSSD-treated foot ulcers in adults were considered. The quality of publications that met inclusion criteria were assessed using the PEDro scale, and a meta-analysis was undertaken to compare percentage healed and percentage of ulcer size reduction. Of the 259 publications identified, 4 met the inclusion criteria but 2 of the 4 did not contain sufficient patient outcomes details for meta-analysis, leaving a sample size of 173 patients. Outcome data for the 2 studies included percentage of ulcers healed between the 2 debridement methods. This difference was not significant (RR = 0.92; 95% CI = 0.76-1.11). The risk of bias for both studies was low. No difference in healing outcomes between NSSD and LFUD debridement of diabetic foot ulcers was found. Well-designed, controlled clinical studies are needed to address the current paucity of studies examining the efficacy and comparative effectiveness of debridement methods.