Ari Salmi

Phase-delayed laser diode array allows ultrasonic guided wave mode selection and tuning

Selecting and tuning modes are useful in ultrasonic guided wave non-destructive testing (NDT) since certain modes at various center frequencies are sensitive to specific types of defects. Ideally one should be able to select both the mode and the center frequency of the launched waves. We demonstrated that an affordable laser diode array can selectively launch either the S0 or A0 ultrasonic wave mode at a chosen center frequency into a polymer plate. A fiber-coupled diode array (4 elements) illuminated a 2 mm thick acrylic plate. A predetermined time delay matching the selected mode and frequency was employed between the output of the elements. The generated ultrasound was detected by a 215 kHz piezo receiver. Our results imply that this array permits non-contacting guided wave ultrasonic NDT. The solution is small, affordable, and robust in comparison to conventional pulsed lasers. In addition, it does not require experienced operators.

Effects of acoustic levitation on the development of zebrafish, Danio rerio, embryos.

Acoustic levitation provides potential to characterize and manipulate material such as solid particles and fluid in a wall-less environment. While attempts to levitate small animals have been made, the biological effects of such levitation have been scarcely documented. Here, our goal was to explore if zebrafish embryos can be levitated (peak pressures at the pressure node and anti-node: 135 dB and 144 dB, respectively) with no effects on early development. We levitated the embryos (n = 94) at 2–14 hours post fertilization (hpf) for 1000 (n = 47) or 2000 seconds (n = 47). We compared the size and number of trunk neuromasts and otoliths in sonicated samples to controls (n = 94), and found no statistically significant differences (p > 0.05). While mortality rate was lower in the control group (22.3%) compared to that in the 1000 s (34.0%) and 2000 s (42.6%) levitation groups, the differences were statistically insignificant (p > 0.05). The results suggest that acoustic levitation for less than 2000 sec does not interfere with the development of zebrafish embryos, but may affect mortality rate. Acoustic levitation could potentially be used as a non-contacting wall-less platform for characterizing and manipulating vertebrae embryos without causing major adverse effects to their development.

Quantifying fatigue generated in high strain rate cyclic loading of Norway spruce

Papermaking, especially mechanical pulping, consumes much energy. To reduce this energy consumption one has to understand and exploit the phenomena present during the pulping. An important phenomenon to understand is wood fatigue. We quantitatively measure the fatigue generated during high strain rate cyclic loading of spruce wood performed under conditions resembling those present during mechanical pulping. We impacted the samples with 5% strain pulses at 500 Hz. The radial direction stiffness drop in the samples was quantified by 500 kHz ultrasonic through-transmission postimpacting. The depth profile of the generated fatigue was also determined. A dependency of the amount of fatigue generated during cyclic straining on the moisture content was detected. A hypothesis about the temporal and spatial evolution of the fatigue during the process is presented. The results, supporting the hypothesis, provide insight into wood behavior under mechanical pulping conditions.

The potential utility of high-intensity ultrasound to treat osteoarthritis.

Osteoarthritis (OA) is a widespread musculoskeletal disease that reduces quality of life and for which there is no cure. The treatment of OA is challenging since cartilage impedes the local and systemic delivery of therapeutic compounds (TCs). This review identifies high-intensity ultrasound (HIU) as a non-contact technique to modify articular cartilage and subchondral bone. HIU enables new approaches to overcome challenges associated with drug delivery to cartilage and new non-invasive approaches for the treatment of joint disease. Specifically, HIU has the potential to facilitate targeted drug delivery and release deep within cartilage, to repair soft tissue damage, and to physically alter tissue structures including cartilage and bone. The localized, non-invasive ultrasonic delivery of TCs to articular cartilage and subchondral bone appears to be a promising technique in the immediate future.

Crystallization and shear modulus of a forming biopolymer film determined by in situ x-ray diffraction and ultrasound reflection methods

The structure and the rigidity of a forming biopolymer film were determined using concurrent x-ray diffraction and ultrasonic reflection measurements. Film formation of a xylan solution (de-ionized water, 10g∕l xylan, 4g∕l glycerol) was studied during water evaporation at 24(±2)°C, 37(±5)%RH. X-ray diffraction (XRD) data showed the crystallization and ultrasonic data the increase of the shear modulus (G) during water evaporation. Xylan crystallized into small xylan dihydrate crystallites, the number of which increased as water evaporated. Crystallization began earlier than the increase in G during film formation. The increase in G also continued after the crystallites were fully formed, indicating still ongoing structural changes in the amorphous parts. The maximum value of G was 0.1–0.5GPa. XRD measurements performed ex situ showed a crystallinity of 16%–19% (±5%) and a fairly isotropic crystallite orientation in the surface plane of the films.

Significance of fatigue for mechanical defibration

The fatigue induced by high-frequency cyclic loading on the compressibility and tensile properties of wood and wood cell walls was quantified. The non-elastic behavior of fatigued and reference samples was similar, whereas their elastic behavior differed, as expected. Next, the effects of the dynamic fatigue on the mechanical pulping process were quantified by grinding fatigued and untreated samples and by comparing the paper strength produced by the two pulps against the consumed pulping energy. Pre-introducing fatigue increased the energy efficiency of grinding and may allow designing a more energy efficient mechanical pulping process.

Delivering Agents Locally into Articular Cartilage by Intense MHz Ultrasound

There is no cure for osteoarthritis. Current drug delivery relies on systemic delivery or injections into the joint. Because articular cartilage (AC) degeneration can be local and drug exposure outside the lesion can cause adverse effects, localized drug delivery could permit new drug treatment strategies. We investigated whether intense megahertz ultrasound (frequency: 1.138 MHz, peak positive pressure: 2.7 MPa, Ispta: 5 W/cm2, beam width: 5.7 mm at −6 dB, duty cycle: 5%, pulse repetition frequency: 285 Hz, mechanical index: 1.1) can deliver agents into AC without damaging it. Using ultrasound, we delivered a drug surrogate down to a depth corresponding to 53% depth of the AC thickness without causing histologically detectable damage to the AC. This may be important because early osteoarthritis typically exhibits histopathologic changes in the superficial AC. In conclusion, we identify intense megahertz ultrasound as a technique that potentially enables localized non-destructive delivery of osteoarthritis drugs or drug carriers into articular cartilage.

Ultrasonic transport of particles into articular cartilage and subchondral bone

Osteoarthritis (OA) is a debilitating musculoskeletal disease without a cure. Delivery of therapeutic compounds is a problem and localized drug therapy could enable new treatment strategies. In this study high-intensity ultrasound was used to deliver micro- and nano-particles (MNPS) into three bovine osteochondral samples: (1) control (C) that was exposed to the particles without sonication, (2) UST-1 that was sonicated prior to immersion in a MNPS and (3) UST-2 that was sonicated in the presence of MNPS. Following treatment samples were cut into 2.9 ± 0.3 mm sections and digital images were obtained by light microscopy. In the sonicated samples (UST-1 and UST-2) MNPS penetrated into articular cartilage and subchondral bone. No MNPS penetration was observed in C. The proposed technique could potentially be used for local drug treatment of OA.

Simultaneous X-ray diffraction and X-ray fluorescence microanalysis on secondary xylem of Norway spruce

Secondary xylem of Norway spruce was studied by X-ray microanalysis. Average dimensions of cellulose crystallites, fraction of oriented cellulose, mean microfibril angle, and nutrient element concentrations of K, Ca, Mn, and Zn were simultaneously determined using microfocused synchrotron radiation and a combination of X-ray diffraction and X-ray fluorescence spectroscopy techniques. The variation of these quantities in the microscopic size scale was noticeable, and similar between samples taken from the same annual ring. The mean microfibril angle and the nutrient concentrations of Ca, Mn, and Zn showed a correlation. The mean values of the structural parameters and their variation as a function of the annual ring were similar as reported in previous studies on Norway spruce.

Repetitive impact loading causes local plastic deformation in wood

The relationship between the impactor velocity and the amount of strain localization in a single impact compression of cellular solids is known. However, few studies report on the effects of repeated high frequency compression. We therefore studied the mechanical behavior of Norway spruce, a cellular viscoelastic material, before, during, and after cyclic high frequency, high strain rate, compression. A custom made device applied 5000-20 000 unipolar (constrained compression and free relaxation) fatigue cycles with a 0.75 mm peak-to-peak amplitude at 500 Hz frequency. The consequences of this treatment were quantified by pitch-catch ultrasonic measurements and by dynamic material testing using an encapsulated Split-Hopkinson device that incorporated a high-speed camera. The ultrasonic measurements quantified a stiffness modulus drop and revealed the presence of a fatigued low modulus layer near the impacting surface. Such a localized plastic deformation is not predicted by classical mechanics. We introduc...