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Non-Contact Resonant Ultrasound Spectroscopy (NC-RUS) has emerged as a powerful tool to determine plant water status in a non-destructive, non-invasive and rapid way. In this study, ultrasonic parameters directly obtained from experimental measurements in the field using NC-RUS - such as resonant frequency (fres), velocity (v) and Q-factor - were evaluated as potential water stress indicators in Citrus plants. The experiments were carried out in two-year-old mandarin trees (Citrus clementina Hort. ex Tan. ‘Clemenules’) grown in pots in an open greenhouse where two different groups of plants were tested: a Control group (full irrigation) and a Drought Stress group (DS) whose irrigation was withdrawn during 7 days, followed by a 16 days recovery period. Soil water content, leaf water potential (Ψleaf) and the considered ultrasonic parameters were measured in the same leaves. fres detected changes between control and DS at day 7 without irrigation. Conversely, v showed differences after day 3, which were statistically significant at day 7, enabling discrimination between C and DS groups. Hence, Q-factor was the ultrasonic parameter that showed statistically significant differences between C and DS groups at days 3 and 7. Consequently, Signal Intensity in Q during the drought treatment showed a similar evolution to Ψleaf, although with slightly lower performance. However, Q-factor sensitivity excels Ψleaf at each day studied. Finally, a linear correlation (R2=0.57) between Ψleaf and Q-factor of all experimental data measured in DS group plants along the drought treatment was found. In conclusion, the ultrasonic parameters obtained using NC-RUS and in particular the Q-factor, demonstrated to be potential new water stress indicators in Citrus trees, with the novelty of being non-destructive, non-invasive and rapid. Future work should explore its suitability for its use in irrigation scheduling for Citrus trees.

As a consequence of the large demand of face masks due to the COVID19 pandemic, cheap, fast and non-destructive tests that can verify in-line the variability of the filtration capacities, prove the potential disinfection and/or evaluate the performance of new filtering materials are needed. Using two different approaches based on air-coupled ultrasounds (0.15–1.6 MHz) with equivalent results, this work shows that each face mask presents a distinctive ultrasonic signature that enables the classification and the evaluation of their performance. Moreover, it is shown that the ultrasonic propagation through the face masks and the main filter layers takes place through the pore space and that low frequency response of the attenuation and the velocity is highly dispersive and is dominated by the interaction between the air in the pores and the fibers in the filters. Hence, the parameters that describe ultrasonic velocity, attenuation and dispersion can be related with their filtration efficiency and breathability. These techniques are fully contactless, non-invasive and fast., This work was supported by: Spanish Agency of Science Technology and Research grant RTC-2017-6314-2 (TGAA, AG). Spanish Ministry of Science grant FJCI-2017-34759 (MDF).

An airborne ultrasonic technique was tested for the determination of textural properties rapidly and contactless on pork burger patties under different compositions both at 5 °C and 20 °C. A high correlation between resonance frequency and firmness at 5 °C was observed (R=0.95), concluding that this technique shows a high potential for its use on meat industry.

The directional freezing of microfiber suspensions is used to assemble highly porous (porosities ranging between 92% and 98%) SiC networks. These networks exhibit a unique hierarchical architecture in which thin layers with honeycomb‐like structure and internal strut length in the order of 1–10 μm in size are aligned with an interlayer spacing ranging between 15 and 50 μm. The resulting structures exhibit strengths (up to 3 MPa) and stiffness (up to 0.3 GPa) that are higher than aerogels of similar density and comparable to other ceramic microlattices fabricated by vapor deposition. Furthermore, this wet processing technique allows the fabrication of large‐size samples that are stable at high temperature, with acoustic impedance that can be manipulated over one order of magnitude (0.03–0.3 MRayl), electrically conductive and with very low thermal conductivity. The approach can be extended to other ceramic materials and opens new opportunities for the fabrication of ultralight structures with unique mechanical and functional properties in practical dimensions.

Described here is the application of a technique based on the excitation, sensing and spectral analysis of thickness resonances of plant leaves using air-coupled and wide-band ultrasound pulses (150–900 kHz) to monitor variations in leaf properties caused by plant responses to different environmental stimuli, such as a sudden variation in light intensity (from 2000 to 150 μmol m −2 s −1 ), sudden watering after a drought period, and along the diurnal cycle (3–5 days, with continuous variation in light intensity from 150 to 2000 μmol m −2 s −1 and change in temperature of about 5°C). Four different widely available species, both monocots and dicots and evergreen and deciduous, with different leaf features (shape, size, thickness, flatness, vascular structure), were selected to test the technique. After a sudden decrease in light intensity, and depending on the species, there was a relative increase in the thickness resonant frequency from 8% to 12% over a 25- to 50-min period. After sudden watering, the relative increase in the resonant frequency varied from 5% to 30% and the period from 10 to 400 min. Finally, along the diurnal cycle, the measured relative variation is between 4% and 10%. The technique revealed differences in both the amplitude of the frequency oscillations and the kinetics of the leaf response for different species and also within the same species, but for specimens grown under different conditions that present different cell structures at the tissue level. The technique can be equally applied to the leaves of any species that present thickness resonances.

The turgor loss point (TLP), which is considered a threshold for many physiological processes, may be useful in plant-breeding programs or for the selection of reforestation species. Obtaining TLP through the standard pressure–volume (p–v) curve method in a large set of species is highly time-consuming and somewhat subjective. To solve this problem, we present an objective and a less time-consuming technique based on the leaf resonance able to calculate the relative water content (RWC) at TLP (RWCTLP). This method uses air-coupled broadband ultrasonic spectroscopy to obtain the sigmoidal relation between RWC and the standardized resonant frequency (f/fo). For the 13 species measured, the inflexion point of the RWC– f/fo relationship (RWCTLP o ff / ) was not statistically different from the value of RWC at the TLP obtained with the p–v curves (RWCTLP p–v).

The main objective of this study was to apply the air-coupled broad-band ultrasonic spectroscopy in attached transpiring leaves of Vitis vinifera L. to monitor changes in leaf water potential (Ψ) through the measurements of the standardized value of the resonant frequency associated with the maximum transmitance (f/fo). With this purpose, the response of grapevine to a drought stress period was investigated in terms of leaf water status, ultrasounds, gas exchange and sugar accumulation. Two strong correlations were obtained between f/fo and Ψ measured at predawn (pd) and at midday (md) with different slopes. This fact implied the existence of two values of Ψ for a given value of f/fo, which was taken as a sign that the ultrasonic technique was not directly related to the overall Ψ, but only to one of its components: the turgor pressure (P). The difference in Ψ at constant f/fo (δ) was found to be dependent on net CO2 assimilation (A) and might be used as a rough estimator of photosynthetic activity. It was then, the other main component of Ψ, osmotic potential (π), the one that may have lowered the values of md Ψ with respect to pd Ψ by the accumulation of sugars associated to net CO2 assimilation. This phenomenon suggests the existence of a diurnal osmotic adjustment in this species associated to sugars production in well-watered plants., This study was supported by the Spanish Ministry of Economy and Competitiveness (IPT-2012-1022-310000) and by Gobierno de Aragón (research group H38). Work of DS-K is supported by a DOC INIA contract co-funded by INIA and ESF.

The potential of additive manufacturing (AM) to revolutionize aspects of industrial production is widely recognized. AM can create objects with non-uniform properties by varying the ratio between deposited materials or altering the internal structure of the object. Amongst many possibilities, such AM objects could benefit the design and fabrication of different passive components of ultrasonic transducers, e.g. backing material, lenses and matching layers. The acoustic properties of AM objects produced using the Polyjet and Fused Deposition Methods were characterized. Initial results suggest that these technologies can easily produce objects with a wide range of tuned acoustic properties by varying either the internal structure or the material composition.

Different tissues in Phormium tenax leaves present different morphologies and mechanical properties according to the different roles or functions that they play during the plant life. This is an example of what is known as functional design, a concept which is used in different scientific fields. Four different ultrasonic techniques comprising air-coupling and gel coupling, longitudinal and shear waves, normal and oblique incidence and low (0.2 MHz) and high frequencies (2.25 MHz) have been employed to study these leaves. By changing these experimental conditions it is possible to propagate longitudinal and shear waves in the different tissues present in these leaves (spongy mesophyll, chlorenchyma and sclerenchyma fibres) and in different directions so it is possible to determine their ultrasonic properties (velocity and attenuation) and hence their main elastic mudulii. Additional analysis of microscopic images of the tissues permit to study the correlation between this elastic and ultrasonic tissues properties and main microscopic features like cell size and cell wall thickness, which are determined by the different function of these tissues.

Particle loaded polymers and elastomers have been largely used in different ultrasonic applications like backing materials and matching layers because composite properties (velocity, attenuation, density and impedance) can be easily engineered by changing the filler concentration. Recently, the use of magnetic particles has been theoretically proposed as a means to produce active matching layers whose response can be modified upon the application of magnetic fields. In this paper, we propose to introduce modifications of the composite properties by using magnetic particles and applying magnetic fields during curing to establish well defined patterns in the spatial distribution of the particles within the elastomer that induce material anisotropy that effectively modify ultrasonic properties.

The possibility to inspect laminates of prepreg carbon fiber reinforced polymer (CFRP) laminates during lay-up fabrication is studied. First ultrasonic properties of the uncured material are determined, this information is used to design an inspection system that is tested during the fabrication of laminates with up to 30 layers, following different compaction schemes and including some Teflon insertions to simulate the presence of delaminations. The paper shows that for the chosen selection of parameters (transducers sensitivity, centre frequency and mold configuration), the inspection is possible, opening a new field of application of air-coupled ultrasonic techniques.

The large water requirements of Vitis vinifera L. together with an increase in temperature and drought events imply the need for irrigation in the driest areas of its distribution range. Generous watering may reduce grape quality so irrigation should be precisely regulated through the development of new methods of accurate irrigation scheduling based on plant 'stress sensing'. Two new methods, the reflectivity in the S-band and the broadband ultrasonic spectroscopy, can be used as non-invasive and reproducible techniques for the study of plant water relations in V. vinifera. On one hand, the measurement of reflectance at frequencies around 2.4 GHz gives an excellent accuracy when the changes in the existing area (S) between two reflectance curves are correlated with the relative water content (RWC). On the other hand, an improvement of the broadband ultrasonic spectroscopy based on the enlargement of the analysis frequency window provides, apart from the determination of the turgor loss point (TLP), additional information about the leaves without additional computational cost or additional leaf information requirements. Before TLP, the frequency associated with the maximum transmittance (f/f(o)), the macroscopic elastic constant of the leaf in the Z direction (c(33)) and, specially, the variation of the attenuation coefficient with the frequency (n), were highly correlated with changes in RWC. Once turgor is lost, a shift in the parameters directly related to the attenuation of the signal was also observed. The use of both techniques allows for a more convincing knowledge of the water status in V. vinifera.

Propagation of Lamb waves, generated and detected using air-coupled piezoelectric transducers (0.1-1.0 MHz), is visualized. Hence phase and group velocities are obtained. The technique is first tested on plates (aluminum and carbon fiber reinforced polymers-CFRP-plates). Then it has been applied to un-cured CFRPs plates and curved surfaces: steel pipes and vessels and to the curved section of CFRP beams. Two different experimental set-ups are proposed: 1) use of monolithic transducers and mechanical scans along the direction of propagation, 2) use of a phased array linear transducer and an electronic scan along the direction of propagation.

Shear waves are investigated in leaves of two plant species using air-coupled ultrasound. Magnitude and phase spectra of the transmission coefficient around the first two orders of the thickness resonances (normal and oblique incidence) have been measured. A bilayer acoustic model for plant leaves (comprising the palisade parenchyma and the spongy mesophyll) is proposed to extract, from measured spectra, properties of these tissues like: velocity and attenuation of longitudinal and shear waves and hence Young modulus, rigidity modulus, and Poisson's ratio. Elastic moduli values are typical of cellular solids and both, shear and longitudinal waves exhibit classical viscoelastic losses. Influence of leaf water content is also analyzed.