Air‐coupled Ultrasonic Transducers

Álvarez-Arenas, Tomás Gómez

doi:10.1002/9781118964156.ch7

Cited by 10 publications

(5 citation statements)

References 134 publications

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“…In particular, requirements for air-coupled ultrasonic transducers for NC-RUS measurements in Coffea arabica and Vitis vinifera leaves have been determined. Following these design criteria, transducers were produced using 1–3 connectivity piezocomposites and matching to the air as described in [ 41 , 42 ]. For Coffea arabica leaves, centre frequency of the transducers is located at 350 kHz with a peak sensitivity of −26 dB and the operation bandwidth covers the frequency range 200–450 kHz, which corresponds to the frequency band 20 dB below the main peak.…”

Section: Discussionmentioning

confidence: 99%

“…Impedance matching to the air follows the basic criteria and materials proposed in references [ 41 , 42 ] where the acoustic impedance of the outer matching layer is always about 0.04 MRayl. A backing block is added to improve the transducers frequency band.…”

Section: Proposed Nc-rus System For Plant Leaves: General Solutionmentioning

confidence: 99%

“…To meet the specifications in Table 2 , 15 mm diameter piezocomposite disks with resonant frequency at 650 kHz , were used to make the transducers. Matching to the air is achieved by following the method of [ 41 , 42 ]. Transmitter transducer was driven by a Olympus 5077 pulser (amplitude 400 V) and the receiver transducer was connected to the receiver stage of the Olympus 5077 (gain 40 dB).…”

Section: Specifications Of the Nc-rus System For Coffea mentioning

confidence: 99%

“…The proposed solution to meet specifications in Table 2 is based on a 1–3 connectivity piezocomposite disk with thickness resonant frequency at 350 kHz and diameter 20 mm; matching to the air is performed by following the method proposed in reference [ 41 , 42 ]. Figure 10 shows the measured signal in the receiver transducer when the transmitter transducer is excited with the Olympus 5077 Pulser/receiver (100 V amplitude) and the receiver is connected directly to an oscilloscope (Tektronix 7054 DPO), separation was 13 mm.…”

Section: Specifications Of the Nc-rus System For Coffea mentioning

confidence: 99%

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Ultrasonic Sensing of Plant Water Needs for Agriculture

Álvarez-Arenas

Gil‐Pelegrín

Ealo

et al. 2016

Sensors

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Fresh water is a key natural resource for food production, sanitation and industrial uses and has a high environmental value. The largest water use worldwide (~70%) corresponds to irrigation in agriculture, where use of water is becoming essential to maintain productivity. Efficient irrigation control largely depends on having access to reliable information about the actual plant water needs. Therefore, fast, portable and non-invasive sensing techniques able to measure water requirements directly on the plant are essential to face the huge challenge posed by the extensive water use in agriculture, the increasing water shortage and the impact of climate change. Non-contact resonant ultrasonic spectroscopy (NC-RUS) in the frequency range 0.1–1.2 MHz has revealed as an efficient and powerful non-destructive, non-invasive and in vivo sensing technique for leaves of different plant species. In particular, NC-RUS allows determining surface mass, thickness and elastic modulus of the leaves. Hence, valuable information can be obtained about water content and turgor pressure. This work analyzes and reviews the main requirements for sensors, electronics, signal processing and data analysis in order to develop a fast, portable, robust and non-invasive NC-RUS system to monitor variations in leaves water content or turgor pressure. A sensing prototype is proposed, described and, as application example, used to study two different species: Vitis vinifera and Coffea arabica, whose leaves present thickness resonances in two different frequency bands (400–900 kHz and 200–400 kHz, respectively), These species are representative of two different climates and are related to two high-added value agricultural products where efficient irrigation management can be critical. Moreover, the technique can also be applied to other species and similar results can be obtained.

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Section: Discussionmentioning

confidence: 99%

Section: Proposed Nc-rus System For Plant Leaves: General Solutionmentioning

confidence: 99%

Section: Specifications Of the Nc-rus System For Coffea mentioning

confidence: 99%

Section: Specifications Of the Nc-rus System For Coffea mentioning

confidence: 99%

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Ultrasonic Sensing of Plant Water Needs for Agriculture

Álvarez-Arenas

Gil‐Pelegrín

Ealo

et al. 2016

Sensors

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“…Despite all these problems, and because of the continuous improvement in air-coupled transducers [4], electronics, signal-processing-like coded excitation [5,6], and inspection techniques, there are good records of successful applications in different fields and by different groups [7].…”

Section: Introductionmentioning

confidence: 99%

Air-Coupled and Resonant Pulse-Echo Ultrasonic Technique

Álvarez-Arenas

Camacho

2019

Sensors

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An ultrasonic, resonant, pulse-echo, and air-coupled nondestructive testing (NDT) technique is presented. It is intended for components, with regular geometries where it is possible to excite resonant modes, made of materials that have a high acoustic impedance (Z) and low attenuation coefficient (α). Under these conditions, these resonances will present a very large quality factor (Q) and decay time (τ). This feature is used to avoid the dead zone, produced by the echo coming from the first wall, by receiving the resonant echo from the whole specimen over a longer period of time. This echo is analyzed in the frequency domain to determine specimen resonant frequency, which can be further used to determine either velocity or thickness. Using wideband air-coupled transducers, we tested the technique on plates (steel, aluminum, and silicone rubber) by exciting the mode of the first thickness. As expected, the higher the Z and the lower the α, the better the technique performed. Sensitivity to deviations of the angle of incidence away from normal (±2°) and the possibility to generate shear waves were also studied. Then, it was tested on steel cylindrical pipes that had different wall thicknesses and diameters. Finally, the use of this technique to generate C-Scan images of steel plates with different thicknesses was demonstrated.

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Relating the ultrasonic and aerosol filtration properties of filters

Alvarez-Arenas,

Sipkens,

Corbin

et al. 2024

Sci Rep

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Non-contact methods are useful to improve the quality control of particle filtration media. The purpose of this paper is to investigate the correlation between the filtration efficiency of a porous sheet and its ultrasonic properties obtained using a non-contact technique. An air-coupled ultrasonic technique is used to obtain rapid measurements without affecting the integrity of the material. High frequencies (from 0.1 to 2.5 MHz) are used to improve technique sensitivity, and transmitted waves are measured to probe the internal properties of the material. Measurements of transmission coefficient spectra (amplitude and phase) and the corresponding ultrasound velocity and attenuation coefficient at different frequencies are obtained for a set of filtration media with well-characterized properties. Results show that the ultrasonic properties of filtration media vary as a function of basis weight, and therefore filtration efficiency, for a given charge state. However, the effect of electrostatic charge on ultrasonic propagation is almost negligible, as expected. We conclude that ultrasonic transmission may provide a valuable tool for the continuous online monitoring of material quality during fabrication and as a method to tease apart mechanical and electrostatic contributions to particle filtration.

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Air‐coupled Ultrasonic Transducers

Cited by 10 publications

References 134 publications

Ultrasonic Sensing of Plant Water Needs for Agriculture

Ultrasonic Sensing of Plant Water Needs for Agriculture

Air-Coupled and Resonant Pulse-Echo Ultrasonic Technique

Relating the ultrasonic and aerosol filtration properties of filters

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