Contribution of the shear wave ultrasonic reflectometry to the stickiness measurements.

Today, non-invasive quantification of the adhesion of a deposit to a surface is always a challenge and, unfortunately, few tools are available in this area. This is an obstacle, in several industrial processes, to the identification of conditions limiting the fouling and to the establishment of eco-efficient cleaning strategies. In this paper, a non-invasive ultrasonic technique was developed in the aim of characterizing the adhesion of viscoelastic fluids or solid deposited on a substrate. We adopted the idea that the more a deposit is difficult to clean the more adherent it is. From this point of view the value of the reflection coefficient of an ultrasonic shear wave informs us about the adhesion of the deposit on a surface. A large bibliography on the adhesion measurement is given. Then the principle of ultrasonic test is presented and cares required for the measurement of the reflection coefficient are widely discussed. The ultrasonic reflection coefficients obtained with different controlled samples covering a wide range of interfaces (liquid/substrate, solid/substrate) are presented and compared with other indicators of adhesion. All the data on various samples showed that the ultrasonic test is a tool to discriminate non-destructively a large range of interface quality, allowing ranking according to the adhesive strength.

Inline high frequency ultrasonic particle sizer.

This paper reports the development of a new method of particle sizing in a liquid. This method uses high frequency focused ultrasounds to detect particles crossing the focal zone of an ultrasonic sensor and to determine their size distribution by processing the reflected echoes. The major advantage of this technique compared to optical sizing methods is its ability to measure the size of particles suspended in an opaque liquid without any dedicated sample preparation. Validations of ultrasonic measurements were achieved on suspensions of polymethyl methacrylate beads in a size range extending from a few micrometer to several hundred micrometer with a temporal resolution of 1 s. The inline detection of aggregate formation was also demonstrated.

Ultrasonic measurement of bulk and shear moduli variations in porous alumina media.

In this paper we studied some acoustical parameters of a porous medium based on the Biot's theory. The basic idea was to find, using an inversion method, variations in the bulk modulus K(b) and the shear modulus G(b) in the frequency domain. This was achieved by comparing the theoretical and experimental results obtained on a selection of porous alumina samples with different physical characteristics. Then, using the transmission coefficient, a numerical process was applied to a virtual porous alumina medium in order to find K(b) and G(b) values at low frequency under static conditions. Using a frequency range of 50kHz to 600kHz, fast and slow waves were considered and both were included in the transmission coefficient.

Numerical and experimental investigation of kerf depth effect on high-frequency phased array transducer.

BACKGROUND: High-frequency ultrasonic transducer arrays are essential for high resolution imaging in clinical analysis and Non-Destructive Evaluation (NDE). However, the structure design and fabrication of the kerfed ultrasonic array is quite challenging when very high frequency (≥100MHz) is required. OBJECTIVE AND METHOD: Here we investigate the effect of kerf depth on the performances of array transducers. A finite element tool, COMSOL, is employed to simulate the properties of acoustic field and to calculate the electrical properties of the arrays, including crosstalk effect and electrical impedance. Furthermore, Inductively Coupled Plasma (ICP) deep etching process is used to etch 36°/Y-cut lithium niobate (LiNbO(3)) crystals and the limitation of etching aspect ratio is studied. Several arrays with different profiles are realized under optimized processes. At last, arrays with a pitch of 25µm and 40µm are fabricated and characterized by a network analyzer. RESULTS: Kerf depth plays an important role in the performance of the transducer array. The crosstalk is proportional to kerf depth. When kerf depth is more than 13µm, the array with crosstalk less than -20dB, which is acceptable for the real application, could provide a desired resolution. Compared to beam focusing, kerf depth exhibits more effect on the beam steering/focusing. The lateral pressure distribution is quantitatively summarized for four types of arrays with different kerf depth. The results of half-cut array are similar to those of the full-cut one in both cases of focusing and steering/focusing. The Full-Width-at-Half-Maximum (FWHM) is 55µm for the half-cut array, and is 42µm for the full-cut one. The 5-µm-cut array, suffering from severe undesired lobes, demonstrates similar behaviors with the no-cut one. ICP process is used to etch the 36°/Y-cut LiNbO(3) film. The aspect ratio of etching profile increases with the kerf width decreasing till it stops by forming a V-shaped groove, and the positive tapered profile angle ranges between 62° and 80°. If the mask selectivity does not limit the process in terms of achievable depth, the aspect ratio is limited to values around 1.3. The measurement shows the electrical impedance and crosstalk are consistent with the numerical calculation. CONCLUSION: The numerical results indicate that half-cut array is a promising alternative for the fabrication of high-frequency ultrasonic linear arrays. In fact, the minimum pitch that could be obtained is around 25µm, equivalent to a pitch of 1.6λ, with a kerf depth of 16µm under the optimized ICP parameters.

Modelling and simulation of high-frequency (100 MHz) ultrasonic linear arrays based on single crystal LiNbO3.

BACKGROUND: High-frequency ultrasonic transducer arrays are essential for high resolution imaging in clinical analysis and Non-Destructive Evaluation (NDE). However, the fabrication of conventional backing-layer structure, which requires a pitch (distance between the centers of two adjacent elements) of half wavelength in medium, is really a great challenge. OBJECTIVE AND METHOD: Here we present an alternative buffer-layer structure with a silicon lens for volumetric imaging. The requirement for the size of the pitch is less critical for this structure, making it possible to fabricate high-frequency (100MHz) ultrasonic linear array transducers. Using silicon substrate also makes it possible to integrate the arrays with IC (Integrated Circuit). To compare with the conventional backing-layer structure, a finite element tool, COMSOL, is employed to investigate the performances of acoustic beam focusing, the influence of pitch size for the buffer-layer configuration, and to calculate the electrical properties of the arrays, including crosstalk effect and electrical impedance. RESULTS: For a 100MHz 10-element array of buffer-layer structure, the ultrasound beam in azimuth plane in water could be electronically focused to obtain a spatial resolution (a half-amplitude width) of 86µm at the focal depth. When decreasing from half wavelength in silicon (42µm) to half wavelength in water (7.5µm), the pitch sizes weakly affect the focal resolution. The lateral spatial resolution is increased by 4.65% when the pitch size decreases from 42µm to 7.5µm. The crosstalk between adjacent elements at the central frequency is, respectively, -95dB, -39.4dB, and -60.5dB for the 10-element buffer, 49-element buffer and 49-element backing arrays. Additionally, the electrical impedance magnitudes for each structure are, respectively, 4kΩ, 26.4kΩ, and 24.2kΩ, which is consistent with calculation results using Krimholtz, Leedom, and Matthaei (KLM) model. CONCLUSION: These results show that the buffer-layer configuration is a promising alternative for the fabrication of high-frequency ultrasonic linear arrays dedicated to volumetric imaging.

Design of low-frequency ultrasonic sensors for the analysis of the draining stage of cheese production.

This work presents a new ultrasonic system with a transmission mode in the 100-200 kHz frequency range. The system, composed of ultrasonic point sources, is used to monitor the mechanical properties of cheese during the early phases of production. First, our specialized sensor system is presented, and then the results obtained with the system model are compared to the results of actual experiments using the system to monitor the evolution of the medium during draining. The results of a rheological compliance test and shock pulse ultrasonic amplitude measurements agree and correspond quite accurately to the mechanical properties of the evolving physical state of the medium. This method could be used in the future to study the effect on the final cheese quality of the process parameters that interfere with cheese grain consolidation during the draining process.

Optimizaition of a low-frequency ultrasonic technique to monitor the change in physical states in viscoelastic media: gelation process

A new low-frequency ultrasonic device (50-100 kHz) in highly sharpened end sensors that behave as point sources were examined. The application of this new ultrasonic technique with two sensors coupled in the near field is to explore the relations between the physical properties measured through the evolution of the wave time of flight and structural changes during gel formation which is related to two factors: the ambient temperature and the mechanical resistance of the medium. The network evolution was interpreted by an approach based on the Flory model. The physical significance of this model was shown through a series of experiments using a low-frequency ultrasonic technique. Response curves demonstrate the different stages during gel formation.

Acoustic measurement of compressibility and thermal expansion coefficient of erythrocytes.

Mechanical properties of human erythrocytes, namely adiabatic compressibility and thermal expansion coefficient, have been determined using a classical ultrasound velocity and attenuation burst transmission technique. The theoretical model concerns the corpuscular part of the elastic wave propagating in a suspension of viscous particles of small size compared with the wavelength. The thermal wave contribution was taken into account. Normal and stiffened red blood cells were suspended in saline of different NaCl concentration.