Acoustic Waves From Microdevices to Helioseismology Part 7 ppsx

Acoustic Waves – From Microdevices to Helioseismology 228 Fig. 15. Set-up of the sensor proposed Flexion modes (s, n) Theoretical (Hz) FEM (Hz) (1.0) 1798 1794 Table 3. Illustration of the deformations. Amplitude perpendicular to the disc plane Flexion mode (1.0) for a frequency of 1.8 kHz (theoretical and using finite elements) Radial modes Analytical calculation (kHz) FEM (kHz) 35.5 35.5 92.6 92.7 Table 4. The resonance frequencies of the first two radial modes for a free aluminium disc (R=5cm; h=2mm) obtained analytically and numerically using finite elements Low Frequency Acoustic Devices for Viscoelastic Complex Media Characterization 229 Radial modes Frequency (kHz) 1 35.9 2 90 Flexion modes (1.0) 1.6 (2.0) 6.5 Table 5. Resonance frequencies of the first radial and flexion modes for the composite sensor 3.5.2 Application for monitoring fermenting bread dough The objective of this application was to establish the links between the product evolution kinetics and the acoustic characteristics measured. From a practical point of view, impulse excitation was used in this system. The excitation was obtained by a controlled mechanical impact (rod of an electromagnet), thus exciting the disc used for the synchronisation. The vibration induced in the dough is received by a receiver disc identical to that of the synchronisation disc (Figure 16). Fig. 16. Experimental measuring device A metrological study of the measuring device carried out using standard samples (for example a pocket of water at 25°C) showed that the standard deviation of the amplitude and the velocity was approximately 2%. Signal acquisition was carried out over 3 hrs. 3.5.3 Dynamic monitoring of the fermentation process of bread dough After controlled kneading of the dough, the measurement chamber was placed in an enclosure in order to control the temperature and humidity. The acoustic values studied were the variation of the time-of-flight and the wave amplitude on reception. Acoustic Waves – From Microdevices to Helioseismology 230 Figure 17 shows the variations in these two values. It can be noted that the critical points and phases appear simultaneously on the two curves. Fig. 17. Evolution of the standardised amplitude and the relative signal delay on reception during the fermentation phase Where: • τ r is the time necessary to reach a relatively stable zone, • T r reflects the period of stability during which the relative delay reaches its maximum and remains relatively constant, • Δt M is the maximum relative delay. It is linked to the gas fraction contained in the dough and therefore the extensibility of the latter. • τ a is the period during which the amplitude of the signal decreases before reaching a plateau, • T a is the period of stability of the amplitude, • A S is defined as being the amplitude of the signal during the period of stability. Low Frequency Acoustic Devices for Viscoelastic Complex Media Characterization 231 A repeatability study was carried out to estimate the dispersion of the parameters (delay and amplitude). Several tests were performed under the same operating conditions. The standard deviation of the measurements of these parameters was around 3%. Table 6 summarises the variations in the characteristic parameters observed on the curves according to the evolution in the temperature 20° 27° 34° τ r (min) 165 105 60 T r (min) 145 70 55 Δt M (µs) 380 385 374 τ a (min) 160 95 55 T a (min) 130 75 50 A S (%) 40 43 44 Table 6. Parameters relating to the variation in temperature It can be noted that the maximum relative delay is relatively constant (approximately 380µs) for the three products made under the same operating conditions. This parameter seems to be independent of the temperature, which is in agreement with the hypothesis that it varies according to the gas fraction contained in the matter and the elastic properties of the matrix. 4. Acoustic sensor for in-line monitoring of a manufacturing process In certain industrial processes it is often difficult to access useful information in real-time due to the conditions imposed on the mechanical and thermal parameters, pressure, hygiene , conditions which require a specific installation of the sensor with regard to its environment. The difficulty thus arises of an integration taking into account both the process constraints and the acoustic constraints. This is the case of a plate heat exchanger which can be considered as a typical example in this category (Figure 18). Fig. 18. Standard plate heat exchanger 4.1 Sensor selection criteria For the exchanger, the sensor selected is not cumbersome and is sensitive over a temperature range reaching over 100°C (Figure 19). The excitation and synchronisation Acoustic Waves – From Microdevices to Helioseismology 232 modes remain the same as the previous case (disc sensor). The principle of the measurement is to excite a vibration mode in one or several plate exchangers and to analyse the evolution under the effect of fouling by measuring the response of the plates using a receiver. A bivariate system-sensor study enabled the geometry of the latter to be defined over the same vibration frequency range as the system (exchanger). Sensor Exchanger plate Electromagnet soliciting a reference sensor Receiver Fig. 19. Positioning of the sensors on an exchanger plate 4.1.1 Sensor excitation mode In order to monitor the evolution of the damping of the plate modes due to fouling of the exchanger, it is necessary to excite these modes with enough energy to preserve the signal- noise ratio (of the signal received) after going through the exchanger. A mechanical shock is the only way of producing enough energy for local excitation. The frequency response obtained by modal analysis in the absence of structural constraints is given in the first column in table 7. This column gathers the different modes specific to the structure studied. Some correspond to simple, longitudinal or transversal displacements, others to more complex displacements (flexions, torsions ). Mode Frequency (Hz) - numerical Frequency (Hz) - experimental 1 1683 1586 2 2387 2894 3 3557 3639 4 5422 5330 5 5734 6639 6 7417 7390 Table 7. The first 6 modes specific to the sensor Low Frequency Acoustic Devices for Viscoelastic Complex Media Characterization 233 The second column shows the modal frequencies obtained from the analysis of the impedance of the sensor mounted on a heat exchanger. The mean standard deviation between the frequencies obtained by modal analysis and those obtained experimentally is 5 %. The good correlation between these results indicates that the numerical modelling provides a good estimation of the resonance frequencies of the sensor. 4.1.2 Excitation by mechanical shock: estimation of the frequency range The mechanical excitation in question is ensured via the core of an electromagnet. As an indication, figures 20a and 20b show the temporal and frequency responses of the sensor. Fig. 20a. Temporal response of a mechanical shock Fig. 20b. Spectral response associated with the shock Acoustic Waves – From Microdevices to Helioseismology 234 The curves show the temporal response and the frequency range of the sensor following a stress induced by a mechanical shock of short duration. The experiments carried out on the overall system (sensor & exchanger) in real configuration show that the temporal response is maximum 4 ms and its frequency response is around a central frequency of approximately 4 kHz. 4.2 Application 4.2.1 Fouling mechanism Heat exchanger fouling is a dynamic process. The phenomenon continues to evolve, generally until equilibrium is reached or cleaning is required. The period of fouling can vary from a few hours to several months. Müller (Müller-Steinhagen & Middis, 1989) looked at five stages in the process of the appearance and development of particulate fouling: • The initiation, which corresponds to the time necessary before fouling, can be observed on a clean surface. The duration depends on the nature of the deposit, the initial state of the surface (material, roughness) and the temperature of the wall. • The denaturing of the product (protein, organic matter ) under the effect of heat and the surrounding parameters (pH ), their aggregation and transport within the vicinity of the wall. • The adhesion of the particles transported to the wall, controlled by surface adhesion forces (Van der Waals, electrostatic ) and cohesion of the deposit. It has been shown that the particles can adhere to a clean surface or adhere to other particles already deposited. • The dislodging of deposited particles, caused by hydrodynamic forces which exert shear stress on the deposit. • The aging of the deposit over time results in changes in its structure which can either weaken or consolidate it. Generally, the initiation phase is rarely taken into account in particulate fouling models. The mechanisms that govern the deposit of particles are generally presented as being the transport of the particles to the surface, then the "adhesion" to the wall and finally the possible dislodging of the particles. 4.2.2 Results Before studying the phenomenon of fouling, the metrological variation of the measurement system was taken into account according to the main technological parameters: • Variation in temperature at constant flow. • Variation in flow at constant temperature. • Variation in viscosity at constant temperature and flow. This phase is essential in order to separate the interferences of acoustic values generated by the fouling phenomenon from those linked to the technological conditions of the exchanger and its environment. The curves in figure 21 show the evolution of the energy of the acoustic signals as well as the pressure drop in the system as a function of the process time. The "Power" curve shows the damping effect linked to the load on the plate caused by fouling. Low Frequency Acoustic Devices for Viscoelastic Complex Media Characterization 235 Fig. 21. Evolution of the power of the acoustic signal received during the fouling test and cleaning In conclusion, this work concerned the monitoring of fouling using acoustics. By adopting a multi-stage experimental protocol we have been able to show that the variation in the acoustic signal can be used to predict variations in the pressure drop as well as the state of fouling in the plate heat exchanger under very specific operating conditions. Finally, this study illustrates an example of a non-intrusive acoustic technique for the local monitoring in real time of the fouling of plate heat exchangers. The results show that it is possible to follow the relative kinetics of the state of fouling in each zone of the exchanger with the right choice and positioning of the sensors. 5. Conclusion This chapter has proposed a synopsis of all the work that has led to the development of novel low frequency sensors. By using structural resonance modes excited by a transducer, these sensors present the advantage of having small sized sources with regard to the acoustic wavelength generated. These sensors are omni-directional but can nevertheless present significant contact areas with the medium to be characterised. This is the case for sensors developed for the characterisation of gels. The close contact of the elements set in resonance with the medium enables phenomena linked to changes in state to be monitored easily. Various applications have led us to develop sensors with very different geometries and which are optimised with the application in mind. Indeed, for each need expressed, the approach consisted in optimising not only the geometry of the sensors but also their optimum position according to the problem posed. Three different cases were thus studied: • identical near-field coupled sensors, through the medium to be characterised. They were used for monitoring the evolution of the ultrasonic values to characterise a sol-gel transition or the cohesion kinetics of a medium. For certain applications, the sensors are immersed in the medium. This direct immersion is essential for characterising fragile media. Acoustic Waves – From Microdevices to Helioseismology 236 • a low frequency receiver associated with an excitation of the medium via a mechanical shock in the case of very absorbent and scattering media. A second identical sensor is used for the synchronisation of the acquisitions thus reducing, by standardisation, the scattering of the values measured. The mechanical shock produces significant vibratory energy over a broad frequency range. • finally, the sensors were coupled to heat exchanger plates in order to characterise fouling. This work has shown the interest of using acoustic sensors to monitor processes, providing an often local and dynamic response to the evolution of the performances of the process. The work carried out provides a solid base of knowledge on ultrasound-complex media interactions. This knowledge could be put to good use in the development of sensors and integrated ultrasonic methods and their applications in the analysis and monitoring of local properties. 6. References Aggarwal R. R., (1952a). Axially Symmetric Vibrations of a Finite Isotropic Disk. I, Journal of acoustical society of America, Vol. 24, N0. 5, pp. 463-467 Aggarwal R. R., (1952b). Axially Symmetric Vibrations of a Finite Isotropic Disk. II, Journal of acoustical society of America, Vol. 24, N°. 6, pp. 663-666 Allsopp, M. W. (1981). The developement and importance of suspension PVC morphology, Pure an applied chemistry, Vol. 53, pp. 449-465. Blevins R. D., (1979). Formulas for natural frequency and mode shape, Van Nostrand Reinhold Co., ISBN 0-4422-0710-7, New York, USA Brekhovskikh, L.M., (1980). Waves in layered media, Academic Press, ISBN 0-12-130560-0, New York, USA Case, L. C. (1960). Molecular distributions in polycondensations involving unlike reactants. VII. Treatment of reactants involving nonindependent groups, Journal of polymer science, Vol. 48, pp. 27-35 Clerc, J. P. ; Giraud, G. ; Roussenq, J. ; Blanc, R. ; Carton, J.P. ; Guyon, E. ; Ottavi, H. & Stauffer, D. (1983). La Percolation: modèles, simulation analogiques et numériques, Annales de Physique, Vol. 8, Masson, Paris, France. Dalgleish, D. G. (1982). Developments in Dairy Chemistry, edited by P. F. Fox (Applied Science, London,), Vol. 1, Chap. 5, ISBN 0-8533-4142-7, London, United kingdom Dalgleish, D.G. (1993). Cheese: Chemistry, Physics and Microbiology, General Aspect, 2nd ed., Vol. 1, p. 69, Fox, P.F., Chapman & Hall, ISBN 0-1226-3652-X, London, United kingdom. De Gennes, P. G. (1989). Scaling Concepts in Polymer Physics, Cornell University Press, Ithaca, ISBN 0-8014-1203-X, New York, USA Degertekin, F. L. & Khury-Yakub, B.T. (1996). Hertzian contact transducers for non- destructive evaluation, Journal of acoustical society of America, Vol. 99, pp. 299-308 Degertekin, F. L. & Khury-Yakub, B.T. (1996). Lamb wave excitation by Hertzian contacts with applications in NDE. IEEE Transactions on Ultrasonics Ferroelectrics and Frequency, Vol. 44, N°. 4, pp. 769-778 Degertekin, F. L. & Khury-Yakub, B.T. (1996). Single mode lamb wave excitation in thin plates by Hertzian contacts, Applied physics letters, Vol. 69, N°. 2, pp. 146-148 [...]... horn, Journal of acoustical society of America, Vol 102, pp.1388-1393 Stauffer, D (1981) Can percolation theory be applied to critical phenomena at gel point?, Pure an applied chemistry, Vol 53, pp 1 479 -14 87 Stauffer, D (1985) Introduction to Percolation Theory, Taylor & Francis Ltd., ISBN 0 -74 840253-5, London, United Kingdom 238 Acoustic Waves – From Microdevices to Helioseismology Stockmayer, W H (1943)... Valenciennes University-France Nikolovski, J P & Royer, D (19 97) Local and selective detection of acoustic waves at the surface of a material”, IEEE Ultrasonics Symposium, pp 699 -70 3, ISBN 0 -78 03-41538, Toronto, Ontario, Canada, October 5-8, 19 97 Noël, Y ; Flaud, P & Quemada, D (1989) Traitement Industriel des Fluides Alimentaires Non Newtoniens, Tome II, Actes du 2ème Colloque la Baule, La Baule, France,... frequencies different from the reference are rejected The fundamentals of this technique and its measuring potential are described in section 2 In section 3, the authors’ own experiments aimed at determining the effect various factors on the electrical function of the Corti organ are described The factors include: vibration 260 Acoustic Waves – From Microdevices to Helioseismology (3.3), ototoxic medicines... powerful tool for quantitative characterization of interfacial biological interfacial processes 6 Acknowledgments We are thankful to Dr Moses Noh for providing supplies and micro-fabrication facilities for polymer coating 254 Acoustic Waves – From Microdevices to Helioseismology 7 Appendix I A The depth of penetration of a shear wave (δ) The depth of penetration of a shear wave (δ) in a Newtonian medium... noise) factors on sound perception are usually done using acoustic waves induced in the external ear canal Stimuli which have been used for this purpose are: clicks, tone bursts, half-sine -waves, single tones or pairs of tones The Corti organ’s responses to the external stimuli have either an electric or acoustic character In the former case, these are cochlear microphonics (CMs) picked up from the... up from the surface or from the inside of the cochlea, which are usually used as an indicator of damage to the organ of Corti in animals In the latter case, these are acoustic waves that appear in the external ear canal as a result of stimulation The acoustic waves have an important clinical value Taking into account the presence of nonlinear distortions in the cochlea, the waves that appear after... of MTSM sensor to antibody binding at 15, 25 and 35 MHz 252 Acoustic Waves – From Microdevices to Helioseismology The properties of the medium were determined at t1 = 10 and t2 = 70 minutes At t1 = 10, the system is modeled as MTSM sensor loaded with semi-infinite Newtonian medium ( DIwater) (fig 10A) The height of the column (2 mm) was much higher than the penetration depth of the acoustic wave at... Piezoelectric MTSM sensors transmit acoustic shear waves into a medium under test, and the waves interact with the medium Shear waves monitor local properties of a medium in the vicinity of the sensor and of the medium/sensor interface (on the order of nm - μm); thus, they provide a very attractive technique to study interfacial processes Measured parameters of acoustic waves are correlated with medium... and Freger C.1991 The Study of Polyimide Film properties and Adhesion Using a Surface Acoustic Wave Sensors, ANTEC ’91, 256 Acoustic Waves – From Microdevices to Helioseismology Conference Proceedings, Society of Plastic Engineers and Plastic Engineering, Montreal, pp 1 679 -1984 Gautam Garaia and B.B Chaudhurib.20 07 Adistributed hierarchical genetic algorithm for efficient optimization and pattern matching... Curtis W Frank 20 07 Employing Two Different Quartz Crystal Microbalance Models To Study Changes in Viscoelastic Behavior upon Transformation of Lipid Vesicles to a Bilayer on a Gold Surface Anal Chem 79 70 27- 7035 Ndiritu J.G and Daniell T M 2001 An improved genetic algorithm for rainfall-runoff model calibration and function optimization Mathematical and Computer Modeling 33 695 -70 6 Newton M I., Evans, . (19 97) . Local and selective detection of acoustic waves at the surface of a material”, IEEE Ultrasonics Symposium, pp. 699 -70 3, ISBN 0 -78 03-4153- 8, Toronto, Ontario, Canada, October 5-8, 19 97. pp. 1 479 -14 87 Stauffer, D. (1985). Introduction to Percolation Theory, Taylor & Francis Ltd., ISBN 0 -74 84- 0253-5, London, United Kingdom Acoustic Waves – From Microdevices to Helioseismology. displacements (flexions, torsions ). Mode Frequency (Hz) - numerical Frequency (Hz) - experimental 1 1683 1586 2 23 87 2894 3 35 57 3639 4 5422 5330 5 573 4 6639 6 74 17 7390 Table 7. The first 6