ULTRASOUND PIEZOCERAMIC TRANSDUCER FOR UNDERWATER ACOUSTICS IN SONOCHEMISTRY

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1 ICSV14 Cairns Australia 9-1 July, 007 ULTRASOUND PIEZOCERAMIC TRANSDUCER FOR UNDERWATER ACOUSTICS IN SONOCHEMISTRY Irinela Chilibon 1, Mihaela Moioi and CarmenitaMateesu 3 1 National Institute of Researh and Development for Optoeletronis, INOE- 000, PO Box MG-5, 7715, Buharest-Magurele, Romania, qilib@yahoo.om University Politehnia of Buharest, Buharest, Romania 3 National Institute for Materials Physis, PO Box MG-7, Buharest-Magurele, Romania Abstrat The effet of ultrasound fields on reative rystallization nuleation ould produe homogeneous nuleation and improve the proess reativity into hemial solutions. Organi moleules or polymers an influene the rystallization of inorgani salts and may at as rystal growth inhibitors. It is not yet lear if the additive interats with dissolved omponents or with the developing phase. Crystallization proess may be ontrolled by various additives. Also, ultrasounds may also affet the proess. Complex phenomena take plae in liquids when an ultrasoni field is applied. Ultrasounds yield avitation bubbles whih aumulate gases and vapors from the liquid phase until they beome too large and ollapse, produing shok waves. The temperature and pressure inside the avitation bubbles and in their viinity are huge and influene all hemial reations taking plae in the liquid phase. Also, ultrasounds indue different reations into the hemial mixed solutions, funtion of ultrasound duration, frequeny, temperature, and appliation manner of solutions (dripping or pouring). Therefore a small size ultrasound piezoerami transduer is suitable to the sonohemistry appliations. The generation is made by a transduer supplied by a signal generator. The ultrasound piezoerami transduer generates ultrasound field whih yields aviational effets suh as: enhanement of gas bubbles, temperature inreasing, mehanial effets, dispersion of solids in liquids, and reativity inreasing. The transduer onverts eletrial signal into mehanial vibrations, whih are propagated into hemial solutions. The small diameter of transduer ase allows get to straiten glass tubes, suh as the hemial flask neks. The ultrasound piezoerami transduer is suitable to generate ultrasound in the same time with the hemial proesses, at 46 khz resonane frequeny. A transduer appliation in sonohemistry proess is the alium arbonate rystallization, ombining the effets of organi additives and ultrasoni field. As final result is alium arbonate powder with large amount of nanometer size rystals.

2 1. INTRODUCTION A possible improvement of the rystallization proess is to use power ultrasound, but this requires an appreiation of all the phenomena ourring during sonorystallization. It has been observed that ultrasoni waves have an influene on the growth rate and the rystals size distribution during rystallization in saturated solutions [1]. For instane, the nuleation rate of the CaSCO 4 rystals has been found multiplied by 10 at ultrasound appliation. The indution time of nuleation is strongly redued in presene of ultrasoni waves for different systems. The growth of sugar rystals has been found to be faster under ultrasound ompared with mehanial agitation. The rystal growth rate depends on the ultrasoni frequeny and intensity. Several authors have noted this aeleration of the rystals growth under ultrasound for different solutes, but today the mehanism of the ultrasound ation is not yet well understood [1]. It has been also found that ultrasound an redue or modify agglomeration and improves the produt handling. It is possible that the ultrasoni wave inreases the probability of ollision between the partiles as in the primary nuleation. So, one an say that the effets of ultrasound on rystallization are very divers, mostly positive, but that they are numerous and diffiult to analyse separately. The implosion of the avitation bubbles plays an important role in the disintegration of the imersed solid partiles. Chemial and some mehanial effets are given when ultrasound irradiates liquid, and most of these effets are a result of the implosive ollapse of avitation bubbles and/or bubble-indued mirostreaming. Ultrasound is applied to various purposes beause of these benefiial effets. For example, ultrasound is used to enhane reation rates, to lean glassware, and to form nanopartiles of metals and pharmaeutial produts. Partiularly in the rystallization proesses, the term sonorystallization is defined as applying ultrasound to rystallization proess, and the following ultrasoni benefiial effets have been reported. It was so far onfirmed that ultrasound exels in ontrolling primary nuleation [], modifying rystal size and rystal size distribution (CSD) [3], induing nuleation and enhaning rystal growth rate [4]. Beause of ultrasoni ability to ontrol the rystal properties, the emphasis is plaed on the appliation of ultrasound to rystallize ative pharmaeutial ingredients. Moreover the following appliations are suggested as the potential appliations of sonorystalization [5]. Manipulation of rystal distribution by ontrolled nuleation Ultrasoni irradiation at modest supersaturation to initiate ontrolled nuleation Manipulation of rystal distribution by ontrolled nuleation was arried out for dodeanedioi aid [6]. As onern as the other substanes, however, ultrasound annot always indue primary nuleation. Therefore a fundamental study for investigating ultrasoni nuleation phenomenon is required to ontrolling primary nuleation. The aoustial demands, for a good effiieny, are onditioned by the neessity to realize a working regime at the resonane frequeny of the avitation bubble, and limited by some fators, suh as: the transduer type, PZT material properties, the transduer manufature mode, et. The ultrasoni piezoerami sandwih transduer has three parts: one entral and ative vibration soure (piezoerami tores), and two end-metal masses (refletor and radiator). The ative soure of vibration is plaed inside the transduer body making one sandwih (metal-piezoerami) struture bonded by two end-metal masses.

3 . PIEZOCERAMIC SANDWICH TRANSDUCER DESIGN The ative element of the devie is a sandwih transduer, made of two piezoerami tores stak with metal ylinders (Figure 1). This eletromehanial transduer works on the basis of the inverse piezoeletri effet, onverting eletrial power into a mehanial displaement in the range of tens of mirons. All devie elements are fixed and pre-stressed by a stainless steel srew, whih indues an initial polarization of the piezoerami stak. The vibration amplitude of the sandwih radiator depends on PZT tores number, PZT material elastiity oeffiients and the metal elastiity oeffiients. Maximum peak to peak displaements of the transduer radiating fae would be in order of tens mirons, when operating at resonane frequeny. The design of a simple metal - piezoerami - metal sandwih transduer ([7], and [8]) to resonate at a given fundamental frequeny,, in the plate thikness diretion is based on the following equation: l v A11v artg A v 1 l 1 A v tg artg v1 A v l tg v (or ) (1) where: l 1, l, l : lengths of 1 st metal, nd metal, erami setions v 1, v, v : sound veloities in 1 st metal, nd metal, erami setions A 1, A, A : ross setions of 1 st metal, nd metal, erami setions 1,, : densities of 1 st metal, nd metal, erami setions If the metal plates are assumed to be idential and the erami plaed symmetrially between them, the alulation of the transduer dimensions an be greatly simplified by approximation. A graphial representation of the general solution is shown as being a rapid and easy solution of the transduer equation (1), and one an determine the optimum omponent lengths of the sandwih transduer. Figure 1 Simple sandwih piezoerami transduer

4 In this ase, the effet of the erami on the resonane frequeny is almost entirely due to its ompliane, and the effet of its mass is negligible. This is fairly obvious when one onsiders that the setion at the enter is subjeted to high stress and strain levels and therefore ontributes to the total potential energy, but experienes little vibratory motion and therefore ontributes little to the total kineti energy. This onlusion may be proven by applying the equation to the ase, in whih the erami is replaed by a metal of the same type and ross-setion as that used for the outer plates, and of length given by: A Y l l () A Y then Y 1, Y and Y E has to be defined the solid metal bar of length l 1 + l 1 has the same resonane frequeny as the original sandwih. This result is derived by assuming that the phase angle aross both erami and equivalent metal setion (i.e. l 0 /v 0 and l 1 /v 1 ) are small enough for the approximation tan = to be used. This formula gives a setion of the same total ompliane as the erami. The sound veloity value of v is obtained from the relation: E Y v (3) If the sound veloity in the erami is the modulus relating to open iruit or onstant displaement onditions, then the antiresonane frequeny of the transduer is found. The oupling oeffiient of the whole transduer may be alulated from the resonane and antiresonane frequenies, f r and f a as follows: k f r f a f (f = f a - f r ) (4) f f a r For the most effetive use of a transduer, it is usually desirable to ahieve as high a value of the oupling oeffiient, k, as possible. The approximate formula for k shows that this means making the proportional differene between f r and f a as great as possible. To do this, the piezoeletri material must be inorporated into the sandwih in suh a way that the effet of the boundary onditions (short or open iruit at the eletrodes) on its elasti modulus will have the maximum influene on the resonane of the sandwih. The simplified model of the piezoerami transduer an only approximate the resonane frequeny for the entire devie. Therefore, it is neessary to manufature several sandwih piezoerami transduers with different dimensions. The eletromehanial sandwih transduer works on the reverse piezoeletri effet, onverting an eletrial power into a mehanial mirodisplaement. Eah PZT tore of the stak ontributes to the entire devie displaement. The L total displaement for a stak made by n piezoerami tores with L length is a funtion of d 33, the piezoeletri oeffiient of the piezoerami material and U the sandwih stak applied voltage, and the relation between them is: L = d 33 n U (5) The simple sandwih piezoeletri transduers produe motion of a too small amplitude for high power appliations. It is ommon pratie to amplify the mehanial motions by

5 means of a tapered resonant horn and the shape of the taper most ommonly hosen is exponential. Also, other onfigurations an be utilized, for example to obtain two resonane frequenies. The stepped horn onsists of two ylinders of different diameter plaed end to end onentrially, and its most useful harateristi is that large motion amplifiation is obtainable. In high power appliations of ultrasound, an exponentially tapered solid horn in half-wave resonane is used. The solutions apply to loosely systems and assume Poisson's ratio may be negleted i.e., lateral dimensions are small ompared with the length (Figure ). Figure Ultrasoni exponential solid horn N = D 0 / D f magnifying fator of the vibration amplitude The length of the ultrasoni exponential solid horn is given by the relation: ln N l 1 f (6) l ln N x n artan (7) As an improvement, the ultrasound aoustial power of the sandwih transduer an be inreased in the following ways: - take an optimum PZT material and metalli elements (for radiator and refletor) - inrease the size (diameter, thikness) of the piezoerami tores - take a greater number of piezoerami tores - use a proper aoustial transformer (different forms and sizes) to amplify the vibrations - realize a narrow aoustial angle of the diretivity pattern. 3. RESULTS The tehnologial manufature requires speial mehanial proesses to realize the piezoerami stak, metalli elements and then to enapsulate all together. In this onstrution (Figure 3), four piezoerami tores are bolted between a pair of end-metal elements (steel ylinder refletor and exponential hard aluminum radiator).

6 Figure 3 Experimental transduer ross setion The piezoerami elements are of pre-polarized lead titanate zironate omposition, whih exhibit high ativity oupled with both low loss and aging harateristis. They are ideally suited to form the basis of an effiient and rugged transduer. The assembly is lamped together by means of a high tensile bolt, whih ensures the eramis are in ompression mode at maximum transduer displaement. Between the PZT tores there are opper eletrodes, to make the eletrial onnetion. The PZT-5A tores dimensions are: mm external diameter, 11 mm inner diameter and 4 mm thikness, the steel ylinder refletor is 50 mm length and the hard aluminium refletor is 70 mm length. The Fig. 4 shows the impedane vs. frequeny harateristi of ultrasound piezoerami transduer, measured by RLC Hioki, equipment, and Fig. 5 presents the phase vs. frequeny harateristi. Fig. 4 Impedane vs. frequeny harateristi of ultrasound piezoerami transduer

7 Fig. 5 Phase vs. frequeny harateristi of ultrasound piezoerami transduer 4. CONCLUSION The ultrasound piezoerami transduer for sonohemistry appliations presents the following advantages: it is possible to ahieve muh grater vibration amplitudes by utilizing a horn with an exponential shape as radiator; as a result of this, muh grater energy densities an be ahieved the aoustial power an be inreased by utilizing a greater number of tores and a large tore surfae. ACKNOWLEDEGEMENTS This study was supported by CEEX X1C15/005 ontrat, and the authors wish to thank CEEX program for the finanial supports. Referenes [1] N. Amara, B. Ratsimba, A. Wilhelm, H. Delmas, Ultrasonis Sonohemistry, 11, 17-1 (004) [] H. Izumi, T. Masakazu, H. Hideto, K. Hiroyuki, Proeedings of The 5th International symp. Teh. Korea and Japan Seoul, Korea, August 19-1, (1999) [3] A. Naera, B. Ratsimba, A. Wilhelm, H. Delmas, Ultrasonis Sonohemistry, 11, (004) [4] L. Hong, J. Wang, Y. Bao, Z. Guo, M. Zhang, Journal of Crystal Growth, 47, , (003) [5] C. Prie, Ultrasound-The key to better Crystals for the Pharmaeutial Industry, Pharmaeutial Tehnology Europe, Publ, No.040, 59-65, Ot (1997) [6] J. Linda, P.W. Cains, P.D. Martin, Use the power of sonorystallization for improved properties, Chem. Eng. Prog. 97, 56-61, (001) [7] Morgan Matro Limited, Transduer Produts Division, Tehnial Publiation TP-35, The design of piezoeletri sandwih transduers [8] M. Wevers, J.P. Lafaut, L. Baert, I. Chilibon, Low-frequeny ultrasoni piezoerami sandwih transduer, Sensors and Atuators A: Physial, 1, (), 84-89, (005)

Part G-4: Sample Exams

Part G-4: Sample Exams 1 Cairo University M.S.: Eletronis Cooling Faulty of Engineering Final Exam (Sample 1) Mehanial Power Engineering Dept. Time allowed 2 Hours Solve as muh as you an. 1. A heat sink