A Study of Applications of Medical Piezoelectrical Ultrasonic Transducer Materials and the Transducers

Transcription

1 A Study of Applications of Medical Piezoelectrical Ultrasonic Transducer Materials and the Transducers Quanlu Li *1, Jing Wu 2, Yinhong Zhang 3 School of Physics and Information Technology, Shaanxi Normal University, No. 199, Chang an South Road, Xi an, Shaanxi , China *1 lql0314@snnu.edu.cn; 2 wujing@snnu.edu.cn; 3 zhangyh@snnu.edu Abstract This paper briefly reports the design, preparation and testing properties of two medical piezoelectrical ultrasonic transducer materials (i.e. SF PZT ( k p of F 2 PZT is 0.52, its Q m is 1010, and tgδ is 2.3), F PZT ( K p of F PZT, is 0.50 and its Q m is 780, but, tgδ, dielectric loss, is 2.3) and F 2 PZT ( k p of F 2 PZT is 0.52, its Q m is 1010, and tgδ is 2.3) ) effect to (Tow apparatuses designed and manufactured with the two piezoelectrical materials mentioned above) high-performance medical piezoelectric ultrasonic diagnosis transducer (i.e. an A-mode medical ultrasonic diagnosis transducer single-probe) and medical piezoelectric ultrasonic therapeutic transducer which were used for clinical practice and obtained the expected results. Moreover, the performance parameters of the clinically-tried A-mode medical ultrasonic diagnosis transducer (single-probe) are superior to the primary probes of the commonly used ultrasonic diagnosis equipments (made in China or imported from abroad). The medical experts who witnessed the whole process of the clinical-trial of the new apparatus agree that the ultrasonic diagnosis transducer proves to be technically mature and clinically efficient and can be applied for diagnosis of all cases of the relevant category of our ultrasonic therapeutic transducers with the ultrasonic therapeutic equipments of acupuncture point of human body, UTM 1 type ultrasonic-thermotherapy-medical therapeutic machine, etc getting good medical treatment effects for different illness at 800~900kHz, to treat many and varied diseases of the patients which are especially remarkable, and there are not any side effects for all of the sufferers. Finally, some problems of the medical piezoelectric materials (including lead-free piezoelectric materials etc) and medical piezoelectric devices (including medical ultrasonic imaging systems, ultrasonic holography and ultrasonic computerized tomography, etc), etc used for the ultrasonic medicine which needs further researches are pointed. Keywords Medical Piezoelectric Ultrasonic Transducer; Piezoelectrical Ultrasonic Transducer Material; Ultrasonic Medicine; Application Introduction Rapid development of medical ultrasonics, including ultrasonic diagnosis and ultrasonic therapy, is needed in the development of new medical ultrasonic apparatus (including medical ultrasonic imaging systems, ultrasonic holography and ultrasonic computerized tomography, etc), especially core of the new apparatus, ultrasonic transducer which is made of the new piezoelectric materials. The present paper reports on preparations and applications of two kind medical piezoelectrical ultrasonic transducer materials, high-performance medical piezoelectric ultrasonic diagnosis transducers and medical piezoelectric ultrasonic therapeutic transducers in present work, these materials and devices for development of ultrasonic medicine will be of significant advance, and increasing the general level of the people s health is of great immediate significance. Preparations of Two Kind Medical Piezoelectrical Ultrasonic Transducer Materials 1) Formulae of the Two Kind Medical Piezoelectrical Ultrasonic Transducer Materials Because of slightly changing the chemical composition of the piezoelectric ceramics, it is possible to emphasize one or more specific properties so that special requirements can be met. The below formula is based on our long-term investigation and study for some PZT. Such complicated composition can be obtained by adding foreign matter in the make-up of a formulation to improve the properties of some PZT. Notes: (for applied fields of acoustoelectric transducing) F shows transmitting type piezoelectric ceramic materials; SF shows transmit-receiving type piezoelectric ceramic materials. SF PZT is expressed as: PbxSr1 x( ZryTi1 y) O 3 (x =0.93~0.96; y=0.52~0.55) 46

2 Studies in System Science (SSS) Volume 2, with small amount of NiCO3, Cr2O 3 and PbO added. F PZT is expressed as: x[ PbySr1 y( ZrmTi 1 m) O3] + ( 1 x) BiFeO 3 with small amount of Fe2O3, MnO 2 and PbO added. 2 (x=0.995~0.998; y=0.91~0.96; m=0.50~0.53) F PZT is expressed as: PbxSr1 x( ZryTi1 y) O3 + m%( wt) K2O + n%( wt) Fe2O 3 (x=0.92~0.96; y=0.50~0.53; m=0.1~0.4; n=0.2~0.6) 2) Flow Chart of Technological Process of the Two Kind Medical Piezoelectrical Ultrasonic Transducer Materials In the present study, we have applied the theory and practice of molecular design to determine the correct formulation and to use dry method ceramic technologies operations, their cardinal processes of development technique and flow chart of technological process are as follows: (1). Designing formulation, selecting raw materials, grinding (class of superfine powder); (2). Calculation, make-up the formula; (3). Mixing of raw materials; (4). pre-pressing; (5). calcination (first sintering); (6). grinding; (7). High speed fluid energy milling or superfine vibration-mill; (8). Granulation; (9). Forming by dry pressing; (10). de-adhesives; (11). Sintering; (12). Finishing after sintering; (13). Metalizing; (14). Polarizing; (15). Ageing; (16). Testing and measuring; (17). Piezoelectric element. After finishing the sintering and metallization, piezoelectric ceramic crystals must be polarized to gain piezoelectricity. Each polarizing condition (voltage V, temperature T and time t) of some piezoelectric ceramics is omitted. 3) Principal properties of Two Kind Medical Piezoelectrical Ultrasonic Transducer Materials After fabrication and metallization, piezoelectric ceramic crystals cannot possess piezoelectricity and become piezoelectric elements when polarized. As these PZT crystalline pellets (made by ourselves) have all passed ageing, their properties must be tested and measured by IEEE standard on piezoelectricity. The principal properties of two kind of medical piezoelectrical ultrasonic transducer materials in present work are shown in Table 1. In the measurements of the PZT piezoelectric ceramics, the electrical properties of a piezoelectric ceramic vibrator are dependent on the elastic, piezoelectric, and dielectric constants of the vibrator materials. Thus, values of performance parameter of the vibrator materials (i.e. for these constants) can be obtained from resonator measurements on a suitably shaped and oriented specimen, provided the theory for the mode of motion of that specimen is known. The basic constant measurements will determine the electrical impedance of the resonator as a function of frequency. In principle it is necessary to measure the resonance and antiresonance frequencies, and the capacitance. The removal of dissipation factor from the resonance range also needs to be measured to obtain the information necessary for finding the material constants. In some instances, an accurate measurement of the antiresonance frequency cannot be made, but it is convenient to characterize the resonator by a lumped-parameter equivalent circuit and to calculate the material constant from the measured parameters of this circuit. The equivalent circuit (the properties of piezoelectrical ceramics and their devices must be tested and measured by IEEE standard on piezoelectricity which refer 1) [1] is shown in Fig. 1; the measured circuit of present work is shown in Fig. 2; and the testing and measuring methods of principal properties of piezoelectric ceramics materials are listed in Table 1 (Notes: the present paper only briefly introduces testing and measuring methods of some important practical parameters of principal properties of piezoelectric ceramics materials, in which d 33 is measured by a d33 -meter that is made in Institute of Acoustics, Chinese Academy Science). TABLE 1 PRINCIPAL PROPERTIES OF THE TWO KIND MEDICAL PIEZOELECTRICAL ULTRASONIC TRANSDUCER MATERIALS. NOMENCLATURE OF PROPERTIES OF PIEZOELECTRIC CERAMICS: K p PLANAR ELECTROMECHANICAL COUPLING FACTOR; Q m MECHANICAL QUALITY FACTOR; Ε T 33 /Ε 0 RELATIVE DIELECTRIC CONSTANT; G 33 PIEZOELECTRIC VOLTAGE CONSTANT; TGΔ DIELECTRIC LOSS; Ρ DENSITY. PROPERTIES IN THE PLANAR MODE ARE MEASURED ON DISCS 20 MM DIAMETER AND 1-MM THICK. Materials K p Q m ε T 33 /ε 0 d 33 g 33 tgδ ρ symbol (pc N 1 ) ( 10 V m N 1 ) ( 10 3 ) ( 10 3 Kg m 3 ) SF PZT F PZT F2 PZT

3 Notes: FIG. 1 EQUIVALENT ELECTRICAL CIRCUIT OF A PIEZOELECTRIC VIBRATOR L series inductance in resonator equivalent circuit; R series resistance in resonator equivalent circuit; C1 series capacitor in resonator equivalent circuit; C0 shunt capacitor in resonator equivalent circuit. Notes: FIG. 2 SCHEMATIC DIAGRAM OF SIMPLE TRANSMISSION-LINE METHOD MEASURING CIRCUIT R T resistance (R T < R 1 ; when anti-resonance frequency, R T = 2Ω, 5Ω, 10Ω, 50Ω, Ω, 10 Ω, etc. ); R 1 the sum of output reactance of the signal generator and input reactance of the frequency meter; R 2 the input reactance of the millivoltmeter. Preparations of High-effect Medical Ultrasonic Diagnosis Transducers and Medical Ultrasonic Therapeutic Transducers For some basic theory of ultrasonic medicine and the ultrasonic transducers, we have prepared high-performance medical ultrasonic diagnosis transducers and medical ultrasonic therapeutic transducers which are made from SF PZT and F PZT (or F 2 PZT ) made by ourselves in present work, to apply them to practice of medical ultrasonics, and, to obtain good effect of medical ultrasonics beyond what have already been reported in the literature. 1) Preparation of High-effect Medical Piezoelectric Ultrasonic Dia gnosis Transducers Medical ultrasonic diagnosis transducers are many and varied, their properties also are different, but, the structures of the medical ultrasonic diagnosis transducers are basically same. We have prepared the medical ultrasonic diagnosis transducer as Fig. 3 is a schematic diagram of structure principle of A-mode medical ultrasonic diagnosis transducer (single-probe). The front end of the probe is the piezoelectric ceramic crystalline pellet, lower and upper surface of the piezoelectric ceramic crystalline pellet is spread on and sinter-permeated 48

4 Studies in System Science (SSS) Volume 2, silver layers (electrodes), and, from each silver layer (electrode) is welded a silver wire. The two wires are separately connected with the centre and shell of contact base of the medical ultrasonic diagnosis transducer. The two links transmit excited high-frequency electric oscillation to the piezoelectric ceramic crystalline pellet and return high-frequency electric signal of the echo of the piezoelectric ceramic crystalline pellet to being transmitted to the receiving amplifier. The shell of the medical ultrasonic diagnosis transducer is made of perspex which is used as a protective support. The front of the piezoelectric ceramic crystalline pellet is spread on the film of epoxy resin which is used to protect the silver layer (electrode) of the piezoelectric ceramic crystalline pellet, the thickness of the protective film of epoxy resin should be 1 2 λ of the wavelength of sound, specific acoustic impedance of the protective film lay between the piezoelectric ceramic crystalline pellet and skin of human body, and, at this acoustic impedance, the transmitting effect of sound is very good. The back of the piezoelectric ceramic crystalline pellet filled in backing layer (sound absorption material) to increase sound damping, and to absorb backward sound waves to be advantageous to ameliorating of longitudinal resolution, and to decrease interference of miscellaneous waves. The backing layer material is more made from epoxy resin and tungsten (W) powder or epoxy resin combined mercuric oxide (HgO). In present work, we prepared the outer diameter of the A-mode medical ultrasonic diagnosis transducer (single-probe) which is approximately 14 mm and 40-mm length. In the A-mode medical ultrasonic diagnosis transducer (single-probe), the diameter of the piezoelectric ceramic crystalline pellet is approximately 12 mm. the schematic diagram of structure principle of A-mode medical ultrasonic diagnosis transducers as is shown in Fig. 3. Fig. 3 THE SCHEMATIC DIAGRAM OF PRINCIPLE OF A-MODE MEDICAL PIEZOELECTRIC ULTRASONIC DIAGNOSIS TRANSDUCERS 2) Preparation of High-effect Medical Piezoelectric Ultrasonic Therapeutic Transducers The schematic diagram of principle of which we have prepared the medical piezoelectric ultrasonic therapeutic transducers as is shown in Fig. 4. In the Fig. 4, 1 the metal cap have two effects: the 1st is fixed piezoelectric ceramic crystalline pellet of F PZT (or F 2 PZT they are all made by ourselves), and 2nd, outer of the metal cap will transmit the ultrasonic energy to the position of human body some of which will be treated by ultrasonics. The metal cap must be grounded with the earth being in same electric potential to be advantageous to the personal safety of patient. 2 the fixing ring is fixed with the chassis of the transducer together by the screw nut close-knit. 3 for the transducer is waterproofed, to pad a rubber ring. 4 the mica spacer is padded between the pressed blank electrode and the piezoelectric ceramic crystalline pellet of F PZT (or F 2 PZT ), the purpose is preventing occasionally a phenomenon which is sparked from the piezoelectric ceramic crystalline pellet of F PZT (or F 2 PZT ) at high frequency. 5 insulating support is propped up the sustaining spring to press the piezoelectric ceramic crystalline pellet of F PZT (or F 2 PZT ) closely, and connects the high-tension core wire and the binding post, to link up the piezoelectric ceramic crystalline pellet which requires high-voltage and high-frequency A-C power supply. 6 the insulating casing pipe is used for increasing high-voltage insulating ability of the whole transducer. As indicated, above method is to fix the piezoelectric ceramic crystalline pellet to be sample, thus convenient for the ultrasonic energy being transmitted to therapeutic position of human body. As the Fig. 4 shows, outward of the ultrasonic therapy transducer is straight form, for all practical purpose, some of the ultrasonic therapy transducers also are curved, but, the inside of these transducers are fixed method of the piezoelectric ceramic crystalline pellet which is roughly the same. The area of the metal cap of ultrasonic therapy 47

5 2 2 transducer which is used to transmit ultrasonic waves has different specifications in 3 cm ~12 cm, the piezoelectric ceramic pellet of ultrasonic therapy transducer which needs high-frequency electricity, is linking up high-frequency oscillating circuit of ultrasonic therapy machine by the high-frequency coaxial cable. FIG. 4 THE SCHEMATIC DIAGRAM OF PRINCIPLE OF MEDICAL PIEZOELECTRIC ULTRASONIC THERAPEUTIC TRANSDUCERS Applications In present work, our medical piezoelectric ultrasonic diagnosis transducers and ultrasonic therapeutic transducers are made by ourselves that have been used for clinical practice and all gain better effects. A-mode medical ultrasonic diagnosis transducers (single-probe) are used to diagnose normal or pathological changes of varied positions of human body at 2.5 MHz, such as, kidney, cholecystitis, hepatomegaly, hepatitis, spleen, hydatidiform mole, etc, get the clear and unambiguous diagnostic results and for all patients there are not harm and sufferings, in their detectable dept and sensitivity, etc, performance parameters of the A-mode medical ultrasonic diagnosis transducers (single-probe) are superior to the primary probes of the ultrasonic diagnosis equipments (made in China or enter port from abroad). Medical experts review the ultrasonic diagnosis transducers that can be applied for diagnosis of all illness of the category of the A-mode ultrasonic diagnosis. Our ultrasonic therapeutic transducers with the ultrasonic therapeutic equipments of acupuncture point of human body, UTM 1 type ultrasonic-thermotherapy-medical therapeutic machine, etc get good medical treatment effects for different illness at 800~900kHz, such as, the curative effects of prostatitis, around shoulder inflammation, relieve pain, subsidence of a swelling, arthritis, anal fissure, anal fistula, stomach trouble, nephritis, hyperplasia of mammary, proctitis, high blood pressure, and for the proving blood circulation, their effects are especially remarkable and there are not any side effects for all of the sufferers. The author of present paper deems it to be necessary for the conditions, in a word, all of the clinical cases of ill of the ultrasonic therapy (or ultrasonic diagnosis) with the transducers of present work are omitted because they are not focal point in present paper. In the ultrasonic therapy, acoustic intensity is a important parameter to affect their therapeutic effect, The selection of the dosage of the acoustic intensity is related to operating conditions, the probe whether or not moves, direct radiation or indirect of the ultrasonic energy, radiation of continuous waves or pulse waves, the time of the radiation, the angle of incidence of acoustical beam, and is current different position of human body, etc. General is regarded as ultrasonic energy at 0.5~1.5 mid-dosage, 3~6 Wcm is largest, under normal conditions they are selected 1 conditions of the ultrasonic therapy must decide as the clinical experimental results. Conclusion Wcm is smaller dosage, 1.5~3 Wcm is Wcm or so. The optimum Ultrasonic medicine (i.e. medical ultrasonics, is the ultrasonic techniques which is used for the concrete development and practice of the basic medicine, the clinical medicine, and hygienics, etc medical field.) is a rapid developing and newly branch of learning, for increasing the general level of the people s health is of great immediate significance. Ultrasonic medicine mainly involves ultrasonic diagnosis and ultrasonic therapy, etc. Ultrasonic diagnosis originates from ultrasonic inspection and measurement in the industry, in view of the modern electronics, acoustical principle combined with the radar techniques, etc to be used as a diagnostic method of clinical medicine. Along with the informational engineering technology developing and joining the ultrasonic diagnosis (including medical ultrasonic imaging systems, ultrasonic holography and ultrasonic computerized tomography, etc) which will be come up to newly advanced standards (the model and sign of the ultrasonic tissue characterization refer 2) [2]. Ultrasonic therapy 50

6 Studies in System Science (SSS) Volume 2, is any method and means which applies ultrasonic energy to cure any illness of human body. In substance, ultrasonic therapy is part of the power ultrasonics (power ultrasonics is a process which makes use of the energy of ultrasonic vibration to change the structure states, characteristics and functions, etc of the substantial organizations, or, to speed up this change. An active applied technology of the dynamic applications is outstanding characteristic of power ultrasonics, has larger acoustic power and higher acoustic intensity). Ultrasonic energy for the tissue of human body will produce lukewarm effect, massage action, biochemistry effect, and, feeble acoustic cavitations in the tissue fluid, etc hybrid actions are the elementary factors of the ultrasonic therapy. Along with the high-techniques developing and is applied to the ultrasonic therapy which will be still more effective on curing the sickness and to have more indications which could be cured with the ultrasonics. Such as, ultrasonic transmission and absorption of oblique plane waves though the human skull are analyzed numerically for frequencies ranging from 1/2 to 1 MHz (the analyzed numerically methods for frequencies refer 3) [3]. These frequencies are optimum for noninvasive ultrasonic therapy of brain disorders where numerical predictions of skull transmission are used to set the phase and amplitude of source elements in the phased array focusing system. But, up to now, piezoelectrical materials and pizeoelectrical ultrasonic transducers occupy an important place in the ultrasonic medicine, these materials and devices are a cornerstone of ultrasonic medicine, and their principal performance directly affects various effects of the ultrasonic medicine. Thus, research and developments of new type piezoelectrical materials and high-performance transducers are long-term assignment in the ultrasonic medicine. The piezoelectrical materials and devices also need to be in company with medical ultrasonic appearances (including ultrasonic power source, electric circuits, etc) to develop forward. The authors are convinced of new developments and applications of ultrasonic medicine which can unquestionable be attained when new-technology and high-techniques (including materials, devices, and, a complete set of equipment, etc) are joined or applied. In the other respect, piezoelectric ceramics have wide-ranging important applications in many fields (including medical piezoelectric ultrasonic diagnosis transducers and medical piezoelectric ultrasonic therapeutic transducers, etc). But, with the deeping of the sense of the human-basic, people s consciousnesses of the environmental protection is future enhancement, the problems of some piezoelectric ceramics (i.e. PT and PZT etc.) with lead bring to people s good health more think deeply. We must give out the present main research directions of medical piezoelectrical ultrasonic transducer materials and the transducers in the lead-free piezoelectric ceramics and lead-free medical piezoelectrical ultrasonic transducers, which are: BaTiO3( BT), Bi05. Na05. TiO3( BNT ) basic lead-free piezoelectric ceramics and bismuth (Bi) layer structure piezoelectric ceramics, which have been used for partial green and environmental protection type medical ultrasonic equipments(including medical ultrasonic imaging systems, ultrasonic holography and ultrasonic computerized tomography, etc), etc. ACKNOWLEDGMENT The authors are grateful to the People s Hospital of Shaanxi Province, the Affiliated Hospital of Fourth Military Medical University, the Second Affiliated Hospital of Xi an University of Medical Sciences, the Fourth People s Hospital of Xi an City and Xi an Institute of Chinese Medicine, etc. who provided clinical experimental conditions (including the ultrasonic diagnosis apparatus (made in China or enter port from abroad), varied ultrasonic therapy machines, a host of cases of illness, etc), analysis of the results for medical ultrasonic diagnosis transducers and medical ultrasonic therapy transducer, and assist some Chinese traditional and herbal drugs of ultrasonic therapy to our work. 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7 [6] Quanlu Li, Jing Wu, Yinhong Zhang, Ran Liao, Haixia Cheng and Qingqing Yang. The Effects of Superfine Powder and Sintering Technique upon Properties and Applications of some Piezoelectric Ceramics. Advanced Materials Research, Vol. 749 (2013), P [7] Quanlu Li, et al. The Lead-free Piezoelectric Ceramic Materials will be used for green and environmental protection type Medical Ultrasonic Equipments, the 10th Western Pacific Acoustics Conference in Beijing, China on September, 2009 (CD Version). [8] Quanlu Li. Research and their applications of high-performance piezoelectric ceramics. Proceedings of the first China international conference on high-performance ceramics, Tsing Hua University Press, 1999, P