Aydin Dogan

Functional composites for sensors, actuators and transducers

Abstract Following the trend in structural applications, composite structures are being used more commonly in transducer applications to improve acoustic, mechanical and electrical performance of piezoelectric devices. Functional composite transducers for actuators and sensors generally consist of an active ceramic phase incorporated with a passive polymer phase, each of which has a phase transition associated with it. In this paper, several polymer–piezoelectric ceramic composite transducers, mostly designed for sensing hydrostatic waves, are discussed based on the connectivity of the constituent phases. Also discussed are some recent examples of metal–ceramic composites, and single element ceramic transducers with modified shapes for improved performance. A comparison of these designs is given based on their hydrophone figure of merit ( d h · g h ).

INFLUENCE OF SAMPLE THICKNESS ON THE PERFORMANCE OF PHOTOSTRICTIVE CERAMICS

Ferroelectric materials with high photovoltaic properties are of interest for new optical devices such as photostrictive ceramic actuators. However, fabrication of these devices requires development of materials exhibiting high photovoltage and photocurrent. In pursuit of these high performance photostrictive materials, the present research examines the influence of illumination intensity, degree of polarization, and sample thickness on the photostrictive response of WO3 doped lanthanum-modified lead zirconate titanate (Pb, La)(Zr, Ti)O3 ceramics prepared by oxide mixing process. A model for calculating the optimum sample thickness for maximum photostrictive response is proposed. This model agrees well with experimental results, and should be useful in designing photostrictive devices.

Displacement amplification of electroactive materials using the cymbal flextensional transducer

Abstract High performance electroactive materials were studied as the driver element for the “cymbal” flextensional transducer. The compositions included were commercially available Navy Type I and PKI552 lead zirconate titanate (PZT) piezoceramic, relaxor lead magnesium niobate-lead titanate (PMN-PT) ceramic, lead zinc niobate-lead titanate (PZN-PT) single crystal, and lead lanthanum stannate zirconate titanate (PLSnZT) ceramic with antiferroelectric to ferroelectric transitions. Displacement amplifications from 14× to 50× were found for various cymbal configurations. The influence of material properties, cymbal design, and drive signal on the displacement amplification factor is discussed.

An Ultrasonic Motor Using a Metal-Ceramic Composite Actuator Generating Torsional Displacement

An ultrasonic motor composed of three components; a stator, a rotor and a ball bearing is proposed. The stator is made of an active piezoelectric ring, poled in the thickness direction and bonded with two windmill-like slotted metal endcaps. The stator is excited through its two electrodes, generating ultrasonic vibration in the radial direction at a radial mode resonance frequency. The two identical metal endcaps on both sides of the ring, bonded after shifting 45? with each others, transfers the radial vibration into longitudinal and tangential vibrations. The combination of these vibrations (longitudinal and tangential) generates rotation due to frictional interaction between the center part of the top endcap and the periphery of the rotor. A prototype motor with 11.0 mm diameter was fabricated and its transient characteristics were measured. The maximum torque of 1.36 mNm was obtained at a speed of 480 rpm.

Design parameter investigation of industrial size ultrasound textile treatment bath.

Design requirements for industrial size ultrasound bath for textile treatments have been determined. For this purpose, effects of sound pressure level, bath temperature, bath volume, textile material type and hydrophility degree of fabric were examined extensively. Finite element analysis (FEA) was used to investigate spacing and alignment of the ultrasound source transducers to reach effective and homogenous acoustic pressure distribution in the bath. It was found that textile material type, bath temperature and volume led to significant changes at sound pressure level. These parameters should be taken into consideration in designing of industrial size ultrasound bath for textile treatments. Besides, wettability of textiles is highly dependent to the distance from the transducers.

Miniature piezoelectric hollow sphere transducers (BBs)

Miniature piezoelectric transducers were prepared from millimeter size hollow spheres which were formed from PZT-5A powder slurries using a coaxial nozzle process. After sintering, the spheres were poled in two ways: radially and tangentially. Principal modes of vibration were found to be a breathing mode near 700 kHz and a thickness mode near 13 MHz for the radially poled spheres, and an ellipsoidal, a circumferential, and a breathing mode near 230, 350, and 700 kHz, respectively, for tangentially poled spheres. Coupled modes were also observed at higher frequencies. These same modes with similar frequencies were obtained from finite element analysis using the ATILA FEM code, and experimental results were shown to be consistent with the modeling study. Hydrostatic d/sub h/ coefficients ranged between 700 and 1,800 pC/N, which is considerably higher than the d/sub h/ of bulk PZT. The hydrophone figure of merits (d/sub h/*g/sub h/) were calculated to be between 68,000 and 325,000*10/sup -15/ m/sup 2//N for various types of poled spheres. These values are three orders of magnitude higher than the bulk PZT figure of merit. Potential applications include ultrasonic imaging, nondestructive testing, and hydrophones.

Solid-State Ceramic Actuator Designs

Smart electromechanical systems consist mainly of sensors, actuators, and data processing units. Actuators are the responding units of many smart systems including those for active vibration control and noise control. Increased demand for actuators with high-displacement, high generative force, and quick-response time has led to a search for new actuator materials and new designs. The performance of traditional piezoelectric transducers with newly designed flextensional transducers is compared.

Accelerometer Application of the Modified Moonie (Cymbal) Transducer

The modified Moonie (Cymbal) transducer has been investigated for an accelerometer application. High effective piezoelectric charge coefficients (d33) of the Cymbal transducer was observed around 15000 pC/N, which is much higher than that of the piezoelectric ceramic itself (~550 pC/N). With this feature the Cymbal trasducer is a good candidate for high sensitive accelerometer applications. The sensitivity of the Cymbal accelerometer was measured as a function of driving frequency and compared with the single plate ceramic disk which was used as driving component in the transducer. Besides, the geometry of the transducer such as endcap thickness, the effect of different Lead Zirconate Titanate (PZT) compositions and metal endcaps on sensitivity was investigated. The sensitivity 50 times higher than the PZT disk was obtained.

Antibacterial functionalization of cotton and polyester fabrics with a finishing agent based on silver-doped calcium phosphate powders

Textiles are suitable materials for the growth of pathogenic microorganisms. Therefore, various antibacterial finishes have already been developed for textile products. In this work an antibacterial finishing agent containing calcium phosphate-based silver-doped powder was developed for the functionalization of textiles and applied to 100% cotton and 100% polyester knitted fabric samples. Firstly, silver-doped antibacterial powder was synthesized by using a wet chemical method. A size reduction process was applied for reducing the particle size of the powder from micron size to submicron scale. The aqueous dispersion was stabilized by coating the powder surfaces with polyethylene glycol. In order to obtain laundering durability, an aqueous emulsion of an acrylic copolymer was added to the antibacterial solution. The resultant product was applied to all fabric samples by a conventional pad-dry-cure method. The treated fabrics were washed 20 times and the antibacterial efficiency was evaluated after each 10 laundry cycles according to the JIS-L 1902:2002 method against Gram (-) E. coli bacteria. To see the effect of antibacterial finishing on the physical properties of fabrics, the bursting strength, air permeability and color efficiency of the treated and untreated samples were measured and compared. It was found that the antibacterial solution did not affect significantly the bursting strength and color efficiency values of the fabrics, while air permeability was decreased. On the other hand, treated fabric samples preserved their strong antibacterial activities against E. coli after 20 laundry cycles.

Computational analysis on cymbal transducer

Finite Element Analysis in collaboration with experimental studies was conducted to investigate the effects of dimensional parameters on the performance of the cymbal transducer. ANSYS 5.5 FEM code was used for computational analysis. Cymbal transducers were fabricated with steel and brass endcap materials and piezoelectric ceramic, PZT-5A, as driving elements. Admittance spectrum was measured by using HP4194A Impedance/Gain phase analyzer. Displacement and generative force characteristics of the transducers were tested by using a LVDT sensor. Experimental and calculated results matched quite well. Device diameter and cavity diameter has strong effect on cymbal transducer characteristic. Adjusting the dimensional parameters can extend potential application areas of cymbal transducer.