Susung Lee

Design and fabrication of a new traveling wave-type ultrasonic linear motor

This paper describes the development of a new traveling wave-type ultrasonic linear motor. The motor consists of a metallic stator and two piezoelectric ceramic plates bonded to the stator, thereby eliminating the need for external vibrators. The two piezoceramic plates excite two ultrasonic standing waves with a certain phase difference, which convert to a traveling wave when combined together. The operation principle of the motor is presented along with the theoretical equations, and the feasibility is verified using the finite element method. Based on the finite element analyses, detailed dimensions and boundary conditions are determined for the proper generation of a traveling wave. Experimental fabrication and characterization of a sample motor is performed to confirm the numerical results and prove the practical applicability of the new structure. The new linear motor presented in this work offers a relatively simple structure compared to traditional traveling wave-types while maintaining all the characteristic features of an ultrasonic motor.

P2O-7 Design and Construction of an Acoustic Horn for High Power Ultrasonic Transducers

Typical high power transducers consist of a piezoelectric or magnetostrictive element of transduction and a solid acoustic horn that acts as a vibration amplifier. In order to obtain high power capacity, the acoustic horn needs to be optimized to match the active element. In this study, we did optimal design of an acoustic horn for a high power magnetostrictive transducer and constructed a sample prototype of the horn to verify the validity of the design. For the design, we derived the theoretical output power of a horn as a function of its dimensions, and determined the optimal dimensions to achieve the maximum power through finite element analyses with ANSYSreg. The analytical method could quite quickly determine the horn length while the finite element method could refine the planar dimensions of the structure. The transducer had the resonant frequency of 19.3 kHz and had the maximum sound pressure level of 199 dB with an omni-directional radiation pattern in water. The analysis method developed in this study is so general that it can be applied to the design of acoustic horns for high power transducers of various operating frequencies and transduction materials

Development of surface point-focussing ultrasonic transducer using PVDF

An ultrasonic contact transducer generating point-focused Rayleigh waves along the flat surface of the specimen was developed as an improved technique for detecting, sizing, and imaging surface cracks and subsurface defects. The cone-type shoe was designed so that the incident angles of rays of longitudinal waves generated at any point on the top convex surface of the shoe were constant and all the Rayleigh waves were propagated along the surface or the subsurface of steel and point-focused by circular geometry. The developed surface point-focusing transducer showed narrow beam width (6 dB width=1.2 mm) and high echo-amplitude (17.5 dB higher than the conventional angle probe using PVDF). The simplified model for echo-amplitude showed good agreement with measured results.<<ETX>>

Photoacoustic imaging probe for detecting lymph nodes and spreading of cancer at various depths

Abstract. We propose a compact and easy to use photoacoustic imaging (PAI) probe structure using a single strand of optical fiber and a beam combiner doubly reflecting acoustic waves for convenient detection of lymph nodes and cancers. Conventional PAI probes have difficulty detecting lymph nodes just beneath the skin or simultaneously investigating lymph nodes located in shallow as well as deep regions from skin without any supplementary material because the light and acoustic beams are intersecting obliquely in the probe. To overcome the limitations and improve their convenience, we propose a probe structure in which the illuminated light beam axis coincides with the axis of the ultrasound. The developed PAI probe was able to simultaneously achieve a wide range of images positioned from shallow to deep regions without the use of any supplementary material. Moreover, the proposed probe had low transmission losses for the light and acoustic beams. Therefore, the proposed PAI probe will be useful to easily detect lymph nodes and cancers in real clinical fields.

Measurement of all the material properties of PMN-PT single crystals grown by the solid-state-crystal-growth (SSCG) method

This paper is about the characterization of the PMN-32%PT crystals having the symmetry of tetragonal 4mm grown by the SSCG method. All the elastic, piezoelectric, and dielectric constants of the crystals were measured by the resonance method. A total of eleven independent material constants such as six elastic compliance constants at constant electric field, two dielectric constants at constant stress, and three piezoelectric constants were extracted from five sets of crystal samples of different geometries each to have different vibration mode. Validity of the measured data was confirmed through comparison of experimental impedance spectra of the single crystals with numerical impedance spectra calculated with the measured material constants.

Measurement of all the elastic, piezoelectric, and dielectric properties of PMN-PT single crystals

PMN-PT single crystals have rhombohedral 3m symmetry. In this paper, all the elastic, piezoelectric, and dielectric constants of the PMN-PT single crystals wre measured by the resonance method. For the rhombohedral symmetry, a total ot twelve independent material constants were measured such as six elastic compliance constants at constant electric field, two dielectric constants at constant stress, and four piezoelectric constants d. Seven sets of the crystal samples of each different geometry were prepared for the measurement of length-thickness extensional, thickness extensional, radial, length extensional and thickness shear modes of vibration, respectively. In order to check the validity of the measurement method, the same technique was applied to the characterization of common PZT ceramics. Experimental impedance spectrum of the PZT ceramics was compared with numerical impedance spectrum calculated with measured material constants. The good agreement between the two spectra confirmed validity of the characterization method in this paper.

MOPA fiber laser for photoacoustic imaging using arrayed ultrasound transducer

An Nd:YAG laser is generally used as the optical source for photoacoustic imaging (PAI) systems, which support a high-power pulsed laser. However, PAI systems based on Nd:YAG lasers have several disadvantages, such as instability against impact and vibration, poor mobility, and large size. To overcome the limitations, we demonstrate a PAI system using a master oscillator power amplifier (MOPA) fiber laser and an arrayed ultrasound transducer. The fabricated MOPA fiber laser has a variable repetition rate in the range of 1–50 kHz, a pulse width of 10–70 ns, and an output power of 160 μJ. Furthermore, it is stable to impact and vibration, mobile, and compact with a size of 427×250×170 mm3. We achieved PAI 150 times faster using MOPA fiber laser than using Nd:YAG laser with the arrayed ultrasound transducer composed of 128 elements. Therefore, we believe that the PAI system based on the MOPA fiber laser has significant potential for use as a clinical ultrasound imaging system.

Development of a highly attenuative backing for ultrasonic transducers with periodic arrangement of polymeric rods inside the backing

Backings for ultrasonic transducers are generally made of composites of metal or metal oxide powder and epoxy resin or rubber. In this work, a new highly attenuative backing has been developed by installing cylindrical silicone rubber rods periodically inside the two phase mixture. The scattering of ultrasonic waves is dramatically increased by the polymeric rods, which results in big improvement of the attenuation. The silicone rubber rods are molded first, and are disposed periodically on a plane. Then a mixture of epoxy and metallic powder is casted around the rods, and is cured not to have any vacancies. Another backing plate was fabricated as well with the same mixture but without the silicone rods. The backing plates were characterized through ultrasonic pulse-echo tests. Significant improvement of the attenuation has been confirmed through the experiments. Acoustic impedance of the backing can be increased if needed by controlling the volume percent of tungsten powder without causing much variation of the attenuation. This highly attenuative backing is applicable to various size-constrained ultrasound probes like TEE and mechanical 3D transducers.

Wide aperture convex array transducer with PMNPT piezoelectric single crystals

The piezoelectric single crystal PMN-PT has lower acoustic impedance and a higher electromechanical coupling coefficient than conventional piezoelectric materials. For these reasons, single crystal PMN-PT can be a good way to enhance the sensitivity and increase the bandwidth of ultrasonic transducers. However the single crystal has certain limitations in size, manufacturability, and a higher electrical impedance. Thus transducer manufacturers commonly use single crystal material only for a small aperture and lower frequency transducer designs such as a phased array transducer. This paper presents the application of single crystal PMN-PT to a convex transducer with a large aperture, including adaptive design and manufacturability considerations.

Design and fabrication of a new multi-active-layer transducer with a single-copper-layer FPCB

A diagnostic ultrasound transducer which operates at low frequency and has a small pitch has a high resultant element electrical impedance, aggravating the impedance mismatch which typically occurs between an ultrasound array and cable. A transducer constructed from multiple layers of active material that are electrically in parallel is one way to improve this impedance mismatch. Such a multi-active-layer transducer is most commonly composed of odd numbers of piezoelectric layers to simplify the electrical connections, so a three-layered structure is the simplest choice. But then the design thickness of each of the three PZT layers for a 3.5MHz transducer would be less than 100μm, which is too thin to fabricate easily and too risky to handle. In this paper, a two-active-layer structure is presented that reduces the breakage risk while achieving a lower impedance and thereby improving the transducer performance. A single-copper-layer flexible printed circuit board (FPCB) is developed to electrically connect the two PZT layers. The two-active-layer transducer presented is a phased array with a 3.5MHz center frequency, 150μm pitch, and 128 elements. The transducer is designed using a finite-element analysis program (PZflex) and then fabricated in accordance with the optimal design. The two-active-layer array performance is compared with a single-active-layer transducer that is similarly optimized.