Yonghwan Hwang

Optical, dielectric and thermal properties of nanoscaled films of polyalkylsilsesquioxane composites with star-shaped poly(ε-caprolactone) and their derived nanoporous analogues

Abstract Nanoscaled films of poly(methylsilsesquioxane-co-ethylenylsilsesquioxane) (PMSSQ–BTMSE) and polymethylsilsesquioxane (PMSSQ) were prepared from the respective soluble prepolymers, and their thermal, optical, and dielectric properties were characterized. The PMSSQ–BTMSE nanofilm containing an ethylenyl bridge comonomer unit BTMSE was found to be thermally more stable than the nanofilm of PMSSQ, a representative polyalkylsilsesquioxane. Further, in comparison to the PMSSQ film the PMSSQ–BTMSE film exhibits a larger refractive index and a larger dielectric constant but a smaller out-of-plane thermal expansion coefficient, when both prepolymers are cured under the same conditions. These characteristics of PMSSQ–BTMSE films are due to the ethylenyl bridge provided by the BTMSE comonomer unit, which promotes the formation of a tighter, more perfect network structure in cured PMSSQ–BTMSE films. Composite films were prepared by solution-blending the pore generator (referred to as the porogen), a star-shaped poly(e-caprolactone), with the soluble prepolymers then drying the resulting solution, and the nature of their curing reactions and extent of porogen calcination were investigated. It was found that the thermal curing and calcination processes of the composite films successfully produce PMSSQ–BTMSE and PMSSQ films containing pores that are about 400 nm in diameter. It was confirmed that the presence of these generated nanopores significantly reduces the refractive indices and the dielectric constants of the dielectric films but increases their out-of-plane thermal expansivity, depending on the initial porogen loading. The porosities of the nanoporous dielectric films were estimated from the measured refractive indices. The surface topographies of these films were also investigated, giving information about the sizes of the pores generated in the films. It was also found that prior to calcination the presence of the porogen increases the refractive index and dielectric constant of the composite dielectric films because of its inherent high polarizability, and also increases the thermal expansivity of MSSQ–BTMSE composite films but very slightly decreases the thermal expansivity of MSSQ composite films. It is demonstrated that PMSSQ–BTMSE films and the related nanometer scale nanoporous films are candidates for use as low and ultra-low dielectric interlayers in the fabrication of advanced microelectronic devices.

A “composite” stepped plate for use in highly directional parametric array loudspeakers

It has been shown that stepped plate radiators with appropriately designed steps can be used in highly directional parametric array (PA) loudspeakers [Hwang and Moon, 170th Meeting of the Acoustical Society of America, 138(3), 1801(2015)]. To improve the performance of the PA loudspeaker, a relatively thin plate with steps needs to be adopted for its higher power efficiency. However, the natural frequencies of the plate and the corresponding mode shapes depend on the mass of the steps. Hence, it can be difficult to design a stepped plate suitable for use in PA loudspeakers. In this paper, we propose a novel plate design, with steps composed of a stiff, lightweight, polymer material. The steps were fabricated with a thickness of 2.3 mm from a polymer material with an elastic modulus of 1 GPa, a Poisson ratio of 0.23, and a mass density of 540 kg/m3 on the plate with a thickness of 1 mm. Experiments and simulations were carried out to determine the acoustic characteristics of our fabricated “composite” step...

Underwater parametric array source transducer composed of PZT rods and thin polymer plate with high power efficiency for wideband sound generation

Nowadays 1-3-type PZT composite transducers are widely used for underwater parametric array (PA) sound source since they can generate highly directional acoustic beam with high intensity, which is the requirements for the PA acoustic phenomenon that results from nonlinearity of a medium. Thanks to the relatively small mechanical quality factor of 1-3 PZT composite, the transducer using it can generate high intensity sounds by relatively low input voltage in the relatively wide frequency band around its resonance frequency. The low mechanical quality factor, however, increase the internal mechanical loss inside the transducer. Consequently, the acoustic radiation efficiency may be lower than expected. In this paper, a dual-resonant-frequency PZT rods are integrated into a thinner polymer plate. Then, the radiation surface increases to enhance radiation power efficiency. The PZT rods with two different lengths, are integrated in the process of molding a polymer plate. The fabricated transducer are operated ...

Design and Development Research of a Parametric Array Transducer for High Directional Underwater Communication

A parametric array is a nonlinear phenomenon that generates a narrow beam of low-frequency sound using the nonlinearity of the medium. The low-frequency sound so generated has a low sound pressure compared with that of sound generated directly. Consequently, a transducer that can generate a primary wave with high directivity and level is required. This study designed, fabricated, and evaluated a multi-resonance transducer as a parametric array source. The designs of the unit transducers and array transducer were based on an analysis model. The design process was repeated to fabricate the optimum transducer. The fabricated transducer array can generate a 189 dB, 190 dB primary wave level at 6.3 m and a 134 dB difference frequency wave using the parametric array phenomenon. The difference frequency wave has a frequency of 15 kHz and high directivity with an half power beam width in a water tank.

A stepped-plate radiator as a parametric array loudspeaker

A parametric array loudspeaker can generate a high directional audible sound beam in the air by the nonlinear acoustic interaction widely known as a “Parametric Array.” The advantage of the parametric array phenomenon is that it creates a narrow beam using the small aperture of an acoustic radiator. It can be used in many applications, including high directivity communication systems. However, the sound pressure level generated by the parametric array is very low, which necessitates a high efficiency and intensity of sound. This paper describes the application of a stepped-plate radiator in a parametric array loudspeaker. The stepped-plate radiator has two resonance frequencies (f 1 = 75 kHz, f 2 = 85 kHz) in the design frequency region, and three different steps that compensate for the phase difference in the flexural vibrating plate. This allows the generation of high directivity audible sound in the wide flat radiation bandwidth of the audible frequencies range (100 Hz to 16 kHz, difference frequency w...

Development of a multi-resonance transducer for highly directional underwater communication

The parametric array is a nonlinear conversion process that generates a narrow beam of low-frequency sound using small aperture. It can be applied to underwater communication between two nodes with known locations, since the highly directional sound beam may provide such benefits as privacy, no interference due to the multi-path. The difference frequency wave (DFW) from the parametric array shows small side lobes and extraordinary directivity. The shortcoming of the DFW generated by the parametric array may be its low sound pressure level relative to that of the directly generated sound beams. In this study, we designed and fabricated a multi-resonance transducer as a parametric array source and evaluated its feasibility as a transmitter. For that purpose, we determined the proper design parameters for midrange communication. We selected 10 kHz as the communication frequency and then determined the primary frequencies as 100 and 110 kHz. We composed the source transducer using the two kinds of unit transducers. The fabricated transducer array and the developed operating techniques enabled us to successfully transmit letters, words, and drawings inside the water tank. By testing the characteristics, we confirmed that the developed operating scheme and transducer can be used for underwater communication. [Work supported by ADD (UD130007DD).]

Study on improving piezoelectricity and PBLG/PMMA composite

Poly-Gamma-benzyl-L-glutamate Poly methyl methacrylate (PBLG-PMMA) composite polymer, a new piezoelectric transduction material, was invented by Yu et al. In our previous study, we have shown that the body composed of this new material can be produced by simultaneous poling and curing of a homogeneous solution comprising Poly-Gamma-benzyl-L-glutamate(PBLG) and methyl methacrylate(MMA) via detachable molding. And, it was also shown that the piezoelectric coefficient(d33) of PBLG-PMMA composite is dependent on the PBLG concentration and the intensity of electric field applied during curing in molds. In this study, we attempt to improve piezoelectricity of PBLG-PMMA composite because the piezoelectric coefficient of PBLG-PMMA was only about one twentieth of that of PVDF and measure the dynamic behaviors of PBLG-PMMA bodies in order to investigate the feasibility to apply this composite to acoustic transducers. In order to improve the piezoelectricity, the PBLG concentration and the electric field intensity a...

Acoustic filter design for precise measurement of parametric array in near-field region

A parametric array is a nonlinear conversion process that generates a narrow beam of low-frequency sound using a small aperture and that is used in active underwater SONAR and communication systems. A parametric array generates a highly directional difference frequency wave (DFW) by nonlinear interaction of bi-frequency primary waves at higher frequencies. However, it is difficult to measure the parametric array effect in the near distance of the transducer, because the high-pressure level of the primary waves may cause the receiving transducer to provide with pseudo-sound signals of difference frequency by its nonlinearity. The pseudo-sound signals make it difficult to measure the real DFW due to the parametric array process. In this study, we confirmed the existence of pseudo-sound and its effects on measurement of the near-distance DFW by the parametric array using numerical simulations based on the KZK equation. Also, a newly designed acoustic filter was proposed to eliminate pseudo-sound signals. Thi...

Stepped-plate transducer as an energy transmitter

Power transmission through acoustic energy may be useful in such cases as supplying power to wireless small sensors. In the case, the radiation and reception power efficiency is important. Even in ultrasonic frequency bands, the power efficiency of most acoustic radiators in air is not high enough. The stepped-plate ultrasonic transducers, introduced by Gallego-Juarez etal. [Ultrasonics 16, 267–271(1978)], may be a good candidate for the radiator for this purpose because it can effectively generate highly directive, large-amplitude, ultrasonic sounds in air. The transducer consists of langevin transducer that causes wave generation, mechanical amplifier, and stepped radiation plate. Although it is reported to achieve 80% of power efficiency, it is not reported how to achieve maximum power efficiency. For design of large-amplitude, high-efficiency stepped-plate transducer, the design of not only individual parts but also system integration of entire transducer is important. In this research, we developed a...

Piezoelectric poly‐g‐benzyl‐L‐glutamate polymethyl methacrylate composite disks fabricated using molds.

Poly‐g‐benzyl‐L‐glutamety Polymethyl methacrylate (PBLG‐PMMA) composite polymer, a new piezoelectric transduction material, was invented by Yu et al. In this study a method is developed to fabricate a disk using detachable molding. Unlike film‐type piezoelectric polymers such as the polyvinylidenefluoride (PVDF), this new material can be used to form a body of various shapes and sizes such as conventional piezoelectric ceramics. The piezoelectric characteristics mainly come from the state of alignment of polygamma‐benzyl alpha, L‐glutamate molecules (PBLG), which have large electric dipole moment. The PBLG can be melted with methyl methacrylate by heating, and mixture with applying electric field can be polymerized as a piezoelectric PBLG‐PMMA composite in the mold. The fabricated specimens have the dimensions of 20 mm in diameter and 3 mm in height. The piezoelectric coefficient (d33) depends on the concentration of PBLG. Measured values were 0.45 and 1.9 pC/N with concentrations of 10 and 30 wt %, respe...