Rardchawadee Silapunt

Theoretical Study of Microwave Transistor Amplifier Design in the Conjugately Characteristic-Impedance Transmission Line (Ccitl) System Using a Bilinear Transformation Approach

Conjugately characteristic-impedance transmission lines (CCITLs) are a class of transmission lines possessing conjugately characteristic impedances (Z § 0 ) for waves propagating in the opposite direction. A typical Z0 uniform transmission line is a special case of CCITLs whose argument of Z § is equal to 0 - . This paper aims to generalize the CCITL system by demonstrating a theoretical study of CCITLs and their applications in the microwave transistor amplifler design. It is found that the bilinear transformation plays an important role in transforming circles in the re∞ection coe-cient i0-plane in the Z0 system to the i-plane in the CCITL system. In addition, Meta- Smith charts, a graphical tool developed for solving problems in the CCITL system, are employed to design matching networks to achieve desired amplifler properties. Results show that stability regions on Meta-Smith charts can be determined, and source and load re∞ection coe-cients can be selected properly to obtain desired operating power gain. In addition, an example shows that Meta-Smith charts ofier a simple approach for matching network design using open-circuited single-stub shunt tuners.

Trapping Electron-Assisted Magnetic Recording Enhancement via Dielectric Underlayer Media

Trapping electron-assisted magnetic recording (TEAMR) has been recently proposed as a method of lowering the magnetic anisotropy of magnetic data storage media during write cycles. In this paper, we studied theoretically the TEAMR feasibility when an additional dielectric nano-underlayer is incorporated within the recording medium. We report a comparative study between a standard TEAMR data storage system and a dielectric underlayer TEAMR system. Our results indicate a substantial improvement in the electron trapping mechanism when a dielectric underlayer is used. A direct consequence of the proposed system is the effective reduction of the local magnetic coercive field when using this modified TEAMR design, which opens up the possibility of future developments based on TEAMR technology.

Optical field enhancement for heat-assisted magnetic recording system using Photonic Crystal waveguide

The Photonic Crystal (PC) waveguide designed for the optical delivery system for HAMR is proposed. Two-dimensional (2D) models of the single-piece PC waveguides are initially designed using square and triangular lattice structures made of silicon surrounded by an array of air holes, with two input wavelengths of interest: 633 and 1,550 nm. The wave guiding component is formed by removing a center row of air holes with a 90° sharp turn created at the input, assuming a normal incident field to the waveguide. It is found that the designed triangular lattice structures can easily associate both transverse electric (TE) and transverse magnetic (TM) modes while only TE mode is possible for the square lattice. The numerical simulation shows that the overall transmission efficiency of both structures is greater than 75%, and almost 80% can be achieved especially with the TE rectangular lattice structure.

CCITL implementation using two-section microstrip transmission lines

Conjugately characteristic impedance transmission lines (CCITLs), possessing conjugate characteristic impedances (Z₀^±) of wave propagating in opposite directions, are implemented using a terminated finite lossless reciprocal periodic structure consisting of a unit cell of 2-section microstrip reciprocal lossless transmission lines (TLs). Numerical simulations show the Z₀^± magnitudes of 50±0.24% Ω with their respective arguments φ^± varying nearly 30° over the frequency range of interest. The S₂₁ magnitude measured from the fabricated 2-section microstrip TL decreases more rapidly with the frequency, than that of the 4-section and reference 50 Ω TLs. It is found that the 2-section TL structure is easier to fabricate than the 4-section structure, with acceptable CCITL characteristics at the certain operating frequency.

A study of Photonic Crystals bending waveguide laser tip for dental treatments

We propose a design and two dimensional (2D) simulation of a Photonic Crystals (PhC) slab waveguide laser tip with triangular lattices for dental treatments. The band diagram is computed in the transverse electric (TE) mode for triangular lattices of air holes in silicon substrate. The power transmission efficiencies of 90° and 120° bending structure with different sizes of defects are measured and compared with the straight waveguide. The result shows that for the bending structure, the efficiency depends relatively on both bending degree and defect size and for this particular design, the highest efficiency is achieved using the 120° structure with W2 defect.

Pattern Transfer Characterization after Double-Level Lithography for a Fabrication of the Three-Dimensional Aluminum Titanium Carbide Air Bearing Surface of the Hard Disk Slider

The transfer characteristics of the three-dimensional (3D) photoresist (PR) pattern to the aluminum titanium carbide (AlTiC) layer made for an air bearing surface (ABS) using the double-level lithography process and reactive ion etching (RIE) is investigated. The simulated process windows for single-level (conventional) and double-level lithography provide the process conditions to obtain desired PR thicknesses. The PR pattern with the underneath AlTiC layer is then etched with the designed recipe that consists of three consecutive etchings using CF4, O2, and CF4, respectively. The triple-step pattern is successfully formed on the AlTiC layer. The nonlinear relationship of the cumulative exposure and the PR thickness is believed to contribute to a decrease in etch selectivity of PR:AlTiC on the double-exposure area with the cumulative exposure.

Noise considerations in the design of potentially unstable microwave transistor amplifiers in the CCITL system

The noise considerations for a design of potentially unstable microwave transistor amplifier integrated with CCITLs are investigated. The bilinear transformation, with a verification using the CC approach, is employed to map graphical solutions from the Z0 system into the CCITL system. The magnitude of Fi decreases rapidly with GA, especially for larger phi, and more slowly as GA approaches MSG for every argument phi. In addition, it increases with the argument phi for every GA in the range of interest implying that smaller noise figures can be achieved at smaller phi values for this test transistor. A rapid increase of (VSWR)in values is observed as GA approaches MSG. This result indicates trade-offs between GA and the input VSWR to obtain the optimal performance in this test amplifier design in the CCITL system.

Investigation of Magnetoelectric Effect in the Bi-Layer Plate Structure

Recently, the magnetoelectric (ME) effect is widely studied to apply in sensing applications. This paper proposes the investigation of ME effect in the bi-layer plate structure, which is the structure that allows deformation in the thickness direction. Mathematical models of the ME coefficients are developed using the constitutive equations of magnetostrictive and piezoelectric. Two modes of interest include longitudinal-transverse (L-T) and transverse-transverse (T-T) modes. Applying the models to the nanolayer of Terfenol-D/PZT in the assumingly low frequency regime yields the optimal thickness ratio of 0.34 for both modes. The maximum ME coefficients for 5, 10, and 10 nm thick structures are equal but occur at different resonant frequencies. They are approximately 480 and 240 mV/Oe cm for T-T and L-T modes, respectively. The maximum ME coefficients of the Terfenol-D/PZT plate structure are sufficiently high for nanoscale magnetic sensing applications.

Fabrication Processes of SOI Structure for Optical Nonreciprocal Devices

Fabrication processes of a magneto-optic waveguide with a Si guiding layer for an optical isolator employing a nonreciprocal guided-radiation mode conversion are investigated. The optical isolator is constructed on a silicon-on-insulator (SOI) structure. The magneto-optic waveguide is fabricated by bonding the Si guiding layer with a cerium-substituted yttrium iron garnet (Ce:YIG). The relationship of waveguide geometric parameters is determined at a wavelength of 1550 nm. The results show that larger tolerance for isolator operation can be obtained at smaller gaps between Si and Ce:YIG. Bonding processes including photosensitive adhesive bonding and surface activated bonding are then compared. It is found that the surface activated bonding process is easier to control and more promising than the photosensitive adhesive bonding.

Compact wideband multi-section quarter-wave-like transformers

This paper proposes quarter-wave-like transformers (QWLTs) with unequal electrical lengths to miniaturize multi-section quarter wave transformers (QWTs) and to enhance the bandwidth. The proposed method extends a study of the approximate theory of small reflections (ATSR) for QWLTs called the extended approximate theory of small reflections (EATSR). The total input reflection coefficient is observed in the frequency range of interest. Results of the EATSR for both two-and three-section unit cells with 25% physical size reduction prove that their impedance bandwidths are broader than those of the standard multi-section QWTs and the ATSR for QWLTs.