• Journal of electromagnetic engineering and science
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• v.16 no.4
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• pp.206-209
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• 2016

This letter proposes a reconfigurable directional coupler that uses a variable impedance mismatch reflector to achieve high isolation characteristics in the antenna front end. The reconfigurable coupler consists of a directional coupler and a single-pole four-throw (SP4T) switch with different load impedances as a variable load mismatch reflector. Selection of the load impedance by the reflector allows cancellation of the reflected signal due to antenna load mismatch and the leakage from the input to isolation port of the directional coupler, resulting in high isolation characteristics. The performance of the proposed architecture in separating the received (Rx) signal from the transmitted (Tx) signal in the antenna front end was verified by implementing and testing the reconfigurable coupler at 917 MHz for UHF radio-frequency identification (RFID) applications. The proposed reconfigurable directional coupler showed an improvement in the isolation characteristics of more than 20 dB at the operation frequency band.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.8 s.251
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• pp.931-940
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• 2006

Defect assessment of a weld zone is important in fitness-for-service evaluation of plant components. Typically a J and $C^*$ estimation method for a defective homogeneous component is extended to a mismatched component, by incorporating the effect due to the strength mismatch between the weld metal and the base material. The key element is a mismatch limit load. For instance, the R6/R5 procedure employs an equivalent material concept, defined by a mismatch limit load. A premise is that if a proper mismatch limit load solution is available, the same concept can be used for any defect location (either a weld centre defect or a heat affected zone (HAZ) defect) and for any material combination (either two-material or multi-material combinations; either similar or dissimilar joints). However, validation is still limited, and thus a more systematic investigation is needed to generalise the suggestion to any geometry, any defect location and any material combination. This paper describes the effect of structural geometry on the $C^*$ integral for defective similar welds, based on systematic elastic-creep 2-D and 3-D finite element (FE) analyses, to attempt to elucidate the questions given above. It is found that the existing 'equivalent material' concept is valid only for limited cases, although it provides conservative estimates of $C^*$ for most of cases. A modification to the existing equivalent material concept is suggested to improve accuracy.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.5
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• pp.411-418
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• 2008

In this work, the effect of strength mismatch on plastic limit loads is quantified for similar metal weld plates with cracks under tension load, via three-dimensional, small strain elastic-perfectly plastic finite element analyses. Relevant variables related to plate geometry and crack length are systematically varied, in addition to the weld width. An important finding is that mis-match limit loads can be uniquely quantified through strength mis-match ratio and one geometry-related parameter. Based on the proposed limit load solutions, reference stress based J-integral estimates is also investigated. When the reference stress is defined by the mis-match limit load, predicted J-integral values agree overall well with FE results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.1
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• pp.68-75
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• 2012

The load-insensitivity of the balanced power amplifier(PA) for W-CDMA handset applications is analyzed. The load impedances of the two parallel amplifiers in the balanced PA depending on the output load mismatch are mathematically calculated and with the result, the phase of reflection coefficient at which the linear output power is severely degraded is investigated. From the analysis, we proposed that the linearity of the balanced PA at the phase can be improved by properly increasing the transistor size and thus, multiple balanced PA's with different transistor size are designed and simulated. The simulation result showed that the balanced PA with larger transistor size has improved linear output power under VSWR=4:1.

• Journal of Mechanical Science and Technology
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• v.14 no.1
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• pp.30-38
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• 2000

This paper presents a framework how to estimate crack driving forces in terms of crack-tip opening displacement and J-integral for mismatched dissimilar joints with interface cracks. The mismatch in elastic, thermal, and plastic hardening properties is not considered, but the mismatch in plastic yield strengths is emphasized here. The main outcome of the present work is that the existing methods to estimate crack driving forces for homogeneous materials can be used with slight modification. Such modification includes (i) mismatch- corrected limit load solutions, and (ii) evaluating the contribution of each material in dissimilar joints to the total crack driving force, which depends on the strength mismatch of the dissimilar joints.

• Journal of Mechanical Science and Technology
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• v.17 no.12
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• pp.1928-1937
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• 2003

Effect of elastic modulus mismatch on the contact crack initiation is investigated to find major parameters in designing desirable surface-coated system. Silicon nitride coated soft materials with various elastic modulus mismatch, E$\_$c//E$\_$s/＝1.06∼356 are prepared for the analysis. Hertzian contact test is conducted for producing contact cracks and the acoustic emission detecting technique for measuring the critical load of crack initiation. The implication is that coating thickness and material strength are controllable parameters to prevent the initiation of contact cracks resulted from the elastic modulus mismatch in the hard ceramic coating layer on the soft materials.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.396-401
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• 2003

In the present study, preliminary investigation were carried out by analysis of energy system(heat and electricity) based on phosphoric acid fuel-cell of 50 kW for eco-apartment houses. Analysis model were consisted of fuel cell energy system, secondary energy unit and residential building of 5 stories with 20 and 40 households. And the investigation results reviewed under load pattern of heat and electric power of the apartment houses. The results showed mismatch between the needed heat load pattern and output of fuel cell energy system. The mismatch rate were assessed about 10-180% of heat load for apartment houses with season. We found that secondary energy unit are needed in order to supply insufficient heat.

• Journal of the Korean Ceramic Society
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• v.35 no.1
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• pp.48-54
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• 1998

The effect of coating thickness on the contact fracture was studied, in Si3N4 coated Si3N4-BN system When the elastic/plastic mismatch is relatively large betwen two layers in bilayer certain critical coating thickness was required to prevent cone crack initiation and this critical thickness was decreased by de-creasing the elastic/plastic mismatch,. In addition the required critical thickness should be increased when higher loads apply. In conclusion an appropriate coating thickness should be designed by elastic/plastic mismatch between two layers and environment (applied load) to prevent the coating fracture

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1830-1835
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• 2007

In the present work, the effect of strength mismatch on plastic limit loads is quantified for strength-mismatched plates with constant-depth surface cracks under tension, via three-dimensional, small strain elastic-perfectly plastic finite element analyses. Relevant variables related to plate and crack geometries are systematically varied, in addition to the weld width. An important finding is that a parameter related to the weld width-to-ligament ratio is proposed, based on which limit loads can be uniquely quantified. The proposed limit load solutions is a valuable input to estimate nonlinear fracture mechanics parameters based on the reference stress approach.

• Journal of Mechanical Science and Technology
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• v.17 no.11
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• pp.1638-1649
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• 2003

A study is made on the characterization of damage tolerance by spherical indentation in hardly coated layer structure with modest elastic modulus mismatch. A hard silicon nitride is prepared for the coating material and silicon nitride with 5wt% of boron nitride composites for underlayer. Hot pressing to eliminate the effect of interface delamination during the fracture makes strong interfacial bonding. The elastic modulus mismatch between the layers is not only large enough to suppress the surface crack initiation from the coating layer but sufficiently small to prevent the initiation of radial crack from the interface. The strength degradation of the layer structure after sphere contact indentation does not significantly occur, while the degradation of silicon nitride-boron nitride composite is critical at a high load and high number of contacts.