• 대한청각학회지
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• 제25권2호
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• pp.80-88
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• 2021

Background and Objectives: Non-linear frequency compression (NLFC) technology compresses and shifts higher frequencies into a lower frequency area that has better residual hearing. Because consonants are uttered in the high-frequency area, NLFC could provide better speech understanding. The aim of this study was to investigate the clinical effectiveness of NLFC technology on the perception of speech and music in patients with high-frequency hearing loss. Subjects and Methods: Twelve participants with high-frequency hearing loss were tested in a counter-balanced order, and had two weeks of daily experience with NLFC set on/off prior to testing. Performance was repeatedly evaluated with consonant tests in quiet and noise environments, speech perception in noise, music perception and acceptableness of sound quality rating tasks. Additionally, two questionnaires (the Abbreviated Profile of Hearing Aid Benefit and the Korean version of the International Outcome Inventory-Hearing Aids) were administered. Results: Consonant and speech perception improved with hearing aids (NLFC on/off conditions), but there was no significant difference between NLFC on and off states. Music perception performances revealed no notable difference among unaided and NLFC on and off states. The benefits and satisfaction ratings between NLFC on and off conditions were also not significantly different, based on questionnaires, however great individual variability preferences were noted. Conclusions: Speech perception as well as music perception both in quiet and noise environments was similar between NLFC on and off states, indicating that real world benefits from NLFC technology may be limited in Korean adult hearing aid users.

• Journal of Audiology & Otology
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• 제25권2호
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• pp.80-88
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• 2021

Background and Objectives: Non-linear frequency compression (NLFC) technology compresses and shifts higher frequencies into a lower frequency area that has better residual hearing. Because consonants are uttered in the high-frequency area, NLFC could provide better speech understanding. The aim of this study was to investigate the clinical effectiveness of NLFC technology on the perception of speech and music in patients with high-frequency hearing loss. Subjects and Methods: Twelve participants with high-frequency hearing loss were tested in a counter-balanced order, and had two weeks of daily experience with NLFC set on/off prior to testing. Performance was repeatedly evaluated with consonant tests in quiet and noise environments, speech perception in noise, music perception and acceptableness of sound quality rating tasks. Additionally, two questionnaires (the Abbreviated Profile of Hearing Aid Benefit and the Korean version of the International Outcome Inventory-Hearing Aids) were administered. Results: Consonant and speech perception improved with hearing aids (NLFC on/off conditions), but there was no significant difference between NLFC on and off states. Music perception performances revealed no notable difference among unaided and NLFC on and off states. The benefits and satisfaction ratings between NLFC on and off conditions were also not significantly different, based on questionnaires, however great individual variability preferences were noted. Conclusions: Speech perception as well as music perception both in quiet and noise environments was similar between NLFC on and off states, indicating that real world benefits from NLFC technology may be limited in Korean adult hearing aid users.

• 전력전자학회논문지
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• 제19권2호
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• pp.173-183
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• 2014

In this paper, an analysis of power losses for the three-level T-type and neutral-point clamped (NPC) PWM inverters is presented, in which the conduction and switching losses of semiconductor devices of the inverters are taken into account. In the inverter operation, the conduction loss depends on the modulation index (MI) and power factor (PF), whereas the switching loss depends on the switching frequency. Power losses for the T-type and NPC inverters are analyzed and calculated at the different operating points of MI, PF and the switching frequency, in which the four different models of semiconductor devices are adopted. In the case of lower MI, the NPC-type is more efficient than the T-type, and vice versa. The validity of the power loss analysis has been verified by the simulation results.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.795-800
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• 2008

The sound transmission loss is a key index to evaluate the acoustic performance of a car-body structure at the high frequency range. From this paper, a new validation method for in-situ sound transmission loss is proposed. First, in-situ sound transmission loss is measured by using PU intensity probe on the condition of complete vehicle. Second, validation test, which is consisted of internal, external and total frequency response function test, is performed by using volume acceleration source and microphones. Then, these test results are compared to validate the accuracy of in-situ sound transmission loss. Finally, the test result of in-site method is compared with results of two reverberant room test method and SEA analytical method. The reliability of in-situ method is confirmed by these procedures.

• Journal of Magnetics
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• 제6권2호
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• pp.66-69
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• 2001

The actual magnetic induction waveform of cores in electrical machines is not sinusoidal i.e. higher harmonics are always included. Thus the core loss in actual electrical machines is different from the core loss which is measured by the standard method, because the waveform of magnetic induction should be sinusoidal in the standard testing method. Core loss analysis under higher harmonic induction is always important in electric machine design. In this works we measured the core loss when a hysteresis loop has only one period of an ac minor loop of higher harmonic frequency, depending on the position of the ac minor loop of relative to the fundamental harmonic frequency. From this experiment, the core loss P(B/sub 0/f/sub 0/, B/sub h/, nf/sub 0/)) under a higher harmonic magnetic induction B/sub h/ could be expressed by the linear combination the core loss at fundamental harmonic frequency P/sub c/(B/sub 0/, f/sub 0/), the core loss of ac minor loop at zero induction region of the major hysteresis loop P/sub cL/ (B/sub h/, nf/sub 0/), and the core loss of an ac minor loop in the high induction region of the major hysteresis loop P/sub cH/ (B/sub h/, nf/sub 0/) i.e., P/sub c/, (B/sub 0/, f/sub 0/, B/sub h/, nf/sub 0/)=P/sub c/ (B/sub 0/, f/sub 0/,)+(n-1)[k₁(B/sub 0/) P/sub cL/ (B/sub h/, nf/sub 0/)+(1-k₁(B/sub 0/)) P/sub cH/ (B/sub h/, nf/sub 0/)]. This will be useful formula for electrical machine designers and one of effective methods to predict core loss including higher harmonic induction.

• Investigative Magnetic Resonance Imaging
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• 제20권1호
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• pp.36-43
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• 2016

Visualization of the tissue loss tangent property can provide distinct contrast and offer new information related to tissue electrical properties. A method for non-invasive imaging of the electrical loss tangent of tissue using magnetic resonance imaging (MRI) was demonstrated, and the effect of loss tangent was observed through simulations assuming a hyperthermia procedure. For measurement of tissue loss tangent, radiofrequency field maps ($B_1{^+}$ complex map) were acquired using a double-angle actual flip angle imaging MRI sequence. The conductivity and permittivity were estimated from the complex valued $B_1{^+}$ map using Helmholtz equations. Phantom and ex-vivo experiments were then performed. Electromagnetic simulations of hyperthermia were carried out for observation of temperature elevation with respect to loss tangent. Non-invasive imaging of tissue loss tangent via complex valued $B_1{^+}$ mapping using MRI was successfully conducted. Simulation results indicated that loss tangent is a dominant factor in temperature elevation in the high frequency range during hyperthermia. Knowledge of the tissue loss tangent value can be a useful marker for thermotherapy applications.

• ETRI Journal
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• 제42권6호
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• pp.827-836
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• 2020

Measuring the diffraction loss for high frequencies, long distances, and large diffraction angles is difficult because of the high path loss. Securing a well-controlled environment to avoid reflected waves also makes long-range diffraction measurements challenging. Thus, the prediction of diffraction loss at millimeter-wave frequency bands relies on theoretical models, such as the knife-edge diffraction (KED) and geometrical theory of diffraction (GTD) models; however, these models produce different diffraction losses even under the same environment. Our observations revealed that the KED model underestimated the diffraction loss in a large Fresnel-Kirchhoff diffraction parameter environment. We collected power-delay profiles when millimeter waves propagated over a building rooftop at millimeter-wave frequency bands and calculated the diffraction losses from the measurements while eliminating the multipath effects. Comparisons between the measurements and the KED and GTD diffraction-loss models are shown. Based on the measurements, an approximation model is also proposed that provides a simple method for calculating the diffraction loss using geometrical parameters.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2001년도 추계학술대회 논문집(Proceeding of the KOSME 2001 Autumn Annual Meeting)
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• pp.120-124
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• 2001

A new technique for improving the efficiency of single-phase high-frequency boost converter is proposed. This converter includes an additional low-frequency boost converter which is connected to the main high-frequency switching device in parallel. The additional converter is controlled at lower frequency. Most of the current flows in the low-frequency switch and so, high-frequency switching loss is greatly reduced accordingly Both switching device are controlled by a simple method; each controller consists of a one-shot multivibrator, a comparator and an AND gate. The converter works cooperatively in high efficiency and acts as if it were a conventional high-frequency boost converter with one switching device. The proposed method is verified by simulation. This paper describes the converter configuration and design, and discusses the steady-state performance concerning the switching loss reduction and efficiency improvement.

• International journal of advanced smart convergence
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• 제8권4호
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• pp.138-146
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• 2019

In this paper, we proposed a soft-switched synchronous buck converter, which can perform charging the battery. The proposed converter has low switching loss even at high frequency operation due to its soft switching characteristics. The converter operates in synchronous mode to minimize conduction loss, resulting in small conduction loss, also. In this reason, the efficiency of the converter can be greatly improved even in high frequency. The size and weight of the converter can be reduced by high frequency operation of the converter. In this paper, we designed a battery charger with a switching frequency of 100 kHz. The designed converter also simulated to prove the converter's characteristics of synchronous operation as well as soft switching operation. The simulation shows that the proposed converter always meets the soft switching conditions of turning on and off switching in the zero voltage and zero current states. Therefore, simulation results have confirmed that the proposed battery charger had soft switching characteristics. The simulation results for transient response to charge current for the designed converter show that the converter responds to charge current commands quickly within 0.05 ms.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.346-352
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• 2002

This paper is the experimental study to estimate the influence of various design parameters on the performance of mufflers with perforated tubes and through-flow partitions. Muffler types considered in the present work include through-flow chamber, through-flow chamber with partition, and cross-flow chamber. The influences of the design parameters on the performance of the mufflers can be outlined as follows. In the case of the through-f]ow type mufflers, increasing the tube thickness and the hole diameter of the perforated tubes does not change the maximum value of the transmission loss but decrease the cutoff frequency. In the case of the through-flow with partitions type mufflers, it is shown that combining a fe w short chambers and long chambers can modify the frequency locations of the resonance frequencies to optimize the performance of the mufflers. For the case of the cross-flow type mufflers, it is shown that the transmission loss of the mufflers is mainly affected by the lower porosity when the porosities are different in both sides of the plug. Overall, it is shown that performance of the through-flow type with partition type mufflers is excellent in the lower frequency region, where the cross-flow type mufflers have better performance in the higher frequency region.