Zobrazeno 1 - 10
of 153
pro vyhledávání: '"Hojong Choi"'
Publikováno v:
Applied Sciences, Vol 14, Iss 19, p 9097 (2024)
The focal length in a typical optical system changes with the angle of view, according to the size of the sensor. This study proposed an optical terahertz (THz) system application where the focal length changed while the angle of view was fixed; thus
Externí odkaz:
https://doaj.org/article/6f7b909030d94d218af1e577bccfecb8
Publikováno v:
Photonics, Vol 11, Iss 4, p 303 (2024)
In an optical system with multiple lens groups and increased zoom magnification levels, achieving a smooth zoom locus is increasingly difficult. Traditional methods for calculating zoom loci often involve complex and time-consuming formulas. Conseque
Externí odkaz:
https://doaj.org/article/fa4cf5ad08b74528862cc03e25c59557
Publikováno v:
Applied Sciences, Vol 14, Iss 4, p 1518 (2024)
The numerical aperture (NA) of objective lens optical (inspection) systems has been increased to achieve higher resolution. However, the depth of focus decreases with an increase in the NA, and focusing becomes difficult. Therefore, the entire optica
Externí odkaz:
https://doaj.org/article/1b680c564f5242afbb8fc5ad1cc67693
Autor:
Hojong Choi
Publikováno v:
Sensors, Vol 24, Iss 3, p 786 (2024)
In diagnostic ultrasound imaging applications, preamplifiers are used as first-stage analog front-end amplifiers for ultrasound transducers because they can amplify weak acoustic signals generated directly by ultrasound transducers. For emerging diag
Externí odkaz:
https://doaj.org/article/c0f12021c91a47c2b567b8e9fe2c4288
Autor:
Hojong Choi
Publikováno v:
Micromachines, Vol 14, Iss 7, p 1342 (2023)
A design analysis of the power amplifiers developed for ultrasound applications was conducted because ultrasound applications require different types of power amplifiers, which are one of the most critical electronic components in ultrasound systems.
Externí odkaz:
https://doaj.org/article/6834ba24b8e645ee9589f453b2ca4516
Autor:
Hojong Choi
Publikováno v:
Sensors, Vol 23, Iss 9, p 4438 (2023)
The gain of class-C power amplifiers is generally lower than that of class-A power amplifiers. Thus, higher-amplitude input voltage signals for class-C power amplifiers are required. However, high-amplitude input signals generate unwanted harmonic si
Externí odkaz:
https://doaj.org/article/7a0e1483a0c846ecbf923b435939061d
Autor:
Hojong Choi
Publikováno v:
Sensors, Vol 23, Iss 7, p 3466 (2023)
An inverse Class-E power amplifier was designed for an ultrasound transducer. The proposed inverse Class-E power amplifier can be useful because of the low series inductance values used in the output matching network that helps to reduce signal disto
Externí odkaz:
https://doaj.org/article/868bb67e874e457f8a632dc9c1b2a7fc
Autor:
Hojong Choi
Publikováno v:
Sensors, Vol 23, Iss 5, p 2406 (2023)
The ultrasound instrumentation uses linear power amplifiers with low power efficiency, generating unwanted heat and resulting in the deterioration of the echo signal quality of measured targets. Therefore, this study aims to develop a power amplifier
Externí odkaz:
https://doaj.org/article/3b90faf878f64bff92bd19c465fb5dbd
Publikováno v:
Biosensors, Vol 12, Iss 12, p 1154 (2022)
The photoacoustic (PA) effect occurs when sound waves are generated by light according to the thermodynamic and optical properties of the materials; they are absorption spectroscopic techniques that can be applied to characterize materials that absor
Externí odkaz:
https://doaj.org/article/6d549c32093c4d6aabe410c099a807e7
Autor:
Hojong Choi, Seung-Hyeok Shin
Publikováno v:
Sensors, Vol 22, Iss 24, p 9709 (2022)
Ultrasound systems have been widely used for consultation; however, they are susceptible to cyberattacks. Such ultrasound systems use random bits to protect patient information, which is vital to the stability of information-protecting systems used i
Externí odkaz:
https://doaj.org/article/3391e8600627429ea654c542fba305c8