• Journal of the Korean Society of Radiology
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• v.16 no.4
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• pp.435-442
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• 2022

The heel effect creates a density difference in the X-ray images because the intensity of the anode and cathode side of the X-ray tube is not equal. The purpose of this study is to evaluate the density difference due to the heel effect by rotating the step wedge by 180 degrees and then changing the distance. After fixing the tube voltage and tube current to 72 kVp and 10 mAs, the forward and reverse directions were taken using a step wedge. At this time, the distance (80 cm ~ 130 cm) was taken at 10 cm intervals, and the density value was measured by setting the region of interest for each step of the step wedge through the M6 program. First, the difference in intensity between the anode and the cathode was confirmed through the radiation exposure test. In addition, when the distance (from 80 cm to 130 cm) was changed, the difference in density between the cathode and the anode decreased as the projection distance increased. As a result, images of uniform density can be obtained as the projection distance increases.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.8
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• pp.880-886
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• 2007

We have proposed a new "hybrid" envelope elimination and restoration(EER) transmitter architecture using an efficiency optimized power amplifier(PA) and modified bias modulator. The efficiency of the PA at the average drain voltage is very important for the overall transmitter efficiency because the PA operates mostly at the average power region of the modulation signal. Accordingly, the efficiency of the PA has been optimized at the region. Besides, the bias modulator has been accompanied with the emitter follower for the minimization of memory effect. A saturation amplifier, class $F^{-1}$ is built using a 5-W PEP LDMOSFET for forward-link single-carrier wideband code-division multiple-access(WCDMA) at 1-GHz. For the interlock experiment, the bias modulator has been built with the efficiency of 64.16% and peak output voltage of 31.8 V. The transmitter with the proposed PA and bias modulator has been achieved an efficiency of 44.19%, an improvement of 8.11%. Besides, the output power is enhanced to 32.33 dBm due to the class F operation and the PAE is 38.28% with ACLRs of -35.9 dBc at 5-MHz offset. These results show that the proposed architecture is a very good candidate for the linear and efficient high power transmitter.