• Journal of KSNVE
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• v.6 no.4
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• pp.513-519
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• 1996

This paper is concerned with the bubble sound at the accumulator which is generated by the difference of the high pressure side and the low pressure side in the cycle of the refrigerator. The causes of the bubble sound generation are verified by the visualized test of the operating refrigerant flow at the accumulator and the measurements of the temperature and pressure. Two cases were tested, one with the accumulator has a orifice and the other with the accumulator hasn't a orifice. So that, it is presented the comparison of the bubble sound levels and spectrums in each cases. To predict the bubble sizes when they are generated, the linearized equation driven by Strasberg is used.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.11
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• pp.1104-1112
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• 2013

This paper presents a wideband Colpitts voltage controlled oscillator(VCO) with nanosecond startup time and a center frequency of 8.35 GHz for a new bubble-type motion detector that has a bubble-layer detection zone at the specific distance from itself. The VCO circuit consists of two parts; one is a negative resistance part with a HEMT device and Colpitts feedback structure and the other is a resonator part with a varactor diode and shorted shunt microstrip line. The shorted shunt microstrip line and series capacitor are utilized to compensate for the input reactance of the packaged HEMT that changes from capacitive values to inductive values at 8.1 GHz due to parasitic package inductance. By tuning the feedback capacitors which determine negative resistance values, this paper also investigates startup time improvement with the negative resistance variation and tuning bandwidth improvement with the reactance slope variation of the negative resistance part. The VCO measurement shows the tuning bandwidth of 2.3 GHz(28 %), the output power of 4.1~7.5 dBm and the startup time of less than 2 nsec.