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Cardiograph Extracts Time-Domain Heart Signals

PREVIOUS RESEARCH TACKLED the extraction of electro-cardiograph (ECG) like waveform signals from a microwave-cardiograph (MCG). Those signals were analyzed in both the frequency and time domains to obtain heart-motion features. Recently, this research evolved to focus on the extraction mechanism and the analysis of the captured MCG graphs, thanks to the efforts of Jun Zheng and Yong Huang from East China Normal University together with Jian Qian from Nanjing University. Their MCG application system comprises two horn antennas, an MCG system unit, an ECG, and a PC.

The system's microwave source is a continuouswave (CW) signal at 1.5 GHz, which comes from a phase-locked oscillator. This signal is sent through two directional couplers and a circulator. In the first coupler, a small portion of power is fed into a balanced mixer for signal extraction. In the second coupler, a small portion of power is fed into a digital attenuator and phase shifter for auto-carrier-wave cancellation. Roughly 70 percent of the emitted power is fed into the emitting antenna.

Carrier-wave cancellation is key to this system. In the carrier-wave cancellation process, a small part of power is taken directly from the source power as a canceling wave. The next step is to use a digital attenuator and digital phase shifter controlled by a microprocessor to adjust the amplitude and phase of the canceling wave. The canceling wave is then added to the received wave in an adder. Finally, a detector is used to check the sum of the adder. If the sum shown on the cancellation indicator is zero when adjusting, the system is zero balanced. See "Extraction Mechanism Study of the Microwave Cardio-Graph (MCG)," Microwave And Optical Technology Letters, October 2009, p. 2348.

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