NI PXI-Based Noncontact Doppler radar Vital Sign Detection System

This thesis proposal presents the motivation behind the work, approach, theoretical explanation of the topic, experimental results and future work of continuous-wave (CW) radar systems for noncontact measurement of respiration and mechanical vibrations using the nonlinear phase modulation effect. Lung cancer causes 28% of cancer deaths in the United States and a major challenge in the treatment of lung cancer is that the tumor is not stationary. Since radiotherapy requires high energy X-rays to kill the cancerous tumor, the concern remains how this can be achieved without affecting the surrounding healthy tissues. Conventionally there are two ways of radiotherapy to treat floating tumors namely- respiration gated radiotherapy and tumor tracking algorithm. And both these methods need respiration and heart-beat measurement. However, the current breathing measurements are either invasive and cause discomfort to the patient or lack the accuracy. This thesis proposes to measure breathing in a non-invasive way with high accuracy. While the concept of noncontact detection of vital signs has been demonstrated before 2000[1, 2], research efforts in this century have been moving the technology towards reality with advanced hardware and signal processing algorithms. Most vital sign detection systems need complicated RF/microwave circuit design [2, 3]. An instrument based Doppler radar system has been introduced for noncontact VSD, which offers a fast solution for an ordinary RF/microwave laboratory to carry out VSD research [4]. However, the VSD system in [4] is based on multiple bulky instruments and does not allow real-time signal processing and visualization.in this thesis, the transceiver has been built using National Instruments PXI system which has made the radar system one compact system requiring less space which makes this system advantageous over the non-contact vital sign detection systems built with microwave components. The proposed radar measures respiration in a non-invasive way. It directly measures the periodic motion of the body, which has better correlation with the lung tumor motion. Moreover, the radar system is insensitive to clothing and chest hair, due to microwave penetration, making it better than the existing contact devices that are sensitive to the surrounding environment. During experiment, a RF single frequency continuous carrier at 2.4GHz has been generated by the transmitter via a 2.4GHz patch antenna and sent to the subject seated at a distance of about a few centimeters from the radar system. The subject should ideally be stationary and breathing normally. The periodic breathing movement of the subject modulates the phase of the carrier. The modulated carrier is received by the radar via another 2.4GHz patch antenna at the input of the receiver. Moreover, the system is capable of performing real –time signal processing simultaneously with data acquisition implemented entirely in LabVIEW. DC calibration has been done by implementing compressed sensing and DACM (Differentiate and Cross Multiply) phase demodulation technique has been used to extract the phase of the carrier. In addition to phase demodulation, the null point problem, present in I/Q constellation has also been avoided with the help of phase shift implemented in the same program in LabVIEW.