Study On Detection Of Human Respiratory Movement Based On Continuous Terahertz Wave

Terahertz wave is electromagnetic wave of 0.1 to 10 THz in frequency, between the microwave and far infrared wave, which is localized in the transition field from electronics to optics in theoretical physics. So it has many unique characteristics, such as low photonic energy, non-damage for biological tissue, the high transmission for most of non-polar and non-metallic materials, the characteristic spectrum for biological macromolecules and so on. These characteristics of terahertz wave support the promising application of terahertz technology in biomedicine. So far, it has great achievement in terahertz radiation effect, terahertz spectrum, and terahertz imaging and so on. However, the study on terahertz application in non-contact detecting human physiological signals is not reported. Whether the terahertz wave can be used in non-contact detection of human physiological signals and related physiological parameters remains to be explored and studied.The micro-motion of human external surface caused by various physiological activities contains abundant physiological information. The detection and analysis of the micro-motion are helpful in clinical diagnosis, health monitoring, and so on. Existing researches shows that the body surface micro-motion includes not only the frequency information of physiological signals, but also quantitative physiological parameters. Therefore, quantitative detection of human body surface micro-motion has practical clinical significance. The main existing method for detecting micro-motion is contact-type detection, but this method disturbs the objectivity of detecting results. Non-contact detection has good advantages. Currently, it mainly apply the optical and biological radar technology for non-contact detection micro-motion. The former is difficult to penetrate clothing or bedding, etc., and the latter is hard to detect the quantitative information of micro-motion.To solve these problems, this issue carried out the basic research on non-contact detection of physiological parameters with continuous terahertz wave, which mainly explore whether and how to detect quantitative information of human external surface micro-motion using terahertz wave. And the non-contact detection of human respiratory movement as the starting point, research methods and theory of detection of human respiratory motion and surface displacement based on continuous terahertz wave. The main works include these contents as following.(1) A complete method and theory of detecting human respiratory movement based on continuous terahertz wave was proposed, which include the analysis of respiratory mechanics model, the development of basic principle, and the establishment of mathematical model.(2) The radiation intensity distribution in transverse section cross-section of collimated terahertz wave in far field was studied in experiments and theory. With two-dimensions scanning point imaging technology, the experiment was carried out, And we resolved and proved the experimental result in theory. That provides the theoretical basis for mathematical model.(3) The terahertz experiment system for detecting human respiratory movement was designed and setup in two-side and single-side assignment. The proposed method was realized in hardware. And the procedure of system adjustment and collimation was summarized. In software, the real-time terahertz data acquisition system based on Lab VIEW with USB data acquisition interface were developed, which can be used for the real-time acquisition, display and record of human respiratory signals.(4) In order to solve the difficulties of terahertz wave calibration, we proposed a method of collimated terahertz wave in far field based on the research result of the radiation intensity distribution in transverse section cross-section of collimated terahertz wave in far field. This method improves the precise of terahertz system.(5) The high precise simulation model of human external surface micro-motion for this study was developed. With this model, we carried out the simulation experiments. For verifying the feasibility of the proposed approach and evaluating the performance of terahertz detection system, the synchronous comparison experiments were carried out. The performance of terahertz system was totally evaluated.(7) In order to verify the feasibility of terahertz detection system for detecting human respiratory movement, we carried out the human target experiments. The respiratory belt transducer and Power Lab data acquisition system were employed as reference devices. Through the synchronous comparison of results measured by both methods, the precision and stability of terahertz system for human target in the different testing position and different respiration type were studied.With above work, the main result and conclusion of this study is as following:(1) Using lateral position of subjects, we solved the basic difficulty that terahertz cannot penetrate human body, and proposed an approach for non-contact detecting respiratory movement based on continuous terahertz wave. Detecting human respiratory movement using terahertz wave was feasible theoretically.(2) With experiments and theoretical proof, the radiation intensity distribution of collimated terahertz wave in the transvers section in far field can be approximately uniform plane wave.(3) We proposed a calibration method about the collimated terahertz wave in far field, half-value method. The proposed calibration method ensures the effect of mathematical model and improves the precision of terahertz detecting system.(4) The simulation model of human external surface micro-motion for this study was developed. It is composed of custom-made water module and linear guide rail. The basic principle is same as the proposed method. The simulation model has the characteristics of the high precision and controllability of parameters.(5) The results of simulation experiments show that the method of detecting the displacement of micro-motion target based on continuous terahertz wave can precisely detecting the displacement and frequency information of micro-motion. In the typical range of human micro-motion and respiratory movement, the results is precise and reliable.(6) The experimental results of human target indicate that the proposed method is feasible and effective for human target. For the respiratory movement in different amplitude and frequency, this method can always obtain the displacement information of human external-surface micro-motion and the respiratory signals with precise frequency information. The supine position and sitting with backrest-chair position can effectively decrease the effect of the body motion and improve the precision of terahertz detecting system and are the prior testing position.(7) The displacement changes of chest wall is approximately linearly relative to the circumferences changes of cross-section of chest wall. The linear relationship was deducted as : DL ?( 2p -4) Dx.The main innovation of this study is as following:(1) This study firstly proposed an approach for detecting human respiratory movement based on continuous terahertz wave, and established relevant mathematical model. With this approach, we not only detect the frequency information of human respiratory movement but also the displacement of micro-motion on the human external surface. We designed and setup a terahertz detecting system, and evaluated the performance of this system with the simulation and human target experiments.(2) The radiation intensity distribution of collimated terahertz wave in far field were firstly studied. The approximate uniform distribution of the radiation intensity distribution of collimated terahertz wave in far field was proved in experiment and theory. So far, we can’t see any reports about the terahertz wave in far field. Therefore, this study not only establishes the theoretical basis for mathematical model, and also provides the theoretical basis for the future possible application of terahertz wave in far field.(3) A new calibration method for the collimated terahertz wave in far field, half-value method, was proposed. Based on the research results of the radiation intensity distribution of collimated terahertz wave in far field, original the calibration problem of principle axis of terahertz wave was converted into the calibration problems about the geometry center of terahertz wave. With the symmetry principle in geometry, we finished the calibration of terahertz wave in far field, and improved the precision of terahertz system.The propose method of detecting the displacement of human external-surface micro-motion and the respiratory movement can’t caused the damage for human tissues, and belong to the non-contact detecting methods. It can not only obtain the displacement information of micro-motion on external surface but also penetrate the cloth, bedding, dressing and so on. It overcomes the limitations of existing detecting technology and methods. Furthermore, the proposed method has good features in real-time, without complicated algorithm or the time cumulative effect.This paper carried out the explored basic research about that continuous terahertz wave non-contact detecting the human respiratory movement and displacement of micro-motion, and had important theoretical significance in non-contact detecting physiological parameters based on terahertz wave. Meanwhile, because the displacement of human external surface micro-motion has actual meaning in clinical, so this study has promising prospects in non-contact detecting physiological parameters in clinical, accurate radiotherapy for real-time tracking tumor, and remove the respiratory movement artifacts in medical imaging.