A Sleep Monitoring Device and Method Based on a Fiber Optic Michelson Interferometer

Abstract

The present invention relates to the fields of fiber optic sensing technology and sleep monitoring, and particularly to a sleep monitoring device and method based on a fiber optic Michelson interferometer. On the one hand, the present invention significantly improves the sleep monitoring sensitivity through phase demodulation, and can accurately monitor the heartbeat, respiration and other weak signals generated during the sleep process. On the other hand, through the simultaneous monitoring of multiple sensor signals and data fusion analysis, the accuracy of the respiration and heartbeat signals required for sleep assessment can be improved, and the body movement information of the human body during the sleep process can be monitored. The present invention can effectively improve the sleep monitoring sensitivity, avoid the problem that the Mach-Zehnder interferometer is vulnerable to polarization interference, and can also realize body movement monitoring through multiple sensors.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology and sleep monitoring, and in particular to a sleep monitoring device and method based on an optical fiber Michelson interferometer. Background Art

[0002] Sleep is an important physiological process that is indispensable for maintaining human physiological functions, promoting cognitive function recovery, and ensuring physical and mental health. Its monitoring technology has received widespread attention in recent years. Traditional polysomnography (PSG) systems have inherent defects such as complex equipment to wear, limited detection environment, high cost, and great impact on sleep. It is difficult to meet the needs of long-term continuous monitoring in home scenarios. In recent years, sleep monitoring sensor systems with less impact on sleep have received a lot of attention.

[0003] Existing sleep monitoring sensor systems are mainly divided into two categories: contact and non-contact. The contact solution mostly uses wearable devices. The national invention patent application "A wristband sleep monitoring device" (publication number: CN102499656A, publication date: 2012-06-20) discloses a wristband sleep monitoring device that obtains physiological signals through a pulse sensor and a temperature sensor. However, such devices have problems such as discomfort when worn and signals are easily interfered by motion artifacts, and long-term use compliance is poor. In the non-contact solution, millimeter wave radar (such as "A sleep monitoring method and system based on millimeter wave radar and pressure sensor" (publication number: CN118965265A, publication date: 2024-11-15)) and video image analysis system (such as a non-contact sleep monitoring method and system, ZL201510166500.7) can achieve non-sensing monitoring, but the former is susceptible to electromagnetic interference and cannot distinguish signals from multiple beds, and the latter has privacy leakage risks and occlusion failure defects.

[0004] In recent years, mattress-type monitoring devices in non-contact sensing systems have gradually become a research hotspot due to their characteristics of no need to wear and non-sensitive detection. The technical implementation paths are mainly divided into two categories: piezoelectric film sensing and optical fiber sensing: Mattress-type sleep monitoring system based on piezoelectric film sensor (publication number CN116649890A, publication date: 2023-08-29) is based on the piezoelectric effect of polyvinylidene fluoride (PVDF), and generates charge signals by detecting micro-strain on the surface of the mattress. Although this type of solution has the advantages of low cost and easy integration, it is limited by the stiffness and sensitivity threshold of piezoelectric materials, and has insufficient response capabilities to low-frequency weak signals (such as breathing signals <0.5Hz). In addition, the temperature and humidity sensitivity of piezoelectric film causes significant signal baseline drift, requiring temperature calibration.

[0005] Compared with electrical sensors, fiber optic sensors have the advantages of high sensitivity, compact structure, light weight, electromagnetic interference resistance, easy multiplexing, etc. Moreover, the solution based on fiber optic sensors has no electrical devices at the sensor end, providing higher security. Currently, most non-contact sleep monitoring systems based on fiber optic sensors adopt fiber Bragg grating or fiber microbend pressure sensing structures. The national invention patent application "Method for Monitoring Human Sleep Health Based on Fiber Bragg Grating Sensors" (Publication No.: CN114469004A, Publication Date: May 13, 2022) discloses a device and method for monitoring human sleep health based on fiber Bragg grating sensors. The national invention patent "Sleep Quality Monitoring Device and Method Based on Fiber Microbend Pressure Sensing" (ZL201910728687.3) discloses a sleep quality monitoring device and method based on fiber microbend pressure sensing. The above two solutions achieve signal sensing based on wavelength demodulation and light intensity demodulation respectively, with relatively low sensing sensitivity. The literature (Sleep condition detection and assessment with optical fiber interferometer based on machine learning. iScience. 2023 Jun 30;26(7):107244) demonstrates a sleep monitoring method based on a Mach-Zehnder interferometer. However, this method has two drawbacks: one is that the Mach-Zehnder interferometer is vulnerable to polarization perturbations, which may distort the measured signal and generate false signals; the other is that there is only one interferometer on the entire mattress, and it cannot separately sense and distinguish signals from different parts of the body. Summary of the Invention

[0006] To overcome the problems existing in the existing mattress-based sleep monitoring methods, the present invention provides a sleep monitoring device and method based on a fiber optic Michelson interferometer, implanting a fiber optic Michelson interferometer sensor array into the mattress to achieve non-contact monitoring of sleep states; on the one hand, the present invention significantly improves the sleep monitoring sensitivity through phase demodulation, and can accurately monitor the heartbeat, respiration and other weak signals generated during sleep; on the other hand, through the simultaneous monitoring of multiple sensor signals and data fusion analysis, it can improve the accuracy of the respiration and heartbeat signals required for sleep assessment, and monitor the body movement information of the human body during sleep. The present invention can effectively improve the sleep monitoring sensitivity, avoid the problem that the Mach-Zehnder interferometer is vulnerable to polarization interference, and can also achieve body movement monitoring through multiple sensors.

[0007] To achieve the above technical objectives, the present invention provides a sleep monitoring device based on a fiber optic Michelson interferometer. The device includes: a single-frequency laser, a fiber optic beam splitter, a sensing array, a multi-channel photodetector, and a signal acquisition and processing module; the output end of the single-frequency laser is connected to the input end of the fiber optic beam splitter for emitting laser light; the N output ends of the fiber optic beam splitter are respectively connected to the N input ends of the sensing array for splitting a beam of light into N beams of light; the N output ends of the sensing array are respectively connected to the N input ends of the multi-channel photodetector, and the multi-channel photodetector is used to convert the optical signal into an electrical signal; the output end of the multi-channel photodetector is connected to the signal acquisition and processing module, and the signal acquisition and processing module is used to achieve the acquisition and phase demodulation of the sensing array signal and extract the respiration, heartbeat signals and body movement information at different positions of the human body; the sensing array is composed of N fiber optic Michelson interferometers, and the N fiber optic Michelson interferometers are implanted at different positions of the mattress for sensing the signals generated during the sleep process at different positions of the human body, where N is an integer greater than 1.

[0008] Further, the single-frequency laser can be a single-frequency tunable laser or an untunable laser;

[0009] Further, Faraday rotators are respectively connected to the ends of the two arms of the fiber optic Michelson interferometer to overcome the interference of polarization fading;

[0010] The present invention also provides a sleep monitoring method based on the above device, and the method is divided into the following steps:

[0011] S1. The output light of the single-frequency laser is split into N beams of light by the fiber optic beam splitter;

[0012] S2. The N beams of light output by the fiber optic beam splitter respectively enter the N fiber optic Michelson interferometers through the N input ends in the sensing array;

[0013] S3. The N fiber optic Michelson interferometers are implanted at different positions of the mattress. When a person lies on the mattress, the signals generated during the sleep process cause the fibers of the N fiber optic Michelson interferometers to deform, resulting in a change in the phase of the output light of the N fiber optic Michelson interferometers;

[0014] S4. The output optical signal of the fiber optic Michelson interferometer enters the multi-channel photodetector through the N output ends of the sensing array, and the optical signal is converted into an electrical signal by the multi-channel photodetector;

[0015] S5. The electrical signal output by the multi-channel photodetector enters the signal acquisition and processing module for processing to demodulate the phase signals of the N fiber optic Michelson interferometers. For the specific demodulation process, refer to the national invention patent "A Fiber Optic Sensing and Demodulation Method and Device Based on an Electro-Optic Phase Modulator" (ZL 202210853498.0).

[0016] S6. The signal acquisition and processing module processes the phase signals of the N demodulated fiber optic Michelson interferometers, extracts the respiration and heartbeat signals at different positions of the human body, and infers the sleep body movement state based on the characteristics of the signal energy and frequency collected by the fiber optic Michelson interferometers at different positions, as follows:

[0017] S6.1 Perform filtering processing on the phase signals of the N demodulated fiber optic Michelson interferometers to extract the respiration and heartbeat signals of different parts of the human body. The filtering processing method is the Butterworth band-pass filtering method, and the specific filtering frequency band range refers to the current standard "Specification for Machine Analysis and Interpretation of Sleep Monitoring Signals" (T / CPAM 002-2020).

[0018] S6.2 Calculate the band energy of the respiration and heartbeat signals of different parts of the human body. The energy size reflects the distance between the sensor and the heart. Based on the band energy and the distribution of the sensor array on the mattress, determine the position of the human heart, where the respiration and heartbeat signals collected by the sensor at this position have the highest accuracy.

[0019] S6.3 Based on the band energy of the sleep signals collected by the N sensors and the distribution of the sensor array on the mattress, the distribution of the total energy generated by human sleep on the mattress can be obtained. The movement of different parts of the human body will cause changes in the energy distribution. By comparing the energy distribution at adjacent times, it can be judged whether different parts of the human body move on the mattress. By synthesizing the position changes of different parts of the human body, the night sleep body movement information can be obtained.

[0020] The present invention has the following beneficial effects:

[0021] On the one hand, the fiber optic Michelson interferometer overcomes the interference of polarization perturbation on the monitoring process, improves the sensitivity of sleep signal monitoring, and can accurately monitor the heartbeat, respiration and other weak signals generated during sleep; on the other hand, by implanting multiple fiber optic Michelson interferometers at different positions of the mattress, accurate monitoring of sleep signals at different positions of the human body can be realized, which can effectively improve the accuracy of respiration and heartbeat signals required for sleep assessment, and at the same time, the monitoring of human activities during sleep can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described in detail below with reference to the drawings

[0023] Figure 1 is a schematic structural diagram of a specific embodiment of the present invention;

[0024] In the figure: 2 is a single-frequency laser, 3 is an optical fiber beam splitter, 4 is a multi-channel photodetector, 5 is a signal acquisition and processing module, and 6-N are fiber optic Michelson interferometers in the sensing array.

[0025] The output end 21 of the single-frequency laser 2 is connected to the input end 31 of the optical fiber beam splitter 3, and the output ends 32 - 3N of the optical fiber beam splitter 3 are respectively connected to the input ends 61, 71......N1 of the fiber optic Michelson interferometers 6 - N in the sensing array. The output ends 62, 72......N2 of the interferometers 6 - N are respectively connected to the input ends 42 - 4N of the multi-channel photodetector 4, and the output end 41 of the photodetector 4 is connected to the input end 51 of the signal acquisition and processing module 5.

[0026] Figure 2 It is a schematic structural diagram of the mattress device provided with the fiber optic Michelson interferometer sensing array;

[0027] In the figure: 1 is the mattress, and the black dots are the fiber optic Michelson interferometers in the sensing array.

[0028] The interferometers are arranged within the areas 11, 12, 13, 14 of the mattress 1 to sense the signals generated by different parts of the human body during sleep.

[0029] Figure 3 It is the respiratory signal waveform with the highest accuracy in one embodiment;

[0030] Figure 4 It is the heartbeat signal waveform with the highest accuracy in one embodiment;

[0031] Figure 5 It is the energy distribution diagram of N sensors on the mattress at a certain moment in one embodiment;

[0032] In the figure: 6 - N on the horizontal axis represents the sensor serial number, and the vertical axis value represents the magnitude of the respiratory and heartbeat signal band energies collected by the sensors. Detailed implementation manners

[0033] Now, various exemplary embodiments of the present application will be described in detail with reference to the accompanying drawings. It should be noted that: Unless otherwise specifically stated, the relative arrangements of components and steps, numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present application.

[0034] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present application, its application, or its use.

[0035] Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such technologies, methods, and devices should be regarded as part of the specification.

[0036] In all the examples shown and discussed here, any specific values should be construed as merely exemplary and not as a limitation. Thus, other examples of the exemplary embodiments may have different values.

[0037] As Figure 1 shown, the sleep monitoring device based on a fiber optic Michelson interferometer of this embodiment includes a single-frequency laser 2, a fiber optic beam splitter 3, a multi-channel photodetector 4, a signal acquisition and processing module 5, and fiber optic Michelson interferometers 6-N in a sensing array. The output end 21 of the single-frequency laser 2 is connected to the input end 31 of the fiber optic beam splitter 3. The output ends 32-3N of the fiber optic beam splitter 3 are respectively connected to the input ends 61, 71......N1 of the fiber optic Michelson interferometers 6-N in the sensing array. The output ends 62, 72......N2 of the interferometers 6-N are respectively connected to the input ends 42-4N of the multi-channel photodetector 4. The output end 41 of the photodetector 4 is connected to the input end 51 of the signal acquisition and processing module 5.

[0038] As Figure 2 shown, the mattress device provided with a fiber optic Michelson interferometer sensor array in this embodiment includes a mattress 1 and fiber optic Michelson interferometers in a sensing array. The interferometers are represented by black dots and are arranged in areas 11, 12, 13, 14 in the mattress 1 to sense signals generated during the sleep process at different positions of the human body.

[0039] The specific implementation manner of the present invention is as follows:

[0040] S1. The output light of the single-frequency laser 2 is split into N beams of light by the fiber optic beam splitter 3;

[0041] S2. The N beams of light output from the output ends 32-3N of the fiber optic beam splitter 3 respectively enter the fiber optic Michelson interferometers 6-N through the input ends 61, 71......N1 of the sensing array;

[0042] S3. The fiber optic Michelson interferometers 6-N are implanted in areas 11, 12, 13, 14 on the mattress 1. When a person lies on the mattress, signals generated by different parts of the human body during sleep cause the fibers of the fiber optic Michelson interferometers 6-N to deform, resulting in a change in the phase of the output light of the fiber optic Michelson interferometers 6-N;

[0043] S4. The output optical signals of the fiber optic Michelson interferometers 6-N are output through the output ends 62, 72......N2 of the sensing array, and respectively enter the multi-channel photodetector 4 through the input ends 42-4N of the multi-channel photodetector. The optical signals are converted into electrical signals by the multi-channel photodetector 4;

[0044] The electrical signal output from the output terminal 41 of the multi-channel photodetector 4 enters the signal acquisition and processing module 5 for processing, and the phase signal of the fiber optic Michelson interferometer 6-N is demodulated;

[0045] S6. The signal acquisition and processing module 5 processes the phase signals of the N fiber optic Michelson interferometers that are demodulated, extracts the respiration and heartbeat signals at different positions of the human body, and infers the sleep body movement state based on the characteristics of the signal energy and frequency collected by the fiber optic Michelson interferometers at different positions, specifically as follows:

[0046] S6.1 Perform filtering processing on the phase signals of the N fiber optic Michelson interferometers that are demodulated to extract the respiration and heartbeat signals of different parts of the human body. The filtering processing method is the Butterworth band-pass filtering method, and the specific filtering frequency band range refers to the current standard "Specification for Machine Analysis and Interpretation of Sleep Monitoring Signals" (T / CPAM 002-2020).

[0047] S6.2 Calculate the band energy of the respiration and heartbeat signals of different parts of the human body. The energy magnitude reflects the distance between the sensor and the heart. Based on the band energy and the distribution of the sensor array on the mattress, determine the position of the human heart. The respiration and heartbeat signals collected by the sensors at this position have the highest accuracy.

[0048] S6.3 Based on the band energy of the sleep signals collected by the N sensors and the distribution of the sensor array on the mattress, the distribution of the total energy generated by human sleep on the mattress can be obtained. The movement of different parts of the human body will cause changes in the energy distribution. By comparing the energy distributions at adjacent times, it can be determined whether different parts of the human body move on the mattress. By comprehensively considering the position changes of different parts of the human body, the sleep body movement information at night can be obtained.

[0049] In this embodiment, the respiration signal waveform with the highest accuracy is as Figure 3 shown, which has obvious large-amplitude fluctuations with a relatively high frequency; the heartbeat signal waveform with the highest accuracy is as Figure 4 shown, with relatively small fluctuations and a relatively low frequency; the energy distribution of the N sensors on the mattress at a certain moment is as Figure 5 shown. The energy magnitudes of the signals collected by the N sensors are different. By comparing the energy distributions on the mattress at adjacent times, the sleep body movement state of the human body can be analyzed.

Claims

1. A sleep monitoring device based on a fiber optic Michelson interferometer, characterized in that: The device includes a single-frequency laser, an optical fiber splitter, a sensing array, a multi-channel photodetector, and a signal acquisition and processing module; the output end of the single-frequency laser is connected to the input end of the optical fiber splitter for emitting laser light; the N output ends of the optical fiber splitter are respectively connected to the N input ends of the sensing array for splitting a beam of light into N beams of light; the N output ends of the sensing array are respectively connected to the N input ends of the multi-channel photodetector, and the multi-channel photodetector is used for converting the optical signal into an electrical signal; the output end of the multi-channel photodetector is connected to the signal acquisition and processing module, and the signal acquisition and processing module is used for realizing the acquisition and phase demodulation of the sensing array signal, and extracting the respiration, heartbeat signals and body movement information at different positions of the human body; the sensing array is composed of N fiber Michelson interferometers, and the N fiber Michelson interferometers are implanted at different positions of the mattress for sensing the signals generated during the sleep process at different positions of the human body, and N is an integer greater than 1; Faraday rotators are respectively connected to the ends of the two arms of the fiber Michelson interferometer to overcome the interference of polarization fading; The method for sleep monitoring using the said device is as follows: S1. The output light of the single-frequency laser is split into N beams of light by the optical fiber splitter; S2. The N beams of light output by the optical fiber splitter respectively enter the N fiber Michelson interferometers through the N input ends in the sensing array; S3. The N fiber Michelson interferometers are implanted at different positions of the mattress. When a human body lies on the mattress, the signals generated during the sleep process cause the optical fibers of the N fiber Michelson interferometers to deform, resulting in a change in the output optical phase of the N fiber Michelson interferometers; S4. The output optical signals of the fiber Michelson interferometers enter the multi-channel photodetector through the N output ends of the sensing array, and the optical signals are converted into electrical signals by the multi-channel photodetector; S5. The electrical signals output by the multi-channel photodetector enter the signal acquisition and processing module for processing to demodulate the phase signals of the N fiber Michelson interferometers; S6. The signal acquisition and processing module processes the demodulated phase signals of the N fiber Michelson interferometers, extracts the respiration and heartbeat signals at different positions of the human body, and infers the sleep body movement state according to the characteristics of the signal energy and frequency collected by the fiber Michelson interferometers at different positions, specifically as follows: S6.1 Filter the demodulated phase signals of the N fiber Michelson interferometers to extract the respiration and heartbeat signals of different parts of the human body; S6.2 Calculate the band energy of the respiration and heartbeat signals of different parts of the human body. The energy size reflects the distance between the sensor and the heart. Based on the band energy and the distribution of the sensor array on the mattress, determine the position of the human heart. The respiration and heartbeat signals collected by the sensors at this position have the highest accuracy; Based on the band energy of the sleep signals collected by N sensors and the distribution of the sensor array on the mattress, the distribution of the total energy generated by human sleep on the mattress can be obtained. The movement of different parts of the human body will cause changes in the energy distribution. By comparing the energy distribution at adjacent times, it can be determined whether different parts of the human body move on the mattress. By comprehensively considering the position changes of different parts of the human body, the body movement information during night sleep can be obtained.

2. The sleep monitoring device based on a fiber optic Michelson interferometer according to claim 1, wherein: The single-frequency laser is a single-frequency tunable laser or a non-tunable laser.

3. The sleep monitoring device based on a fiber optic Michelson interferometer according to claim 1, characterized in that: In S6.1, the filtering processing method is the Butterworth band-pass filtering method.

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