Radio frequency identification sensor and vital sign monitoring method based on same

Abstract

The invention discloses a radio frequency identification sensor and a vital sign monitoring method based on the same. The sensor is composed of at least one flexible RFID sensor tag, a set of RFID read-write system and an upper computer. The flexible RFID sensor tag is composed of a microcontroller module, an RFID transceiver module, a capacitive pressure sensor module, a capacitance digital conversion module and a power supply module. The RFID read-write system is composed of an RFID reader-writer and a reader-writer antenna. According to the invention, a radio frequency identification heartbeat and breathing signal measurement technology and an integration scheme combining sensitive element integration and phase calculation are developed, weak heartbeat signals of a human body are sensed by utilizing a capacitive pressure sensor, and breathing signals are reconstructed by adopting an RFID phase calculation method; hardware integration and data transmission are completed by using a flexible electronic device, a substrate, a corresponding preparation technology and an RFID EPC code user data segment coding analysis wireless transmission technology.

Description

Technical Field

[0001] The invention relates to the technical field of wireless sensors, in particular to a radio frequency identification sensor and a vital sign monitoring method based on the sensor. Background Art

[0002] The effective monitoring and analysis of key vital signs signals such as human breathing and heartbeat are of great significance in the fields of medical care, health assessment, search and rescue, and motion status analysis. The current mainstream contact measurement technology limits the convenience of measurement due to the presence of signal leads and power batteries, making the measurement process inevitably restricting human daily behavior; while non-contact measurement technologies such as radar are susceptible to multi-target interference and the influence of human free movement, making it difficult to simultaneously identify multiple adjacent human targets and monitor the vital signs of each target. UHF RFID sensors have technical characteristics such as wireless power supply, wireless data transmission, non-line-of-sight measurement, synchronous identification and perception, and have unique advantages in low power consumption, miniaturization, convenience, and reducing interference with human daily behavior. At the same time, because the reading distance of UHF RFID technology can reach more than 10 meters, this technology is easy to build a measurement system and measurement network for simultaneous monitoring of multiple people.

[0003] RFID sensors can realize identity recognition and monitoring of vital signs parameters by integrating sensitive components with RFID transceivers, effectively reducing power consumption, reducing volume, and improving wear comfort by integrating flexible devices. Because both heartbeat and respiratory signals are relatively weak and the signal measurement cycle is long, it is difficult to obtain both at the same time. Researchers from Auburn University and California State University in the United States have developed a driving environment respiratory detection method based on commercial RFID tags, which mainly solves the noise suppression problems caused by frequency hopping technology, random sampling, and car vibration. Ma Yongtao's team at Tianjin University uses RFID tags to measure human respiratory signals and uses Doppler frequency shift to eliminate the influence of human free movement on respiratory chest fluctuation signals, but this method cannot measure heartbeat signals. The Distributed Computing Laboratory of Nanjing University uses commercial fully passive RFID arrays to simultaneously measure respiratory and heartbeat signals, and constructs a radio frequency signal reflection model and a multi-tag signal fusion model to calculate heartbeat signals, but the array angle affects the measurement effect, and multiple people will have mutual influence during simultaneous measurement. In addition, the large structure of the RFID array leads to poor comfort when worn for a long time. Scholars from the University of Alberta in Canada have developed a passive RFID sensor consisting of a heart rate monitoring module, an energy recovery module and a three-port RFID structure. The system achieves real-time heart rate monitoring by integrating heart rate monitoring sensitive elements with RFID transceivers. However, the system is composed of hard devices and has a large structure, which is not suitable for wearability. In addition, the reading distance is limited by the efficiency of radio frequency energy recovery.

[0004] In summary, among the existing solutions, sensor-enhanced RFID sensors with integrated sensitive elements cannot measure respiratory signals, while phase calculation technology based on commercial tags relies on tag arrays and computational models, neither of which can simultaneously achieve wearable and untethered measurement of heart rate and respiration. Therefore, there is still a lack of flexible RFID sensor design and integration solutions that can achieve continuous, wearable and convenient measurement of vital signs. Developing sensitive elements for heartbeat and respiration measurement and effectively integrating them with RFID technology to achieve multi-person identity recognition and simultaneous acquisition of respiration and heartbeat signals are key technical challenges currently facing this field. Summary of the invention

[0005] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a radio frequency identification sensor and a vital signs monitoring method based on the sensor.

[0006] The technical solution of the present invention to solve the above-mentioned sensor technical problem is to provide a radio frequency identification sensor, which is composed of at least one flexible RFID sensor tag, a set of RFID reading and writing system and a host machine; The flexible RFID sensor tag is composed of a microcontroller module, an RFID transceiver module, a capacitive pressure sensor module, a capacitance-to-digital conversion module and a power supply module; The microcontroller module, the RFID transceiver module, the capacitance digital conversion module and the power module are integrated on a flexible substrate; the microcontroller module is connected to the capacitance digital conversion module and the RFID transceiver module; the capacitive pressure sensor module is connected to the input end of the capacitance digital conversion module; the power module supplies power to the microcontroller module, the RFID transceiver module and the capacitance digital conversion module; The RFID reading and writing system is composed of an RFID reader and a reader antenna; the RFID reader is connected to the host computer for communication; the reader antenna is connected to the RFID reader and is connected to the RFID transceiver module for communication.

[0007] The technical solution of the present invention to solve the technical problem of the method is to provide a vital sign monitoring method based on the radio frequency identification sensor, the method comprising the following steps: Step 1: Assembly of RFID sensor; Step 2, installation of the flexible RFID sensor tag: stick the flexible RFID sensor tag to the chest surface of the object to be measured, so that the capacitive pressure sensor module directly contacts the chest skin of the human body; Step 3, initialization of the flexible RFID sensor tag: After the flexible RFID sensor tag is powered on, the microcontroller module runs the program to initialize the tag function, and initializes the function configuration of the capacitance digital conversion module and the RFID transceiver module; in the execution process, the RFID read response function of the RFID reader is first disabled to complete the collection and processing of capacitance data and the update of the user data segment of the EPC code; after the collection and processing of the read heartbeat signal is completed and the encoding of the heart rate data is completed, the read response function of the RFID reader is enabled; when the read query of the RFID reader is completed, the microcontroller module will trigger a new round of capacitance data collection according to the timer cycle; Step 4: Acquisition of initial heartbeat signal and initial breathing signal; For the initial heartbeat signal, the capacitive pressure sensor module senses the change in the distance between the capacitors caused by the heartbeat change, and converts the pressure change caused by the chest movement caused by the heartbeat into a capacitance change, thereby establishing a relationship between the capacitance signal and the initial heartbeat signal and completing the acquisition of the initial heartbeat signal; For the breathing signal, the flexible RFID sensor tag uses the chest fluctuation to modulate the phase information of the electromagnetic wave, and couples the chest fluctuation caused by the initial breathing into the phase information of the flexible RFID sensor tag, which is obtained by the RFID reader during the reading process of the flexible RFID sensor tag, thus completing the acquisition of the initial breathing signal; Step 5, acquisition of heart rate data and respiratory rate data: the microcontroller module processes the collected initial heartbeat signal to obtain heart rate data; the host computer filters the received initial respiratory signal and performs phase expansion, and then obtains the peak arrival time of the expanded phase signal to calculate the respiratory rate data, thereby achieving simultaneous acquisition of heart rate data and respiratory rate data.

[0008] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention develops a radio frequency identification heartbeat and breathing signal measurement technology and an integrated solution combining sensitive element integration with phase calculation, uses a capacitive pressure sensor to sense the weak heartbeat signal of the human body, uses an RFID phase calculation method to reconstruct the breathing signal, and uses flexible electronic devices, substrates and corresponding preparation technologies and RFID EPC code user data segment coding analysis wireless transmission technology to complete hardware integration and data transmission. Ultimately, the system achieves low power consumption, miniaturization, and flexibility, and improves the comfort of wearing to reduce interference with the user's daily behavior. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a schematic diagram of the overall structure of the radio frequency identification sensor of the present invention; Figure 2 is a system block diagram of the flexible RFID sensor tag of the present invention; Figure 3It is a structural schematic diagram of a capacitive pressure sensor module of the present invention; Figure 4 It is a schematic diagram of the installation of the radio frequency identification sensor of the present invention; Figure 5 A schematic diagram of the respiratory rate measurement principle of the phase calculation of the present invention; Figure 6 This is a schematic diagram of the initialization process of the flexible RFID sensor tag of the present invention; Figure 7 is a flow chart for calculating heart rate data of the present invention; Figure 8 is a flow chart for calculating the respiratory rate data of the present invention; Fig. 9 This is a schematic diagram of the data encoding structure design of the flexible RFID sensor tag of the present invention; Fig.10 A schematic diagram of a method for encoding heart rate data in a user data segment of an EPC code according to the present invention; Fig.11 It is the real-time detection interface of the upper computer visualization display software of the present invention; Fig.12 It is the historical data query interface of the upper computer visualization display software of the present invention.

[0010] In the figure, flexible RFID sensor tag 1, RFID reading and writing system 2, host computer 3; Microcontroller module 11 , RFID transceiver module 12 , capacitive pressure sensor module 13 , capacitance-to-digital conversion module 14 , power supply module 15 ; RFID reader / writer 21 , reader / writer antenna 22 . DETAILED DESCRIPTION

[0011] The specific embodiments of the present invention are given below. The specific embodiments are only used to further illustrate the present invention in detail and do not limit the protection scope of the present invention.

[0012] The present invention provides a flexible wearable radio frequency identification sensor (referred to as sensor) for monitoring vital signs signals, the sensor comprising at least one flexible RFID sensor tag 1, a set of RFID reading and writing system 2 and a host computer 3; The flexible RFID sensor tag 1 is composed of a microcontroller module 11, an RFID transceiver module 12, a capacitive pressure sensor module 13, a capacitance-to-digital conversion module 14 and a power supply module 15; The microcontroller module 11, the RFID transceiver module 12, the capacitance digital conversion module 14 and the power module 15 are integrated on a FPCB flexible substrate by welding with liquid solder paste; the capacitive pressure sensor module 13 is integrated by conductive silver glue and flexible leads; the microcontroller module 11 is connected to the capacitance digital conversion module 14 through the SPI serial bus, and is connected to the RFID transceiver module 12 through the I2C serial bus; the capacitive pressure sensor module 13 is connected to the input end of the capacitance digital conversion module 14; the power module 15 supplies power to the microcontroller module 11, the RFID transceiver module 12 and the capacitance digital conversion module 14; The RFID reading and writing system 2 is composed of an RFID reader 21 and a reader antenna 22; the RFID reader 21 is connected to the host computer 3 through a network cable, and is used to read the ID data of the flexible RFID sensor tag 1 encoded with heart rate data, and at the same time obtain the phase information of the reading process of the RFID tag 1 for calculating the respiratory rate, and send the read data to the host computer 3 for further processing, display and storage; the reader antenna 22 is connected to the RFID reader 21 through a radio frequency coaxial line, and is wirelessly connected to the RFID transceiver module 12 through a radio frequency wireless signal.

[0013] Preferably, the host computer 3 is a desktop computer or a laptop computer, which is installed with developed host computer software to realize data collection, processing, display, storage and historical data query.

[0014] Preferably, the microcontroller module 11 is composed of TI 1.8V ultra-low voltage, 126µA / MHz ultra-low power consumption, 4×4mm QFN small package microcontroller MSP430FR2433 and its peripheral circuits, and its performance and packaging ensure the low power consumption, miniaturization and flexibility of the flexible RFID sensor tag 1. The microcontroller module 11 serves as the control core of the flexible RFID sensor tag 1, and realizes the initialization configuration, data acquisition, data processing and logic control of the flexible RFID sensor tag 1. The initialization configuration of the flexible RFID sensor tag 1 mainly completes the initialization of the functions of the capacitance digital conversion module 14 and the RFID transceiver module 12; the microcontroller module 11 controls the capacitance digital conversion module 14 through a timer to complete the digitization of the capacitance value, and reads it into the memory of the microcontroller module 11 to realize the collection of heartbeat data; the microcontroller module 11 processes the initial heartbeat signal in the memory and calculates the heart rate data; the microcontroller module 11 writes the calculated heart rate data into the user data segment of the EPC code of the RFID transceiver module 12 and enables the RFID read-write function, and controls the RFID transceiver module 12 to send the measured data to the RFID read-write system 2 to complete the data transmission. During the working process, the microcontroller module 11 reads the initial heartbeat signal collected by the pressure sensor module 13 and the capacitance digital conversion module 14 in real time, and calculates the heart rate data.

[0015] Preferably, the RFID transceiver module 12 includes an RFID radio frequency transceiver chip and a tag antenna to realize the unique identification of the object under test and the wireless data transmission function; first, the identity of the object under test is completed through the unique identification code of the RFID; secondly, the heart rate data sent by the microcontroller module 11 through the I2C serial bus is received and stored in the user data segment of the EPC code, and under the logical control of the microcontroller module 11, the data is sent to the RFID reading and writing system 2 in the EPC C1G2 protocol to complete the transmission of the heart rate data; then, the phase change caused by the change in the distance between the flexible RFID sensor tag 1 and the reader antenna 22 caused by the chest rise and fall during the RFID reading and writing process is obtained, and the continuous phase change is sent to the host computer 3 along with the ID data for respiratory signal reconstruction.

[0016] Preferably, the capacitive pressure sensor module 13 is a flexible device with a porous slotted structure of polydimethylsiloxane (PDMS), which is flexible and wearable, highly sensitive, and has surface insulation and anti-interference capabilities through PDMS materials, porous slotted structure design, conductive silver glue bonding, and thermal curing processes. The PDMS porous slotted structure flexible device includes five layers: the top and bottom layers are PET film insulation layers, which mainly play an insulating role; the middle layer is a flexible PDMS base material layer, which is made by thermally curing a porous slotted structure PDMS base material and a cross-linking curing agent, and serves as a dielectric layer of a capacitor to sense pressure changes and convert the pressure size into a change in the pole distance of the capacitive pressure sensor; between the two layers of PET film insulation layers and the PDMS material base material layer are two layers of silver electrodes coated with conductive silver glue to form a parallel plate capacitor, which uses the pole distance change caused by pressure to reflect the pressure size, and uses a flexible lead to communicate and connect the two poles of the capacitive pressure sensor module 13 with the two input ends of the capacitance digital conversion module 14, and convert the pressure change into a capacitance change.

[0017] Preferably, the capacitance-to-digital conversion (CDC) module 14 is a capacitance measurement circuit composed of an integrated 24-bit high-precision, 200μA ultra-low power consumption, 4×4mm QFN small package capacitance-to-digital conversion chip PCAP02; the capacitance-to-digital conversion module 14 is connected to the two electrodes of the capacitive pressure sensor module 13 through two pins as input ends, and obtains the capacitance size through the charging and discharging time of the capacitor and converts it into relative data; the capacitance-to-digital conversion module 14 receives the initialization function configuration of the microcontroller module 11, and realizes continuous data collection of the pressure signal generated by the heartbeat under the logic control of the microcontroller module 11.

[0018] Preferably, the power module 15 includes a thin-film lithium battery and a DC-DC converter, which is used to power the entire sensor to achieve heartbeat pressure signal acquisition, heart rate calculation, heart rate data RFID user data segment encoding, and continuous reading response of RFID tags.

[0019] The present invention also provides a method for monitoring vital signs based on the flexible wearable radio frequency identification sensor (hereinafter referred to as the method), which comprises the following steps: Step 1, assembly of radio frequency identification sensor: microcontroller module 11, RFID transceiver module 12, capacitance digital conversion module 14 and power module 15 are integrated on a FPCB flexible substrate by welding with liquid solder paste; capacitive pressure sensor module 13 is integrated by conductive silver glue and flexible lead; microcontroller module 11 is connected to capacitance digital conversion module 14 through SPI serial bus, and is connected to RFID transceiver module 12 through I2C serial bus; capacitive pressure sensor module 13 is connected to the input end of capacitance digital conversion module 14; power module 15 supplies power to microcontroller module 11, RFID transceiver module 12 and capacitance digital conversion module 14.

[0020] The RFID reading and writing system 2 is composed of an RFID reader 21 and a reader antenna 22; the RFID reader 21 is connected to the host computer 3 via a network cable; the reader antenna 22 is connected to the RFID reader 21 via a radio frequency coaxial line, and is wirelessly connected to the RFID transceiver module 12 of the flexible RFID sensor tag 1 via radio frequency wireless signals; Step 2, installation of the flexible RFID sensor tag 1: sticking the flexible RFID sensor tag 1 to the chest skin or clothing surface of the object to be measured, thereby achieving direct contact between the capacitive pressure sensor module 13 and the chest skin of the human body; Step 3, initialization of the flexible RFID sensor tag 1: After the flexible RFID sensor tag 1 is powered on, the microcontroller module 11 runs the program to initialize the tag function, completes the initialization of the microcontroller chip peripherals, and initializes the capacitance digital conversion module 14 and the RFID transceiver module 12. Function configuration; in the execution process, first disable the RFID read response function of the RFID reader 21 to complete the collection and processing of capacitance data and the update of the user data segment of the EPC code; after the heartbeat signal is read and processed and the heart rate data is encoded, the read response function of the RFID reader 21 is enabled; when the read query of the RFID reader 21 is completed, the microcontroller module 11 will trigger a new round of capacitance data collection according to the timer cycle; this process ensures the efficient coordination of each functional module and the accurate processing of data; Step 4: Acquisition of initial heartbeat signal and initial breathing signal; For the initial heartbeat signal, the capacitive pressure sensor module 13 senses the change in the distance of the capacitor caused by the change in the heartbeat, and converts the pressure change caused by the chest movement caused by the heartbeat into a capacitance change, thereby establishing a relationship between the capacitance signal and the initial heartbeat signal and completing the acquisition of the initial heartbeat signal; For the breathing signal, the flexible RFID sensor tag 1 utilizes the chest fluctuation to modulate the phase information of the electromagnetic wave, and couples the chest fluctuation caused by the initial breathing into the phase information of the flexible RFID sensor tag 1, which is obtained by the RFID reader 21 during the reading process of the flexible RFID sensor tag 1, thereby completing the acquisition of the initial breathing signal; Preferably, in step 4, the specific steps of obtaining the initial heartbeat signal are as follows: The initial capacitance before applying pressure to the capacitive pressure sensor module 13 is: (1) In formula (1), C is the capacitance, ε0 is the dielectric constant of free space, and ε r is the effective dielectric constant, A is the electrode area, h is the capacitance distance, and ε is the equivalent dielectric constant; When pressure is applied, the capacitor distance decreases h, reduced to h', expressed as: h'=h- h (2) At the same time, the air gap in the flexible PDMS base material layer in the capacitive pressure sensor module 13 is compressed, resulting in a decrease in the relative volume of air, which in turn causes the equivalent dielectric constant to increase from ε to ε', with an increase of ε, expressed as: ε'=ε+ ε (3) The reduction of the inter-electrode distance and the increase of the dielectric constant both increase the capacitance of the sensor, changing it from C to C+. C, which will improve the sensitivity of the capacitive pressure sensor module 13, expressed as: (4) In formula (4), C is the increase in capacitance; Changes in capacitance distance due to pressure h is much smaller than h, so equation (4) is simplified to equation (5): (5).

[0021] Preferably, in step 4, the specific steps of acquiring the initial breathing signal are as follows: The EPC code of the flexible RFID sensor tag 1 is read by the reader antenna 22, and the original respiratory phase signal caused by the respiratory change at the reading time is obtained; wherein the original respiratory phase signal is the remainder of the full phase between the interval [0,2π], and its formula is shown in formula (6): (6) In formula (6), is the original respiratory phase signal; d is the distance between the flexible RFID sensor tag 1 and the RFID reading and writing system 2, which changes periodically with the rise and fall of the human chest during breathing; λ is the wavelength of the RFID radio frequency signal; θ Tx , θ Rx and θ Tag They represent the phase changes caused by the radio frequency transceiver circuit of the reader antenna 22 and the radio frequency transceiver circuit of the RFID transceiver module 12 respectively. These parameters remain unchanged under the same environment and can be regarded as constants. Therefore, the original breathing phase signal of the flexible RFID sensor tag 1 It can reflect the periodic fluctuation of the chest during the breathing process, thereby establishing the relationship between the breathing signal and the phase signal and completing the acquisition of the initial breathing signal.

[0022] Step 5, acquisition of heart rate data and respiratory rate data: the microcontroller module 11 processes the collected initial heartbeat signal to obtain heart rate data; the host computer 3 filters the received initial respiratory signal and performs phase expansion, and then obtains the peak arrival time of the expanded phase signal to calculate the respiratory rate data, thereby achieving simultaneous acquisition of heart rate data and respiratory rate data.

[0023] Preferably, in step 5, the acquisition of heart rate data is specifically as follows: under the control logic of the microcontroller module 11, the initial heartbeat signal is converted from analog to digital through the capacitor digital conversion module 14, and then data is collected at a sampling rate of 100 Hz under the control of the microcontroller module 11, and the converted data is sent to the microcontroller module 11 to calculate the initial heartbeat signal to obtain the heart rate data, and then the heart rate data is encoded into the user data segment of the EPC code of the RFID transceiver module 12, and transmitted to the RFID reader 21 in the form of wireless radio frequency backscattering, and then read by the host computer 3 and the host computer software parses the encoded data to obtain the heart rate data.

[0024] Preferably, in step 5, the microcontroller module 11 calculates the initial heartbeat signal to obtain the heart rate data specifically as follows: the microcontroller module 11 filters the pressure signal caused by the periodic changes in the heartbeat to obtain the pressure peak arrival time, which is used to calculate the heart rate data, that is, first, the original capacitance signal change sequence caused by the heartbeat is obtained, the abnormal values ​​are eliminated, and a second-order low-pass Butterworth filter with a cutoff frequency of 5.0Hz is used to remove the high-frequency components caused by the measurement noise, so as to obtain a measurement signal reflecting the corresponding relationship between the heartbeat and the capacitance change; then, the filtered measurement signal is smoothed by an infinite impulse response (IIR) high-pass filter with a cutoff frequency of 0.05Hz to remove the DC component, so as to eliminate the influence of human body movement on the capacitance change; finally, the peak time of the processed signal is obtained by a peak detection algorithm to estimate the heart rate data.

[0025] Preferably, in step 5, the acquisition of respiratory rate data is specifically as follows: first, the initial respiratory signal caused by the backscattered respiratory changes of the RFID transceiver module 12 is acquired by the RFID reader 21, and then sent to the host computer 3 by the RFID reader 21. The host computer 3 performs phase expansion on the phase signal to obtain the expanded phase signal, and obtains a measurement signal reflecting the corresponding relationship between the phase change and the chest movement; then, the host computer 3 uses empirical mode decomposition (EMD) to remove high-frequency noise in the signal, and uses an infinite impulse response (IIR) high-pass filter with a cutoff frequency of 0.05 Hz to perform smoothing to remove the DC component, so as to eliminate the phase change caused by human body movement; finally, the peak time of the processed signal is obtained by the peak detection algorithm, which is used to estimate the respiratory rate data.

[0026] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A radio frequency identification sensor, characterized in that: The sensor is composed of at least one flexible RFID sensor tag (1), an RFID reading and writing system (2) and a host computer (3); The flexible RFID sensor tag (1) is composed of a microcontroller module (11), an RFID transceiver module (12), a capacitive pressure sensor module (13), a capacitance-to-digital conversion module (14), and a power supply module (15); The microcontroller module (11), the RFID transceiver module (12), the capacitance digital conversion module (14) and the power module (15) are integrated on a flexible substrate; the microcontroller module (11) is communicatively connected to the capacitance digital conversion module (14) and is communicatively connected to the RFID transceiver module (12); the capacitive pressure sensor module (13) is communicatively connected to the input end of the capacitance digital conversion module (14); and the power module (15) supplies power to the microcontroller module (11), the RFID transceiver module (12) and the capacitance digital conversion module (14); The RFID reading and writing system (2) is composed of an RFID reader / writer (21) and a reader / writer antenna (22); the RFID reader / writer (21) is communicatively connected to a host computer (3); the reader / writer antenna (22) is communicatively connected to the RFID reader / writer (21) and is also communicatively connected to an RFID transceiver module (12).

2. The RFID sensor according to claim 1, characterized in that: The RFID transceiver module (12) comprises an RFID radio frequency transceiver chip and a tag antenna.

3. The RFID sensor according to claim 1, characterized in that: The power module (15) includes a thin-film lithium battery and a DC-DC converter, and is used to supply power to the entire sensor.

4. A method for monitoring vital signs based on the radio frequency identification sensor according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: Step 1: Assembly of RFID sensor; Step 2, installation of the flexible RFID sensor tag (1): affixing the flexible RFID sensor tag (1) to the chest surface of the object to be measured, so that the capacitive pressure sensor module (13) directly contacts the chest skin of the human body; Step 3, initialization of the flexible RFID sensor tag (1): After the flexible RFID sensor tag (1) is powered on, the microcontroller module (11) runs a program to initialize the tag function, and initializes the function configuration of the capacitance digital conversion module (14) and the RFID transceiver module (12); in the execution process, the RFID read response function of the RFID reader (21) is first disabled to complete the collection and processing of capacitance data and the update of the user data segment of the EPC code; after the collection and processing of the read heartbeat signal is completed and the encoding of the heart rate data is completed, the read response function of the RFID reader (21) is enabled; when the read query of the RFID reader (21) is completed, the microcontroller module (11) will trigger a new round of capacitance data collection according to the timer cycle; Step 4: Acquisition of initial heartbeat signal and initial breathing signal; For the initial heartbeat signal, the capacitive pressure sensor module (13) senses the change in the distance between the capacitors caused by the change in the heartbeat, and converts the pressure change caused by the chest movement caused by the heartbeat into a capacitance change, thereby establishing a relationship between the capacitance signal and the initial heartbeat signal and completing the acquisition of the initial heartbeat signal; For the breathing signal, the flexible RFID sensor tag (1) utilizes the chest fluctuation to modulate the phase information of the electromagnetic wave, and couples the chest fluctuation caused by the initial breathing into the phase information of the flexible RFID sensor tag (1), which is obtained by the RFID reader (21) during the reading process of the flexible RFID sensor tag (1), thereby completing the acquisition of the initial breathing signal; Step 5, acquisition of heart rate data and respiratory rate data: the microcontroller module (11) processes the collected initial heartbeat signal to obtain heart rate data; the host computer (3) filters the received initial respiratory signal and performs phase unfolding, and then obtains the peak arrival time of the unfolded phase signal to calculate the respiratory rate data, thereby achieving simultaneous acquisition of heart rate data and respiratory rate data.

5. The vital signs monitoring method according to claim 4, characterized in that: In step 4, the specific steps for obtaining the initial heartbeat signal are as follows: The initial capacitance C before applying pressure to the capacitive pressure sensor module (13) is: （1） In formula (1), ε0 is the dielectric constant of free space, ε r is the effective dielectric constant, A is the electrode area, h is the capacitance distance, and ε is the equivalent dielectric constant; When pressure is applied, the capacitor distance decreases h, reduced to h', expressed as: h’=h- h (2) At the same time, the air gap in the capacitive pressure sensor module (13) is compressed, resulting in a decrease in the relative volume of air, which in turn causes the equivalent dielectric constant to increase from ε to ε', with an increase of ε, expressed as: e'=e+ e (3) The reduction of the inter-electrode distance and the increase of the dielectric constant both increase the capacitance of the sensor, changing it from C to C+. C, expressed as: （4） In formula (4), C is the increase in capacitance; Changes in capacitance distance due to pressure h is much smaller than h, so equation (4) is simplified to equation (5): （5）。 6. The vital signs monitoring method according to claim 4, characterized in that: In step 4, the specific steps of obtaining the initial breathing signal are as follows: The EPC code of the flexible RFID sensor tag (1) is read by the reader antenna (22), and the original breathing phase signal caused by the breathing change at the reading time is obtained; wherein the original breathing phase signal is the remainder of the full phase between the interval [0,2π], and its formula is shown in formula (6): （6） In formula (6), is the original respiratory phase signal; d is the distance between the flexible RFID sensor tag (1) and the RFID reading and writing system (2), which changes periodically with the rise and fall of the human chest during breathing; λ is the wavelength of RFID radio frequency signal; θ Tx , θ Rx and θ Tag They respectively represent the phase changes caused by the radio frequency transceiver circuit of the reader antenna (22) and the radio frequency transceiver circuit of the RFID transceiver module (12).

7. The vital signs monitoring method according to claim 4, characterized in that: In step 5, the acquisition of the heart rate data is specifically as follows: under the control logic of the microcontroller module (11), the initial heartbeat signal is converted from analog to digital through the capacitor digital conversion module (14), and then data collection is performed under the control of the microcontroller module (11), and the converted data is sent to the microcontroller module (11) to calculate the initial heartbeat signal to obtain the heart rate data, and then the heart rate data is encoded into the user data segment of the EPC code of the RFID transceiver module (12), and transmitted to the RFID reader (21) in the form of wireless radio frequency backscattering, and then read by the host computer (3) and the host computer software parses the encoded data to obtain the heart rate data.

8. The vital signs monitoring method according to claim 7, characterized in that: In step 5, the microcontroller module (11) calculates the initial heartbeat signal to obtain the heart rate data as follows: first, the microcontroller module (11) obtains the original signal change sequence of the capacitor caused by the heartbeat, removes the abnormal values, and uses a second-order low-pass Butterworth filter to remove the high-frequency components caused by the measurement noise, thereby obtaining a measurement signal reflecting the corresponding relationship between the heartbeat and the capacitance change; then, the filtered measurement signal is smoothed using an infinite impulse response high-pass filter to remove the DC component, so as to eliminate the influence of human body movement on the capacitance change; finally, the peak time of the processed signal is obtained through a peak detection algorithm to estimate the heart rate data.

9. The vital signs monitoring method according to claim 4, characterized in that: In step 5, the respiratory rate data is obtained specifically as follows: first, the initial respiratory signal caused by the backscattered respiratory changes of the RFID transceiver module (12) is obtained through the RFID reader (21), and then the RFID reader (21) sends it to the host computer (3). The host computer (3) performs phase expansion on the phase signal to obtain the expanded phase signal, and obtains the measurement signal reflecting the corresponding relationship between the phase change and the chest movement; then, the host computer (3) uses empirical mode decomposition to remove high-frequency noise in the signal, and uses an infinite impulse response high-pass filter to perform smoothing to remove the DC component, so as to eliminate the phase change caused by human body movement; finally, the peak time of the processed signal is obtained through the peak detection algorithm, which is used to estimate the respiratory rate data.

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