An ultra-low power electrocardiogram monitoring system based on backscattering communication and a method thereof

Abstract

The application relates to the technical field of backscatter communication and discloses an ultra-low-power electrocardio monitoring system and method based on backscatter communication. The system comprises a signal source for emitting a radio frequency carrier, a backscatter tag comprising an electrocardio signal acquisition module, a signal processing and modulation control module and a reconfigurable backscatter communication module, which is used for acquiring and processing electrocardio signals, generating modulation control signals according to the electrocardio signals, and reflecting and modulating the carrier through a same-phase quadrature load modulation architecture and a subcarrier frequency shift technology, and a receiving device for receiving and demodulating the reflected signals to obtain electrocardio data. The application utilizes a passive backscatter communication mechanism, significantly reduces the communication power to the order of 132 pJ / bit, overcomes the distance limitation of traditional near-field communication, realizes reliable data transmission of up to 10 meters, and is suitable for long-term and dynamic clinical electrocardio monitoring.

Description

Technical Field

[0001] This invention relates to the field of backscatter communication technology, specifically to an ultra-low power electrocardiogram monitoring system and method based on backscatter communication. Background Technology

[0002] With the development of flexible electronics technology, electronic skin (e-skin) has become an important platform for real-time health monitoring. As a key physiological parameter, the long-term, continuous monitoring of electrocardiogram (ECG) signals is of great significance for the early diagnosis of cardiovascular diseases and the management of chronic diseases. Currently, most mainstream wearable ECG monitoring devices use active wireless communication technologies such as Bluetooth Low Energy (BLE) or Wi-Fi. However, the RF front-end (such as power amplifiers and frequency synthesizers) of these technologies has high power consumption, ranging from tens of milliwatts for BLE to hundreds of milliwatts for Wi-Fi, severely limiting the device's battery life. Users need to charge frequently or wear large-capacity batteries, affecting the user experience.

[0003] While passive technologies such as Near Field Communication (NFC) can achieve low-power communication and wireless power transfer, their effective communication distance is usually limited to within 4 centimeters, which greatly restricts the user's freedom of movement and cannot meet the needs of unrestricted and continuous monitoring in daily home or community environments.

[0004] Therefore, existing technologies present a contradiction between high communication power consumption and short communication distance. There is an urgent need for a wireless ECG signal transmission solution that can balance low communication power consumption and long communication distance with high signal quality, so as to promote the practical application of wearable medical devices.

[0005] Backscatter communication technology transmits data by modulating and reflecting existing radio frequency carriers in the environment (such as signals from Wi-Fi routers or dedicated transmitters), avoiding the energy-intensive radio frequency signal generation process. Theoretically, it can reduce communication power consumption to extremely low picojoules per bit levels, making it an ideal solution to the aforementioned contradictions. However, how to stably and effectively apply backscatter communication to the monitoring of physiological signals (such as electrocardiograms) with extremely high signal quality requirements, and achieve seamless integration with flexible wearable devices, remains a pressing technical challenge. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an ultra-low power electrocardiogram (ECG) monitoring system and method based on backscatter communication. This system can reduce the wireless communication power consumption of ECG signals to the picojoule per bit level, while extending the reliable communication distance to the meter level, and ensuring clinical-grade ECG signal quality, thus laying a solid technical foundation for long-term, continuous dynamic ECG monitoring.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides an ultra-low power electrocardiogram monitoring system based on backscatter communication, comprising:

[0009] A signal source used to transmit radio frequency carrier waves into the space environment;

[0010] A backscatter tag is used to receive the radio frequency carrier, collect and process electrocardiogram (ECG) signals, and modulate the ECG data onto the radio frequency carrier for transmission via reflection.

[0011] A receiving device is used to receive and demodulate the reflected signal from the backscatter tag to obtain electrocardiogram data;

[0012] The backscattering tag includes:

[0013] The electrocardiogram (ECG) signal acquisition module is used to acquire human ECG signals and amplify and filter them.

[0014] The signal processing and modulation control module is connected to the electrocardiogram signal acquisition module and is used to perform analog-to-digital conversion and framing of the electrocardiogram signal to generate a modulation control signal.

[0015] A reconfigurable backscatter communication module, connected to the signal processing and modulation control module, is used to receive a radio frequency carrier emitted by the signal source and, in response to the modulation control signal, to reflect and modulate the carrier, thereby reflecting and transmitting ECG data to the receiving device.

[0016] Furthermore, the predetermined frame structure of the signal processing and modulation control module combination includes:

[0017] A preamble, with a minimum length of 3 bytes, is used to detect the start of a data packet.

[0018] The synchronization word, which is 4-8 bytes long, is used for frame synchronization.

[0019] The payload, with a length of 0-66 bytes, is used to carry ECG data;

[0020] Cyclic Redundancy Check (CRC) is an optional field with a length of 3 bytes, used for error detection;

[0021] The payload includes:

[0022] The Length field is an optional field with a length of 1 byte, used to indicate the payload length.

[0023] Node Address, an optional field, is 1 byte long and is used to indicate the node address;

[0024] The Message field, with a length of 0-20 bytes, is used to carry the actual valid ECG data.

[0025] Furthermore, the signal processing and modulation control module is also used to generate a square wave signal of a predetermined frequency as a subcarrier, and to shift the spectrum of the reflected signal from the carrier frequency to a predetermined offset frequency through the subcarrier, thereby realizing frequency domain separation between the reflected signal and the ambient carrier and improving the signal-to-noise ratio.

[0026] Furthermore, the subcarrier signal is a square wave signal, and the main components after Fourier series expansion are sine waves of the same frequency. The square wave approximates the sine wave to reduce system power consumption.

[0027] Furthermore, the reconfigurable backscatter communication module is the core for achieving ultra-low power consumption and precise modulation, and it includes an in-phase quadrature (IQ) load modulation circuit. The IQ load modulation circuit includes:

[0028] Wilkinson power dividers are used to split carrier signals received by an antenna into two signals with equal amplitude and phase.

[0029] A λ / 8 phase delay line is connected to one of the signals, creating a 90-degree phase difference between the two signals, thus forming two branches: in-phase (I) and quadrature (Q).

[0030] Two controllable impedance units (such as field-effect transistors) respectively regulate the terminal load impedance values ​​of the two branches to achieve joint modulation of the amplitude and phase of the reflected signal;

[0031] Furthermore, the controllable impedance element is a field-effect transistor. By changing the load impedance values ​​of the two transistors, the gate-source bias voltage can be adjusted independently, thereby achieving joint control of the amplitude and phase of the reflected signal.

[0032] This invention also provides a method for wireless transmission of ultra-low power ECG signals in an ultra-low power ECG monitoring system based on backscatter communication, comprising:

[0033] The signal source transmits a radio frequency carrier;

[0034] The backscatter tag collects and processes electrocardiogram signals to generate modulation control signals;

[0035] The backscatter tag receives the radio frequency carrier and performs reflection modulation on the carrier based on the modulation control signal;

[0036] The receiving device receives the reflected signal and demodulates it to obtain electrocardiogram data;

[0037] Furthermore, the step of the backscatter tag performing reflection modulation on the carrier includes:

[0038] Electrocardiogram (ECG) signals are acquired using surface electrodes, and these ECG signals are then amplified and filtered.

[0039] The amplified and filtered analog electrocardiogram signal is converted into a digital signal, combined into a predetermined protocol frame, and a modulation control signal is generated.

[0040] The system receives a radio frequency carrier emitted by the signal source and changes the load impedance according to the modulation control signal, thereby modulating the electrocardiogram data onto the ambient carrier and reflecting it to the receiving device.

[0041] Specifically, the reflected signal is modulated by IQ load modulation: the received carrier signal is divided into two signals with equal amplitude and phase; a phase delay line is used to generate a 90-degree phase delay in one of the signals, thereby forming two branches, in-phase (I) and quadrature (Q); two controllable impedance units are used as the terminal loads of the two branches respectively, and the impedance values ​​of the two controllable impedance units are independently controlled by the modulation control signal to achieve joint modulation of the amplitude and phase of the reflected signal.

[0042] Specifically, by generating a square wave signal of a predetermined frequency as a subcarrier, the spectrum of the reflected signal is shifted from the ambient carrier frequency to a predetermined offset frequency, thereby achieving frequency domain separation between the reflected signal and the ambient carrier and improving the signal-to-noise ratio.

[0043] Compared with the prior art, the present invention has the following significant advantages:

[0044] Ultra-low power consumption: This invention utilizes backscatter communication technology, resulting in extremely low communication power consumption. Experimental measurements show that the system's communication power consumption can be as low as 132 pJ / bit, which is only 1.39% of that of the commercial BLE nRF51822 chip. This makes it possible to integrate miniaturized, long-lasting power supplies, greatly extending the device's battery life.

[0045] 2. Long communication distance: The effective communication distance of this invention can reach 10 meters, which is 250 times the limit of NFC technology, greatly increasing the user's freedom in daily activities.

[0046] 3. High signal quality: This invention effectively improves the signal-to-noise ratio (SNR) by employing subcarrier frequency shifting technology. Experimental results show that the SNR of the received signal remains above 18 dB at a distance of 10 meters, ensuring that the PQRST feature points of the ECG waveform are clearly distinguishable and meeting the requirements of clinical-grade ECG monitoring.

[0047] 4. High system integration: The core circuit of the backscatter tag of this invention is composed of passive components and switching transistors, eliminating the need for complex active radio frequency chips. It is easy to combine with flexible circuit board technology to achieve a thin, flexible, and highly integrated electronic skin form. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the structure of an ultra-low power ECG monitoring system based on backscatter communication provided in an embodiment of the present invention.

[0049] Figure 2 This is a schematic diagram of the LoRa protocol frame structure provided in an embodiment of the present invention.

[0050] Figure 3 This is a spectrum diagram of the subcarrier frequency shifting technology provided in an embodiment of the present invention.

[0051] Figure 4 This is a schematic diagram of the voltage conversion circuit structure provided in an embodiment of the present invention.

[0052] Figure 5 This is a schematic diagram of the output signal waveforms of each voltage conversion process provided in the embodiments of the present invention.

[0053] Figure 6 This is a schematic diagram of the circuit structure of the reconfigurable backscatter communication module provided in an embodiment of the present invention.

[0054] Figure 7 This is a schematic diagram of the in-phase quadrature load modulation architecture provided in an embodiment of the present invention.

[0055] Figure 8 This is a flowchart illustrating the ultra-low power ECG signal wireless transmission method based on the system provided in this embodiment of the invention.

[0056] Figure 9 This is a waveform diagram of an electrocardiogram signal received by the system provided in this embodiment of the invention at a distance of 10 meters.

[0057] Figure 10 This is a comparison chart of the long-term working life and signal stability of the system provided in this embodiment of the invention powered by a flexible hydrogel battery. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0059] This invention provides an ultra-low power electrocardiogram (ECG) monitoring system based on LoRa backscatter communication, such as... Figure 1 As shown, the system includes:

[0060] Signal source, backscatter tag, and receiving device; among which,

[0061] The signal source serves to provide a stable radio frequency carrier signal to the space environment where the backscatter tag is located. In this embodiment, the signal source is a radio frequency signal generator capable of outputting continuous waves, with its operating frequency set to 915 MHz and its output power set to 20 dBm.

[0062] The backscatter tag is the core of the system. It is used to receive the radio frequency carrier, collect and process electrocardiogram (ECG) signals, modulate the ECG data onto the radio frequency carrier, and transmit it by reflection.

[0063] The receiving device receives reflected signals and decodes specific frame structures to obtain electrocardiogram (ECG) data. In this embodiment, an unmodified commercial LoRa protocol receiver, the Semtech SX1276, is used with a sensitivity set to -148 dBm. After the SX1276 chip's receiving antenna receives the reflected signal from the backscatter tag, the chip internally amplifies, down-converts, and demodulates the signal to ultimately recover the digital ECG data packet, which can then be transmitted to a smartphone, computer, or other host computer for display, storage, and further analysis.

[0064] In the above system, the backscattering tag specifically includes:

[0065] The module comprises an electrocardiogram (ECG) signal acquisition module, a signal processing and modulation control module, and a reconfigurable backscatter communication module; among which:

[0066] The ECG signal acquisition module is used to acquire, amplify, and filter ECG signals. In this embodiment, it is implemented using the commercial analog front-end chip AD8232 and its related peripheral circuits. The Ag / AgCl electrodes on the body surface are used to acquire weak, low-frequency ECG signals (amplitude range 0.5-2 mV, frequency range 0.5-100 Hz) and input them to the AD8232. The AD8232 has a fixed internal gain of 100. By configuring the resistors in the peripheral circuit, the operational amplifier gain is set to 11, and the total system gain can reach 1100 V / V, effectively suppressing electromyographic noise, electric field interference, baseline drift, and motion artifacts.

[0067] The signal processing and modulation control module is connected to the ECG signal acquisition module and is used to perform analog-to-digital conversion and framing of the ECG signal to generate a modulation control signal. This module employs an ultra-low-power microcontroller unit (MCU), preferably the STMicroelectronics STM32L072 series (based on the ARM Cortex-M0+ core), and its workflow is as follows:

[0068] Analog-to-digital conversion: The analog ECG signal from the ECG signal acquisition module is digitized using the embedded analog-to-digital converter (ADC) integrated within the MCU at a sampling rate of 250 Hz.

[0069] Data framing: The MCU frames the digitized ECG data according to a predetermined frame structure compatible with the LoRa communication protocol. For example... Figure 2 The diagram shows the standard and simplified forms of the frame structure. To reduce overhead, this embodiment uses the simplified frame structure, omitting the three optional fields: payload length field, node address, and cyclic redundancy check (CRC). Each data frame contains: a 3-byte preamble (0x555555), a 4-byte synchronization word (0x69817E96), and a payload carrying ECG data (containing 10 ECG sampling points, occupying 20 bytes).

[0070] Generating Modulation Control Signal: This embodiment employs the lowest power consumption switch-button modulation (OOK), modulating the data frame into a baseband signal based on its bit sequence. To better separate the weak reflected signal from the strong RF carrier at the receiving end, this system introduces subcarrier frequency shifting technology. The signal processing and modulation control module generates a subcarrier signal of a predetermined frequency, modulates the subcarrier according to the baseband signal, generates a modulation control signal, and multiplies and mixes it with the received RF carrier in the reconfigurable backscatter communication module. In this embodiment, the subcarrier signal is a 4MHz square wave signal, whose main component after Fourier series expansion is a sine wave of the same frequency. The square wave approximation of the sine wave reduces system power consumption. Figure 3 As shown, the final reflected signal spectrum was shifted from the carrier center frequency of 915 MHz to 915 MHz ± 4 MHz, thus achieving effective separation from the radio frequency carrier in the frequency domain.

[0071] Voltage transformation: A schematic diagram of the circuit structure for voltage transformation is shown below. Figure 4 As shown, the output signal waveforms of each voltage conversion process are as follows: Figure 5 As shown. The baseband signal waveform is as follows: Figure 5 The baseband is shown in the diagram. To achieve precise voltage control, an enhancement-mode metal-oxide-semiconductor field-effect transistor (MOSFET) is used for voltage conversion. Its operating principle is based on gate control characteristics: when the gate-source voltage... Below the threshold voltage When, the drain-source path is closed; when Higher than When the drain-source path is open, the drain output becomes the source signal. The modulation control signals output from ports GPIO1 and GPIO2 (waveforms shown in the image) are then used to control the signal. Figure 5 middle (As shown) The DC bias voltage generated by the MCU's digital-to-analog converter (DAC) is applied to the gate of the MOSFET. and (The waveforms are as follows) Figure 5 (As shown in DAC1 and DAC2) is applied to the drain of the MOSFET. With this configuration, the source output signal of the MOSFET is the signal at 0V and the bias voltage. or Modulated waveforms switching between (waveforms are as follows) Figure 5 (As shown in Output1 and Output2). These two independent signals, with precisely controllable voltage values, are input as the final modulation control signals to the gates of the in-phase and quadrature branches of the field-effect transistors in the reconfigurable backscatter communication module, respectively. In this embodiment, the transistor is a BF1109, with a threshold voltage of... The bias voltage is 1.2V. Through electromagnetic simulation analysis, the bias voltage is selected as follows: , This is to ensure that the reconfigurable backscatter communication module achieves optimal impedance matching.

[0072] The reconfigurable backscatter communication module receives an RF carrier from the signal source and, in response to a modulation control signal generated by the signal processing and modulation control module, modulates the ECG data onto the carrier and reflects it. This module employs an in-phase quadrature (IQ) load modulation architecture, such as... Figure 6 As shown, its specific circuit configuration includes:

[0073] A Wilkinson power divider is used to split the radio frequency carrier signal received by the antenna into two signals with equal amplitude and phase.

[0074] A λ / 8 phase delay line is connected to one of the signals, causing a 45-degree phase shift in that signal. Since the reflection path passes through the delay line again, a 90-degree phase difference is ultimately created between the two signals, resulting in two components: an in-phase (I) branch and a quadrature (Q) branch.

[0075] Two controllable impedance units are used to adjust the terminal load impedance of the I and Q branches, respectively. In this embodiment, an Agilent ATF54143 enhancement-mode gallium arsenide field-effect transistor (GaAs FET) is used.

[0076] The working principle of the in-phase quadrature load modulation architecture is as follows: it utilizes two independent bias voltages output by the signal processing and modulation control module. and The voltage is applied to the gates of two field-effect transistors. By changing the gate voltage, the drain-source resistance of the transistors can be precisely controlled, thereby controlling the reflection coefficient at the antenna port. Specifically, the principle of the in-phase quadrature load modulation architecture is as follows: Figure 7 As shown, the scattering matrix of the Wilkinson power divider The reflected signal at the antenna port is defined as a function of the reflected signals from its two output arms, given by the following formula:

[0077]

[0078]

[0079] in, , These represent the incident signals at the two ports, , These represent the reflected signals at the two ports. The reflection coefficients of the two branches. , It is obtained from the following formula:

[0080]

[0081]

[0082] in, This represents the characteristic impedance of the transmission line. and These represent the drain-source resistances of the two transistors, respectively. Based on the relationship of the incident signal... The final calculated reflection coefficient of the antenna port as follows:

[0083]

[0084] It can be seen that the terminal load factors of the two branches constitute the real and imaginary parts of the antenna reflection coefficient, respectively. Therefore, by independently adjusting the gate bias voltages of the two field-effect transistors... , To change its drain-source resistance , This allows for the precise and continuous synthesis of any desired reflection coefficient point on the Smith chart. This architecture requires only a purely resistive load to achieve control of the reflection coefficient in the complex plane, simplifying circuit design. In this embodiment, the lowest power consumption switch-button OOK modulation is used, controlling the transistor in the reflection state (…). ) and absorption state ( Switching between ) to encode digital bits "1" and "0" respectively.

[0085] This invention also provides an ultra-low power wireless transmission method for electrocardiogram signals based on the above system, such as... Figure 8 As shown, the method includes the following steps:

[0086] S1, Signal Transmission: A specific radio frequency carrier is transmitted from a signal source to the space environment.

[0087] S2, Signal Acquisition and Processing: Backscatter tags acquire ECG signals, and amplify, filter, convert analog to digital and frame data to generate modulation control signals.

[0088] S3, Backscatter Modulation: The backscatter tag receives the radio frequency carrier and, based on the modulation control signal, changes the load impedance through in-phase quadrature load modulation to modulate the ECG data onto the radio frequency carrier and reflect it out.

[0089] S4, Signal Reception and Demodulation: The receiving device receives the reflected signal and demodulates it to finally restore the electrocardiogram data.

[0090] To verify the actual performance of the system and method provided in this embodiment of the invention, the following test was conducted: The backscattering tag prepared in this embodiment was worn on the chest of a healthy adult volunteer, powered by a flexible hydrogel battery, and a receiving device was set up at a distance of 10 meters. Detailed clinical feature analysis of the electrocardiogram waveforms acquired by the system of this invention is crucial for verifying its signal quality. For example... Figure 9 As shown, the reconstructed waveform completely contains the PQRST feature points of a standard electrocardiogram. The clinical significance of each waveform is as follows:

[0091] P wave: The waveform is smooth and rounded, with normal amplitude and duration. It represents the depolarization process of atrial myocardium, and its morphology is the basis for judging whether atrial activity is normal.

[0092] QRS complex: The waveform is steep and sharp, with a duration within the normal range (0.06-0.10 seconds), representing rapid ventricular depolarization. Its morphology, width, and amplitude are the core criteria for diagnosing ventricular hypertrophy, conduction block, and myocardial infarction (such as pathological Q waves);

[0093] T wave: The waveform is smooth and broad, with a normal morphology, representing rapid ventricular repolarization. Abnormal T wave morphology is an important indicator of myocardial ischemia, electrolyte imbalance, etc.

[0094] Furthermore, the key intervals in the waveform, such as the PR interval (reflecting atrioventricular conduction time) and the QT interval (reflecting ventricular total repolarization time), are accurately measured without significant distortion. The complete preservation and clear discernibility of these feature points fully demonstrate that the ECG signals transmitted by the system of this invention retain complete clinical diagnostic information, and their quality meets clinical-grade standards that can be used to assist doctors in screening and diagnosing cardiovascular diseases.

[0095] like Figure 9As shown, the wirelessly received and reconstructed ECG signal waveform is clear, with distinct features such as the P wave, QRS complex, and T wave. This waveform is highly morphologically consistent with the signal synchronously recorded by a commercial clinical-grade PowerLab acquisition system, and its Pearson correlation coefficient R = 0.56. At a distance of 10 meters, the signal-to-noise ratio (SNR) of the received signal remains stable above 18 dB, meeting clinical monitoring requirements.

[0096] In terms of power consumption, the two gallium arsenide field-effect transistors (ATF 54143), which serve as controllable impedance elements, are the main energy-consuming units in the reconfigurable backscatter communication module. Their energy consumption primarily comes from the energy consumed in charging and discharging the transistor gate capacitors. According to the energy calculation formula, the total energy consumption for transmitting a data packet is... It can be represented as:

[0097]

[0098] in, The gate capacitance is approximately 2 pF. This is the gate control voltage, approximately 0.5 V. The switching frequency, i.e., the subcarrier frequency, is 4 MHz. The time required to send one data packet is 13333. .

[0099] Since the module contains two identical transistors, the total energy consumption for transmitting each data packet is calculated to be approximately 26 nJ. Assuming each data packet contains a 196-bit payload, the overall system communication energy consumption is as low as 132 pJ / bit. If an ultra-low-power field-programmable gate array (FPGA) or application-specific integrated circuit (ASIC) is used instead of the MCU, the system power consumption is expected to be further significantly reduced.

[0100] To verify the long-term continuous operation capability of the system in practical applications, battery life and signal stability tests were conducted. The system performed continuous ECG monitoring and wireless data transmission for up to 30 hours under conditions powered solely by a flexible hydrogel battery. The test results are as follows: Figure 10 As shown, during the initial operation phase (1 hour), the ECG signal waveforms wirelessly transmitted and reconstructed via the backscatter communication link were clear and stable, with clearly identifiable PQRST characteristic waves and a high signal-to-noise ratio, demonstrating excellent initial performance. After 30 hours of continuous operation, the transmitted ECG signal waveforms remained intact, with key features such as the core QRS complex clearly visible. Although there was a slight baseline drift and a slight attenuation of high-frequency details compared to the initial signal, the main morphological and diagnostic features of the signal were preserved, fully meeting the clinical requirements for long-term trend monitoring.

[0101] The above experimental results fully demonstrate that the ECG monitoring system and method based on backscatter communication provided by this invention has excellent performance in achieving ultra-low power consumption, long communication distance, high signal quality and high system integration, and verify the practicality and reliability of the system and method of this invention in achieving long-term, dynamic ECG monitoring.

[0102] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An ultra-low power electrocardiogram monitoring system based on backscatter communication, characterized in that, include: A signal source used to transmit radio frequency carrier waves into the space environment; A backscatter tag is used to receive the radio frequency carrier, collect and process electrocardiogram (ECG) signals, modulate ECG data onto the radio frequency carrier, and transmit it by reflection. A receiving device is used to receive and demodulate the reflected signal from the backscatter tag to obtain electrocardiogram data; The backscattering tag includes: The electrocardiogram (ECG) signal acquisition module is used to acquire ECG signals and amplify and filter them. The signal processing and modulation control module is connected to the electrocardiogram signal acquisition module and is used to perform analog-to-digital conversion on the analog electrocardiogram signal from the electrocardiogram signal acquisition module and combine it into a predetermined frame structure to generate a modulation control signal. A reconfigurable backscatter communication module is connected to the signal processing and modulation control module. It adopts an in-phase quadrature IQ load modulation architecture to receive the radio frequency carrier transmitted by the signal source and, in response to the modulation control signal, perform reflection modulation on the carrier to reflect and transmit ECG data to the receiving device. The signal processing and modulation control module employs subcarrier frequency shifting technology to generate a subcarrier signal of a predetermined frequency, which is multiplied and mixed with the radio frequency carrier received by the reconfigurable backscatter communication module to shift the spectrum of the reflected signal from the carrier frequency to the predetermined offset frequency, thereby achieving effective separation of the reflected signal from the radio frequency carrier in the frequency domain. The in-phase quadrature IQ load modulation architecture of the reconfigurable backscatter communication module includes: A Wilkinson power divider is used to split a received carrier signal into two equivalent signals with equal amplitude and phase. A λ / 8 phase delay line is connected to one of the lines as a quadrature Q branch to generate a 45-degree phase delay for the signal in that line, and the other line as an in-phase I branch to generate a 90-degree phase difference between the two signals. Two controllable impedance elements are used to adjust the terminal load impedance values ​​of the in-phase I branch and the quadrature Q branch, respectively. The controllable impedance element is a field-effect transistor. By changing the load impedance values ​​of the two transistors, the gate-source bias voltage can be adjusted independently, thereby achieving joint control of the amplitude and phase of the reflected signal.

2. The ultra-low power ECG monitoring system based on backscatter communication according to claim 1, characterized in that, The predetermined frame structure of the signal processing and modulation control module combination includes: A preamble, with a minimum length of 3 bytes, is used to detect the start of a data packet; Synchronization word, 4-8 bytes in length, is used for frame synchronization; The payload, with a length of 0-66 bytes, is used to carry ECG data. Cyclic Redundancy Check (CRC) is an optional field with a length of 3 bytes, used for error detection. The payload includes: The length field is an optional field with a length of 1 byte, used to indicate the payload length; Node address, an optional field, is 1 byte long and is used to indicate the node address; The information field, with a length of 0-20 bytes, is used to carry the actual valid electrocardiogram data.

3. The ultra-low power ECG monitoring system based on backscatter communication according to claim 1, characterized in that, The subcarrier signal is a square wave signal. After Fourier series expansion, its fundamental component is a sine wave of the same frequency. The square wave approximates the sine wave to reduce system power consumption.

4. A method for wireless transmission of ultra-low power electrocardiogram (ECG) signals in an ultra-low power ECG monitoring system based on backscatter communication, used in the ultra-low power ECG monitoring system based on backscatter communication as described in any one of claims 1-3, characterized in that, Includes the following steps: The signal source transmits a radio frequency carrier; The backscatter tag acquires and processes electrocardiogram signals to generate modulation control signals; The backscatter tag receives the radio frequency carrier and performs reflection modulation on the carrier according to the modulation control signal; The receiving device receives and demodulates the reflected signal to obtain electrocardiogram data.

5. The ultra-low power ECG signal wireless transmission method of the ultra-low power ECG monitoring system based on backscatter communication according to claim 4, characterized in that, The step of the backscatter tag performing reflection modulation on the carrier includes: The radio frequency carrier from the signal source is amplified, filtered, and converted from analog to digital, and then combined into a predetermined frame structure to generate a modulation control signal. The radio frequency signal is decomposed into two signals with equal amplitude and the same phase. A phase delay is introduced into one of the signals to form two signal components that are in phase and quadrature. By utilizing the two independent bias voltages contained in the modulation control signal, the load impedances of the in-phase and quadrature branches are independently modulated, thereby encoding the electrocardiogram data onto the radio frequency carrier and reflecting it to the receiving device.

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