Heart rate and blood oxygen detection and transparent capacitance fingerprint multiplexing composite sensor device and method

Abstract

The invention relates to the technical field of biological feature recognition and health monitoring, and discloses a heart rate and blood oxygen detection and transparent capacitance fingerprint multiplexing composite sensor device which comprises an upper layer (contact layer) and a transparent capacitance electrode array. A middle layer (optical layer), a light-transmitting isolation and photoelectric device layer; and a lower layer (processing layer), a signal processing and control unit. The working method of the composite sensor device for heart rate and blood oxygen detection and transparent capacitance fingerprint multiplexing comprises the following time division multiplexing processes: 1, a fingerprint identification stage (0-100ms); and 2, a heart rate and blood oxygen detection stage (100-600ms). Compared with the prior art, the system has the advantages that 1, the system has an integration advantage (corresponding to layered structure design); 2, high-efficiency user experience (corresponding to a time division multiplexing process) is realized; 3, low-power-consumption design (corresponding to time sequence control and power management); and 4, high compatibility and precision (corresponding materials and signal processing) are realized.

Description

Technical Field

[0001] This invention relates to the field of biometric identification and health monitoring technology, specifically to a composite sensor device and method for heart rate and blood oxygen detection and transparent capacitive fingerprint multiplexing. Background Technology

[0002] Biometric identification and health monitoring technologies are rapidly developing in fields such as smart wearables, mobile terminals, and medical devices. Fingerprint recognition, as a mature identity authentication technology, is evolving from physical buttons to under-display transparent designs; heart rate and blood oxygenation (PPG) detection is a core technology for portable health monitoring, widely used in smartwatches and medical monitoring devices. However, in existing technologies, these two types of functional modules are designed independently, resulting in problems such as hardware redundancy, large space occupation, and high power consumption, urgently requiring integrated solutions.

[0003] Existing fingerprint recognition technologies:

[0004] Capacitive fingerprint sensors sense fingerprint texture through silicon-based capacitor arrays, but their non-transparent structure cannot be integrated with optical devices. While transparent capacitor technology (such as ITO electrodes) achieves light transmission, its grid structure easily blocks the PPG optical path, resulting in light signal attenuation of >30%, and the spatial layout conflict between the electrodes and the light source / detector remains unresolved.

[0005] Current heart rate and blood oxygenation detection technologies:

[0006] PPG sensors require a fixed distance of 2-10mm between the light source (660nm red light, 940nm infrared light) and the detector to ensure signal strength. In traditional designs, they are placed side by side with the fingerprint module (such as the fingerprint module in the crown and the PPG module in the strap in smartwatches), resulting in low internal space utilization and a significant increase in thickness.

[0007] Common drawbacks of existing technologies:

[0008] Independent hardware leads to wasted space: stacking the fingerprint module (1-1.5mm thick) and the PPG module (1-2mm thick) increases the total thickness of the device by 20%-30% (e.g., a traditional smartwatch is 12mm thick, but after stacking, it becomes 14.4-15.6mm), making it difficult to adapt to ultra-thin devices (e.g., foldable screen phones require a thickness of <8mm).

[0009] High latency in function switching: Independent modules require users to manually switch functions (such as unlocking before starting health monitoring), which is cumbersome and takes more than 1 second to switch, resulting in a poor user experience.

[0010] Power consumption redundancy: When the two modules are powered independently, the standby power consumption is >50mW (10mW for the fingerprint module and 40mW for the PPG module), which limits the battery life (e.g., the battery life of a smartwatch is shortened from 7 days to less than 5 days).

[0011] Severe signal interference: If physically approached, the high-frequency excitation signal (100kHz) of the capacitive sensor will interfere with the weak photocurrent (nA level) of the PPG, resulting in a heart rate detection error of >±5bpm. Summary of the Invention

[0012] The technical problem to be solved by the present invention is to overcome the above-mentioned technical difficulties and provide a composite sensor device and method for multiplexing heart rate and blood oxygen detection and transparent capacitive fingerprint, which solves the problems of hardware separation, space waste and high power consumption in the prior art and realizes the efficient user experience of "one touch for dual detection".

[0013] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0014] A composite sensor device for multiplexing heart rate and blood oxygen detection with transparent capacitive fingerprint recognition includes:

[0015] Upper layer (contact layer), transparent capacitor electrode array:

[0016] Utilizing silver nanowire material, the light transmittance is ≥90%, sheet resistance is ≤10Ω / □, with a mesh-like distribution, mesh spacing of 0.2-0.4mm, linewidth of 40-60μm, and pre-reserved optical path vias with a diameter of 0.4-0.6mm, and a density of ≥200 nanowires / cm². 2 ;

[0017] Middle layer (optical layer), light-transmitting and insulating layer with optoelectronic devices:

[0018] It includes a light-transmitting silicone substrate with a thickness of 1.0-1.2mm, a built-in micro LED light source and photodiode array, a 3mm distance between the light source and the detector, and a light-shielding partition wall between the light source and the detector with a light-shielding rate of >99%;

[0019] Lower layer (processing layer), signal processing and control unit:

[0020] It includes a capacitance detection chip, a PPG analog front-end, and a main control MCU, and adopts COB packaging technology with a thickness of ≤0.8mm;

[0021] Key component connection relationships:

[0022] Transparent capacitor electrodes are made of ITO conductive adhesive (conductivity 10). 4 The S / m signal is connected to the input terminal of the capacitance detection chip to transmit the capacitance signal.

[0023] The LED and PD are connected to the I / O port of the PPG analog front end through gold-plated pads (0.3mm in diameter) to transmit optical signals;

[0024] The main control MCU connects to the capacitance detection chip and the PPG analog front end via the SPI interface (10Mbps) to achieve timing control.

[0025] The operating method of the composite sensor device for multiplexing heart rate and blood oxygen detection and transparent capacitive fingerprint includes the following time-division multiplexing process:

[0026] First, the fingerprint recognition stage (0-100ms):

[0027] Triggering condition: When the user's finger touches the upper electrode array and the capacitance value changes by more than 10fF, the MCU automatically starts fingerprint detection.

[0028] Signal acquisition: The MCU sends a trigger signal to the capacitance detection chip and applies a 100kHz AC excitation voltage (amplitude 1V); the electrode array senses the difference between the fingerprint ridges (contact electrodes, capacitance > 50fF) and valleys (non-contact electrodes, capacitance < 20fF), and converts them into digital signals via a 24-bit ADC;

[0029] Image processing: The algorithm removes noise by dynamic thresholding (threshold = mean + 3σ), and then fills the image holes caused by optical path through holes by Delaunay triangulation algorithm (filling accuracy > 98%) to generate a complete fingerprint image (resolution 500dpi). It also extracts feature points such as endpoints and bifurcation points (≥30) and matches them with the template (matching time < 20ms).

[0030] Second, the heart rate and blood oxygenation detection phase (100-600ms):

[0031] Triggering condition: After successful fingerprint recognition, the MCU automatically switches to PPG mode (no user operation required);

[0032] Light signal emission: The MCU controls the LED to alternately emit red light (660nm) and infrared light (940nm), with a pulse frequency of 100Hz and a duty cycle of 50% (to avoid overheating of the light source). The light signal reaches the skin of the finger through the upper through-hole.

[0033] Optical signal reception: The PD receives the reflected light through the finger (red light / infrared light corresponds to the absorption difference of oxygenated / deoxygenated hemoglobin in the blood, respectively), converts it into nA-level photocurrent, amplifies it into a voltage signal (1V corresponds to 1nA photocurrent) through a transimpedance amplifier, and then extracts the AC component (pulse fluctuation) and DC component (baseline) through a 50Hz low-pass filter (to filter out power frequency interference).

[0034] Data calculation: Based on the Beer-Lambert law, using the formula... Calculate blood oxygen saturation; calculate heart rate using peak detection method (identifying peaks with an interval > 300ms) (sampling rate 100Hz, 50 data points can be collected within 500ms to ensure accuracy).

[0035] The anti-interference design principle of this technical solution is as follows:

[0036] Spatial isolation: The upper electrode and the middle optoelectronic device are physically separated through optical vias, and there is no direct coupling between the capacitive signal (electric domain) and the optical signal (optical domain);

[0037] Temporal isolation: Fingerprint detection (0-100ms) and PPG detection (100-600ms) are performed in a time-sharing manner to avoid high-frequency electrical signals interfering with weak light signals;

[0038] Power isolation: The capacitor detection module is powered by 3.3V and the PPG module is powered by 1.8V. Each is connected in series with an LC filter circuit (10μH inductor + 100nF capacitor) to suppress power supply noise (noise suppression ratio > 40dB).

[0039] Electromagnetic shielding: A 50nm thick graphene grounding shield is laid under the processing layer to absorb external electromagnetic radiation (EMI < 30dBμV / m) and ensure that the PPG signal signal-to-noise ratio (SNR) reaches 18dB.

[0040] The advantages of this invention compared to the prior art are:

[0041] 1. Integration advantages (corresponding to layered structure design):

[0042] The thickness of each layer is: top layer (<0.1mm) + middle layer (1.2mm) + bottom layer (0.8mm) = 2.0mm, which reduces the space by 50% compared to the independent module (1-1.5mm + 1-2mm = 2-3.5mm), and can be adapted to smartphones and foldable screen devices with a thickness of <8mm.

[0043] 2. Efficient user experience (corresponding to time-sharing reuse process):

[0044] Fingerprint recognition speed <100ms, heart rate and blood oxygen detection latency <500ms (total time <600ms), no manual switching required, achieving "one-touch verification + synchronous acquisition of health data", reducing operation time by 80%.

[0045] 3. Low-power design (corresponding to timing control and power management):

[0046] In time-sharing mode, the capacitance detection module is activated only from 0-100ms (power consumption 30mW), and the PPG module is activated only from 100-600ms (power consumption 20mW), with an average power consumption of 25mW, which is 50% lower than that of independent modules (>50mW), and the device's battery life is extended by more than 20% (e.g., smartwatches are extended from 7 days to 8.5 days).

[0047] 4. High compatibility and accuracy (for compatible materials and signal processing):

[0048] The silver nanowire electrode has a light transmittance of 92%, ensuring that the PPG light signal attenuation is <8%; combined with the anti-interference design, the heart rate detection error is <±2bpm and the SpO2 error is <±2%, meeting the medical-grade accuracy requirements (compliant with ISO 80601-2-61 standard). Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the composite sensor device for heart rate and blood oxygen detection and transparent capacitive fingerprint multiplexing of the present invention (as shown in the figure, from top to bottom: upper layer, middle layer and lower layer). Detailed Implementation

[0050] In the description of this invention, it should be understood that the terms "center," "lateral," "upper," "lower," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more. Additionally, the term "comprising" and any variations thereof are intended to cover non-exclusive inclusion.

[0051] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings.

[0052] A composite sensor device for multiplexing heart rate and blood oxygen detection with transparent capacitive fingerprint recognition includes:

[0053] Upper layer (contact layer), transparent capacitor electrode array:

[0054] Material: Silver nanowires (92% transmittance, 8Ω / □ sheet resistance), which combine high transmittance and conductivity (superior to ITO's 85% transmittance and 15Ω / □ sheet resistance);

[0055] Structure: Mesh distribution (mesh spacing 0.3mm, line width 50μm), with reserved circular optical vias of 0.5mm diameter (density 200 vias / cm²). 2 The vias correspond one-to-one with the light source / detector in the intermediate layer to ensure that the optical path is unobstructed;

[0056] Thickness: <0.1mm (negligible), bonded to the upper part of the intermediate layer with optical adhesive (0.05mm thick).

[0057] Middle layer (optical layer), light-transmitting and insulating layer with optoelectronic devices:

[0058] Substrate: 1.2mm thick translucent silicone (refractive index 1.45, matching the glass cover to reduce light reflection loss);

[0059] Optoelectronic devices: Built-in miniature LED light source (660nm red light, 940nm infrared light, 5mW power) and photodiode (PD) array. Each pair of light source-detector corresponds to one optical path aperture on the upper layer, with a spacing of 3mm (the optimal distance for optimizing signal strength).

[0060] Optical isolation design: A light-shielding partition (0.8mm high, made of black silicon, with a light-shielding rate of >99%) is set between the light source and the detector to avoid optical crosstalk between different channels (crosstalk rate <1%).

[0061] Lower layer (processing layer), signal processing and control unit:

[0062] Core components:

[0063] Capacitance detection chip (ADC accuracy 24-bit, sampling rate 1MHz, supports 100kHz AC excitation);

[0064] PPG analog front end (noise < 1nV / √Hz, including transimpedance amplifier gain 10) 6 V / A, 50Hz low-pass filter);

[0065] The main control MCU (ARM Cortex-M7, 200MHz) is responsible for timing control and data processing;

[0066] Thickness: 0.8mm (using COB packaging technology to reduce component stacking thickness).

[0067] Key component connection relationships:

[0068] Transparent capacitor electrodes are made of ITO conductive adhesive (conductivity 10). 4 The S / m signal is connected to the input terminal of the capacitance detection chip to transmit the capacitance signal.

[0069] The LED and PD are connected to the I / O port of the PPG analog front end through gold-plated pads (0.3mm in diameter) to transmit optical signals;

[0070] The main control MCU connects to the capacitance detection chip and the PPG analog front end via the SPI interface (10Mbps) to achieve timing control.

[0071] The operating method of the composite sensor device for multiplexing heart rate and blood oxygen detection and transparent capacitive fingerprint includes the following time-division multiplexing process:

[0072] First, the fingerprint recognition stage (0-100ms):

[0073] Triggering condition: When the user's finger touches the upper electrode array and the capacitance value changes by more than 10fF, the MCU automatically starts fingerprint detection.

[0074] Signal acquisition: The MCU sends a trigger signal to the capacitance detection chip and applies a 100kHz AC excitation voltage (amplitude 1V); the electrode array senses the difference between the fingerprint ridges (contact electrodes, capacitance > 50fF) and valleys (non-contact electrodes, capacitance < 20fF), and converts them into digital signals via a 24-bit ADC;

[0075] Image processing: The algorithm removes noise by dynamic thresholding (threshold = mean + 3σ), and then fills the image holes caused by optical path through holes by Delaunay triangulation algorithm (filling accuracy > 98%) to generate a complete fingerprint image (resolution 500dpi). It also extracts feature points such as endpoints and bifurcation points (≥30) and matches them with the template (matching time < 20ms).

[0076] First, the heart rate and blood oxygenation detection phase (100-600ms):

[0077] Triggering condition: After successful fingerprint recognition, the MCU automatically switches to PPG mode (no user operation required);

[0078] Light signal emission: The MCU controls the LED to alternately emit red light (660nm) and infrared light (940nm), with a pulse frequency of 100Hz and a duty cycle of 50% (to avoid overheating of the light source). The light signal reaches the skin of the finger through the upper through-hole.

[0079] Optical signal reception: The PD receives the reflected light through the finger (red light / infrared light corresponds to the absorption difference of oxygenated / deoxygenated hemoglobin in the blood, respectively), converts it into nA-level photocurrent, amplifies it into a voltage signal (1V corresponds to 1nA photocurrent) through a transimpedance amplifier, and then extracts the AC component (pulse fluctuation) and DC component (baseline) through a 50Hz low-pass filter (to filter out power frequency interference).

[0080] Data calculation: Based on the Beer-Lambert law, using the formula... Calculate blood oxygen saturation; calculate heart rate using peak detection method (identifying peaks with an interval > 300ms) (sampling rate 100Hz, 50 data points can be collected within 500ms to ensure accuracy).

[0081] In specific implementation of the embodiments of the present invention:

[0082] Example 1

[0083] Wearable device application examples (smartwatch)

[0084] Structural parameters:

[0085] The composite sensor measures 30mm × 15mm and is embedded in the crown area of ​​a smartwatch; the electrode via density is increased to 300 per cm². 2 (To improve light signal density), a flexible silver nanowire electrode (bending radius 5mm) is used to fit the crown surface (curvature radius 5mm); the middle silicone substrate is reinforced with a toughening agent (hardness ShoreA 60) to withstand 100,000 presses without deformation.

[0086] Workflow:

[0087] When the user presses the crown, the finger touches the electrode array → fingerprint unlocking is completed in 0-80ms (algorithm optimized to adapt to curved surface contact, recognition accuracy is 99.5%) → PPG detection is automatically started in 80-580ms → heart rate (e.g., 72bpm) and blood oxygen (e.g., 98%) data are output to the screen for display within 5s, and stored in the local health database at the same time.

[0088] Example 2

[0089] Mobile terminal application examples (smartphones)

[0090] Structural parameters:

[0091] The sensor is integrated into the power button area of ​​the mobile phone (size 8mm×20mm). The upper electrode is covered by a 0.5mm thick glass cover plate (95% light transmittance), the middle layer is made of ultra-thin silicone (1.0mm thick), and the lower processing layer is connected to the mobile phone motherboard via FPC (length 10mm, impedance 50Ω). The electrode bending radius is <5mm, which is compatible with the curvature of the mobile phone frame.

[0092] Workflow:

[0093] When the phone screen is on, the user presses and holds the power button to trigger fingerprint authentication (0-90ms, unlocks the phone after successful authentication) → simultaneously starts heart rate monitoring during exercise (90-590ms) → the detection result (e.g., heart rate of 105 bpm after exercise) is simultaneously uploaded to the health management APP, supporting abnormal heart rate warnings (pop-up notification when heart rate is >120 bpm).

[0094] The present invention and its embodiments have been described above, and this description is not restrictive. If those skilled in the art are inspired by this description and design similar embodiments without departing from the spirit of the invention, such embodiments should fall within the protection scope of the present invention.

Claims

1. A composite sensor device for heart rate and blood oxygen detection and transparent capacitive fingerprint multiplexing, characterized in that, Comprise: Upper layer (contact layer), transparent capacitive electrode array: Silver nanowire material is adopted, light transmittance is greater than or equal to 90%, square resistance is less than or equal to 10 ohms / square, grid distribution, grid spacing is 0.2-0.4 mm, line width is 40-60 microns, light path through hole with a reserved diameter of 0.4-0.6 mm, density is greater than or equal to 200 per cm 2 ; Middle layer (optical layer), light isolation and optoelectronic device layer: Including light-transmitting silicone substrate, thickness 1.0-1.2mm, built-in micro-LED light source and photodiode array, light source and detector spacing 3mm, light source and detector between the setting light barrier wall, light shielding rate > 99%; Lower layer (processing layer), signal processing and control unit: Including capacitive detection chip, PPG analog front end and master MCU, using COB packaging technology, thickness ≤0.8mm; Key component connection relationship: Transparent capacitive electrode is connected with the input end of capacitive detection chip through ITO conductive adhesive, and the capacitive signal is transmitted; LED and PD are connected with the I / O port of PPG analog front end through gold-plated pad, and the light signal is transmitted; The master MCU is connected with the capacitive detection chip and the PPG analog front end through SPI interface respectively, and time sequence control is realized.

2. The composite sensor device of claim 1, wherein: The transparent capacitive electrode layer is adhered above the middle layer optical isolation layer through optical adhesive, and the thickness is <0.1mm.

3. The composite sensor device of claim 1, wherein: The master MCU is connected with the capacitive detection chip and the PPG analog front end through SPI interface respectively, and time division multiplexing control is realized.

4. The composite sensor device of claim 3, wherein, The time division multiplexing control includes: Fingerprint identification stage: 0-100ms, complete capacitive signal acquisition, image processing and feature matching; Heart rate and blood oxygen detection stage: 100-600ms, complete light signal emission, reception and data processing.

5. The working method of the composite sensor device for heart rate and blood oxygen detection and transparent capacitive fingerprint multiplexing according to any one of claims 1-4, characterized in that, The time division multiplexing process includes: First, the fingerprint identification stage (0-100ms): Trigger condition: when the user's finger contacts the upper electrode array and the capacitance value changes >10fF, the MCU automatically starts fingerprint detection; Signal acquisition: the MCU sends a trigger signal to the capacitive detection chip, and applies a 100kHz AC excitation voltage; the electrode array senses the difference between the fingerprint ridges and valleys, and converts it into a digital signal through a 24-bit ADC; Image processing: the algorithm removes noise through dynamic threshold segmentation, and fills the image holes caused by light path throughholes through the Delaunay triangulation algorithm, generates a complete fingerprint image, extracts feature points such as endpoints and branch points, and matches with the template; Second, the heart rate and blood oxygen detection stage (100-600ms): Trigger condition: after fingerprint identification, the MCU automatically switches to PPG mode; Light signal emission: the MCU controls the LED to alternately emit red light and infrared light, with a pulse frequency of 100Hz and a duty cycle of 50%, and the light signal directly reaches the skin through the upper layer throughhole; Light signal reception: the PD receives the reflected light through the finger, converts it into nA-level photocurrent, amplifies it into a voltage signal through a transimpedance amplifier, and extracts AC and DC components through a 50Hz low-pass filter; Data calculation: According to the Beer-Lambert law, the oxygen saturation is calculated by the formula Oxygen saturation is calculated; heart rate is calculated by peak detection method.

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