Flexible wearable electronic heart sound stethoscope

Abstract

The flexible wearable electronic heart sound stethoscope comprises a sampler, a preamplifier, an anti-aliasing filter and an analog-to-digital conversion module which are sequentially connected, the sampler is packaged through a flexible material, two silicon microphones are used for collecting heart sound and noise respectively, and each silicon microphone comprises an MEMS simulation acoustic sensor installed on an FPCB. According to the invention, the sampler adopts the FPCB circuit board, so that the purposes of comfort and keeping the sound cavity closed are achieved, and the subsequent signal processing part adopts the hard PCB circuit board, so that the requirements of high integration level and stable signal processing are met; according to the flexible electronic heart sound stethoscope, the two circuit boards are connected through the interface, so that the sampler is easy to replace, meanwhile, the FPCB part with the short service life can be replaced in time, and the use cost of the flexible electronic heart sound stethoscope is reduced. In addition, through reasonable acoustic structure design, signals received by the MEMS simulation acoustic sensor are large.

Description

Technical Field

[0001] The invention belongs to the technical field of medical electronic equipment, and in particular relates to a flexible wearable electronic heart sound stethoscope. Background Art

[0002] At present, the domestic industry mainly focuses on hard electronic stethoscopes, and few use flexible materials to make electronic stethoscopes. Hard electronic stethoscopes have the problems of poor wearing comfort and unstable heart sound pickup, making them difficult to be applied to wearable stethoscope devices.

[0003] A few studies, such as reference 1 [Lee SH, Kim YS, Yeo MK, Mahmood M, Zavanelli N, Chung C, Heo JY, Kim Y, Jung SS, Yeo WH. Fully portable continuous real-time auscultation with a soft wearable stethoscope designed for automated disease diagnosis [J]. Science Advances, 2022, 8(21): eabo5867], proposed a design for a flexible electronic stethoscope. However, since the signal processing and transmission circuit and the acoustic sensor are designed on the same FPCB (Flexible Printed Circuit Board), this design is too expensive to use as a disposable wearable device.

[0004] In addition, there is currently little research on the fixing method of the flexible electronic stethoscope on the skin. During the use of the flexible electronic heart sound stethoscope, the signal-to-noise ratio of the flexible electronic heart sound stethoscope is relatively low during auscultation due to the lack of support provided by the hand when using a conventional stethoscope. In this regard, it is necessary to apply a stable support to the flexible electronic heart sound stethoscope to improve the signal-to-noise ratio of the flexible electronic heart sound stethoscope; Reference 1 supports the flexible electronic stethoscope with pressurized tape and studies the effect of different tapes on the signal-to-noise ratio. This method improves the signal-to-noise ratio during auscultation, but does not fully discuss the specific mechanism that leads to the improvement of the signal-to-noise ratio. After physically modeling the stethoscope system, it can be understood that the flexible electronic stethoscope needs to add a stable displacement support to ensure that the sensor diaphragm of the stethoscope and the skin have relative movement. At the same time, the device designed in Reference 1 does not have a noise reduction method configured in hardware, but only filters through a computer, which will cause some weak key sounds in the heart sound signal to be filtered out.

[0005] Through patent search, it is found that the noise reduction methods applied to electronic stethoscopes include algorithmic noise reduction and hardware noise reduction. Among them, the Chinese patent application with publication number CN118924323A provides an electronic stethoscope, which uses an active noise reduction method. It adopts a dual microphone method, one of which is used to receive heart sounds, but it will inevitably receive noise; the other microphone is specifically used to receive noise. After the signals received by the two microphones are differentiated, a relatively pure heart sound signal can be obtained. This patented technology corrects the total sound data collected by the first sound collector by setting a second sound collector to collect the second noise data, so that the first noise data in the total sound data collected by the first sound collector can be screened out, thereby realizing accurate body sound data collection through a low-cost ordinary pickup, and improving the accuracy of the test results. However, after testing, the design of using sound-absorbing materials around the periphery of the first sound collector mentioned in the patented technology is unnecessary, and may even cause the noise signals collected by the two microphones to be different in size at different frequencies, making it difficult to exclude noise in a wide frequency range by differentiation. Summary of the invention

[0006] In view of the above, the present invention provides a flexible wearable electronic heart sound stethoscope, which can filter out the noise of the heart sound stethoscope, solve the problems of too low service life and too high cost when the equipment is designed completely with FPCB, and is less affected by movement during wearing.

[0007] A flexible wearable electronic heart sound stethoscope is composed of a sampler, a preamplifier, an anti-aliasing filter and an analog-to-digital conversion module connected in sequence. The sampler is packaged by a flexible material and uses two silicon microphones to collect heart sounds and murmurs respectively. The silicon microphones include a MEMS (Micro-Electro-Mechanical System) analog acoustic sensor installed on a FPCB.

[0008] Furthermore, the preamplifier, anti-aliasing filter and analog-to-digital conversion module are mounted on a hard PCB (Printed Circuit Board).

[0009] Furthermore, one of the two silicon microphones is in contact with the chest skin through a closed sound cavity to collect heart sounds, and the other is in contact with the chest skin through an open sound cavity to collect murmurs.

[0010] Furthermore, the MEMS analog acoustic sensors of the silicon microphones are both arranged toward the skin, rather than one facing the skin and the other facing the outside, to prevent the two silicon microphones from receiving different noises due to noise reflection on the skin. This arrangement can filter out as much noise as possible.

[0011] Furthermore, the analog-to-digital conversion module is connected to a Bluetooth transmission module, which can convert the heart sounds into digital signals and upload them to the user's mobile device for viewing.

[0012] Furthermore, the top of the silicon microphone used to collect heart sounds is provided with a support of sufficient rigidity so that the silicon microphone does not displace relative to the whole person, ensuring relative movement between the MEMS simulated acoustic sensor and the chest skin; the top of the silicon microphone used to collect noise does not need to be supported. When the flexible electronic stethoscope is worn on the body, there is no hand to provide support, so the silicon microphone and the skin cannot be guaranteed to have relative movement, so the signal received by the silicon microphone is very weak; in the test, it was found that the hand needs to add sufficient support to ensure that the received signal is large enough, but in the actual wearing process, it is impossible to use the hand to press all the time; after physical modeling, it was found that as long as the back of the sampler has no displacement relative to the whole person (not the chest skin), it can ensure that the chest skin and the sampler have relative displacement, thereby ensuring that the acoustic signal received by the sampler is large enough.

[0013] Furthermore, the closed sound cavity is composed of chest skin, flexible material and FPCB from bottom to top, and the silicon microphone is arranged on the FPCB. Both the flexible material and the FPCB are provided with through holes, which are aligned with the sound receiving holes of the MEMS analog acoustic sensor of the silicon microphone. The closed sound cavity receives vibrations transmitted by the chest skin. Since the silicon microphone is supported, the silicon microphone as a whole does not move, while the surface of the chest skin moves due to the beating of the heart, resulting in relative movement between the silicon microphone and the surface of the chest skin. Due to the use of a closed sound cavity, a large proportion of the energy of the chest skin vibration is transmitted to the silicon microphone, thereby making the heart sound signal-to-noise ratio higher. Since the sampler is made of flexible material as a whole, it can be fixed on the curved skin, and after a certain supporting force is given, the sound cavity is relatively stable.

[0014] Furthermore, the open sound cavity has the same structural composition as the closed sound cavity, except that the flexible material of the open sound cavity has a channel connected to the air along the plane of the skin; the open sound cavity can receive heart sounds to a lesser extent, and such a design can achieve the goal of filtering out heart sounds as little as possible during signal differentiation.

[0015] Furthermore, the diameter of the sound receiving hole of the MEMS analog acoustic sensor is smaller than the diameter of the through hole on the FPCB, and the diameter of the through hole on the FPCB is smaller than the diameter of the through hole on the flexible material; this design can significantly reduce the resonance phenomenon caused by mismatched apertures and prevent distortion of sound signals.

[0016] The present invention adopts a closed sound receiving cavity structure, so that the sound propagation path is effectively controlled; the closed sound cavity design helps to concentrate and strengthen the conduction of heart sound signals, thereby improving the strength and quality of the signal. Compared with the traditional open design, the closed cavity can greatly reduce the interference of environmental noise, so that the received signal mainly comes from the vibration of the chest skin, while reducing the influence of external noise. This optimized structure effectively improves the signal-to-noise ratio of the heart sound signal.

[0017] In the present invention, the silicon microphone is sealed in a flexible material, thereby avoiding the sound leakage problem caused by the gap in the silicon microphone after welding. This design effectively improves the stability of the sound receiving cavity and the signal strength received by the sensor, thereby improving the clarity and accuracy of the heart sound signal.

[0018] Since the present invention uses flexible material packaging, the device can fit closely to the curved surface of the human body, reducing noise interference caused by human movement. At the same time, the closed sound receiving cavity structure ensures the stability of the audio signal in the cavity during exercise. This design takes into account the various activities that users may perform during use (such as exercise, walking, etc.), so that the device can maintain good heart sound collection quality even in motion.

[0019] In the present invention, the sampler adopts an FPCB circuit board to achieve the purpose of comfort and keeping the sound cavity closed, while the subsequent signal processing part adopts a hard PCB circuit board to achieve the requirements of high integration and stable signal processing; the two circuit boards are connected through an interface, so that the sampler is easy to replace, and the FPCB part with a lower lifespan can be replaced in time, reducing the use cost of the flexible electronic heart sound stethoscope.

[0020] Therefore, the present invention has the following beneficial technical effects:

[0021] 1. The present invention achieves noise filtering through active noise reduction technology.

[0022] 2. The present invention divides the PCB board and the FPCB board into zones according to their functions, so that the FPCB part with a shorter service life can be easily replaced.

[0023] 3. The present invention uses the design of a flexible stethoscope probe to allow the sound receiving cavity to form a stable space that is less affected by human body movements.

[0024] 4. The closed sound receiving cavity of the present invention changes the propagation path of sound and effectively improves the signal-to-noise ratio.

[0025] 5. The present invention uses reasonable acoustic structure design to make the signal received by the acoustic sensor larger. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1The figure is a schematic diagram of the circuit structure of the flexible wearable electronic heart sound stethoscope of the present invention.

[0027] Figure 2 The figure is a schematic diagram of the silicon microphone used for collecting heart sounds of the present invention.

[0028] Figure 3 The figure is a schematic diagram of the silicon microphone used for collecting noise according to the present invention.

[0029] Figure 4 This is a physical hardware schematic diagram of the flexible wearable electronic heart sound stethoscope of the present invention.

[0030] Figure 5 Schematic diagram of the stethoscope output signal (including noise) without support, the noise signal, and the signal waveform after wavelet denoising.

[0031] Figure 6 Schematic diagram of the stethoscope output signal (including noise), noise signal and signal waveform after wavelet denoising when supported.

[0032] Figure 7 Schematic diagram of the stethoscope output signal (including noise) without active noise reduction, the noise signal, and the signal waveform after wavelet denoising.

[0033] Figure 8 Schematic diagram of the stethoscope output signal (including noise), noise signal and signal waveform after wavelet denoising under active noise reduction. DETAILED DESCRIPTION

[0034] In order to describe the present invention more specifically, the technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0035] like Figure 1 As shown, the flexible wearable electronic heart sound stethoscope of the present invention includes a sampler, a hard PCB circuit board and an interface for connecting the sampler and the hard PCB circuit board, the sampler includes two MEMS analog acoustic sensors mounted on the FPCB, and the sampler is packaged by a flexible material; the hard PCB circuit board includes a preamplifier, an anti-aliasing filter and an analog-to-digital conversion module.

[0036] The key design is in the sampler part, which uses two silicon microphones to collect heart sounds and murmurs respectively. The silicon microphones contain MEMS analog acoustic sensors mounted on the FPCB. Figure 2 As shown, one of the MEMS analog acoustic sensors of Silicon Wheat is in contact with the chest skin through a closed sound cavity to collect heart sounds, thereby receiving heart sounds to a greater extent; the closed sound cavity is surrounded by the flexible material, chest skin and FPCB.

[0037] like Figure 3As shown, another MEMS analog acoustic sensor of Silicon Wheat is in contact with the chest skin through an open sound cavity to collect noise; the composition structure of the open sound cavity is the same as that of the closed sound cavity, the difference is that the flexible material of the open sound cavity has a channel connected to the air along the plane of the skin; the open sound cavity is used to receive heart sounds to a lesser extent. Through such a design, it is possible to filter out heart sounds as little as possible when differentiating the signals.

[0038] like Figure 2 As shown in the figure, the sound receiving hole of the silicon microphone receives the vibration transmitted by the chest skin from the closed sound cavity composed of flexible material, chest skin and FPCB. Since the silicon microphone is supported, the silicon microphone as a whole does not move, while the chest skin surface moves due to the beating of the heart, resulting in relative movement between the silicon microphone and the chest skin surface. Due to the use of a closed sound cavity, a large proportion of the energy of the chest skin vibration is transmitted to the silicon microphone, resulting in a higher signal-to-noise ratio of heart sounds; since the sampler is made of flexible material as a whole, it can be fixed on the curved skin, and after a certain support force is given, the sound cavity is relatively stable.

[0039] In this embodiment, the two silicon microphones of the sampler attached to the chest skin are placed facing the skin, rather than one facing the skin and the other facing the outside, to prevent the two silicon microphones from receiving different noises due to noise reflection on the skin. This can filter out as much noise as possible.

[0040] The sampler uses FPCB circuit to achieve the purpose of comfort and keep the sound cavity closed, while the subsequent signal processing part uses hard PCB board to achieve high integration and stable signal processing. The two circuit boards are connected through an interface, making the sampler easy to replace, and the FPCB part with a lower life span can be replaced in time, reducing the cost of using the flexible electronic heart sound stethoscope.

[0041] This embodiment Figure 2 The silicon microphone shown in the figure is supported on the top, and the support stiffness is sufficient to prevent the sampler from being displaced relative to the human body as a whole, thereby ensuring relative movement between the MEMS simulated acoustic sensor and the chest skin. When the flexible electronic stethoscope is worn on the body, there is no hand to provide support, so the silicon microphone and the skin cannot be guaranteed to have relative movement, and therefore the signal received by the silicon microphone is very weak. In the test, we need to add sufficient support by hand to ensure that the received signal is large enough; but in the actual wearing process, it is impossible to use the hand to press all the time. After physical modeling, we found that as long as the back of the sampler has no displacement relative to the human body as a whole (not the chest skin), it can ensure that the chest skin and the sampler have relative displacement, thereby ensuring that the acoustic signal received by the sampler is large enough. As for Figure 3 The silicon microphone shown does not require any support.

[0042] In this embodiment, the preamplifier uses an active operational amplifier and a resistor to form a single-power in-phase proportional amplifier to amplify the analog signal by 10 times. The anti-aliasing filter uses a second-order RC low-pass filter, and the cutoff frequency needs to be set above 800Hz and below half the sampling frequency. Because the frequency range of the heart sound signal is 50-800Hz, the cutoff frequency needs to be higher than 800Hz to prevent filtering out part of the heart sound signal; the frequency of the anti-aliasing filter needs to be lower than half the sampling frequency to prevent the high-frequency signal from being identified as a low-frequency signal. After filtering, the voltage follower can be used to increase the voltage output capacity to ensure that the measured voltage will not be affected by the ADC impedance. The analog-to-digital conversion module uses the SAADC (Successive Approximation Analog-to-Digital Converter) module of the Nrf52 series, which has a limited range (generally 0-3.6V), the input signal needs to be DC biased to 1.8V, and the sampling rate of 8kHz is selected (higher than the maximum frequency of twice the signal 800Hz), and this sampling rate has low requirements for the equipment.

[0043] In addition, in this embodiment, a Bluetooth transmission module is connected to the output end of the analog-to-digital conversion module, which can realize the conversion of heart sounds into digital signals and upload them to the host computer. After the host computer collects the heart sounds, the digital signals collected by the two channels are subtracted to obtain the heart sound signals after active noise reduction; further, the differential signal can be denoised by wavelet transform to filter out the remaining noise in the signal.

[0044] Verification Example

[0045] In this verification example, we built the hardware circuit of the electronic heart sound stethoscope and tested it. Figure 4 As shown in the figure, the red dotted box is a flexible FPCB board, and the blue dotted box is a hard PCB circuit board. In the test phase, we used the wavelet denoising method to denoise the signal, which has basically filtered out the noise. Therefore, when calculating the signal-to-noise ratio, we use the signal power after wavelet denoising as the numerator and the noise power filtered by wavelet denoising as the denominator to measure the signal-to-noise ratio of the sampler.

[0046] Next, we will conduct a controlled variable experiment by taking whether to add support to the back of the sampler and whether to actively reduce noise as two variables and controlling the noise to be the same in the same group of experiments.

[0047] Back support verification:

[0048] The signal waveform without support is as follows Figure 5 As shown, the calculated signal-to-noise ratio is 7.73dB; the signal waveform after adding support on the back is as follows Figure 6As shown, the calculated signal-to-noise ratio is 20.05dB; it can be seen that under the same noise, the signal-to-noise ratio of the sampled signal is improved after providing support on the back of the sampler, and the signal strength is also improved.

[0049] Active noise reduction effect verification:

[0050] The signal waveform without active noise reduction is as follows Figure 7 As shown, the calculated signal-to-noise ratio is 13.72dB; the signal waveform after active noise reduction is as follows Figure 8 As shown, the calculated signal-to-noise ratio is 19.07dB; it can be seen that under the same noise, the signal-to-noise ratio of the signal obtained after active noise reduction is improved, and part of the noise is filtered out.

[0051] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art to the present invention based on the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A flexible wearable electronic heart sound stethoscope, which is composed of a sampler, a preamplifier, an anti-aliasing filter and an analog-to-digital conversion module connected in sequence, characterized in that: The sampler is encapsulated by a flexible material and utilizes two silicon microphones to collect heart sounds and murmurs respectively. The silicon microphones include a MEMS analog acoustic sensor mounted on a FPCB.

2. The flexible wearable electronic heart sound stethoscope according to claim 1, characterized in that: The preamplifier, anti-aliasing filter and analog-to-digital conversion module are mounted on a hard PCB.

3. The flexible wearable electronic heart sound stethoscope according to claim 1, characterized in that: One of the two silicon microphones is in contact with the chest skin through a closed sound cavity to collect heart sounds, and the other is in contact with the chest skin through an open sound cavity to collect murmurs.

4. The flexible wearable electronic heart sound stethoscope according to claim 1, characterized in that: The MEMS analog acoustic sensors of the silicon microphone are all arranged toward the skin.

5. The flexible wearable electronic heart sound stethoscope according to claim 1, characterized in that: The analog-to-digital conversion module is connected to a Bluetooth transmission module.

6. The flexible wearable electronic heart sound stethoscope according to claim 1, characterized in that: The top of the silicon microphone used to collect heart sounds is provided with a support of sufficient rigidity to prevent the silicon microphone from shifting relative to the human body, thereby ensuring relative movement between the MEMS simulated acoustic sensor and the chest skin. The top of the silicon microphone used to collect noise does not need to be provided with a support.

7. The flexible wearable electronic heart sound stethoscope according to claim 3, characterized in that: The closed sound cavity is composed of chest skin, flexible material and FPCB from bottom to top, and the silicon microphone is set on the FPCB. Through holes are opened on the flexible material and the FPCB, and are aligned with the sound receiving holes of the MEMS analog acoustic sensor of the silicon microphone.

8. The flexible wearable electronic heart sound stethoscope according to claim 7, characterized in that: The open sound cavity has the same structure as the closed sound cavity, except that the flexible material of the open sound cavity has a channel connected to the air along the plane of the skin.

9. The flexible wearable electronic heart sound stethoscope according to claim 7, characterized in that: The diameter of the sound receiving hole of the MEMS analog acoustic sensor is smaller than the diameter of the through hole on the FPCB, and the diameter of the through hole on the FPCB is smaller than the diameter of the through hole on the flexible material.

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