Nanofiber acoustoelectric device with flat frequency response and method of manufacturing the same

Abstract

The application relates to a nanofiber acoustoelectric device with a flat frequency response and a preparation method thereof. The nanofiber acoustoelectric device comprises a nanofiber membrane, an upper electrode and a lower electrode, the nanofiber membrane is located between the upper electrode and the lower electrode to form a sandwich structure, and the nanofiber acoustoelectric device is formed. The elliptical through-hole structure utilizes the flexibility of the long axis direction to induce the nanofiber membrane to excite multiple high-order vibration modes under the excitation of sound waves, multiple resonance peaks are superimposed in the frequency domain, the response trough of a traditional device is filled, and thus the intrinsic flat frequency response in the target frequency band is realized. The single elliptical through-hole is expanded into a multi-hole array structure, the effective vibration area can be further expanded and the internal stress of the membrane can be improved through hole coupling, the flat bandwidth is widened, the output voltage is improved, high-fidelity and low-distortion acoustoelectric signal conversion can be realized without a complex external equalization circuit, and the application has important application value in the field of flexible wearable acoustics sensing.

Description

Technical Field

[0001] This invention relates to the field of acoustic-electric device technology, specifically to a nanofiber acoustic-electric device with a flat frequency response and its preparation method. Background Technology

[0002] Voice, as one of the most natural and efficient mediums for human-computer interaction, has been widely used in scenarios such as intelligent voice assistants, wearable terminals, in-vehicle voice control, remote conferencing systems, and voiceprint recognition. To achieve high-fidelity voice acquisition and stable voiceprint feature extraction, the front-end acoustic sensor, in addition to possessing high sensitivity and signal-to-noise ratio, should also have the flattest possible frequency response within the target detection frequency band to reduce the impact of waveform distortion and frequency-dependent gain differences on the robustness of voiceprint feature extraction and speech recognition.

[0003] In recent years, acoustic sensors based on electrospun piezoelectric polymer nanofiber membranes have become an important research direction in the fields of flexible microphones and wearable voice acquisition due to their advantages such as high flexibility, adaptability, strong wearability and integration, and the ability to achieve sound-to-electric conversion without the need for an external bias voltage. Existing research has made progress in improving sensitivity and expanding response bandwidth by controlling the piezoelectric material system, fiber structure, and device structure.

[0004] However, from a system application perspective, a flat frequency response remains a key limitation restricting further performance improvement. The vibration response of most existing piezoelectric nanofiber acoustic sensors is still dominated by low-order modes, typically exhibiting a significant resonance peak at a certain low frequency, with the output amplitude rapidly decreasing as the frequency increases. Alternatively, sharp resonance peaks may appear at several discrete frequencies, resulting in large fluctuations and poor flatness in the frequency response curve, leading to an imbalance in the sensor's acoustic response across different frequencies. To obtain signals usable for high-quality acquisition and recognition, the system often requires complex circuit equalization or algorithm compensation to meet subsequent application requirements, weakening its advantages in low-power, flexible wearable scenarios.

[0005] Nanofiber acousto-electric devices have the following technical problems:

[0006] 1. Existing piezoelectric nanofiber acousto-electric devices can mostly be equated to lightly damped single-degree-of-freedom or few-degree-of-freedom vibration systems. Their frequency response often exhibits a single sharp resonance peak or a few discrete resonance peaks. Far from the resonance region, the output sensitivity decays rapidly with increasing frequency, leading to unbalanced amplification or attenuation of different frequency components, resulting in spectral distortion and acoustic feature distortion. To compensate for the inherent frequency selectivity of these structures, existing systems often rely on back-end filtering, electronic equalization, or algorithmic correction, leading to complex system structures, increased power consumption, and decreased reliability and wearable integration. Therefore, how to achieve an intrinsically flat frequency response solely through the device structure itself and reduce reliance on external circuit compensation remains a pressing technical challenge.

[0007] 2. Regarding the issue of balancing flatness and high output voltage:

[0008] Existing flat frequency response acoustic devices primarily rely on capacitive operating mechanisms or achieve a relatively flat output by pushing the structural resonant frequency away from the effective bandwidth. However, these strategies often result in smaller amplitudes within the effective response bandwidth, leading to weaker output signals. They typically require high-voltage bias circuits and low-noise preamplifiers, significantly increasing system power consumption and complexity. For piezoelectric devices using nanofiber membranes as sensing units, simply suppressing the resonant peak further reduces the membrane vibration amplitude and effective piezoelectric strain, causing a drop in output voltage. This makes it difficult to simultaneously meet the requirements of a flat frequency response and high output / high sensitivity. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a nanofiber acoustic-electric device with a flat frequency response and its fabrication method. The nanofiber acoustic-electric device includes a nanofiber membrane, an upper electrode, and a lower electrode. The nanofiber membrane is located between the upper and lower electrodes, forming a sandwich structure. Its elliptical through-hole structure utilizes the flexibility of its long axis to induce multiple high-order vibration modes in the nanofiber membrane under acoustic excitation. The corresponding multiple resonance peaks superimpose in the frequency domain, filling the response troughs of traditional devices, thereby achieving an intrinsic flat frequency response within the target frequency band. Expanding a single elliptical through-hole into a multi-hole array can further expand the effective vibration region and increase the internal stress of the membrane through inter-hole coupling, thereby widening the flat bandwidth and increasing the output voltage. This invention achieves high-fidelity, low-distortion acoustic-electric signal conversion without complex external equalization circuits, and has significant application value in the field of flexible wearable acoustic sensing.

[0010] The technical problem solved by this invention is achieved through the following technical solution:

[0011] A nanofiber acousto-electric device with a flat frequency response includes a nanofiber membrane, an upper electrode, and a lower electrode, wherein the nanofiber membrane is located between the upper electrode and the lower electrode to form a nanofiber acousto-electric device.

[0012] The nanofiber membrane has a fiber diameter range of 1–1000 nm and a fiber membrane thickness range of 10 μm–1 mm;

[0013] Both the upper and lower electrodes are composed of a plastic film and a metal conductive layer on the surface of the plastic film. A single elliptical through hole or multiple elliptical through holes are formed on the plastic film and the metal conductive layer by laser cutting. Multiple elliptical through holes form a porous array structure. Through the inter-hole coupling of the elliptical through holes, the nanofiber acoustic-electric device can achieve a flat frequency response of ±2dB in the range of 219-676Hz.

[0014] Furthermore, the nanofiber membrane is prepared by electrospinning technology, and the spinning polymer raw material is polyacrylonitrile polyvinylidene fluoride, polyvinylidene fluoride-trifluoroethylene copolymer, polylactic acid, polyimide, polyimide copolymer or other piezoelectric polymers.

[0015] Furthermore, both the upper and lower electrodes are 30×40mm. 2 The plastic film is made of polyethylene terephthalate, polypropylene, polyethylene or paper-based materials.

[0016] Furthermore, the metal conductive layer is selected from gold, silver, copper, platinum, nickel or other metal conductive materials, and its thickness ranges from 50 to 1000 nm.

[0017] Furthermore, the aspect ratios of the elliptical through holes are 1:1, 4:3, 2:1, 3:1, and 4:1, respectively.

[0018] A method for fabricating the nanofiber acousto-electric device with a flat frequency response as described above:

[0019] A method for fabricating a single elliptical through-hole nanofiber acousto-electric device includes the following steps:

[0020] Step 1: Preparation of oriented polyacrylonitrile nanofiber membranes:

[0021] Using polyacrylonitrile as the spinning raw material, polyacrylonitrile was dissolved in N,N-dimethylformamide at 50°C to prepare a homogeneous spinning solution with a mass fraction of 14 wt%.

[0022] The spinning solution was injected into an electrospinning machine, and the spinning parameters were set as follows: flow rate of 1 mL / h, spinning distance of 15 cm, spinning voltage of 20 kV, and roller speed of 300-2100 rpm to prepare an oriented polyacrylonitrile nanofiber membrane.

[0023] Step 2: Prepare the upper and lower electrodes with a single elliptical through-hole:

[0024] A 100 nm thick gold conductive layer was deposited on one side of a polyethylene terephthalate (PET) film using high-vacuum evaporation. Elliptical through-holes were then cut into the PET film and the gold conductive layer using a laser. The aspect ratios of the elliptical through-holes were 1:1, 4:3, 2:1, 3:1, and 4:1, respectively, to create an upper electrode and a lower electrode with a single elliptical through-hole.

[0025] Step 3: Assemble a single elliptical through-hole nanofiber acousto-electric device:

[0026] Oriented polyacrylonitrile nanofiber membranes were cut into 30×40 mm pieces using a laser. 2 As a sensing layer;

[0027] An oriented polyacrylonitrile nanofiber membrane is placed between an upper electrode with a single elliptical through-hole and a lower electrode with a single elliptical through-hole, and fixed with a plastic clamp to form a sandwich structure. This is then assembled into a single elliptical through-hole nanofiber acousto-electric device. The metal conductive layers of the upper and lower electrodes are in contact with the nanofiber membrane to collect piezoelectric charges.

[0028] Step 4, Acoustic and electrical performance testing:

[0029] Commercial loudspeakers with adjustable frequency and sound pressure level were used as the sound source. The sound source frequency was scanned in the range of 100–1000 Hz. A single elliptical through-hole nanofiber acousto-electric device was clamped and fixed on a high-quality substrate with a fixture. The open-circuit voltage output of the single elliptical through-hole nanofiber acousto-electric device at different frequencies was recorded. ±2dB was used as the criterion for flat bandwidth. The flat bandwidth and the corresponding flat voltage were calculated.

[0030] A method for fabricating a nanofiber acousto-electric device with multiple elliptical through holes includes the following steps:

[0031] Step 1: Preparation of oriented polyacrylonitrile nanofiber membranes:

[0032] Using polyacrylonitrile as the spinning raw material, polyacrylonitrile was dissolved in N,N-dimethylformamide at 50°C to prepare a homogeneous spinning solution with a mass fraction of 14 wt%.

[0033] The spinning solution was injected into an electrospinning machine, and the spinning parameters were set as follows: flow rate of 1 mL / h, spinning distance of 15 cm, spinning voltage of 20 kV, and roller speed of 300-2100 rpm to prepare an oriented polyacrylonitrile nanofiber membrane.

[0034] Step 2: Fabricate the upper and lower electrodes with multiple elliptical through holes:

[0035] A 100 nm thick gold conductive layer was deposited on one side of a polyethylene terephthalate (PET) film using high-vacuum evaporation. Elliptical vias were then cut into the PET film and the gold conductive layer using a laser. The aspect ratios of the elliptical vias were 1:1, 4:3, 2:1, 3:1, and 4:1, respectively. Multiple elliptical vias were arranged in an array with an adjacent spacing of 1 mm to form a porous array structure. An upper electrode and a lower electrode with multiple elliptical vias were then fabricated.

[0036] Step 3: Assemble multiple elliptical through-hole nanofiber acoustic-electric devices:

[0037] Oriented polyacrylonitrile nanofiber membranes were cut into 30×40 mm pieces using a laser. 2 As a sensing layer;

[0038] An oriented polyacrylonitrile nanofiber membrane is placed between an upper electrode with multiple elliptical through holes and a lower electrode with multiple elliptical through holes, and fixed with a plastic clamp to form a sandwich structure. This is then assembled into a nanofiber acousto-electric device with multiple elliptical through holes. The metal conductive layers of the upper and lower electrodes are in contact with the nanofiber membrane to collect piezoelectric charges.

[0039] Step 4: Acoustic and electrical performance testing:

[0040] A commercial loudspeaker with adjustable frequency and sound pressure level was used as the sound source. The sound source frequency was scanned in the range of 100 to 1000 Hz. Multiple elliptical through-hole nanofiber acousto-electric devices were clamped and fixed on a high-quality substrate around the perimeter using a fixture. The open-circuit voltage output of multiple elliptical through-hole nanofiber acousto-electric devices at different frequencies was recorded. The flat bandwidth and the corresponding flat voltage were calculated using ±2dB as the criterion for determining the flat bandwidth.

[0041] The advantages and positive effects of this invention are:

[0042] This invention relates to a nanofiber acoustic-electric device with a flat frequency response and its fabrication method. Starting from the design of device geometry and modal control, a nanofiber membrane is prepared by electrospinning and assembled with a plastic film electrode with elliptical through holes formed by laser cutting to form a sandwich structure.

[0043] By introducing an elliptical through-hole structure on the electrode, the high flexibility of the elliptical through-hole along the long axis direction is utilized to induce and regulate multi-node high-order vibration modes that can be effectively excited along the long axis direction, thereby forming multiple resonance peaks in the target frequency band. The multiple resonance peaks are superimposed in the frequency domain and fill the low response region to reduce the fluctuation amplitude of the output with frequency variation, thus achieving an intrinsically flat frequency response of the structure.

[0044] Expanding a single elliptical through-hole into a porous array structure introduces inter-hole coupling and enhances overall vibration participation, thereby expanding the effective vibration region, increasing the average stress on the nanofiber membrane surface, broadening the flat bandwidth, and increasing the output voltage. This reduces reliance on front-end amplification and digital equalization, enabling a flat frequency response with high sensitivity and low spectral distortion without complex electronic equalization while maintaining high output. The nanofiber acousto-electric device achieves a flat frequency response of ±2dB in the 219-676Hz range, avoiding frequency-selective amplification or attenuation of traditional single-peak resonant devices from the source, and significantly reducing frequency distortion of speech signals. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the structure of the nanofiber acousto-electric device with a flat frequency response according to the present invention;

[0046] Figure 2 (a) is a schematic diagram of the upper and lower electrodes of the two elliptical through holes of the nanofiber acoustic-electric device with flat frequency response of the present invention;

[0047] Figure 2 (b) is a schematic diagram of the upper and lower electrodes of the three elliptical through holes of the nanofiber acoustic-electric device with flat frequency response of the present invention.

[0048] Figure 2 (c) is a schematic diagram of the upper and lower electrodes of the four elliptical through holes of the nanofiber acousto-electric device with flat frequency response of the present invention.

[0049] Figure 2 (d) is a schematic diagram of the upper and lower electrodes of the five elliptical through holes of the nanofiber acoustic-electric device with flat frequency response of the present invention;

[0050] Figure 3 (a) is a fiber morphology diagram of an oriented polyacrylonitrile nanofiber membrane according to Embodiment 1 of the present invention;

[0051] Figure 3 (b) is a diagram showing the fiber diameter of the oriented polyacrylonitrile nanofiber membrane of Embodiment 1 of the present invention;

[0052] Figure 3 (c) is a fiber orientation angle distribution diagram of the oriented polyacrylonitrile nanofiber membrane of Embodiment 1 of the present invention;

[0053] Figure 4 In the middle (a), the open-circuit voltage of a single elliptical through-hole nanofiber acousto-electric device with an aspect ratio of 1:1 varies with the frequency of the sound wave.

[0054] Figure 4(b) shows the curve of open-circuit voltage versus sound frequency for a single elliptical through-hole nanofiber acousto-electric device with an aspect ratio of 4:3.

[0055] Figure 4 (c) shows the curve of open-circuit voltage versus sound frequency for a single elliptical through-hole nanofiber acousto-electric device with an aspect ratio of 2:1.

[0056] Figure 4 In the middle (d), the open-circuit voltage of a single elliptical through-hole nanofiber acousto-electric device with an aspect ratio of 3:1 varies with the sound wave frequency.

[0057] Figure 4 In the middle (e), the open-circuit voltage of a single elliptical through-hole nanofiber acousto-electric device with an aspect ratio of 4:1 varies with the frequency of the sound wave.

[0058] Figure 4 In the middle (f), the flat bandwidth and flat voltage of a single elliptical through-hole nanofiber acousto-electric device with different aspect ratios are shown (the test sound pressure level is 115dB).

[0059] Figure 5 Image (a) is a fiber morphology diagram of the oriented polyacrylonitrile nanofiber membrane of Example 2 of the present invention;

[0060] Figure 5 (b) is a diagram showing the fiber diameter of the oriented polyacrylonitrile nanofiber membrane in Example 2 of the present invention;

[0061] Figure 5 (c) is a fiber orientation angle distribution diagram of the oriented polyacrylonitrile nanofiber membrane of Embodiment 2 of the present invention;

[0062] Figure 6 (a) shows the curve of open-circuit voltage versus sound frequency for a single elliptical through-hole nanofiber acousto-electric device with randomly oriented fibers.

[0063] Figure 6 (b) shows the curve of open-circuit voltage versus sound frequency for a single elliptical through-hole nanofiber acousto-electric device with the fiber perpendicular to the major axis of the ellipse.

[0064] Figure 6 In the middle (c), the open-circuit voltage of a single elliptical through-hole nanofiber acousto-electric device, with the fiber parallel to the major axis of the ellipse, varies with the sound wave frequency.

[0065] Figure 6 In the middle (d), the flat bandwidth and flat voltage of a single elliptical through-hole nanofiber acousto-electric device with different fiber orientations are shown (the test sound pressure level is 115dB).

[0066] Figure 7In the middle (a), the open-circuit voltage of a 1-hole nanofiber acousto-electric device varies with the frequency of sound waves.

[0067] Figure 7 (b) shows the open-circuit voltage of a 2-hole nanofiber acousto-electric device as a function of sound frequency.

[0068] Figure 7 (c) is a graph showing the open-circuit voltage of a 3-hole nanofiber acousto-electric device as a function of sound frequency.

[0069] Figure 7 The middle (d) graph shows the open-circuit voltage of the 4-hole nanofiber acousto-electric device as a function of the sound wave frequency.

[0070] Figure 7 The graph in (e) shows the open-circuit voltage of a 5-hole nanofiber acousto-electric device as a function of sound frequency.

[0071] Figure 7 (f) shows the flat bandwidth and flat voltage of multiple elliptical through-hole nanofiber acousto-electric devices with different numbers of elliptical through-holes (tested sound pressure level is 115dB).

[0072] Figure 8 (a) shows the voltage and power variation curves of a 1-hole nanofiber acousto-electric device with different resistances under load.

[0073] Figure 8 Figure (b) shows the voltage and power variation curves of a 2-hole nanofiber acousto-electric device with two elliptical through holes when the load is different resistances.

[0074] Figure 8 (c) shows the voltage and power variation curves of a 3-hole nanofiber acousto-electric device with three elliptical through holes under different resistances.

[0075] Figure 8 The middle (d) graph shows the voltage and power changes of the 4-hole nanofiber acousto-electric device under different resistance loads.

[0076] Figure 8 (e) shows the voltage and power variation curves of the 5-hole nanofiber acousto-electric device with different resistances under load.

[0077] Figure 8 In the middle (f), the internal resistance and maximum output power of multiple elliptical through-hole nanofiber acousto-electric devices with different numbers of elliptical through-holes are shown (the test sound source conditions are 150Hz and 115dB). Detailed Implementation

[0078] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0079] like Figure 1 As shown, a nanofiber acousto-electric device with a flat frequency response includes a nanofiber membrane, an upper electrode, and a lower electrode. The nanofiber membrane is located between the upper and lower electrodes to form the nanofiber acousto-electric device, which has a size of 30×40mm. 2 .

[0080] Nanofiber membranes are prepared using electrospinning technology. The spinning polymer raw materials include polyacrylonitrile-polyvinylidene fluoride, polyvinylidene fluoride-trifluoroethylene copolymer, polylactic acid, polyimide, polyimide copolymer, or other piezoelectric polymers. The fiber diameter of the nanofiber membrane ranges from 1 to 1000 nm, and the membrane thickness ranges from 10 μm to 1 mm. As the core sensing layer responding to sound waves, the nanofiber membrane exhibits strain under the influence of sound waves, thereby generating an electrical signal.

[0081] Both the upper and lower electrodes are composed of a plastic film and a conductive metal layer on the surface of the plastic film. Both the upper and lower electrodes are 30×40mm in size. 2 The plastic film is made of polyethylene terephthalate (PET), polypropylene, polyethylene, or paper-based materials. The conductive metal layer is made of gold, silver, copper, platinum, nickel, or other conductive metals, prepared by high-vacuum evaporation, magnetron sputtering, chemical deposition, etc., with a thickness ranging from 50 to 1000 nm. Single or multiple elliptical through-holes are formed on the plastic film and the conductive metal layer by laser cutting. Multiple elliptical through-holes form a porous array structure. The aspect ratios of the elliptical through-holes are 1:1, 4:3, 2:1, 3:1, and 4:1, preferably 3:1. The area of ​​the elliptical through-hole is preferably 2.54 cm². 2 The major axis of the elliptical through-hole is aligned with the long side of the assembled nanofiber acousto-electric device, and the total exposed area of ​​the multiple elliptical through-holes is consistent with the exposed area of ​​a single elliptical through-hole.

[0082] Based on the number of elliptical through holes on the surfaces of the upper and lower electrodes, assembled nanofiber acousto-electric devices with multiple elliptical through holes are classified into the following four types:

[0083] like Figure 2 As shown in (a), a nanofiber acousto-electric device with two elliptical through holes on the surfaces of the upper and lower electrodes;

[0084] like Figure 2 As shown in (b), there are multiple elliptical through-hole nanofiber acoustic-electric devices with three elliptical through-holes on the surfaces of the upper and lower electrodes.

[0085] like Figure 2 As shown in (c), there are multiple elliptical through-hole nanofiber acoustic-electric devices with four elliptical through-holes on the surfaces of the upper and lower electrodes.

[0086] like Figure 2 As shown in (d), there are multiple elliptical through-hole nanofiber acoustic-electric devices with five elliptical through-holes on the surfaces of the upper and lower electrodes.

[0087] Working principle of the invention:

[0088] A nanofiber membrane is placed between an upper electrode with a single elliptical through-hole and a lower electrode with a single elliptical through-hole, and fixed with a plastic clamp to form a sandwich structure, thus assembling a nanofiber acousto-electric device with a single elliptical through-hole. The metal conductive layers of the upper and lower electrodes are in contact with the nanofiber membrane to collect piezoelectric charges. The plastic clamp is used to fix the membrane to prevent delamination and slippage under acoustic excitation, ensuring long-term stable operation.

[0089] A nanofiber membrane is placed between an upper electrode with multiple elliptical through holes and a lower electrode with multiple elliptical through holes, and fixed with a plastic clamp to form a sandwich structure. This is used to assemble a nanofiber acousto-electric device with multiple elliptical through holes. The metal conductive layer of the upper and lower electrodes is in contact with the nanofiber membrane to collect the piezoelectric charge. The plastic clamp is used to fix the membrane to prevent delamination and slippage under acoustic excitation and to ensure long-term stable operation.

[0090] Elliptical vias induce regular higher-order modes along the long axis, forming multiple peaks to achieve a flat response: elliptical vias have a larger equivalent span and lower equivalent bending stiffness along the long axis, giving the nanofiber acousto-electric device higher compliance in this direction. Under acoustic excitation, this compliance helps guide the membrane-electrode composite structure to generate effectively excitable multi-nodal vibration modes, i.e., higher-order vibrations, along the long axis of the via, thus forming multiple observable resonance peaks in the target frequency band. As the number of modes participating in the response increases, the frequency spacing between equivalent modes tends to decrease. Multiple resonance peaks superimpose in the frequency domain and "fill" in the original low-response region, thereby reducing the fluctuation amplitude of the output with frequency variation and forming a flatter frequency response.

[0091] In comparison, circular through-holes have higher geometric symmetry, and higher-order modes are more likely to exhibit degenerate / symmetric paired mode shapes. Under specific excitation and charge collection boundary conditions, some symmetric mode shapes may cancel each other out in terms of effective strain / charge contribution or be difficult to collect effectively, resulting in a response characteristic in the spectrum that is more likely to be dominated by lower-order modes, with a limited number of resonance peaks and a tendency to decay rapidly with frequency.

[0092] A porous array expands the effective vibration region and increases the average stress through inter-pore coupling, thereby broadening the flat frequency response and improving the voltage output. While maintaining the total exposed area of ​​multiple elliptical vias consistent with that of a single elliptical via, the elliptical vias are expanded from a single via to a porous array structure with multiple elliptical vias. The compliant regions corresponding to the elliptical vias are coupled to the upper and lower electrodes through the nanofiber membrane, resulting in richer modal participation in the overall vibration. This coupling significantly increases the effective vibration region of the device and enhances the average stress of the nanofiber membrane, increasing the vibration amplitude of the upper and lower electrodes, thus broadening the flat frequency response and voltage output.

[0093] This invention effectively solves the single-peak response mode of traditional passive acoustic devices by constructing an electrode architecture with elliptical through holes, forming an intrinsically flat frequency response characteristic, and providing a path for realizing a high-fidelity acoustic sensor.

[0094] A method for fabricating a nanofiber acousto-electric device with a flat frequency response:

[0095] Example 1:

[0096] Methods for fabricating single elliptical through-hole nanofiber acousto-electric devices with different aspect ratios:

[0097] A method for fabricating a single elliptical through-hole nanofiber acousto-electric device includes the following steps:

[0098] Step 1: Preparation of oriented polyacrylonitrile nanofiber membranes:

[0099] Using polyacrylonitrile (PAN) as the spinning raw material, polyacrylonitrile (PAN) was dissolved in N,N-dimethylformamide at 50°C to prepare a homogeneous spinning solution with a mass fraction of 14 wt%.

[0100] The spinning solution was injected into an electrospinning machine, and the spinning parameters were set as follows: flow rate of 1 mL / h, spinning distance of 15 cm, spinning voltage of 20 kV, and roller speed of 2100 rpm to prepare an oriented polyacrylonitrile nanofiber membrane.

[0101] Step 2: Prepare the upper and lower electrodes with a single elliptical through-hole:

[0102] A 100 nm thick gold conductive layer is deposited on one side of a polyethylene terephthalate (PET) film using a high-vacuum evaporation method. Elliptical through-holes are then cut into the PET film and the gold conductive layer using a laser. The aspect ratios of the elliptical through-holes are 1:1, 4:3, 2:1, 3:1, and 4:1, with 3:1 being preferred. This process creates an upper electrode and a lower electrode with a single elliptical through-hole.

[0103] Step 3: Assemble a single elliptical through-hole nanofiber acousto-electric device:

[0104] Oriented polyacrylonitrile nanofiber membranes were cut into 30×40mm pieces using a laser. 2 As a sensing layer;

[0105] An oriented polyacrylonitrile nanofiber membrane is placed between an upper electrode with a single elliptical through-hole and a lower electrode with a single elliptical through-hole, and fixed with a plastic clamp to form a sandwich structure. This is then assembled into a single elliptical through-hole nanofiber acousto-electric device. The metal conductive layers of the upper and lower electrodes are in contact with the nanofiber membrane to collect piezoelectric charges.

[0106] During assembly, the orientation of the nanofiber membrane and the major axis of the elliptical through-holes are aligned with the long side of the individual elliptical through-hole nanofiber acousto-electric device. To further prevent interlayer delamination or relative slippage caused by acoustic vibration, plastic clamps are used for fixation, preventing delamination and slippage under acoustic excitation and ensuring long-term stable operation.

[0107] Step 4, Acoustic and electrical performance testing:

[0108] A commercial loudspeaker with adjustable frequency and sound pressure level was used as the sound source. The sound source frequency was scanned in the range of 100–1000 Hz. A single elliptical through-hole nanofiber acousto-electric device was clamped and fixed on a high-quality substrate around the perimeter using a fixture. The open-circuit voltage output of the single elliptical through-hole nanofiber acousto-electric device at different frequencies was recorded. The flat bandwidth and the corresponding flat voltage were calculated using ±2dB as the criterion for determining the flat bandwidth.

[0109] Test Result Analysis:

[0110] 1. Fiber morphology characterization, such as Figure 3 As shown in (a), (b), and (c):

[0111] The nanofiber membrane prepared by the above method has a fiber diameter of 327±32nm, a fiber orientation angle ranging from -30° to 30°, and a fiber membrane thickness of 30±5µm.

[0112] 2. Sound-to-electricity conversion performance:

[0113] The acoustoelectric properties of single elliptical through-hole nanofiber acoustoelectric devices with different aspect ratios are as follows: Figure 4 As shown in (a), (b), (c), (d), (e), (f) and Table 1, the flat bandwidth and flat voltage of the acoustic-electric device gradually increase with the increase of the aspect ratio of the elliptical through hole, reaching the maximum value at an aspect ratio of 3:1, with a flat bandwidth of 270-518 Hz and a flat voltage of 9.93±0.74V.

[0114] When the elliptical through-hole is circular or nearly circular, the spectral response curve of the acousto-electric device shows a rapid decay. When the aspect ratio of the elliptical through-hole increases to 2:1, the spectral response curve of the acousto-electric device shows a clear plateau region. Within this region, as the sound wave frequency increases, the open-circuit voltage output of the nanofiber acousto-electric device remains stable.

[0115] Table 1. Summary of the acoustic and electrical properties of single elliptical through-hole nanofiber acoustic-electric devices with different aspect ratios.

[0116]

[0117] Example 2:

[0118] Methods for fabricating single elliptical through-hole nanofiber acousto-electric devices with different fiber orientations:

[0119] Step 1: Preparation of oriented polyacrylonitrile nanofiber membranes:

[0120] Using polyacrylonitrile (PAN) as the spinning raw material, polyacrylonitrile (PAN) was dissolved in N,N-dimethylformamide at 50°C to prepare a homogeneous spinning solution with a mass fraction of 14 wt%.

[0121] The spinning solution was injected into an electrospinning machine, and the spinning parameters were set as follows: flow rate of 1 mL / h, spinning distance of 15 cm, spinning voltage of 20 kV, and roller speed of 300 rpm to prepare an oriented polyacrylonitrile nanofiber membrane.

[0122] Step 2: Prepare the upper and lower electrodes with a single elliptical through-hole:

[0123] A 100 nm thick gold conductive layer is deposited on one side of a polyethylene terephthalate (PET) film using a high-vacuum evaporation method. Elliptical through-holes are then cut into the PET film and the gold conductive layer using a laser. The aspect ratios of the elliptical through-holes are 1:1, 4:3, 2:1, 3:1, and 4:1, with 3:1 being preferred. This process creates an upper electrode and a lower electrode with a single elliptical through-hole.

[0124] Step 3: Assemble a single elliptical through-hole nanofiber acousto-electric device:

[0125] Oriented polyacrylonitrile nanofiber membranes were cut into 30×40 mm pieces using a laser. 2 As a sensing layer;

[0126] An oriented polyacrylonitrile nanofiber membrane is placed between an upper electrode with a single elliptical through-hole and a lower electrode with a single elliptical through-hole, and fixed with a plastic clamp to form a sandwich structure. This is then assembled into a single elliptical through-hole nanofiber acousto-electric device. The metal conductive layers of the upper and lower electrodes are in contact with the nanofiber membrane to collect piezoelectric charges.

[0127] During assembly, the orientation of the nanofiber membrane and the major axis of the elliptical through-holes are aligned with the long side of the individual elliptical through-hole nanofiber acousto-electric device. To further prevent interlayer delamination or relative slippage caused by acoustic vibration, plastic clamps are used for fixation, preventing delamination and slippage under acoustic excitation and ensuring long-term stable operation.

[0128] Step 4, Acoustic and electrical performance testing:

[0129] A commercial loudspeaker with adjustable frequency and sound pressure level was used as the sound source. The sound source frequency was scanned in the range of 100 to 1000 Hz. A single elliptical through-hole nanofiber acousto-electric device was clamped and fixed on a high-quality substrate with a fixture. The open-circuit voltage output of the single elliptical through-hole nanofiber acousto-electric device at different frequencies was recorded. The flat bandwidth and the corresponding flat voltage were calculated using ±2dB as the criterion for flat bandwidth.

[0130] Test Result Analysis:

[0131] 1. Fiber morphology characterization, such as Figure 5 As shown in (a), (b), and (c):

[0132] The nanofiber membrane prepared by the above method has a fiber diameter of 329±33nm, a fiber orientation angle ranging from -90° to 30°, and a membrane thickness of 30±5µm.

[0133] 2. Sound-to-electricity conversion performance:

[0134] The acoustoelectric properties of single elliptical through-hole nanofiber acoustoelectric devices with different fiber orientations are as follows: Figure 6 As shown in (a), (b), (c), (d) and Table 2, when the fibers are arranged parallel to the major axis of the elliptical through-hole, the flat bandwidth and flat voltage of the acoustic-electric device reach their maximum, with a flat bandwidth of 270–518 Hz and a flat voltage of 9.93 ± 0.74 V.

[0135] Comparing the output spectrum curves of single elliptical through-hole nanofiber acousto-electric devices with different fiber orientations, it can be seen that under the same elliptical through-hole structure and test conditions, the spectrum curves of the acousto-electric devices can all exhibit approximately flat bandwidths. This indicates that the flat frequency response generated by a single elliptical through-hole structure has certain structural dominance characteristics and is not easily affected by the relative arrangement of fibers and through-holes. However, the relative relationship between fiber orientation and the long axis of the through-hole will affect the output level of the open-circuit voltage. That is, fiber orientation mainly regulates the amplitude of the device's output voltage, rather than the position and width of the flat bandwidth range.

[0136] Table 2. Summary of the acoustic and electrical properties of single elliptical through-hole nanofiber acoustic and electrical devices with different fiber orientations.

[0137]

[0138] Example 3:

[0139] A method for fabricating a nanofiber acousto-electric device with multiple elliptical through holes includes the following steps:

[0140] Step 1: Preparation of oriented polyacrylonitrile nanofiber membranes:

[0141] Using polyacrylonitrile (PAN) as the spinning raw material, polyacrylonitrile (PAN) was dissolved in N,N-dimethylformamide at 50°C to prepare a homogeneous spinning solution with a mass fraction of 14 wt%.

[0142] The spinning solution was injected into an electrospinning machine, and the spinning parameters were set as follows: flow rate of 1 mL / h, spinning distance of 15 cm, spinning voltage of 20 kV, and roller speed of 2100 rpm to prepare an oriented polyacrylonitrile nanofiber membrane.

[0143] Step 2: Fabricate the upper and lower electrodes with multiple elliptical through holes:

[0144] A 100 nm thick gold conductive layer is deposited on one side of a polyethylene terephthalate (PET) film using high-vacuum evaporation. Elliptical vias are then cut into the PET film and the gold conductive layer using a laser. The aspect ratios of the elliptical vias are 1:1, 4:3, 2:1, 3:1, and 4:1, with 3:1 being the preferred ratio. Multiple elliptical vias are arranged in an array with an adjacent spacing of 1 mm to form a porous array structure. An upper electrode and a lower electrode with multiple elliptical vias are then fabricated.

[0145] Step 3: Assemble multiple elliptical through-hole nanofiber acoustic-electric devices:

[0146] Oriented polyacrylonitrile nanofiber membranes were cut into 30×40mm pieces using a laser. 2 As a sensing layer;

[0147] An oriented polyacrylonitrile nanofiber membrane is placed between an upper electrode with multiple elliptical through holes and a lower electrode with multiple elliptical through holes, and fixed with a plastic clamp to form a sandwich structure. This is then assembled into a nanofiber acousto-electric device with multiple elliptical through holes. The metal conductive layers of the upper and lower electrodes are in contact with the nanofiber membrane to collect piezoelectric charges.

[0148] Based on the number of elliptical through holes on the surfaces of the upper and lower electrodes, assembled nanofiber acousto-electric devices with multiple elliptical through holes are classified into the following four types:

[0149] like Figure 2 As shown in (a), a nanofiber acousto-electric device with two elliptical through holes on the surfaces of the upper and lower electrodes;

[0150] like Figure 2 As shown in (b), there are multiple elliptical through-hole nanofiber acoustic-electric devices with three elliptical through-holes on the surfaces of the upper and lower electrodes.

[0151] like Figure 2 As shown in (c), there are multiple elliptical through-hole nanofiber acoustic-electric devices with four elliptical through-holes on the surfaces of the upper and lower electrodes.

[0152] like Figure 2 As shown in (d), there are multiple elliptical through-hole nanofiber acoustic-electric devices with five elliptical through-holes on the surfaces of the upper and lower electrodes.

[0153] Step 4: Acoustic and electrical performance testing:

[0154] A commercial loudspeaker with adjustable frequency and sound pressure level was used as the sound source. The sound source frequency was scanned in the range of 100 to 1000 Hz. Multiple elliptical through-hole nanofiber acousto-electric devices were clamped and fixed on a high-quality substrate around the perimeter using a fixture. The open-circuit voltage output of multiple elliptical through-hole nanofiber acousto-electric devices at different frequencies was recorded. The flat bandwidth and the corresponding flat voltage were calculated using ±2dB as the criterion for determining the flat bandwidth.

[0155] The equivalent internal resistance of a device is measured using the external resistance method: Under the same acoustic excitation conditions, by changing the external load resistance and recording the voltage across it, the output power of the device reaches its maximum when the external resistance is equal to the internal resistance of the acoustic-electric device. The external resistance is approximately equal to the equivalent internal resistance of the acoustic-electric device. Based on this, the equivalent internal resistance of the acoustic-electric device is determined. The internal resistance of the acoustic-electric device can be used as a reference parameter for system noise assessment.

[0156] Test Result Analysis:

[0157] Under the excitation condition of a sound source with a sound pressure level of 115 dB, the acousto-electric performance of the nanofiber acousto-electric device with multiple elliptical through holes is as follows: Figure 7(a), (b), (c), (d), (e), (f) Figure 8 As shown in (a), (b), (c), (d), (e), (f) and Table 3, under the action of a 150Hz, 115dB sound wave, the maximum voltage of a single elliptical through-hole nanofiber acousto-electric device is 28.73±0.47 V, and its response bandwidth is 100~700Hz. Using ±2dB as the flat bandwidth standard, the flat bandwidth is 270-518Hz, the flat voltage is 9.93±0.74V, and the equivalent internal resistance of multiple elliptical through-hole nanofiber acousto-electric devices is 3.73±0.23MΩ. The maximum voltage of multiple elliptical through-hole nanofiber acousto-electric devices with 5 elliptical through-holes is 26.93±0.44V, and its response bandwidth is 100-950Hz. The flat bandwidth is 219~676Hz, the flat voltage is 14.61±0.92V, and the equivalent internal resistance of multiple elliptical through-hole nanofiber acousto-electric devices is 3.62±0.26MΩ. Further calculation of the spectral energy to evaluate the output energy of the device reveals that in multiple elliptical through-hole nanofiber acousto-electric devices, the spectral energy increases significantly with the increase in the number of elliptical through-holes, indicating that porous structures can achieve higher broadband output energy levels while maintaining a consistent total open area.

[0158] Furthermore, although increasing the number of elliptical vias alters the electrode architecture of the multi-elliptical via nanofiber acousto-electric device and improves the output voltage level, the equivalent internal resistance of the multi-elliptical via nanofiber acousto-electric device remains basically stable under different numbers of elliptical vias, without significant increase. Therefore, while the porous structure improves the output and expands the bandwidth, it does not cause a significant increase in the internal system noise level of the device due to a significant increase in internal resistance.

[0159] Table 3. Summary of the acoustic and electrical performance of nanofiber acoustic-electric devices with multiple elliptical through holes

[0160]

[0161] Although embodiments and drawings of the present invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A nanofiber acousto-electric device with a flat frequency response, characterized in that: It includes a nanofiber membrane, an upper electrode, and a lower electrode, wherein the nanofiber membrane is located between the upper electrode and the lower electrode to form a nanofiber acoustic-electric device; The nanofiber membrane has a fiber diameter range of 1–1000 nm and a fiber membrane thickness range of 10 μm–1 mm; Both the upper electrode and the lower electrode are composed of a plastic film and a metal conductive layer on the surface of the plastic film. A single elliptical through hole or multiple elliptical through holes are formed on the plastic film and the metal conductive layer by laser cutting. Multiple elliptical through holes form a porous array structure. The aspect ratio of the elliptical through hole is 2:1 or 3:1; The fiber orientation is parallel to the major axis of the elliptical through-hole.

2. The nanofiber acousto-electric device with a flat frequency response according to claim 1, characterized in that: The nanofiber membrane is prepared by electrospinning technology, and the spinning polymer raw materials are polyacrylonitrile polyvinylidene fluoride, polyvinylidene fluoride-trifluoroethylene copolymer, polylactic acid, polyimide, and polyimide copolymer.

3. The nanofiber acousto-electric device with a flat frequency response according to claim 1, characterized in that: Both the upper and lower electrodes are 30×40mm. 2 The plastic film is made of polyethylene terephthalate, polypropylene, polyethylene or paper-based materials.

4. The nanofiber acousto-electric device with a flat frequency response according to claim 1, characterized in that: The conductive metal layer is made of gold, silver, copper, platinum, or nickel, and its thickness ranges from 50 to 1000 nm.

5. A method for fabricating the nanofiber acousto-electric device with a flat frequency response as described in claim 1: A method for fabricating a single elliptical through-hole nanofiber acousto-electric device includes the following steps: Step 1: Preparation of oriented polyacrylonitrile nanofiber membranes: Using polyacrylonitrile as the spinning raw material, polyacrylonitrile was dissolved in N,N-dimethylformamide at 50°C to prepare a homogeneous spinning solution with a mass fraction of 14 wt%. The spinning solution was injected into an electrospinning machine, and the spinning parameters were set as follows: flow rate of 1 mL / h, spinning distance of 15 cm, spinning voltage of 20 kV, and roller speed of 300-2100 rpm to prepare an oriented polyacrylonitrile nanofiber membrane. Step 2: Prepare the upper and lower electrodes with a single elliptical through-hole: A 100 nm thick gold conductive layer is deposited on one side of a polyethylene terephthalate (PET) film using high vacuum evaporation. Elliptical through-holes are then cut into the PET film and the gold conductive layer using a laser. The aspect ratio of the elliptical through-holes is 2:1 or 3:1, thus creating an upper electrode and a lower electrode with a single elliptical through-hole. Step 3: Assemble a single elliptical through-hole nanofiber acousto-electric device: Oriented polyacrylonitrile nanofiber membranes were cut into 30×40 mm pieces using a laser. 2 As a sensing layer; An oriented polyacrylonitrile nanofiber membrane is placed between an upper electrode with a single elliptical through-hole and a lower electrode with a single elliptical through-hole, and fixed with a plastic clamp to form a sandwich structure. This is then assembled into a single elliptical through-hole nanofiber acousto-electric device. The metal conductive layers of the upper and lower electrodes are in contact with the nanofiber membrane to collect piezoelectric charges. Step 4, Acoustic and electrical performance testing: Commercial loudspeakers with adjustable frequency and sound pressure level were used as the sound source. The sound source frequency was scanned in the range of 100–1000 Hz. A single elliptical through-hole nanofiber acousto-electric device was clamped and fixed on a high-quality substrate with a fixture. The open-circuit voltage output of the single elliptical through-hole nanofiber acousto-electric device at different frequencies was recorded. ±2dB was used as the criterion for flat bandwidth. The flat bandwidth and the corresponding flat voltage were calculated. A method for fabricating a nanofiber acousto-electric device with multiple elliptical through holes includes the following steps: Step 1: Preparation of oriented polyacrylonitrile nanofiber membranes: Using polyacrylonitrile as the spinning raw material, polyacrylonitrile was dissolved in N,N-dimethylformamide at 50°C to prepare a homogeneous spinning solution with a mass fraction of 14 wt%. The spinning solution was injected into an electrospinning machine, and the spinning parameters were set as follows: flow rate of 1 mL / h, spinning distance of 15 cm, spinning voltage of 20 kV, and roller speed of 300-2100 rpm to prepare an oriented polyacrylonitrile nanofiber membrane. Step 2: Fabricate the upper and lower electrodes with multiple elliptical through holes: A 100 nm thick gold conductive layer is deposited on one side of a polyethylene terephthalate (PET) film using high-vacuum evaporation. Elliptical vias are then cut into the PET film and the gold conductive layer using a laser. The aspect ratio of the elliptical vias is 2:1 or 3:

1. Multiple elliptical vias are arranged in an array with an adjacent spacing of 1 mm to form a porous array structure. An upper electrode and a lower electrode with multiple elliptical vias are then fabricated. Step 3: Assemble multiple elliptical through-hole nanofiber acoustic-electric devices: Oriented polyacrylonitrile nanofiber membranes were cut into 30×40 mm pieces using a laser. 2 As a sensing layer; An oriented polyacrylonitrile nanofiber membrane is placed between an upper electrode with multiple elliptical through holes and a lower electrode with multiple elliptical through holes, and fixed with a plastic clamp to form a sandwich structure. This is then assembled into a nanofiber acousto-electric device with multiple elliptical through holes. The metal conductive layers of the upper and lower electrodes are in contact with the nanofiber membrane to collect piezoelectric charges. Step 4: Acoustic and electrical performance testing: A commercial loudspeaker with adjustable frequency and sound pressure level was used as the sound source. The sound source frequency was scanned in the range of 100 to 1000 Hz. Multiple elliptical through-hole nanofiber acousto-electric devices were clamped and fixed on a high-quality substrate around the perimeter using a fixture. The open-circuit voltage output of multiple elliptical through-hole nanofiber acousto-electric devices at different frequencies was recorded. The flat bandwidth and the corresponding flat voltage were calculated using ±2dB as the criterion for determining the flat bandwidth.

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