Acceleration measurement structure and method based on photonic crystal

Abstract

The invention belongs to the technical field of acceleration sensing, and particularly discloses a photonic crystal-based acceleration measurement structure and method, the photonic crystal-based acceleration measurement structure comprises a photonic crystal and a sound wave transceiver, the sound wave transceiver is used for emitting sound waves at one side of the photonic crystal and receiving the sound waves at the other side of the photonic crystal; defects exist in the photonic crystal, and the photonic crystal has a band gap within a certain frequency range; the phononic crystals comprise a fixed phononic crystal and a movable phononic crystal; when the structure is subjected to acceleration, the movable phononic crystal moves, the distance between the fixed phononic crystal and the movable phononic crystal changes, the change of the distance causes the deviation of the resonant frequency of the emitted sound wave, and the acceleration is measured by detecting the deviation of the resonant frequency of the sound wave. According to the invention, the sensitivity of acceleration detection can be obviously improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of acceleration sensing, and more specifically, relates to an acceleration measurement structure and method based on phononic crystals. Background Art

[0002] In recent years, the main acceleration sensing methods currently used include capacitive, piezoelectric, piezoresistive, resonant, and photoelectric. Although capacitive acceleration measurement is widely used, it suffers from a trade-off between sensitivity and bandwidth. Furthermore, the maximum detectable signal is largely limited by the supply voltage of the interface circuit, making it unable to achieve a high dynamic range. Piezoelectric acceleration measurement offers high sensitivity and is suitable for high-frequency acceleration measurement, but the performance of its piezoelectric material is significantly affected by temperature, and long-term material stability and aging issues can lead to a decrease in accuracy. Piezoresistive acceleration measurement generally exhibits good linearity and can achieve a high dynamic range, but has lower sensitivity than other sensor types. Resonant acceleration measurement is less susceptible to temperature and humidity changes and offers high stability, but its response to low-frequency acceleration changes is poor and requires high-precision frequency detection technology. Photoelectric acceleration measurement offers very high sensitivity, but its system structure is generally complex, resulting in high cost and low system integration. Summary of the Invention

[0003] In response to the above defects or improvement needs of the prior art, the present invention provides an acceleration measurement structure and method based on phononic crystals, the purpose of which is to improve the sensitivity of acceleration measurement.

[0004] To achieve the above objectives, according to one aspect of the present invention, a phononic crystal-based acceleration measurement structure is proposed, comprising a phononic crystal and an acoustic wave transceiver, wherein:

[0005] The phononic crystal has defects and has a band gap within a certain frequency range; the phononic crystal includes a fixed phononic crystal and a movable phononic crystal; when the structure is subjected to acceleration, the movable phononic crystal moves, causing the distance between the fixed phononic crystal and the movable phononic crystal to change; the sound wave transceiver is used to emit sound waves on one side of the phononic crystal and receive sound waves on the other side.

[0006] As a further preference, both the fixed phononic crystal and the movable phononic crystal are unit cell arrays composed of periodically arranged unit cells; and there are unit cell vacancies in the unit cell array along a first direction, which is the acceleration direction.

[0007] As a further preference, the unit cell includes a silicon material in the middle and air material surrounding the silicon material.

[0008] As a further preference, the unit cell as a whole is a rectangular parallelepiped, and the silicon material in the middle is a cylinder.

[0009] As a further preferred embodiment, a mass block is further included, and the mass block includes a fixed mass block and a movable mass block. The fixed phononic crystal is mounted on the fixed mass block, and the movable phononic crystal is mounted on the movable mass block.

[0010] As a further preferred embodiment, suspension beams are installed on both sides of the movable mass block, and the suspension beams are used to support the movable mass block so that the movable mass block is suspended and movable.

[0011] As a further preferred embodiment, by optimizing the unit cell size and the physical properties of the material, the phononic crystal forms a significant band gap at 7.5 MHz to 12.8 MHz.

[0012] According to another aspect of the present invention, there is provided an acceleration measurement method based on the above-mentioned phononic crystal-based acceleration measurement structure, comprising:

[0013] Sound waves are emitted on one side of the phononic crystal and received on the other side. There is a band gap in the phononic crystal within the frequency range of the sound waves. At the same time, due to the existence of defects, the received sound waves have a resonance peak within the band gap.

[0014] When the structure is subjected to acceleration, the distance between the fixed phononic crystal and the movable phononic crystal changes. This distance change causes the resonance peak to shift, and the acceleration is determined based on the shift of the resonance peak.

[0015] In general, the above technical solutions conceived by the present invention have the following technical advantages compared with the existing technology:

[0016] The present invention utilizes the band gap characteristics and local resonance effect of acoustic metamaterial phononic crystals. By introducing defects into the phononic crystals to form a resonant cavity, the sound wave generates a resonant mode within the band gap. This resonant frequency is very sensitive to the length of the resonant cavity. Therefore, the acceleration can be measured by detecting the offset of the sound wave resonant frequency, significantly improving the sensitivity of acceleration detection and overcoming the sensitivity shortcomings of existing accelerometers. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of an acceleration measurement structure based on phononic crystals according to an embodiment of the present invention;

[0018] Figure 2 (a) and (b) are diagrams of the layout and structural design of the phononic crystal material according to an embodiment of the present invention;

[0019] Figure 3 This is the FEM phononic crystal band diagram of an embodiment of the present invention;

[0020] Figure 4(a) and (b) are the transmission curve and linear fitting result diagram of the embodiment of the present invention under different accelerations, respectively;

[0021] Figure 5 This is a schematic diagram of the installation of the acceleration measurement structure according to an embodiment of the present invention.

[0022] In all figures, the same reference numerals are used to denote the same elements or structures, where: 1 - mass, 2 - fixed phononic crystal, 3 - movable phononic crystal, 4 - suspended beam. DETAILED DESCRIPTION

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0024] An embodiment of the present invention provides an acceleration measurement structure based on phononic crystals, such as Figure 1 As shown, the device comprises a phononic crystal and an acoustic wave transceiver. The phononic crystal has defects and a band gap within a certain frequency range. The phononic crystal includes a fixed phononic crystal 2 and a movable phononic crystal 3. The acoustic wave transceiver is configured to emit acoustic waves on one side of the phononic crystal and receive them on the other side. When the structure is subjected to acceleration, the fixed phononic crystal 2 remains stationary while the movable phononic crystal 3 moves. This change in distance causes the resonant frequency (resonance peak) of the emitted acoustic wave to shift. Acceleration is measured by detecting this shift in the acoustic wave's resonant frequency.

[0025] Furthermore, the acceleration measurement structure also includes a mass block 1, which includes a fixed mass block and a movable mass block. The fixed phononic crystal is mechanically coupled to the fixed mass block, and the movable phononic crystal is mechanically coupled to the movable mass block, that is, the movable phononic crystal is driven to move by the movable mass block.

[0026] Furthermore, suspension beams 4 are fixed on both sides of the active mass block. The suspension beams are similar to springs. The active mass block is suspended in the air and supported by the four suspension beams. When acceleration is applied to the device, an inertial force F=ma is generated. Assuming that the stiffness of the suspension beam is k, then F=kx, where x is the displacement of the mass block. Figure 5 As shown, the fixed mass block is fixed to the external wall surface; one end of the suspension beam 4 is mounted on the external wall surface, and the other end is mounted on the movable mass block, so that the movable mass block is suspended and movable.

[0027] Furthermore, both the fixed phononic crystal and the movable phononic crystal are unit cell arrays composed of periodically arranged unit cells; and in the unit cell array, defects exist along a first direction, which is the acceleration direction and the sound wave propagation direction.

[0028] Further, such as Figure 2 As shown, the unit cell includes a cylindrical silicon material in the middle and air material wrapped outside the silicon material, and the unit cell as a whole is a rectangular parallelepiped; there are unit cell vacancies in each column of the unit cell array, so that the sound wave can pass directly through the defect when propagating along the first direction.

[0029] Specifically, according to the basic principles of phononic crystals, the propagation characteristics of sound waves are closely related to the periodic structure of the material. When the periodic structure of the phononic crystal resonates with the propagation characteristics of sound waves within a specific frequency range, the propagation of the sound waves will be hindered, forming a band gap.

[0030] By optimizing the unit cell size and the physical properties of the material, the phononic crystal can form a band gap in a certain frequency range. Specifically, the range of the band gap is related to the unit cell size, and the physical properties of the material (the density and sound velocity of the material) need to have a large acoustic impedance mismatch with the air to produce a band gap. Furthermore, by introducing defects into the phononic crystal to form a resonant cavity, a significant peak value, i.e., a resonance peak, can be generated in the band gap when receiving the sound wave. The appearance of this resonance peak is the basis of phononic crystal acceleration sensing. The work of the sensor is to rely on the change of this resonance peak to measure and detect, which can significantly improve the sensitivity of acceleration detection. The acceleration measurement structure of the present invention can realize acceleration detection in high-precision dynamic environments such as missile guidance, intelligent ammunition navigation, and inertial navigation systems, and has excellent anti-interference ability and high-sensitivity response characteristics.

[0031] The principle and effect of the acceleration measurement structure are further explained below through examples:

[0032] The interest in acoustic and elastic wave propagation in periodic media is related to the presence of spectral gaps in the band structure, analogous to electronic band gaps in solids. Several commonly used methods exist for calculating the band structure of phononic crystals, such as the plane wave expansion (PWE) method and the finite element method (FEM), which are commonly used numerical methods. This paper employs the finite element method for its research.

[0033] For phononic crystals, specific material layout and structural design are adopted, e.g. Figure 2 shown. Figure 2 (a) is a single unit cell of a phononic crystal. The green part is silicon material, and the white part is air material. The size of the phononic crystal is a×a (16um×16um), and the diameter of the middle silicon column is d=10um. Figure 2(b) shows a row of phononic crystals with a defect length of L = 16 μm. By optimizing the periodic unit size of the phononic crystal and the physical properties of the material, a significant band gap is formed between 7.5 MHz and 12.8 MHz.

[0034] In order to improve the understanding of the characteristics of phononic crystals, the finite element method (FEM) in COMSOL Multiphysics is used. Given that the height of all components is much higher than the lattice constant, the numerical model of the present invention is set up using a two-dimensional (2D) simplified method. In this two-dimensional model, the propagation of sound waves only considers the propagation characteristics along the plane (usually the xy plane), while ignoring the fluctuations in the z-axis direction. This simplification not only significantly reduces the computational complexity, but also effectively describes the performance of phononic crystals within a reasonable accuracy range. In particular, for periodic structures, the two-dimensional model is sufficient to provide accurate predictions about the band structure and band gap position. From the acoustic wave equation, it can be obtained:

[0035]

[0036] Where ρ is the density, c is the speed of sound, w is the angular frequency, and r is the space vector, expressed as x1e1+x2e2. The Floquet-Bloch theorem uses periodic boundary conditions for the interface between two-dimensional unit cells as follows:

[0037]

[0038] Where r is the lattice vector and k is the wave vector. The band structure of the phononic crystal can be obtained by scanning the wave vector k across the first irreducible Brillouin zone. Set the size of the phononic crystal to a×a (16um×16um) and the diameter of the middle silicon column to d=10um. Combined with formula (2), add Bloch-Floquet periodic boundary conditions at the outer boundaries of the unit cell. To obtain the band structure of the phononic crystal, it is necessary to calculate a set of wave vector-related characteristic frequencies on the edge of the first irreducible Brillouin zone of the phononic crystal. The FEM phononic crystal band diagram is calculated, as shown in the following example: Figure 3 As shown, the light blue shadow indicates the region of the band gap in the ΓX direction. The first band gap extends from 7.5 MHz to 12.8 MHz, within which the acoustic wave is prevented from propagating.

[0039] In order to further study the resonant characteristics of phononic crystals, the present invention forms a resonant cavity by introducing defects into the perfect phononic crystal and calculates the transmission coefficient curve of the phononic crystal containing the resonant cavity, such as Figure 4 As shown in (a), a significant peak, known as the resonance peak, appears within the first band gap. This resonance peak is the basis of the phononic crystal acceleration sensing principle, and the sensor's operation relies on the changes in this resonance peak for measurement and detection.

[0040] In order to explore the influence of acceleration on the resonance peak in the above band gap, the change of acceleration is introduced. Due to the effect of acceleration, the mass block is displaced. The displacement sensitivity is obtained by simulation: 25.45nm / g. The transmission curve results are as follows: Figure 4 As shown in (a). Linear fitting is performed to obtain the acceleration sensitivity of 5.09KHz / g, as shown in Figure 4 As shown in (b).

[0041] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An acceleration measurement structure based on phononic crystal, characterized in that: It includes a phononic crystal and an acoustic wave transceiver, wherein: The phononic crystal has defects and has a band gap within a certain frequency range; the phononic crystal includes a fixed phononic crystal and a movable phononic crystal; when the structure is subjected to acceleration, the movable phononic crystal moves, causing the distance between the fixed phononic crystal and the movable phononic crystal to change; the sound wave transceiver is used to emit sound waves on one side of the phononic crystal and receive sound waves on the other side.

2. The phononic crystal-based acceleration measurement structure according to claim 1, wherein: The fixed phononic crystal and the movable phononic crystal are both unit cell arrays composed of periodically arranged unit cells; and there are unit cell vacancies in the unit cell array along a first direction, which is the acceleration direction.

3. The phononic crystal-based acceleration measurement structure according to claim 2, wherein: The unit cell includes a silicon material in the middle and air material surrounding the silicon material.

4. The phononic crystal-based acceleration measurement structure according to claim 3, wherein: The unit cell is a rectangular parallelepiped as a whole, and the silicon material in the middle is a cylinder.

5. The phononic crystal-based acceleration measurement structure according to any one of claims 1 to 4, characterized in that: The device also includes a mass block, which includes a fixed mass block and a movable mass block. The fixed phononic crystal is installed on the fixed mass block, and the movable phononic crystal is installed on the movable mass block.

6. The phononic crystal-based acceleration measurement structure according to claim 5, wherein: Suspension beams are installed on both sides of the movable mass block, and the suspension beams are used to support the movable mass block so that the movable mass block is suspended and movable.

7. The phononic crystal-based acceleration measurement structure according to any one of claims 1 to 4, characterized in that: By optimizing the unit cell size and the physical properties of the material, the phononic crystal forms a significant band gap at 7.5MHz to 12.8MHz.

8. An acceleration measurement method based on the phononic crystal-based acceleration measurement structure according to any one of claims 1 to 7, characterized in that: include: Sound waves are emitted on one side of the phononic crystal and received on the other side. There is a band gap in the phononic crystal within the frequency range of the sound waves. At the same time, due to the existence of defects, the received sound waves have a resonance peak within the band gap. When the structure is subjected to acceleration, the distance between the fixed phononic crystal and the movable phononic crystal changes. This distance change causes the resonance peak to shift, and the acceleration is determined based on the shift of the resonance peak.

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