Piezoelectric beam bidirectional micro-mechanical vibration energy harvester with eccentric mass

Abstract

The application discloses a piezoelectric beam type bidirectional micro mechanical vibration energy collector with eccentric mass, which comprises a substrate, a cantilever beam and a mass with an eccentricity R0; the cantilever beam is arranged on the substrate, the upper surface of the cantilever beam is provided with a piezoelectric layer, the position starting point of the piezoelectric layer is at the root of the cantilever beam, and the width of the piezoelectric layer is equal to the width of the cantilever beam; the eccentricity of the mass is R0=L / 2, wherein L is the length of the cantilever beam, and L E is the length of the piezoelectric layer. Compared with the mass in the prior art, the mass center of the mass is far away from the longitudinal axis of the cantilever beam, and the vibration energy in the horizontal direction cannot be collected; the piezoelectric beam type bidirectional micro mechanical vibration energy collector with eccentric mass can collect the vibration energy in two directions simultaneously, the mass center of the mass is far away from the longitudinal axis of the cantilever beam, and the size is relatively large; when the foundation is horizontally vibrated, the mass generates a larger horizontal inertia moment, causes the cantilever beam to vibrate and deform, and simultaneously converts the vibration energy in the horizontal and vertical directions into electric energy.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of silicon micro-machining manufacturing technology, and particularly relates to a piezoelectric beam type bidirectional micro-mechanical vibration energy collector with eccentric mass for converting vibration energy in horizontal and vertical directions into electric energy. BACKGROUND

[0002] The piezoelectric vibration energy collector is a device for converting mechanical vibration energy into electric energy by using piezoelectric effect. The piezoelectric vibration energy collector is divided into common type and micro type according to size. The common type device has a total size of more than 5 mm, and the micro type device has a total size of less than 5 mm. The common piezoelectric vibration energy collector is composed of a mass and a cantilever beam. The cantilever beam is provided with a piezoelectric layer. When the ground vibrates, the cantilever beam bends and vibrates under the action of the inertial force of the mass. The piezoelectric layer on the cantilever beam converts the strain energy of the beam into electric energy output. Figure 1 is a current typical micro vibration energy collector for collecting ground vertical vibration energy. The micro device is manufactured by using silicon-based materials. Figure 2 is a current schematic diagram of a cantilever beam device with a piezoelectric layer. The ground vibrates vertically, the device is fixed on the ground, and the starting point of the piezoelectric layer is at the root of the beam, that is, the piezoelectric layer is arranged at a position where the beam has a large strain. In order to collect more energy, the length L E of the piezoelectric layer is equal to the length L of the cantilever beam.

[0003] A considerable number of environmental vibrations are multidirectional, not only vertical but also horizontal. However, for the current commonly used device, such as Figure 2 , the mass center of the mass is very close to the longitudinal axis (x-axis) of the cantilever beam, and cannot generate a large enough inertial moment in the horizontal direction (x-axis direction), which is unidirectional sensitive and cannot collect vibration energy in the horizontal direction (x-axis).

[0004] The current most commonly used method for simultaneously collecting vibration energy in two directions is to arrange two Figure 1 unidirectional sensitive devices in a 90-degree direction to simultaneously collect vibration energy, that is, the energy in two directions is independently collected by two unidirectional collectors arranged closely together.

[0005] Therefore, how to improve the prior art and use one mass to simultaneously collect energy in two directions is a technical problem to be solved. SUMMARY

[0006] Invention purposes: In view of the fact that the center of mass of the device mass block in the prior art is close to the longitudinal axis x of the cantilever beam, it cannot generate sufficient inertial torque along the horizontal direction x, it cannot collect the vibration energy in the horizontal direction, and it can only collect the vibration energy in the vertical direction, the present application proposes a piezoelectric beam type bidirectional micro mechanical vibration energy collector with an eccentric mass block, which simultaneously collects vibration energy in two directions by using an eccentric mass block, the center of mass of the mass block of the present application is far away from the longitudinal axis of the cantilever beam, and when the foundation vibrates horizontally, the mass block generates a larger horizontal inertial torque, causing the cantilever beam to vibrate and deform; the energy collector of the present application simultaneously converts the vibration energy in the horizontal and vertical directions into electrical energy.

[0007] Technical scheme: The piezoelectric beam type bidirectional micro mechanical vibration energy collector with an eccentric mass block of the present application comprises a substrate, a cantilever beam, and a mass block with an eccentricity R0; the cantilever beam is arranged on the substrate; the upper surface of the cantilever beam has a piezoelectric layer; the position of the piezoelectric layer starts at the root of the cantilever beam, and the width of the piezoelectric layer is equal to the width of the cantilever beam.

[0008] Figure 3 It is the first device of the present application, and the mass block is supported by a cantilever beam with a piezoelectric layer. Figure 4 It is the first device of the present application without a foundation. The present application does not contain a foundation.

[0009] In order to have the same energy collection capacity in the vertical and horizontal directions, it satisfies the following relationship: the eccentricity of the mass block is Wherein, L is the length of the cantilever beam, L E is the length of the piezoelectric layer. When the length L E of the piezoelectric layer is equal to the length L of the cantilever beam, the eccentricity of the mass block is

[0010] The open circuit voltage of the vibration energy collector in the vertical and horizontal directions must be the same, and the open circuit voltage calculation formula is:

[0011]

[0012] In the formula, b is the width of the piezoelectric layer, which is also the width of the beam; h0 is the thickness of the piezoelectric layer, L E is the length of the piezoelectric layer, A=b*L E is the area of the piezoelectric layer, h 31 is the piezoelectric constant, and the constant u(x,t) is the deformation curve of the cantilever beam:

[0013] u(x,t)=φ(x)q(t) (2)

[0014] In the formula, φ(x) is a known deformation function, and q(t) is a time function.

[0015] The deformation curve of the cantilever beam under the vertical inertial force F is:

[0016]

[0017] where F 垂直 = ma 垂直 is the vertical inertial force, m is the mass of the mass block, a 垂直 is the vertical acceleration, E is the Young's modulus of the beam material, and I is the cross-sectional moment of inertia of the beam.

[0018] The second derivative integral of the deformation curve in the corresponding open circuit voltage is:

[0019]

[0020] The deformation curve of the cantilever beam under the horizontal inertial moment is:

[0021]

[0022] where M 水平 = ma 水平 R0 is the horizontal inertial moment, a 水平 is the vertical acceleration, m is the mass of the mass block, E is the Young's modulus of the beam material, and I is the cross-sectional moment of inertia of the beam.

[0023] The second derivative integral of the deformation curve in the corresponding open circuit voltage is:

[0024]

[0025] The open circuit voltages must satisfy: a 水平 = a 垂直 and Using the above two formulas, the eccentric moment R0 of the mass block and the length L of the beam and the length L E of the piezoelectric layer are related

[0026]

[0027] In particular, when the length of the piezoelectric layer is equal to the length of the beam, the eccentric moment of the mass block is exactly Figure 5 The cantilever beam type bidirectional vibration energy harvester of the present application has a piezoelectric layer length equal to the length of the beam.

[0028] Figure 6 The second device of the present application is a mass block supported by two identical cantilever beams with piezoelectric layers on the left and right sides of the mass block, and the length of the piezoelectric layer is L E . Figure 7Figure of the two-directional vibration energy collector of the double-cantilever beam support of the present application without foundation. In order to have the same energy collecting capacity in the vertical and horizontal directions, it satisfies the following relationship: the eccentricity of the mass block is R0=L E When the piezoelectric layer length L E is equal to the length L of the left and right cantilever beams, the eccentricity of the mass block is R0=L.

[0029] For the vertical direction excitation, the deformation curve of the left cantilever support beam is

[0030]

[0031] In the formula, E is the Young's modulus of the beam material, and I is the cross-sectional moment of inertia of the beam.

[0032] The second derivative integral value of the deformation curve in the corresponding open circuit voltage is

[0033]

[0034] For the vertical direction excitation, the deformation curve of the right cantilever support beam of the mass block is equal to the deformation curve of the left cantilever support beam, and it is obtained that:

[0035]

[0036] The left and right side beams of the present application are equal in length, and under the action of the horizontal moment of inertia, the deformation curve of the left cantilever support beam is

[0037]

[0038] The second derivative integral value of the deformation curve in the corresponding open circuit voltage is

[0039]

[0040] The deformation curve of the right cantilever support beam is

[0041]

[0042] The second derivative integral value of the deformation curve in the corresponding open circuit voltage is

[0043]

[0044] Using formula (11) and (12), it is obtained that

[0045]

[0046] The open circuit voltage must satisfy: a 水平 = a 垂直 and D 水平 =D 垂直R0= L E R0= L

[0047] R0= L E (16)

[0048] R0= L Figure 8 Figure 1 is a mechanical schematic diagram of a piezoelectric layer length equal to the length of the beam of the two- cantilever beam type bidirectional vibration energy harvester of the present application.

[0049] Working principle: the current device mass block centroid is very close to the longitudinal axis (x-axis) of the cantilever beam, and cannot generate sufficient inertial torque in the horizontal direction (x-axis), and cannot collect horizontal vibration energy, and can only collect vertical vibration energy. The micro-mechanical vibration energy harvester of the present application uses a cantilever beam with an eccentric mass block, and simultaneously completes the collection of vertical and horizontal vibration energy. The mass block centroid of the present application is larger in size from the longitudinal axis of the cantilever beam, and when the foundation vibrates horizontally, the mass block also generates a larger horizontal inertial torque, causing the cantilever beam to vibrate and deform. The present application is also applicable to macro-mechanical vibration energy harvesters. The difference between the above-mentioned macro-mechanical vibration energy harvester and the present application is that the base and the cantilever beam of the macro-mechanical vibration energy harvester are made of other materials and processes. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 Figure 1 is a structural diagram of a current typical micro-mechanical vibration (unidirectional) energy harvester that collects vertical vibration energy of the foundation;

[0051] Figure 2 Figure 1 is a structural diagram of a current typical micro-mechanical vibration (unidirectional) energy harvester that collects vertical vibration energy of the foundation;

[0052] Figure 3 Figure 1 is a structural diagram of a current typical micro-mechanical vibration (unidirectional) energy harvester that collects vertical vibration energy of the foundation;

[0053] Figure 4 Figure 1 is a structural diagram of a current typical micro-mechanical vibration (unidirectional) energy harvester that collects vertical vibration energy of the foundation;

[0054] Figure 5 Figure 1 is a structural diagram of a current typical micro-mechanical vibration (unidirectional) energy harvester that collects vertical vibration energy of the foundation;

[0055] Figure 6 Figure 1 is a structural diagram of a current typical micro-mechanical vibration (unidirectional) energy harvester that collects vertical vibration energy of the foundation;

[0056] Figure 7 Figure 1 is a structural diagram of a current typical micro-mechanical vibration (unidirectional) energy harvester that collects vertical vibration energy of the foundation;

[0057] Figure 7 (a) is the front view of the double cantilever beam supported bidirectional vibration energy collector (without foundation) of the present application;

[0058] Figure 7 (b) is the top view of the double cantilever beam supported bidirectional vibration energy collector (without foundation) of the present application;

[0059] Figure 8 The mechanical principle diagram of the double cantilever beam bidirectional vibration energy collector of the present application with the piezoelectric layer length equal to the beam length;

[0060] Figure 9 The structural diagram of the double cantilever beam bidirectional vibration energy collector of the present application with the piezoelectric layer length equal to the beam length;

[0061] Figure 10 The embodiment diagram (without substrate and foundation) of the present application;

[0062] Figure 11 The voltage comparison diagram of the vertical vibration displacement (solid line) and the horizontal vibration displacement (dashed line) of the present application. DETAILED DESCRIPTION

[0063] The piezoelectric beam bidirectional micro-mechanical vibration energy collector of the present application with eccentric mass block includes a substrate 1, a cantilever beam 3, and a mass block 4 with eccentricity R0; the cantilever beam 3 is arranged on the substrate 1; the upper surface of the cantilever beam 3 has a piezoelectric layer 2, and the mass block 4 is supported by the cantilever beam 3. In order to collect more energy, the piezoelectric layer 2 position starting point is at the beam root, and the piezoelectric layer 2 length L E is equal to the cantilever beam length L. The piezoelectric layer thickness h0 is relatively small compared to the thickness t of the beam, which does not affect the vibration performance of the beam. The y direction is the direction of the thickness h0 and t.

[0064] Figure 3 The first structural diagram of the bidirectional micro-mechanical vibration energy collector of the present application, in which the mass block is supported by a cantilever beam with a piezoelectric layer. When the energy collector works, the rigid substrate is tightly fixed on the vibrating foundation, and the foundation vibration causes the mass block to vibrate, resulting in the deformation of the cantilever beam.

[0065] In order to have the same energy collection capacity in the vertical and horizontal directions, it satisfies the following relationship: the eccentricity of the mass block is wherein L is the length of the cantilever beam, L E is the length of the piezoelectric layer. When the length L E of the piezoelectric layer is equal to the length L of the cantilever beam, the eccentricity of the mass block is

[0066] Figure 4The two-way vibration energy collector of the present application is without foundation. The length, width and thickness directions of the beam are x, z and y directions respectively. The mass center of the mass block of the present application is far from the x axis with a dimension R0. When the foundation vertically vibrates, the present application is the same as the prior art Figure 1 However, when the foundation horizontally vibrates, the mass block of the present application has a large inertia force arm to generate a large horizontal inertia moment to cause the cantilever beam to vibrate and deform, so that the piezoelectric layer generates electric charge to complete energy conversion. Compared with the prior art Figure 1 , the mass center of the current device mass block is very close to the x axis, the inertia force arm is small, and sufficient horizontal inertia moment cannot be generated.

[0067] In order to make the energy collector have the same vibration energy collection capacity in the vertical and horizontal directions, the open circuit voltages in the vertical and horizontal directions should be equal, and the open circuit voltage calculation formula is:

[0068]

[0069] In the formula, b is the width of the piezoelectric layer, which is also the width of the beam, h0 is the thickness of the piezoelectric layer, L E is the length of the piezoelectric layer, A=b*L E is the area of the piezoelectric layer, h 31 is the piezoelectric constant, and the constant u(x,t) is the deformation curve of the cantilever beam, which is written as:

[0070] u(x,t)=φ(x)q(t) (2)

[0071] In the formula, φ(x) is a known deformation function, and q(t) is a time function.

[0072] The deformation curve of the cantilever beam under the action of the vertical inertia force F is:

[0073]

[0074] In the formula, F 垂直 =ma 垂直 is the vertical direction inertia force, m is the mass of the mass block, a 垂直 is the vertical direction acceleration, E is the Young's modulus of the beam material, and I is the cross-sectional moment of inertia of the beam.

[0075] The integral of the second derivative of the deformation curve in the corresponding open circuit voltage is:

[0076]

[0077] The deformation curve of the present application under the action of the horizontal inertia moment is:

[0078]

[0079] In the formula, M 水平= ma 水平 R0 is the horizontal direction inertia moment, a 水平 is the vertical direction acceleration, m is the mass of the mass block, E is the Young's modulus of the beam material, and I is the cross-sectional inertia moment of the beam.

[0080] The second derivative of the deformation curve in the open circuit voltage is integrated as follows:

[0081]

[0082] The open circuit voltage must satisfy the following equation: a 水平 = a 垂直 and The mass block eccentric moment R0 and the length L of the beam and the length L of the piezoelectric layer are related as follows: E

[0083]

[0084] In particular, when the length of the piezoelectric layer is equal to the length of the beam, the eccentric moment of the mass block is Figure 5 The piezoelectric layer length of the present application is equal to the length of the cantilever beam bidirectional vibration energy harvester.

[0085] Figure 6 The second device of the present application is that the mass block is supported by two identical cantilever beams with piezoelectric layers on the left and right sides of the mass block, and the length of the piezoelectric layer is L E In order to have the same energy harvesting capacity in the vertical and horizontal directions, it satisfies the following relationship: the eccentric distance of the mass block is R0=L E When the length of the piezoelectric layer L E is equal to the length L of the left and right cantilever beams, the eccentric distance of the mass block is R0=L.

[0086] For vertical excitation, the deformation curve of the left cantilever support beam is:

[0087]

[0088] In the formula, E is the Young's modulus of the beam material, and I is the cross-sectional inertia moment of the beam.

[0089] The second derivative of the deformation curve in the open circuit voltage is integrated as follows:

[0090]

[0091] For vertical excitation, the deformation curve of the right cantilever support beam of the mass block is equal to the deformation curve of the left cantilever support beam, so:

[0092]

[0093] In the formula, D​垂直 Integral of the second derivative of the deformation curve in the open circuit voltage.

[0094] The left and right side beams of the present application have equal length, and under the action of the horizontal inertia moment, the deformation curve of the left cantilever support beam is:

[0095]

[0096] The second derivative integral value of the deformation curve in the corresponding open circuit voltage is:

[0097]

[0098] The deformation curve of the right cantilever support beam is:

[0099]

[0100] The second derivative integral value of the deformation curve in the corresponding open circuit voltage is:

[0101]

[0102] Using formula (11) and (12), we have:

[0103]

[0104] The open circuit voltage must satisfy: a 水平 = a 垂直 And |D 水平 | = |D 垂直 |, the mass eccentricity R0 and the length L of the cantilever beam and the length L of the piezoelectric layer are obtained. E Relationship:

[0105] R0 = L E (16)

[0106] In particular, when the piezoelectric layer length is equal to the beam length, the mass eccentricity R0 = L. Figure 8 The piezoelectric layer length of the present application is equal to the length of the double cantilever beam type bidirectional vibration energy harvester.

[0107] Embodiment:

[0108] The specific effects of the present application are shown in the following embodiments.

[0109] As Figure 9 , consider that the micro cantilever beam type vibration energy collector is placed on the vibrating foundation, and the natural frequency of the vibration energy collector is set to 500Hz. Set the vertical vibration and horizontal vibration of the foundation to be equal, both 200Hz, and the amplitude is 10 microns, that is, y(t) = x(t) = a0sinω1t, wherein ω1=1256.6 rad / s.

[0110] Both the mass and the beam are made of single crystal silicon or polycrystalline silicon material. In this embodiment, the mass and the beam are made of single crystal silicon material, Young's modulus E = 130 GPa, density p = 2330 kg / m3. -3 The length, width and thickness of the cantilever beam are x direction, z direction and y direction respectively. The length, width and thickness of the cantilever beam are 3000 μm, 1000 μm and 20 μm respectively. The mass of the mass corresponding to the natural frequency is 9.757 x 10 -7 kg. The length and width of the piezoelectric layer are equal to the length and width of the cantilever beam. The thickness of the piezoelectric layer is 0.2 μm, which is very small compared with the thickness of the beam and does not affect the vibration performance of the beam. The piezoelectric constant is 17 pm / V.

[0111] In this embodiment, the mass is a rectangular hexahedron. According to the working principle of the application, the size of the mass is determined as follows. First, the eccentricity of the mass Therefore, the length (y direction size) of the mass is equal to the length of the cantilever beam 3000 μm; second, the width (z direction) of the mass is equal to the width of the cantilever beam 1000 μm; finally, the thickness (x direction size) of the rectangular mass is 1396 μm according to the mass, length, width and density of the mass. Figure 10 is the main size diagram of the embodiment, the width direction of the beam is the z direction, and the substrate and the foundation are not included. Figure 11 is the output open circuit voltage of this example under horizontal and vertical excitation respectively. From Figure 11 it can be seen that the difference between the two voltages is less than 20% under the same size excitation, so the horizontal and vertical directions have the same energy harvesting capability, and the vibration energy in two directions is collected at the same time.

[0112] If the length of the piezoelectric layer of this example is not equal to the length of the cantilever beam, for example: L E = 2000 μm, then because R0= L-L E / 2, the length (y direction size) of the mass must be equal to the length of the cantilever beam 4000 μm; the width (z direction) of the mass is equal to the width of the cantilever beam 1000 μm. The thickness (x direction size) of the rectangular mass is 1047 μm according to the mass, length, width and density of the mass.

Claims

1. A piezoelectric beam-type bidirectional micromechanical vibration energy harvester with an eccentric mass block, characterized in that: Includes a substrate (1), a cantilever beam (3), and a mass block (4) with an eccentricity R0; the cantilever beam (3) is disposed on the substrate (1); the upper surface of the cantilever beam (3) has a piezoelectric layer (2); the starting point of the piezoelectric layer (2) is at the root of the cantilever beam, and the width of the piezoelectric layer (2) is equal to the width of the cantilever beam; The eccentricity of the mass block (4) is Where L is the length of the cantilever beam, L E The length of the piezoelectric layer; The open-circuit voltage of the vibration energy harvester is equal in both the vertical and horizontal directions. The formula for calculating the open-circuit voltage is: In the formula, b is the width of the piezoelectric layer, which is also the beam width; h0 is the thickness of the piezoelectric layer, and L... E For the length of the piezoelectric layer, A = b × L E h is the area of ​​the piezoelectric layer. 31 piezoelectric constant. u(x,t) is the deformation curve of the cantilever beam: u(x,t)=φ(x)q(t) (2) In the formula, φ(x) is a known transformation function, and q(t) is a time function; The deformation curve of the cantilever beam under the action of vertical inertial force F is as follows: In the formula, F 垂直 =ma 垂直 The force is the vertical inertial force, where m is the mass of the mass block, and a is the inertial force. 垂直 Let E be the vertical acceleration, E be the modulus of the beam material, and I be the moment of inertia of the beam section. The second derivative integral of the deformed curve in the corresponding open-circuit voltage is: The deformation curve of the cantilever beam under the action of horizontal moment of inertia is as follows: In the formula, M 水平 =ma 水平 R0 is the horizontal inertial torque, a 水平 Let m be the horizontal acceleration, E be the mass of the mass block, E be the modulus of the beam material, and I be the moment of inertia of the beam section. The second derivative integral of the corresponding open-circuit voltage deformation curve is: When the open-circuit voltage is equal, the eccentricity R0 of the mass block and the length L of the beam and the length L of the piezoelectric layer are used as the basis for determining the relationship between the open-circuit voltage and the open-circuit voltage. E relation When the length of the piezoelectric layer is equal to the length of the beam, the eccentricity of the mass block is 2. The piezoelectric beam-type bidirectional micromechanical vibration energy harvester with an eccentric mass block according to claim 1, characterized in that: The mass block (4) is supported on both sides by a left cantilever beam and a right cantilever beam with the same piezoelectric layer (2), the piezoelectric layer (2) having a length of L. E The eccentricity of the mass block (4) is R0 = L E .

3. The piezoelectric beam-type bidirectional micromechanical vibration energy harvester with an eccentric mass block according to claim 1, characterized in that: The mass block (4) is supported on both sides by a left cantilever beam and a right cantilever beam with the same piezoelectric layer (2), the piezoelectric layer (2) having a length L. E The eccentricity of the mass block (4) is R0 = L, which is equal to the length L of the left and right cantilever beams.

4. The piezoelectric beam-type bidirectional micromechanical vibration energy harvester with an eccentric mass block according to claim 1, characterized in that: The mass block (4) and the cantilever beam (3) are made of monocrystalline silicon.

5. The piezoelectric beam-type bidirectional micromechanical vibration energy harvester with an eccentric mass block according to claim 3, characterized in that: The deformation curve of the left cantilever beam under vertical excitation is as follows: In the formula, E is the modulus of the beam material, and I is the moment of inertia of the beam section; The integral value of the second derivative of the deformed curve in the corresponding open-circuit voltage is For vertical excitation, the deformation curve of the right cantilever beam of the mass block is equal to the deformation curve of the left cantilever beam, thus: In the formula, D 垂直 Represents the integral in the vertical direction.

6. The piezoelectric beam-type bidirectional micromechanical vibration energy harvester with an eccentric mass block according to claim 3, characterized in that: The deformation curve of the left cantilever beam under horizontal moment of inertia is as follows: The second derivative integral of the deformed curve in the corresponding open-circuit voltage is: The deformation curve of the right cantilever beam is as follows: The integral value of the second derivative of the deformed curve in the corresponding open-circuit voltage is: From equations (12) and (14), we obtain a 水平 =a 垂直 and D 水平 =D 垂直 Then the open-circuit voltages are equal, and the eccentricity R0 of the mass block is equal to the length L of the cantilever beam and the length L of the piezoelectric layer. E relation R0=L E (16).

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