CN101895232A - Piezoelectric energy harvester with elastic element linkage - Google Patents

Abstract

The invention provides a piezoelectric energy harvester with elastic element linkage. The piezoelectric energy harvester comprises a piezoelectric bimorph beam, wherein the piezoelectric bimorph beam comprises two piezoelectric lamellas polarized in the thickness direction and a metal layer which is compounded between the two piezoelectric lamellas; the piezoelectric energy harvester also comprises a shell; the interior of the shell at least comprises a wafer group; the wafer group comprises two or more than two piezoelectric bimorph beams which are arranged in a row along the thickness direction of the piezoelectric lamellas; one end of each piezoelectric bimorph beam is fixed on one inner side wall of the shell, and the other end thereof is a free end; and the freed ends of the two adjacent piezoelectric bimorph beams in the wafer group are connected through elastic elements. The working frequency band of the piezoelectric energy harvester with elastic element linkage is broadened, and frequency modulation is carried out according to requirements of multi-frequency and variable- frequency environments, thereby increasing the output power.

Description

Has the piezoelectric harvester that flexible member connects

Technical field

The present invention relates to the energy accumulator of captures energy from environment, relate in particular to a kind of piezoelectric harvester that flexible member connects that has.

Background technology

In recent years, because microelectronic component is civilian, the extensive use of military and medical aspect has caused the concern of more and more researchers for the energy accumulator of its energy supply.Compare with traditional energy supply source battery, the advantage of energy accumulator spare is: output is stable, and the life-span is longer, more environmental protection.Among a large amount of prisoner's energy means, prisoner's energy efficiency of piezoelectric harvester is the highest, also the most rising.

Yet existing piezoelectric harvester designs the electric coupling that main energy all concentrates between piezoelectric structure and the prisoner's energy circuit.Main contact between each piezoelectric chip in prisoner's energy system also is set at the conductivity between them, and in fact, the mechanical couplings between each piezoelectric device also can produce material impact to whole service behaviour of captureing the energy system.In addition, existing piezoelectric harvester is the device of steady job frequency after producing, yet well-known, and the frequency in ambient vibration source may all change constantly, and moreover, same environment vibration source also may comprise a plurality of vibration frequency spectrums.And under as influence of various factors such as temperature, electromagnetic field, gravitation variations, the frequency of environment vibration source may be drifted about.In case the ambient vibration frequency departure piezoelectricity prisoner can structure natural frequency, interaction therebetween just very a little less than.Under this complicated natural environment situation, the power output of traditional energy accumulator spare can decay significantly, is difficult to guarantee the operate as normal of microelectronic component.

Summary of the invention

Technical problem to be solved by this invention is: at above-mentioned the deficiencies in the prior art, provide a kind of wideer operating frequency band that has, and can have a piezoelectric harvester that flexible member connects to what frequency band was regulated.

The present invention for the technical scheme that problem adopted of the above-mentioned proposition of solution is:

A kind of piezoelectric harvester with flexible member connection, it comprises the piezoelectric bimorph beam, and described piezoelectric bimorph beam is included in two piezoelectricity lamellas and metal level that polarizes on the thickness direction, and metal level is compounded between two piezoelectricity lamellas; Described piezoelectric harvester also comprises housing, comprises a wafer set in the described housing at least, and described wafer set comprises two or more piezoelectric bimorph beams, and the piezoelectric bimorph beam in the described wafer set is arranged in row along the thickness direction of piezoelectricity lamella; One end of described piezoelectric bimorph beam is fixed on the madial wall of housing, and the other end of described piezoelectric bimorph beam is a free end, connects by described flexible member between the free end of adjacent two piezoelectric bimorph beams in the described wafer set.

The center of gravity deflection of described housing is a side of piezoelectric bimorph beam fixedly.

The thickness of the sidewall that is used for fixing the piezoelectric bimorph beam of described housing is greater than the thickness of the sidewall of opposite side on the other side.

Described flexible member is a spring.

Have at least the thickness of piezoelectricity lamella of a piezoelectric bimorph beam different in the described wafer set with the thickness of the piezoelectricity lamella of other piezoelectric bimorph beam.

The thickness of two piezoelectricity lamellas in piezoelectric bimorph beam is identical.

Have at least the thickness of piezoelectricity lamella of each piezoelectric bimorph beam of the thickness of piezoelectricity lamella of each piezoelectric bimorph beam of a wafer set and other wafer set incomplete same.

The thickness of the piezoelectricity lamella of piezoelectric bimorph beam has nothing in common with each other in the described piezoelectric harvester.

Compared to prior art, piezoelectric harvester of the present invention is compared with traditional energy accumulator, operating frequency band with piezoelectricity prisoner energy system of flexible member connection has obtained effectively widening, thereby and can carry out frequency modulation according to concrete needs and increase power output, the use value in actual multifrequency frequency conversion environment increases substantially.

Description of drawings

Fig. 1 is the structural representation with piezoelectric harvester that flexible member connects that the embodiment of the invention provides.

Fig. 2 is the structural representation of the piezoelectric bimorph beam among Fig. 1.

Fig. 3 is the schematic diagram that the piezoelectric harvester among Fig. 1 is connected with load circuit.

When Fig. 4 was the pure series connection of three piezoelectric bimorph beams, the power output of piezoelectric harvester was with the variation diagram of driving frequency.

When Fig. 5 was three piezoelectric bimorph beams parallel connections, the power output of piezoelectric harvester was with the variation diagram of driving frequency.

Fig. 6 is three wafer set parallel connections, and when three piezoelectric bimorph beams of each wafer set were connected, the power output of piezoelectric harvester was with the variation diagram of driving frequency.

Among the figure: 1-housing, 2-wafer set, 3-piezoelectric bimorph beam, 4-lead, 5-electrode, 6,7-piezoelectricity lamella, 8-metal level, 9-load, the madial wall of 11-housing, 12-spring

Embodiment

See also Fig. 1 to Fig. 3, a kind of piezoelectric harvester that it provides for the embodiment of the invention with flexible member connection.Piezoelectric harvester comprises a housing 1 and is placed in n wafer set 2 in the housing 1 that n is the natural number more than or equal to 1.Each wafer set 2 comprises m piezoelectric bimorph beam 3, and m is the natural number more than or equal to 2.In order to be illustrated more clearly in the present invention, Fig. 1 only demonstrates the part of housing 1.

Each piezoelectric bimorph beam 3 comprises two piezoelectricity lamellas 6 that polarize and 7 and at interval two piezoelectricity lamellas 6 and 7 metal level 8 on thickness direction.In the present embodiment, piezoelectricity lamella 6 and 7 thickness equate.Two electrodes 5 are arranged at the upper surface and the lower surface of each piezoelectric bimorph beam 3 respectively.Two electrodes 5 and metal level 8 are electrically connected with load 9 by lead 4.One end of each piezoelectric bimorph beam 3 is fixed on the madial wall 11 of housing 1, and the other end is a free end.The free end of adjacent two piezoelectric bimorph beams 3 connects by spring 12 in each wafer set 2.Two free-ended modes of spring 12 connections have multiple, for example can fix by clamping structure, are convenient for changing spring like this.Have at least the piezoelectricity lamella 6 or 7 the thickness of the piezoelectricity lamella 6 of a piezoelectric bimorph beam 3 or 7 thickness and other piezoelectric bimorph beam 3 different in the wafer set 2.Have at least the piezoelectricity lamella 6 or 7 the thickness of each piezoelectric bimorph beam 3 of the piezoelectricity lamella 6 of each piezoelectric bimorph beam 3 of a wafer set 2 or 7 thickness and other wafer set 2 incomplete same.In the present embodiment, the thickness of the piezoelectricity lamella of all piezoelectric bimorph beams 3 has nothing in common with each other in the piezoelectric harvester.M piezoelectric bimorph beam 3 forms a line at interval along the thickness direction of piezoelectricity lamella 6 or 7.M piezoelectric bimorph beam 3 is parallel to each other and is oppositely arranged.

The side that the center of gravity deflection piezoelectric bimorph beam 3 and the housing 1 of housing 1 fixed, to guarantee the stability and the fatigue durability of whole piezoelectric harvester vibration, it can be accomplished in several ways, and the thickness of sidewall of fixedly piezoelectric bimorph beam 3 that for example can make housing 1 is greater than the thickness of the sidewall of opposite side on the other side.In the present embodiment, housing 1 is a cuboid.Housing 1 selects for use material of greater hardness to make, and whole piezoelectric harvester is played fixing and anti-tampering effect, as dustproof, and antimagnetic effect.

We use index (i) represent the sequence number of each piezoelectric bimorph beam 3 in the piezoelectric harvester (i=1,2 ..., nm) to determine its position.Each piezoelectric bimorph beam 3 corresponding amount of deflection note is done

Governing equation by the different piezoelectric bimorph beam of a plurality of thickness 3 structures can reduce following form:

$-D^{\left(i\right)}{u}_{\mathrm{3,1111}}^{\left(i\right)}={m\stackrel{\·\·}{u}}_3^{\left(i\right)}---\left(1\right)$

Its mechanical boundary conditions about shearing force is:

$-N^{\left(i\right)}(l,t)=D^{\left(i\right)}{u}_{\mathrm{3,111}}^{\left(i\right)}(l,t)=k(u_3^{(i+1)}(l,t)+u_3^{(i-1)}(l,t)-2u_3^{\left(i\right)}(l,t)),---\left(2\right)$

Each piezoelectric bimorph beam 3 surface electrode

On average free charge be:

$Q_p^{\left(i\right)}=-b{\&Integral;}_0^l\frac{1}{h^{\left(i\right)}}\underset{c^{\left(i\right)}}{\overset{c^{\left(i\right)}+h^{\left(i\right)}}{\&Integral;}}{D}_3^{\left(i\right)}{\mathrm{<figure-callout\; id="3"\; label="dx"\; filenames="HDA0000024188230000011.png,HDA0000024188230000021.png"\; state="\{\{state\}\}">dx</figure-callout>}}_3{\mathrm{dx}}_1---\left(3\right)$

The electric current that is flowed out from the electrode 5 of each piezoelectric bimorph beam 3 is

$i_p^{\left(i\right)}=-{\stackrel{\&CenterDot;}{Q}}_p^{\left(i\right)}---\left(4\right)$

N ⁽ⁱ⁾Be the shearing force on each piezoelectric bimorph beam 3 cross-sectional area, k is the Hookean elasticity coefficient of spring 12, h ⁽ⁱ⁾And 2c ⁽ⁱ⁾The piezoelectricity lamella 6 or 7 and the thickness of central metal layer 8 of representing each piezoelectric bimorph beam 3 respectively,

Be the electric displacement component of each piezoelectric bimorph beam 3, s ₁₁, d ₃₁With

Be respectively the softness factor of each piezoelectric bimorph beam 3, piezoelectric modulus and dielectric coefficient.

Represent the limit pole plate of each piezoelectric ceramic piece and the electrical potential difference between the pole plate of center.According to the circuit topology relation, conclusion electricity boundary condition is as follows:

$\underset{j=1}{\overset{k_s}{\mathrm{\&Sigma;}}}{V}_p^{\left(j\right)}=2\underset{i=1}{\overset{k_p}{\mathrm{\&Sigma;}}}{i}_p^{(m\&CenterDot;i)}{Z}_L---\left(5\right)$

The mechanical oscillation of considering environment have periodically, and the power output P of then total piezoelectric harvester is

$P=\frac{1}{T}{\&Integral;}_0^{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="HDA0000024188230000011.png,HDA0000024188230000021.png"\; state="\{\{state\}\}">T</figure-callout>}}2\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}{I}_p^{\left(i\right)}\underset{j=1}{\overset{m}{\mathrm{\&Sigma;}}}{V}_p^{(1,j)}\mathrm{dt}---\left(6\right)$

In the present embodiment, piezoelectricity lamella 6 or 7 material are PZT-5H, and its major parameter is as follows:

(s ₁₁，d ₃₁，ε ₃₃)＝(16.5×10 ^-12m ²/N，-274×10 ^-12C/N，3400ε ₀)，

${\stackrel{\&OverBar;}{\mathrm{\&epsiv;}}}_{33}={\mathrm{\&epsiv;}}_{33}(1-k_{31}^2),$ $k_{31}^2=d_{31}^2/\left({\mathrm{\&epsiv;}}_{33}{s}_{11}\right),$ ε ₀＝8.854×10 ^-12F/m，ρ＝7500kg/m ³

The material of metal level 8 is aluminium in the present embodiment, its Young's modulus E=70GPa, density p=2700kg/m ³We choose the width b=10mm of piezoelectricity lamella 6 or 7 in the analog computation, length l=70mm, and piezoelectricity lamella 6 or 7 compares c/h=0.4 with the thickness of metal level 8.For forced vibration,, substitute sij (Q is the quality factor of material, gets Q=50) with s11 (1-iQ-1) in order to consider damping effect.The equivalent capacity and the equivalent eccentric electrical impedance of piezoelectric bimorph beam 3 are respectively And Z ₀=1/ (i ω ₀C ₀).The electrical impedance that we get load 9 in calculating is Z _L=iZ ₀In the calculating, housing 1 with ground with Asin2 π f ₀T vertically vibrates, and the vibration acceleration amplitude Be taken as 1m/s ²Therefore, the boundary condition of piezoelectric bimorph beam 3 stiff ends is: Asin2 π f is pressed in the displacement of vertical direction ₀T changes; At free-ended boundary condition be: the moment of flexure at this place equals zero, and the shear stress on the cross section makes a concerted effort to cause lumped mass acceleration in vertical direction.

We choose m=3, and n=1 illustrates.Piezoelectricity lamella 6 in three piezoelectric bimorph beams 3 or 7 thickness are respectively 0.30mm, 0.305mm, 0.31mm.

As shown in Figure 4, when it is 3 series connection of three piezoelectric bimorph beams, under the effect of spring 12 with different coefficient of elasticity k, power output that under above-mentioned experiment condition, obtains and driving frequency ω ₀Between relation.The graph of a relation that Fig. 5 obtains when then being 3 parallel connections of three piezoelectric bimorph beams.As can be seen from Figure 4 and Figure 5, when the end did not have the spring connection, (curve a) all had 3 output peaks to occur under series connection and parallel form when promptly setting k=0.And the main peak of tandem type is first output peak, parallel connection type then be last.When the intensity of spring 12 improved, the center at output peak began drift, and output raises, and peak number reduces.This means that power output increases, and operating frequency is wideer by after 12 connections of the spring between the piezoelectric bimorph beam 3.When spring 12 intensity increased to a certain degree, its output performance tended towards stability.

When choosing m=3, during n=3, the piezoelectricity lamella 6 of three wafer set 2 or 7 thickness are followed successively by 0.30,0.305,0.31mm; 0.315,0.32,0.325mm; 0.33,0.335,0.34mm (order from top to bottom).Fig. 6 is power output and the driving frequency ω that obtains under the effect of the spring 12 with different coefficient of elasticity k ₀Between relation.As can be seen from Figure 6, the spring 12 that the free end of piezoelectric bimorph beam 3 connects can strengthen power output effectively, and the operating frequency band of control piezoelectric harvester.And the operating frequency band of piezoelectric harvester can be easily regulated vibration source frequency not stop in conforming to change to spring structure.For example, when the environmental excitation frequency is 95Hz, then the elastic coefficient k should be adjusted into 50Nm ^-1When driving frequency is 100Hz, then k should be 100Nm ^-1So that power output is carried out optimization.

Be understandable that, can also use other flexible members to replace spring 12, for example, the rectangle diaphragm that bellows, elastomeric material are made etc.

Compared to prior art, piezoelectric harvester of the present invention is compared with traditional energy accumulator, operating frequency band with piezoelectricity prisoner energy system of elasticity connection has obtained effectively widening, thereby and can carry out frequency modulation according to concrete needs and increase power output, the use value in actual multifrequency frequency conversion environment increases substantially.

Protection scope of the present invention is not limited to the above embodiments, and obviously, those skilled in the art can carry out various changes and distortion and do not depart from the scope of the present invention and spirit the present invention.If these changes and distortion belong in the scope of claim of the present invention and equivalent technologies thereof, then the intent of the present invention also comprises these changes and is out of shape interior.

Claims (8)

1. one kind has the piezoelectric harvester that flexible member connects, and it comprises the piezoelectric bimorph beam, and described piezoelectric bimorph beam is included in two piezoelectricity lamellas and metal level that polarizes on the thickness direction, and metal level is compounded between two piezoelectricity lamellas; It is characterized in that, described piezoelectric harvester also comprises housing, at least comprise a wafer set in the described housing, described wafer set comprises two or more piezoelectric bimorph beams, and the piezoelectric bimorph beam in the described wafer set is arranged in row along the thickness direction of piezoelectricity lamella; One end of described piezoelectric bimorph beam is fixed on the madial wall of housing, and the other end of described piezoelectric bimorph beam is a free end, connects by described flexible member between the free end of adjacent two piezoelectric bimorph beams in the described wafer set.

2. piezoelectric harvester as claimed in claim 1 is characterized in that: the center of gravity deflection of described housing is a side of piezoelectric bimorph beam fixedly.

3. piezoelectric harvester as claimed in claim 2 is characterized in that: the thickness of the sidewall that is used for fixing the piezoelectric bimorph beam of described housing is greater than the thickness of the sidewall of opposite side on the other side.

4. piezoelectric harvester as claimed in claim 1 is characterized in that: described flexible member is a spring.

5. piezoelectric harvester as claimed in claim 1 is characterized in that: have at least the thickness of piezoelectricity lamella of a piezoelectric bimorph beam different with the thickness of the piezoelectricity lamella of other piezoelectric bimorph beam in the described wafer set.

6. piezoelectric harvester as claimed in claim 5 is characterized in that: the thickness of two piezoelectricity lamellas in piezoelectric bimorph beam is identical.

7. piezoelectric harvester as claimed in claim 1 is characterized in that: have at least the thickness of piezoelectricity lamella of each piezoelectric bimorph beam of the thickness of piezoelectricity lamella of each piezoelectric bimorph beam of a wafer set and other wafer set incomplete same.

8. piezoelectric harvester as claimed in claim 1 is characterized in that: the thickness of the piezoelectricity lamella of piezoelectric bimorph beam has nothing in common with each other in the described piezoelectric harvester.

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