CN102324869A - Dumbbell type statically indeterminate piezoelectric beam energy harvester - Google Patents

Abstract

The invention discloses a dumbbell type statically indeterminate piezoelectric beam energy harvester which comprises a support shell and a dumbbell type piezoelectric bimorph beam, wherein both ends of the dumbbell type piezoelectric bimorph beam are fixed on the support shell, and the piezoelectric bimorph beam comprises a pair of piezoelectric sheet layers and a metal layer located between the piezoelectric sheet layers, and the metal layer is used for enhancing the vibration fatigue resistance and the durability of the energy harvester. Both sides of the energy harvesting structure piezoelectric bimorph beam are completely restricted on the vibration support shell to form a statically indeterminate structure, and the entire system becomes safer and more stable. The piezoelectric beam is a dumbbell type structure, i.e. both edges of the piezoelectric sheet layers and the metal layer in the length direction are concave curved lines, both edges in the width direction are linear lines, so that not only is enough strength at the root of the energy harvesting structure ensured and the stress at the root is reduced, but also the space in the middle with relatively small stress is saved. Therefore, on the condition of ensuring output power density, the overall service life of the energy harvesting system is greatly prolonged.

Description

A kind of indeterminate piezoelectric beam energy accumulator of dumbbell shape

Technical field

The invention belongs to and a kind ofly be converted into electric energy through the vibrational energy in the absorbing environmental through piezoelectric and come the piezoelectric harvester spare than high fatigue life arranged, be specifically related to a kind of indeterminate piezoelectric beam energy accumulator of dumbbell shape what microelectronic component was supplied power.

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.Roundy etc. are through can think that prisoner's energy efficiency of piezoelectric harvester is the highest, also the most rising after the analysis relatively of means to the prisoner in a large number.

Existing piezoelectric harvester all concentrates on main energy on the optimal design of device output performance.Yet as the substitute products of conventional batteries, be not much accounted of the fatigue life of energy accumulator self.Yet in fact; The length of the active time of energy accumulator spare with and operating state under fail safe directly determined the necessity that it exists with stability; If its work fatigue life-span is lower than the power-on time of existing battery, then the advantage of its unlimited passive power supply can't embody.

In conventional piezoelectric prisoner ability system, piezoelectric beam is one of most important prisoner's ability structure always.But this structure is a statically determinate structure, and promptly the constraint number on the structure just equates with its degree of freedom, if in case one of them constraint goes wrong, then total can't work on.And wherein placing end in the knee wall to bear whole effect counter-forces that the prisoner can body, the Root Stress concentration phenomenon is obvious, makes greatly reduce this fatigue life that changes structure, has also therefore influenced the work service life that whole prisoner can system.Consider from the another one angle, if the integral width or the thickness of piezoelectric beam is increased, also can improve the ability that it meets with stresses, but the shared space of corresponding devices is just bigger, the power density that the prisoner can system can reduce.

Summary of the invention

So to above problem, this patent has been invented a kind ofly to be had than the indeterminate piezoelectric beam energy accumulator of the dumbbell shape of high fatigue life.When the constraint on the beam body outnumbers its degree of freedom, be referred to as statically indeterminate beam.Therefore, the indeterminate support of the prisoner of this energy accumulator ability agent structure makes whole system safer stable, even one of them constraint is ineffective, whole system also can be worked as usual.In addition; And the vertical actuating force of this structure is born by two ends jointly; The stress of root greatly reduces, and the dumbbell shape structure both guaranteed the prisoner can the structure root enough intensity, saved the space at the less relatively middle part of stress again; Thereby under the prerequisite that guarantees output power density, significantly improve the whole service life of prisoner's ability system.

The present invention is achieved in that

A kind of indeterminate piezoelectric beam energy accumulator of dumbbell shape; Comprise the bearing shell; And two ends are fixed on the piezoelectric bimorph beam of the dumbbell shape on the bearing shell; Said piezoelectric bimorph beam comprises the metal level that a pair of piezoelectricity lamella is middle with being positioned at the piezoelectricity lamella, and metal level is in order to strengthen the anti-vibration fatigue durability of this floating ability device.The both sides of the length direction of piezoelectricity lamella and metal level are the camber line that concaves, and the both sides of Width are straight line, thereby make the piezoelectric bimorph beam form dumbbell shape.In use, piezoelectricity lamella and metal level are except thickness is different, and the specification of length and width is all identical.

Scheme further is: the exradius R=of camber line (4 α 2b2+L2)/(8 α b), and wherein α is the safety clearance coefficient, value 0.1～0.3, b is the width of piezoelectricity lamella, L is the length of piezoelectricity lamella.

Scheme further is: intermediate metal layer is 0.8 with the thickness ratio of single piezoelectricity lamella.

The piezoelectricity lamella polarizes on thickness direction, and the piezoelectricity lamella all is coated with thin electrodes at upper and lower surfaces.

The thin electrodes of the top piezoelectricity lamella upper surface of the piezoelectric bimorph beam of dumbbell shape and the thin electrodes of lower piezoelectric lamella lower surface are connected the back through lead and are connected with the microelectronic element load impedance, are wired to metal level again.

Said piezoelectricity lamella is a piezoelectric ceramic piece.

Said thin electrodes is a silver electrode.

In order to improve prisoner's ability effect, the piezoelectric bimorph beam of a plurality of dumbbell shapes can be set in each bearing shell.

Vibration mounting shell of the present invention is fixed on the ground absorbing from the vibrational energy in the environment, and dustproof, antimagnetic effect is arranged.It is A as amplitude that shell is fixed in vertical direction, and frequency is on the ground of simple harmonic vibration of f.Load is the working impedance of external connected electronic device.

The basic principle of institute of the present invention foundation is: piezoelectric ceramic piece can produce the electric polarization phenomenon under the mechanical external force effect,

${\mathrm{<figure-callout\; id="3"\; label="D"\; filenames="HDA0000092934390000011.png"\; state="\{\{state\}\}">D</figure-callout>}}_3=s_{11}^{-1}{d}_{31}(-x_3{u}_{\mathrm{3,11}})-{\stackrel{\&OverBar;}{\mathrm{\&epsiv;}}}_{33}{V}_p/h,---\left(1\right)$

In the following formula, D ₃Be the electric displacement component of each piezoelectric unit, s ₁₁, d ₃₁With

Be respectively the softness factor of each piezoelectric beam, piezoelectric modulus and dielectric coefficient ,-x ₃u _3,11Be vertical normal strain, V _pRepresent the limit pole plate of each piezoelectric ceramic piece and the electrical potential difference between the pole plate of center, h is the thickness of piezoelectric ceramic piece.So the upper and lower surfaces of each double piezoelectric ceramic sheet beam all polarization charge Q can occur _p

$Q_P=-b\underset{0}{\overset{L}{\&Integral;}}(1/h)\underset{c/2}{\overset{c/2+\mathrm{<figure-callout\; id="3"\; label="h\; D"\; filenames="HDA0000092934390000011.png"\; state="\{\{state\}\}">h</figure-callout>}}{\&Integral;}}{D}_{}{}_3{\mathrm{<figure-callout\; id="3"\; label="dx"\; filenames="HDA0000092934390000011.png"\; state="\{\{state\}\}">dx</figure-callout>}}_3{\mathrm{dx}}_1---\left(2\right)$

C is the thickness of central metal layer, and L is the length of piezoelectricity lamella.On the piezoelectric bimorph wherein the output current of monolithic be:

$I_p=-{\stackrel{\&CenterDot;}{Q}}_p---\left(3\right)$

According to circuit relationships, conclusion electricity boundary condition is following:

2I _pZ _L＝V _p (4)

The mechanical oscillation of considering environment have periodically, and the power output P of then total piezoelectricity prisoner ability system does

$P=\frac{1}{T}{\&Integral;}_0^{T}2I_p{V}_p\mathrm{dt},---\left(5\right)$

The present invention compares with existing piezoelectric harvester and has the following advantages:

1) both sides of prisoner's ability structure piezoelectric bimorph beam all are constrained on the vibration mounting shell fully; Form the statically indeterminate beam structure; Its indeterminate support makes whole system safer stable, even wherein side constraint is ineffective, whole system also can be worked as usual; And the vertical actuating force of this structure born by two ends jointly, and the concentrated stress of root greatly reduces.

2) piezoelectric beam is the dumbbell shape structure; Its both guaranteed the prisoner can the structure root enough intensity, reduce Root Stress, saved the space at the less relatively middle part of stress again; Thereby under the prerequisite that guarantees output power density, significantly improve the whole service life of prisoner's ability system.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 connects sketch map for the piezoelectric bimorph beam and the circuit of dumbbell shape of the present invention;

Fig. 3 is the graph of a relation between the present invention's floating ability device output voltage and the environmental excitation frequency;

Fig. 4 can capture ability structure each locational displacement and stress envelope by device for the present invention is floating.

Embodiment

Below in conjunction with accompanying drawing and embodiment the present invention is done further detailed description.

Shown in accompanying drawing 1; A kind of indeterminate piezoelectric beam energy accumulator of dumbbell shape comprises bearing shell 6, and two ends are fixed on the piezoelectric bimorph beam of the dumbbell shape on the bearing shell; Said piezoelectric bimorph beam comprises the metal level 2 that a pair of piezoelectricity lamella 1 is middle with being positioned at the piezoelectricity lamella; Metal level 2 is the anti-vibration fatigue durabilities that originally float the ability device in order to strengthen, and the piezoelectricity lamella polarizes on thickness direction, and the piezoelectricity lamella all is coated with thin electrodes 3 at upper and lower surfaces.

Where necessary, a plurality of piezoelectric bimorph beams are installed in bearing shell 6 inside again.

Shown in accompanying drawing 2, the thin electrodes of the top piezoelectricity lamella upper surface of the piezoelectric bimorph beam of dumbbell shape and the thin electrodes of lower piezoelectric lamella lower surface are connected the back through lead 4 and are connected with microelectronic element load impedance 5, are connected to metal level 2 through lead 4 again.

Said piezoelectricity lamella is a piezoelectric ceramic piece.

Said thin electrodes is a silver electrode.

Select for use PZT-5H as piezoelectric, its major parameter is following:

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

ε ₀＝8.854×10 ^-12F/m，ρ＝7500kg/m ³

Intermediate metal layer is an aluminium alloy, its Young's modulus E=70GPa, density p=2700kg/m ³We choose the width b=10mm of piezoelectricity lamella in the analog computation, length L=70mm, and individual layer piezoelectric patches layer thickness h=0.5mm gets exradius R=(4 α ²b ²+ L ²)/(8 α b), wherein α is a proportionality coefficient, α=0.1～0.3.Intermediate metal layer compares c/h=0.8 with the thickness of piezoelectricity lamella.The acceleration amplitude of getting excitation is for forced vibration; For the Considering Damping effect, get damping coefficient Q=0.01.We get the anti-Z of load resistance of load impedance in calculating _LBe 100k Ω.In the calculating, shell with ground with Asin ω ₀T vertically vibrates, the t express time.The vertical vibration acceleration amplitude

Be taken as 1m/s ²Numerical simulation calculation result below in conjunction with Finite Element Method describes.

Accompanying drawing 3 is depicted as the output voltage of piezoelectric harvester and the relation between the environmental excitation frequency.Along with the increase of driving frequency, itself and energy accumulator natural frequency (about 206Hz) are constantly approaching, and the interaction aggravation between this moment environment and the energy accumulator raises its output voltage gradually; Then, when the environmental excitation frequency continued to increase, it was progressively away from the energy accumulator natural frequency, and the output voltage of energy accumulator decreases.Can find that at the peak value place, the output voltage of energy accumulator is up to 1.2V.

Accompanying drawing 4 comprehensively and three-dimensional displaying external environment driving frequency when being 210Hz, single order mode and each locational displacement and stress distribution situation that the prisoner can structure.Can find that maximum stress point appears at the root of piezoelectric beam really, and indeterminate constraint makes the vertical actuating force of this structure born jointly by two ends, the concentrated stress of root greatly reduces.The design of dumbbell kenel is captureed under the prerequisite of the enough intensity of ability structure root in assurance, has saved central space, thereby under the prerequisite that guarantees output power density, significantly improves the whole service life of captureing the ability system.

Claims (9)

1. the indeterminate piezoelectric beam energy accumulator of a dumbbell shape; Comprise the bearing shell; It is characterized in that: said energy accumulator comprises that also two ends are fixed on the piezoelectric bimorph beam of the dumbbell shape on the bearing shell; Said piezoelectric bimorph beam comprises the metal level that a pair of piezoelectricity lamella is middle with being positioned at the piezoelectricity lamella, and the both sides of the length direction of piezoelectricity lamella and metal level are the camber line that concaves, and the both sides of Width are straight line.

2. according to the indeterminate piezoelectric beam energy accumulator of the said dumbbell shape of claim 1, it is characterized in that: exradius R=(4 α of said camber line ²b ²+ L ²)/(8 α b), wherein α is a proportionality coefficient, value 0.1～0.3, and b is the width of piezoelectricity lamella, L is the length of piezoelectricity lamella.

3. according to the indeterminate piezoelectric beam energy accumulator of the said dumbbell shape of claim 1, it is characterized in that: said intermediate metal layer is 0.8 with the thickness ratio of single piezoelectricity lamella.

4. according to the indeterminate piezoelectric beam energy accumulator of the said dumbbell shape of claim 1, it is characterized in that: said piezoelectricity lamella polarizes on thickness direction, and the piezoelectricity lamella all is coated with thin electrodes at upper and lower surfaces.

5. according to the indeterminate piezoelectric beam energy accumulator of the said dumbbell shape of claim 1; It is characterized in that: the thin electrodes of the top piezoelectricity lamella upper surface of the piezoelectric bimorph beam of said dumbbell shape and the thin electrodes of lower piezoelectric lamella lower surface are connected the back through lead and are connected with the microelectronic element load impedance, are connected with metal level through lead again.

6. according to the indeterminate piezoelectric beam energy accumulator of the said dumbbell shape of the arbitrary claim of claim 1 to 5, it is characterized in that: said metal level is an aluminium alloy.

7. according to the indeterminate piezoelectric beam energy accumulator of the said dumbbell shape of the arbitrary claim of claim 1 to 5, it is characterized in that: said piezoelectric patches layer material is PZT-5H.

8. according to the indeterminate piezoelectric beam energy accumulator of the said dumbbell shape of the arbitrary claim of claim 1 to 5, it is characterized in that: said thin electrodes is a silver electrode.

9. according to the indeterminate piezoelectric beam energy accumulator of the said dumbbell shape of the arbitrary claim of claim 1 to 5, it is characterized in that: the quantity of the piezoelectric bimorph beam of dumbbell shape is at least one in the said bearing shell.

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