WO2011134789A1

WO2011134789A1 - Piezogenerator comprising different piezoelements and electronic circuit

Info

Publication number: WO2011134789A1
Application number: PCT/EP2011/055752
Authority: WO
Inventors: Alexander Frey; Ingo KÜHNE; Matthias Schreiter
Original assignee: Siemens Aktiengesellschaft
Priority date: 2010-04-30
Filing date: 2011-04-13
Publication date: 2011-11-03
Also published as: DE102010018875A1

Abstract

A piezogenerator for converting mechanical into electrical energy is constructed from two different piezoelements, which are applied one above the other or alongside one another on a carrier (1). The second piezoelement (3, 8, 13, 15) has a higher output voltage (U2>U1) in comparison with the first piezoelement (2, 9, 12, 14), in conjunction with a lower efficiency, and has a smaller area (A2), as a result of which the higher energy conversion of the first piezoelement (2, 9, 12, 14) is dominant. The higher output voltage (U2) serves primarily for driving high-impedance loads such as e.g. the gate of a transistor.

Description

description

Piezoelectric generator with various piezo elements and electronic circuit

The invention relates to a piezoelectric generator with different piezo elements and an associated electronic circuit.

The use of sensors, driven by new applications, but also by falling costs through a realization in MEMS technology (Micro-Electro-Mechanical Systems), is spreading to more and more areas of application. Particularly interes ^¬ sant here are sensor nodes and networks that work energieau ^¬ autarkic. Such systems do not obtain the electrical energy necessary for the operation of the individual components from the mains supply or a battery, but via a suitable converter from the available energy in the environment such. As vibration, heat or sun.

One way to provide electrical energy is to take advantage of the piezoelectric effect to convert mechanical energy into electrical energy. The voltage and energy generated in the piezoelectric element is generally not directly suitable for an electrical load and in particular not for the system components of a wireless sensor node. For this reason, a specific energy management circuit is used between piezo ^¬ generator and consumer. Such an energy management circuit in CMOS technology is known from "A New Rectifier and Trigger Circuit for a Piezoelectric Microgenerator" (Proceedings of the Eurosensor XXIII, Conference September 2009, Pages 1447-1450).

The object of the invention is to provide a cheap and simple piezoelectric generator for converting mechanical in electrical energy with high efficiency and short system startup times.

The object is achieved by the features of the independent claim.

Further developments of the invention are listed in the dependent claims. This invention relates to a novel arrangement, ba ^¬ sierend to realize on the piezoelectric effect, for example, a self-contained power supply module for operating a wire ^¬ contact sensor node. The piezoelectric effect is used to convert mechanical energy into electrical energy. Such genes ^¬ rator is realized for example by means of a bending beam structure. An external environmental force F acts on the piezo layer shown in blue, which is laterally clamped on one side or on two sides. The induced mechanical clamping ^¬ voltage over the piezo specific material constants d (charge constant), and ε (permittivity) is σ converted into an electric energy or voltage Vp Wp.

The following relationships apply:

In order to maximize the converted electrical energy, a piezoelectric element is used which has as large a value as possible for d and at the same time a small value for ε. By choosing the material for optimizing the energy, the voltage level is determined by equation (2). Examples of piezospecific material constants are shown in the following table:

With PZT can be compared to ZnO according to equation (1), an approximately 3.7-fold amount of energy to be converted. On the ^¬ to whose side the generated voltage in the case of ZnO is about a factor of 3 larger compared with PZT. Energy and voltage can not be set independently.

The basic principles of a circuit for converting mechanical energy into electrical energy by means of a piezo ^¬ electric generator are described below:

The generator is shown as a current source with parallel connected capacity. The primary electrical energy

(electrical voltage) has according to the mechanical An ^¬ movement an oscillating course. With the help of a first circuit block, this alternating signal must be rectified. The electrical energy is then present at a ^DC voltage level at a first in-circuit storage capacity. The energy and voltage at this node is also typically used to supply the first circuit block. For booting up the system, that is to say at a point in time when there is not enough energy available for operation at the first storage ^node , a startup circuit is required which functions passively. Since the voltage level at the first storage node is usually not sufficient for the actual consumer, it is adapted in a second stage to the needs of the consumer. For this purpose ^¬ who used, for example, charge pumps.

The higher output voltage is primarily used to drive high-impedance loads such as the gate of a transistor. The Combining the arrangement of the piezoelectric generator and the associated circuit architecture allows the simultaneous optimization of power delivery and voltage levels. The total power flow from the primary environmental energy to the system load can be maximized. This allows greater functionality to be realized, increases system reliability, and reduces system startup times. In the following figures, various embodiments of the invention are shown.

Show it:

Figure 1: the piezoelectric bending transducer of a Piezieher- rators

Figure 2: another embodiment of the piezoelectric

Bending transducer of Figure 1

Figure 3: another embodiment of the piezoelectric

Bending transducer of Figure 1

Figure 4: another embodiment of the piezoelectric

Bending transducer of a piezoelectric generator

Figure 5 is a block diagram of the electrical circuit of

Piezoelectric generator which is nachschaltbar a piezoelectric bending ^{¬ converter}

Figure 6a: a clamped between two fasteners piezoelectric bending transducer

In the figures, identical or corresponding units have the same reference numerals. The figures are described in groups together.

In FIG. 1 a piezoelectric transducer designed as a piezoelectric bending transducer is shown in plan view. In figure lb the piezoelectric generator 100 is shown in Figure la in side view ent ^¬ long the line C. The piezoelectric bending transducer of Figure la, b has a carrier 1, whose basic shape is triangular. The carrier 1 is laterally borrowed in a fixture 10 clamped. On the carrier 1, two piezoelectric layers 2,3 are applied next to each other sur fa ^¬ chig:

a first piezoelectric element 2 having a first height h 1 and having a triangular basic shape, which is adapted to the triangular shape of the carrier 1 facing away from the fastening 10.

- A second piezoelectric element 3 of a second height h 2 and, the element between the attachment 10 and the first Piezoele 2 is arranged and adapted to the base of the carrier 1 is trapezoidal.

At the top of the first and the second piezoelectric element 2, 3 are each a first and second upper electrode surface 5, 7 are arranged. At the bottom of the first and second

Piezo elements 2, 3 are each a first and second lower, the carrier 1 facing the electrode surface 4, 6 are arranged. The first and second piezoelectric elements 2, 3 are arranged at a distance from one another in order to ensure electrical insulation of their upper 5, 7 and lower 4, 6 electrode surfaces.

The carrier 1 is designed to be movable and vibratable by its one-sided mounting on the actuating buildin ^¬ 10 at the opposite side of the twentieth By applying an alternating force F, the attachment 10 of the opposite side 20 of the carrier 1 moves up and down in an oscillating movement x. As a result of this movement, the first and the second piezoelement 2, 3 are subjected to tension or pressure with a first σ 1 and a second mechanical stress σ 2, whereby voltage differences U 1, U 2 between the two

Upper and lower sides of the first and second piezoelectric element 2, 3 arise, which are tapped via the respective upper electrodes 5, 7 and lower electrodes 4, 6 and can be adapted for example by a downstream electrical circuit according to Figure 5 to a load L. ,

The oscillating movement of the carrier 1 opposite side 10 of the carrier 1 can also by vibrations of the Attachment 1 are generated. The mechanical dimensions of the voltage generator 100 are preferably designed so that the vibration frequency of the attachment 1 in the region of the resonant frequency fR of the carrier 1 with the piezo elements 2, 3, whereby a higher electrical power can be achieved.

The preferably triangular surface shape of the carrier 1 serves for the uniform distribution of the first and second mechanical stresses σΐ, σ 2 within the first and second, respectively

Piezo elements 2, 3 between the attachment 10 and its opposite side eleventh

The first piezoelectric element 3 is designed to optimize the efficiency of the conversion of mechanical energy into electrical energy. The second piezoelectric element 3 is ^{ausgebil ¬} det for optimizing and achieving the highest possible electrical voltage level with compared to the first Piezoele ^¬ ment 2 lower required amount of energy.

The piezo elements 2, 3 therefore have the following properties:

The charge constants d1, d2 and the permittivities εΐ, ε2 of the first piezoelectric element 2 and of the second piezoelectric element 3 have the following relations to one another: dl Ιε \ <ά2 / ε2 and dl ² / εί> ά2 ² / ε2

Thus, the first piezoelectric element 2 is preferably from the group of PZT compounds (lead zirconate titanate) and the second piezoelectric element 3 preferably from the group of zinc oxide compounds (ZnO). The area AI of the first piezoelectric element 2 is greater than the area A2 of the second piezoelectric element 3, preferably at least by a factor of 2, whereby a high overall efficiency of the piezoelectric generator 100 is achieved.

Alternatively, the heights h1, h2 of the first and second piezoelectric elements 2, 3 may differ from one another. To achieve a high overall efficiency of the piezoelectric generator 100 which Hö ^¬ he hl of the first piezo element 2 is preferably at least a factor 2 larger than the height h2 of the second piezoelectric element. 3

Alternatively, the volumes h1 * A1, h2 * A2 of the first and second piezoelements 2, 3 may differ from one another. To achieve a high overall efficiency of the piezator

100 is the volume hl * Al of the first piezo element 2 virtue ^¬ example by at least a factor of 2 greater than the volume h2 * A2 of the second piezo element 3. There are the following proportionalities between:

(3) t / 1, t / 2 * h1, h1, AI, A2, h1 * AI, h1 * AI

(4) Wpl, Wpl, ~ hl, hl, Al, Al, hl * Al, hl * Al

By combining the height, area or volume ratios of the first and the second piezoelectric element 2, 3 to ^¬ each other and the materials of the first and the piezoelectric element itself can be optimized depending on the available space and the cost specifications of the piezoelectric generator 100.

Thus, for example, the first and the second piezoelectric element 2, 3 consist of the same piezoelectric material, and the second piezoelectric material 3 to achieve a desired voltage overshoot U2 / U1 corresponding height ratio h2 / hl have, creating a manufacturing process for the use of a further piezoelectric element is possible. The piezoelectric generator is adapted to the electrical circuit described in FIG. In this, the higher clamping ^¬ voltage U2 of the second piezo element 3 8 while the lower voltage Ul is used with higher available energy to drive the load L is, 13, 15 in Wesentli ^¬ chen for controlling electric switches.

FIGS. 2 a, 2 b illustrate a further piezoelectric generator 100, in which, compared to FIG. 1, the first piezoelectric element 9 is located between the attachment 10 and the second

Piezo element 8 is located. The second piezoelectric element 8 is triangular-shaped adapted to the basic shape of the carrier 1, the first piezoelectric element 9 is trapezoidal adapted to the basic shape of the carrier 1. The area and volume ratios of the first and the second piezoelectric element 9, 8 essentially correspond to the information given in FIG.

FIG. 3 shows a further embodiment of the piezoelectric generator 100, with basic forms of the first and second piezoelements 12, 13 that differ from those of FIGS. 1 and 2:

Arranged in the shape of an arrow on the triangular support 1 is the first piezoelectric element 12, wherein the tip of the arrow shape points from the attachment 10 to its opposite side 11. In the triangular recess 13 of the arrow-shaped first piezoelectric element 12, the second piezo ^¬ element 13 is embedded. The area and volume ratios of the first and the second piezoelectric element 12, 13 essentially correspond to the information given in FIG.

FIG. 4 illustrates a further piezoelectric generator 100, in which the first and the second piezo element 14, 15 are not arranged next to one another, but one above the other, in contrast to the previous FIGS.

The first piezoelectric element 14 is applied with its lower, carrier-side electrode 16 to the carrier 1 with a according to the carrier 1 adapted triangular basic shape.

The second piezoelectric element 15 is applied with appropriately adapted to the first piezoelectric element 13 Three ^¬ ecksform on the force applied to the first piezoelectric element 14 central electrode 17th On the second piezoelectric element 15 is an upper

Electrode surface 18 applied. The middle electrode 17 is the first piezoelectric element 14 as the upper and the second piezoelectric element 15 as a lower electric ^¬ de. The base area A2 of the second piezoelectric element 15 is be ^¬ vorzugt smaller than the base of the first AI Piezoele ^¬ ments fourteenth

Alternatively, the piezoelectric generator 100 may strapless be formed (not shown) in Figure 4, when the total height hl + h2 of the first and second piezoelectric element ensures a suffi ^¬ sponding mechanical stability. The piezoelectric bending transducer 100 essentially consists of the first and the second piezoelectric elements arranged one above the other.

The geometric basic shapes of the carrier 1 and / or of the first 2, 9, 12, 14 and of the second piezoelement 3, 8, 13, 15 illustrated in FIGS. 1 to 4 may alternatively deviate from the specified shapes and, for example, rectangular, polygonal or semicircular. In Figure 6, the respective piezoelectric generator 100 is formed from the figures 1 to 4 cuboid and bilaterial ^¬ tig between a first attachment 1 and clamped a further attachment. 11 Relative movements between the two fasteners 10 and 11 lead to bending of the piezoelectric generator 100 and the already described above converting mechanical energy into electrical energy. FIG. 5 shows the block diagram of a circuit architecture for adapting the output voltages of a piezoelectric generator 100 from FIGS. 1 to 4 and 6 to a load L.

For each piezoelectric generator part, i. for the first piezoelectric element 2, 9, 12, 14 and the second piezoelectric element 3, 8, 13, 12 is a corresponding separate first and second, preferably designed as a voltage converter circuit block SP1, SP2 for generating a rectified voltage signal to a respective first and second capacitor Cl, C2 of a first and second storage node Kl, K2 provided. However, each circuit block SP1, SP2 has its own startup circuit ST1, ST2. The storage node K2 with higher voltage U02 supplies voltage parts, which preferably consume very little energy, but clearly benefit from a high voltage. A prominent example of such a case is the exemplified as a CMOS transistor switch SW1 of the first circuit block SP1, the gate control line Sl can be acted upon by the higher voltage U02. The gate capacitance of such a transistor must be charged once to a minimum voltage level in order then to enable virtually a low-impedance connection / circuit. The transistor conducts the better, the more voltage is applied to the gate.

Similar considerations can be made for other circuit parts. As a result, an optimized voltage application is guaranteed.

In this case, the piezoelectric generator 100 is shown with the first 2, 9, 12, 14 and the second 3, 8, 13, 15 piezoelectric element as a current source with a capacitance C connected in parallel. The primary energy, ie the voltage has entspre ^¬ accordingly the mechanical excitation an oscillating course. Using a first circuit block SP1 is the output ^¬ voltage UL of the first piezo element 2, 9, 12, 14 on U01 rectified. Accordingly, the output voltage U2 of the second piezoelectric element 3, 8, 13, 15 is rectified by the second circuit block SP2 to U02. The electrical energy is then present at a respective voltage level UO1, U02 at the first and second storage capacitance C1, C2. For booting up the system, that is, at a time when there is not enough power to operate at the memory node K1, K2, a start-up circuit is needed that works passively. A corresponding startup circuit ST1, ST2 is provided in the first and in the second circuit block. Furthermore, the higher output voltage U02 of the second circuit block SP2 is used to support the formwork ^¬ processing block 1, for example for faster power-up or for operating the electronic switch SW2. The output voltage U02 on the capacitor C2 becomes the

Sl control of the electric switch SWl supplied. The output voltages UO1 and U02 are supplied to a downstream post-processing circuit PPC for adapting the output voltages UC1, UC2 to the loads L. The higher output voltage U02 at the capacitor C2 is supplied to a large voltage auxiliary circuitry LVAUX. Accordingly, the output voltage Uol of the f ^¬ th circuit block SPl a low voltage auxiliary circuit (small auxiliary voltage circuitry) SVAUX is supplied. At the same time, the output voltage Uol of the first circuit ^¬ blocks SPl a main power processing circuit (Main Power Processing Unit) is supplied MPPU1 which provides the main power from the first circuit block SPl with high efficiency to the load L.

Claims

claims

1. Piezoelectric generator with a first piezoelectric element (2, 9, 12, 14) and a second piezoelectric element (3, 8, 13, 15), which are in mechanical operative connection with each other and at least at one point, preferably on one side of a Fixing ^¬ tion (1) are clamped or clamped, wherein a) the respective charge constants dl, d2 of the first piezoelement (2, 9, 12, 14) and the second piezoelectric element (3, 8, 13, 15) and the permittivities εΐ, ε2 of the first piezo ^¬ elements (2, 9, 12, 14) and said second piezoelectric element (3, 8, 13, 15) have the following relationships to one another: dl / £ l <d2 / £ 2

simultaneously

dl ² / l> d 2 ^2/2

and or

b) the height (h2) of the second piezoelectric element (3, 8, 13, 15) is greater than the height (hl) of the first piezoelectric element (2, 9, 12, 14), preferably at least by a factor of 2; and / or c) the area (AI) and / or the volume (h1 * A1) of the first piezoelement (2, 9, 12, 14) is greater than the area (A2) or the volume (h1 * A2) of the second one Piezo element (3, 8, 13, 15) is, preferably at least by a factor of 2.

2. Piezoelectric generator according to claim 1, characterized in that the first piezoelectric element (2, 9, 12, 14) from the group of lead zirconate titanate compounds (PZT) and the second Pie ^¬ zoelement (3, 8, 13, 15 ) from the group of zinc oxides (ZnO).

3. Piezoelectric generator according to claim 1, characterized in that the first (2, 9, 12, 14) and the second piezoelectric element, the second piezoelectric element (3, 8, 13, 15) are the same or at least from the same group of piezoelectric materials.

4. Piezoelectric generator according to one of the preceding claims, characterized in that the first (2, 9, 12, 14) and the second piezoelectric element (3, 8, 13, 15) are arranged one above the other and / or ne ^¬ beneinander.

5. Piezoelectric generator according to one of the preceding claims, characterized in that the first (2, 9, 12, 14) and the second piezoelectric element (3, 8, 13, 15) on at least ei ^¬ ner side (10) or between two sides (10, 11) is arrange ^¬ th carrier (1) are applied and each act as a bending transducer for converting kinetic energy into electrical energy, said second piezoelectric element (3, 8, 13, 15) in such ^¬ derholter movement of the Support (1) generates a higher electrical voltage (U2> U1) than the first piezoelectric element (2, 9, 12, 14).

6. Piezoelectric generator according to one of the preceding claims, characterized in that the first (2, 9, 12, 14) Piezoele ^¬ ment generated from the predetermined mechanical movements a higher amount of electrical energy than by the second piezo ^¬ element (3, 8, 13 , 15) is convertible from the mechanical energy.

7. Electronic circuit, can be fed by a piezoelectric generator according to one of the preceding claims, characterized in that the first piezoelectric element (2, 9, 12, 14) is electrically connected to a first voltage converter (SP1), the second piezoelectric element (3, 8, 13, 15) is electrically connected to a second voltage converter (SP2), the output of the second voltage converter (SP2) being connected to the control input (S1) of at least one first electronic switch (SW1) and / or further components of the first voltage converter (SP1). is assigned, wherein in after the startup of the first clamping ^¬ voltage converter (SP1), the level of the voltage at the output of the second voltage converter (SP2) for driving the electronic switch (SW1) and / or additional components of the first voltage converter (SP1) is sufficient.

8. An electronic circuit according to claim 7, characterized in that the first and / or the second voltage converter (SP1, SP2) each have a passive startup circuit (ST1, ST2), with the aid of which the respective voltage converter (SP1, SP2) accelerates up.

9. An electronic circuit according to claim 7 or 8, characterized in that the first and the second voltage converter ^¬ (SP1, SP2) a post-processing circuit (PPC) for adjusting the output power of the first voltage converter (SP1) to the load (L) is arranged ,