Patent ID: 12209913

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG.1shows an arrangement comprising a device1and an electronics system2. The arrangement shown inFIG.1can be operated as a sensor system and/or as an actuator system.

For operation as a sensor system, the device1is configured to convert a physical input signal into an electric output signal. The physical input signal is, for example, a force which acts on the device1. The device1comprises, inter alia, a piezoelectric transducer element3. The piezoelectric transducer element3converts, based on the piezoelectric effect, the physical input signal into an electric output signal which is transferred from the device1to the electronics system2.

The electronics system2is configured to further process the electric output signal of the device1. For example, the electronics system2can be configured to evaluate the electric output signal generated by the device1and convert it into a digital signal.

For operation as an actuator system, an electric input signal is transferred from the electronics2to the device1. The piezoelectric transducer element3converts the electric input signal into a mechanical deformation, which fulfills the actuator function.

In the arrangement described here, the requirements on a signal processing in the electronics system2can be kept low since the device1is configured to provide a strong response signal as electric output signal in sensor operation and to produce a strong mechanical deformation of the piezoelectric transducer element3as an actuator signal in actuator operation. The strong response signal or the strong actuator signal are in particular achieved by a suitable choice of the properties of a support4of the device1.

FIG.2shows a first exemplary embodiment of the device1. The device1comprises the piezoelectric transducer element3and the support4. The piezoelectric transducer element3is disposed directly on the support4. A bottom side of the piezoelectric transducer element3lies on a top side of the support4. The piezoelectric transducer element3and the support4are mechanically connected to one another. In particular, the piezoelectric transducer element3and the support4form an assembly and can only be deformed jointly, e.g. bent.

The piezoelectric transducer element3comprises a piezoelectric layer5, an upper electrode6and a lower electrode7, wherein the piezoelectric layer5is disposed between the lower electrode6and the upper electrode7. During actuator operation a voltage is applied between the two electrodes6,7, which brings about a mechanical deformation of the piezoelectric layer5. In sensor operation the piezoelectric layer5can be deformed by a force acting on the device1from outside and consequently generates an electric voltage which is tapped at the electrodes6,7.

The piezoelectric layer5can comprise a ferroelectric polymer or consist of a ferroelectric polymer. Ferroelectric polymers have the mechanical properties of a plastic and combine these with the electrical properties of ceramic materials. A layer of a ferroelectric polymer can be produced by screen printing, stencil printing or inkjet printing. Alternatively, a layer of a ferroelectric polymer can be produced by vapor deposition or sputtering or by means of doctor blading. The said methods each require a support4on which the piezoelectric transducer element is applied.

Alternatively, the piezoelectric layer5can also comprise a piezoelectric ceramic material or consist of a piezoelectric ceramic material. Alternatively, the piezoelectric layer5can also comprise a composite material, comprising a polymer matrix and a piezoelectric ceramic material, or consist of such a composite material.

The support4can consist of a plastic, for example, polyimide, PET, or PEN.

The support4substantially co-determines the mechanical and electrical properties of the assembly comprising piezoelectric transducer element3and support4. The mechanical and electrical properties of the assembly are determined by means of a suitable choice of the structural properties of the support4, for example, such as its thickness, its modulus of elasticity, and the material. This relationship is explained in detail with reference toFIG.3, which shows a device1on which the external force F is acting.

The device1shown inFIG.3is clamped at a first end8. The force F acts on a second end9of the device1opposite the first end8. The device1thus comprises a beam clamped on one side. However, the device1is by no means restricted to such configurations. Alternatively, the device1could be clamped, for example, at the first and second end8,9and a central region of the device1, which is disposed between the first and the second end, could be bent as a result of a force acting on the device1.

The piezoelectric transducer element3and the support4bend as a result of the force acting on the device1, wherein the piezoelectric transducer element3and the support4are moved at the second end9and remain unmoved at the first end8. The piezoelectric transducer element3, which is disposed on a top side of the device1, is stretched by the bending, i.e. the length from the first end8to the second end9is increased. A bottom side of the support4, which points away from the piezoelectric transducer element3, is compressed by the bending, i.e. the length from the first end8to the second end9is reduced.

The mechanical stress, which is produced locally at various positions inside the device1, is indicated by arrows inFIG.3.FIG.3shows that particularly high mechanical stresses are formed close to the top side and close to the bottom side of the device and that the mechanical stresses produced decrease toward a neutral fiber10, which is arranged centrally in the device1. The neutral fiber10designates the plane of the device1, which undergoes no change in length as a result of the acting stress. The precise position of the neutral fiber10is not necessarily in the geometric center of the piezoelectric transducer element3but is influenced by the moduli of elasticity and the geometric designs of the piezoelectric transducer element3and the support4.

In the exemplary embodiment shown inFIG.3the neutral fiber10is disposed in the support4and far away from the piezoelectric transducer element3. The piezoelectric transducer element3undergoes a change in length over its entire volume and an electric voltage is generated in the entire volume.

FIG.4shows a comparative device, in which the support is thinner compared with the device shown inFIG.3. As a result of the thinner support, the neutral fiber is shifted into the piezoelectric transducer element. As a result of the force acting on the device in the comparative device shown inFIG.4, the piezoelectric transducer element experiences a significantly smaller mechanical stress than in the exemplary embodiment shown inFIG.3. Accordingly, in the exemplary embodiment shown inFIG.4, only a lower electric voltage is generated in the piezoelectric layer and the electric output signal generated by the device is smaller compared with the device shown inFIG.3.

The comparison of the devices inFIGS.3and4shows that by means of a suitable choice of the thickness of the support4, it can be ensured that the piezoelectric layer5of the piezoelectric transducer element3experiences a high mechanical stress. In this way, a strong electric output signal of the device1is ensured in sensor operation. In actuator operation a strong mechanical deformation of the device1is made possible by a sufficiently thick support4.

The thickness of the support4should be at least so large that the neutral fiber10lies inside the support4. The thicker the support4is configured to be, the deeper the neutral fiber10can be shifted into the support4and the stronger the signal generated by the piezoelectric transducer element3can be.

The influence of the support geometry on the signal provided by the piezoelectric transducer element3was investigated in a comparative measurement by means of two devices1having structurally the same piezoelectric transducer elements3.FIG.5shows the results of the comparative measurement.

Both devices1each have a length of 20 mm and a width of 10 mm. The length gives the extension from the first end8to the second end9. The width gives the extension in a direction perpendicular thereto. The thickness of the device1gives an extension of the device1in a stacking direction in which the support4and the piezoelectric transducer element3are stacked one above the other. The thickness is perpendicular to the width and to the length.

Both devices1comprise a piezoelectric transducer element3with a piezoelectric layer5, which consists of a ferroelectric polymer, PVDF:TrFE, in a thickness of 10 μm. The lower electrode7consists of PEDOT:PSS and the upper electrode6consists of carbon. A support4consisting of polyimide was used for both devices1. The two devices1merely differ in the thickness of the support4. The first device1has a support4having a thickness of 75 μm. The second device1has a support4having a thickness of 25 μm. Both devices1were deformed in a test rig at the same deformation rate over the same deformation path. The deformation rate was 0.4 m/s and the deformation path 4 mm.

InFIG.5the electric output signal of the first device1is plotted in curve K1and the electric output signal of the second device1is plotted in curve K2. In this case, the time in seconds is plotted on the horizontal axis. The electric output signal in volts is plotted on the vertical axis. It can be seen that the electric output signal of the first device1is significantly larger with the same deformation and the same properties of the piezoelectric transducer element3. In particular, the electric output signal of the first device1is approximately 9 times the electric output signal of the second device1. The significantly higher electric output signal of the first device results from the fact that in the first device the neutral fiber10has a more favorable position compared to the second device. In the first device as a result of the greater thickness of the support4, the neutral fiber10is disposed further away from the piezoelectric transducer element3and the piezoelectric transducer element3undergoes a stronger deformation.

FIG.6shows the results of a simulation which was carried out by means of the finite element method. In the simulation two devices1are considered, which each have a piezoelectric transducer element4having a piezoelectric layer5comprising PVDF:TrFE. The support4consists of polyimide in both devices1. The support4of a second device1has a fivefold mechanical strength compared to the support4of a first device1.

The time is plotted in ms on the horizontal axis. The output voltage is plotted in V on the vertical axis. The curve K3shows the magnitude of the electric voltage generated by the piezoelectric transducer element3of the second device1over the time of a deformation. The curve K4shows the electric voltage generated by the piezoelectric transducer element3of the first device1over the time of the deformation. Both devices are deformed over the same distance. The second device generates a higher voltage in its output signal. Since the mechanical strength of the support4is greater in the second device, the neutral fiber10is shifted deeper into the support4and therefore further away from the piezoelectric transducer element3. Accordingly, the piezoelectric transducer element3undergoes a greater mechanical deformation and therefore generates a higher voltage.

FIG.7andFIG.8show the results of a further simulation. In each case, the mechanical stress produced locally inside the device in a device1configured as a beam clamped on one side is observed inFIGS.7and8. Two structurally identical beams which are deflected by the same distance are considered here. However, the beam shown inFIG.7differs from the beam shown inFIG.8in the modulus of elasticity of the support4. In the beam considered inFIG.7, the support4has a lower strength. A comparison ofFIGS.7and8shows that with the same design and the same deflection in the piezoelectric transducer element3that is applied to a support4having a high strength, higher mechanical stresses and therefore higher electric voltages are generated. By means of a suitable choice of the mechanical strength or the modulus of elasticity of the support4, it can be ensured that the piezoelectric transducer element3delivers a good output signal or brings about a strong mechanical deformation during actuator operation.

FIG.9shows schematically a second exemplary embodiment of the device1. The device1shown inFIG.9differs from the device shown inFIG.2in the material of the support4. The device shown inFIG.9has a support made of a conductive material, for example, a metal support.

A separate lower electrode7of the piezoelectric transducer element3is not necessary in this case. Rather, a material of the support4can take over the electric contacting of the piezoelectric layer5of the piezoelectric transducer element3. The piezoelectric layer5can then be applied directly to the support4. The support4has contact surfaces11via which an electric voltage can be applied. The contact surfaces11consist of an electrically conductive connecting material, for example, silver or silver epoxide resin.

FIG.10shows a plan view of the top side of the device1according to the first exemplary embodiment.

Although the invention has been illustrated and described in detail by means of the preferred embodiment examples, the present invention is not restricted by the disclosed examples and other variations may be derived by the skilled person without exceeding the scope of protection of the invention.