Ferroelectric sensor

Abstract

To provide a sensor which generates a measurement signal on the basis of different physical effects.SOLUTION: A sensor 1 is provided, consisting of a first electrode 3a, a ferroelectric layer 2 and a second electrode 3b, the second electrode 3b being connected to ground and the ferroelectric layer 2 being arranged between the first electrode 3a and the second electrode 3b.SELECTED DRAWING: Figure 13

Description

Technical Field

[0001] The present invention relates to a ferroelectric sensor.

Background Art

[0002] Currently, due to the progress of digitization promoted under the terms of Industry 4.0 or the Internet of Things, the interaction between machines and with humans is becoming increasingly common in daily life. One of many challenges is to increase the safety of humans and machines in these interactions by avoiding accidents.

[0003] In this context, various types of sensors based on various physical effects are increasingly being incorporated into more intelligent machines to detect hazards and avoid possible collisions. On the one hand, optical sensors or camera modules can be used for the early detection of possible hazards due to the extent of their detection areas. On the other hand, ultrasonic sensors are suitable for, for example, short-range measurements and can thus detect obvious hazards. In the immediate vicinity, i.e., when contact occurs between the machine and the surroundings, capacitive or resistive sensors, such as contact protection strips, can be used for the detection of contact.

[0004] In most cases, multiple different types of sensors are incorporated into partially or fully autonomous machines to prevent collisions. Since the sensors cover different areas, a more complete picture of the surroundings can be created.

[0005] Nevertheless, incorporating multiple sensors of different types into an application is costly. Furthermore, the use of different types of sensors is associated with high technical costs. Different sensor types require their own control and evaluation electronics, which makes the overall sensor system more complex and larger. Additionally, at least one continuous and unique functional test for each different type of sensor must be applied, which constantly checks the sensors and electronics and further expands the overall system.

[0006] Therefore, a sensor that functions based on various physical effects and integrates different types of sensors within itself is desirable.

Summary of the Invention

Problems to be Solved by the Invention

[0007] The problem of the present invention is to provide a sensor that generates a measurement signal based on various physical effects.

Means for Solving the Problems

[0008] This problem is solved by the sensor according to claim 1. Further advantageous embodiments and possible configurations can be taken from the further claims.

[0009] A sensor is described that consists of a first electrode, a ferroelectric layer, and a second electrode. The ferroelectric layer is disposed between the two electrodes, and the second electrode is connected to ground.

[0010] The measurement signal can be picked up as a voltage change between the electrodes. The ground can be at earth potential.

[0011] The ferroelectric layer can here consist of a material that exhibits ferroelectric properties in an electric field. Preferably, the layer can consist of a ferroelectric material having piezoelectric properties, and particularly preferably, a ferroelectric material having pyroelectric properties.

[0012] Since all pyroelectric materials are also piezoelectric materials, the functional layer between the electrodes is sensitive not only to temperature changes but also to any deformation of the sensor due to the piezoelectric effect. Since one of the electrodes is grounded, a significant approach of the electrode or contact with the electrode can change the capacitance between the approaching object and the electrode and can also result in a voltage change between the electrodes. In this way, three different physical effects, namely the capacitive effect, the piezoelectric effect, and the pyroelectric effect, can be effectively utilized within one sensor.

[0013] Integrating the pyroelectric effect, piezoelectric effect, and capacitive effect within a single sensor is particularly advantageous because the three effects are suitable for detecting different events. The pyroelectric effect can record temperature changes originating from the environment. For example, temperature changes resulting from human body temperature or machine heat generation can be determined non - contact and from a distance. The capacitive effect can also be used for non - contact detection, but for this, a large - scale approach to the sensor is required. However, it is advantageous that the capacitive effect can detect the approach even when the pyroelectric effect produces little or no sensor signal due to the approach of an object at the same temperature. To complement the pyroelectric effect and to detect contact of the sensor with other objects, the piezoelectric effect or the capacitive effect can be effectively utilized. Furthermore, the piezoelectric effect or the capacitive effect can enable improved detection. This is because, in the same sensor, the voltage signal generated by the pyroelectric effect is 10 to 100 times weaker compared to the piezoelectric effect or the capacitive effect. For a voltage change at the electrode, in the piezoelectric effect, an active spatial deformation of the piezoelectric layer must occur, whereas in the capacitive effect, a static contact already causes a voltage change, which differentiates the piezoelectric effect from the capacitive effect. Thus, in the case of the piezoelectric effect, for example, in the case of a spatially externally arranged sensor that is flexible and bent by an approaching object, a voltage change is caused by the curvature of the piezoelectric layer. The voltage change is suitable for measuring the distance to the approaching object because the magnitude of the voltage change depends on the degree of curvature. In contrast, when the deformed piezoelectric layer is stationary or no deformation occurs, no voltage change due to the piezoelectric effect occurs. In this case, the capacitive effect acts, and the capacitive effect causes a voltage change between the electrodes even without layer deformation when the grounded electrode comes into contact.

[0014] Since the sensor can utilize various physical effects as the basis for detection, the number of different types of sensors that must be incorporated into the application can be reduced. Furthermore, the required control and evaluation electronics do not need to be provided separately for each sensor type, so they can be simplified and made more compact. Additionally, when various physical effects covering complementary detection areas are used in the sensor, a more accurate overview of the surroundings is provided, and thus the approach of an object can be confirmed.

[0015] The measured change in the electrical signal can include a change in signal-time evolution and / or amplitude and / or time scale and / or time dynamics and / or polarity. Thus, it is possible to grasp the entire dynamics of the electrical signal.

[0016] The electrical signal can include voltage and / or charge and / or capacitance and / or polarity. Thus, the electrical signal can be independent of the type of measurement, or the measurement can be performed based on different measurement principles.

[0017] The ferroelectric layer can include a polymer, ceramic or polymer-ceramic matrix. As the polymer, polyvinylidene fluoride (PVDF) and its copolymers can be used. As the ceramic, lead zirconate titanate (PZT) or BaTiO3 can be used. The above examples are ferroelectric materials having pyroelectric properties and meeting industrial requirements. PVDF is flexible and thus a particularly suitable pyroelectric plastic. Suitable methods for coating PVDF onto the first electrode can be spin coating, screen printing or inkjet printing. In contrast, PZT and BaTiO3 are pyroelectric ceramics that are flexible only as thin layers. PZT ceramics can additionally have Na, Ca or La added to adapt their electrical properties. When the pyroelectric layer is PZT, BaTiO3 or other lead-free or lead-containing ceramics, this can be coated onto the first electrode, for example, by thin film processes such as CVD, PVD, a combination of the sol-gel method and spin coating, or screen printing.

[0018] Both the first and second electrodes can be made of a material that is transparent and / or thermally conductive in the ultraviolet-visible region and / or preferably in the infrared region. Thereby, it can be ensured that infrared thermal radiation directly reaches the ferroelectric layer, thus increasing the sensitivity of the sensor. Suitable materials can be, for example, ITO, PEDOT:PSS, graphite, metal nanowires, carbon nanotubes or graphene.

[0019] In addition, the electrode can consist of one or more layers of a metal such as Al, Cr, Ni, Ag, Cu, or a mixture, intermetallic compound, and alloy of these elements, or can contain these elements. It is preferably a sputter layer. In the case of a sputter layer, multiple layers of different metals, for example, Cr / Ni / Ag, can also be sputtered in an overlapping manner. Through the selection of each metal, for example, the contact of the sensor by soldering can be improved. Because better adhesion becomes possible. The electrode made of metal has high electrical conductivity and thermal conductivity, whereby the sensitivity of the sensor is not significantly impaired.

[0020] Furthermore, the sensor can have a further first electrode, a second electrode, and a ferroelectric layer, and the ferroelectric layer is disposed between the first electrode and the second electrode. By realizing the sensor as a multilayer member, multiple functional ferroelectric layers can be arranged in sequence, and both the sensitivity and accuracy of the sensor can be improved.

[0021] The arrangement on or between components can be either a direct arrangement where the arranged components are in contact with each other and directly placed on top of each other, or an indirect arrangement where there can be further components between the overlapping components. In any case, the electrode is directly disposed on the ferroelectric layer, and as a result, the electrode contacts the ferroelectric layer to establish electrical contact.

[0022] In a multilayer member, it is possible to contact the individual functional layers separately. In this case, the first electrode is electrically contacted with a separate first contact element respectively, and the second electrode is electrically contacted with a separate second contact element respectively. Thereby, separate sensor signals can be evaluated for each functional layer, and furthermore, it is possible to pick up different types of sensor signals for the individual functional layers.

[0023] Instead, in a multilayer member, all the first electrodes can be electrically contacted with the same first electrical contact element, and all the second electrodes can be electrically contacted with the same second electrical contact element, respectively. Therefore, all the first electrodes are connected in parallel with each other, and all the second electrodes are connected in parallel with each other. The electrical signal can be picked up between the contact elements. Thereby, in the sense of signal addition of the sensor signal from the signals of the individual functional layers, the amplified signal can be used for evaluation.

[0024] Furthermore, the first electrode can be arranged inside the sensor, the ferroelectric layer can cover the first electrode, and the second electrode can cover the ferroelectric layer. Such an embodiment can preferably be formed in a cylindrical or plate shape. The layers in the sensor can be arranged such that the spread of the sensor in the direction perpendicular to the layers of the sensor is shorter compared to the spread of the sensor along the layers. This embodiment enables numerous further applications for the sensor according to the present invention. Furthermore, the cylindrical shape of the sensor is beneficial for enhancing the sensitivity to deformation. Also, the coated sensor can be manufactured in an endless process, similar to the manufacture of wires or cables, thereby enabling inexpensive manufacture.

[0025] According to one possible use of the term "coated", when the coating layer covers most but not all of the layer below it, the layer can also be considered to be coated by the other layer. When a cross-sectional image of the layer is taken, if more than 90%, 95%, 99% or 99.9% of the cross-sectional image does not have a defect site that extends across the entire thickness of the layer within the coating layer, the layer can be considered to be coated. During the manufacture of the layer, defect sites or cracks may inevitably occur within the layer, which may make complete coating difficult. Even during operation, cracks may occur within the layers of the sensor due to mechanical loads, but the interference with the function of the sensor thereby is limited. The layer or component coated by the layer may alternatively be completely enclosed by the layer.

[0026] Furthermore, the sensor can have an insulating layer on which the first electrode or the second electrode can be disposed, and the sensor can be wound such that the insulating layer is located inside. The inner surface faces toward the central axis of the sensor and away from the outer covering surface of the sensor in the wound sensor. By winding, a spiral electrode in a cross-section passing through the sensor and a ferroelectric layer that is spiral in a cross-section passing through the sensor and extends sandwiched between the similarly spiral electrodes are provided. Accordingly, one of the electrodes not directly disposed on the insulating layer forms the outer covering surface of the wound sensor.

[0027] The wound sensor can preferably be formed in a cylindrical shape. By winding the sensor, it is also possible to manufacture a cylindrical sensor by a manufacturing process for a flat layer. The insulating layer is mainly used to electrically insulate the electrodes that would otherwise short-circuit when wound. When the sensor is wound multiple times, a multi-layer member is generated, but the sensor has only the first and second electrodes. The electrical behavior is significantly different from that of the coated embodiment having a plurality of stacked layers. This is because, in the case of the wound sensor, a single capacitance corresponding to the parallel connection of capacitors is formed, while in the case of the coated embodiment having a plurality of stacked layers, the capacitance formed between the electrodes corresponds to the series connection of capacitors. Therefore, for the same number of layers, material, and dimensions, a higher capacitance occurs for the wound sensor, whereby the capacitive effect becomes significantly more prominent within the sensor.

[0028] Furthermore, the sensor can have a carrier material. Depending on the application area, the carrier material can be inelastic or elastic. An inelastic carrier material can improve the mechanical stability of the sensor. Especially with respect to the transport and incorporation of components, high mechanical stability can be useful for avoiding damage. For certain applications, an arrangement on a carrier material consisting of glass, concrete or steel may be necessary, although this reduces the piezoelectric effect thereby. Elastic materials that can be considered as carrier materials can be, inter alia, rubber, plastic or a fabric such as, for example, polyester.

[0029] The first electrode or the second electrode can be arranged on the carrier material. It should be noted that sufficient adhesion between the electrode and the carrier material is necessary. Sufficient adhesion is obtained by appropriately selecting the material of the carrier material and the electrode. Surface treatment of the carrier material, such as roughening, can also be carried out to improve the adhesion between the carrier material and the electrode.

[0030] Furthermore, the sensor can have an insulating layer on which the first electrode or the second electrode is arranged, and the sensor is wound such that the insulating layer is located on the carrier material. Thus, through the selection of the carrier material, the mechanical stability of the wound sensor can be controlled. Since various materials and even articles can be considered as carrier materials, such an arrangement opens up numerous possible application areas for the sensor. By winding the sensor, the capacitive effect of the sensor is increased.

[0031] In a further embodiment, the carrier material can be arranged inside the sensor, with the first electrode covering the carrier material, the ferroelectric layer covering the first electrode, and the second electrode covering the ferroelectric layer. Through the selection of the carrier material, the sensor can be configured and optimized to be more rigid or more flexible depending on the application. This embodiment can also preferably be formed in a cylindrical or plate shape. Furthermore, a sensor configured in this way can also be manufactured in an endless process and thus inexpensively.

[0032] A sensor having a first electrode inside can have a further first electrode, a second electrode and a ferroelectric layer. The first and second electrodes are arranged alternately in the radial direction, and one ferroelectric layer is arranged between one of the first electrodes and one of the second electrodes. In this way, a plurality of functional ferroelectric layers can be arranged in sequence, so that both the sensitivity and accuracy of the sensor can be improved.

[0033] Coated sensors and wound sensors can have a further first electrode, a second electrode and a ferroelectric layer regardless of whether they have a carrier material or not, and one ferroelectric layer is arranged between one of the first electrodes and one of the second electrodes. Therefore, similar to the stacked multi-layer member, the signal strength of the sensor, and thus the sensitivity and accuracy, are improved.

[0034] The carrier material for the coated or wound sensor can be, for example, textile fibers. This sensor can be woven into, for example, clothing, covers or carpets. Artificial textile fibers made of, for example, polyester are outstandingly suitable for this use. However, natural fibers can also be used if they can withstand the manufacturing process.

[0035] Furthermore, the carrier material can be glass fibers. This can be used to convey externally through color output or color change the system state, for example, whether direct contact of the sensor has occurred or there is proximity to a heat source.

[0036] A sensor layer that is optically reactive can be applied to a part of the outer surface of the glass fiber. This reactive layer can react, for example, to the pH value or O2 content in the environment by a change in color. With the help of the glass fiber, this color change can be measured, and the sensor can be extended to include additional sensory dimensions. It is also possible to use a fiber Bragg grating as the carrier material, which can increase the information output of the sensor.

[0037] It may be advantageous to form the sensor in a cylindrical shape. Thus, the sensor is radially symmetric, and for example, the measurement signal generated by the deformation of the sensor is direction-independent. It is also possible to form the sensor in a plate shape. In the case of a plate shape, the width and length can be at least 10 times the height. Thereby, the manufacturing process for a flat layer can be used for the manufacture of the sensor.

[0038] Furthermore, the sensor can have at least one mechanical amplification element. The mechanical amplification element can be, for example, a hairy or bristly protrusion that transmits mechanical contact to the sensor. In this way, the effective range that causes piezoelectric and capacitive effects due to deformation can be expanded. The mechanical amplification element can be made of a composite material or a plastic such as PET, a thermosetting resin, or Teflon®.

[0039] The mechanical amplification element can be formed from the first and / or second electrodes. The manufacture of the mechanical amplification element can be integrated into the electrode manufacturing process, whereby the sensor can be extended to include a mechanical amplification element in an inexpensive and uncomplicated way.

[0040] If the sensor has a carrier material, at least one mechanical amplification element can also be formed from the carrier material. Especially in the case of a cylindrical sensor, the carrier material arranged inside can protrude from the sensor, whether it is coated or wound, and thus, a mechanical amplification element can be formed in a simple way.

[0041] Alternatively, at least one mechanical amplification element can be formed from the first electrode and the carrier material. This embodiment is also particularly suitable for cylindrical sensors. In this case, the carrier material and the electrode disposed on the carrier material protrude from the sensor. Thus, not only the effective range of the piezoelectric effect but also the effective range of the capacitive effect of the sensor is extended.

[0042] The individual layers of the sensor, namely the ferroelectric layer and the first and second electrodes, can each be made thinner than 50 μm. By configuring the sensor to be extremely thin, the sensor is flexible and can be bent, which is particularly advantageous in measurements based on the piezoelectric effect. In particular, making the pyroelectric layer thin enables the low thermal mass of the sensor and thus improves the response time and sensitivity of the sensor to temperature changes.

[0043] An advantageous configuration can have the sensor and the evaluation electronics described above. The evaluation electronics can be configured to measure the voltage generated within the ferroelectric layer and to detect changes in the voltage due to the piezoelectric effect, pyroelectric effect, and capacitive effect. The evaluation electronics should be designed to classify the measurement signal into one or more of the physical effects based on amplitude, time scale, time dynamics, and polarity from the signal-time evolution. Based on the classification of the voltage change into one or more physical effects, the evaluation electronics can detect whether an object is approaching the sensor or whether an object is in contact with the sensor.

[0044] In a further advantageous configuration, a plurality of sensors can be arranged in a matrix. By arranging the sensors in a matrix, measurements with spatial resolution can be performed and thus movement can also be tracked. For example, planar sensors can be arranged on a substrate, or cylindrical sensors can be arranged to protrude from the substrate like a carpet.

[0045] The sensor can be integrated into a robot. Autonomous robots, such as cleaning robots, lawn mowing robots, delivery robots or transport robots, benefit from a simplified sensor that can confirm the approach to the robot. When the approach is recorded by the sensor, the robot can act accordingly by reducing its speed, stopping or avoiding obstacles.

[0046] The cooperative system with the sensor according to the invention also benefits from the possibility of recording the approach. In a cooperative system, a large number of interactions occur between the machine and humans and other machines with a risk of collision. Reliable detection of the environment by the sensor minimizes the risk of accidents and promises a safe working process.

[0047] The sensor according to the invention can also be integrated into automatic doors, in particular automatic revolving doors or elevator doors. When the sensor detects the approach of a person, the door can open, prevent the door from closing, or reduce the rotational speed of the revolving door to prevent collision or pinching of the approaching person.

[0048] A further aspect relates to a method for manufacturing the above-described sensor, wherein the ferroelectric layer is applied onto the first electrode by a thin-film process such as CVD or PVD, or by a combination of the sol-gel method and spin coating.

[0049] In the following, the invention will be explained in detail based on schematic illustrations.

Brief Description of the Drawings

[0050]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Figure 22

Figure 23

Figure 24

DETAILED DESCRIPTION OF THE INVENTION

[0051] The same elements, similar or clearly identical elements are provided with the same reference numerals in the drawings. The drawings and the ratios of the sizes in the drawings are not to scale.

[0052] FIG. 1 shows a schematic cross-sectional view of the sensor 1 according to the present invention. A ferroelectric layer 2 is disposed on the first electrode 3a, and a second electrode 3b is disposed thereon. The second electrode 3b is electrically contacted and grounded.

[0053] The ferroelectric layer can here consist of a material which exhibits ferroelectric properties in an electric field. Preferably, the layer can consist of a ferroelectric material having piezoelectric properties, and particularly preferably, a ferroelectric material having pyroelectric properties.

[0054] The electrodes 3a, 3b are electrically contacted (not shown), and for example, a voltage change between the electrodes 3a, 3b can be read out as a measurement signal. Similarly, the pyroelectric layer 2 which is also piezoelectric reacts to both temperature changes and deformations with charge separation, and this charge separation results in a voltage change at the electrodes 3a, 3b. Since the second electrode 3b is grounded, a voltage change between the electrodes 3a, 3b occurs in the case of large-scale approach or contact as a result of a capacitance change between the second electrode 3b and an object approaching it. The sensor 1 of the present invention effectively utilizes three different physical effects, namely, a capacitive effect, a piezoelectric effect, and a pyroelectric effect, to cover different detection regions.

[0055] Thanks to the pyroelectric effect, temperature changes that may be several meters away from the heat source can be detected. The capacitive effect can also be used for non-contact detection, but for this purpose, it is necessary for the object to be detected to approach the sensor 1 on a large scale up to several centimeters. The piezoelectric effect and the capacitive effect can be used to confirm contact with other objects of the sensor 1. For the voltage change in the electrodes 3a and 3b, in the piezoelectric effect, an active spatial deformation of the pyroelectric layer 2 must occur, whereas in the capacitive effect, the piezoelectric effect is distinguished from the capacitive effect in that a static contact already brings about a voltage change.

[0056] The ferroelectric layer 2 contains PVDF or PZT. Both materials are pyroelectric. PVDF is particularly suitable as an elastic pyroelectric plastic. This is because the ferroelectric layer 2 can be easily deformed, and thus a voltage change can be caused by the piezoelectric effect. The ferroelectric layer 2 made of PVDF can be applied, for example, by spin coating, screen printing or inkjet printing. In contrast, PZT is a pyroelectric ceramic that exhibits flexibility as a very thin layer. It is possible to add Na, Ca or La to the PZT ceramic to adapt the electrical properties. PZT or other pyroelectric ceramics can be applied, for example, with the help of thin film processes such as CSD or PVD. PVDF has the advantage that it can be applied to a larger area without problems compared to ceramics such as PZT. This is because a ceramic as a large area layer may crack due to internal tension and pressure.

[0057] Preferably, the first and second electrodes 3a, 3b are made of a transparent and conductive material such as, for example, ITO, PEDOT:PSS, silver, graphite, metal nanowires, carbon nanotubes or graphene. Materials that are transparent in the ultraviolet-visible region and / or infrared region and / or exhibit good thermal conductivity are particularly suitable as the electrodes 3a, 3b. This facilitates the heat input into the ferroelectric layer 2. This is because the infrared thermal radiation hits the ferroelectric layer 2 directly. Therefore, the sensitivity of the sensor 1, particularly the sensitivity regarding the pyroelectric effect, increases. The electrodes 3a, 3b can also be made of a metal, a mixture of metals, an intermetallic compound or an alloy such as Al, Cr, Ni, Ag, Cu. Since metals have high electrical conductivity and thermal conductivity, they are also suitable as electrode materials.

[0058] The layers of the sensor 1 are each thinner than 50 μm, whereby the entire sensor 1 is flexible and can be bent. Therefore, the sensor 1 can be easily deformed, which results in a voltage change between the first and second electrodes 3a, 3b due to the piezoelectric effect. Since the sensor 1 is extremely thin, it has a small heat mass, whereby the response time is shortened and the sensitivity of the sensor 1 to temperature changes is increased.

[0059] The sensor 1 does not necessarily have to be composed of only one pyroelectric layer 2 as shown in FIG. 1, but can be realized in a multilayer structure by a plurality of pyroelectric layers 2 as well as a plurality of first and second electrodes 3a, 3b. Here, the pyroelectric layer 2 is always arranged between the first and second electrodes 3a, 3b, and the first and second electrodes 3a, 3b are arranged alternately in the stacking direction. By realizing the sensor 1 as a multilayer member, both the sensitivity and the accuracy of the sensor 1 can be improved.

[0060] The measurement signals picked up as voltage changes at the first and second electrodes 3a, 3b are transferred to an evaluation electronic device. The evaluation electronic device 7 may here be arranged on the same carrier material 4 as the sensor 1 as shown in FIG. 2, or may not be arranged on the same carrier material 4 as shown in FIG. 3. The evaluation electronic device 7 is in contact with the sensor 1 either directly or via the carrier material 4 as shown in FIG. 3. When a voltage change occurs in the sensor 1 due to a measurement event, this voltage change is transferred analogously to the evaluation electronic device 7 as can be seen in FIG. 4. The evaluation electronic device 7 has, inter alia, a signal amplifier, a comparator and a microprocessor and is designed to classify the measurement curve into a piezoelectric effect, a pyroelectric effect or a capacitive effect. Next, the signal is sent digitally to a digital evaluation unit 8, which outputs an output signal again.

[0061] FIG. 5 shows an example of a curve showing the voltage change after mechanical or thermal excitation of the sensor 1. In the graph of FIG. 5, as in the graphs of FIGS. 6, 7 and 8, the voltage is plotted against time. FIG. 6 shows a voltage change due purely to the pyroelectric effect. A heat source is switched on at site Y1 and switched off again at site Y2. FIG. 7 shows a measurement curve originating only from the piezoelectric effect. Deformation is caused by applying pressure at site X1 and the pressure application is removed again at site X2. The measurement curve of FIG. 8 shows the voltage change at the sensor 1, which is due solely to the capacitive effect.

[0062] The swing of the measurement curve due to the pyroelectric effect is slower, for example, than the swing due to the piezoelectric effect or the capacitive effect as shown by the comparison of FIG. 6 with FIGS. 7 and 8. Furthermore, as can be seen in FIG. 6, the progression of the curve in the case of the pyroelectric effect can have discontinuities when the heat source acts on the sensor 1 (Y1) or when it is switched off or shielded afterwards (Y2). In this case, switching off the heat source acts as a negative temperature difference, thereby changing the polarity and causing the measurement curve to change its sign abruptly.

[0063] In the case of the piezoelectric effect as well, a change in sign can occur in the measurement curve when, as shown in FIG. 7, for example, sensor 1 is released (X2) after being pre-deformed (X1). However, in contrast to the pyroelectric effect, the transition of the curve is continuous and can be much faster. The amplitude or voltage change is typically 10 to 100 times smaller in the case of the pyroelectric effect than in the case of the piezoelectric effect, but this is not obvious in the comparison between FIGS. 6 and 7 of FIG. 6 because the curve is correspondingly pre-amplified.

[0064] On the other hand, the capacitive effect cannot cause a change in sign in the measurement curve, and as can be seen in FIG. 8, the swing can be faster in time than the swing due to the piezoelectric effect. The two measurement curves in FIG. 8 were recorded by sensor 1 where the second electrode 3b is grounded in one case and not grounded in the other case. Since no voltage change occurs in the measurement curve without the ground connection of the second electrode 3b, it can be confirmed that the voltage change should simply be due to the capacitive effect and that the piezoelectric effect that would cause a voltage change regardless of the ground connection of the second electrode 3b does not occur. Through the analysis of the measurement curves for these different characteristics, the evaluation electronic device 7 can classify the physical effects.

[0065] When sensor 1 exists as a multilayer member as shown in FIG. 9, all the first electrodes 3a can be electrically contacted with the same first electrical contact element and all the second electrodes can be electrically contacted with the same second electrical contact element, respectively. Thus, the individual first and second electrodes are connected in parallel. Thereby, in the sense of signal addition, the electrical signals S of the individual functional layers and the amplified electrical signal S1 can be used for evaluation.

[0066] In an alternative embodiment, as shown in FIG. 10, the individual functional layers are contacted separately. In this case, the first electrodes are each electrically contacted with separate first contact elements, and the second electrodes are each electrically contacted with separate second contact elements. Thereby, separate electrical signals (S1, S2, S3, S4) can be evaluated for each functional layer, and furthermore, different types of sensor signals can be picked up for the individual functional layers and distinguished according to the physical effects.

[0067] FIG. 11 shows a schematic cross-sectional view of a plate-shaped coated embodiment in which the first electrode 3a is arranged inside the sensor 1, the ferroelectric layer 2 covers the first electrode 3a, and the second electrode covers the ferroelectric layer 2. Such a sensor 1 can be constructed layer by layer with the aid of a suitable manufacturing process for flat layers, such as screen printing for example. In this case, in order to achieve the coating, it may be advantageous to overprint the inner layer with a layer that is larger in area. However, when manufacturing the coating, it may also be convenient to first apply the layer that is to be placed thereon to one side of the inner layer, then invert the member, and apply the same type of layer to the other side. Before inversion, the applied layer is dried.

[0068] FIG. 12 shows a schematic cross-sectional view similar to FIG. 11 of a plate-shaped coated embodiment of the sensor 1, in which case the carrier material 4 is arranged inside the sensor. This embodiment can also be manufactured using a manufacturing process for flat layers as in FIG. 11, and the layers are applied successively or by inverting the member for each coating layer.

[0069] The carrier material 4 may be inelastic or elastic. The inelastic carrier material 4, such as a substrate, enhances the stability of the sensor 1. For the selected application, an arrangement on a carrier material 4 made of, for example, glass, concrete or steel may be preferred in some cases. Elastic materials contemplated as carrier material 4 can be, inter alia, rubber, plastic or a fabric such as cotton thread for example.

[0070] FIG. 13 shows a schematic cross-sectional view of the sensor 1 similar to FIG. 1. The sensor 1 is disposed on a carrier material 4 and has a mechanical amplification element 5 on the second electrode 3b.

[0071] The mechanical amplification element 5 shown as a hairy or bristly protrusion in FIG. 13 can mechanically transmit the contact to the second electrode 3b. Since the ferroelectric layer 2 is fixed to the second electrode 3b, this contact is also transferred to the ferroelectric layer 2, thus deforming the ferroelectric layer 2. Thereby, the detection region that can be covered by the piezoelectric effect is expanded. The mechanical amplification element 5 is made of a composite material or any of plastics such as PET, thermosetting resin, or Teflon (registered trademark).

[0072] The mechanical amplification element 5 can also be coated or formed on the cylindrical sensor 1 and on the sensor 1 not disposed on the carrier material 4. Preferably, as shown in FIG. 14, the amplification element 5 is mounted in the axial direction as an extension of the first electrode 3a and / or the carrier material 4. Preferably, the amplification element 5 is not additionally coated here, but is realized by the first electrode 3a and the carrier material 4. In the region functioning as the amplification element 5, no further ferroelectric layer 2 and no further second electrode 3b are coated on the first electrode 3a and the carrier material 4. A cross-sectional view of the sensor embodied in this way is shown in FIG. 15. Such cylindrical sensors 1 provided with the amplification element 5 for additional signal amplification can be grouped together into a bundle consisting of a plurality of individual sensors 1.

[0073] Alternatively, the amplification element 5 can also be formed only from the carrier material 4. In the cylindrical embodiment where the carrier material 4 is disposed inside, the first electrode 3a is also omitted in the region of the amplification element 5. When the sensor 1 is disposed on a carrier material 4 having a size larger than the sensor 1 itself, the protruding portion of the carrier material 4 also acts as the amplification element 5. In an embodiment where the first electrode 3a instead of the carrier material 4 is disposed inside, the amplification element 5 can also be formed only from the first electrode 3a. In that case, the first electrode 3a protrudes from the sensor 1, and the ferroelectric layer 2 and the second electrode 3b are omitted.

[0074] FIG. 16 shows a schematic cross-sectional view of the sensor 1 embodied in a cylindrical shape. Inside, a first electrode 3a covered by a pyroelectric layer 2 is disposed. The ferroelectric layer 2 is covered by a second electrode 3b. The second electrode 3b is grounded, but this is not shown in FIG. 16.

[0075] The first electrode 3a can be a commercially available wire. Preferably, the first electrode 3a is kept very thin with a diameter of about 150 μm to 250 μm in order to reduce the thermal mass of the sensor 1. For the same reason, the ferroelectric layer 2 is embodied with a thickness of less than 5 μm. In the case of the second and outermost electrode in this embodiment, a balance must be struck between the sensitivity of the sensor 1 and the protection of the pyroelectric layer 2 when selecting the layer thickness. In practice, a thickness of about 10 μm has been found to be an advantageous compromise.

[0076] The cylindrical shape of the sensor 1 is particularly advantageous for applications where the sensor 1 has to be inserted into a narrow opening. Furthermore, the cylindrical shape of the sensor 1 is beneficial for increasing the sensitivity to deformation. Furthermore, the cylindrical embodiment enables the sensor 1 to be manufactured in an endless process, similar to the manufacture of wires or cables. This simplifies the manufacturing and reduces the manufacturing cost.

[0077] FIG. 17 shows a schematic cross-sectional view of the sensor 1 embodied in a cylindrical shape, similar to FIG. 14. Inside, a carrier material 4 is arranged. Two first and second electrodes 3a, 3b each cover the carrier material 4 alternately, and one ferroelectric layer 2 is arranged between the first and second electrodes 3a, 3b. The layers inside the sensor 1 are also thinner than 5 μm in this embodiment. The thickness of the second electrode 3b forming the outermost layer is preferably 10 μm. By using a plurality of pyroelectric layers 2, the accuracy of the sensor 1 can be increased compared to the embodiment having one pyroelectric layer 2.

[0078] The carrier material 4 can be, for example, textile fibers, glass fibers or fiber Bragg gratings. When textile fibers are used as the carrier material 4, the textile fibers can be woven into clothing, covers, carpets and other textile products. Textile fibers made of plastics such as polyester are suitable as the carrier material 4. Natural fibers made of, for example, cotton can also be used. Glass fibers as the carrier material 4 can be used for indicating the system state, for example, whether direct contact or proximity has occurred, by certain colors of light passing through the glass fibers. It is also possible to use fiber Bragg gratings as the carrier material 4. These can expand sensor technology, for example, by being used as force sensors. However, it should be noted that for this purpose, a further set of optical evaluation devices is required.

[0079] FIG. 18 shows a longitudinal sectional view of the sensor 1 embodied in a cylindrical shape. Inside, glass fibers coated by the first and second electrodes 3a, 3b are arranged, and the ferroelectric layer 2 is arranged between the first and second electrodes 3a, 3b. A part of the outer surface of the glass fiber is not coated with the first and second electrodes 3a, 3b and the ferroelectric layer 2, and instead, an optically reactive sensor layer 6 is coated. This optically reactive layer 6 can react to the pH value or O2 content in the environment, for example, by a change in color or a change in fluorescence. With the help of the evanescent light wave coming out of the glass fiber, this change in color can be measured. In this way, the sensor technology and the potential application fields for the sensor 1 can be extended.

[0080] FIG. 19 shows a schematic sectional view of an embodiment having an insulating layer 9, and the sensor 1 is wound such that the insulating layer 9 is located inside. The insulating layer is an electrically insulating flexible layer and can also be made of a flexible and thin carrier material 4. The insulating layer 9 prevents the first and second electrodes 3a / 3b from short-circuiting when being wound.

[0081] The wound embodiment enables the production of the cylindrical sensor 1 by a planar manufacturing process. It should be noted that by winding the sensor 1 multiple times, a multilayer member can be manufactured, and the electrodes continuous in the radial direction are not electrically separated from each other as in the case of the coated sensor 1, but are connected to each other. Therefore, the wound sensor 1 has an increased capacitance and a more significant capacitive effect compared to the coated sensor 1.

[0082] FIG. 20, similar to FIG. 19, shows a schematic sectional view of an embodiment having an insulating layer 9, and the sensor 1 is wound around the carrier material 4. With the help of the carrier material 4, the mechanical properties of the wound sensor 1 can be affected.

[0083] Combinations of different embodiments are also possible. Thus, for example, the coated sensor 1 can function as the carrier material 4, and further sensors are wound around the coated sensor 1. Thus, the significant capacitive effect of the wound sensor 1 can be combined with the advantages of the coated sensor 1.

[0084] All examples can further include a protective layer made of, for example, plastic to protect the sensor 1 from a harmful environment.

[0085] FIG. 21 exemplarily shows an autonomous transport robot for a general robot. The box in the lower region of the robot indicates an advantageous position for mounting the sensor 1 according to the present invention. When the robot approaches a human, for example, at a distance of several meters, a voltage change due to the pyroelectric effect of the electrodes 3a, 3b of the sensor 1 is confirmed. As a result, the robot can, for example, reduce its speed. When the robot approaches the human further, a voltage change generated by the capacitive effect is confirmed from a distance of about one meter. At this point, since the robot is approaching the human, it will be able to change its moving direction. Nevertheless, if the robot collides with the human, the sensor 1 is deformed and a voltage change is detected as a result of the piezoelectric effect. Here, the robot will be able to stop or turn back so as not to cause damage. If the robot stops and thereby the deformation of the ferroelectric layer does not change, the voltage change due to the piezoelectric effect disappears. Nevertheless, the contact can continue to be detected by the capacitive effect.

[0086] Figure 22 shows a cooperative system in which the sensor 1 according to the present invention is integrated. In particular, the end of the robotic arm that can come particularly close to the collaborating humans is suitable for positioning the sensor 1. Figures 23 and 24 show advantageous positions of the sensor 1 on an automatic door. The automatic revolving door could, for example, reduce its rotational speed in case of approach and increase the rotational speed again in case of contact with the sensor 1. An automatic elevator door as shown in Figure 24 could, for example, already keep the door open in case of human approach. As a result, safety can be enhanced compared to frequently used light barriers. This is because the sensor can already detect the approach of a human to the door and does not react only when this human is already inside the door.

Explanation of Signs

[0087] 1 Sensor 2 Ferroelectric layer 3a First electrode 3b Second electrode 4 Carrier material 5 Mechanical amplification element 6 Optically reactive layer 7 Evaluation electronics 8 Digital evaluation unit 9 Insulating layer S Signal

Claims

1. A sensor (1), a first electrode (3a), Ferroelectric layer (2), a second electrode (3b), having the second electrode (3b) is grounded, and the ferroelectric layer (2) is disposed between the first electrode (3a) and the second electrode (3b); The sensor (1) comprises a carrier material (4) and an insulating layer (9), The ferroelectric layer (2) comprises a lead-free or lead-containing ceramic, The ceramic includes PZT, and Na, Ca, or La is additionally added to the ceramic including PZT; The ceramic is a thin film, the sensor (1).

2. The sensor (1) according to claim 1, wherein the first electrode (3a) or the second electrode (3b) is arranged on the insulating layer (9).

3. 3. The sensor (1) according to claim 1 or 2, wherein the insulating layer (9) is arranged on the carrier material (4).

4. The sensor (1) according to any one of claims 1 to 3, wherein the sensor (1) is rolled such that the insulating layer (9) is arranged on the carrier material (4).

5. The sensor (1) according to any one of the preceding claims, wherein the ferroelectric layer (2) comprises a polymer, a ceramic or a polymer-ceramic matrix.

6. The sensor (1) according to any one of claims 1 to 5, wherein the ferroelectric layer (2) is applied onto the first electrode (3a) by a thin film process such as CVD or PVD, by a combination of a sol-gel process and spin coating, or by screen printing.

7. The sensor (1) according to any one of the preceding claims, further comprising a protective layer.

8. The sensor (1) according to any one of claims 1 to 7, wherein the first electrode (3a) and / or the second electrode (3b) comprises a metal or metals, the metal or metals comprising Al, Cr, Ni, Ag, Cu, Fe, as well as mixtures or alloys of these elements.

9. The sensor (1) according to any one of the preceding claims, wherein the ferroelectric layer (2) and / or the first electrode (3a) and / or the second electrode (3b) are thinner than 50 μm.

10. The sensor (1) according to any one of claims 1 to 9, wherein the sensor (1) comprises a further first electrode (3a), a second electrode (3b) and a ferroelectric layer (2), the ferroelectric layer (2) being arranged between the first electrode (3a) and the second electrode (3b).

11. The sensor (1) according to any one of the preceding claims, wherein the ferroelectric layer (2) comprises a piezoelectric or pyroelectric material.

12. at least one evaluation electronic device (7), at least one sensor (1) according to any one of claims 1 to 11, An apparatus having The evaluation electronics (7) is configured to measure the electrical signal (S) generated by the sensor (1) and to recognise the piezoelectric, pyroelectric and capacitive effects through variations in the electrical signal (S).

13. 13. The device according to claim 12, wherein the evaluation electronics (7) is configured to recognize, based on a change in the measured electrical signal, whether an object is approaching or in contact with the sensor (1).

14. The device according to claim 12 or 13, wherein the changes in the measured electrical signal (S) comprise changes in the signal-time course and / or amplitude and / or time scale and / or time dynamics and / or polarity.

15. Apparatus according to any one of claims 12 to 14, wherein the electrical signal (S) comprises a voltage and / or a charge and / or a capacitance and / or a polarity.

16. A sensor (1) according to any one of claims 1 to 11, Including, The sensors (1) are arranged in a matrix. An apparatus according to any one of claims 12 to 15.

17. A sensor (1), a first electrode (3a), Ferroelectric layer (2), a second electrode (3b), carrier material (4), having the second electrode (3b) is grounded, and the ferroelectric layer (2) is disposed between the first electrode (3a) and the second electrode (3b); The carrier material (4) is a glass fiber, on a part of the outer surface of which an optically reactive sensor layer (6) is applied.

Images