Piezoelectric transformer

Abstract

The invention relates to a piezoelectric transformer (1) having an input region (2) and an output region (3), wherein the input region (2) is configured to convert an applied alternating voltage into a mechanical oscillation, wherein the output region (3) is configured to convert the mechanical oscillation into a voltage, and wherein the piezoelectric transformer (1) has a longest edge (13) and a shortest edge (14), wherein the longest edge (13) has a length which is at most twenty times as long as the length of the shortest edge (14).

Description

Technical Field

[0001] This invention relates to a piezoelectric transformer. Piezoelectric transformers can be used to generate plasma, particularly non-thermal atmospheric pressure plasma. Background Technology

[0002] In known cuboid piezoelectric transformers, plasma ignition has been observed occurring along the edge of the longitudinal side of the output region. This plasma ignition leads to undesirable feedback, where mechanical stress is generated in the piezoelectric material of the output region, which can cause cracks in the material. This may shorten the lifespan of the piezoelectric transformer. Summary of the Invention

[0003] Therefore, the object of the present invention is to describe an improved piezoelectric transformer, which, for example, can have a longer service life.

[0004] This objective is achieved by a piezoelectric transformer according to claim 1.

[0005] A piezoelectric transformer with an input region and an output region is proposed, wherein the input region is configured to convert an applied alternating voltage into a mechanical oscillation, and wherein the output region is configured to convert the mechanical oscillation into a voltage. Furthermore, the piezoelectric transformer has a longest edge and a shortest edge, wherein the length of the longest edge is at most twenty times the length of the shortest edge.

[0006] The ratio of the length of the longest edge to the length of the shortest edge is also known as the aspect ratio. It can be shown that in piezoelectric transformers with an aspect ratio ≤ 20:1, undesirable plasma ignition along the longitudinal edges of the output region can be avoided. Correspondingly, no significant mechanical load occurs on the piezoelectric material in the output region in these transformers, thus preventing cracking and maintaining a stable service life.

[0007] Piezoelectric transformers can be, for example, Rosen type transformers. Piezoelectric transformers can also be configured with a length-to-width ratio of ≥2:1, preferably ≥5:1.

[0008] As an edge, this can refer to the lines on the two sides of a piezoelectric transformer that are adjacent to each other.

[0009] Piezoelectric transformers can be substantially cuboid in shape. The edges of the transformer can be rounded. Specifically, the edges can be rounded with a very small radius, for example, ≤ 0.5 mm.

[0010] The longest edge can extend in the longitudinal direction from the input region to the output region. The shortest edge can be the edge of the output side end face. The output side end face is the end face furthest from the input region.

[0011] As mentioned above, piezoelectric transformers with an aspect ratio ≤ 20:1 have a longer service life because there is no significant mechanical load in the output area. Furthermore, such transformers offer other advantages. A preferred aspect ratio of ≤ 20:1 leads to improved ozone generation efficiency. In particular, with an aspect ratio ≤ 20:1, more ozone can be produced for the same input power per unit volume of the piezoelectric transformer. This improvement in ozone generation efficiency is due to improved impedance matching between the piezoelectric transformer's output impedance and the impedance generated by the plasma, which occurs with an aspect ratio ≤ 20:1.

[0012] The piezoelectric transformer can be used to generate plasma. Here, the plasma is preferably a non-thermal atmospheric pressure plasma.

[0013] Preferably, the longest edge has a length of less than 45 mm. More preferably, the longest edge has a length of less than 35 mm. The longest edge may have a minimum length of 10 mm.

[0014] This shortened structural form of the piezoelectric transformer has many advantages. The polarization voltage required to polarize such a piezoelectric transformer is essentially dependent on the length of the transformer. Correspondingly, for the polarization of transformers with a longest edge length of less than 45 mm or less than 35 mm, only a very small voltage is required. This simplifies the manufacturing process of the corresponding piezoelectric transformer.

[0015] Furthermore, the resonant frequency of the corresponding piezoelectric transformer depends on the length of its longest edge. A shorter longest edge allows for the manufacture of piezoelectric transformers with higher resonant frequencies. For example, a resonant frequency greater than 100 kHz can be achieved using a longest edge shorter than 35 mm. This resonant frequency is particularly advantageous in plasma generators used in medical applications.

[0016] Furthermore, a higher resonant frequency results in a steeper edge to the output voltage, which in turn has a positive impact on the efficiency of ozone generation.

[0017] A first external electrode may be disposed on a first side of the input region. A second external electrode may be disposed on a second side of the input region opposite to the first side. The input region may have piezoelectric layers and electrodes stacked together along a stacking direction. The electrodes may alternately contact the first external electrode or the second external electrode in the stacking direction. The output region may have a monolithic piezoelectric layer. The piezoelectric material of the piezoelectric layer in the output region may be the same as the piezoelectric material of the piezoelectric layer in the input region.

[0018] The longest edge can extend from the input region to the output region. The shortest edge can be perpendicular to the longest edge.

[0019] Piezoelectric transformers can have resonant frequencies greater than 100 kHz. These frequencies are particularly advantageous for applications in the medical field.

[0020] The longest edge can be up to fifteen times the length of the shortest edge of the piezoelectric transformer. Correspondingly, an aspect ratio of ≤15:1 is possible. By choosing such a small aspect ratio, it can be ensured that plasma ignition does not occur along the long edge. The efficiency of ozone generation can also be further improved in this way.

[0021] The shortest edge can have a length between 10 mm and 1 mm. Preferably, the shortest edge has a length between 5 mm and 2 mm. The length of the shortest edge is chosen such that a favorable aspect ratio of ≤20:1 is achieved.

[0022] Plasma ignition along the longest edge in the output region can be avoided by using the ratio of the longest edge length to the shortest edge length. Correspondingly, insulation devices, such as heat-shrink tubing partially surrounding the output region, can be omitted. Therefore, piezoelectric transformers can operate without insulation in the output region. In particular, piezoelectric insulators can be without heat-shrink tubing.

[0023] The mechanical load on the piezoelectric material in the output region can be reduced by using the ratio of the length of the longest edge to the length of the shortest edge.

[0024] Improved ozone generation efficiency can be achieved by adjusting the ratio of the longest edge to the shortest edge. In particular, this aspect ratio selection allows for a reduction in component size while maintaining or even improving ozone generation efficiency.

[0025] Another aspect of the invention relates to a plasma generator having the aforementioned piezoelectric transformer. This plasma generator is particularly suitable for generating non-thermal atmospheric pressure plasma. Attached Figure Description

[0026] The present invention will now be described with reference to the accompanying drawings.

[0027] Figure 1 A piezoelectric transformer is shown in perspective.

[0028] Figure 2 The results of the measurement are shown, in which... Figure 1 The ozone production of the piezoelectric transformer shown is compared with that of a comparative example.

[0029] Figure 3 The results of the measurements are shown, taking into account ozone generation per unit volume. Detailed Implementation

[0030] Figure 1The piezoelectric transformer 1 is shown in perspective. The piezoelectric transformer 1 can be used in a device for generating non-thermal atmospheric pressure plasma.

[0031] Piezoelectric transformer 1 is a resonant transformer structure, which is based on piezoelectricity and is an electromechanical system compared to a conventional magnetic transformer. Piezoelectric transformer 1 is, for example, a Rosen type transformer.

[0032] The piezoelectric transformer 1 has an input region 2 and an output region 3. In the input region 2, the piezoelectric transformer 1 has an electrode 4 to which an alternating voltage can be applied. The electrode 4 extends in the longitudinal direction L of the piezoelectric transformer 1. The electrode 4 is alternately stacked with piezoelectric material 5 in a stacking direction S perpendicular to the longitudinal direction L. The piezoelectric material 5 is polarized here along the stacking direction S.

[0033] Electrode 4 is arranged inside the piezoelectric transformer 1 and is also referred to as the internal electrode. The piezoelectric transformer 1 has a first side 6 and a second side 7 opposite to the first side 6. A first external electrode 8 is arranged on the first longitudinal side 6. A second external electrode (not shown) is arranged on the second side 7. The internal electrode 4 is alternately in electrical contact with either the first external electrode 8 or the second external electrode in the stacking direction S.

[0034] Input region 2 can be driven by a low alternating voltage applied between electrodes 4. Due to the piezoelectric effect, the alternating voltage applied to the input side is first converted into mechanical oscillations. The frequency of these mechanical oscillations depends primarily on the geometry and mechanical structure of the piezoelectric transformer 1.

[0035] Output region 3 has a piezoelectric material 9 and no internal electrodes. The piezoelectric material 9 in the output region is polarized along the longitudinal direction L. The piezoelectric material 9 in output region 3 can be the same material as the piezoelectric material 5 in input region 2, wherein piezoelectric materials 5 and 9 can have different polarization directions. In the output region, the piezoelectric material is formed as a unique monolayer that is completely polarized along the longitudinal direction L. Here, the piezoelectric material in the output region has only one polarization direction.

[0036] If an alternating voltage is applied to electrode 4 in input region 2, a mechanical wave is formed within piezoelectric materials 5 and 9. This mechanical wave generates an output voltage through the piezoelectric effect in output region 3. Output region 3 has an output-side end face 10. Therefore, the voltage generated in output region 3 is located between end face 10 and the end of electrode 4 in input region 2. Here, a high voltage exists at end face 10 on the output side. Here, a high potential difference is also formed between the end face on the output side and the environment of the piezoelectric transformer, which is sufficient to generate a strong electric field, causing the process gas to be ionized.

[0037] In this way, the piezoelectric transformer 1 generates a high electric field that can ionize a gas or liquid through electrical excitation. Here, the atoms or molecules of the corresponding gas or liquid are ionized and form a plasma. Ionization always occurs when the electric field strength on the surface of the piezoelectric transformer 1 exceeds the ignition field strength of the plasma. Here, the field strength required to ionize atoms or molecules is called the ignition field strength of the plasma.

[0038] Plasma ignition occurs not only at the longitudinal edge 11 on the side but also at the edge 12 of the end face 10 on the output side. Plasma ignition along the longitudinal edge 11 on the side leads to undesirable feedback, generating high mechanical stress in the piezoelectric material 9 of the output region 3. This high mechanical stress may cause cracks in the piezoelectric transformer 1 during continuous operation, thereby shortening its service life. To avoid such damage to the piezoelectric transformer 1 due to plasma ignition, the piezoelectric transformer 1 is configured such that plasma ignition occurs primarily at the end face 10 on the output side and avoids plasma ignition at the longitudinal edge 11 on the side.

[0039] In the case of piezoelectric transformer 1, plasma ignition occurs particularly at the location where the maximum potential appears in the output region 3 of piezoelectric transformer 1. The following explains in more detail how piezoelectric transformer 1 is constructed to minimize plasma ignition at the longitudinal edge 11 on the side.

[0040] The piezoelectric transformer 1 has a cuboid shape, wherein the piezoelectric transformer 1 has a longest edge 13 and a shortest edge 14. The output side end face 10 has a rectangular shape, wherein the shortest edge of the end face 10 is the shortest edge 14 of the piezoelectric transformer 1. The longest edge 13 of the piezoelectric transformer 1 is perpendicular to the output side end face 10 and extends from the input region 2 to the output region 3. The longest edge 13 is the longitudinal edge 11 of the side.

[0041] The ratio of the length of the longest edge 13 to the length of the shortest edge 14 is called the aspect ratio. It has been shown that the piezoelectric transformer 1, especially when the piezoelectric converter 1 is constructed such that an aspect ratio of ≤20:1 is obtained, generates plasma at the output-side end face 10 to a greater extent.

[0042] The aspect ratio affects the capacitance of the output region 3 of the piezoelectric transformer 1. The location in the output region 3 where the maximum potential is reached is shifted according to the capacitance of the output region 3. The output capacitance increases as the aspect ratio decreases. It can be shown both experimentally and theoretically that a sufficiently large output capacitance can be achieved with an aspect ratio ≤20:1, at which the maximum output potential is located on the output-side end face 10. If an aspect ratio greater than 20:1 is chosen, the output capacitance decreases, and the maximum output potential shifts away from the output-side end face 10 along the longitudinal edge 11 of the side surface in the direction pointing towards the input region 2. In this case, undesirable plasma ignition occurs along the edge 11.

[0043] In the first embodiment, the longest edge 13 has a length of 41 mm. The edge 12 of the output-side end face 10 has lengths of 6 mm and 3 mm. Correspondingly, the 3 mm long edge of the end face 10 is the shortest edge 14 of the piezoelectric transformer 1. Thus, an aspect ratio of 13.667:1 is obtained, which is a favorable aspect ratio less than or equal to 20:1.

[0044] In one experimental study, 10 piezoelectric transformers 1 according to the first embodiment were observed to operate continuously for 1,000 hours, during which no cracks were generated in any of the transformers 1 in the output region 3, and correspondingly no failure of one of the piezoelectric transformers 1 occurred.

[0045] According to the second embodiment, the longest edge 13 can be less than 35 mm. For example, the piezoelectric transformer 1 can have a longest edge 13 with a length of 30 mm. The end face 10 has edge lengths of 3 mm and 2.4 mm. In this case, an advantageous aspect ratio of ≤20:1 is also achieved. In particular, an aspect ratio of 12.5:1 is obtained.

[0046] The resonant frequency of piezoelectric transformer 1 depends on the length of the longest edge 13. The second embodiment results in a resonant frequency greater than 100 kHz.

[0047] A piezoelectric transformer 1 with a resonant frequency greater than 100 kHz can be particularly useful in medical applications. One example of such medical application is tissue cutting using plasma ablation. Stimulation of nerves should be avoided in this process. When the frequency is above 100 kHz, the ionic conductivity of nerves decreases significantly. Accordingly, a plasma generator operating at frequencies above 100 kHz is particularly well-suited for plasma tissue cutting. The piezoelectric transformer 1 described above according to the second embodiment can be used in such a plasma generator.

[0048] Figure 2The results of the comparative measurements are shown, in which the piezoelectric transformer 1 according to the first embodiment is compared with a comparison transformer having a length of 71 mm and a cross-section of 6 mm × 3 mm at the end face. In both cases, air is used as the process gas and is ionized by the corresponding piezoelectric transformer 1.

[0049] exist Figure 2 In the diagram, the power in W is plotted on the horizontal axis, and the corresponding piezoelectric transformer 1 is operated using this power. The ozone production in mg / h is plotted on the vertical axis. Figure 2 The measurement results shown indicate that no significant difference in ozone production was found. In particular, with piezoelectric transformer 1 having a favorable aspect ratio of ≤20:1, essentially the same amount of ozone can be produced at the same input power, where piezoelectric transformer 1 with an aspect ratio of ≤20:1 has a significantly shorter length relative to the comparison transformer.

[0050] Figure 3 The comparison between the piezoelectric transformer according to the first embodiment and the comparison transformer, which does not have a preferred aspect ratio of ≤20:1, is also shown. In this case, the product of the input power and volume of the respective transformer is considered. The dimensions are plotted on the horizontal axis in W x cm. 3 The value is the product of the input power and volume per unit. The amount of ozone produced per hour, in milligrams, is also plotted on the vertical axis. Air is used as the process gas. It can be clearly seen that the piezoelectric transformer 1, with its preferred length-to-height ratio per unit volume, produces a greater amount of ozone. Correspondingly, the piezoelectric transformer 1 has a higher ozone generation efficiency.

[0051] The improved ozone generation efficiency from air observed experimentally due to the favorable aspect ratio can also be explained theoretically. The ozone generation efficiency depends on the matching of the output impedance of the piezoelectric transformer 1 with the impedance generated by the plasma, and on the steepness of the output voltage edge. The steepness of the output voltage edge is essentially dependent on the resonant frequency under sinusoidal voltage. Accordingly, the piezoelectric transformer 1, with its longest side 13 having a small length and correspondingly a high resonant frequency, has a steep edge, which in turn positively impacts the ozone generation efficiency.

[0052] It can also be shown that the favorable aspect ratio improves the impedance matching of the piezoelectric transformer 1 with the impedance generated by the plasma.

[0053] Both the longitudinal edge 11 and the edge 12 of the output side end face of the piezoelectric transformer can be rounded. If the radius of curvature of the rounded edge is chosen to be small enough, for example less than 0.5 mm, the piezoelectric transformer 1 can be approximated as a cuboid.

[0054] In some embodiments of the piezoelectric transformer 1, the piezoelectric transformer has an insulating layer in the output region 3, which is formed, for example, by heat-shrink tubing. The insulating layer may be exposed at the output end face 10 and at least partially cover the remaining sides of the output region 3. The insulating layer should prevent unwanted plasma ignition along the longitudinal edge 11 of the side surface and for this purpose cover said longitudinal edge. Because plasma ignition along the longitudinal edge 11 of the side surface is not expected due to the advantageous aspect ratio, the piezoelectric transformer 1 may not have an insulating layer in the output region 3. In alternative embodiments, such an insulating layer may be provided to further improve the insulation of the output region 3.

[0055] List of reference numerals

[0056] 1. Piezoelectric Transformer

[0057] 2 Input Area

[0058] 3 Output Area

[0059] 4 electrodes

[0060] 5. Piezoelectric materials

[0061] 6 First side view

[0062] 7 Second side view

[0063] 8 First external electrode

[0064] 9. Piezoelectric materials

[0065] 10. Output side end face

[0066] 11. The longitudinal edge of the side

[0067] 12. Edge of the end face

[0068] 13 Longest Edge

[0069] 14 Shortest Edge

[0070] L (vertical direction)

[0071] S stacking direction

Claims

1. A method for generating plasma using a plasma generator, said plasma generator having a piezoelectric transformer (1). The piezoelectric transformer has an input region (2) and an output region (3). The piezoelectric transformer (1) has a longest edge (13) and a shortest edge (14), wherein the length of the longest edge (13) is at most twenty times the length of the shortest edge (14), wherein the longest edge (13) extends from the input region (2) to the output region (3), and wherein the shortest edge (14) is perpendicular to the longest edge (13). An alternating voltage is applied to the input region (2), and the input region converts the applied alternating voltage into mechanical oscillation. The output region (3) converts mechanical oscillations into voltage, and The piezoelectric transformer (1) ignites plasma at the end face (10) on the output side of the piezoelectric transformer (1). The piezoelectric transformer (1) has rounded edges with a radius of ≤ 0.5 mm.

2. The method according to claim 1, wherein the longest edge (13) has a length of less than 45 mm.

3. The method according to any one of the preceding claims, wherein the longest edge (13) has a length of less than 35 mm.

4. The method according to claim 1 or 2, wherein a first external electrode (8) is arranged on a first side (6) of the input region (2), and a second external electrode is arranged on a second side (7) of the input region (2) opposite to the first side (6). The input region (2) has piezoelectric layers (5) and electrodes (4) stacked in the stacking direction (S), wherein the electrodes (4) are alternately in contact with a first external electrode (8) or a second external electrode in the stacking direction (S), and The output region (3) therein has a monolithic piezoelectric layer (9).

5. The method according to claim 1 or 2, wherein the piezoelectric transformer (1) has a resonant frequency greater than 100 kHz.

6. The method according to claim 1 or 2, wherein the length of the longest edge (13) is at most fifteen times the length of the shortest edge (14) of the piezoelectric transformer (1).

7. The method according to claim 1, wherein the shortest edge (14) has a length between 10 mm and 1 mm.

8. The method according to claim 1 or 2, wherein plasma ignition along the longest edge (13) in the output region (3) is avoided by the ratio of the length of the longest edge (13) to the length of the shortest edge (14).

9. The method according to claim 1 or 2, wherein the mechanical load on the piezoelectric material in the output region (3) is reduced by the ratio of the length of the longest edge (13) to the length of the shortest edge (14).

10. The method according to claim 1 or 2, wherein air is used as the process gas, wherein improved ozone generation efficiency is achieved by the ratio of the length of the longest edge (13) to the length of the shortest edge (14) of the piezoelectric transformer (1) to the length of the shortest edge (14) of the piezoelectric transformer (1) while maintaining the same input power per unit volume of the piezoelectric transformer, compared to a comparison transformer that does not have a preferred ratio of ≤20:1 for the length of the longest edge (13) to the length of the shortest edge (14).

11. The method according to claim 1 or 2, wherein the piezoelectric transformer is used for medical applications.

12. The method according to claim 1 or 2, wherein the piezoelectric transformer is used to cut tissue by means of plasma cutting.

13. The method according to claim 1 or 2, wherein the impedance of the piezoelectric transformer (1) is matched with the impedance generated by the plasma.

14. The method according to claim 1 or 2, wherein by converting mechanical oscillations into voltage in the output region (3), a high potential difference is formed between the end face (10) on the output side and the environment of the piezoelectric transformer (1), the high potential difference being sufficient to generate a strong electric field that causes the process gas to be ionized.

15. The method according to claim 1 or 2, wherein in the output region (3), the maximum potential is located on the end face (10) on the output side.

16. The method according to claim 1 or 2, wherein the position of the maximum potential generated by the piezoelectric transformer is shifted according to the capacitance of the output region (3) and wherein the capacitance of the output region increases when the ratio of the length of the longest edge to the length of the shortest edge decreases.

17. The method of claim 1 or 2, wherein air is used as a process gas and generates ozone.

18. The method of claim 17, wherein the piezoelectric transformer produces an ozone concentration between 30 and 35 mg / h and an input voltage is applied to the piezoelectric transformer, wherein, in the case of the input voltage, the product of the input voltage and the volume of the piezoelectric transformer is 1 W × cm. 3 ,or The piezoelectric transformer produces ozone levels between 50 and 55 mg / h, and an input voltage is applied to the piezoelectric transformer at this input voltage, wherein the product of the input voltage and the volume of the piezoelectric transformer is 2 W × cm. 3 ,or The piezoelectric transformer produces ozone levels between 70 and 75 mg / h, and an input voltage is applied to the piezoelectric transformer. At this input voltage, the product of the input voltage and the volume of the piezoelectric transformer is 3 W × cm. 3 .

19. A medical device having a plasma generator having a piezoelectric transformer (1) for generating plasma. The piezoelectric transformer has an input region (2) and an output region (3). The input region (2) is configured to convert the applied alternating voltage into mechanical oscillation. The output region (3) is configured to convert mechanical oscillations into voltage. The piezoelectric transformer (1) has a longest edge (13) and a shortest edge (14), wherein the length of the longest edge (13) is at most twenty times the length of the shortest edge (14), wherein the longest edge (13) extends from the input region (2) to the output region (3), and wherein the shortest edge (14) is perpendicular to the longest edge (13). The piezoelectric transformer (1) is configured to ignite plasma at the end face (10) on the output side of the piezoelectric transformer (1). The piezoelectric transformer (1) has rounded edges with a radius of ≤ 0.5 mm.

20. The medical device of claim 19, wherein the medical device is configured for plasma cutting of tissue.

21. A method for generating plasma using a plasma generator, said plasma generator having a piezoelectric transformer (1). The piezoelectric transformer has an input region (2) and an output region (3). The piezoelectric transformer (1) has a longest edge (13) and a shortest edge (14), wherein the length of the longest edge (13) is at most twenty times the length of the shortest edge (14), wherein the longest edge (13) extends from the input region (2) to the output region (3), and wherein the shortest edge (14) is perpendicular to the longest edge (13). An alternating voltage is applied to the input region (2), and the input region converts the applied alternating voltage into mechanical oscillation. The output region (3) converts mechanical oscillations into voltage, and The piezoelectric transformer (1) ignites plasma at the end face (10) on the output side of the piezoelectric transformer (1). The location in the output region where the maximum potential is reached shifts according to the capacitance of the output region, wherein the capacitance of the output region increases as the aspect ratio decreases.

22. A medical device having a plasma generator having a piezoelectric transformer (1) for generating plasma. The piezoelectric transformer has an input region (2) and an output region (3). The input region (2) is configured to convert the applied alternating voltage into mechanical oscillation. The output region (3) is configured to convert mechanical oscillations into voltage. The piezoelectric transformer (1) has a longest edge (13) and a shortest edge (14), wherein the length of the longest edge (13) is at most twenty times the length of the shortest edge (14), wherein the longest edge (13) extends from the input region (2) to the output region (3), and wherein the shortest edge (14) is perpendicular to the longest edge (13). The piezoelectric transformer (1) is configured to ignite plasma at the end face (10) on the output side of the piezoelectric transformer (1). The location in the output region where the maximum potential is reached shifts according to the capacitance of the output region, wherein the capacitance of the output region increases as the aspect ratio decreases.

Images