Self-cleaning cuvette window

Abstract

The invention relates to a self-cleaning cuvette window (100, 200) comprising a pane (110, 210) made of an optically transparent material. According to the invention, the pane (110, 210) is surrounded by a frame (120, 220) having at least one actuator (130, 230), wherein the at least one actuator (130, 230) sets the pane (110, 210) into mechanical vibration by being electrically triggered.

Description

[0001] Watergenics GmbH

[0002] 27.01.2026 P05103WO

[0003] Self-cleaning cuvette window

[0004] The present invention relates to a self-cleaning cuvette window designed for use in a probe for long-term stable quality monitoring of liquids. This monitoring is particularly important for mine water, industrial wastewater, sewage treatment water, and cooling water, as the concentration of specific ions, such as sulfate or phosphate, must be determined precisely and continuously over extended periods. Ion-selective electrodes are frequently used for the electrochemical analysis of these ions, enabling selective detection of the target ions. However, these electrodes have significant limitations because their surfaces are irreversibly damaged by organic and inorganic electrode toxins during long-term use.The degradation of the electrodes caused by these poisonings leads to a significant reduction in their service life, making reliable long-term monitoring hardly possible, especially in heavily contaminated liquids such as mine or sewage water.

[0005] To circumvent these disadvantages, spectrometric analysis, particularly Raman spectroscopy, is increasingly used for liquid monitoring. This method is based on physical interactions between light and matter, so no chemical reaction with the liquid being analyzed is required. In Raman spectroscopy, monochromatic laser light is shone into the liquid. The liquid molecules scatter the incident light, with a small portion of the scattered light exhibiting a frequency-dependent shift that is characteristic of the molecular vibrational structure of the respective analytes. This so-called Raman shift is a key characteristic of the analysis.

[0006] 27.01.2026 P05103WO

[0007] enables precise and specific identification of molecules such as sulfate or phosphate directly in the liquid.

[0008] To perform Raman spectroscopy, a probe is immersed in the liquid to be analyzed. This probe contains either a miniaturized spectrometer or optical fibers that guide the laser light to the probe's cuvette window and direct the backscattered light generated by Raman scattering back to the spectrometer. The probe's cuvette window forms the optical interface between the liquid and the measurement equipment and is crucial for the quality of the measurements, as both the incident laser light and the backscattered Raman light must propagate unimpeded through the window.

[0009] A major problem with the long-term use of such probes is the fouling of the cuvette window. In mine water, amorphous deposits of iron and manganese oxides form, creating a brown, opaque layer that significantly reduces radiation transmission. In wastewater, biofilms develop, formed by microorganisms and organic residues, which coat the cuvette window. In cooling water, limescale deposits and flocculant residues form, causing similar optical impairment. The reduction in the optical transparency of the cuvette window significantly impairs the accuracy of Raman spectroscopy and can completely preclude its use in long-term operation.

[0010] Mechanical cleaning systems such as wipers or brushes, which are regularly run across the window surface, are frequently used to clean cuvette windows. However, these systems have significant disadvantages, as the mechanical components are exposed to the chemical stress of the fluid, leading to material fatigue and increased maintenance. Brushes can become clogged with incrustations or overgrown with biofouling. Wipers made of rubber, polyphosphaze, or silicone degrade. (Watergenics GmbH)

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[0012] They deteriorate due to chemical aging processes and become unusable. Furthermore, mechanical cleaning systems are often ineffective against stubborn or rapidly forming deposits.

[0013] Other systems utilize ultrasonic cleaning, in which an ultrasonic probe is placed near the outer surface of the cuvette window and generates strong ultrasonic pulses. These pulses cause the formation of cavitation bubbles in the water. When these bubbles collapse, high local pressure peaks occur, resulting in a powerful cleaning action. However, the cavitation effect can damage the surface of the cuvette window, leading to surface erosion over time.

[0014] The object of the present invention is to provide a self-cleaning cuvette window that avoids the aforementioned disadvantages. The invention achieves this object by connecting the cuvette window pane to at least one actuator, wherein the at least one actuator, by electrical control, sets the pane into mechanical vibration. Further advantageous embodiments are specified in the dependent claims.

[0015] According to the principle of the invention, the cuvette window itself is set into vibration, so that adhering deposits are loosened from the surface by the induced movement. The mechanical excitation can be carried out in the acoustic sound range as well as in the ultrasonic range. It is particularly advantageous to excite the cuvette window disc at one of its mechanical resonant frequencies, as this generates a high vibration amplitude and maximizes cleaning efficiency.

[0016] The disk's vibration can exhibit various natural frequencies. In a zero-order natural frequency, the entire surface of the disk moves synchronously in the vertical direction without forming a nodal line. In a first-order natural frequency, a nodal line forms, along which the direction of vibration reverses. In a second-order natural frequency... (Watergenics GmbH)

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[0018] In this order, two mutually perpendicular nodal lines are created, further subdividing the vibration zones of the disk. The resonant frequencies of these vibration modes differ depending on the order and are dependent on the geometric and material properties of the disk. Additionally, different vibration modes can be excited simultaneously by superimposing multiple excitation frequencies. This allows the cleaning effect to be specifically optimized, for example, by combining a large-area, low-order vibration with a high-frequency excitation that generates additional surface acceleration.

[0019] The resonant frequency of a circular disk made of quartz glass, a commonly used material for cuvette windows, is described in more detail below. The resonant frequency for a circular disk can be calculated for certain vibration modes (e.g., radial or flexural modes) from the theory of thin plates. The fundamental frequency f o is approximately described by the following formula:

[0020]

[0021] with

[0022] β: Dimensionless factor that depends on the vibration mode. For the fundamental mode (0th order), β ~ 2.405.

[0023] E Elastic modulus.

[0024] p density.

[0025] h: Thickness of the disc.

[0026] d: Diameter of the disc.

[0027] v: Poisson number.Watergenics GmbH

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[0029] The Poisson number (also called Poisson ratio, symbol v) is a dimensionless material constant that describes how a material behaves under tension or compression. It gives the ratio between the relative transverse and longitudinal strain of a material.

[0030] When a material is stretched or compressed in one direction, it typically responds with an opposite deformation in the other directions. The Poisson's ratio describes the relationship between the relative transverse strain and the lateral strain. £ transverse and the relative longitudinal strain e Zän5S :

[0031] >

[0032]

[0033] Longitudinal strain - Relative strain perpendicular to the direction of loading (negative when the cross-section is reduced).

[0034] £ longitudinal - Relative strain in the direction of loading (positive for stretching, negative for compression).

[0035] Poisson number values:

[0036] The Poisson number typically ranges from 0 to 0.5:

[0037] v = 0.5: An ideal, incompressible material (like rubber). The volume remains constant when deformed.

[0038] v = 0.5: Perfectly rigid-body-like behavior with no transverse strain. Negative values: For certain exotic materials (e.g., auxetic materials) that expand transversely when stretched.

[0039] Examples of materials:

[0040]

[0041] Watergenics GmbH

[0042] 27.01.2026 P05103WO

[0043]

[0044] For a quartz glass disc with a thickness of 1 mm and a diameter of 1 cm, the zeroth order resonance frequency can be calculated as follows:

[0045] Geometry of the disc:

[0046]

[0047] Material properties of quartz glass:

[0048]

[0049] From these figures, the fundamental frequency of a cuvette window with a diameter of 1 cm and a thickness of 1 mm is calculated to be 1.77 kHz.

[0050] For the first order, the dimensionless factor β changes to approximately 3.83. Therefore, the frequency of the first-order oscillation of a cuvette window with a diameter of 1 cm and a thickness of 1 mm is approximately 4.3 kHz.

[0051] If ruby ​​or the very similar sapphire, synthetic aluminum oxide with small amounts of chromium, is used as the cuvette window, the fundamental frequency and the first-order frequency are calculated at a density (p): 3.980 kg / m³ 3 , an elastic modulus (E) of 3.4*10 11 Pa and a Poisson number of 0.27 to 2.99 kHz and 6.14 kHz.

[0052] These frequencies are below the very high ultrasonic frequencies of the well-known ultrasonic probes used in laboratories. The advantage of the lower frequencies...Watergenics GmbH

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[0054] The frequency is such that cavitation, imploding water bubbles, is significantly less pronounced and therefore the surface of the cuvette windows suffers less damage from erosion.

[0055] The invention is explained in more detail with reference to the following figures. They show:

[0056] Figure 1 shows a self-cleaning cuvette window 100 according to the invention in a first embodiment,

[0057] Figure 2 is a perspective view of a zero-order oscillation of disk 110 according to Bessel.

[0058] Figure 3 is a perspective representation of a Bessel 1st order oscillation of disk 110.

[0059] Figure 4 is a perspective representation of a second-order oscillation of disk 110 according to Bessel.

[0060] Figure 5 shows a self-cleaning cuvette window 200 according to the invention in a second embodiment.

[0061] Figure 1 shows a first embodiment of a self-cleaning cuvette window 100 according to the invention. The cuvette window 100 has a disk 110 that separates the liquid to be analyzed from the optical path of a spectrometer behind it. In this embodiment, the disk 110 is held in a frame 120 made of a magnetostrictive metal, such as nickel. This frame 120 serves as an actuator 130. To excite the actuator 130, a magnetic coil 140 is provided, which is shown here symbolically on the frame 120. To increase the magnetic flux through the frame 120, the diameter of the magnetic coil 140 can be significantly larger than the diameter of the frame 120. If the magnetic coil 140 is subjected to alternating current at a mechanical resonance frequency of the disk 110, the diameter of the frame 120 changes minimally.Since the rim 120 itself vibrates due to its magnetostrictive properties, the resonant frequency of the disc 110Watergenics GmbH.

[0062] 27.01.2026 P05103WO

[0063] The vibration occurring is transferred to the disc 110. Depending on its mechanical natural frequency, this can then produce a zero-order, a first-order, or a second-order vibration. In this process, the disc 110 vibrates like a drumhead, shaking off incrustations and fouling.

[0064] Figure 1 shows a sectional drawing AA on the right, depicting a zero-order vibration. The surface of disk 110 bulges alternately outwards and inwards.

[0065] This oscillation is sketched in perspective in Figure 2. Without a nodal line, the surface of the disk 110 rises and falls. If this occurs at the mechanical resonance frequency of a natural oscillation, maximum cleaning performance is achieved. However, it is not necessary to excite the disk 110 at a resonance frequency. It is also possible to mechanically excite the disk 110 at a significantly higher frequency than the resonance frequency, for example, with an ultrasonic frequency between 10 kHz and 50 kHz. The higher frequency results in a higher acceleration of the surface of the disk 110, albeit with a lower amplitude. The higher acceleration leads to a higher cleaning performance, although cavitation can occur on the liquid side, which can erode the surface. If the disk 110 of the self-cleaning cuvette window 100 has a diameter of approximately 1 cm and a thickness of approximately...If the disk is 1 mm thick and made of quartz, the natural frequency of the simplest zero-order oscillation is between 1 kHz and 2 kHz. The cavitation effect on the liquid side is still comparatively small; nevertheless, the disk 110 cleans itself through the maximum oscillation amplitude that the quartz glass disk 110 can undergo.

[0066] If the disk 110 is excited at the natural frequency of a first-order natural oscillation, a nodal line is formed. The position of the nodal line can be predetermined by the design of the frame 120. Watergenics GmbH

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[0068] Flattening or reinforcing the edging 120 on opposite sides results in the node line forming exactly between these geometric changes of the edging 120.

[0069] Figure 3 shows a first-order oscillation of disk 110 with a nodal line. In the oscillation shown here, the half of disk 110 facing the viewer is bulged downwards. A stationary nodal line forms in the horizontal center of disk 110, and the half of disk 110 facing backwards behind the plane of the paper is bulged upwards. These bulges form for a fraction of a second, and the orientation of the bulge, downwards or upwards, alternates with the mechanical resonance frequency.

[0070] Figure 4 shows the oscillation of disk 110 with two lines of nodes. A first line of nodes runs horizontally in the plane of the paper, and a second line of nodes runs vertically perpendicular to the plane of the paper in the perspective plane.

[0071] Figure 5 shows an alternative embodiment of the self-cleaning cuvette window 200. Here, a disk 210 is equipped with and connected to a regular pattern of piezoelectric actuators 220 at its edge. On the side opposite the disk 210, on the back side of the actuators 220, there is a glass or metal ring. The actuators 220 can be excited independently of one another with alternating current at the resonant frequency of the disk 210. By controlling the phase of the individual actuators 220, the position of the nodal line can be deliberately controlled during first-order or second-order excitation. It is also possible to make the nodal line wander or rotate by controlling the phase of the different actuators 220, so that the entire disk 210 cleans itself.It may also be possible to control a number of actuators 220 individually or in groups, using different actuators 220 or Watergenics GmbH.

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[0073] Different groups of actuators 220 can be controlled with different phases or frequencies. Frequencies can also be superimposed so that zeroth and first order oscillations occur simultaneously.

[0074] When the self-cleaning cuvette windows 100, 200 presented here are used in a spectrometer, the cuvette windows 100, 200 can be regularly cleaned with a pulse-pause ratio between 1:1 and 1:10. 6The disc is set into vibration. During the longer pause, there is enough time for a spectrometer to perform its measurements. During the shorter pulse time, however, the spectrometer is switched off or does not take a measurement, and the disc 110, 210 cleans itself. To prevent the formation of very firmly adhering incrustations or heavily adhering fouling, the vibration with the aforementioned pulse-pause ratio can be operated over the lifetime of the cuvette window, i.e., for several years. Watergenics GmbH

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[0076] REFERENCE MARK LIST

[0077] 100 cuvette windows 200 cuvette windows

[0078] 110 disc 210 disc

[0079] 130 actuator 230 actuator

[0080] 140 magnetic coil

Claims

Watergenics GmbH 27.01.2026 P05103WO Self-cleaning cuvette window PATEN TA NSPRÜCHE 1. Featuring a self-cleaning cuvette window (100, 200) a disc (110, 210) made of an optically transparent material, characterized in that the disk (110, 210) is connected to at least one actuator (130, 230), wherein the at least one actuator (130, 230) sets the disk (110, 210) into a mechanical vibration by electrical control.

2. Self-cleaning cuvette window according to claim 1 , characterized by the fact that 3. Self-cleaning cuvette window according to claim 1 or 2, characterized in that at least one actuator (230) consists of a piezoelectric material which can be piezoelectrically excited by an electrical voltage.

4. Self-cleaning cuvette window according to one of claims 1 to 3, characterized in that the disc (110) is soldered to a frame (120), the frame acting as an actuator (130).

5. Self-cleaning cuvette window according to one of claims 1 to 4, characterized in that more than one actuator (130, 230) is arranged in a regular pattern around the disk (110, 210) and can be controlled individually or in groups.

6. Method for controlling a self-cleaning cuvette window according to one of claims 1 to 5, characterized by Excitation of at least one actuator (130, 230) with an excitation frequency that - in the range of the resonance frequency of a zero-order oscillation of the disk or - lies in the range of the resonance frequency of a first-order oscillation of the disk or in the range of the resonance frequency of a second-order vibration of the disk.

7. Method for controlling a self-cleaning cuvette window according to one of claims 1 to 5, characterized by Excitation of at least one actuator (130, 230) with an excitation frequency that represents a superposition of a resonance frequency of a 0th order oscillation of the disk (110, 210), a resonance frequency of a 1st order oscillation of the disk (110, 210) and / or a resonance frequency of a 2nd order oscillation of the disk (110, 210).

8. Method for controlling a self-cleaning cuvette window according to one of claims 6 or 7, characterized by Stimulating at least one actuator (130, 230) with a pulse-pause ratio in the range of 1:1 to 1:10 6 .

9. Method for controlling a self-cleaning cuvette window according to one of claims 6 to 8, characterized by Individual or group control of a plurality of actuators (130, 230), wherein different actuators (130, 230) or different groups of actuators (130, 230) are controlled with different phases or with different frequencies.

10. Use of a self-cleaning cuvette window (100, 200) according to one of claims 1 to 5 in an online spectrometer for spectrometric monitoring of the quality of: industrial wastewater, mine water, sewage treatment water, industrial cooling water.

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