阅读说明：本技术 用于检测膜中/膜上出现的波的系统和方法 (System and method for detecting waves present in/on a membrane ) 是由 安蒂·科蒂奥拉 阿勒·萨尔米 里斯托·蒙托宁 爱德华·黑格斯特伦 于 2020-02-05 设计创作，主要内容包括：本发明涉及一种检测在膜中/膜上出现的波的系统,包括：源(101),用于将激励信号倾斜地指向膜；接收器(102),用于测量从膜的前表面反射的激励信号的第一部分和从所述膜的后表面反射的激励信号的第二部分之间的干涉。系统包括处理装置(103),用于基于所测量的干涉的变化来检测波。波的检测基于由波在激励信号的第二部分的传播路径的V形部分的光学长度上引起的变化,其中传播路径的V形部分在膜内部。(The invention relates to a system for detecting waves present in/on a membrane, comprising: a source (101) for directing an excitation signal obliquely to the membrane; a receiver (102) for measuring interference between a first portion of the excitation signal reflected from the front surface of the film and a second portion of the excitation signal reflected from the back surface of the film. The system comprises processing means (103) for detecting the wave based on the measured change in interference. The detection of the wave is based on a change caused by the wave over the optical length of a V-shaped portion of the propagation path of the second part of the excitation signal, wherein the V-shaped portion of the propagation path is inside the membrane.)

1. A system for detecting waves present in/on a membrane, the system comprising:

-a source (101), the source (101) directing a signal to the membrane, an

A receiver (102), the receiver (102) measuring interference between a first portion of the signal reflected from the front surface of the film and a second portion of the signal reflected from the back surface of the film,

characterized in that the source and the receiver are positioned tilted with respect to each other such that the signal is directed obliquely to the membrane when the receiver receives the reflected first and second portions of the signal, and the system comprises a processing device (103), the processing device (103) detecting the wave based on the measured change in interference.

2. The system according to claim 1, wherein the source and the receiver are positioned tilted with respect to each other such that an angle (a) between a transmission direction of the source and a reception direction of the receiver is in a range of 15 degrees to 120 degrees.

3. The system according to claim 2, wherein the source and the receiver are positioned tilted with respect to each other such that the angle (a) is in the range of 45 to 90 degrees.

4. A system according to any of claims 1 to 3, wherein the system comprises a support structure (108), the support structure (108) being arranged to mechanically support the source (101) and the receiver (102) such that an angle (a) between a transmission direction of the source and a reception direction of the receiver is variable.

5. The system according to any of claims 1 to 4, wherein the processing device is configured to control the source to vary the wavelength of the signal and to estimate the thickness (T) of the film based on interference measured by different wavelengths of the signal.

6. The system according to any of claims 1 to 5, wherein the source (101) comprises a laser source.

7. The system of claim 6, wherein the laser source is a vertical cavity surface emitting laser.

8. The system of any of claims 1 to 7, wherein the receiver comprises an array of sensor elements (105).

9. A method of detecting waves present in/on a membrane (107), the method comprising:

-directing (201) a signal to the membrane, an

-measuring (202) interference between a first portion of the signal reflected from the front surface of the film and a second portion of the signal reflected from the back surface of the film,

characterized in that the signal is directed obliquely (201) to the membrane and the method comprises detecting (203) the wave based on the measured change in interference.

10. The method of claim 9, wherein the signal is obliquely directed at the film such that an angle (β) between a direction of the signal to the film and a geometric perpendicular to the film is in a range of 7 to 60 degrees.

11. The method of claim 10, wherein the angle (β) is in a range of 22 to 45 degrees.

12. The method according to any of claims 9 to 11, wherein the method comprises selecting an angle (β) between a direction of arrival of the signal at the membrane and a geometric perpendicular to the membrane such that a distance between a point (a) at which the second part of the signal enters the membrane and another point (C) at which the second part of the signal leaves the membrane is substantially the length of the wave.

13. The method of any of claims 9 to 12, wherein the method comprises varying a wavelength of the signal and estimating the thickness of the film based on the measured interference corresponding to different wavelengths of the signal.

14. The method of any of claims 9 to 13, wherein the signal is generated using a laser source.

15. The method of any of claims 9 to 14, wherein the interference is measured with an array of sensor elements.

Technical Field

The present disclosure relates to a system for detecting waves that occur in/on a membrane (e.g., in/on a cornea of an eye). Furthermore, the present disclosure relates to a method for detecting waves present in/on a membrane.

Background

In many cases, it is desirable to detect waves that appear in/on the membrane, such as membrane waves or lamb waves. The wave may be a standing wave or a traveling wave. In this document, the term "film" is not limited to substantially two-dimensional structures of extremely small thickness, and the term "film" may refer to any layer of material, sheet, plate, or another structure whose thickness is significantly less than the other dimensions. The detection of waves present in/on the cornea can be used, for example, in tonometry, where an excitation such as an air pulse, an ultrasonic tone burst, a shockwave, or some other suitable excitation is used to deform the cornea, after which an estimate of the tonus is obtained based on the waves caused by the excitation in/on the cornea. Waves occurring in/on the membrane can be detected, for example, using interferometry, wherein radiation is directed to the membrane in question and to a reference reflector. The wave causes a change in the optical length of the propagation path of the radiation reflected from the film surface. Thus, the wave causes a change in the interference between the radiation reflected by the reference reflector and the radiation reflected by the film surface. Therefore, the wave can be detected based on the change in the interference described above.

However, in many applications the above-described interferometric-based methods for detecting waves present in/on the membrane are not without challenges. For example, it may be challenging to keep the reference reflector sufficiently stationary with respect to the eye being measured in conjunction with the tonometry so that inadvertent changes in the position and/or orientation of the reference reflector with respect to the eye do not interfere too much with the tonometry. Thus, there is a need for a technical solution for detecting waves present in/on a membrane, so that no reference reflector or some other element that has to be precisely stationary with respect to the membrane carrying the waves to be detected is required.

Disclosure of Invention

The following presents a simplified summary in order to provide a basic understanding of some aspects of various inventive embodiments. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplary and non-limiting embodiments of the invention.

In this document, the term "geometry" when used as a prefix denotes a geometrical concept and is not necessarily part of any physical object. The geometric concept may be, for example, a geometric point, a straight or curved geometric line, a geometric plane, a non-planar geometric surface, a geometric space, or any other geometric entity in zero, one, two, or three dimensions.

In accordance with the present invention, a novel system for detecting waves that occur in/on a membrane (e.g., in/on the cornea of an eye) is provided. The membrane may be any layer of material, sheet, plate or another structure having a thickness significantly less than the other dimensions. The system according to the invention comprises:

a source for directing a signal to the membrane, an

-a receiver for measuring interference between a first part of the signal reflected from the front surface of the film and a second part of the signal reflected from the rear surface of the film, an

-processing means for detecting the wave based on the measured change in interference.

The source and receiver are positioned obliquely with respect to each other such that when the receiver receives the reflected first and second portions of the signal, the signal is obliquely directed toward the membrane.

The detection of the wave present on the membrane is based on the variation caused by the wave over the length of the V-shaped part of the propagation path of the above-mentioned second part of the signal, which is inside the membrane. The way in which the wave changes the length of the aforementioned V-shaped part will be explained later in this document with reference to the drawings.

Since the detection of the wave is based on the interference between a first portion of the signal reflected by the front surface of the membrane and a second portion of the signal reflected by the rear surface of the membrane, there is no need for a reference reflector and/or another element that must be precisely stationary with respect to the membrane carrying the wave to be detected.

According to the present invention, there is also provided a new method for detecting waves that occur in/on a membrane (e.g. in/on the cornea of an eye). The method according to the invention comprises the following steps:

-directing the signal obliquely towards the membrane, an

-measuring interference between a first portion of the signal reflected from the front surface of the film and a second portion of the signal reflected from the back surface of the film, and

-detecting a wave based on the measured change in interference.

Various exemplary and non-limiting embodiments are described in the accompanying dependent claims.

The exemplary and non-limiting embodiments, both as to organization and method of operation, together with additional objects and advantages thereof, may be best understood from the following description of specific exemplary embodiments when read in connection with the accompanying drawings.

The verbs "comprising …" and "comprising …" are used in this document as open-ended limitations that neither exclude nor require the presence of unrecited features. The features recited in the dependent claims may be freely combined with each other, unless explicitly stated otherwise. Furthermore, it should be understood that the use of "a" or "an" throughout this document, i.e., the singular, does not exclude the plural.

Drawings

Exemplary and non-limiting embodiments of the present invention and its advantages are explained in more detail below with reference to the attached drawing figures, wherein:

figure 1a shows a system for detecting waves present in/on a membrane according to an exemplary and non-limiting embodiment,

FIGS. 1b to 1d show the operating principle of the system shown in FIG. 1a, an

Fig. 2 shows a flow diagram of a method for detecting waves present in/on a membrane according to an exemplary and non-limiting embodiment.

Detailed Description

The specific examples provided in the following description should not be construed as limiting the scope and/or applicability of the appended claims. The list of examples and set of examples provided in the following description are not exhaustive unless explicitly stated otherwise.

Fig. 1a shows a system for detecting waves present in/on a membrane 107 according to an exemplary and non-limiting embodiment. In the exemplary case shown in fig. 1a, the membrane 107 is the cornea of the eye 106. The waves travelling along the membrane 107 are shown in fig. 1b, 1c and 1d, which show at time t₀、t₁And t₂Cross-sectional view of the membrane 107 at different times, where t₂>t₁>t₀. The system shown in fig. 1a comprises a source 101 for directing a signal to a membrane 107. The source 101 may comprise, for example, a light source 104, and the light source 104 may be, for example, a laser source, such as a vertical cavity surface emitting laser "VCSEL" for emitting a signal. In this exemplary case, the signal is a light beam, for example, a laser beam. The source 101 may further comprise a lens system for focusing the light beam to the membrane 107. The beam is advantageously focused on or behind the front surface of the membrane 107. The front surface is the surface of the membrane 107 that the signal first reaches. The diameter of the radiation spot, e.g. a laser spot, on the surface of the membrane 107 may be, for example, in the range of 0.5mm to 6 mm. The signal may also be some other propagating wavefront, for example, an ultrasound wavefront. The system includes a receiver 102 to measure interference between a first portion of the signal reflected from the front surface of the film 107 and a second portion of the signal reflected from the back surface of the film 107. In FIGS. 1 b-1 d, the first part of the signalIndicated by dashed arrows and a second part of the signal is indicated by dashed arrows. In the exemplary case where the signal is electromagnetic radiation, such as a laser beam, the receiver 102 may include, for example, a lens system and a multi-point sensor comprising an array of sensor elements 105. Each sensor element may be, for example, a photodiode or a phototransistor. The receiver 102 may also include a charge coupled device "CCD". The system further comprises processing means 103 for detecting the wave based on the change in interference measured by the receiver 102. In a system according to an exemplary and non-limiting embodiment, the receiver 102 includes a dual photodiode or an array of photodiodes, where differential sensing of adjacent photodiodes is used to improve sensitivity.

The source 101 and the receiver 102 are positioned tilted with respect to each other such that when the receiver 102 receives the reflected first and second portions of the signal, the signal is directed obliquely towards the membrane 107. In the system according to the exemplary and non-limiting embodiment, the source 101 and the receiver 102 are positioned tilted with respect to each other such that an angle α between a transmitting direction of the source 101 and a receiving direction of the receiver 102 is in a range of 15 degrees to 120 degrees. In the system according to the exemplary and non-limiting embodiment, the angle α is in the range of 45 degrees to 90 degrees.

The detection of waves is explained below with reference to fig. 1b to 1 d. In the case shown in fig. 1b, the wave has not yet reached the irradiated area of the membrane 107. The interference between the first and second portions of the signal is determined by the wavelength of the signal and the length of the V-shaped portion A-B-C of the propagation path of the second portion of the signal. In the exemplary case where the signal is electromagnetic radiation (e.g., a laser beam), the term "length" is assumed to include the effect of the refractive index of the material of the film 107. As shown in fig. 1b to 1d, the V-shaped part of the propagation path is inside the membrane 107. In the situation shown in fig. 1c, the wave has reached the excitation area of the membrane 107. As shown in fig. 1B and 1C, the distance a-B in the case shown in fig. 1C is longer than in the case shown in fig. 1B, and the distance B-C is substantially the same in the cases shown in fig. 1B and 1C. In the case shown in fig. 1d, the wave has moved further in the propagation direction than in the case shown in fig. 1 c. As shown in fig. 1B to 1d, the distances a-B and B-C in the case shown in fig. 1d are shorter than in the case shown in fig. 1B and 1C. The above-described variation in the length of the V-shaped portion a-B-C of the propagation path of the second part of the signal causes a variation in the interference between the first and second parts of the signal. As shown in fig. 1B-1 d, the length of the V-shaped portion a-B-C varies most strongly when the distance between the point a where the second part of the signal enters the membrane 107 and the point C where the second part of the signal separates the membrane 107 is substantially the length of the wave present in/on the membrane.

The system according to the exemplary and non-limiting embodiment comprises a support structure 108, the support structure 108 being arranged to mechanically support the source 101 and the receiver 102 such that the above-mentioned angle α shown in fig. 1a is variable. This enables the user of the system to select the angle alpha such that the distance between the point a where the second part of the signal enters the membrane 107 and the point C where the second part of the signal separates from the membrane 107 is substantially the length of the wave that appears in/on the membrane.

In the system according to the exemplary and non-limiting embodiment, the processing device 103 is configured to estimate the rate of change of the measured interference. The rate of change may be expressed as Hz, for example. In some exemplary cases, the rate of change may be, for example, above 1 kHz.

In the system according to the exemplary and non-limiting embodiment, the processing device 103 is configured to estimate the speed of travel of the wave based on the measured rate of change of the interference and pre-stored data indicating the length of the wave. It is also possible to have two measurement points on the film at a known distance from each other at the same time and to estimate the speed of travel based on the time difference between the known distance and the corresponding change in the interference occurring for the two measurement points.

In the system according to the exemplary and non-limiting embodiment, the processing device 103 is configured to control the source 101 to vary the wavelength of the signal and estimate the thickness of the film 107 based on the interference measured with different wavelengths of the signal. The thickness is indicated by T in fig. 1b to 1 d. In this exemplary case, the source 101 may comprise, for example, a vertical cavity surface emitting laser "VCSEL" for enabling wavelength scanning of the signal. The wavelength of the signal emitted by the VCSEL can be varied by varying the current of the VCSEL. Thus, the VCSEL can be driven with a ramp current pulse in direct intensity modulation, and the inherent characteristics of the VCSEL produce a wavelength swept output by self-heating effects. The signal emitted by the VCSEL has a long coherence length, which makes it possible to measure the thickness of a film whose thickness is a few millimeters, while the wavelength sweep obtained by varying the current of the VCSEL makes it possible to detect white light interference with a coherence width of a few hundred micrometers. The system may include an air gap that serves as a thickness determination reference. Data indicative of the thickness being determined may be obtained by means of a fourier transform of the measured interference signal. Since the measurement is performed not vertically but obliquely, the influence of the inclination, i.e. the cosine error, is advantageously compensated for in the thickness estimation. For another example, the thickness estimation may be based on a pre-stored reference model obtained, for example, by experiments performed with a reference film having a predetermined thickness, wherein the reference model indicates the behavior of the interference according to the wavelength of the signal and according to the thickness of the film, i.e., the interference ═ f (λ, T), λ being the wavelength of the signal, T being the thickness of the film. The reference model may be implemented, for example, using a two-dimensional look-up table. The influence of the refractive index of the film material may be included in the reference model. The thickness of the film can be estimated by finding the thickness value in the reference model so that the behavior of the interference according to wavelength indicated by the reference model is as close as possible to the behavior of the measured interference according to wavelength. It is also possible to estimate the thickness of the film using a mathematical model based on wave optics theory. The mathematical model gives a thickness estimate when a parameter indicative of the behaviour of the measured interference as a function of wavelength is given as input data.

The processing device 103 may be implemented with one or more processor circuits, each of which may be a programmable processor circuit equipped with appropriate software, a special-purpose hardware processor, such as an application-specific integrated circuit "ASIC", or a configurable hardware processor, such as a field-programmable gate array "FPGA". Further, the processing device 103 may include one or more memory circuits, each of which may be, for example, a random access memory "RAM" circuit.

Fig. 2 shows a flow diagram of a method for detecting waves present in/on a membrane according to an exemplary and non-limiting embodiment. The method comprises the acts of:

-an action 201: directing the signal obliquely to the membrane, an

-an action 202: measuring interference between a first portion of the signal reflected from the front surface of the film and a second portion of the signal reflected from the back surface of the film, an

-an action 203: the wave is detected based on the measured change in interference.

In a method according to an exemplary and non-limiting embodiment, the signal is obliquely directed toward the membrane such that an angle β between a direction of the signal reaching the membrane and a geometric perpendicular of the membrane is in a range of 7 degrees to 60 degrees. The angle β is shown in fig. 1b to 1 d. In the method according to the exemplary and non-limiting embodiment, the above-mentioned angle β is in the range from 22 degrees to 45 degrees.

In the method according to an exemplary and non-limiting embodiment, the angle β is selected such that a distance between a point at which the second portion of the signal enters the membrane and another point at which the second portion of the signal separates from the membrane is substantially the length of the wave.

A method according to an exemplary and non-limiting embodiment includes estimating a rate of change of a measured interference.

The method according to an exemplary and non-limiting embodiment includes estimating a travel speed of the wave based on a measured rate of change of the interference and pre-stored data indicating a length of the wave.

A method according to an exemplary and non-limiting embodiment includes varying a wavelength of a signal and estimating a thickness of a film based on measured interference corresponding to different wavelengths of the signal.

In a method according to an exemplary and non-limiting embodiment, the signal is generated using a laser source, for example, a vertical cavity surface emitting laser.

In a method according to an exemplary and non-limiting embodiment, interference is measured with an array of sensor elements.

The non-limiting, specific examples provided in the description given above should not be construed as limiting the scope and/or applicability of the appended claims. Moreover, any list or group of examples presented in this document is not exhaustive unless explicitly stated otherwise.