KR20190077699A - Fabry-perot interference ultrasound sensor with optical fiber and MEMS fabrication method - Google Patents

Abstract

The present invention relates to a Fabry-Perot interference ultrasound sensor using an optical fiber and a micro electro mechanical system (MEMS) process. The ultrasound sensor can perform mass production through the MEMS process, reduce a product price, and is an optical fiber ultrasound sensor of light, small, high-accuracy, and no-electromagnetic interference. The present invention uses a Fabry-Perot interference structure to increase ultrasound resolution with regard to a region of interest which is the same as the boundary part of a cancer tissue in an RF-acoustic imaging (RFAI) system and the like, and increase a degree of geometric freedom when manufacturing an ultrasound probe.

Description

[0001] Fabry-Perot interferometer type ultrasonic sensor using optical fiber and MEMS process [0002] Fabry-perot interference ultrasound sensor with optical fiber and MEMS fabrication method [

The present invention relates to an ultrasonic sensor, and more particularly, to a Fabry-Perot interferometer type ultrasonic sensor using an optical fiber and a MEMS (Micro Electro Mechanical Systems) process.

However, in the case of electromagnetic induction ultrasound diagnostic equipment such as RF-Acoustic Imaging (RFAI, RF ultrasound imaging) systems that emit electromagnetic waves and receive ultrasound, ultrasound probes are used There is a problem that it is difficult to normally detect the electromagnetic wave guided ultrasonic wave by the piezoelectric (piezoelectric) type ultrasonic sensor. Further, the conventional piezoelectric (ultrasonic) type ultrasonic sensor has a problem in that it is bulky and heavy and expensive.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and it is an object of the present invention to provide a semiconductor device capable of mass production through a microelectromechanical system (MEMS) It is a fiber optic ultrasonic sensor without electromagnetic interference. It improves the ultrasonic resolution for region of interest (ROI) such as the boundary of cancer tissue in RF-Acoustic Imaging (RFAI, RF ultrasound imaging) And a Fabry-Perot interferometer type ultrasonic sensor capable of increasing the degree of freedom.

In order to achieve the above object, an optical fiber sensor array according to one aspect of the present invention includes an optical fiber sensor tip arranged in a one-dimensional or two-dimensional array at a plurality of holes of an SOI substrate, Wherein the optical fiber sensor tip of the optical fiber sensor chip includes a structure in which a fiber ferro interferometer is formed by combining optical fiber lines at respective positions of the plurality of holes.

According to another aspect of the present invention, there is provided an ultrasonic sensor including: a first optical coupler for transmitting and receiving an optical signal; A main sensor connected to the first optical coupler through an optical fiber, in the form of a sensor array including an optical fiber sensor tip arranged one-dimensionally or two-dimensionally at a plurality of holes of an SOI substrate, each optical fiber sensor tip comprising: At each location, the main sensor comprising a structure that combines optical fiber lines to form a Fabry-Perot interferometer; A first detector for photoelectrically converting the reflected wave received by the main sensor through the optical fiber line via the first optical coupler; And a signal processor for processing a signal output from the first detector and generating a signal for outputting the ultrasound image.

The ultrasonic sensor includes: a second optical coupler; An auxiliary sensor formed on the SOI substrate and having a sensor array having the same structure as the Fabry-Perot interferometer structure of the main sensor array; A photodetector included between the second optical coupler and the auxiliary sensor; And a second detector for photoelectrically converting the reflected wave received by the auxiliary sensor through the optical fiber line via the second optical coupler, wherein the signal processing unit includes a first detector and an output from the second detector A signal for outputting the ultrasound image can be generated.

The auxiliary sensor detects a phase range to which a phase of an optical signal belongs, and the main sensor can detect a detailed phase of the optical signal within the phase range.

Wherein the structure of the Fabry-Perot interferometer of each optical fiber sensor tip is formed at a position of each of the plurality of holes passing through the base layer silicon, the insulating film, and the surface silicon of the SOI substrate, Is smaller than the opening diameter of the sub-silicon.

The hole of the surface silicon which is narrower than the opening diameter of the base layer silicon is used as an air cavity.

Wherein the structure of the Fabry-Perot interferometer of each of the optical fiber sensor tips comprises a first mirror coupled to an opening of the base layer silicon, the first mirror being formed at an end of the optical fiber wrapped with a core by a cladding, A second mirror formed to cover the cavity, and a membrane formed on the second mirror.

The Fabry-Perot interferometer type ultrasonic sensor according to the present invention can be mass-produced through a microelectromechanical system (MEMS) process and can lower the price of a product. Lightweight, compact, high-precision and electromagnetic interference There is an advantage that there is no. In other words, mass production is possible through the MEMS (Micro Electro Mechanical System) process and the price of the product can be lowered. Also, by replacing the conventional piezoelectric ultrasonic sensor with the optical fiber ultrasonic sensor, there is no interference by electromagnetic waves, (RFAI, RF ultrasound image) system, it is possible to detect a region of interest (ROI) such as the boundary of a cancer tissue. It is possible to improve the resolution of the ultrasonic probe and to increase the geometric freedom when manufacturing the ultrasonic probe.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
FIG. 1 is a graph showing the penetration depth of biomedical tissue of various general medical image technologies and the resolution thereof.
2 shows a conceptual diagram of an ultrasound medical imaging technique of a general RFAI system.
FIG. 3 is a view for explaining a Fabry-Perot interferometer type ultrasonic sensor 100 according to an embodiment of the present invention.
4 is a view for explaining the structure of the sensor array 200 provided at the end of the sensor head 140 of the present invention.
5 is a view for explaining a MEMS processing process of the SOI substrate 210 for the sensor array 200 of the sensor head 140 of the present invention.
FIG. 6 is a view for explaining a Fabry-Perot interferometer structure formed in each hole of the MEMS processed SOI substrate 210 of the present invention.
7 is a schematic perspective view of the sensor head 140 of the present invention.
FIG. 8 is a graph showing the transmittance T according to Finesse of the Fabry-Perot interferometer.
9 is a hypothetical view of an ultrasonic output waveform showing RF-Acoustic response characteristics of a phantom to an RF pulse signal input (e.g., pulse width 1 μs).

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same components are denoted by the same reference symbols as possible. In addition, detailed descriptions of known functions and / or configurations are omitted. The following description will focus on the parts necessary for understanding the operation according to various embodiments, and a description of elements that may obscure the gist of the description will be omitted. Also, some of the elements of the drawings may be exaggerated, omitted, or schematically illustrated. The size of each component does not entirely reflect the actual size, and therefore the contents described herein are not limited by the relative sizes or spacings of the components drawn in the respective drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. The following terms are defined in consideration of the functions of the present invention, and may be changed according to the intention or custom of the user, the operator, and the like. Therefore, the definition should be based on the contents throughout this specification. The terms used in the detailed description are intended only to describe embodiments of the invention and should in no way be limiting. Unless specifically stated otherwise, the singular form of a term includes plural forms of meaning. In this description, the expressions "comprising" or "comprising" are intended to indicate certain features, numbers, steps, operations, elements, parts or combinations thereof, Should not be construed to preclude the presence or possibility of other features, numbers, steps, operations, elements, portions or combinations thereof.

It is also to be understood that the terms first, second, etc. may be used to describe various components, but the components are not limited by the terms, and the terms may be used to distinguish one component from another .

First, the present invention relates to a method and apparatus for converting ultrasound signals generated by an electromagnetic wave-guided ultrasonic diagnostic apparatus such as an RF-Acoustic Imaging (RFAI) system into an optical fiber ultrasonic transducer instead of a focused array system comprising a general piezoelectric ultrasonic transducer It has been proposed to improve the resolution of ultrasound for region of interest (ROI) such as the boundary of cancer tissue, and to increase geometric freedom in the production of ultrasound probes, thereby enabling a small and lightweight receiver.

RFAI provides new multiwave medical imaging information that combines high conductivity and permittivity contrast for living tissue and high spatial resolution of ultrasound. In RFAI, biotissue absorbs a small fraction of the incident RF pulsed wave energy (depending on penetration depth and frequency, but mainly less than 1%) and thermoacoustic energy conversion process, resulting in thermoelastic ultrasonic waves.

The thermoacoustic energy conversion process is summarized as follows.

1) Energy In: RF energy radiation

2) Heating: The living tissue receives RF energy and instantly experiences a temperature rise (10 ^-5 to 10 ^-3 ° C).

3) Thermal Expansion: Temperature increase causes thermal / mechanical expansion of living tissue. In some cases, a moving deformation phenomenon may predominate.

4) Acoustic Wave: Thermal expansion generates sound waves.

The possibility of medical imaging of this thermoacoustic phenomenon was first proposed by Theodore Bowen (professor at Arizona State University) in 1981, and the first 3D tomography was demonstrated at the Indiana State University in 1998, It seemed possible as a device. However, as Lihong Wang, who studied RFAI in the 2000s, has been converting the electromagnetic energy source from radio frequency (RF) / microwave to laser (laser) (thermoacoustic) technology, RFAI-related research has been relatively reduced, and photoacoustic imaging technology has made remarkable progress.

Due to numerous R & D investments, photoacoustic technology has overcome the scattering limit, diffusion limit and dissipation limit in order, and by 2015, soft tissue 5cm (contrast agent) ), But the deep tissue area of about 10 cm still does not show any improvement due to the optical limitations. Research in this field is the development of a contrast agent And is demanding a new alternative technology such as deflecting. Since the contrast agent is a technique that avoids it as much as possible due to its toxicity, RFAI technology is being considered as an alternative to photoacoustic imaging technology in the field of deep tissue functional imaging.

FIG. 1 is a graph showing the penetration depth of biomedical tissues of various general medical image technologies and the resolution thereof (see Stephan Kellberger, dissertation, TUM 2012). In this figure, TAT (ThermoAcoustic Tomography) belongs to the same group as RFAI, and comparable technologies are US (Ultrasound) and OAT (OptoAcoustic Tomography). Of these, US technology is not suitable for functional imaging, so OAT is the only real comparison. Although this figure is not entirely consistent with current technology trends, it is theoretically known that TAT technology is much more advantageous than OAT technology in terms of depth of penetration. Therefore, it is necessary to develop an RFAI related technology capable of observing cancer tissue at a depth of 10 cm or less at a resolution of 1 mm or less.

Accordingly, the present invention is directed to ultrasonic detection technology, which is one of core technologies of RFAI, and ultimately to application to ultra-small optical fiber receiver technology for miniaturization and weight reduction of electromagnetic induction ultrasound diagnostic equipment such as RFAI system.

2 shows a conceptual diagram of an ultrasound medical imaging technique of a general RFAI system (see ENDRA LIFE SCIENCE). As shown in FIG. 2, in a medical function imaging system such as an RFAI system, when an image signal is generated from an energy conversion aspect, when RF pulse energy is applied to a human body part, ultrasonic waves are generated from the living tissue through RF- thermoacoustic phenomenon, Detecting and reconstructing the image through an inverse transformation such as a radon transform can be used to predict what happened to the living tissue.

To investigate the RFAI, the method for each module shown in FIG. 2 is shown in Table 1 below.

[Table 1] Methodology for RFAI Research

[Table 1] is based on the RFAI literature review and is a table explaining how the research method to be implemented is derived. The UHF (Ultra High Frequency) band, which is the most studied RFAI by single frequency, is 434MHz band, which is analyzed as ISM (Industry-Science-Medical) band and expectation for deep tissue. However, in the present invention, a pulsed RF system with a high frequency VHF band, which is more suitable for deep tissues than the 434 MHz band, is applied in the previous research experience. However, the present invention is not limited to this, and frequencies of other bands may be applied as needed.

The most important part in defining and understanding this RFAI system is the thermoacoustic transfer function between RF-tissue (rf-tissue) expressed as T / F (Transfer Function) Therefore, various mathematical models are proposed and used in the simulation.

Among them, the system equation model to be used in the present invention is a thermoacoustic differential equation derived from a continuous equation form between RF energy and acoustic energy (see Tam 1986, Xu and Wang 2006, and Mashal 2009) Is equal to Equation (1) when the medium is homogeneous.

[Equation 1]

Here, p (r, t) is the acoustic pressure, β _e is the volume expansion coefficient, T (r, t) is the temperature increase due to RF absorption and ρ is the density. Commercial packages (for example, cst, comsol) that can solve these system equations are widely available, so the simulation can be carried out by selecting a package that can be secured among them.

In the case of the RF pulse, assuming that the RF pulse width is 1 μs, the thermoacoustic response of the living tissue lasts for about 1 μs. Therefore, Frequency. In general, since the penetration depth of the living tissue of the ultrasonic wave of 1 MHz sufficiently exceeds 10 cm, the RF pulse width is determined to be 1 μs in the present invention.

There are three important fields of research in constructing an actual RFAI system: pulsed RF radiation, ultrasound detection, and image reconstruction. In the present invention, ultrasound detection, Will be described. However, since determining the technical specification of the pulsed RF determines the performance of the whole system, the technical specification range of the pulsed RF is limited to the knowledge obtained through the prior studies, and the present invention is applied to the experiment of the present invention.

Considering the fabrication cost of the RF module and the content to be verified, the RF power for verifying the effect of the optical fiber ultrasonic detector can be relatively low, so the output will be reduced as much as possible (in the range of 100W to 200W). Although RFAI is a deep tissue, it is possible to experiment with low RF power if the RF field and the acoustic field are divided into only the acoustic field.

RF emission and RF-Phantom coupling have the following problems: 1) SAR (Specific Absorption Rate) is 1.6W / Kg (ICNIRP (International Noxious Radiation Protection Association) criteria: 2.0W / Kg), 2) radiation exposure should be designed in consideration of the Public exposure Standard of 0.5mW / cm ² of the FCC (Federal communications Commission).

Direct comparison of regulatory values may not be meaningful because the exposure standard and measurement method are different from each other. However, when the FCC 0.5mW / cm ² is converted to the SAR value at constant exposure, it is 70mW / Kg = 0.7). This value is 1/20 or less compared with 1.6W / Kg of SAR domestic standard. Therefore, FCC 0.5mW / cm ² will be applied to this invention rather than SAR limit value.

On the other hand, the RF applied to the RFAI system and the generated ultrasonic wave coexist at a specific point in time. However, since the RFAI system is connected to the RF generating unit and the ultrasonic measuring unit through the phantom or the living tissue, it is difficult to completely shield the RF generating unit, and a certain portion of the RF is radiated into the unwanted space. At this time, EMI (Electro Magnetic Interference) induced in the lead wire and the electronic circuit of the ultrasonic measuring part acts as a strong high frequency noise in the ultrasonic measuring circuit, so it must be removed.

RFAI currently does not have a way to improve ROI resolution compared to photoacoustic imaging and ultrasound imaging. In the case of ultrasonic imaging, the beam forming technique of the ultrasonic wave by the focused array enables to obtain a high resolution for the region of interest by spatially synchronizing the ultrasonic wave input portion and the ultrasonic wave detecting portion. This focused array technology is also applied to photoacoustic imaging.

In the case of photoacoustic imaging, focusing the beam waist of a coherent laser in the region of interest and synchronously synchronizing (beam waist) the beam waist by the focused array of ultrasound to the same region, the same effect as the forming effect can be obtained. However, the development of high-sensitivity receivers and broadband receivers is still underway due to the regulation of the biosensing of the laser source (ANSI limit 20 mJ / cm ² ), which is also an energy source. From the detected low SNR analog data, digital signal processing Etc.) have been actively researched to restore more clear medical images. At the same time, much attention has been focused on the medical imaging system, which does not require an agent (contrast agent), and a lot of research has been done in the past 10 years. The photoacoustic method itself is limited to solve the deep tissue problem. Ironically, The development of an agent for improving the contrast of the cells is actively under way.

In the thermoacoustic medical imaging studies reported so far, the thermoacoustic transfer function for living tissues is very complicated, so unified theory that can be generally used is not presented. However, the SNR of the ultrasound detection stage is not limited to EM (RF), laser, etc.) It is well known that energy is proportional to the amount of energy radiated into living organisms.

Since RFAI is also one of the thermoacoustic medical imaging techniques, it is expected that the SNR of the ultrasound detection stage will increase in proportion to the RF output of the input stage. However, since RF biometry is more restrictive than laser biometry, the RFAI medical imaging case is less free of input EM energy radiation than thermoacoustic medical imaging.

Here, RFAI has two branches to choose. One is to effectively modulate the RF to detect a desired level of ultrasound signals, and the other is to design the detector precisely. Of course, there are a lot of ideas on how to modulate RF in RF properties (multi-frequency, resonance, uwb (Ultra Wide Band), etc.), but the detector design is quite limited. This is partly due to the dependence of the detector on the source, but there are also several additional factors such as geometric constraints, burden on process development, sensor reliability, manufacturing issues, and so on.

Therefore, the development direction of the detection part should be defined as a simpler structure. Second, since the RFAI is a functional image utilizing the RF propagation characteristic rather than the anatomical image, the receiver is required to monitor the rf- Should be designed.

Another problem is in deep tissue observation. In RFAI, the higher the RF frequency, the higher the resolution, but the depth of RF penetration is rapidly reduced, so if the target is 10cm deep tissue, it should be at least 500MHz. In deep tissues, there is not only a reduction in RF attenuation (2.0 dB / cm on the average in the living body) but also a significant level of attenuation of the acoustic wave (0.54 dB / cm on average in the living body) It becomes more important.

In summary, the problem that arises from the difficulty of focusing RF for deep tissues on the ROI is that the directionality of the focused array at the receiver end, the focal length Length) and beam waist (beam waist). However, in this method, in order to improve the spatial resolution, the technology advances in the direction of increasing the number of elements of the focused array. In this case, the signal-to-noise ratio (SNR) increases but the uncertainty of the sound source position information also increases. It requires separate signal processing in order to increase the cost.

In addition to the detector focusing problem in the ultrasonic detector of the RFAI system, the EMI problem induced in the detector must also be solved. Since the RF generator and the ultrasonic wave measuring unit are connected to each other through the phantom or the living tissue, it is difficult to completely shield the RF generator and the RF Some parts of it are also emitted into unwanted spaces. At this time, the EMI induced in the lead wire and the electronic circuit of the ultrasonic measuring part acts as strong high frequency noise in the ultrasonic measuring circuit, and thus it is very expensive to remove it.

When a Faraday cage is used to eliminate such noise, complete shielding is difficult and the system becomes complicated. The method of separating the RF emission time and the ultrasonic detection time in the time band is that the electrically disconnectable source and the detector are electrically connected through the digital sequence and thus there is a noise problem and when the ROI is some distance from the ultrasonic detector There is also a problem that the blind area of the diagnosis may occur when applying to the diagnosis because it is an effective method. The signal processing method for separating the applied RF and the frequency band of the ultrasonic wave to be detected is not separated at all in the frequency domain because the applied RF is modulated into a square wave pulse represented by a sinc function in the frequency domain.

Therefore, in the present invention, the ultrasonic wave detecting unit of the RF-ultrasound imaging apparatus or the electromagnetic wave guiding ultrasonic diagnostic apparatus is replaced with the optical fiber ultrasonic wave sensor in the conventional piezoelectric element, and the advantage of being lightweight, compact, high- Respectively. That is, by replacing the conventional piezoelectric type ultrasonic sensor with the optical fiber ultrasonic sensor, it is suitable for detecting weak ultrasonic signal under strong electromagnetic wave environment because there is no interference by electromagnetic wave and sensitivity is improved by improvement of signal-to-noise ratio.

Ultrasonic waves generated by the thermoacoustic characteristics propagate in all directions, but the signal detection region is narrower than the ultrasonic waves. Therefore, it is difficult to distinguish the positions of the sound sources that generate different ultrasonic waves. In order to distinguish the positions of these sound sources, the receiver is given the directionality, which is mainly focused array. Focused arrays can improve the resolution of the area of interest by adjusting the beam waist by beam steering techniques, but the resolution that can be improved is limited due to limitations in reducing beam waist. However, if a directional detector is used as an element, the spatial resolution can be obtained even with a small number of elements.

Since the RFAI system is a deep tissue monitoring system, RF source is required to solve the problem of RF-induced acoustic signal detection with very low SNR (Signal to Noise Ratio). In this study, the effect of the proposed detection method is verified by varying the RF pulse generator in UHF single frequency, pulse width 0.5uS ~ 1uS, period 1mS ~ 10mS, and RF output 100W ~ 200W. Although the center frequency is a very important determinant in this study, we selected the high frequency VHF band using the results of previous research. However, expert consultation, data analysis and simulation are required to continue to review the band that is suitable for deep tissue imaging and has no problem in commercialization.

For RFAI, focusing sources is not easy. In particular, if a high-frequency VHF band is used as in the present invention, since the wavelength (600 cm) is longer than that of living tissue, the living organ undergoes spatially almost the same phase (? / 4 = 150 cm) Since it is regarded as a plane wave, focusing itself becomes meaningless. Of course, if the frequency is raised by the methods such as 3GHz, 5GHz, and 10GHz, focusing can be performed to some extent, but the penetration depth is one-tenth of the high frequency VHF band. Assuming that it is used in hospitals, it is not easy to design an antenna with effective directivity that is far (tens of centimeters) far field (far field) to still focus even if using RF of several GHz band. In the case of RF / Microwave imaging, a near field focusing scheme using several RF generators is also proposed, but it does not seem to be an appropriate research direction because the volume of the source generating system becomes large. As a result, in the case of RFAI, attempts to improve the resolution of the contrast image by focusing the region of interest at the RF source stage appear to be a hindrance to commercialization.

Therefore, in order to improve the resolution of the contrast image of the living tissue while using the RF of the relatively low frequency band, a new detection that increases the SNR by obtaining the maximum effective (or correct) information from the sound wave generated through the thermoacoustic process Method is needed. To date, there have been no ultrasonic sensors for RFAI alone, and various types of ultrasonic receivers have been proposed for photoacoustic imaging systems. Among them, research on ultrasonic arrays employing microelectromechanical systems (MEMS) implemented from various types and materials, and studies on ultrasonic sensors utilizing the inherent characteristics of optical fibers have been conducted most actively . In addition to the Fresnel zone plate detector proposed by Hui Wang, there has been an interesting attempt to verify the effect of direct Fresnel diffraction of the near field by using optical Fresnel zone plate detector. However, the receiver structure is complicated and difficult to commercialize Seems to be.

The present invention proposes a Fabry-Perot interferometer type ultrasonic sensor that can be mass-produced through a microelectromechanical system (MEMS) process, can reduce the price of a product, and is lightweight, compact, high-precision, and free from electromagnetic interference. The Fabry-Perot interferometer type ultrasonic sensor of the present invention uses a Fabry-Perot resonator structure that can be single-ended in an optical fiber interferometer and will be described with reference to FIGS. 3 to 7 below.

FIG. 3 is a view for explaining a Fabry-Perot interferometer type ultrasonic sensor 100 according to an embodiment of the present invention.

3, a Fabry-Perot interferometer type ultrasonic sensor 100 according to an exemplary embodiment of the present invention includes a plurality of optical couplers 111, 112 and 113, an optical signal generator 120, a detector 130, And a sensor head 140, a photodiode 145, and a signal processor 150. The sensor head 140 includes a main sensor 141 and an auxiliary sensor 142 and a detector 130 including a photodiode or the like includes a first detector 131 and a second detector 132 . Hereinafter, a laser diode 120 will be described as an example of the optical signal generator 120.

The sensor head 140, that is, the main sensor 141 and the auxiliary sensor 142 each include a sensor tip array (for example, a one-dimensional or two-dimensional array sensor tip) for receiving ultrasound And the like). Such a sensor tip is provided at the ends of the optical fibers (e.g., single mode) (lines) 115 and 116 and has a Fabry-Perot resonator structure. A schematic perspective view of the sensor head 140 of the present invention is shown in Fig.

A signal branched by the first optical coupler 111 connected to the optical signal generated by the optical signal generator 120 is transmitted from the main sensor 141 through the second optical coupler 112, (Reflected wave) is photo-electrically converted in the first detector 131 via the main sensor 141, the optical fiber 115 and the second optical coupler 112, (150).

Another optical signal branched by the first optical coupler 111 is radiated to a target object (e.g., biological tissue) from the auxiliary sensor 142 via the third optical coupler 113 and the photodetector 145, The signal (reflected wave) is photoelectrically converted in the second detector 132 via the auxiliary sensor 142, the optical fiber 116 with the photodetector 145, the third optical coupler 113, and outputted to the signal processing unit 150 . The photodiode smoke 145 delays the optical signal for a predetermined time (e.g., 0.5 μs, 1.0 μs, 1.5 μs, 2.0 μs, ...) according to the design.

The auxiliary sensor 142 may have a low resolution Fabry-Perot resonator structure and may be inexpensive and the main sensor 141 has a high resolution Fabry-Perot resonator structure It can be expensive. For example, the auxiliary sensor 142 detects a wide phase range to which the phase of the optical signal belongs, and the main sensor 141 can be applied to detect the detailed phase of the optical signal within the corresponding wide phase range. The wide phase range of the auxiliary sensor 142 may be a low resolution area of the fringe range greater than 0.0005 fringe and the position of the main sensor 141 may be a high resolution area of the fringe range smaller than 0.0005 fringe . Here, the main sensor 141 and the auxiliary sensor 142 are provided so as to face the same or similar direction, that is, substantially the same direction with respect to the target object, and may be fabricated integrally. In some cases, when resolution is not important, only one of the main sensor 141 and the auxiliary sensor 142 may be used, and the rest may not be applied.

The signal processor 150 processes the photoelectrically converted signals received from the first detector 131 and the second detector 132 and generates a signal for outputting the ultrasound image of the target object. When only one of the main sensor 141 and the auxiliary sensor 142 is used, the signal processing unit 150 processes the photoelectrically-converted signal received from the first detector 131 or the second detector 132, The ultrasound system 100 may generate a signal for outputting the ultrasound image.

4 is a view for explaining the structure of the sensor array 200 provided at the end of the sensor head 140 of the present invention.

4, the sensor head 140 of the present invention, that is, the sensor array 200 provided at the ends of the main sensor 141 and the auxiliary sensor 142 is connected to the optical coupler 112/113 via the optical fiber 0.0 > 115/116 < / RTI >

The sensor array 200 has a sensor array configuration including optical fiber sensor tip (s) 220 arranged one-dimensionally or two-dimensionally at a plurality of holes of a SOI (Silicon on Insulator) substrate 210. Although the figure shows the two-dimensionally arrayed optical fiber sensor tip (s) 220, the optical fiber sensor tip (s) 220 can be arranged in various forms, such as two-dimensional arrays or one- .

In particular, in the present invention, each optical fiber sensor tip 220 has a structure in which a fiber ferro interferometer structure is formed by joining optical fiber lines at respective positions of a plurality of holes of the SOI substrate 210, A plurality of holes of the SOI substrate 210 are processed by a MEMS (Micro Electro Mechanical System) process, and a Fabry-Perot interferometer structure can be easily formed, thereby facilitating mass production and lowering the cost of a product. , Small size, high precision, and no electromagnetic interference.

5, a through hole is formed on the SOI substrate 210 through the MEMS process to the position of the optical fiber sensor tip (s) 220, and then, as shown in Figs. 6A and 6B, Similarly, at each of the through-holes of the SOI substrate 210, an additional process may be performed to join the fiber optic lines to form a Fabry-Perot interferometer structure.

5 is a view for explaining a MEMS processing process of the SOI substrate 210 for the sensor array 200 of the sensor head 140 of the present invention.

Referring to FIG. 5, first, an SOI substrate 210 is prepared (S110). The SOI substrate 210 may be a semiconductor wafer including a base layer silicon (layer) 10, an insulating film (layer) 11, and a surface silicon (layer) The insulating film 11 may be a silicon oxide film such as SiO 2, and may have a thickness of about 0.5 to 5 μm. The thickness of the base layer silicon 10 may be 200 to 1000 占 퐉, and the thickness of the surface silicon 12 may be 100 to 500 占 퐉.

When the SOI substrate 210 is prepared, a photoresist 13 is coated on the surface silicon 12 of the upper layer and a pattern is formed so that the photoresist is removed at the processing position 14 to be opened (S120). The processing position 14 to be the aperture becomes the position of the optical fiber sensor tip (s) 220.

The SOI substrate 210 on which the pattern of the photoresist 13 is formed may be wet etched or dry etched to form the opening pattern 15 of the upper surface silicon 12 (S130). In the wet etching method, a mixed solution of hydrofluoric acid (HF), nitric acid, or the like may be used. As the dry etching method, a reactive ion etching (RIE ) method or a deep reactive ion etching (DRIE ) method may be used.

After the opening pattern 15 is formed on the surface silicon 12 of the upper layer of the SOI substrate 210 as described above, the photoresist 16 is applied to the base layer silicon 10 of the lower layer of the SOI substrate 210, A pattern is formed so that the photoresist is removed at the processing position 17 (S140). The working position 17 to be an aperture is the position of the optical fiber sensor tip (s) 220.

The SOI substrate 210 on which the pattern of the photoresist 16 is formed on the base layer silicon 10 of the lower layer is wet etched or dry etched to form the opening pattern 18 of the base layer silicon 10 of the lower layer (S150). A solution such as KOH or TMAH (tetramethyl ammonium hydroxide) may be used in the wet etching method, and a dry etching method such as reactive ion etching (RIE ) or deep reactive ion etching (DRIE) may be used. Etching can be performed more deeply than the etching of the surface silicon 12.

The diameter of the opening 15 of the surface silicon 12 of the upper layer is smaller than the diameter of the opening 18 of the base layer silicon 10 and the diameter of the opening 15 of the base layer silicon 10 is smaller than the diameter of the opening 18 of the base layer silicon 10, The insulating film 11 remains under the surface silicon 12 in the opening 18 of the secondary silicon 10 and can be removed by wet or dry etching as described above. After machining the through hole with respect to the position of the optical fiber sensor tip (s) 220, a silicon resonator for fabricating a Fabry-Perot interferometer (or Fabry-Perot resonator) structure is obtained (S160).

The diameter of the opening 18 of the base layer silicon 10 and the diameter of the opening 15 of the surface silicon 12 may be 100 to 1000 占 퐉 and may be appropriately selected according to the design purpose. The diameter of the opening 18 of the base layer silicon 10 and the diameter of the opening 15 of the surface silicon 12 may be the same. However, the diameter of the opening 18 of the base layer silicon 10 may be wider than the diameter of the opening 15 of the surface silicon 12 to facilitate coupling of the fiber optic line for Fabry-Perot interferometer formation , Where the diameter difference may be between 50 and 500 mu m.

Next, as shown in FIG. 6, an additional process for forming the Fabry-Perot interferometer structure may be performed by joining the optical fiber lines at the respective positions of the through holes of the SOI substrate 210.

FIG. 6 is a view for explaining a Fabry-Perot interferometer structure formed in each hole of the MEMS processed SOI substrate 210 of the present invention.

6, the SOI substrate 210 is subjected to MEMS processing to form respective hole positions passing through the base layer silicon 10, the insulating film 11, and the surface silicon 12 of the SOI substrate 210 formed as shown in FIG. 5 A structure of a Fabry-Perot interferometer is formed.

That is, the optical fiber in which the first mirror 21 is formed on the optical fiber end portion where the core is wrapped by the cladding is inserted into the opening 18 of the base layer silicon 10, And the second mirror 22 and the membrane 23 can be formed on the surface silicon 12. [

A first mirror 21 formed on the end of the optical fiber wrapped by the cladding and coupled to the aperture 18 of the base layer silicon 10, A structure of the Fabry-Perot interferometer is formed, which includes a cavity, a second mirror 22 formed to cover the cavity, and a membrane 23 formed on the second mirror 22, and a one-dimensional or two- Fiber optic sensor tip (s) 220 can be obtained.

The first and second mirrors 21 and 22 may be formed of a metal oxide film such as TiO 2, SnO 2, or ZnO to have a thickness of about 1 to 5 μm. have.

On the other hand, the operation principle of the Fabry-Perot interferometer (or Fabry-Perot resonator) is well known and will be briefly described. The RF signal (e.g., laser) entering the Fabry-Perot interferometer is interfered with by the two mirrors 21 and 22 and the interfering light is returned to the detector 130 such as a photodiode through the couplers 112 and 113 again Lt; / RTI >

At this time, a round-trip phase shift ø that the RF signal (eg, laser) experiences while reciprocating in the Fabry-Perot interferometer (FPI) is expressed by Equation (2).

&Quot; (2) "

Here, lambda is an optical wavelength, n is a refractive index, and l is a resonator length. Fabry-Perot is multiple reflection interference, but when used as a sensor it mostly uses only a single round-trip phase shift. That is, although there are infinitely many interference waves due to infinitely many reflected waves in the resonator, two waves of the largest power (reflected light from the first mirror 21 and the reflected light from the second mirror 22 are reflected by the first mirror 21 ) Of the light source) are interested only in the interference of the light waves.

The sensitivity δø / δp of the resonator with respect to the acoustic pressure p can be expressed by the rate of change δl and δn of the resonator length and the refractive index with respect to the negative pressure change rate δp, and is expressed by the following equation (3).

&Quot; (3) "

Since the phase change of the interference waves in the resonator with respect to the acoustic pressure is mainly caused by strain, the second term, which is the rate of change in refractive index in the equation (3), is neglected. Assuming that the mirrors on both sides of the resonator are the same, the transmittance can be expressed by Equation (4), where R is the reflectance and T is the transmittance with respect to the first mirror.

&Quot; (4) "

대신 사용하는 보조함수이고, Finesse

는 [수학식5]로 표현된다. Where F is Finesse,

Instead, it's an auxiliary function, Finesse

Is expressed by Equation (5).

&Quot; (5) "

The transmittance T according to this Finesse is shown in FIG.

In the Fabry-Perot interferometer shown in FIG. 8, the transmittance T according to the Finesse can be used to estimate the dynamic range of the sensor, so it is necessary to determine the Finesse value according to the purpose of the sensor. Most of the Finesse used in the sensor is determined to have a low sensitivity for flat sensitivity and wide dynamic range.

In the present invention, the principle of the Fabry-Perot interferometer is used in the present invention. As described above, the end of the sensor tip 200 is formed through a micro electro mechanical system (MEMS) process to facilitate the fabrication of the array.

FIG. 9 is a hypothetical view of the ultrasonic output waveform showing the RF-Acoustic response characteristic of the phantom to the RF pulse signal input (for example, a pulse width of 1 μs). The latency time between the input and the output in the bio- (Transfer) and thermoacoustic process (thermoacoustic process) is almost negligible, it depends only on the time of the acoustic wave. Acoustic waves propagate at a rate of 1.54 mm / μs in living tissues (eg tissue average), so that the main lobe experiences a time delay of several tens of microseconds. As shown in the figure, the side lobes due to reverberation Can be expected.

As described above, the Fabry-Perot interferometer type ultrasonic sensor 100 according to the present invention can be mass-produced through a microelectromechanical system (MEMS) process and can lower the product price, , Small size, high precision and no electromagnetic interference. In other words, mass production is possible through the MEMS (Micro Electro Mechanical System) process and the price of the product can be lowered. Also, by replacing the conventional piezoelectric ultrasonic sensor with the optical fiber ultrasonic sensor, there is no interference by electromagnetic waves, (RFAI, RF ultrasound image) system, it is possible to detect a region of interest (ROI) such as the boundary of a cancer tissue. It is possible to improve the resolution of the ultrasonic probe and to increase the geometric freedom when manufacturing the ultrasonic probe.

As described above, the present invention has been described with reference to particular embodiments, such as specific elements, and specific embodiments and drawings. However, it should be understood that the present invention is not limited to the above- Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the essential characteristics of the invention. Therefore, the spirit of the present invention should not be construed as being limited to the embodiments described, and all technical ideas which are equivalent to or equivalent to the claims of the present invention are included in the scope of the present invention .

The optical couplers 111, 112, and 113,
The optical signal generator 120,
Detector 130,
The smoke of light (145)
The signal processor 150,
The sensor head 140,
The main sensor 141,
The auxiliary sensor (142)
Detector 130,
The first detector 131,
The second detector 132,
The sensor array (200)
SOI substrate 210,
The fiber optic sensor tip (220)
The base layer silicon (10)
The insulating film (11)
The surface silicon (12)

Claims (7)

The optical fiber sensor tip comprising a one-dimensional or two-dimensional arrangement of the plurality of holes of the SOI substrate,
Each of the optical fiber sensor tips has a structure in which a fiber ferro interferometer is formed by combining optical fiber lines at positions of each of the plurality of holes
And an optical fiber array. A first optical coupler for transmitting and receiving optical signals;
A main sensor connected to the first optical coupler through an optical fiber, in the form of a sensor array including an optical fiber sensor tip arranged one-dimensionally or two-dimensionally at a plurality of holes of an SOI substrate, each optical fiber sensor tip comprising: At each location, the main sensor comprising a structure that combines optical fiber lines to form a Fabry-Perot interferometer;
A first detector for photoelectrically converting the reflected wave received by the main sensor through the optical fiber line via the first optical coupler; And
A signal processor for processing a signal output from the first detector and generating a signal for outputting an ultrasound image,
And an ultrasonic sensor. 3. The method of claim 2,
A second optical coupler;
An auxiliary sensor formed on the SOI substrate and having a sensor array having the same structure as the Fabry-Perot interferometer structure of the main sensor array;
A photodetector included between the second optical coupler and the auxiliary sensor; And
Further comprising a second detector for photoelectrically converting the reflected wave received by the auxiliary sensor through the optical fiber line via the second optical coupler,
Wherein the signal processing unit processes signals output from the first detector and the second detector to generate a signal for outputting the ultrasound image. The method of claim 3,
Wherein the auxiliary sensor detects a phase range to which a phase of an optical signal belongs, and the main sensor detects a detailed phase of the optical signal within the phase range. 3. The method of claim 2,
Wherein the structure of the Fabry-Perot interferometer of each optical fiber sensor tip comprises:
A plurality of holes formed in the base layer silicon, the insulating film, and the surface silicon of the SOI substrate,
Wherein an opening diameter of the surface silicon is narrower than an opening diameter of the base layer silicon. 6. The method of claim 5,
Wherein a hole of the surface silicon narrower than an opening diameter of the base layer silicon is used as an air cavity. 3. The method of claim 2,
Wherein the structure of the Fabry-Perot interferometer of each optical fiber sensor tip comprises:
A first mirror coupled to the opening of the base layer silicon, the first mirror being formed at an end of the optical fiber wrapped with a cladding by a cladding, the cavity formed by the hole of the surface silicon, a second mirror formed to cover the cavity, And a membrane formed on the mirror.

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