CN204535846U - Measure the optical fiber grating sonic device of high-frequency transducer near-field acoustic pressure distribution - Google Patents

Abstract

The utility model discloses an optical fiber grating hydrophone for measuring the near-field sound pressure distribution of a high-frequency transducer. Traditional piezoelectric ceramic or PVDF ultrasonic hydrophones have low spatial resolution and strong scattering of high-frequency sound waves. The utility model comprises a D-type standard single-mode optical fiber, a polymer ridge-shaped film optical waveguide Bragg grating and a polymer coating filling layer; the D-type standard single-mode optical fiber is a silicon oxide standard single-mode optical fiber whose side is polished to form a coating groove; polymerization The object ridge type thin film optical waveguide Bragg grating covers the bottom surface of the D-type standard single-mode optical fiber filling groove, and the polymer coating filling layer covers the polymer ridge type thin film optical waveguide Bragg grating; the polymer ridge type thin film optical waveguide Bragg grating includes Polymer Ridge Thin Film Optical Waveguides and Grating Scribes. The utility model can solve the problems of low measurement efficiency, poor precision and low sound pressure sensitivity of the high-frequency transducer sound field, and is suitable for near-field characteristic measurement of the high-frequency sound field.

Description

Fiber Bragg Grating Hydrophone for Measuring Near Field Sound Pressure Distribution of High Frequency Transducer

technical field

The utility model belongs to the field of high-frequency ultrasonic field measurement, in particular to an optical fiber grating hydrophone for measuring the near-field sound pressure distribution of a high-frequency transducer.

Background technique

With the widespread use of medical ultrasound, high-frequency transducers are used more and more widely, and the measurement of their sound field characteristics, especially the near-field sound pressure distribution, is attracting people's attention. The sound field characteristics of high-frequency transducers are usually detected by hydrophones, and the near-field sound pressure distribution is acquired by spatial scanning of hydrophones to obtain acoustic signals (amplitude, phase) at different positions and then obtained by data processing. Considering the need to reduce the disturbance of the hydrophone to the sound field to be measured as much as possible during near-field measurement, it is generally required that the effective size of the hydrophone should be much smaller than a quarter of the wavelength of the sound wave. In addition, according to the Nyquist sampling law, the accuracy and effectiveness of sound pressure signal acquisition are determined by the density of sampling data points within a single wavelength, and the density of sampling points depends on the effective size and spatial scanning accuracy of the hydrophone. Considering the above two factors comprehensively and reducing the effective size of the sensitive element of the hydrophone, the near-field sound pressure distribution of the high-frequency transducer can be accurately measured and drawn. Traditional hydrophones are usually made of piezoelectric ceramics or PVDF films as sensitive elements, which are limited by the design and manufacturing process, and their effective size is generally on the order of a few millimeters to tens of millimeters. For high-frequency transducers with a working frequency of 1 MHz or higher, the corresponding sound wave wavelength is below 1.5 mm. According to the above conclusions, traditional hydrophones will not be able to accurately map the near-field sound pressure distribution of the transducer.

Thanks to the small size of the optical fiber (standard single-mode or multi-mode optical fiber diameter is only 0.1mm), strong multiplexing capability and the rapid development of fiber grating sensing technology, fiber grating is used as the sensitive element of the hydrophone. It has become a current research and development hotspot, and it is expected to solve engineering application problems such as small-scale arrays and large-scale multiplexing. Among them, the fiber Bragg grating (FBG) is a grating with a periodic distribution of refractive index formed at the fiber core by photolithography. The sensitive components of the earphone can obtain much higher spatial resolution and directivity than the traditional piezoelectric hydrophone, thus meeting the basic requirements for spatial resolution and sound field perturbation in the near-field measurement of high-frequency hydrophones. However, bare fiber gratings used as hydrophones often have the problem of low sound pressure sensitivity (only 0.007nm/MPa). Therefore, in practical engineering applications, complex external structure sensitization technology and higher-precision wavelength resolution are usually used. The former will increase the size of the hydrophone and thus reduce the spatial resolution and measurement accuracy, while the latter will increase the complexity of the system and the difficulty of detection. It is also worth mentioning that the FBG hydrophone using the external structure sensitization technology can only be used as a single-array device, which loses the inherent advantage of optical fiber arraying. Therefore, improving the sound pressure sensitivity of the hydrophone by sensitizing the internal structure is expected to achieve accurate measurement of the near-field sound pressure distribution of the high-frequency transducer.

The sound pressure sensitivity of the fiber grating hydrophone is related to the Young's modulus of the silica glass material. Using materials with a smaller Young's modulus to enhance the sensitivity design of the internal structure of the hydrophone's sensitive components is expected to improve the sound pressure sensitivity. Improve the above existing problems. The Young's modulus (1GPa) of polymer materials is much smaller than that of silica glass (70GPa), and it is also the basic material for making integrated optical waveguide devices, with low cost, low optical transmission loss, and high refractive index. , small device size, easy integration and other advantages. Using the currently mature semiconductor film and other large-scale optoelectronic device integration processes (film throwing, photolithography, nanoimprinting, etc.), polymer micro-nano optical waveguides and Bragg grating waveguide structures with excellent optical properties can be prepared. On the other hand, optical fibers with D-shaped structure prepared by side polishing technology have also been mature and widely used as the basic unit of optical waveguides and optical sensors. If the polymer thin film waveguide Bragg grating and the D-structure optical fiber are combined as the sensitive element of the hydrophone, the advantages of the light-guiding characteristics and evanescent wave coupling effect of the D-type optical fiber and the high sound pressure sensitivity of the polymer grating can be used to achieve high Accurate measurement of the near-field performance of the high-frequency sound field, and at the same time is expected to achieve a breakthrough in the field of weak-sound high-frequency signal detection.

Contents of the invention

The purpose of this utility model is to solve the problems of traditional piezoelectric ceramics or PVDF ultrasonic hydrophones with large size, low spatial resolution, strong scattering of high-frequency sound waves, and low sound pressure sensitivity of ordinary bare fiber grating hydrophones, etc., to provide a A fiber grating hydrophone for measuring the near-field sound pressure distribution of a high-frequency transducer. The fiber grating hydrophone has the advantages of compact structure, high spatial resolution, high sound pressure sensitivity, and arrayability. A series of problems such as low efficiency, poor precision, and low sound pressure sensitivity exist in the measurement of the sound field of the transducer, and it is suitable for the near-field characteristic measurement of the high-frequency sound field.

The utility model is achieved through the following technical solutions:

The utility model comprises a D-type standard single-mode optical fiber, a polymer ridge-type film optical waveguide Bragg grating and a polymer coating filling layer; Optical fiber; the polymer ridge-type thin-film optical waveguide Bragg grating covers the bottom surface of the D-type standard single-mode optical fiber, and the polymer coating filling layer covers the polymer ridge-type thin-film optical waveguide Bragg grating; the polymer ridge-type The thin-film optical waveguide Bragg grating includes polymer ridge-type thin-film optical waveguide and grating reticles; the grating reticles are made in the polymer ridge-type thin-film optical waveguide by ultraviolet light exposure.

The length of the filling and coating groove is 5-10 mm, and the groove depth is 1-2 μm.

The material of the polymer coating filling layer is polyamine.

The length of the polymer ridge film optical waveguide is 3-8 mm, and the thickness is 1-2 μm.

The material of the polymer ridge film optical waveguide may be polymethyl methacrylate, polystyrene or polycarbonate.

The grating lines change periodically, the period is 572-660nm, and the total length of the formed grating is 4-8mm.

The beneficial effects of the utility model are: the utility model has the characteristics of compact structure, small size, good spatial resolution, high sound pressure sensitivity, arrayable and good phase-amplitude consistency between array elements, and is suitable for high-frequency switching Near-field sound pressure distribution measurement of transducers, which can realize near-field detection of high-frequency transducers of 200kHz and above.

Description of drawings

Fig. 1 is the structural representation of the utility model.

In the figure: 1. D-type standard single-mode optical fiber, 2. Polymer ridge-type film optical waveguide Bragg grating, 3. Polymer coating filling layer.

Detailed ways

Below in conjunction with accompanying drawing and embodiment the utility model is described in detail.

As shown in Figure 1, the fiber Bragg grating hydrophone for measuring the near-field sound pressure distribution of the high-frequency transducer consists of a D-type standard single-mode fiber 1, a polymer ridge-shaped thin-film optical waveguide Bragg grating 2 and a polymer-coated filling layer 3 components; D-type standard single-mode optical fiber 1 is a silicon oxide standard single-mode optical fiber whose side is polished to form a coating groove. The ridge type film optical waveguide Bragg grating 2 covers the bottom surface of the filling groove of the D-type standard single-mode fiber 1; the polymer coating filling layer 3 covers the polymer ridge type film optical waveguide Bragg grating 2; the polymer coating filling layer The material of 3 is polyamine, which is used for encapsulation protection and further acoustic sensitization; polymer ridge film optical waveguide Bragg grating 2 is composed of polymer ridge film optical waveguide and grating lines; the length of polymer ridge film optical waveguide The thickness is 3-8mm, and the thickness is 1-2μm. The material can be polymethyl methacrylate, polystyrene or polycarbonate; the grating lines are made in the polymer ridge-shaped film optical waveguide by ultraviolet light exposure, which is periodically changed. , the period is 572-660nm, and the total length of the formed grating is 4-8mm.

The working principle of the fiber grating hydrophone for measuring the near-field sound pressure distribution of the high-frequency transducer is as follows:

The sensing unit of the fiber grating hydrophone is placed in the sound field, and the sound signal to be measured acts vertically on the polymer-coated filling layer 3, so that the polymer-coated filling layer 3 generates a vibration component along the fiber axis. This vibration component has the following two effects: First, the forced vibration of the polymer-coated filling layer 3 will directly act on the polymer ridge-shaped film optical waveguide Bragg grating 2, so that the grating pitch is the same as the acoustic signal to be measured Frequency change; since the Young's modulus of the polymer-coated filling layer 3 is much smaller than that of vitreous silica, the resulting strain is relatively larger, and the resulting frequency shift of the grating reflection spectrum is also larger. Secondly, the axial vibration component of the polyamine material will also be reflected by the two polished end faces of the D-type standard single-mode optical fiber 1 filling the coating groove, forming an acoustic resonant cavity, which helps to further amplify the acoustic signal, and its The resonant frequency is determined by the cavity length of the resonant cavity and the sound velocity in the polyamide material. In terms of the interaction between light and grating and optical signal detection, the incident light (broadband continuous light source) is coupled in from one end face of the optical fiber and propagates along the optical fiber to the polishing place, that is, the polymer ridge-type film optical waveguide Bragg grating 2, a part The light energy will be coupled into the polymer ridge film optical waveguide Bragg grating 2 in the form of evanescent light, and then reflected by the grating to form a reflection spectrum; the remaining light energy will pass through the other end of the fiber to form a transmission spectrum . Since the transmission spectrum contains a large proportion of optical signals that do not interact with the grating, the signal-to-noise ratio is worse than that of the reflection spectrum. In practical applications, the frequency shift of the reflection spectrum is chosen to be tested. Under the action of the sound signal to be measured, by measuring the frequency shift of the reflected spectral signal, information such as the sound pressure intensity, phase, and amplitude corresponding to the sound field to be measured can be obtained.

The measurement effect of the fiber grating hydrophone on the near-field sound pressure distribution of the high-frequency transducer is described below in conjunction with specific numerical values.

If the length of the filling groove (that is, the length of the acoustic resonance cavity) is 5mm, the corresponding resonance acoustic wave wavelength l is 10mm, and the sound velocity c of the polyamine material is 2000m/s, then the resonance frequency can be calculated according to f=c/l f is 200kHz. That is, the fiber grating hydrophone is particularly sensitive to the acoustic signal of 200 kHz, in addition to responding to the acoustic signal of any frequency.

The above specific embodiments are used to explain the utility model, rather than to limit the utility model. Within the spirit of the utility model and the protection scope of the claims, any modifications and changes made to the utility model fall into the scope of the utility model. A new type of protection.

Claims (6)

1. The fiber grating hydrophone for measuring the near-field sound pressure distribution of the high-frequency transducer comprises a D-type standard single-mode optical fiber, a polymer ridge-type film optical waveguide Bragg grating and a polymer coating filling layer, and is characterized in that: The D-type standard single-mode optical fiber is a silicon oxide standard single-mode optical fiber whose side is polished to form a coating groove; the polymer ridge-shaped thin-film optical waveguide Bragg grating covers the bottom surface of the D-type standard single-mode optical fiber. The coating filling layer is covered on the polymer ridge-type thin film optical waveguide Bragg grating; the polymer ridge-type thin-film optical waveguide Bragg grating includes the polymer ridge-type thin-film optical waveguide and grating lines; the grating lines are made by ultraviolet light exposure In polymer ridge thin film optical waveguides. 2. The fiber Bragg grating hydrophone for measuring the near-field sound pressure distribution of a high-frequency transducer according to claim 1, characterized in that: the length of the filling groove is 5-10 mm, and the groove depth is 1-2 μm. 3. The fiber Bragg grating hydrophone for measuring the near-field sound pressure distribution of a high-frequency transducer according to claim 1, wherein the material of the polymer-coated filling layer is polyamine. 4. The fiber grating hydrophone for measuring the near-field sound pressure distribution of a high-frequency transducer according to claim 1, characterized in that: the length of the polymer ridge film optical waveguide is 3 to 8 mm, and the thickness is 1 mm. ~2μm. 5. the fiber grating hydrophone measuring the near-field sound pressure distribution of the high-frequency transducer according to claim 1, is characterized in that: the material of the polymer ridge-type film optical waveguide can be polymethyl methacrylate , polystyrene or polycarbonate. 6. The fiber grating hydrophone for measuring the near-field sound pressure distribution of a high-frequency transducer according to claim 1, characterized in that: the grating lines vary periodically, with a period of 572 to 660 nm, and the formed grating The total length is 4-8mm.