CN103913787A - Lens structure body of acoustical super lens, acoustical super lens and imaging device thereof - Google Patents

Abstract

The invention provides a lens structure body of an acoustical super lens, the acoustical super lens and an imaging device thereof. The acoustical super lens comprises the lens structure body and light media, the imaging device of the acoustical super lens comprises a signal generator, a power amplifier, a transmitting transducer, the acoustical super lens and a receiving transducer array, the signal generator is connected with the power amplifier through a transmission line, the power amplifier is connected with the transmitting transducer through a transmission line, the front face of the lens structure body is a lens receiving face of the acoustical super lens, the lens receiving face of the acoustical super lens right faces the signal emission direction of the transmitting transducer, the receiving transducer array comprises a plurality of receiving transducers, and the receiving transducers are arranged at the geometric center of a square through hole of the acoustical super lens. According to the lens structure body of the acoustical super lens, the acoustical super lens and the imaging device thereof, high-resolution acoustical imaging can be conducted on an object at a certain distance, and evanescent waves can be well received, amplified and used for improving imaging quality.

Description

A kind of mirror structure of acoustics super lens and acoustics super lens and imaging device thereof

Technical field

The present invention relates to acoustics imaging field, particularly a kind of mirror structure of acoustics super lens and acoustics super lens and imaging device thereof.

Background technology

Acoustics imaging is a kind of basic skills of detecting material structure and composition composition.Traditional acoustics imaging equipment is due to the restriction of diffraction limit, and its imaging resolution can only reach surveys 1/2nd of wavelength.The ripple that those horizontal wave vectors are greater than the wave vector k of background media is called evanescent wave, the detailed information that they are carrying object.In all natural mediums, once evanescent wave leaves object, carry out the decay of exponential type, cannot be received by traditional imaging device, thereby limit imaging resolution.

In recent years, acoustics metamaterial is because its novel acoustic effect and potential using value are subject to extensive concern.Wherein just there are some in theory, experimentally to utilize acoustics metamaterial to break the trial of imaging diffraction limit, obtain various acoustics metamaterials and also shown manual control, handled evanescent wave to improve the possibility of imaging resolution.For example, document S.Zhang, L.L.Yin, and N.Fang, Phys.Rev.Lett.102,194301 (2009) and F.Lemoult, M.Fink, and G.Lerosey, Phys.Rev.Lett.107,064301 (2011) has designed the two negative acoustics metamaterial by negative density, negative bulk modulus, and produces a super lens with this.Evanescent wave is not only decayed when through this structure, has obtained on the contrary enhancing.Document J.Zhu, J.Christensen, J.Jung, L.Martin-Moreno, X.Yin, L.Fok, X.Zhang, and F.J.Garcia-Vidal, Nat.Phys.7,52 (2011) have designed the acoustics super lens of a three-dimensional perforation holes structure.Coupling in this structure utilization perforation between Fabry-Perot resonance and evanescent wave, makes evanescent wave can transfer to output terminal, finally obtains the high resolving power of 1/50th wavelength, and this is the highest resolution that can reach experimentally so far.

But in all these researchs, the object being imaged must be placed on the surface of imaging device, guarantee evanescent wave signal is received by equipment before disappearing completely like this.Here " surface " refers to that object can not exceed to the distance of imaging device receiving end the per mille of surveying wave length of sound, and some even requires object directly and the receiving end of imaging device is close together.This requirement has had a strong impact on the feasibility in practical application undoubtedly, and such as the inspection to hypodermis structure in medical diagnosis, the detection of industrial nondestructive testing to material internal defect etc., they all cannot meet this requirement.

Summary of the invention

Technical matters to be solved by this invention is, traditional acoustics imaging equipment is due to the restriction of diffraction limit, its imaging resolution can only reach surveys 1/2nd of wavelength, and high-resolution acoustics super lens requires the object being imaged must be placed on the surface of imaging device, have a strong impact on the feasibility in practical application.

Technical scheme of the present invention is as follows:

A mirror structure for acoustics super lens, described mirror structure is the Nogata body structure of being made up of hard material, two foursquare faces of described Nogata body are respectively lens front and lens bottom surface; The through hole that is provided with Nogata body structure between described lens front and lens bottom surface, described through hole has multiple, is the square trellis of transverse and longitudinal and arranges; At the positive place of lens plane, the solid walls thickness a between length of side a and the adjacent through-holes of described through hole ₁sum is less than 5mm.

Preferably, the solid walls thickness a between length of side a and the adjacent through-holes of described through hole ₁sum is less than 1mm.

Preferably, in the positive place of lens plane, the length of side a of described through hole is not less than the solid walls thickness a between adjacent through-holes ₁.

Preferably, the material of described mirror structure is copper or steel.

A kind of acoustics super lens, comprises the mirror structure described in lightweight medium and the claims 1～4 any one; Described lightweight Filled Dielectrics is in the through hole of described mirror structure; The density p of described lightweight medium _abe less than described mirror structure density p _b1/5.

Preferably, described lightweight medium is gas.

Preferably, described lightweight medium is water.

A kind of acoustics super lens imaging device, comprises the acoustics super lens described in signal generator, power amplifier, transmitting transducer, receiving transducer array, claim 5～7 any one; Described signal generator is connected with power amplifier by transmission line, and described power amplifier is connected with described transmitting transducer by transmission line; Described signal generator produces electric signal, described power amplifier amplifies electric signal power, electric signal is converted into the acoustic signals identical with electric signal frequency by described transmitting transducer, and described receiving transducer array is used for receiving acoustic signals and described acoustic signals is converted into electric signal; The front of described mirror structure is the lens receiving plane of acoustics super lens, and the lens receiving plane of described acoustics super lens is right against the signal transmit direction of described transmitting transducer; Described receiving transducer array comprises multiple receiving transducers; Described receiving transducer is placed on the geometric center of the through hole of described mirror structure; The corresponding receiving transducer of geometric center of each through hole of described mirror structure; The multiple receiving transducers that are placed in the through hole of described mirror structure form described receiving transducer array; Wavelength corresponding to described signal generator frequency of operation is to satisfy condition between the mirror structure height L of λ and described acoustics super lens: L=n λ/2, wherein n is positive integer.

Wherein, Nogata body refers to that two faces that are parallel to each other are foursquare rectangular parallelepipeds; The height L of mirror structure refers to the distance between described mirror structure front and bottom surface.

Technique effect of the present invention is:

1, when the present invention utilizes evanescent wave to propagate in the acoustics super lens of anisotropic, the enlargement factor of its sound pressure amplitude and evanescent wave lateral wave vector k _ybetween be linear increment relation, in other words, larger lateral wave vector k _ycarrying object is more the information of details, and larger k _ythe multiple being exaggerated in the time that this inside configuration is propagated also larger, like this, different wave vectors are exaggerated multiple difference, see that on the whole imaging results has been equivalent to improve the contrast of picture, thereby can be used for improving the image contrast of the imaging device such as medical diagnosis, industrial nondestructive testing.

2, the acoustics super lens that the present invention adopts is different from negative index super lens.The main path that realizes negative index is to utilize the local resonance of microstructure, and this resonance brings very large energy loss can have a strong impact on the coupled mode of evanescent wave, thereby affects imaging resolution.There is not local resonance effect in acoustics super lens of the present invention, energy loss is very little, and evanescent wave can be received well, amplify and for improving image quality.

3, acoustics super lens of the present invention is in realizing high-resolution imaging, the target object of also having realized the receiving end certain distance l that adjusts the distance carries out imaging, can be applicable to the detection to material internal defect in the inspection to hypodermis structure and industrial nondestructive testing in medical diagnosis.

4, super lens of the present invention simple in structure, be easy to preparation, operation element volume is little, designability is strong.

Accompanying drawing explanation

Fig. 1 is acoustics super lens schematic diagram.

Fig. 2 is acoustics super lens imaging device schematic diagram.

Embodiment

Below in conjunction with accompanying drawing, content of the present invention is described in further detail.

Embodiment 1

In conjunction with Fig. 1, a kind of mirror structure of acoustics super lens, described mirror structure is the Nogata body structure of being made up of hard material, and described mirror structure material can be copper or steel etc., and two foursquare faces of described Nogata body are respectively lens front and lens bottom surface; The through hole that is provided with Nogata body structure between described lens front and lens bottom surface, described through hole has multiple, is the square trellis of transverse and longitudinal and arranges; In the positive place of lens plane, because the solid walls thickness a between the length of side a of described through hole and adjacent through-holes ₁sum Λ has determined the resolution of acoustics super lens, the less representation theory of Λ resolution can be higher, generally get excitation sound wave tens of/mono-, and excitation sound wave frequency is generally KHz level, so the solid walls thickness a between length of side a and the adjacent through-holes of described through hole ₁sum should be less than 5mm, the solid walls thickness a between length of side a and the adjacent through-holes of preferred described through hole ₁sum is less than 1mm.As preferred version, in the positive place of lens plane, the length of side a of described through hole is not less than the solid walls thickness a between adjacent through-holes ₁, because the too small meeting of through hole causes the generation of viscid impedance, thereby be lowered into image quality.

Embodiment 2

In conjunction with Fig. 1, a kind of acoustics super lens, comprises the mirror structure described in lightweight medium and embodiment 1; Described lightweight Filled Dielectrics is in the through hole of described mirror structure; The density p of described lightweight medium _abe less than described mirror structure density p _b1/5; Described lightweight medium can be gas, as air, nitrogen, oxygen etc., can be also water;

The equivalent acoustics density p of this acoustics super lens and the expression formula of bulk modulus κ are:

$\mathrm{\ρ}=\left(\begin{array}{cc}{\mathrm{\ρ}}_0& 0\\ 0& {\mathrm{\ρ}}_y\end{array}\right),\left\{\begin{array}{c}\frac{1}{{\mathrm{\ρ}}_x}=\frac{1}{1+\mathrm{\η}}(\frac{1}{{\mathrm{\ρ}}_A}+\frac{\mathrm{\η}}{{\mathrm{\ρ}}_B})\\ {\mathrm{\ρ}}_y=\frac{{\mathrm{\ρ}}_A+{\mathrm{\η\ρ}}_B}{1+\mathrm{\η}}\end{array}\right.,\frac{1}{\mathrm{\κ}}=\frac{1}{1+\mathrm{\η}}(\frac{1}{{\mathrm{\κ}}_A}+\frac{\mathrm{\η}}{{\mathrm{\κ}}_B})$

Wherein, η=a ₁solid walls thickness described in the plane of the positive place of/a lens between adjacent through-holes and the length of side a ratio of described through hole, ρ _a, ρ _bbe respectively the density of lightweight medium and mirror structure, κ _a, κ _bbe respectively the bulk modulus of lightweight medium and mirror structure.The density p of this lightweight medium _abe less than described mirror structure density p _b1/5, therefore obtain the equivalent acoustics density relationship ρ of super lens _x< ρ _y, equivalent density tensor is anisotropic.

Owing to not relating to negative material parameter, the dispersion relation in this EFFECTIVE MEDIUM is expressed as:

$\frac{k_{\mathrm{mx}}^2}{{\mathrm{\&rho;}}_x}+\frac{k_{\mathrm{my}}^2}{{\mathrm{\&rho;}}_y}=\frac{{\mathrm{\&omega;}}^2}{\mathrm{\&kappa;}}$

Wherein ω is angular frequency, k _mx, k _myfor the wave vector along x, y direction respectively, at anisotropic ρ _x< ρ _ycondition under, can be obtained by dispersion relation

Suppose that length is that the super lens of L is placed in background media, a tangential wave vector is k _yplane wave impinge perpendicularly on the lens receiving plane of super lens, omit time factor e ^{-i ω t}, being distributed as of whole sonic pressure field:

$p\left(x\right)=P_i\left\{\begin{array}{c}{e}^{i\sqrt{k^2-k_y^{2}x}+{\mathrm{Re}}^{-i\sqrt{k^2-k_y^{2}x}}},x<0\\ {\mathrm{Ae}}^{{\mathrm{ik}}_{\mathrm{mx}}x}+{\mathrm{Be}}^{-{\mathrm{ik}}_{\mathrm{mx}}x},0<x<L\\ {\mathrm{Te}}^{i\sqrt{k^2-k_y^2}(x-L),}x>L\end{array}\right.$

Wherein, P _ifor incident wave amplitude, k is the incident wave wave vector under background media, and R and T are reflection, transmission coefficient, and A and B are the amplitude coefficient of acoustics super lens inside along x positive and negative direction propagation wave.In the continuity in conjunction with boundary condition x=0 and x=L place sonic pressure field, velocity field, can obtain above-mentioned coefficient:

$A=\frac{2}{M}\sqrt{1-\frac{k_y^2}{k^2}}(\frac{k}{k_{\mathrm{mx}}}+\sqrt{1-\frac{k_y^2}{k^2}})$

$B=\frac{2}{M}\sqrt{1-\frac{k_y^2}{k^2}}(\frac{k}{k_{\mathrm{mx}}}-\sqrt{1-\frac{k_y^2}{k^2}})e^{2{\mathrm{ik}}_{\mathrm{mx}}L}$

$R=\frac{(e^{2i{k}_{\mathrm{mx}}L}-1)}{M}[{\left(\frac{k}{k_{\mathrm{mx}}}\right)}^2-(1-\frac{k_y^2}{k^2})]$

$T=\frac{{4e}^{i{k}_{\mathrm{mx}}L}}{M}\frac{k}{k_{\mathrm{mx}}}\sqrt{1-\frac{k_y^2}{k^2}}$

Wherein $M={(\frac{k}{k_{\mathrm{mx}}}+\sqrt{1-\frac{k_y^2}{k^2}})}^2-{(\frac{k}{k_{\mathrm{mx}}}-\sqrt{1-\frac{k_y^2}{k^2}})}^2{e}^{2{\mathrm{ik}}_{\mathrm{mx}}L}.$ Meet Fabry-Perot resonant condition k at super lens L _mxl=n π, getting n=1 is here example, above-mentioned simplification of coefficient is:

$A=\frac{1}{2}(1+\frac{k_{\mathrm{mx}}}{k}\sqrt{1-\frac{k_y^2}{k^2}})$

$B=\frac{1}{2}(1-\frac{k_{\mathrm{mx}}}{k}\sqrt{1-\frac{k_y^2}{k^2}})$

R＝0 T＝-1

Now the evanescent wave of super lens internal communication (| k _y| > k) amplitude is at k _yin the situation of >>k, the multiple that evanescent wave amplitude is exaggerated and k _y/ k ratio relation in direct ratio, carries the evanescent wave of less detailed information, its k _ylarger, the multiple being exaggerated in acoustics super lens inside is also larger.Acoustics super lens of the present invention utilizes this characteristic just, not only can carry out sub-wavelength imaging, more utilizes the amplification of structure to evanescent wave, has greatly improved the contrast of imaging.This contrast significantly promotes and also makes can the adjust the distance object of lens receiving plane certain distance of acoustics super lens of the present invention carry out sub-wavelength imaging.

Embodiment 3

In conjunction with Fig. 1, Fig. 2, a kind of acoustics super lens imaging device, comprises the acoustics super lens described in signal generator, power amplifier, transmitting transducer, receiving transducer array, embodiment 2; Described signal generator is connected with power amplifier by transmission line, and described power amplifier is connected with described transmitting transducer by transmission line; Described signal generator produces electric signal, described power amplifier amplifies electric signal power, electric signal is converted into the acoustic signals identical with electric signal frequency by described transmitting transducer, and described receiving transducer array is used for receiving acoustic signals and described acoustic signals is converted into electric signal; The front of described mirror structure is the lens receiving plane of acoustics super lens, and the lens receiving plane of described acoustics super lens is right against the signal transmit direction of described transmitting transducer; Described receiving transducer array comprises multiple receiving transducers; Described receiving transducer is placed on the geometric center of the through hole of described mirror structure; The corresponding receiving transducer of geometric center of each through hole of described mirror structure; The multiple receiving transducers that are placed in the through hole of described mirror structure form described receiving transducer array; For meeting the requirement of Fabry-Perot resonance, wavelength corresponding to described signal generator frequency of operation is to satisfy condition between the mirror structure height L of λ and described acoustics super lens: L=n λ/2, wherein n is positive integer.

Signal generator produces pumping signal, sending excitation sound wave through power amplifier rear drive transmitting transducer gets on object under test, excitation sound direction of wave travel is right against lens receiving plane of the present invention, object under test is placed on the front of super lens receiving plane, distance is l, and l is preferably no more than 0.06 λ.A receiving transducer is installed in each through hole of described mirror structure, form described receiving transducer array, the signal that receiving transducer is received is input in the data processing software of computing machine, the signal detecting in each perforation is shown on its corresponding position, finally obtain imaging results.

Claims (8)

1. a mirror structure for acoustics super lens, is characterized in that, described mirror structure is the Nogata body structure of being made up of hard material, and two foursquare faces of described Nogata body are respectively lens front and lens bottom surface; The through hole that is provided with Nogata body structure between described lens front and lens bottom surface, described through hole has multiple, is the square trellis of transverse and longitudinal and arranges; At the positive place of lens plane, the solid walls thickness a between length of side a and the adjacent through-holes of described through hole ₁sum is less than 5mm.

2. a mirror structure for acoustics super lens, is characterized in that, the solid walls thickness a between length of side a and the adjacent through-holes of described through hole ₁sum is less than 1mm.

3. the mirror structure of acoustics super lens according to claim 1, is characterized in that, in the positive place of lens plane, the length of side a of described through hole is not less than the solid walls thickness a between adjacent through-holes ₁.

4. the mirror structure of acoustics super lens according to claim 1, is characterized in that, the material of described mirror structure is copper or steel.

5. an acoustics super lens, is characterized in that, comprises the mirror structure described in lightweight medium and the claims 1～4 any one; Described lightweight Filled Dielectrics is in the through hole of described mirror structure; The density p of described lightweight medium _abe less than described mirror structure density p _b1/5.

6. acoustics super lens according to claim 5, is characterized in that, described lightweight medium is gas.

7. acoustics super lens according to claim 5, is characterized in that, described lightweight medium is water.

8. an acoustics super lens imaging device, is characterized in that, comprises the acoustics super lens described in signal generator, power amplifier, transmitting transducer, receiving transducer array, claim 5～7 any one; Described signal generator is connected with power amplifier by transmission line, and described power amplifier is connected with described transmitting transducer by transmission line; Described signal generator produces electric signal, described power amplifier amplifies electric signal power, electric signal is converted into the acoustic signals identical with electric signal frequency by described transmitting transducer, and described receiving transducer array is used for receiving acoustic signals and described acoustic signals is converted into electric signal; The front of described mirror structure is the lens receiving plane of acoustics super lens, and the lens receiving plane of described acoustics super lens is right against the signal transmit direction of described transmitting transducer; Described receiving transducer array comprises multiple receiving transducers; Described receiving transducer is placed on the geometric center of the through hole of described mirror structure; The corresponding receiving transducer of geometric center of each through hole of described mirror structure; The multiple receiving transducers that are placed in the through hole of described mirror structure form described receiving transducer array; Wavelength corresponding to described signal generator frequency of operation is to satisfy condition between the mirror structure height L of λ and described acoustics super lens:

L=n λ/2, wherein n is positive integer.