JPH0835956A - Ultrasonic probe - Google Patents

Abstract

PURPOSE:To provide effective measures against echo noises due to side surface reflection waves without losing the mechanical strength of an acoustic lens for a high-resolution ultrasonic probe. CONSTITUTION:A tooth-shaped concave surface lens groove 8 with its depth being approximately ultrasonic wavelength is formed on an entire surface reaching a taper region from an upper surface on the cylindrical side surface of an acoustic lens 5 with an upper surface where a piezoelectric element 3 is bonded and a lower surface and a lower surface with a taper region 7 and a concave lens 6. The direction along the teeth of the tooth-shaped concave lens groove 8 is in parallel with the longer axis of the acoustic lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high resolution ultrasonic probe mainly used in an ultrasonic microscope.

[0002]

2. Description of the Related Art In recent years, ultrasonic measurement methods have become widespread with the development of ultrasonic technology and image signal processing technology. Ultrasonic waves are widely used for flaw detection of solid and liquid samples because they have the characteristics that the wavelength can be freely changed, they are easy to handle, and attenuation in solids and liquids is significantly less than electromagnetic waves.

In particular, the ultrasonic microscope can examine the elastic properties of substances that cannot be measured by an optical microscope or an electron microscope, and the interface of different substances can be clearly detected as a difference in elastic properties. By combining with a circuit, it is possible to obtain a two-dimensional image of a solid sample having high resolution.

In the ultrasonic microscope, the characteristics of the ultrasonic probe as a sensor are very important. The ultrasonic probe
It is composed of a piezoelectric element and an acoustic lens. An ultrasonic element composed of an upper electrode / piezoelectric element / lower electrode is closely arranged on the upper end surface of the acoustic lens. In the case of the one-point focusing probe, the acoustic lens is formed of a cylindrical ultrasonic wave propagation medium.
A tapered region is provided at the lower end of the tapered region, and a spherical concave lens is provided around the central axis of the acoustic lens at the center of the tapered region. The plane wave radiated from the piezoelectric element is refracted by the concave lens surface and focused. It has the function of radiating the ultrasonic beam while focusing it. At this time, liquid couplant is filled between the concave lens and the sample surface as a medium of the ultrasonic beam emitted toward the subject sample.

Since the resolution of the ultrasonic microscope is about the wavelength of the ultrasonic wave, the resolution of 1 to 10 G is used for the purpose of increasing the resolution.
The high frequency range of Hz is used. For example, when water is used as couplant at 1 GHz, the resolution is about 1 μm. The resolution is about 0.5 μm when an ultrasonic beam is emitted from a concave sapphire surface with a radius of curvature of 40 μm at 3 GHz through a water couplant at 60 ° C. In order to transmit and receive ultrasonic waves of such a high frequency, the piezoelectric element of the ultrasonic probe has a thin film shape and is arranged in close contact with a plane perpendicular to the central axis of the acoustic lens. In order to enhance the adhesion between the lower surface electrode and the upper end surface of the acoustic lens, the lead wire is connected to the lower electrode by extending the lower electrode to the upper surface electrode side and performing the connection on the upper surface electrode side.

Another important factor affecting resolution is noise. In particular, a scattered wave reflected from the side surface of the acoustic lens called echo noise reduces the S / N ratio of the signal wave. This phenomenon will be described with reference to FIGS. FIG. 2 is a vertical cross-sectional view showing the relative position of the ultrasonic probe and the sample and the reflection of the ultrasonic beam in the acoustic lens. An ultrasonic element composed of an upper electrode 17, a piezoelectric element 18, and a lower electrode 19 is closely arranged on the upper end surface of a cylindrical acoustic lens 20. A taper region and a concave lens are provided at the lower end of the acoustic lens 20. The piezoelectric element 18 and the acoustic lens 20 are the main components of the ultrasonic probe 16. A liquid couplant 21 is filled between the concave lens and the sample 22. Usually, the diameter of the upper electrode 17 and the diameter of the concave lens are designed to be substantially the same.

Now, the lens / sample distance is selected at the position where the concave lens focus of the acoustic lens 20 is on the surface of the sample 22, and the piezoelectric element is driven to perform ultrasonic oscillation. As shown in FIG. 2, the upper electrode 17 is usually designed to have a diameter smaller than that of the lower electrode 19, and when a pulse voltage is applied between the upper and lower electrodes, ultrasonic waves are generated directly below the upper electrode 17 in the piezoelectric element region. Is excited only in. Therefore, the reception of ultrasonic waves from the acoustic lens 20 and the conversion into the signal voltage also occur only in the relevant part.

Ultrasonic wave (plane wave) excited by a piezoelectric element
Propagates down the acoustic lens 20 and is radiated from the concave lens interface into the liquid couplant 21. A straight line and an arrow in the acoustic lens 20 of FIG. 2 indicate the traveling direction of the ultrasonic wave. Of the ultrasonic waves excited and radiated in the region of the piezoelectric element 18 immediately below the upper electrode 17, the highest radiant energy on the concave lens is the ultrasonic wave radiated at zero radiation angle, that is, the central axis of the lens. . This ultrasonic wave propagates the shortest distance from the piezoelectric element and reaches the concave lens, part of which is reflected at the interface and returns to the original path, part of which is radiated into the liquid couplant 21 and further on the surface of the sample 22. Part of the light will be absorbed and the rest will be reflected and follow the original path back to the piezoelectric element. The wave reflected by the surface of the sample 22 and returned is the received signal wave.

The ultrasonic wave radiated from the piezoelectric element, which does not travel the shortest distance, is partially reflected by the concave lens, and the path of the reflected wave is deviated from the central axis of the lens as shown in the figure. In FIG. 2, for simplicity, only the waves radiated from the piezoelectric element at a radiation angle of zero are shown, but in reality, there are also waves radiated at a certain radiation angle, and the waves reflected by the concave lens are also lenses. Acoustic lens 20 deviated from the central axis
It becomes a wave that is re-reflected on the side of.

FIG. 3 shows a pulse pattern converted from the acoustic lens 20 back to the piezoelectric element and converted into an electric signal, and its source. In the figure, "lens echo" refers to the wave reflected and returned by the concave lens at the shortest distance, and "sample echo" refers to the signal wave. "Scattered waves" distributed in the meantime
Indicates a reflected wave on the side surface of the acoustic lens 20. These scattered waves, that is, the multiple reflected waves, are echo noises, and components appearing in the vicinity of the signal wave cause interference with the signal wave, thereby reducing the S / N ratio of the signal wave. As a result, there is a problem that the resolution of the ultrasonic microscope is lowered.

As a method for solving this problem, for example, in Japanese Patent Laid-Open No. 62-130351, a cylindrical side surface of an acoustic lens is directly below an ultrasonic wave excitation area of a piezoelectric element (a radiation angle connecting the excitation area and a concave lens aperture). Zero ultrasonic radiation area)
The acoustic lens for ultrasonic probes is disclosed in which a groove is deeply cut in a circular shape so as to reach the deep part of the acoustic lens, and an ultrasonic absorber having an acoustic impedance substantially equal to that of the acoustic lens is buried in the groove. There is.

By using this technique, the reflected wave incident on the side surface of the acoustic lens loses most of its energy by the ultrasonic absorbing material, and the re-reflected wave is rapidly attenuated, so that the scattered wave as shown in FIG. It can be significantly suppressed. Since the acoustic impedance of the ultrasonic absorber buried in the groove is almost equal to that of the acoustic lens, the ultrasonic wave incident on the interface between the acoustic lens and the ultrasonic absorber is not scattered, and the ultrasonic absorber is effectively used as the ultrasonic absorber. It is incident and loses energy.

[0013]

According to the above-mentioned prior art, the energy of the ultrasonic wave reflected by the concave lens and then re-reflected by the side surface of the acoustic lens can be considerably attenuated by the absorbing effect. However, the circular distribution groove formed on the side surface of the acoustic lens is deeply cut by the concave lens up to the area excluding the aperture. As described above, when a high frequency ultrasonic wave of several GHz is used to improve the resolution of the ultrasonic microscope, the diameter of the concave lens is 100 μm or less. However, since the acoustic lens is composed of a high hardness brittle material such as sapphire or quartz, it is generally difficult to form the shape, and when the deep groove is circumferentially formed as described above, the mechanical strength of the acoustic lens is significantly reduced. .

It can be said that the absorber has an acoustic impedance substantially equal to that of the acoustic lens, and the ultrasonic wave incident on the interface between the two does not enter vertically, and the reflection component at the interface cannot be avoided. Therefore, high S / N
It is not always possible to obtain a sufficient side surface reflected wave suppressing effect to obtain the ratio. An object of the present invention is to provide an acoustic lens equipped with a highly effective countermeasure against side reflected wave noise without impairing the mechanical strength of the acoustic lens.

[0015]

In order to achieve the above object, according to the present invention, an acoustic lens having a cylindrical portion, and a piezoelectric element formed on an upper end surface forming a plane perpendicular to the central axis of the lens, In an ultrasonic probe having a tapered region provided on the lower end surface of an acoustic lens and a concave lens having a spherical shape around the central axis, the acoustic lens has a cylindrical region from the upper end face to the tapered region. The ultrasonic probe is characterized in that a sawtooth-shaped notch groove having a depth of about the wavelength excited by the piezoelectric element is formed so as to have a circular sawtooth shape in each cylindrical cross section. Disclose the child.

[0016]

The saw-toothed notch groove of the present invention has a depth of about the wavelength of ultrasonic waves (about 100 μm), so that it is easy to process and the risk of impairing the mechanical strength of the acoustic lens is small.
Furthermore, since it has a sawtooth shape and the direction along the teeth is the direction along the long axis of the acoustic lens, the noise reflected wave from the concave lens becomes a reflection close to irregular reflection, and the amount of incidence on the piezoelectric element also decreases. It has a noise removal function.

[0017]

The present invention will be described in more detail based on the following examples. FIGS. 1A and 1B show an ultrasonic probe structure using an acoustic lens according to an example. 1A is a top view, and FIG. 1B is a cross-sectional view taken along the line AA ′ of FIG. It should be noted that in the drawing, for simplicity, the conductor wire for the lower electrode is omitted. In the figure, 1 is an ultrasonic probe, 2 is an upper electrode, 3 is a piezoelectric element, 4 is a lower electrode, 5 is a cylindrical acoustic lens, 6 is a concave lens, 7 is a tapered region, 8 is a sawtooth notch groove. Is.

The acoustic lens 5 is made by processing sapphire or quartz, and is provided with a taper region 7 at the lower end and a concave lens 6 which squeezes ultrasonic waves into a point shape and radiates it to a focal position. The sawtooth-shaped lens groove 8 is a sawtooth-shaped uneven groove having a depth d (a depth of about 1 to several wavelengths of ultrasonic waves) in each cylindrical cross section on the cylindrical side surface of the acoustic lens 5. It is provided from the upper end surface to the taper region. The depth d of the groove depends on the wavelength of the ultrasonic wave (1 to several wavelengths), but may be about 100 μm. Such groove processing can be relatively easily performed by grinding without impairing the mechanical strength of the acoustic lens 5.

According to the present embodiment, the reflected wave Q from other than the central axis of the concave lens 6 is shown in FIGS. The concave peak position P ₁ , the convex peak position P ₃ and the taper part P _{2 of the} saw tooth exhibit different reflection patterns. (1) Recessed peak position P ₁ , recessed peak position P ₃ ... Reflected in the reflection angle direction determined by the incident angle of the reflected wave Q of the concave lens 6. There is the piezoelectric element 3 in this reflection direction and it becomes a noise component. However, since the area occupied by the recess peak positions P ₁ and P ₃ occupies a small portion of the entire reflection surface, it is a small noise component which is negligible. Further, the path length of the reflected wave is different between P ₁ and P ₃ , and it is impossible to further reduce the sound pressure of the reflected wave by offsetting the phase by canceling the phase by setting the groove depth. (2), tapered portion of sawtooth P ₂ ... A reflected portion having energy of 95% or more in the noise reflected wave Q from the concave lens surface. In this taper portion, the taper portions facing each other are reflected and reflected. This path length is large, and the noise reflection component to the piezoelectric element 3 is reduced by shifting the reflection direction from the piezoelectric element 3. According to this embodiment, the acoustic lens 5 is in the AA 'plane.
The reflection of the side surface of the ultrasonic wave is scattered, and the input amount of the scattered wave to the ultrasonic piezoelectric element 3 is reduced.

[0020]

As described above, according to the present invention, the echo noise caused by the side reflected wave of the acoustic lens can be effectively suppressed by the relatively simple processing without deteriorating the mechanical strength of the acoustic lens. be able to. As a result, the S / N ratio of the reflected signal from the sample can be improved, which can contribute to the improvement of the resolution of the ultrasonic probe image.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an ultrasonic probe of the present invention.

FIG. 2 is a diagram showing a trajectory of an ultrasonic probe and a side reflected wave according to a conventional example.

FIG. 3 is a diagram showing an output pattern of a conventional ultrasonic probe.

[Explanation of symbols]

1 Piezoelectric element 2, 17 Upper electrode 3, 18 Piezoelectric element 4, 19 Lower electrode 5, 20 Acoustic lens 6 Concave lens 7 Tapered area 8 Cylindrical notch groove 9, 21 Liquid couplant 10 Test sample 16 Ultrasonic probe 22 Sample d Groove depth D _L Acoustic lens P, Q, O Concave lens reflection point M Concave lens focus

Claims (1)

[Claims] 1. An acoustic lens having a cylindrical portion, a piezoelectric element formed on an upper end surface of a plane perpendicular to the central axis of the lens, a taper region and the central axis provided on the lower end surface of the acoustic lens. In an ultrasonic probe having a concave lens having a spherical shape around the acoustic lens, the acoustic lens has a depth that is excited by the piezoelectric element over the entire surface from the upper end surface of the cylindrical side surface to the taper region. An ultrasonic probe characterized in that a sawtooth-shaped notch or groove having a wavelength of about a wavelength is formed so as to have a circular sawtooth shape in each cylindrical cross section.