JPH0238906B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an imaging device that utilizes high frequency ultrasound energy, and particularly to an ultrasound microscope.

[Background of the invention] The sound wave frequency is lGHz, and therefore the sound wavelength in water is approximately 1
A mechanical scanning ultrasound microscope (Scanning Acoustic
Microscope (hereinafter abbreviated as SAM) has been proposed.

That is, as shown in FIG. 1, a cylindrical crystal 20 such as sapphire, which is the first sound wave propagation medium, has one end face that is an optically polished plane and the other end face that has a concave hemispherical hole having a predetermined focal point. is formed to form a spherical lens.

A signal line 10 is connected to a piezoelectric thin film 15 formed on a flat plate.
An RF electric signal is applied to radiate a plane wave RF sound wave within the crystal 20. This plane sound wave is transmitted to the interface 2 between the crystal 20 formed in the concave hole of the spherical lens and the medium 30 (usually water) that is the second sound wave propagation medium.
5, with a positive lens that utilizes the sound speed difference between the two,
The light is focused at a predetermined focal point F. As is well known, F is the ratio of the focal length to the aperture diameter, which indicates the brightness of the lens.
When the number is small enough, this configuration can create a significantly narrower ultrasound beam.

Due to the sample placed near the focal point, this focused sound wave is disturbed by reflection, scattering, and transmission attenuation, so by detecting the energy of this disturbed sound wave, we can generate an electrical signal that reflects the elastic properties of the sample. I can get the signal. While mechanically scanning the sample in two dimensions, this electrical signal is synchronized with this scanning.
If displayed on a CRT, a sonic microscope image can be obtained.

A configuration for detecting such similar disturbance energy is shown in FIGS. 2a and 2b. FIG. 2a shows a reflection type configuration in which the reflected sound of the sample 60 in water 70 is detected again using the probe system 40 that generates an ultrasonic beam, and FIG. 2b shows the probe system 40 that generates an ultrasonic beam. A transmission-type configuration is shown in which another probe system 50 identical to that shown in FIG.

Conventionally, the biological sample 60 and the like have been attached to a sample stand 80, and a thin Mylar film mounted on a metal frame has been used as the sample stand. This is because the acoustic impedance of Mylar membrane is almost the same as that of water, and the presence of the supporting membrane can be ignored.

The reflection type is used to observe devices such as ICs and LSIs, and thick metal samples, while the transmission type is used for thin samples and especially biological samples. This is because the acoustic impedance of a biological sample is very similar to that of water, so a sufficient reflected signal cannot be obtained.

By the way, the transmission configuration not only requires two probe systems, but also requires alignment to set the two probe systems confocal, which is significantly more difficult to set up than the reflection configuration. It has its drawbacks. Therefore, if it is possible to detect the transmitted signal obtained in the transmission configuration while keeping the reflection configuration, it is expected that these difficulties will be solved and the price will be reduced.

[Purpose of the Invention] The present invention has been made in view of the above points, and an object of the present invention is to obtain a signal equivalent to a transmitted signal obtained in a transmission configuration using a reflection configuration using only a single probe system. do.

[Summary of the Invention] The present invention aims to achieve the object by making the lower surface of the sample flat and by making contact with the lower surface of the sample and a sound wave propagation medium having a different acoustic impedance to form an acoustic interface. It is. That is,
As conventionally used, 1~
Instead of using a Mylar film with a thickness of 2 μm and attaching the sample to the back side, first, the sample is sandwiched between two Mylar films, and the back side is air, and the second method is to use metal, glass, etc. A support stand with a multilayer structure is used. For water and biological samples,
Air, glass, and metal are perfect reflectors. With reference to FIG. 3, it will be explained why such a perfect reflector can be used to obtain a transmitted signal despite the reflective configuration.

The upper surface of a biological sample 100 having a certain thickness is designated as _l1 , and the lower surface is designated as _l2 , and the lower surface _l2 is lined with the third sound wave propagation medium 110 of the present invention. The ultrasonic beam 120 incident from above the sample is first partially reflected at the interface _l1 , and most of it propagates into the sample 100. The reflected wave from this interface l ₁ is extremely weak in biological samples. Now, the wave propagated in the sample 100 is the interface l ₂
and propagates upward through the sample again, reaching the interface l ₁
The sound waves exit into the water 130 through the water, and are detected by the probe system 140 as reflected sound waves. here,
Since the reflection at interface l ₂ is almost complete reflection and this reflected signal is extremely large, the reflected signal in this configuration is determined by the reflected sound wave from interface l ₂ , which is much larger than the reflected wave at interface l ₁ . I can say that. It is thought that this reflected signal is subjected to the same disturbance as when it passed through the sample twice. It will also be clear from the broken line configuration in FIG. 4, in which the backing material of the perfect reflector is considered to be a mirror 200.

That is, the configuration shown in FIG. 3 has a probe system 21 facing the confocal area by a mirror surface 200 as shown in FIG.
This is because it is equivalent to a configuration in which a sample 230 having an equivalent thickness of 0.0 and 220 and inserted therebetween is placed in water 240, and is the same as a conventional transmission configuration.

In fact, where the thickness of the biological sample is d and the attenuation rate is αs, the acoustic impedances of the biological sample, water, and the backed third sound propagation medium are Z _S , Z _W , respectively.
If Z _B , then Z _S Z _W , Z _S = Z _W + ΔZ ΔZ≪Z _S , Z _W (1) Then, the reflected signal r _S and transmitted signal t _S in the conventional configuration and the reflected signal r _S ′ in the present invention I calculated the size of. According to this, in the configuration shown in Figure 2, the transmitted signal t _S = e ^- 〓 ^s

Claims (1)

[Claims] 1 A first sound wave propagation medium, a piezoelectric body provided at one end of the first medium, a spherical lens formed at the other end and having a predetermined focus, and a piezoelectric material provided between the spherical lens and a predetermined sample. The sample is placed in the vicinity of the predetermined focal point using a sonic probe system consisting of a second acoustic wave propagation medium, and the ultrasonic wave emitted from the piezoelectric body to the sample via the spherical lens is transmitted to the sample. In an ultrasonic imaging device that receives reflected sound waves from the piezoelectric body through the spherical lens and obtains an ultrasonic image of the sample using the received echoes, the lower surface of the sample is flat and the acoustic impedance of the sample is has an interface brought into contact with a third sound wave propagation medium having an acoustic impedance different from An ultrasonic microscope characterized in that it is used to obtain ultrasonic images.