JPS5950937B2 - ultrasound microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of an ultrasound focusing lens used in an ultrasound microscope.

The idea of using ultrasound instead of light to observe the microscopic structure of objects has been around for a long time, and mechanical scanning ultrasound microscopes have recently been developed.

In principle, this ultrasonic microscope mechanically scans the sample surface with a narrowly focused ultrahigh-frequency ultrasonic beam, collects the ultrasonic waves scattered by the sample, and converts them into electrical signals.
The signals are displayed two-dimensionally on the display screen of a cathode ray tube to obtain a microscopic image. The configuration depends on the method of detecting the ultrasonic waves, that is, detecting the ultrasonic waves that have passed through the sample while being scattered or attenuated, and detecting the ultrasonic waves that have been reflected due to differences in the acoustic properties within the sample. Depending on the case of detection, there are two types: transmission type and reflection type. FIG. 1 is a diagram showing the principle of a reflection-type ultrasound microscope, in which a signal from a high-frequency oscillator 1 is supplied to a transducer 3 for transmitting and receiving purposes by a directional coupler 2.

This signal is converted into an ultrasonic wave and is radiated inside from one surface of an ultrasonic focusing lens 4 made of an ultrasonic propagation medium material such as sapphire for both transmitting and receiving waves. The other end of the ultrasonic focusing lens 4 is hollowed out into a spherical shape to form a spherical lens portion 4.
a, and a sample holding plate 5 is shown facing the spherical lens portion 4a. A sound field medium 6 made of water is interposed between the ultrasonic focusing lens 4 and the holding plate 5, and the sample 7 is attached to the holding plate 5 at the focal point of the spherical lens portion 4a. The holding plate 5 is moved by a scanning device 8 in the X and Y directions. The scanning device 8 is controlled by a scanning circuit 9. The ultrasonic waves incident on the ultrasonic focusing lens 4 from the transducer 3 are focused and reach the sample 7. The reflected wave is again collected by the ultrasonic focusing lens 4, converted into an electrical signal by the transducer 3, and supplied to the display device "0" through the directional coupler 2. However, in reality, not only the reflected waves reflected from the surface of the sample 7 but also the reflected waves from the boundary surface of the spherical lens portion 4a of the ultrasonic focusing lens 4 are reflected by the transducer 3 as shown in FIGS. 2 and 3. is extracted as an electrical signal.

In FIG. 3, a is a leakage signal B, b, in which the transmission pulse of the high-frequency oscillator 1 leaks from the directional coupler 2. , b. , b'' are the first, second, third, and
The fourth reflected signal, c, is the sample signal reflected from the sample 7. Therefore, these reflected signals b, ~B, due to multiple reflections within the ultrasonic focusing lens 4 and the sample signal c from the sample 7
If they overlap, they will be superimposed due to their phase relationship,
Alternatively, they cancel each other out, so that the amplitude of the output does not depend on the intensity of the sample signal c. Therefore, the sample signal c is
~Fourth reflected signal B, ~B. It needs to appear between. In view of the above points, the present invention enables the sample signal to appear at a different position from the reflected signal by setting the structure of the ultrasonic focusing lens to predetermined dimensions in advance. Hereinafter, the present invention will be explained with reference to the drawings. Fig. 2 shows the dimensions of the ultrasonic focusing lens 4 and the distance from the lens 4 to the surface of the sample 7. The height of the lens portion 4a to the apex 4b,
d is the distance from the vertex 4b of the spherical lens section 4a to the surface of the sample 7, r is the radius of the spherical lens section 4a, and C1 and C2 are the velocities of the ultrasonic waves within the ultrasound focusing lens 4 and the sound field medium 6.

Now, when the reflected signal and sample signal are idealized and shown in FIG. 4, B, ~B. are the first to fourth reflected signals, and the signals B, ~
B. is a decaying signal with a period of T, time. In addition,
The pulse width is, for example, Δt time. It is assumed that c is a sample signal reflected from the surface of the sample 7, and the signal c appears after a time T2 after the pulse is transmitted from the high frequency oscillator 1. These times tl and t'' can be expressed by the following formula from the dimensions of the ultrasonic focusing lens 4 and their sound speeds.T
,=21/C,... (a)T.

=21/C, +2d/C.・・ ・ ・ ・ (Ex) Now, if T2 = Ktl, then from the above equations (a) and (ex), l = Dc, / (k-1)C.・ ・ ・ ・ ・
・It becomes (− −). Note that d is expressed by the formula d=r/(1-C./C,) using the radius r of the spherical lens portion 4a. Here, the sample signal c is each reflected signal b,
〜B, is the condition that the time T2 until the sample signal c is displayed is Nt, +△t≦T2≦ (n
+1) T, -△t, (n is a positive integer), therefore, n+△t /cl≦k≦ (n+1)△
t/TO (n is a positive integer). If k is set within this range and the ultrasonic focusing lens 4 is selected to fit the above equation (-◆), the sample signal number c will not overlap the reflected signals B, ~B, and each reflected signal B, ~ B. Therefore, the ultrasonic focusing lens 4 can be made of sapphire,
When the sound field medium 6 is water, the sound speeds C and C.

are 11.2mm/μSec and soil 5mm/μS, respectively.
ec, from the formula d=r/(l-C./C,), d=
It becomes 1.155r. Therefore, for example, R, k can be written as follows [
If the values shown in Table 1 are set, the values of l can be determined from the above equation (-1). As mentioned above, since the present invention makes the sample signal c appear between the multiple reflection signals bl to B4 from inside the ultrasonic focusing lens 4, the blanking circuit is used to generate the reflection signals B, . By erasing B2, there is a remarkable effect that only the desired sample signal c can be obtained in a clear form.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the principle of a reflection type ultrasound microscope, Fig. 2 is an explanatory diagram showing the relationship between the ultrasound focusing lens and the sample, and Fig. 3 is a diagram showing the output waveforms of the reflected signal and the sample signal. FIG. 4 is an explanatory diagram that idealizes and represents the output waveform of FIG. 3. 4...; Ultrasonic focusing lens, 4a...
Spherical lens part, 4b... Vertex, 6...
Sound field medium, 7... Sample.

Claims (1)

[Scope of Claims] 1. An ultrasonic focusing lens having a spherical lens portion provided at one end of the ultrasonic propagation medium material converts the ultrasonic beam generated by the transducer provided at the other end of the ultrasonic propagation medium material into sound. In an ultrasonic microscope that focuses on a sample through a field medium and collects reflected waves from the sample using the ultrasonic focusing lens, it is converted into an electrical signal, l=dc_1/(t_2/t_1- 1) c_2n+
△t/t_1≦t_2/t^1≦(n+1)−△t/t
_1 However, l; Height d from one end of the ultrasonic focusing lens on the transducer side to the apex of the spherical lens portion; Distance from the apex of the spherical lens portion to the sample c_1; Speed of ultrasound within the ultrasonic focusing lens c_2; Speed of ultrasound in the sound field medium t_1; Period △t of the multiple reflection signal between the interface between the spherical lens part and the sound field medium and the other end of the ultrasound lens; Pulse width of this multiple reflection signal t_2: Time from when a drive signal is applied to the transducer until the sample signal reflected from the sample surface is detected n: Positive integer An ultrasonic microscope characterized in that it satisfies the above relational expression.