JP3168754B2 - Method and apparatus for adjusting focus of ultrasonic sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for adjusting the focus of an ultrasonic sensor.

[0002]

2. Description of the Related Art As an apparatus for ultrasonic spectroscopy in a continuous frequency domain, there is an ultrasonic spectrum microscope disclosed by the present inventors in Japanese Patent Application Laid-Open No. Hei 2-251751. An ultrasonic lens or sensor of this ultrasonic spectrum microscope is an SPP (spherical) having a concave (typically spherical) lens and a planar lens.
al planar pair lens) lens.

[0003] The SPP lens measures and analyzes reflected ultrasonic waves from the subject while rotating only the two lenses or the plane lens around the focal point with the focal point positioned on the surface of the subject. Is used to measure the elastic constant of a minute region of the subject. It is also used to measure the reflectivity of the ultrasonic wave when the incident angle is continuously changed for evaluating the subject.

In such a measurement, in order to maximize the characteristics of the SPP lens, the focal point of the SPP lens is held at a reference height position at an arbitrary height with respect to the subject surface or the subject surface. There is a need. SP like this
In the conventional method for adjusting the focus of the P lens, first, a feature point is determined from a time waveform when the focus is located on the object plane, and then, in each measurement, the SPP is set so that the feature point is reproduced. Adjust the lens height manually.

[0005]

However, a similar time waveform cannot be obtained when measurement is performed in a plurality of different areas on the object surface or when an elastic wave is excited. Therefore, the characteristic points are unclear, and it becomes difficult to adjust the focus of the SPP lens. Some problems when the focus adjustment accuracy of the SPP lens is low are listed below.

I) When collecting reflected waves from a minute observation point while changing the incident angle by tilting the SPP lens, the observation point moves with the tilt of the SPP lens.

Ii) The positional relationship between the receiving surface of the receiving lens and the observation point becomes inappropriate, and in the worst case, no reflected wave can be received.

Iii) In general, the phase curve of an arbitrary frequency component of the reflected wave becomes flatter as the degree of matching between the focal point of the concave lens and the central axis of tilt of the SPP lens increases. However, when the focal position of the SPP lens changes, the analysis becomes difficult because the phase curve does not become flat.

It is an object of the present invention to provide a method and an apparatus for adjusting the focus of an ultrasonic sensor which solve the above-mentioned problems. More specifically, it is an object of the present invention to provide a method and an apparatus that can achieve high-accuracy vertical focus adjustment of an ultrasonic sensor and that can be automated.

[0010]

According to one aspect of the present invention, the method includes first and second ultrasonic transducers,
A method is provided for adjusting a vertical distance between a focal point of an ultrasonic sensor for transmitting and receiving ultrasonic waves and a surface of a subject, at least one of which has a plane facing the surface of the subject. This method comprises the steps of (a) transmitting an ultrasonic wave from the first ultrasonic transducer of the ultrasonic sensor to the surface of the object, and (b) reflecting the ultrasonic wave from the surface of the object by the second ultrasonic transducer of the ultrasonic sensor. (C) obtaining a relationship between the frequency f and the phase of the reflected ultrasonic wave received by the second ultrasonic transducer; (d) obtaining the relationship; The vertical distance Δz between the focus position of the ultrasonic sensor and the subject surface is measured based on a predetermined relationship between the frequency f and the phase of the reflected ultrasound when the focus is located on the subject surface. And (e) a step of vertically moving the ultrasonic sensor relative to the object surface such that the focal point of the ultrasonic sensor is located on the surface of the object based on the measured vertical distance Δz, Is provided.

According to another aspect of the present invention, a first ultrasonic transducer for transmitting ultrasonic waves to the surface of a subject and a second ultrasonic transducer for receiving reflected ultrasonic waves from the surface of the subject are provided. An apparatus is provided for adjusting a vertical distance between a focal point of an ultrasonic sensor and a surface of a subject, at least one of which has a plane facing the surface of the subject. This apparatus includes means for determining the relationship between the frequency f and the phase of the reflected ultrasonic wave received by the second ultrasonic transducer, the determined relation, and the time when the focal point of the ultrasonic sensor is located on the surface of the subject. Means for measuring a vertical distance Δz between the focal position of the ultrasonic sensor and the surface of the subject based on a predetermined relationship between the frequency f and the phase of the reflected ultrasonic wave; Means for vertically moving the ultrasonic sensor relative to the surface of the subject so that the focal point of the ultrasonic sensor is located on the surface of the subject.

In this case, the other ultrasonic transducer has a flat surface or a concave surface facing the surface of the subject.

According to an embodiment of the present invention, the vertical distance Δz in the apparatus and method described above is given by the following equation: Δz = {(P _fref (f) -P _f (f)) / f} · {(V ₀・ Cos θ) / 2 π
(1 + cos2θ)} (where f is the frequency of the ultrasonic wave, P _fref (f) is a reference phase curve when the focal point of the ultrasonic sensor is located on the surface of the object, P
_f (f) is the phase curve when the focal point of the ultrasonic sensor is at an arbitrary position, V ₀ is the sound velocity in the ultrasonic wave propagating medium interposed between the ultrasonic sensor and the subject, and θ is the ultrasonic wave having a plane. Angle of incidence defined between acoustic transducer and subject surface)
Is calculated according to

[0014]

The relationship between the frequency f and the phase of the reflected ultrasonic wave received by the second ultrasonic transducer having a plane depends on the vertical distance Δz between the focal position of the ultrasonic sensor and the surface of the subject. Change. Therefore, by obtaining this change, the vertical distance Δz at which the focal position of the ultrasonic sensor should be moved vertically can be obtained.

[0015]

FIG. 1 shows a height adjusting device for an ultrasonic sensor according to the present invention.

The SPP lens 12 is a transmission / reception independent ultrasonic sensor having a concave transducer 14 and a flat transducer 16. Each of the concave and planar transducers 14, 16 is, for example, a ZuO piezoelectric film transducer. These two transducers 14, 16
Are integrally supported by a support 18. A predetermined opposing angle φ is maintained between a normal line N ₁ passing through the center of the concave surface 14 a of the concave transducer 14 and a normal line N ₂ passing through the center of the plane 16 a of the flat transducer 16.

The support 18 is supported by a θ stage 20 that tilts the ultrasonic sensor 12 in the θ direction. θ
The stage 20 is supported by a Z stage 22 that moves the stage 20 in the vertical direction (Z-axis direction). The drive mechanism (not shown) of the Z stage 22 is, for example, a stepping motor having a 0.5 μm step.

The subject 24 is mounted on a mounting surface 26a of a stage 26 below the SPP lens 12. Here, the mounting surface 26a is in an XY plane perpendicular to the Z axis. The height position of the SPP lens 12 is a distance in the Z-axis direction from the surface of the subject. An ultrasonic wave propagation medium (typically, water) 28 is interposed between the SPP lens 12 and the subject 24.

A pulse generator 30 for exciting the transducer and transmitting an ultrasonic wave is connected to the transmitting side transducer (for example, the concave transducer 14) of the SPP lens 12.

The reflected wave output of the receiving transducer (for example, the planar transducer 16) is supplied to a waveform measuring device, for example, a digital oscilloscope 32, where the time waveform of the reflected wave is measured. This time waveform is subjected to fast Fourier transform by an FFT operation device 34 having a fast Fourier transform (FFT) function.

The stage controller 36 controls the θ and Z stages 20 and 22 according to instructions from the operator, and controls the Z stage 2 according to instructions from the arithmetic unit 34.
2 is controlled.

Even when the angle of incidence of the ultrasonic wave with respect to the subject 24 is changed, the SPP lens 12 maintains the normal N ₀ passing through the observation point on the surface 24 a of the subject and the above-mentioned normal N ₂ of the plane transducer 16. It is possible to output a reflected wave of only the angle component defined between. Therefore, if the detection angle (incident angle) of the concave transducer 18 is set to be the same as the incident angle (detection angle) of the flat transducer 16, only the component of the set angle affects the output. This means that the change in the angle of the concave transducer 18 with respect to the subject need not be considered.

Such characteristics are not limited to the SPP lens 12, but also apply to a transmission / reception independent sensor in which at least one is a flat transducer.

According to the sensor or the SPP lens 12 having such a plane transducer, the phase change of an arbitrary frequency component between the reference focal position Z ₀ and the arbitrary focal position Z _n of the sensor is as follows. It can be approximately expressed.

As shown in FIG. 2, a reference focal position Z ₀ of the SPP lens 12 is set on the surface 24a of the subject, and an arbitrary focal position (actual focal position) Z _{n of the} subject surface 24a and the SPP lens 12 is set. Is defined as ΔZ in the Z-axis direction. Also, the linear distance between the observer and Z _n l _1, ultrasonic wave propagation distance and the focal position Z from the plane transducer 16 from the plane transducer 16 to the surface of the object 24a
The difference from the ultrasonic wave propagation distance up to _n is l ₂ .

L ₁ + l ₂ = (ΔZ / cos θ) + {(ΔZ / cos θ) · cos2θ} (1) Therefore, the phase difference PΔZ of the ultrasonic wave of the frequency f is PΔZ = 2πf · ( 1 / V _W ) ・ (l ₁ + l ₂ ) = 2πf ・ (1 / V _W ) ・ {(ΔZ / cos θ) ・ (1 + cos 2θ)} …… (2) where V _W is ultrasonic wave propagation The speed of sound of the medium (typically water).

[0027] Rewriting equation _{(2), ΔZ = (PΔZ · V W} · cos θ) / {2πf (1 + cos 2θ)} Here, if the PΔZ / f and _{ΔP f, ΔZ = ΔP f ·} { (V _W · cos θ) / 2π (1 + cos 2θ)} (3) Referring now to FIG. 3, P _ref (f) is the SPP lens 1
2 is a phase curve at the reference height Z ₀ , and P
_f (f) is the phase curve when SPP lens 12 is at the desired height Z _n. However, these phase curves P _ref (f),
P _f (f) is a phase unwrap described later.
It is standardized by As is clear from FIG. 3, ΔP _f is ΔP _f = (P _ref (f) −P _f (f)) / f (4) That is, ΔP _f means a slope.

From the above, Δz is expressed as follows: Δz = {(P _fref (f) −P _f (f)) / f} · {(V ₀ · cos θ) / 2 π (1 + cos 2θ)} (5) ).

The equation (5) is stored in the arithmetic unit 34 in advance.

The operation of the focus adjusting device of the present invention is as follows.

(I) The focal point of the SPP lens 12 is positioned on the surface 24a of the subject, and ultrasonic waves are transmitted and received between the SPP lens 12 and the subject 24.

(Ii) The arithmetic unit 34 obtains a phase curve of the spectrum of the waveform in the case of (i). After normalizing this by phase unwrapping, the reference phase curve P _fref (f)
In the memory (not shown) of the arithmetic unit 34.

(Iii) In actual measurement, an ultrasonic wave is transmitted and received between the SPP lens 12 and the subject 24.

(Iv) The arithmetic device 34 obtains the phase curve P _f (f) of the spectrum of the waveform in the case (iii), normalizes it by phase unwrapping, and stores it in the memory of the arithmetic device 34.

(V) The arithmetic unit 34 calculates ΔP _f according to the equation (4) for one or more frequency domains.

(Vi) ΔP _f is calculated by the arithmetic unit 34 in (5)
Substituting into the equation, the height deviation ΔZ is calculated.

(Vii) The stage controller 36 drives the Z stage 22 in accordance with ΔZ output from the arithmetic unit 34 and sets the SPP lens 12 so that ΔZ becomes substantially zero.
Is moved vertically.

As described above, the focal position of the SPP lens 12 is located on the surface of the subject.

A measurement example of the focus adjusting device will be described.
In this example, the frequency band is 10 MHz to 100 MHz,
The incident angle θ is 30 °. In addition, ultrasonic wave propagation medium (water)
The speed of sound inside was 1500 m / s. The calculation in the following description was performed by the arithmetic unit 34.

First, using Teflon as a reference object, a reference phase curve P _fref (f) was obtained as shown in FIG. Next, tin was used as an actual specimen, and a phase curve P _f (f) was obtained as shown in FIG. These phase curves P _fref (f), P _f (f)
Are displayed discontinuously, so that they were normalized to continuous display as shown in FIGS. 6 and 7 by phase unwrapping. One method of phase unwrapping is
Compare the phase curve of a certain frequency band and the phase curve of the frequency band immediately before it among the phase curves of the discontinuous display,
It is determined whether or not the phase makes one rotation (2π), and 2π is added to the part that has made one rotation. Thereby, the discontinuous display is standardized to the continuous display.

The standardized reference phase curve P shown in FIG.
_{By subtracting the normalized} phase curve P _f (f) of FIG. 7 from _fref (f), a straight line shown in FIG. 8 was obtained. From this straight line, ΔP _f = 7.26 × 10 ⁻⁸ was obtained according to (4). This was substituted into equation (5) to obtain Δz = 10 μm. The stage controller 36 determines S
The PP lens 12 was moved in the Z direction by 10 μm.

FIG. 9 shows another method for calculating the equation (4). As in FIG. 8, when the phase curve P _f (f) was obtained having a unique region A exhibit different properties from other regions, the phase curve P _f (f) and the reference phase curve in the specific area A P _fref (f) may be deleted, and the slope between P _f (f) and P _fref (f) in another region may be selectively used.

Further, a reference phase curve P _fref (f, θ) at an incident angle different depending on the θ stage 20 is measured, and
Using the phase curve P _f (f, θ) corresponding to each incident angle, Δ
Z may be determined.

The present invention is not limited to the embodiment described above, and various modifications are possible. For example, the ultrasonic sensor to which the present invention is applied is not limited to the SPP lens 12, but may be a transmission / reception independent sensor in which one is a flat transducer.

The Z stage 22 may be provided on the subject 24 instead of the SPP lens 12. If the incident angle does not need to be variably controlled, the θ stage need not be particularly provided.

Further, the combination of the digital oscilloscope 32 and the arithmetic unit 34 includes a spectrum analyzer for analyzing the frequency of the reflected wave, a tracking generator for measuring the phase as a function of frequency, and an arithmetic unit 34 for calculating ΔZ. May be replaced with a combination of

[0047]

According to the ultrasonic sensor focus adjusting method and apparatus of the present invention, the focal position of the ultrasonic sensor and the object are determined based on the relationship between the frequency and the phase of the reflected ultrasonic wave received by the ultrasonic sensor. Since the vertical distance from the surface can be measured, the focus can be adjusted with high precision, and the focus adjustment can be automated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a focus adjusting device for an ultrasonic lens according to the present invention.

FIG. 2 is a diagram showing a relationship between a focal point of an ultrasonic lens of the apparatus of FIG. 1 and a subject.

FIG. 3 is a graph showing a standardized reference phase curve and a standardized measured phase curve.

FIG. 4 is a graph showing a reference phase curve before standardization in a measurement example.

FIG. 5 is a graph showing a measured phase curve before standardization in a measurement example.

FIG. 6 is a graph showing the reference phase curve of FIG. 4 in a normalized manner.

FIG. 7 is a graph showing the measured phase curve of FIG. 5 normalized.

FIG. 8 is a graph for calculating a vertical distance ΔZ in a measurement example.

FIG. 9 is a graph showing a measurement phase curve having a unique region.

[Explanation of symbols]

12: SPP lens (ultrasonic sensor), 12: planar transducer, 12a: planar, 14: concave transducer, 14a: concave surface, 34: arithmetic unit (means for determining the relationship between frequency f and phase, vertical distance measuring means) 36 ... Z
Stage (moving means).

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-251551 (JP, A) JP-A-4-198751 (JP, A) JP-A-59-104547 (JP, A) JP-A-60-1985 18755 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 29/00-29/28

Claims (6)

(57) [Claims] 1. A focal point of an ultrasonic sensor for transmitting and receiving ultrasonic waves, comprising a first and a second ultrasonic transducer, at least one of which has a plane facing a surface of the object, and the object. (A) transmitting ultrasonic waves from a first ultrasonic transducer of the ultrasonic sensor to the surface of the subject; and (b) adjusting a vertical distance of the ultrasonic sensor from the first ultrasonic transducer of the ultrasonic sensor. (C) receiving a reflected ultrasonic wave from the surface of the subject by the second ultrasonic transducer; (c) obtaining a relationship between the frequency f and the phase of the reflected ultrasonic wave received by the second ultrasonic transducer; d) The focal position of the ultrasonic sensor and the focal position of the ultrasonic sensor are determined based on the obtained relationship and the predetermined relationship between the frequency f and the phase of the reflected ultrasonic wave when the focal point of the ultrasonic sensor is located on the surface of the subject. Vertical distance from specimen surface (e) based on the measured vertical distance Δz, the ultrasonic sensor is vertically moved relative to the subject surface so that the focal point of the ultrasonic sensor is located on the subject surface. And a focus adjusting method for the ultrasonic sensor. 2. The vertical distance Δz is given by the following equation: Δz = {(P _fref (f) −P _f (f)) / f} · {(V ₀ · cos θ) / 2 π
(1 + cos2θ)} (where f is the frequency of the ultrasonic wave, P _fref (f) is a reference phase curve when the focal point of the ultrasonic sensor is located on the surface of the object, P
_f (f) is the phase curve when the focal point of the ultrasonic sensor is at an arbitrary position, V ₀ is the speed of sound in the ultrasonic wave propagation medium interposed between the ultrasonic sensor and the subject, and θ is an ultrasonic Angle of incidence defined between acoustic transducer and subject surface)
2. The focus adjustment method for an ultrasonic sensor according to claim 1, wherein the focus is calculated according to the following equation. 3. A method according to claim 1, further comprising a first ultrasonic transducer for transmitting ultrasonic waves to the surface of the subject, and a second ultrasonic transducer for receiving ultrasonic waves reflected from the surface of the subject. An apparatus for adjusting a vertical distance between a focal point of an ultrasonic sensor having a plane facing a sample surface and a surface of the object, wherein a frequency f of reflected ultrasonic waves received by a second ultrasonic transducer Means for determining the relationship between the phase and the phase, based on the determined relationship and a predetermined relationship between the frequency f and the phase of the reflected ultrasonic wave when the focal point of the ultrasonic sensor is located on the surface of the subject, Means for measuring a vertical distance Δz between the focal position of the ultrasonic sensor and the surface of the subject, and an ultrasonic wave based on the measured vertical distance Δz such that the focal point of the ultrasonic sensor is located on the surface of the subject. Sensor Focusing apparatus of an ultrasonic sensor comprising a means for relatively vertically moving with respect to the body surface. 4. The focus adjusting device for an ultrasonic sensor according to claim 3, wherein the other ultrasonic transducer has a concave surface facing the surface of the subject. 5. The focus adjusting device for an ultrasonic sensor according to claim 3, wherein the other ultrasonic transducer has a plane facing the surface of the subject. 6. The vertical distance Δz is given by the following equation: Δz = {(P _fref (f) −P _f (f)) / f} · {(V ₀ · cos θ) / 2 π
(1 + cos2θ)} (where f is the frequency of the ultrasonic wave, P _fref (f) is a reference phase curve when the focal point of the ultrasonic sensor is located on the surface of the object, P
_f (f) is the phase curve when the focal point of the ultrasonic sensor is at an arbitrary position, V ₀ is the sound velocity in the ultrasonic wave propagating medium interposed between the ultrasonic sensor and the subject, and θ is the ultrasonic wave having a plane. Angle of incidence defined between acoustic transducer and subject surface)
4. The focus adjusting device for an ultrasonic sensor according to claim 3, wherein the focal length is calculated according to the following equation.