JPS6146192B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of transmitting high frequency ultrasonic power with low loss.

Ultrasonic power is widely used for purposes such as diffusing and cleaning substances in liquids, heating substances, and promoting chemical reactions. Ultrasonic power is often used, and relatively high frequency ultrasonic power, for example 300KHz or 500KHz, is often desired for heating substances or promoting chemical reactions.

Therefore, to transmit ultrasonic power at low frequencies of about several tens of KHz, a metal rod with a diameter considerably smaller than the wavelength of the sound wave is usually used, and longitudinal waves propagating in the axial direction with the same phase are used. However, when transmitting high frequency ultrasonic power of several hundred KHz, if the diameter of the metal rod is made smaller compared to the wavelength, the cross-sectional area will decrease, so it is possible to transmit with a single metal rod. The power will decrease, and if the diameter of the metal rod is about the same as the wavelength, even if the end face of the rod is excited with the same phase, the vibration displacement in the radial direction of the rod will become significant, which may increase transmission loss. be.

However, since it is desirable to use high-frequency ultrasonic power to heat substances and promote chemical reactions, there is a need for the development of a method that can efficiently transmit this power.

The present invention was made from the above-mentioned viewpoint with the purpose of providing a method that can efficiently transmit ultrasonic power at a high frequency of several hundred KHz.
When transmitting high-frequency ultrasonic power with a frequency of 100KHz or higher, the wavelength of the longitudinal ultrasonic wave is a rod whose diameter is determined by the resonant frequency of the vibrator and the material constant of the rod. , the length of the rod is an integral multiple of 1/2 of the wavelength of the ultrasonic wave in the rod, and three times or more the diameter is joined,
It is characterized in that ultrasonic power is transmitted by the metal rod.

That is, in order to achieve the object of the present invention, the inventors of the present invention first analyzed the propagation characteristics of an axially symmetrical ultrasonic wave transmitted through an infinitely long circular cross-section rod. The results are shown in Figure 4.

In this diagram, the vertical axis is the propagation velocity Vz of the ultrasonic wave propagating in the axial direction of the rod and the propagation velocity (called the sound velocity) of longitudinal waves in a sufficiently thin rod, which can be determined immediately by specifying the material of the rod Co (E / ρ , E: longitudinal elastic modulus of the rod material, ρ: density of the rod material), and the horizontal axis represents the ultrasonic frequency f and the rod diameter D.
It shows the value of the product fD and the ratio fD/Co with the above-mentioned Co.

Furthermore, the numbers attached to the curves in the above diagram indicate the number of waves that vibrate in the axial direction of the rod and in the direction perpendicular to it (diameter direction) when ultrasonic vibrations are transmitted by a transmission rod. (Hereinafter, this number will be referred to as the mode number), and the above curve shows the ultrasonic waves in the axial direction of the rod when fD/Co is changed, while the number of waves in the diametrical direction is the same as in the above. This is a plot of the value of the ratio Vz/Co between the propagation velocity Vz and the aforementioned Co.

Therefore, in other words, if the material of the rod is the same, if you change the product fD of the rod diameter D and the ultrasonic frequency f, the number of waves in the diametrical direction will be the same, but the axial direction of the rod will change. When the propagation velocity of the propagating ultrasonic wave Vz changes and the number of waves riding in the diametrical direction changes,
This shows that the changes in Vz with respect to fD are different.

Therefore, since the unit of Vz is m/sec and the unit of Co is also m/sec, the value of Vz/Co on the vertical axis is a dimensionless quantity without a unit and is independent of the material of the rod. This means that it can be expressed without thinking, and it shows a universal expression.

Also, fD/Co on the horizontal axis is fD/Co=D/(Co/
f) = D/λ (λ = Co/f, λ is the wavelength of the ultrasonic wave that propagates in the axial direction in a sufficiently thin rod, and since Co is immediately determined by specifying the material of the rod, the frequency of the ultrasonic wave is given as f) and λ is determined), which represents the ratio D/λ of the diameter D of the rod and λ, and the unit of f is Hz=
1/sec, the unit of D is m, and the unit of Co is m/sec, so the value of fD/Co is a dimensionless quantity like that of the vertical axis, and after all, it is a universal value that does not depend on material, frequency, diameter, etc. It is expressed as a numerical value.

As mentioned above, in the diagram of Figure 4, the values on the vertical and horizontal axes are both dimensionless quantities and are expressed in universal numerical values, so it is possible to determine the material, diameter, and frequency of the rod. However, all the charts are universally applicable.

Next, how to read the chart in FIG. 4 above will be explained.

Now, in Figure 4, if the value of the vertical axis Vz/Co is 1.5,
Draw a horizontal line from the point of Vz/Co = 1.5 on the horizontal axis, find the points of intersection with the curves of mode numbers 4, 5, and 6, and designate each intersection as A, B, and C. The value fD/Co is A=1.8, B=2.2, C=2.8
becomes.

Therefore, if the materials of the rods are the same and the diameters of the rods are also the same, then D/Co is determined because Co and D are constant, and fD/Co giving each intersection is different, so
After all, the value of f is the lowest at intersection A, the intermediate value at intersection B, and the highest at intersection C, indicating that the more waves riding in the diametrical direction, the higher the frequency f becomes. , it shows that if the material is the same and the frequency is the same, the larger the number of waves in the diametrical direction, the larger the diameter.

Also, looking at the curves in Figure 4, curves with mode numbers 2 or higher approach the shear wave velocity Cs in an infinite medium as the fD product increases, while the propagation of ultrasonic waves propagating in the axial direction of the rod Speed Vz
changes significantly, and when this Vz approaches the longitudinal wave velocity Cd in an infinite medium, a shoulder k portion appears where the change in fD value is gradual, and a horizontal portion appears at the shoulder k for curves with mode number 7 or higher. It's coming.

The inventors of the present invention focused on this shoulder k part, and found that fD/Co=D/λ is 4 or more, in other words,
Regarding a rod whose diameter is set to four times the wavelength λ or more,
When we calculated the distribution of axial vibration displacement in the diametrical direction in a cross section perpendicular to the axial direction of the rod, we found that at shoulder k, the axial displacement had the same phase distribution over the entire cross section. did.
From this, it was determined that ultrasonic vibrations could be transmitted efficiently if a rod with a circular cross section with a diameter of four times or more the wavelength λ was used as a transmission rod as a condition for realizing the shoulder k portion.

Therefore, we actually used aluminum alloy as the material of the transmission rod, and at an operating frequency of 599KHz, fD/Co =
Design and prototype a finite length rod with a diameter of 4 or more,
An ultrasonic generation vibrator with a resonance frequency of 500 KHz was attached to one end of the rod, and the diametrical distribution of the axial vibration displacement on one end of the rod was measured.
They found that the results were substantially consistent with the calculation results for the infinitely long rod described earlier, and completed the present invention.

In the present invention, the length of the circular cross-section rod is an integral multiple of 1/2 of the wavelength of the ultrasonic wave in the rod and 3 times the diameter of the rod.
The reason for making the length more than twice as long is to make the length not too short and easy to use since the purpose of the method of the present invention is to transmit strong ultrasonic power.

Also, from FIG. 4, the larger the mode number, the larger the value fD/Co on the horizontal axis indicating shoulder k,
If the material of the rod and the frequency of the ultrasonic wave are the same, the larger the mode number, the larger the diameter.On the other hand, even with the same mode number, the part representing the shoulder k is not a single point, but a certain spread. Since we have
Even if the number of waves traveling in the diameter direction is the same, if the material and diameter of the rod are the same, the frequency of the ultrasonic wave will have a certain spread, and if the material of the rod and the frequency of the ultrasonic wave are the same, the diameter of the rod will each have a certain spread. This can be said to be advantageous from a design and practical standpoint.

Next, embodiments of the present invention will be described with reference to the drawings.

1 has a diameter of 60 mm, a thickness of 4 mm, and a nominal resonant frequency.
A piezoelectric ceramic vibrator made of a 500KHz lead zirconate titanate compound, 2 and 2a are electrodes provided on both sides of the vibrator 1, and 3 is a transmission rod glued to the electrode 2a side of the vibrator 1. Rod 3 has a diameter of oscillator 1
The same diameter is 60mm, the length is 221mm, and this diameter is 60mm.
is converted to the wavelength of the ultrasonic wave in the infinite medium of the transducer 1, which is 4.8 wavelength, and the length of 221 mm is also the same.
This corresponds to 18 wavelengths.

The tip of the transmission rod 3 of the ultrasonic vibrator configured as described above is immersed in water, a continuous sine wave of 10 V is applied to the vibrator 1, and the current at that time is measured to determine the apparent load factor. As shown in Figure 2,
The actual operating frequency was 513.4KHz, the load factor was over 80%, and it was confirmed that ultrasonic power was transmitted with high efficiency. In addition, the load factor did not change significantly even if the length of the part of the transmission rod 3 immersed in water changed, but this is because the vibration displacement in the radial direction of the transmission rod 3 is small and the radiation from the sides is small. , and even if the side of the transmission rod 3 was actually restrained by hand, the load factor hardly changed.

Next, when the water tank was shallowly filled with water, the transmission rod 3 was immersed diagonally, and the vibrator 1 was driven with an electrical input of 40V and 67W, the water surface rose significantly, and then when the electrical input was increased to 70V and 67W. A fine mist began to form from the surface of the water. The above phenomenon is caused by transmission rod 3
This shows that powerful ultrasonic power was emitted from the tip of the

In the above embodiment, a straight rod is used as the transmission rod 3, but the present invention is not limited to this, and other rods, such as a tapered rod, may be used.

By the way, set the diameter of transmission rod 3 to 20mm, which is close to the wavelength.
(1.6 wavelength), applied a continuous sine wave of 10V to the vibrator 1 in the same way as above, measured the current at that time, and found the apparent load factor, as shown in Figure 3. Actual frequency is 537.4KHz, load factor is 52% ~
It was about 66%, so the ultrasonic power was not transmitted with high efficiency, and when the length of the portion of the transmission rod 3 immersed in water changed, the load factor varied considerably.

As described above, according to the method of the present invention, ultrasonic power is transmitted with high efficiency because the transducer displacement in the axial direction of the rod is distributed in the same phase at the radiation end of the rod, and The fact that the diametrical vibration displacement perpendicular to is small, especially on the outer circumferential surface of the rod, is
That's the reason. The fact that this diametrical vibrational displacement is extremely small on the outer peripheral surface makes it easy to support the transmission rod with minimal loss of ultrasonic power.

That is, in conventional ultrasonic vibration devices, in order to stably support the transmission rod, a flange is provided at the part of the transmission rod that corresponds to the node of the transmitted ultrasonic vibration, and the flange is fixed to the support. This prevents the transmission rod from being affected by vibrational displacement in its diametrical direction.In order to provide flanges at appropriate locations on the transmission rod, cutting and other extremely troublesome work is required, but the method of the present invention In this case, since the diametrical vibration displacement on the outer peripheral surface of the transmission rod is small, it is hardly affected by its support, so it is sufficient to attach it to the support at any point on the outer peripheral surface of the transmission rod. This makes support extremely easy.

As described above, the present invention not only can efficiently transmit ultrasonic power at a high frequency of several hundred KHz, but also can easily support the transmission rod, so it can be used to heat materials and promote chemical reactions. This is suitable as a method of transmitting high frequency ultrasonic power to be used.

[Brief explanation of the drawing]

Fig. 1 is a front view of an example of an ultrasonic vibration device for carrying out the method of the present invention, and Fig. 2 is a diagram showing the relationship between the load factor and the length of the portion immersed in water when the device shown in Fig. 1 is operated. , Figure 3 is a chart showing the relationship between the load factor during driving and the length of the water-soaked part when the diameter of the transmission rod is approximately the same as the vibration wavelength of the vibrator. Calculate the propagation velocity Vz of the ultrasonic wave in the axial direction of the rod in each vibration state for the axially symmetrical wave propagating through the circular cross-section rod,
It is a chart shown as a function of the product fD of frequency f and diameter D. 1... Ultrasonic transducer, 2... Transmission rod.

Claims (1)

[Claims] 1. When transmitting high-frequency ultrasonic power with a frequency of 100 KHz or higher, the diameter of the rod is four times the wavelength of the longitudinal ultrasonic wave of the rod determined by the resonant frequency of the vibrator and the material constant of the rod. The above is characterized in that a metal rod whose length is an integral multiple of 1/2 the wavelength of the ultrasonic wave in the rod and three times or more the diameter is joined, and ultrasonic power is transmitted by the metal rod. A method of transmitting high-frequency ultrasonic power.