CN216500292U - Drive circuit for ultrasonic vibrator and ultrasonic atomizing device - Google Patents

Abstract

The utility model provides a drive circuit of an ultrasonic vibrator and an ultrasonic atomizing device. The ultrasonic atomization device atomizes a liquid by applying vibration energy to the liquid from ultrasonic waves generated using an ultrasonic vibrator formed in a disk shape, the ultrasonic vibrator including a 1 st electrode formed on one surface thereof and a 2 nd electrode formed on the other surface thereof. The region in which the 2 nd electrode is formed on the other surface of the ultrasonic transducer is narrower than the region in which the 1 st electrode is formed on the one surface, and the entire region is included in the region in which the 1 st electrode is formed on the one surface in a plan view of the ultrasonic transducer. The ultrasonic transducer includes: a 1 st vibration mode in which the entire body vibrates in the thickness direction; and a 2 nd vibration mode vibrating in a thickness direction between a region of the 2 nd electrode formed on the other face and a region corresponding to the 2 nd electrode in the one face, and driven at a frequency of the 2 nd vibration mode.

Description

Drive circuit for ultrasonic vibrator and ultrasonic atomizing device

Technical Field

The present invention relates to a drive circuit of an ultrasonic transducer for generating mist by directly applying ultrasonic energy to liquid, and an ultrasonic atomizing device.

Background

An ultrasonic atomizing device for atomizing a liquid such as water by ultrasonic vibration is known, and the ultrasonic atomizing device is used in a humidifier, an inhaler, and the like. As shown in fig. 22, the ultrasonic atomizing device 100 includes a container 10 that contains a liquid F and an ultrasonic transducer 40 that applies ultrasonic vibration to the liquid F. In the ultrasonic atomization device 100, if a high-frequency voltage is applied to the ultrasonic transducer 40, the vibration of the ultrasonic wave S is transmitted to the liquid F in the container 10, and a liquid column R with a raised liquid surface is formed. The surface of the liquid column R held by the surface tension of the liquid F is broken by the vibration of the ultrasonic wave S, and the atomized particles M, that is, the mist of the liquid F is generated.

In the ultrasonic atomization device 100, it is difficult to relate all the vibration energy of the ultrasonic wave S generated from the ultrasonic transducer 40 to the generation of the atomized particles M. Thus, various attempts for obtaining higher atomization efficiency have been made. Patent document 1 discloses a technique of selecting a region in which a reactance between a series resonance frequency fr and a parallel resonance frequency fa of a transducer becomes inductive as a frequency at which a mist generation amount is largest. Patent document 2 discloses a technique of driving a piezoelectric vibrator at maximum power by making the phase of a driving voltage in an equivalent circuit of the piezoelectric vibrator coincide with the phase of a current in a series resonant circuit, thereby automatically tracking the driving frequency of the piezoelectric vibrator to the series resonant frequency.

Prior art documents

Patent document

Patent document 1: japanese laid-open patent publication No. 50-156018

Patent document 2: japanese laid-open patent publication (Kokai) No. 2012 and 110867

In the technique described in patent document 1, since the frequency range in which the generation of mist is maximized is narrower than the frequency range between the series resonance frequency (resonance frequency) and the parallel resonance frequency (anti-resonance frequency), it is difficult to obtain high atomization efficiency even when the vibrator is driven at a frequency between the resonance frequency and the anti-resonance frequency. Further, in the technique described in patent document 1, since the oscillator circuit of the oscillator is configured by a kopitz (Korpitz) type circuit, it is difficult to perform low-power driving using a battery or the like as a power source. In the technique described in patent document 2, a circuit is assumed in which only 1 series resonant circuit is provided as an equivalent circuit for driving the piezoelectric vibrator of the piezoelectric vibrator with maximum power, and therefore, when a plurality of series resonant circuits are present in the equivalent circuit, it is difficult to control the driving frequency.

SUMMERY OF THE UTILITY MODEL

Problem to be solved by utility model

In view of the above problems, an object of the present invention is to provide a drive circuit for an ultrasonic transducer and an ultrasonic atomizing device that can achieve high atomizing efficiency even when driven at low power.

Means for solving the problems

The present invention solves the above problems, and includes the following.

[1] An ultrasonic atomizing device for atomizing a liquid by applying vibrational energy to the liquid from ultrasonic waves generated by an ultrasonic vibrator formed in a disk shape, the ultrasonic vibrator including a 1 st electrode formed on one surface of the ultrasonic vibrator and a 2 nd electrode formed on the other surface of the ultrasonic vibrator, a region in which the 1 st electrode is formed being a 1 st region provided on the one surface and a region in which the 2 nd electrode is formed being a 2 nd region provided on the other surface, the 2 nd region being narrower than the 1 st region and being entirely included in the 1 st region in a plan view of the ultrasonic vibrator, the ultrasonic vibrator having, as a vibration mode when a drive voltage is applied between the 1 st electrode and the 2 nd electrode: a 1 st vibration mode that vibrates in the opposing direction between the entire region of the one surface and the entire region of the other surface; and a 2 nd vibration mode that vibrates in the opposing direction between the 2 nd region in the other surface and a region corresponding to the 2 nd region in the one surface, the ultrasonic transducer being driven at a frequency of the 2 nd vibration mode.

[2] The ultrasonic atomizing device according to [1], wherein a frequency of the ultrasonic vibrator vibrating in the opposing direction is set within ± 3% of a resonance frequency of the 2 nd vibration mode.

[3] The ultrasonic atomizing device according to [1] or [2], wherein the 1 st vibration mode is a vibration mode in which the ultrasonic vibrator is vibrated at a 1 st resonance frequency, and the 2 nd vibration mode is a vibration mode in which the ultrasonic vibrator is vibrated at a 2 nd resonance frequency higher in frequency than the 1 st resonance frequency.

[4] The drive circuit of the ultrasonic vibrator includes: an ultrasonic vibrator configured to vibrate when a driving voltage is applied; a pseudo oscillator connected in parallel to the ultrasonic oscillator as a compensation circuit; a subtracting unit that subtracts a voltage corresponding to a current flowing to the pseudo vibrator when the drive voltage is applied to the pseudo vibrator, from a voltage corresponding to a current flowing to the ultrasonic vibrator when the ultrasonic vibrator vibrates; a phase difference detection unit that detects a voltage corresponding to a phase difference between a phase of the drive voltage and a phase of the subtracted voltage; and a voltage-controlled oscillation unit that controls a frequency of the driving voltage based on the detected voltage, the ultrasonic vibrator vibrating at the controlled frequency.

[5] A drive circuit of an ultrasonic transducer including an ultrasonic transducer formed in a disk shape, the ultrasonic transducer including a 1 st electrode formed on one surface of the ultrasonic transducer, and a 2 nd electrode and a 3 rd electrode formed on another surface of the ultrasonic transducer, a region where the 1 st electrode is formed being a 1 st region provided on the one surface, a region where the 2 nd electrode is formed being a 2 nd region provided on the other surface, the 2 nd region being narrower than the 1 st region, the 3 rd electrode being formed outside the 2 nd electrode on the other surface, the drive circuit of the ultrasonic transducer including: a phase difference detection unit that detects a voltage corresponding to a phase difference between a phase of the driving voltage and a phase of a voltage generated between the 1 st electrode and the 3 rd electrode when the driving voltage is applied between the 1 st electrode and the 2 nd electrode; and a voltage-controlled oscillation unit that controls a frequency of the driving voltage based on the detected voltage, and drives the ultrasonic transducer at the controlled frequency.

The ultrasonic atomizing device atomizes the liquid by applying vibration energy to the liquid from ultrasonic waves generated by a drive circuit using the ultrasonic vibrator described in [6], [4], or [5 ].

Effect of the utility model

According to the present invention, a drive circuit for an ultrasonic transducer and an ultrasonic atomizing device can be obtained which can achieve high atomizing efficiency even under low-power driving.

Drawings

Fig. 1 is a plan view schematically showing the structure of an ultrasonic transducer according to embodiment 1 of the present invention.

Fig. 2 is a circuit diagram showing a state where an ac voltage is applied to the ultrasonic transducer shown by the X-X cross section of fig. 1.

Fig. 3 is a graph showing a relationship between the frequency and the impedance of the vibrator in each vibration mode in the circuit shown in fig. 2.

Fig. 4A to 4D are diagrams illustrating a relationship between a vibration mode of the ultrasonic transducer and generated ultrasonic waves.

Fig. 5 is a graph showing a relationship between the frequency of the ultrasonic transducer and the atomization amount when driven at high power.

Fig. 6 is a graph showing a relationship between the frequency of the ultrasonic transducer and the atomization amount when the ultrasonic transducer is driven at low power.

Fig. 7 is a block diagram schematically showing a drive circuit of an ultrasonic transducer according to embodiment 2 of the present invention.

Fig. 8A to 8C are circuit diagrams showing specific examples of the dummy vibrator used in embodiment 2.

Fig. 9 is a diagram showing an equivalent circuit when a dummy oscillator is configured by an LCR series circuit and a parallel circuit of C.

Fig. 10 is a graph showing the relationship of frequency, impedance, and phase difference characteristics according to the presence or absence of a dummy oscillator formed by an LCR series circuit.

Fig. 11 is a diagram showing an equivalent circuit when a pseudo oscillator is formed by a ceramic oscillator.

Fig. 12 is a graph showing a relationship among frequency, impedance, and phase difference characteristics according to the presence or absence of a pseudo oscillator formed of a ceramic oscillator.

Fig. 13 is a graph showing a relationship between the presence or absence of a pseudo oscillator formed by a ceramic oscillator and the atomization amount.

Fig. 14 is a block diagram schematically showing a driving circuit of the ultrasonic transducer according to embodiment 3.

Fig. 15 is a plan view schematically showing the structure of the ultrasonic transducer according to embodiment 3.

Fig. 16 is a circuit diagram showing a state where an ac voltage is applied to the ultrasonic transducer shown by the Y-Y cross section of fig. 15.

Fig. 17 is a diagram showing the relationship between the frequency, the impedance, and the phase difference characteristic in the transducer of the circuit of fig. 16.

Fig. 18 is a plan view schematically showing the structure of an ultrasonic transducer according to a modification of embodiment 3.

Fig. 19 is a plan view schematically showing the structure of an ultrasonic transducer according to another modification of embodiment 3.

Fig. 20 is a plan view schematically showing the structure of an ultrasonic transducer according to embodiment 3 as a further modification.

Fig. 21 is a schematic view showing an atomization state in a case where the ultrasonic transducer of embodiment 1 is applied to an ultrasonic atomization apparatus.

Fig. 22 is a schematic diagram showing an atomization state in the ultrasonic atomization apparatus.

Description of the symbols

2: an ultrasonic vibrator;

5: a 1 st electrode;

6: a 2 nd electrode;

7: a power source;

22: a pseudo oscillator;

22 c: a ceramic oscillator;

35: and a feedback electrode.

Detailed Description

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

(embodiment 1)

Embodiment 1 of the present invention will be described with reference to fig. 1 and 2. Fig. 1 is a plan view schematically showing the structure of an ultrasonic transducer according to embodiment 1, and fig. 2 is a circuit diagram showing a state where an ac voltage is applied to the ultrasonic transducer as shown by the cross section X-X in fig. 1.

The ultrasonic transducer 2 shown in fig. 1 and 2 is suitable for generating ultrasonic waves used for atomizing a liquid, and has a disk-like shape. In fig. 1, the upper surface in the figure is referred to as an upper surface or a top surface, and the lower surface is referred to as a lower surface or a bottom surface. In the ultrasonic transducer 2, the opposing upper and lower surfaces have the same area. The term "equal area" includes the case where the areas of the upper surface and the lower surface are different from each other for reasons such as manufacturing.

An electrode 5 as a 1 st electrode is formed on the upper surface of the ultrasonic transducer 2. The electrode 5 may be provided over the entire upper surface of the ultrasonic transducer, or may be provided in a region narrower than the entire region. On the other hand, an electrode 6 as a 2 nd electrode is formed on the lower surface of the ultrasonic transducer 2. The area of the region in which the electrode 6 is formed is narrower than the area of the region in which the electrode 5 is formed in the upper surface, and the region in which the electrode 6 is formed is entirely included in the region in which the electrode 5 is formed in the upper surface in a plan view of the ultrasound transducer 2. The plan view of the ultrasonic transducer 2 means that the ultrasonic transducer 2 is viewed from a direction along the thickness direction of the ultrasonic transducer 2. Between the electrodes 5 and 6, a driving voltage V as an alternating voltage is applied to drive the ultrasonic transducer 2₀From this alternating current I₀And (4) flowing.

In this way, if a driving voltage V is applied as an alternating current between the electrodes 5, 6₀The ultrasonic transducer 2 generates primary vibration that vibrates in the longitudinal direction in fig. 1, that is, in the thickness direction, due to the inverse piezoelectric effect. The longitudinal direction is also the direction in which the electrodes 5, 6 are opposed. The primary vibration has a plurality of vibration modes according to the area of the electrode formed on the ultrasonic transducer 2. The 1 kind of vibration mode is a mode of primary vibration 12 that vibrates the entire ultrasonic transducer 2 in the longitudinal direction corresponding to the entire region of the ultrasonic transducer 2, and is referred to as a vibration mode a. The other 1 vibration mode is a mode in which a region in which the vibration electrode 6 is formed as a part of the ultrasonic transducer 2 is formed in the longitudinal direction in accordance with the area of the electrode 6The mode of the primary vibration 13 is referred to as vibration mode B. The vibration mode a and the vibration mode B are the 1 st vibration mode and the 2 nd vibration mode, respectively. Among the resonance frequencies of the ultrasonic transducer 2, there are a resonance frequency FrA that causes the vibration mode a and a resonance frequency FrB that causes the vibration mode B.

As a method for forming the electrode in the ultrasonic transducer 2, it is possible to use: known techniques include screen printing, various coating methods of metal powder and molten metal, and a method of forming a film formed by sputtering or vapor deposition using a fine processing technique such as photolithography. The disk-shaped ultrasonic transducer includes a case where the 2-dimensional planar shape of the transducer is a perfect circle and a case where the transducer can be understood as a circle at a glance, and further includes a case where the ratio of the radius in the major axis direction to the radius in the minor axis direction in the 2-dimensional planar shape is 0.8 or more.

Next, the relationship between the frequency and the impedance of the ultrasonic transducer 2 in the circuit of fig. 2 will be described with reference to fig. 3. Fig. 3 shows the relationship between the frequency of the transducer and the impedance Z in the vibration mode a of the primary vibration 12 and the vibration mode B of the primary vibration 13, and the value obtained by measuring the frequency characteristic of the impedance Z of the ultrasonic transducer 2 using the circuit shown in fig. 2. In fig. 3, the horizontal axis represents the frequency (MHz) of the transducer, and the vertical axis represents the impedance Z (Ω). Referring to fig. 3, it is understood that the resonance frequency Fr and the antiresonance frequency Fa exist in the frequency characteristics of the entire ultrasonic transducer 2 obtained from the actual measurement value of the impedance Z. It is understood that the resonance frequency FrA of the vibration mode a is substantially equal to the resonance frequency Fr of the entire ultrasonic transducer 2. Further, it is found that the resonance frequency FrB for the vibration mode B is between the resonance frequency Fr and the anti-resonance frequency Fa of the entire ultrasonic transducer 2 and is higher than the resonance frequency FrA for the vibration mode a. In the embodiments described below, the resonance frequency of the ultrasonic transducer 2 is described on the premise that the resonance frequency FrB that causes the vibration mode B is used. The reason for this will be described with reference to fig. 4A to 4D. Fig. 4A to 4D are diagrams illustrating a relationship between a vibration mode of the ultrasonic transducer and generated ultrasonic waves, and show that the ultrasonic transducer 3 vibrates in the longitudinal direction by hatching formed by lines extending in the vertical direction.

In the ultrasonic transducer 2 described with reference to fig. 1 and 2, a drive voltage V is applied from the power supply 7 to between the electrodes 5 and 6₀Make an alternating current I₀And (4) flowing. As shown in fig. 4A, the ultrasonic transducer 2 vibrates in the longitudinal direction due to the inverse piezoelectric effect. If the frequency of the drive voltage is set to the resonance frequency FrA of the vibration mode a to vibrate the ultrasonic transducer 2, the entire ultrasonic transducer 2 is vibrated, and thus a large amount of drive energy is required. On the other hand, as shown in fig. 4B, if the ultrasonic transducer 2 is vibrated at the resonance frequency FrB of the vibration mode B, the portion of the ultrasonic transducer 2 corresponding to the electrode B is vibrated in the longitudinal direction by the primary vibration 13 under the condition that the atomization amount becomes the maximum efficiency (see fig. 5). This is because, when the ultrasonic transducer 2 is vibrated at the resonance frequency FrB of the vibration mode B, the portion corresponding to the electrode 6 is vibrated in accordance with the portion mainly radiating the ultrasonic energy, and thus the driving energy for the vibration may be small.

When the ultrasonic transducer 2 is attached to the ultrasonic atomizing device to atomize the liquid, the ultrasonic transducer generated from a predetermined region in the center of the surface of the transducer is used as the ultrasonic wave generated from the ultrasonic transducer 2 because of the mechanical restriction as described later, as shown in fig. 4C. Therefore, as shown in fig. 4A, when the primary vibration 12 of the vibration mode a is used, the primary vibration 12 generated at the illustrated left and right end portions P1 and P2 of the ultrasonic transducer 2 becomes useless as shown in fig. 4D. Therefore, in the present embodiment, as shown in fig. 4B, the primary vibration 13 of the vibration mode B generated at the portion P3 of the ultrasonic transducer 2 corresponding to the electrode 6 due to the inverse piezoelectric effect of the electrode 6 is used.

The following describes the results of experiments performed by the inventors of the present invention with respect to embodiment 1.

< example 1>

In the ultrasonic atomizing apparatus, in order to obtain high atomizing efficiency, an experiment was performed under the following conditions with respect to the relationship between the oscillation frequency of the ultrasonic transducer 2 and the atomizing amount of the ultrasonic atomizing apparatus. Fig. 5 shows a relationship between the frequency of the ultrasonic transducer 2 and the amount of atomization when the ultrasonic transducer 2 is driven at a high power. The horizontal axis represents the frequency (MHz) of the oscillator, and the vertical axis represents the impedance Z (Ω) and the atomization amount (%). The resonance frequency FrB in vibration mode B was set to 1.705MHz, the input power of the ultrasonic transducer 2 was set to 22W, the atomizing spray was tap water, and the water temperature was set to 23 ℃. The ultrasonic atomization device was driven for 10 minutes, and the atomization amount was calculated from the weight difference before and after the driving of the ultrasonic atomization device.

As a result of the experiment, the atomization amount reached 100% at a resonance frequency FrB of a vibration mode B in which a portion of the ultrasonic transducer 2 corresponding to the formation region of the electrode 6 was caused to vibrate in the longitudinal direction, which was 1.705 MHz. Accordingly, it is found that when the frequency of the ultrasonic transducer 2 is within a range of 1.705MHz ± 0.05MHz, that is, a frequency of FrB ± 3%, the atomization amount becomes 80% or more with respect to the maximum value, and a high atomization efficiency is obtained.

< example 2>

In the ultrasonic atomizing apparatus, in order to obtain high atomizing efficiency, an experiment was performed under the following conditions with respect to the relationship between the oscillation frequency of the ultrasonic transducer 2 and the atomizing amount of the ultrasonic atomizing apparatus. Fig. 6 shows a relationship between the frequency of the ultrasonic transducer 2 and the atomization amount when the ultrasonic transducer 2 is driven at low power. The horizontal axis represents the frequency (MHz) of the oscillator, and the vertical axis represents the impedance Z (Ω) and the atomization amount (%). The resonance frequency FrB in vibration mode B was set to 1.705MHz, the input power of the ultrasonic transducer 2 was set to 10W, the atomizing spray was tap water, and the water temperature was set to 23 ℃. The ultrasonic atomization device was driven for 10 minutes, and the atomization amount was calculated from the weight difference before and after the driving of the ultrasonic atomization device.

As a result of the experiment, the atomization amount reached 100% at a resonance frequency FrB of a vibration mode B in which a portion of the ultrasonic transducer 2 corresponding to the formation region of the electrode 6 was caused to vibrate in the longitudinal direction, which was 1.705 MHz. Accordingly, it is found that if the frequency of the ultrasonic transducer 2 is within a range of 1.705MHz ± 0.025MHz, that is, a frequency of FrB ± 1.4%, the atomization amount becomes 80% or more with respect to the maximum value, and a high atomization efficiency can be obtained. Even when the ultrasonic transducer 2 is driven at low power, high atomization efficiency can be achieved.

In the present embodiment, a mode in which the ultrasonic transducer 2 is vibrated by the inverse piezoelectric effect is set, and the resonance frequency FrB of the vibration mode B is set to the driving frequency of the ultrasonic transducer 2, whereby high atomization efficiency can be obtained. Further, according to the present embodiment, high atomization efficiency can be obtained even in low-power driving in which a battery or the like is used as an example of a power source. In order to obtain these effects, the driving frequency of the ultrasonic transducer 2 is preferably set to be within ± 3% of the resonance frequency of the vibration mode B.

(embodiment 2)

< Structure of Driving Circuit of ultrasonic transducer >

Next, embodiment 2 of the present invention will be described with reference to fig. 7. Fig. 7 is a block diagram schematically showing a driving circuit of the ultrasonic transducer according to embodiment 2. As shown in the figure, the drive circuit 200 of the ultrasonic transducer includes a drive signal generation amplifier circuit 20, an ultrasonic transducer 2, a dummy transducer 22 as a compensation circuit, a subtraction circuit 24, a phase difference detection circuit 26, and a VCO (Voltage Controlled Oscillator) 18.

The drive signal generation amplifier circuit 20 outputs a drive voltage V for driving the ultrasonic transducer 2 with the drive frequency signal 19 output from the VCO18 as an input₀. The ultrasonic transducer 2 is driven by a drive voltage V output from a drive signal generating amplifier circuit 20₀Driven as an input and vibrating. The ultrasonic transducer 2 outputs a transducer driving current I corresponding to the transducer driving current I from a current detection element connected in series with the ultrasonic transducer 2 to the subtraction circuit 24₀The voltage signal 21. The current detection element is, for example, a capacitor C1 shown in fig. 9 described later. The pseudo oscillator 22 is formed of an element or circuit network of the analog ultrasonic oscillator 2 and generates the drive voltage V from the drive signal generating amplifier circuit 20₀As an inputOutputs a current I equivalent to the current flowing to the pseudo oscillator 22 to the subtraction circuit 24_P Voltage signal 23. The current flowing through the dummy oscillator 22 is detected by a current detection element connected in series with the dummy oscillator 22. The current detection element here is, for example, a capacitor C2 shown in fig. 9 described later. As the current detection element, a resistance element can be used instead of the capacitors C1 and C2, and current detection can be performed in the same manner.

The subtraction circuit 24 drives the current I from the oscillator₀The voltage signal 21 is subtracted by the current I flowing to the pseudo oscillator 22_P Voltage signal 23. The subtraction circuit 24 outputs a subtracted signal 25 obtained by the subtraction to the phase difference detection circuit 26. The phase difference detection circuit 26 uses the oscillator drive voltage V outputted from the drive signal generation amplification circuit 20₀And a subtracted signal 25 output from the subtraction circuit 24 as an input, and outputs a voltage corresponding to a phase difference of the two signals as a VCO control signal 27. The VCO18 receives the VCO control signal 27 as an input, and changes the frequency of the drive frequency signal 19 output to the drive signal generation amplification circuit 20 in accordance with the value of the VCO control signal 27. The circuit configuration of the driving circuit 200 can suppress the vibration frequency of the ultrasonic transducer 2 within a generally predetermined range. This point will be explained in the following operation column.

Here, a specific circuit configuration of the dummy oscillator 22 as a compensation circuit will be described with reference to fig. 8A to 8C. The dummy oscillator 22 shown in fig. 8A has a circuit configuration 28 in which an LCR series circuit, which is a circuit in which a capacitor (C) is connected in series with a coil (L), a capacitor (C), and a resistor (R), is connected in parallel. The pseudo oscillator 22 shown in fig. 8B has an electronic component 29 such as a piezoelectric oscillator, a ceramic oscillator, and a quartz oscillator, in which an equivalent circuit is shown as a circuit configuration in which a capacitor C is connected in parallel to an LCR series circuit. The dummy vibrator 22 shown in fig. 8C has a circuit configuration 30 in which a plurality of LCR series circuits are connected in parallel, and further capacitors C are connected in parallel. In the example shown in fig. 8C, 2 LCR series circuits are connected in parallel, but the number of parallel LCR series circuits can be set to any number. By using such a dummy transducer 22, even when an ultrasonic transducer 2 having a plurality of series resonant circuits in an equivalent circuit is used, the driving frequency can be controlled as described below.

< operation of ultrasonic drive Circuit >

Next, the operation of the ultrasonic transducer driving circuit 200 will be described with reference to fig. 7. First, it is assumed that the subtracted signal 25 output from the subtraction circuit 24 and the transducer drive voltage V output from the drive signal generation amplification circuit 20₀The resulting phase difference between the signals of (1) is phi. Then, particularly, when the resonance frequency FrB at which the vibration mode B is caused to occur is a desired resonance frequency and the ultrasonic vibrator 2 vibrates at the desired resonance frequency, the vibrator driving voltage V is set to be the vibrator driving voltage V₀The phase difference between the subtracted signal 25 and the signal of (B) is represented by Φ B. Hereinafter, the desired resonance frequency is referred to as a drive frequency.

There is a characteristic that if the frequency of the drive circuit 200 becomes higher than the resonance frequency FrB at which the vibration mode B is caused to occur, the phase difference Φ becomes larger than the phase difference Φ B when the ultrasonic transducer 2 is driven at the resonance frequency FrB. Further, there is a characteristic that if the frequency of the drive circuit 200 becomes lower than the resonance frequency FrB at which the vibration mode B is caused to occur, the phase difference Φ becomes smaller than the phase difference Φ B when the ultrasonic transducer 2 is driven at the resonance frequency FrB. Therefore, the phase difference detection circuit 26 performs the operation described below. That is, if the phase difference Φ of the input 2 signals, i.e., the transducer driving voltage V₀When the phase difference Φ between the signal (2) and the subtracted signal (25) becomes larger than the phase difference Φ B, the VCO control signal (27) to be outputted is reduced. Further, if the phase difference Φ of the input 2 signals becomes smaller than the phase difference Φ B, the operation is such that the VCO control signal 27 output therefrom is increased.

The VCO18 operates to automatically follow the drive frequency to the resonant frequency FrB by increasing the output drive frequency signal 19 if the input VCO control signal 27 is large and decreasing the output drive frequency signal 19 if the VCO control signal 27 is small. This can suppress the driving frequency of the ultrasonic transducer 2 within a predetermined range. That is, in the frequency characteristic of the phase difference Φ in the vicinity of the drive frequency, the relationship between the phase difference Φ and the frequency tends to have a single slope (also referred to as a monotonic slope) having no inflection point and no flat characteristic, as will be described later, and thus the desired drive frequency can be suppressed within a predetermined range. In addition, according to the present embodiment, the driving circuit 200 of the ultrasonic transducer is configured only by components such as the amplifying circuit 20 for generating a driving signal, the ultrasonic transducer 2, the dummy transducer 22, the subtraction circuit 24, the phase difference detection circuit 26, and the VCO 18. Therefore, it is not necessary to provide a member for heat radiation of a radiator or the like. This has the effect of reducing the structural restrictions.

A specific example of the driving circuit 200 including the dummy oscillator 22 will be described below.

< example 1>

A case where an LCR series circuit is used as the dummy vibrator 22 will be described with reference to fig. 9. Fig. 9 shows a circuit including the ultrasonic vibrator 2 and the pseudo vibrator 22 by an equivalent circuit constituted by an LCR series circuit and a parallel circuit of C. In fig. 9, the ultrasonic transducer 2 includes a series resonant circuit 120 that generates a vibration mode a, a series resonant circuit 130 that generates a vibration mode B, and a brake capacitor 140. The series resonant circuit 120 that generates the vibration mode a is an LCR series circuit in which the coil Lm1, the capacitor Cm1, and the resistor Rm1 are connected in series. Further, the series resonant circuit 130 that generates the vibration mode B is an LCR series circuit in which the coil Lm2, the capacitor Cm2, and the resistor Rm2 are connected in series. In the series resonant circuit of the 2 vibration modes, a braking capacitor 140 including a capacitor Cd is connected in parallel. On the other hand, the dummy vibrator 22 is a circuit in which an LCR series circuit in which the coil Lm1x, the capacitor Cm1x, and the resistor Rm1x are connected in series is connected in parallel with the capacitor Cdx.

In the equivalent circuit shown in fig. 9, the value of the circuit constant of each of the coil Lm1x, the capacitor Cm1x, and the resistor Rm1x of the dummy transducer 22 and the electric constant of the coil Lm1, the capacitor Cm1, and the resistor Rm1 of the series resonant circuit 120 that generates the vibration mode a of the ultrasonic transducer 2 are set to be equal to each otherThe value of the path constant is almost the same, and the value of the capacitor Cdx of the pseudo oscillator 22 is made almost the same as the value of the capacitor Cd as the braking capacitance 140 of the ultrasonic oscillator 2. This is because the subtraction circuit 24 (see fig. 7) drives the current I from the oscillator equivalent₀The voltage signal 21 is subtracted by the current I flowing to the pseudo oscillator 22_PSo that only a voltage signal corresponding to the current flowing to the series resonant circuit 130 causing the vibration mode B remains in the subtracted signal 25.

Fig. 10 shows the relationship between the frequency, the impedance Z, and the phase difference in the case where the dummy oscillator 22 is configured by an LCR series circuit and the dummy oscillator 22 is used. In the figure, a broken line 31 shows that when the dummy transducer 22 is used, the current I is driven from the transducer equivalent to the transducer₀The voltage signal 21 is subtracted by the current I flowing to the pseudo oscillator 22_PA subtracted signal 25 obtained from the voltage signal 23 and a vibrator driving voltage V₀The phase difference of the signals of (a).

When the dummy oscillator 22 is not used, it corresponds to the oscillator drive current I₀Voltage signal 21 and oscillator drive voltage V₀The phase difference of the signal (2) has a characteristic as shown by the one-dot chain line 32 in fig. 10. In this case, the phase difference characteristic indicated by the one-dot chain line 32 has an inflection point in the region L in the vicinity of the resonance frequency FrB that causes the vibration mode B, and thus it becomes difficult to uniquely determine the drive frequency using the phase difference detection circuit 26 (see fig. 7). On the other hand, when the dummy transducer 22 is used, the phase difference characteristic shown as the broken line 31 in fig. 10 has a single slope shown in the upper right in fig. 10 in the region N in the vicinity of the resonance frequency FrB that causes the vibration mode B, and therefore the drive frequency can be uniquely determined by the phase difference detection circuit 26 (see fig. 7). In this way, when the ultrasonic transducer 2 has 2 vibration modes, i.e., the vibration mode a and the vibration mode B, the desired drive frequency can be set to a predetermined fixed frequency by making the frequency characteristic of the phase difference Φ in the vicinity of the desired resonance frequency have a single slope. The desired resonant frequency here is the resonant frequency FrB of vibration mode B。

< example 2>

Next, a case where a ceramic oscillator as a pseudo resonant circuit is used as the pseudo oscillator 22 functioning as a circuit for compensation will be described with reference to fig. 11. Fig. 11 is a diagram showing an equivalent circuit when the ceramic oscillator 22c is used to form the dummy oscillator 22. In fig. 11, the ultrasonic transducer 2 includes a series resonant circuit 121 for generating a vibration mode a, a series resonant circuit 131 for generating a vibration mode B, and a brake capacitor 141. The series resonant circuit 121 that generates the vibration mode a is an LCR series circuit in which the coil L3, the capacitor C7, and the resistor R4 are connected in series. The series resonant circuit 131 that generates the vibration mode B is an LCR series circuit in which the coil L4, the capacitor C1, and the resistor R1 are connected in series. The brake capacitance 141 including the capacitor C8 is connected in parallel with respect to the series resonant circuit of the 2 vibration modes. On the other hand, the ceramic oscillator 22C is configured by an LCR series circuit in which the coil L1, the capacitor C5, and the resistor R2 are connected in series, and a circuit in which the capacitors C2 and C4 are connected in parallel.

In the equivalent circuit of fig. 11, the ultrasonic transducer 2 is provided with a voltage signal attenuation capacitor C6 for attenuating a voltage V1 corresponding to a transducer driving current of the ultrasonic transducer 2. The ceramic oscillator 22C is provided with a capacitor C3 for attenuating a voltage signal corresponding to a voltage V2 of a current flowing in the ceramic oscillator 22C. The ceramic oscillator 22c is generally commercially available, and only a ceramic oscillator having a predetermined circuit constant exists. Therefore, the circuit constant in the equivalent circuit of the ceramic oscillator 22c generally does not match the circuit constant of the series resonant circuit 121 having the resonant frequency FrA of the ultrasonic transducer 2 that generates the vibration mode a and the circuit constant of the brake capacitor 141. That is, since a difference occurs between the current value flowing through the series resonant circuit 121 and the brake capacitor 141 of the ultrasonic transducer 2 and the current value flowing through the ceramic oscillator 22c, even if the voltage signal corresponding to the current value is directly subtracted by the subtraction circuit 24, a desired phase difference characteristic cannot be obtained.

Therefore, in this circuit, the capacitor C6 is connected in series to the output terminal of the ultrasonic transducer 2, and the resistor R3 and the capacitor C3 are connected in series in this order to the output terminal of the ceramic oscillator 22C. The capacitor C18 is connected in parallel to the resistor R3, and the capacitor C12 is connected in parallel to the ceramic oscillator 22C. The capacitors C3 and C6 are provided to divide the voltage at the output terminals. By providing the resistor and the capacitor in addition to the above, the output levels of the voltage signal 21c corresponding to the divided voltage of the transducer driving current, i.e., the voltage V1 in fig. 11, and the voltage signal 23c corresponding to the divided voltage of the current flowing through the dummy transducer, i.e., the voltage V2 in fig. 11, can be adjusted. Then, in the subtraction circuit 24, the voltage signal 23c corresponding to the divided voltage of the current flowing to the dummy transducer is subtracted from the voltage signal 21c corresponding to the divided voltage of the transducer driving current. As a result, only the voltage signal corresponding to the current flowing through the series resonant circuit 131 in the vibration mode B remains in the post-subtraction signal 25.

Fig. 12 shows the relationship between the frequency, the impedance Z, and the phase difference in the case where the pseudo oscillator is configured by the ceramic oscillator 22c and the pseudo oscillator is used. The phase difference characteristic with respect to frequency in the subtracted signal 25 becomes such a characteristic as shown in fig. 12. In fig. 12, a broken line 31c shows a subtracted signal 25 obtained by subtracting a voltage signal 23c corresponding to a current flowing through the ceramic oscillator 22c from a voltage signal 21c corresponding to a vibrator driving current, and a vibrator driving voltage V when the ceramic oscillator 22c is used₀The phase difference of the signals of (a).

When the ceramic oscillator 22c is not used, the oscillator drive voltage V and the voltage signal 21c corresponding to the oscillator drive current₀The frequency characteristic of the phase difference of the signal (c) becomes a characteristic as shown by a one-dot chain line 32c in fig. 12. In this case, the phase difference characteristic shown as the one-dot chain line 32c has an inflection point in the region Lc in the vicinity of the resonance frequency FrB that causes the vibration mode B, and thus it becomes difficult to uniquely determine the drive frequency using the phase difference detection circuit 26 (see fig. 7). On the other hand, when the ceramic vibrator 22c is used, the phase difference characteristic shown by the broken line 31c in fig. 12 is in the vicinity of the resonance frequency FrB at which the vibration mode B is generatedSince the region Nc has a single slope shown at the upper right in fig. 12, the driving frequency can be uniquely determined by using the phase difference detection circuit 26 (see fig. 7). As described above, when the ultrasonic transducer 2 has 2 vibration modes, that is, the vibration mode a and the vibration mode B, in the specific example shown here, the frequency characteristic of the phase difference Φ in the vicinity of the desired resonance frequency, which is the resonance frequency FrB of the vibration mode B, can be made to have a single slope, and the desired drive frequency can be made to be a fixed frequency which is normally determined in advance.

As described above, in the present embodiment, by extracting the current signal flowing through the series resonant circuit, which indicates the resonant frequency FrB that causes the vibration mode B, a high atomization efficiency can be obtained. Further, the ceramic oscillator 22C is selected to have a resonant frequency close to the resonant frequency FrA for generating the vibration mode a, and the constants of the capacitors C12, C6, and C3 are adjusted, whereby the phase difference characteristic with a single slope can be obtained.

In the present embodiment, an example is described in which a voltage signal 23 corresponding to a current flowing to a dummy transducer 22 having a circuit for generating a vibration mode a is subtracted from a voltage signal 21 corresponding to a transducer driving current of an ultrasonic transducer 2 having a circuit for generating a vibration mode a and a vibration mode B. In addition, a plurality of circuits for generating the vibration mode a may be connected in parallel to each of the circuit of the ultrasonic transducer 2 and the circuit of the dummy transducer 22, and only a voltage signal corresponding to a current flowing through the series resonant circuits 130 and 131 for generating the vibration mode B may be left by subtraction. This enables control of the drive frequency even when a plurality of series resonant circuits are present.

The results of the experiment conducted by the inventors of the present invention with respect to embodiment 2 will be described below.

< example 3>

In order to obtain high atomization efficiency in the ultrasonic atomization apparatus, experiments were performed under the following conditions with respect to the relationship between the presence or absence of the pseudo oscillator and the atomization amount of the ultrasonic atomization apparatus. Fig. 13 shows the results of comparison of the atomization amount with the presence or absence of the pseudo oscillator formed by the ceramic oscillator 22c, and the vertical axis shows the atomization amount (%). As the ultrasonic transducer 2, an ultrasonic transducer having a resonance frequency FrA in the vibration mode a of 4.0MHz and a resonance frequency FrB in the vibration mode B of 4.2MHz was used. As the ceramic oscillator 22c, a ceramic oscillator having a resonance frequency froc of 4.0MHz close to the resonance frequency FrA of the ultrasonic transducer 2 that generates the vibration mode a is used. The input power of the ultrasonic transducer 2 was 2.2W, the atomizing spray was tap water, and the water temperature was 23 ℃ as the measurement conditions. The ultrasonic atomization device was driven for 10 minutes, and the atomization amount was calculated from the weight difference before and after the driving of the ultrasonic atomization device.

As a result of the experiment, it was found that when the ceramic oscillator 22c was used as the pseudo oscillator, the atomization amount was increased by 40% or more as compared with the case where the ceramic oscillator 22c was not used, and it was found that a higher atomization efficiency was obtained by using the ceramic oscillator 22 c. Thus, even when the ultrasonic atomizing device is driven at low power, high atomizing efficiency can be achieved. In example 3, the ceramic oscillator 22c is used as the pseudo oscillator 22, but an oscillator such as a quartz oscillator may be used.

(embodiment 3)

< Structure of Driving Circuit of ultrasonic transducer >

Next, embodiment 3 of the present invention will be described with reference to fig. 14. Fig. 14 is a block diagram schematically showing a driving circuit of the ultrasonic transducer according to embodiment 3. As shown in fig. 14, the driving circuit 201 of the ultrasonic transducer according to embodiment 3 includes a driving signal generating amplifier circuit 20, an ultrasonic transducer 2, a phase difference detection circuit 26, and a VCO18, and a feedback electrode 35 is provided on the ultrasonic transducer 2. Here, only a portion different from the driver circuit shown in fig. 7 will be described.

The ultrasonic transducer 2 is driven by a transducer driving voltage V outputted from a driving signal generating amplifier circuit 20₀Driven for input and vibrated. If the ultrasonic vibrator 2 is driven by a vibrator driving voltage V₀Vibrating for input, thenThe feedback electrode 35 outputs a voltage generated by the piezoelectric effect to the phase difference detection circuit 26 as a feedback electrode generation signal 36. The phase difference detection circuit 26 uses the oscillator drive voltage V outputted from the drive signal generation amplification circuit 20₀And a feedback electrode generation signal 36 outputted from the feedback electrode 35 as an input, and outputs a voltage corresponding to a phase difference between the two signals as the VCO control signal 27. The VCO18 receives the VCO control signal 27 as an input, and changes the frequency of the drive frequency signal 19 to be output from the drive signal generation amplification circuit 20 in accordance with the value of the VCO control signal 27. The circuit configuration of the driving circuit 201 can suppress the variation range of the vibration frequency of the ultrasonic transducer 2 within a predetermined range. The operations of the phase difference detection circuit 26, the VCO18, and the drive signal generation amplifier circuit 20 in the drive circuit 201 are the same as those of the drive circuit 200 described with reference to fig. 7, and therefore detailed description thereof is omitted.

< method for determining drive frequency Using feedback electrode >

A method of determining a driving frequency using the feedback electrode 35 according to the present embodiment will be described with reference to fig. 15 and 16. Fig. 15 is a plan view schematically showing the structure of the ultrasonic transducer according to embodiment 3, and fig. 16 is a circuit diagram showing a state in which an ac voltage is applied to the ultrasonic transducer shown by a cross section Y-Y in fig. 15. As shown in fig. 15 and 16, the electrodes 5 and 6 are formed on the upper surface and the lower surface of the ultrasonic transducer 2, respectively, as described in embodiment 1 with reference to fig. 1 and 2. In the present embodiment, an annular feedback electrode 35 is further formed on the lower surface of the ultrasound transducer 2 outside the electrode 6. And, if the vibrator driving voltage V is applied between the electrode 5 and the electrode 6₀While flowing an alternating current I₀Primary vibration in which the ultrasonic transducer 2 vibrates in the longitudinal direction by the inverse piezoelectric effect is generated. Then, the piezoelectric effect is generated in the ultrasonic transducer 2 by the primary vibration, and as shown in fig. 16, a voltage V is generated as a feedback electrode generation signal 36 between the electrode 5 on the upper surface side and the feedback electrode 35 on the lower surface side₁。

The relationship between the frequency, the impedance, and the phase difference of the ultrasonic transducer 2 in the drive circuit 201 shown in fig. 16 will be described with reference to fig. 17. Relative to vibrator driving voltage V₀The phase difference characteristic of the frequency of the signal of (a) and the feedback electrode generation signal 36 generated by the piezoelectric effect is shown as a thick line 37 in fig. 17. The phase difference characteristic shown as the thick line 37 has a single slope at the upper right in fig. 17 in the region K in the vicinity of the resonance frequency FrB where the vibration mode B is caused to occur. Therefore, it is understood that by using the feedback electrode 35, the driving frequency can be uniquely determined by using the phase difference detection circuit 26 (see fig. 14) without using a dummy oscillator.

< modification example >

The shape of the feedback electrode 35 is not limited to the shape shown in fig. 15 and 16, and the same effect as described above can be obtained even when a feedback electrode 35 having a shape other than the shape is used. For example, the feedback electrode shown in fig. 18 is a feedback electrode obtained by dividing the annular feedback electrode 35 shown in fig. 15 into a plurality of parts. In fig. 18, the annular feedback electrode 35 is divided at 90 ° intervals as viewed from the center of the disk-shaped ultrasonic transducer 2, and a total of 4 feedback electrodes 35 are provided. As shown in fig. 19, a circular feedback electrode 35 may be provided on the lower surface of the ultrasound transducer 2 on the outer peripheral side of the electrode 6, which is the 2 nd electrode, apart from the electrode. In the configuration shown in fig. 19, the shape of the feedback electrode 35 may be a polygon as shown in fig. 20. In the feedback electrode shown in fig. 20, the feedback electrode 35 has a hexagonal shape. The shape of the feedback electrode 35 can be various shapes other than the shape described here.

(ultrasonic atomizing device)

Next, an ultrasonic atomizing device according to the present invention will be described. Fig. 21 is a sectional view showing an ultrasonic atomizing device including the ultrasonic transducer 2 according to embodiment 1. In the ultrasonic atomizing device 101 shown in fig. 21, the ultrasonic transducer 2 is placed on the bottom surface of the container 10 which is a reservoir tank for liquid, and the liquid F is contained in the container 10. In the container 10 and the ultrasonic vibrator2, an annular rubber gasket 4 is provided to prevent liquid leakage. As described with reference to fig. 2, the electrode 5 is formed to cover substantially the entire upper surface of the substantially disk-shaped ultrasonic transducer 2, and the electrode 5 is in contact with the bottom surface of the liquid F. Further, on the lower surface of the ultrasound transducer 2, the electrode 6 is formed so as to cover a region narrower than the electrode 5, and is entirely included in the region of the electrode 5. If a vibrator driving voltage V is applied between 2 electrodes 5, 6 in order to vibrate the ultrasonic vibrator 2 in a primary vibration mode in the longitudinal direction at a resonance frequency₀Then, the ultrasonic wave S is generated from the ultrasonic transducer 2. A wave is generated at a center position where the sound pressure of the ultrasonic wave S is high, and the ultrasonic energy is further concentrated, thereby producing a liquid column R. At this time, countless fine surface waves are formed on the surface of the liquid column R on the liquid surface, and the surface tension of the liquid is reduced, whereby the liquid F is broken up and the liquid droplets are scattered as atomized particles M.

Using driving voltage V by vibrator₀The ultrasonic transducer 2 vibrates in the primary vibration 13 of the vibration mode B due to the inverse piezoelectric effect of the application of (B), thereby generating the ultrasonic wave S. In this case, the diameter of the electrode 6 is preferably set to a size smaller than the inner diameter of the rubber gasket 4. This is for the same reason as described with reference to fig. 4. That is, the ultrasonic wave S generated from the ultrasonic transducer 2 is generated in the range of the electric field 11 formed between the electrodes 5 and 6, but when the outer diameter of the electrode 6 is larger than the inner diameter of the rubber gasket 4, the following problem occurs. This is a problem as follows: when the outer diameter of the electrode 6 is made larger than the inner diameter of the rubber pad 4, the energy of the ultrasonic wave S is absorbed by the rubber pad 4 and lost in a portion where the electrode 6 and the rubber pad 4 overlap each other in the thickness direction of the ultrasonic transducer 2. In this case, only the ultrasonic wave S corresponding to the inner diameter area of the rubber gasket 4 is used for atomization, and thus atomization efficiency is deteriorated.

Therefore, in the ultrasonic atomizing device 101 according to the present invention, the inner diameter of the electrode 6 is set to be equal to or smaller than the inner diameter of the rubber gasket 4, and the transducer driving voltage V is applied between the electrode 5 and the electrode 6₀To drive the ultrasonic transducer 2, thereby responding toAn electric field 11 is generated in the region of the formation region of the electrode 6. The resonance frequency FrB of the primary vibration 13 of the vibration mode B generated in the range corresponding to the formation region of the electrode 6 is set as the drive frequency of the ultrasonic transducer 2. In this manner, by setting the inner diameter of the electrode 6 to a size equal to or smaller than the inner diameter of the rubber gasket 4, the energy of the ultrasonic wave S generated from the ultrasonic transducer 2 can be efficiently transmitted to the liquid F. This can achieve high atomization efficiency. Although not shown, the same effect can be obtained even when the ultrasonic transducer described using fig. 16 is placed on the bottom surface portion of the container 10 of the ultrasonic atomizing device 101.

In addition, although the ultrasonic atomization device 101 shown in fig. 21 has been described using the example in which the ultrasonic transducer 2 according to embodiment 1 is mounted, the drive circuit of the ultrasonic transducer described in embodiment 2 or embodiment 3 may be mounted on the ultrasonic atomization device 101.

The present invention has been described above with reference to the embodiments, and the present invention is not limited to the embodiments. Various modifications can be made in the details and arrangement of the present invention within the scope of the claims.

Claims (6)

1. An ultrasonic atomization device is characterized in that,

the ultrasonic atomizing device atomizes a liquid by applying vibration energy to the liquid from ultrasonic waves generated by an ultrasonic vibrator formed in a disk shape,

the ultrasonic transducer includes a 1 st electrode formed on one surface of the ultrasonic transducer and a 2 nd electrode formed on the other surface of the ultrasonic transducer,

a region in which the 1 st electrode is formed on the one surface is a 1 st region, and a region in which the 2 nd electrode is formed on the other surface is a 2 nd region, the 2 nd region being narrower than the 1 st region and being entirely included in the 1 st region in a plan view of the ultrasonic transducer,

the ultrasonic transducer includes, as a vibration mode when a drive voltage is applied between the 1 st electrode and the 2 nd electrode: a 1 st vibration mode that vibrates in the opposing direction between the entire region of the one surface and the entire region of the other surface; and a 2 nd vibration mode vibrating in the opposing direction between the 2 nd region in the other face and a region corresponding to the 2 nd region in the one face,

the ultrasonic transducer is driven at the frequency of the 2 nd vibration mode.

2. The ultrasonic atomizing device of claim 1,

the frequency of the ultrasonic transducer vibrating in the opposing direction is set within ± 3% of the resonance frequency of the 2 nd vibration mode.

3. The ultrasonic atomizing device according to claim 1 or 2,

the 1 st vibration mode is a vibration mode in which the ultrasonic transducer vibrates at a 1 st resonance frequency, and the 2 nd vibration mode is a vibration mode in which the ultrasonic transducer vibrates at a 2 nd resonance frequency higher in frequency than the 1 st resonance frequency.

4. A drive circuit for an ultrasonic transducer, comprising:

an ultrasonic vibrator configured to vibrate when a driving voltage is applied;

a pseudo oscillator connected in parallel to the ultrasonic oscillator as a compensation circuit;

a subtracting unit that subtracts a voltage corresponding to a current flowing to the pseudo vibrator when the drive voltage is applied to the pseudo vibrator, from a voltage corresponding to a current flowing to the ultrasonic vibrator when the ultrasonic vibrator vibrates;

a phase difference detection unit that detects a voltage corresponding to a phase difference between the phase of the drive voltage and the phase of the subtracted voltage; and

a voltage controlled oscillation unit that controls a frequency of the driving voltage based on the detected voltage,

the ultrasonic vibrator vibrates at the controlled frequency.

5. A drive circuit of an ultrasonic vibrator is characterized in that,

the drive circuit of the ultrasonic vibrator includes an ultrasonic vibrator formed in a disk shape,

the ultrasonic transducer includes a 1 st electrode formed on one surface of the ultrasonic transducer, and a 2 nd electrode and a 3 rd electrode formed on the other surface of the ultrasonic transducer,

a region in which the 1 st electrode is formed on the one surface is a 1 st region, and a region in which the 2 nd electrode is formed on the other surface is a 2 nd region, the 2 nd region being narrower than the 1 st region,

in the other face, the 3 rd electrode is formed outside the 2 nd electrode,

the drive circuit of the ultrasonic vibrator includes:

a phase difference detection unit that detects a voltage corresponding to a phase difference between a phase of the driving voltage and a phase of a voltage generated between the 1 st electrode and the 3 rd electrode when the driving voltage is applied between the 1 st electrode and the 2 nd electrode; and

a voltage controlled oscillation unit that controls a frequency of the driving voltage based on the detected voltage,

driving the ultrasonic vibrator at the controlled frequency.

6. An ultrasonic atomization device is characterized in that,

atomizing a liquid by applying vibration energy to the liquid from ultrasonic waves generated from a drive circuit using the ultrasonic vibrator described in claim 4 or 5.

Images