Ultrasonic transducer driving circuit with air-core transformer

Abstract

The invention provides an ultrasonic transducer high-performance resonance matching drive circuit based on an air-core transformer. And the application requirements of megahertz frequency, high instantaneous power and high sine degree required by the excitation waveform of the transducer are met. A resonance matching circuit is adopted to overcome the defects that in an existing drive circuit, a magnetic core of a large-current transformer is prone to saturation, and output waveforms are seriously distorted, the adopted resonance matching circuit has the capacity of adjusting gain and resonance parameters easily and conveniently, and corresponding adjustment can be carried out under the condition that deviation exists in static capacitance and resonant frequency of a transducer. The application range of the driving circuit is widened, and the driving waveform performance difference caused by the individual parameter offset of the transducer is reduced. The related resonance matching circuit only comprises an air-core transformer and a resonance capacitor, and an extra resonance matching inductor is not needed. Meanwhile, a high-permeability magnetic core does not need to be adopted. According to the invention, the resonance matching circuit of the megahertz ultrasonic transducer with high instantaneous power is easy to miniaturize.

Description

Technical Field

[0001] The invention belongs to the field of electronics, and in particular relates to a high-performance resonant matching driving circuit of a megahertz ultrasonic transducer based on an air-core transformer. Background Art

[0002] With the continuous development of power electronics technology, ultrasonic technology has been widely used in various fields. As a new type of energy conversion device, ultrasonic transducers can convert input electrical energy into mechanical energy and output it in the form of sound waves. The internal material of ultrasonic transducers is made of piezoelectric ceramics. The piezoelectric effect of piezoelectric ceramics is used to convert electrical energy into mechanical vibrations, generate sound waves to be transmitted in the medium, and the energy loss of the transducer itself is extremely low. At present, ultrasonic transducers have been widely used in the fields of medical treatment, industrial cleaning and energy transmission, with the advantages of safety, stability, convenient maintenance, energy saving and environmental protection.

[0003] The ultrasonic transducer drive circuit is a necessary condition to ensure the safe and reliable operation of the ultrasonic transducer system. With the continuous increase of the operating frequency of the transducer, the requirements for the drive circuit are also getting higher and higher. As an important part of the ultrasonic system, the drive circuit contains an inverter circuit, a resonant matching circuit, and a high-frequency transformer. When the switching frequency of the inverter circuit is close to the inherent operating frequency of the ultrasonic transducer, the ultrasonic transducer can generate high-frequency resonance and emit ultrasonic waves to meet the needs of actual applications. At present, the operating frequency of the ultrasonic transducer drive circuit is mostly kilohertz (kHz) and uses a magnetic core transformer.

[0004] Due to the limitation of current magnetic core materials, for high-frequency, high-current, and high-voltage applications, the high-frequency loss of the magnetic core is large, and magnetic saturation occurs. The inductance of the transformer drops significantly under saturation conditions, causing the drive output waveform to be distorted, making it difficult to drive megahertz (MHz) ultrasonic transducers.

[0005] The existing high-power ultrasonic transducer driver has a low applicable frequency and is usually used in applications below 500kHz. For ultrasonic transducer applications with high megahertz frequency, high current, and high instantaneous power, the current driving scheme is difficult to apply. There are problems such as limited driving frequency, low output current, voltage, and instantaneous power. Due to manufacturing process limitations, ultrasonic transducers generally have a certain static capacitance and resonant frequency deviation, which makes it difficult for the resonant matching circuit to obtain a consistent output waveform, and the output waveform is prone to distortion. Summary of the invention

[0006] In order to overcome the deficiencies in the prior art, the present invention proposes a high-performance resonant matching drive circuit for a megahertz ultrasonic transducer based on a loosely coupled air-core transformer. The circuit realizes the megahertz frequency, high instantaneous power, and high sinusoidal application requirements of the transducer excitation waveform. The circuit overcomes the shortcomings of the existing drive circuit, such as the easy saturation of the core of the high-current transformer and the serious distortion of the output waveform. 。 The resonant matching circuit used has the ability to easily adjust the gain and resonance parameters, and can be adjusted accordingly when there are deviations in the static capacitance and resonance frequency of the transducer, thereby increasing the application range of the driving circuit and reducing the difference in driving waveform performance caused by the deviation of individual transducer parameters. The resonant matching circuit involved only includes an air-core transformer and a resonant capacitor, and does not require an additional resonant matching inductor. At the same time, since there is no need to use a high-permeability magnetic core, the present invention makes it easy to miniaturize the resonant matching circuit of a high instantaneous power megahertz ultrasonic transducer.

[0007] To achieve the above object, the technical solution of the present invention is:

[0008] The present invention adopts an ultrasonic transducer driving circuit with an air-core transformer, which is characterized in that the resonance matching of the inverter module and the ultrasonic transducer module is achieved through the air-core transformer with an adjustable coupling coefficient.

[0009] Among them, the ultrasonic transducer driving circuit includes an inverter module, a resonant transformer module and an ultrasonic transducer module; the output end of the inverter module is connected to the input end of the resonant transformer module, and the output end of the resonant transformer module is connected to the ultrasonic transducer module;

[0010] The resonant transformer module includes a filter capacitor C1 and an air-core transformer; the ultrasonic transducer module includes a capacitor C0, an inductor L d , capacitor C d , resistor R d ;

[0011] The air-core transformer includes a primary inductor L1, a secondary inductor L2 and an auxiliary winding inductor L a ; Primary inductance L1, secondary inductance L2 and auxiliary winding inductance L a These three elements are electromagnetically coupled in pairs through the air gap;

[0012] Among them, the inductance L of the ultrasonic transducer module d , capacitor C d , resistor R d These three components are connected in series in a loop, and the capacitor C0 is connected to the inductor L d , capacitor C d , resistor R dThe three sets of components are connected in parallel to form a resonant structure, in which the ideal working resonant frequency of the ultrasonic transducer is

[0013] Among them, when the auxiliary winding inductance L of the air-core transformer of the resonant transformer module a With adjustable impedance R a When connected to form a closed circuit, the air-core transformer has an equivalent circuit. The air-core transformer equivalent circuit includes self-inductance, primary side equivalent inductance L 1e , secondary side equivalent inductance L 2e , at this time the air-core transformer coupling coefficient is k 12e ; The formulas for each device are as follows:

[0014]

[0015] Among them, M 1a is the primary side mutual inductance coefficient, M 2a is the secondary side mutual inductance coefficient, M 12 is the mutual inductance coefficient of the primary and secondary sides, ω is: ω=2πf, f is the circuit operating frequency;

[0016] Among them, when the ultrasonic transducer module resonant frequency f d When there is an offset, by adjusting R a The resonance matching parameters satisfy L0 = L 2e , and obtain the new working resonant frequency

[0017] Among them, when the ultrasonic transducer module works in the resonant mode and the auxiliary winding inductance L a With adjustable impedance R a When connected to form a closed circuit, the air-core transformer equivalent circuit is simplified to an ideal transformer with a turns ratio of 1:n and its excitation inductance L0, leakage inductance L k ;

[0018] Among them, the input and output AC voltage amplitudes of the resonant matching circuit are V in With V out , the equivalent transformer turns ratio is

[0019] Among them, the turns ratio of the ideal transformer and the actual air-core transformer is not equal; the equivalent leakage inductance L of the air-core transformer k satisfy That is L k It is a series inductor-capacitor resonance with C1 and is used for series resonant filtering of input high-frequency current;

[0020] At this time, the primary coil inductance of the air-core transformer satisfies

[0021] At this time, the design coupling coefficient of the air-core transformer is:

[0022] Among them, when the auxiliary winding inductance L a The device connected to the output end is an adjustable resistor R a Replace with a switch S that can open and close the circuit a When , the circuit parameters are equivalent to:

[0023] When S a When open circuit, L1=L 1e , L2=L 2e , k 12 =k 12e ;

[0024] When S a When closed, the equivalent parameters satisfy:

[0025]

[0026] Among them, M 1a is the primary side mutual inductance coefficient, M 2a is the secondary side mutual inductance coefficient, M 12 is the mutual inductance coefficient of the primary and secondary sides.

[0027] Wherein, the switch S that can be opened and closed a Including relays and semiconductor switches.

[0028] Among them, the air-core transformer of the resonant module has an auxiliary winding inductance L a and adjustable resistor R a , can be composed of multiple groups of auxiliary windings and loads, including L a1 ~L an , R a1 ~R an .

[0029] The structure of the inverter module includes:

[0030] The inverter adopts a full-bridge topology; the switch tube Q1 and the switch tube Q3 form the bridge arm 1, and the switch tube Q2 and the switch tube Q4 form the bridge arm 2; the Disable end is the switch tube drive signal V gs1～4 The disable signal; its working characteristics are as follows:

[0031] At 0-t1, the full-bridge inverter is working normally, Disable is low, and the phase angle between bridge arm 1 and bridge arm 2 is At this time, from 0 to 0.5t1, the switch tubes Q1 and Q4 are turned on in half a cycle, and from 0.5t1 to t1, the switch tubes Q2 and Q3 are turned on in half a cycle, and the ultrasonic transducer excites V out Normal output;

[0032] In the t1-t2 phase, the inverter sets the phase shift angle to 0 so that the inverter output voltage V in is 0, so that the ultrasonic transducer excites V out =0;

[0033] At time t2, the Disable signal is sent by the control chip, and the switch tubes Q1 to Q4 all start to remain off until time t4; for megahertz application scenarios, there is a certain delay in Disable, that is, the Disable terminal in the shaded area in the figure is set to a high level, so that the actual disable time is in the area t2-t3;

[0034] At t4, the control chip sends a Disable low signal to prepare the ultrasonic transducer excitation signal to start. The Disable reset operation is completed during the t4-t5 phase, and at t6, the phase shift angle of the bridge arm group of the control switch tube Q2 and the switch tube Q4 is converted from 0° to After the phase shift is completed, the full-bridge inverter resumes normal working mode and the gate drive starts to output; thus, the next transducer wave generation cycle begins.

[0035] The structure of the inverter module may also adopt a class E inverter module; when the class E inverter module is adopted, the resonant transformer module performs output filtering on the class E inverter.

[0036] In addition, the external structural characteristics of the air-core transformer are as follows:

[0037] The primary inductor L1 of the air-core transformer is wound on the frame 1, and the secondary inductor L2 is wound on the frame 2; the relative position of the frame 1 and the frame 2 can be mechanically moved to achieve the coupling coefficient k 12e Adjustable;

[0038] The mutual inductance coefficient M is realized by rotating or moving up and down the secondary inductor L2 wound on the frame 2. a1 and M a2 Adjustable.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. The air-core transformer of the present invention is not limited by the magnetic saturation phenomenon and can enable the drive circuit to operate at a higher frequency.

[0041] 2. The resonant matching circuit used in the present invention only includes a capacitor and an air-core transformer, requiring only a relatively small number of resonant matching components.

[0042] 3. The equivalent impedance parameters of the air-core transformer of the present invention are adjustable, and the impedance can be adjusted according to different gains and ultrasonic transducer parameter offsets, so that the drive circuit works in the best state. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a driving circuit diagram of the ultrasonic transducer of the present invention.

[0044] Figure 2 This is the ultrasonic transducer driving equivalent circuit diagram of the present invention.

[0045] Figure 3 This is a resonant matching circuit diagram with an auxiliary switch of the present invention.

[0046] Figure 4 The present invention is a resonant matching circuit diagram with multiple auxiliary coils and adjustable impedance.

[0047] Figure 5 This is a full-bridge drive waveform timing diagram of the present invention.

[0048] Figure 6 This is a driving circuit diagram of an ultrasonic transducer using a Class E inverter according to the present invention.

[0049] Figure 7 This is a driving waveform timing diagram of the Class E inverter of the present invention.

[0050] Figure 8 It is the structural diagram of the hollow transformer of the present invention. DETAILED DESCRIPTION

[0051] like Figure 1 The ultrasonic transducer driving circuit with a hollow transformer, wherein the ultrasonic transducer driving circuit includes an inverter module, a resonant transformer module and an ultrasonic transducer module; the output end of the inverter module is connected to the input end of the resonant transformer module, and the output end of the resonant transformer module is connected to the ultrasonic transducer module;

[0052] The resonant transformer module includes a filter capacitor C1 and an air-core transformer; the ultrasonic transducer module includes a capacitor C0, an inductor L d , capacitor C d , resistor R d ;

[0053] The air-core transformer includes a primary inductor L1, a secondary inductor L2 and an auxiliary winding inductor L a ; Primary inductance L1, secondary inductance L2 and auxiliary winding inductance L a These three elements are electromagnetically coupled in pairs through the air gap;

[0054] Among them, the inductance L of the ultrasonic transducer moduled , capacitor C d , resistor R d These three components are connected in series in a loop, and the capacitor C0 is connected to the inductor L d , capacitor C d , resistor R d The three sets of components are connected in parallel to form a resonant structure, in which the ideal working resonant frequency of the ultrasonic transducer is When the ultrasonic transducer operates at the resonant frequency f d When , the ultrasonic transducer absorbs the maximum power under the same voltage excitation amplitude conditions.

[0055] Among them, the air-core transformer of the resonant module is composed of the primary inductance L1 of the air-core coil, the secondary inductance L2 and the auxiliary winding inductance L a The auxiliary winding inductance L a The output terminal is connected to an adjustable impedance R a When the transformer has an equivalent circuit, the equivalent circuit consists of self-inductance L 1e , L 2e , the coupling coefficient is k 12e The double-coil loosely coupled air-core transformer is composed of:

[0056]

[0057] Among them, M 1a is the primary side mutual inductance coefficient, M 2a is the secondary side mutual inductance coefficient, M 12 is the primary-secondary mutual inductance coefficient, ω is: ω=2πf, f is the circuit operating frequency.

[0058] When the transducer parameter C0 or the resonant frequency f d When there is an offset, by adjusting R a The resonant matching parameters satisfy L0 = L 2e , and obtain the new working resonant frequency

[0059] When the ultrasonic transducer module works in resonant mode and the auxiliary winding inductance L a With adjustable impedance R a When connected to form a closed circuit, Figure 2 As shown, the equivalent circuit can be further equivalent to an ideal transformer with a turns ratio of 1:n and its excitation inductance L0, leakage inductance L k When the excitation inductance L0 and the equivalent circuit C0 of the ultrasonic transducer module are resonantly matched, the operating resonant frequency satisfies

[0060] Among them, the input and output AC voltage amplitudes of the resonant matching circuit are V in With V out , in order to obtain the required final voltage gain, the equivalent transformer turns ratio is

[0061] Among them, the turns ratio of the equivalent transformer is not equal to that of the actual loosely coupled air-core transformer; the equivalent leakage inductance L of the loosely coupled air-core transformer k satisfy That is L k It is a series inductor-capacitor resonance with C1 and is used for series resonant filtering of input high-frequency current;

[0062] At this time, the primary coil inductance of the air-core transformer satisfies

[0063] At this time, the design coupling coefficient of the air-core transformer is:

[0064] When the transformer consists of the primary inductance L1 of the air-core coil, the secondary inductance L2 and the auxiliary winding inductance L a Constitute and at the same time L a The device connected to the output end is an adjustable resistor R a Replace with a switch S that can open and close the circuit a When Figure 3 As shown, the circuit parameters can be equivalent to:

[0065] When S a When open circuit, L1=L 1e , L2=L 2e , k 12 =k 12e ;

[0066] When S a When closed, the equivalent parameters satisfy:

[0067]

[0068] Among them, M 1a is the primary side mutual inductance coefficient, M 2a is the secondary side mutual inductance coefficient, M 12 is the mutual inductance coefficient of the primary and secondary sides.

[0069] Wherein, the switch S that can be opened and closed a , is composed of hardware that can achieve open circuit and short circuit impedance, including relays and semiconductor switches.

[0070] Among them, the air-core transformer of the resonant module, the auxiliary coil La and the adjustable impedance R a is not unique. Figure 4 As shown, the loosely coupled air-core transformer contains multiple La With R a , named L a1 ~L an , R a1 ~R an Through the coordination of multiple auxiliary coils, a wider range of equivalent inductance and matching parameter adjustment can be achieved.

[0071] Specific implementation

[0072] Combine the following Figure 1 The specific example in the figure specifically illustrates the specific working mode of a dual-input low ripple buck Cuk LED driving circuit in CCM mode of the present invention:

[0073] When the inverter adopts Figure 1 In the full-bridge topology shown in the figure, the switch tube Q1 and the switch tube Q3 form the bridge arm 1, and the switch tube Q2 and the switch tube Q4 form the bridge arm 2; the Disable terminal is the switch tube drive signal V gs1～4 The disable signal; its working characteristics are as follows:

[0074] At 0-t1, the full-bridge inverter is working normally, Disable is low, and the phase angle between bridge arm 1 and bridge arm 2 is At this time, the switch tubes Q1 and Q4 are turned on in the half cycle from 0 to 0.5t1, and the switch tubes Q2 and Q3 are turned on in the half cycle from 0.5t1 to t1, and the ultrasonic transducer excites V out Normal output;

[0075] In the t1-t2 phase, the inverter sets the phase shift angle to 0 so that the inverter output voltage V in is 0, so that the ultrasonic transducer excites V out =0;

[0076] At time t2, the Disable signal is sent by the control chip, and the switch tubes Q1 to Q4 all start to remain off until time t4; for megahertz application scenarios, there is a certain delay in Disable, that is, the Disable terminal in the shaded area in the figure is set to a high level, so that the actual disable time is in the area t2-t3;

[0077] At t4, the control chip sends a Disable low signal to prepare the ultrasonic transducer excitation signal to start. The Disable reset operation is completed during the t4-t5 phase, and at t6, the phase shift angle of the bridge arm group of the control switch tube Q2 and the switch tube Q4 is converted from 0° to After the phase shift is completed, the full-bridge inverter resumes normal working mode and the gate drive starts outputting, thus entering the next transducer wave generation cycle.

[0078] When the high-frequency inverter topology used is a Class E inverter, its structure is as follows: Figure 6 The loosely coupled air-core transformer used in the present invention can achieve output filtering of the class E inverter, thereby reducing the use of filter inductance in the ultrasonic transducer drive. When a push-pull class E inverter is used as the driving topology, L f1 , L f2 and C f1 , C f2 The parameter values ​​are consistent.

[0079] The push-pull E-type inverter driving waveform timing diagram is as follows Figure 7 The work contents of each period are as follows:

[0080] At t0-t1, the switch tube Q1 is turned off, and the current of the switch tube Q1 is diverted to the parallel capacitor C f1 , inductor current i Lf1 and the transformer primary current i L1 Common for C f1 Charging, the voltage across the switch tube Q1 begins to rise, that is, i Cf1 =i Lf1 +i L1 , at this time the current direction of the transformer primary side is from bottom to top. Switch tube Q2 is turned on, and the inductor L f2 Upper current i Lf2 Flows to Q2 and the primary side of the transformer, i Lf2 =i Q2 +i L1 At t1, the primary current of the load transformer is i L1 =0.

[0081] At t1-t2, the primary current of the transformer reverses from top to bottom. Lf1 The current flows to the primary side of the transformer and the capacitor C f1 , i.e. i Lf1 =i L1 +i Cf1 At time t2, the capacitor C f1 Complete charging, i Cf1 =0, at this time the voltage across the switch tube Q1 reaches the maximum value. The current of the switch tube Q2 is i Q2 =i L1 +i Lf2 .

[0082] At t2-t3, since switch Q2 is turned on and Q1 is turned off, capacitor C f1 Reverse charging, that is, the voltage across the switch tube Q1 begins to drop, the discharge current increases first and then decreases, and at t3 the current drops to zero, and the voltage across it is also zero.

[0083] At t3-t4, the switch tube Q1 is turned on, and the inductor L f1Upper current i Lf1 Flows to Q1, the primary current of the transformer is i L1 =i Lf1 -i Q1 At t4, the current value drops to zero. The switch tube Q2 is turned off, and the inductor L f2 The upper current and the transformer primary current are capacitor C f2 Charging, that is, Cf2 =i Lf2 +i L1 .

[0084] At t4-t5, the primary current of the transformer reverses from bottom to top. f2 Upper current i Lf2 Flows to the primary side of the transformer and capacitor C f2 , i.e. i Cf2 =i Lf2 -i L1 At t5, the capacitor C f2 Charging is completed, current i Cf2 Drops to zero, the transformer primary current i L1 =i Lf2 The current of the switch tube Q1 is the sum of the transformer primary current and the inductance L f1 The upper current, i Q1 =i Lf1 +i L1 .

[0085] At t5-t6, since switch tube Q1 is turned on and Q2 is turned off, capacitor C f2 Reverse charging, that is, the voltage across the switch tube Q1 begins to drop, the discharge current increases first and then decreases, and the current drops to zero at t6, and the voltage across the two ends is also zero. L1 =i Lf2 , the switch tube Q2 current i Q2 =i Lf1 +i Lf2 .

[0086] In addition, if Figure 8 The transformer shown in the figure includes three coils, corresponding to the primary inductance L1, the secondary inductance L2 and the auxiliary winding inductance L a The primary inductor L1 of the air-core transformer is wound on the frame 1, and the secondary inductor L2 is wound on the frame 2; the relative position of the frame 1 and the frame 2 can be mechanically moved to achieve the coupling coefficient k 12e Adjustable; wherein the secondary inductor L2 wound on the frame 2 is rotated or moved up and down to achieve M a1 and M a2 Adjustable.

[0087] Typically, the position adjustment of the frame and the coil position can be pre-adjusted during the production process to accommodate individual differences in transducer parameters. a You can connect an adjustable impedance R a , or a series switch device. According to different requirements, the coil and the frame may be different, but still within the scope of the present invention.

[0088] The present invention has the following advantages:

[0089] 1. The air-core transformer of the present invention is not limited by the magnetic saturation phenomenon and can enable the drive circuit to operate at a higher frequency.

[0090] 2. The resonant matching circuit used in the present invention only includes a capacitor and an air-core transformer, requiring only a relatively small number of resonant matching components.

[0091] 3. The equivalent impedance parameters of the air-core transformer of the present invention are adjustable, and the impedance can be adjusted according to different gains and ultrasonic transducer parameter offsets, so that the drive circuit works in the best state.

[0092] The above are preferred embodiments of the present invention. Any changes made according to the technical solution of the present invention, as long as the resulting functions do not exceed the scope of the technical solution of the present invention, belong to the protection scope of the present invention.

Claims

1. An ultrasonic transducer driving circuit having an air-core transformer, characterized in that: The resonance matching between the inverter module and the ultrasonic transducer module is achieved through an air-core transformer with an adjustable coupling coefficient.

2. The ultrasonic transducer driving circuit with an air-core transformer according to claim 1, characterized in that: The ultrasonic transducer driving circuit includes an inverter module, a resonant transformer module and an ultrasonic transducer module; the output end of the inverter module is connected to the input end of the resonant transformer module, and the output end of the resonant transformer module is connected to the ultrasonic transducer module; The resonant transformer module includes a filter capacitor C1 and an air-core transformer; the ultrasonic transducer module includes a capacitor C0, an inductor L d , capacitor C d , resistor R d ; The air-core transformer includes a primary inductor L1, a secondary inductor L2 and an auxiliary winding inductor L a ; Primary inductance L1, secondary inductance L2 and auxiliary winding inductance L a These three elements are electromagnetically coupled in pairs through the air gap; Among them, the inductance L of the ultrasonic transducer module d , capacitor C d , resistor R d These three components are connected in series in a loop, and the capacitor C0 is connected to the inductor L d , capacitor C d , resistor R d The three sets of components are connected in parallel to form a resonant structure, in which the ideal working resonant frequency of the ultrasonic transducer is 3. The ultrasonic transducer driving circuit with an air-core transformer according to claim 2, characterized in that: When the auxiliary winding inductance L of the air-core transformer of the resonant transformer module a With adjustable impedance R a When connected to form a closed circuit, the air-core transformer has an equivalent circuit. The air-core transformer equivalent circuit includes self-inductance, primary side equivalent inductance L 1e , secondary side equivalent inductance L 2e , at this time the air-core transformer coupling coefficient is k 12e ; The formulas for each device are as follows: Among them, M 1a is the primary side mutual inductance coefficient, M 2a is the secondary side mutual inductance coefficient, M 12 is the mutual inductance coefficient of the primary and secondary sides; Where ω is: ω = 2πf, f is the operating frequency of the circuit; Among them, when the ultrasonic transducer module resonant frequency f d When there is an offset, by adjusting R a The resonant matching parameters satisfy L0 = L 2e , and obtain the new working resonant frequency 4. The ultrasonic transducer driving circuit with an air-core transformer according to claim 3, characterized in that: When the ultrasonic transducer module works in resonant mode and the auxiliary winding inductance L a With adjustable impedance R a When connected to form a closed circuit, the air-core transformer equivalent circuit is simplified to an ideal transformer with a turns ratio of 1:n and its excitation inductance L0, leakage inductance L k ; Among them, the input and output AC voltage amplitudes of the resonant matching circuit are V in With V out , the equivalent transformer turns ratio is Among them, the turns ratio of the ideal transformer and the actual air-core transformer is not equal; the equivalent leakage inductance L of the air-core transformer k satisfy That is L k It is a series inductor-capacitor resonance with C1 and is used for series resonant filtering of input high-frequency current; At this time, the primary coil inductance of the air-core transformer satisfies At this time, the design coupling coefficient of the air-core transformer is:

5. The ultrasonic transducer driving circuit with an air-core transformer according to claim 3, characterized in that: When the auxiliary winding inductance L a The device connected to the output end is an adjustable resistor R a Replace with a switch S that can open and close the circuit a When , the circuit parameters are equivalent to: When S a When open circuit, L1=L 1e , L2=L 2e , k 12 =k 12e ; When S a When closed, the equivalent parameters satisfy: Among them, M 1a is the primary side mutual inductance coefficient, M 2a is the secondary side mutual inductance coefficient, M 12 is the mutual inductance coefficient of the primary and secondary sides.

6. The ultrasonic transducer driving circuit with an air-core transformer according to claim 5, characterized in that: The switch S that can open and close the circuit a Including relays and semiconductor switches.

7. The ultrasonic transducer driving circuit with an air-core transformer according to claim 3, characterized in that: The air-core transformer of the resonant module has an auxiliary winding inductance L a and adjustable resistor R a , can be composed of multiple groups of auxiliary windings and loads, including L a1 ~L an , R a1 ~R an .

8. The ultrasonic transducer driving circuit with an air-core transformer according to claim 2, characterized in that: The inverter module adopts a full-bridge topology structure, and its characteristics include the following: The inverter adopts a full-bridge topology; the switch tube Q1 and the switch tube Q3 form the bridge arm 1, and the switch tube Q2 and the switch tube Q4 form the bridge arm 2; the Disable end is the switch tube drive signal V gs1～4 The disable signal; its working characteristics are as follows: At 0-t1, the full-bridge inverter is working normally, Disable is low, and the phase angle between bridge arm 1 and bridge arm 2 is At this time, from 0 to 0.5t1, the switch tubes Q1 and Q4 are turned on in half a cycle, and from 0.5t1 to t1, the switch tubes Q2 and Q3 are turned on in half a cycle, and the ultrasonic transducer excites V out Normal output; In the t1-t2 phase, the inverter sets the phase shift angle to 0 so that the inverter output voltage V in is 0, so that the ultrasonic transducer excites V out =0; At time t2, the Disable signal is sent by the control chip, and the switch tubes Q1 to Q4 all start to remain off until time t4; for megahertz application scenarios, there is a certain delay in Disable, that is, the Disable terminal in the shaded area in the figure is set to a high level, so that the actual disable time is in the area t2-t3; At t4, the control chip sends a Disable low signal to prepare the ultrasonic transducer excitation signal to start. The Disable reset operation is completed during the t4-t5 phase, and at t6, the phase shift angle of the bridge arm group of the control switch tube Q2 and the switch tube Q4 is converted from 0° to After the phase shift is completed, the full-bridge inverter resumes normal working mode and the gate drive starts to output; thus, the next transducer wave generation cycle begins.

9. The ultrasonic transducer driving circuit with an air-core transformer according to claim 2, characterized in that: The structure of the inverter module adopts an E-class inverter module; when the E-class inverter module is adopted, the resonant transformer module performs output filtering on the E-class inverter.

10. A hollow transformer, applied to an ultrasonic transducer driving circuit having a hollow transformer as claimed in any one of claims 1 to 9, characterized in that: The external structural features of the air-core transformer are as follows: The primary inductor L1 of the air-core transformer is wound on the frame 1, and the secondary inductor L2 is wound on the frame 2; by adjusting the relative position of the frame 1 and the frame 2, the coupling coefficient k is achieved. 12e Adjustable.

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