Ultrasonic transducer circuit design principle

- Aug 09, 2018-


An ultrasonic transducer is an energy conversion device necessary for generating ultrasonic waves, and converts the energy of ultrasonic electromagnetic oscillation into sound waves. Figure 3 is an ultrasonic transducer, also known as a horn transducer, which is characterized by light weight, small size, and high energy. In the figure:

1. is a metal front cover.

2. is an electrode wire.

3. is a piezoelectric ceramic piece.

4. is a metal rear cover. 

5. is a pre-assembly screw.

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The piezoelectric ceramic sheets of each adjacent two sheets are polarized in opposite directions, and the number of wafers is an even number, so that the front and rear metal cover plates are connected to the electrodes of the same polarity, otherwise an insulating gasket is interposed between the front and rear cover plates and the wafer. Between the two wafers, a thin piece of brass (thickness less than 0.1 mm) is usually sandwiched between the wafer and the metal cover as a soldering electrode lead; the wafer, the electrode copper, the metal support, and the metal front and rear covers are strongly used. Glued, pre-stressed screws can be tightened before or after curing of the epoxy. Since the compressive stress of piezoelectric ceramics is much greater than the compressive stress; the cemented layer is also easily destroyed in the stretching stage under large amplitude, so the pre-supplement screw is used to pressurize the wafer and the gluing portion of the vibrator. To ensure the safe operation of the device. The amount of prestress applied should be properly controlled. In the future, the compact fit will require a disc-shaped spring washer and washer between the pre-stressed screw and the cover. In addition, the prestressed screw has a small effect on the resonance frequency, and the electroacoustic conversion efficiency does not change. The maximum power that can be absorbed can be multiplied, and the main functions of the transducer are as follows:

1, vibrator

   Piezoelectric ceramics are called electroacoustic transducers. For a one-half-wavelength vibrator, when vibrating, the amplitude of both ends is the largest, and there is a section with zero vibration velocity in the middle, which becomes the nodal plane, and the position of the nodal plane The density, sound connection and size of the back cover and wafer stack vary. The section plate is placed at the nodal position to fix the vibrator and consider the transducer structure as a whole. If an ultrasonic voltage equal to the natural frequency of the vibrator is applied to the vibrator electrode and the vibrator vibrates in proportion to this voltage amplitude, the longitudinal movement of the two metal cover plates is pushed to propagate the ultrasonic energy.

2, front and rear speed cover

   The metal front cover is made of light metal such as hard aluminum or magnesium alloy, and the rear cover is made of steel or brass heavy metal to make the front cover produce a displacement much larger than the rear cover. According to the law of conservation of momentum and the working principle of the transducer, it can be seen that the momentum on both sides of the section is equal and opposite in direction, and the speed of motion is inversely proportional to the density. Aluminum is used as the front cover, and steel is used as the rear cover, and the displacement ratio is about three to one. In this case, the light metal has a large surface displacement that radiates a large portion of the vibrational energy stored in the vibrator.

  The light metal front cover is designed to be flared to match the hard aluminum (specific gravity 27) and water (specific gravity 1) for directional transmission of ultrasonic energy.

   The ultrasonic generator is an ultrasonic frequency electronic oscillator. When the ultrasonic frequency voltage generated by the oscillator is applied to the piezoelectric ceramic of the ultrasonic transducer, the piezoelectric ceramic component generates longitudinal vibration under the action of an electric field. When the piezoelectric element is ultrasonically oscillated, it seems to be a small piston with a small amplitude of about 1~10-20μm, but the acceleration of this vibration is very large, which is 10~103 times of the gravity acceleration, so the electromagnetic oscillating energy Converted into vibrational energy, this huge ultrasonic energy travels in a specific direction.

3, ultrasonic oscillator (drive circuit)

  Ultrasonic transducers must convert ultrasonic energy into ultrasonic energy. Ultrasonic oscillators must be provided, or ultrasonic signal generator circuits must be formed. There are self-excited oscillators, other oscillators, self-tracking, phase-locked loops. An oscillator circuit or the like is divided into a bipolar transistor vibration circuit or the like from the use of components