JPH0323697Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an ultrasonic transducer that generates bulk waves in a direction perpendicular to the surface of a piezoelectric body.

(Prior Art) Surface acoustic wave elements, in which an excitation transducer and a reception transducer called interdigital electrodes or interdigital electrodes are formed on a piezoelectric plate, are used in filters, delay lines, oscillators, and the like. This type of surface acoustic wave device is called an IDT, and is either a piezoelectric material that has already been polarized, or
It is constructed by forming an excitation transducer and a reception transducer called interdigital electrodes or interdigital electrodes on a plate made of a natural piezoelectric material such as crystal.

This surface acoustic wave element converts an electric signal into a surface acoustic wave signal using an excitation converter, and receives this surface acoustic wave signal and converts it into an electric signal using a receiving converter. bulk waves are difficult to generate.

Separately from the surface acoustic wave element, interdigital electrodes are provided on the surface of a plate-like dielectric material such as piezoelectric ceramics, lithium niobate, and lithium tantalate that has not been subjected to polarization treatment. After applying polarization treatment between the electrodes, when the electrodes are excited with a DC or AC power source, unlike the surface acoustic wave elements described above, bulk waves such as longitudinal waves or transverse waves can be generated in a direction perpendicular to the surface. I can do it. Such a transducer will be referred to as a surface-excited ultrasonic transducer. To explain this surface excitation type ultrasonic transducer, FIG. 1a is a surface view showing a state in which interdigital electrodes 2 and 3 are provided on the surface of a piezoelectric plate 1, and FIG. 1b is a sectional view of the same. , FIG. 1c shows the piezoelectric plate 1
FIG. In this surface-excited ultrasonic transducer, the first
As shown in Figure c, bulk waves are generated in the direction perpendicular to the surface of the piezoelectric plate, but unnecessary surface waves and transverse waves are more likely to occur. FIG. 2a is a sectional view of another example of a surface-excited ultrasonic transducer, and the second
Figure b is a front view showing the electrode arrangement. In this surface excitation type ultrasonic transducer, since the cut groove 4 from the piezoelectric plate surface is provided, the polarization distribution straddles the cut groove, and the polarization distribution is changed from the piezoelectric plate 1 to forms a sharp angle with respect to the surface of Therefore, surface waves are less likely to be generated, and the cut grooves prevent surface waves from propagating on the surface of the piezoelectric plate 1, making it possible to efficiently generate bulk waves in the direction of the arrow in FIG. 2a. .

(Problems with the prior art) When using ultrasonic waves by emitting bulk waves in the direction of the arrow above to another medium, the acoustic impedance of the piezoelectric plate Z ₀ and the acoustic impedance Z of the medium from which the ultrasonic waves are to be emitted When _M is significantly different, a large amount of energy is reflected at the interface, and the efficiency of emitting ultrasonic waves to the medium decreases. At the same time, energy remains in the piezoelectric body for a long time, so when a pulse wave is used, the pulse width becomes wide, which causes problems such as echo ranging.

(Purpose of the invention) The present invention solves the above-mentioned conventional drawbacks and efficiently radiates ultrasonic waves generated by a surface excitation type ultrasonic transducer in a direction perpendicular to the surface of a piezoelectric material to a medium. With the goal.

(Summary of the invention) In order to achieve the above object, a pair of interdigital electrodes are provided on the surface of a piezoelectric plate, and a bulk wave in a vertical direction is generated on the surface of the piezoelectric plate to radiate ultrasonic waves. In the transducer, an acoustic matching layer is provided on the ultrasonic radiation surface of the piezoelectric plate, and its acoustic thickness t is set to t=n· with respect to the wavelength λ of the ultrasonic wave.
An object of the present invention is to provide an ultrasonic transducer characterized in that λ/4 (where n is an integer).

(Example) Fig. 3a is a cross-sectional view showing an embodiment of the present invention for radiating bulk wave ultrasound from a surface-excited ultrasonic transducer into a medium, and is similar to Fig. 2a. are indicated by the same reference numerals. 5 is piezoelectric plate 1
It is a medium that receives ultrasonic radiation, and its acoustic impedance is _ZM . 6 is the acoustic matching layer according to the present invention, and its acoustic impedance is Z ₁ , where Z ₁ is the acoustic impedance Z ₀ of the piezoelectric material that generates ultrasonic waves according to transmission theory, and the acoustic impedance of the medium that receives ultrasonic radiation. It has a geometric mean acoustic impedance √0・_M with respect to Z _M , and its acoustic thickness t is the wavelength λ of the ultrasonic wave used
For, t=n・λ/4 (where n is an integer)
Use a material with a thickness of . FIG. 3b is a front view showing the electrode arrangement of the surface excitation type ultrasonic transducer.

Next, the operation of the above embodiment will be explained with reference to FIG. Polarization occurs inside the piezoelectric material as shown in FIG. This polarization distribution forms a sharp angle with respect to the surface, and therefore bulk waves are efficiently generated in the direction of the arrow, that is, in the direction perpendicular to the piezoelectric material surface. A bulk wave in the direction of the downward arrow in FIG. 3a is radiated from the piezoelectric body of acoustic impedance Z ₀ through the acoustic matching layer 6 to the medium 5 of acoustic impedance Z _M. Here, as mentioned above,
The acoustic matching layer 6 has an acoustic impedance Z1 (=
√0・_M ), for example, as shown in page 143 (b) of the Official Electronics and Communication Pocketbook published by Ohmsha, there is a gap between the ultrasound transducer and the acoustic matching layer 6, and The difference in acoustic impedance between the acoustic impedance layer 6 and the medium 5 receiving ultrasonic radiation is reduced. Also,
The thickness t is t for the wavelength λ of the ultrasonic wave used.
=n・λ/4 (where n is an integer) material has an acoustic thickness, so it is well matched acoustically.
No reflection occurs at the boundary surface. Therefore, the ultrasonic waves generated by the piezoelectric plate 1 are efficiently radiated to the medium 5.

(Effects of the invention) As described above, according to the invention, in the surface excitation type ultrasonic transducer, since the acoustic matching layer is provided between the piezoelectric material that generates ultrasonic waves and the medium that receives ultrasonic radiation, Reflection at the interface can be prevented, ideal acoustic matching can be achieved, and ultrasonic transmission efficiency can be achieved.

[Brief explanation of the drawing]

FIG. 1a shows interdigital electrodes 2 on the surface of the piezoelectric plate 1.
1b is a sectional view of the same, FIG. 1c is a sectional view of the same showing the state of polarization in the piezoelectric plate 1, and FIG. 2a is a surface excitation of another example. 2b is a front view showing the electrode arrangement thereof; FIG. 3a is a sectional view showing an embodiment of the surface-excited ultrasonic transducer according to the present invention; Figure b is a front view showing the electrode arrangement. 1... Piezoelectric plate, 2, 3... Interdigital electrode, 4...
... cut groove, 5 ... medium, 6 ... acoustic matching layer.

Claims (1)

[Scope of utility model registration request] A pair of interdigital electrodes are provided on one surface of the piezoelectric plate, grooves are provided on the surface of the piezoelectric plate between the interdigital electrodes parallel to the interdigital electrodes, and on the other surface of the piezoelectric plate, An acoustic matching layer having an acoustic thickness t of t=n·λ/4 (where n is an integer) with respect to the wavelength λ of the ultrasonic waves generated within the piezoelectric plate is provided, and the acoustic matching layer The impedance is Z1, and the acoustic impedance of the piezoelectric plate is Z
0. An ultrasonic transducer characterized in that Z1=√0〓, where ZM is the acoustic impedance of a medium that receives ultrasonic radiation.