JPH01190097A - Aerial ultrasonic transducer - Google Patents

Abstract

PURPOSE:To make unnecessary a process for adhering a resin plate for an acoustic matching layer to a case and to reduce the cost of the materials and that of the manufacture of the title device by forming a low density area at the fitting part of an oscillator and making this low density area into the acoustic matching layer at the time of molding the case. CONSTITUTION:An oscillator 2 has an upper part as an ultrasonic radiating surface and is fitted to the inner central part of a case 1. For the oscillator 2, electrodes are formed on both main surfaces of disk-shaped piezoelectric ceramics, and pull out the electrodes for connection onto a surface opposite to a case fitting surface. In the case 1, an area A, to which the oscillator 2 is fitted, is the low density area, and the other area B is a high density area. This is because microballoon 10 are concentrated on the area A in a resin. Consequently, acoustic impedance pc is lowered in the area A, and the area A is worked as the acoustic matching layer. Further, the thickness of the acoustic matching layer can be adjusted arbitrarily by the mixing ratio of the resin and the microballoon.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to an airborne ultrasonic transducer used for measuring distance or moving speed in the air.

3) Prior Art Figure 3 shows the structure of a conventional aerial ultrasonic transducer. The figure shows a longitudinal section, and 2 is a vibrator made of a piezoelectric element, 7 is a resin plate forming an acoustic matching layer, and 8 is a case. Resin plate 7 and vibrator 2 and resin plate 7 and case 8
They are each joined with adhesive. A board 3 covers the case 8 and is used for attaching lead terminals, and has two lead terminals 11 and 12 attached thereto. The vibrator 2 is provided with two opposing electrodes, and is connected to a lead terminal 11.1 via a lead wire.
It is electrically connected to 2.

Since the structure is as described above, lead terminals 11 and 12
By supplying a drive signal of a predetermined frequency between them, the vibrator 2 vibrates and emits ultrasonic waves upward in the figure through the resin plate 7. In addition, glass and organic microballoons are dispersed in the upper resin and molded into a plate shape.
The acoustic impedance is set to match the acoustic impedance ρC (density×sound velocity) of the vibrator 2 and the acoustic impedance in the air. This increases the radiation efficiency of ultrasonic waves into the air.

(C) Problems to be Solved by the Invention However, when manufacturing such a conventional aerial ultrasonic transducer, a case, a vibrator, and a resin plate for acoustic matching are used, so the number of parts is large. Moreover, since many of them are assembled by adhesion, there are problems of increased manufacturing costs and decreased reliability.

An object of the present invention is to solve these conventional problems and provide a low-cost and highly reliable aerial ultrasonic transducer.

(d) Means for Solving the Problems The aerial ultrasonic transducer of the present invention has a transducer housed in a case and an acoustic matching layer provided on the ultrasonic radiation surface of the transducer. Usa is characterized by forming a low-density area at the vibrator mounting part when molding the case, and using this low-density area as an acoustic matching layer.

(e) Function In the airborne ultrasonic transducer of the present invention, the vibrator is attached to a part of the case, and the attachment part is a low-density area formed when the case is molded. Therefore, the low-density region of the case has a lower acoustic impedance than other regions, and acts as an acoustic matching layer.

(f) Embodiment FIG. 1 is a longitudinal sectional view showing the structure of an aerial ultrasonic transducer according to an embodiment of the present invention. In the figure, 1 is a case, 2 is a vibrator made of a piezoelectric element, 3 is a substrate, and 4 is a lead wire. In the figure, the transducer 2 has an ultrasonic emission surface at its upper part, and is attached to the center of the inner surface of the case 1. The vibrator 2 has electrodes formed on both main surfaces of a disk-shaped piezoelectric ceramic, and when attached to the case, connection electrodes are drawn out on the opposite surface. In the case 1, an area A where the vibrator 2 is attached is a low density area, and the other area B is a high density area. This concentrates the microballoons in the area A in the resin.

Next, a method for manufacturing the above-mentioned aerial ultrasonic transducer will be described.

FIGS. 2(A) and 2(B) are diagrams showing the manufacturing process of case 1, and 5 and 6 indicate molds. First, a solution of epoxy resin mixed with glass or organic microballoons is poured into a mold as shown in FIG. 2(A). By keeping this mold at a high temperature, the viscosity of the resin decreases rapidly, and the resin component separates into two layers, the higher density resin component on the bottom and the lower density microballoons on the top. FIG. 2(B) shows this state. In the figure, 10 is a schematic representation of microballoons, which are concentrated in the area indicated by A in FIG. By curing in this state, a partial case partially including the acoustic matching layer can be obtained. In this way, the process of manufacturing the acoustic matching layer and the case separately and bonding them later can be omitted.

In addition, a space for holding the vibrator is provided in the lower mold 6 shown in FIG. It becomes possible to perform the adhesion process at the same time.

Note that the thickness of the acoustic matching layer can be arbitrarily adjusted by adjusting the mixing ratio of the resin and the microballoons. Therefore, post-processing to adjust the thickness of the acoustic matching layer is not required after molding the case with a mold. fg) Effects of the Invention As described above, according to the present invention, the number of parts is reduced, and the resin for the acoustic matching layer Since the step of bonding the plate and the case is not necessary, material costs and manufacturing costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing the structure of an airborne ultrasonic transducer according to an embodiment of the present invention, and FIGS. 2(A) and (B)
) is a diagram showing the manufacturing process of the case that constitutes the transducer. FIG. 3 is a longitudinal sectional view showing the structure of a conventional airborne ultrasonic transducer. 1-case, 2-oscillator, A-low density region. Applicant Murata Manufacturing Co., Ltd.

Claims (1)

[Claims] (1) In an airborne ultrasonic transducer in which a transducer is housed in a case and an acoustic matching layer is provided on the ultrasonic emission surface of the transducer, a low-density area is formed at the mounting part of the transducer when the case is molded. , an aerial ultrasonic transducer characterized in that this low-density region is used as an acoustic matching layer.