JPS5845208B2 - Polar mechanical filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a folded transverse vibrating acoustic bar using a second-mode bent transverse vibrating acoustic bar as a folding resonator, and a longitudinal vibrating thin rod coupler connected in cascade in two rows. Among mechanical filters, the present invention relates to a polarized mechanical filter that is small, has little harmful spurious response, and is easy to manufacture.

Attempts to miniaturize the resonators by arranging them in two rows using folded resonators are well known.

On the other hand, it is also well known to skip an adjacent resonator and couple it with another resonator using an additional coupler to form a polar type.

Therefore, in order to have one pole each in the low and high attenuation regions of the passband, an additional coupler is used to couple the resonators with an even number of resonators in between, and a cut is made. It is also well known that vibrations propagated through the main coupler and vibrations propagated by the additional coupler are connected so as to cancel each other out in the low-frequency damping region close to off.

Figure 1 shows, based on the above technical thinking, a second-mode bent transverse vibration sound piece is used as a folding resonator, and a first-mode bent transverse vibration main resonator and a longitudinal vibration thin rod coupler are arranged in two rows. FIG. 2 is a perspective view showing a conventional structure of a nine-element polarized mechanical filter, which is a folded mechanical filter connected in cascade, and has two attenuation poles in each attenuation region on both sides of a passband.

In the figure, L3, 4, 5, 7, 8, 9 degrees 10 are vibrating main resonators that perform first-mode bending transverse vibration, and are made of a constant elastic material such as nickel-span C type.

Piezoelectric ceramic plates 2 and 11 made of PZT or the like are bonded to 1 and 10, and serve as output conversion resonators.

Reference numeral 6 denotes a folding resonator made of a constant elastic material, and as shown in the figure, it is a vibrating unit resonator with second-mode bending transverse vibration.

Reference numerals 12, 13, . . . 19 are longitudinally vibrating thin bar main connectors made of a constant elastic material, which are butt-welded at the center of the layer lines of each vibrating unit resonator.

Reference numeral 20.21 denotes an additional coupler, which connects the two main resonators 4, 5 and 7, 8 to the pole resonators 3 and 9 and the folding resonator 6 by connecting the side surfaces 22, 23 of these to the pole resonators 3 and 9 and the folding resonator 6. (not visible in the figure) and welded connections at 24.25.

As is well known, each resonator of the filter vibrates as shown by the broken line in the lower attenuation range, so 22 and 23, 24 and 25
The points are in opposite phase.

Therefore, the distance between the welding points of the additional coupler 20.21, that is, the effective length l is 0<l<λ/2 (1) or λ<1<3/ 2λ (2).

However, for example, if the center frequency is 130kHz, λ
:37mm, and the condition that allows the most change in length in equation (1) is l'-:1/4λ, so lζ9.25
In this regard, if the thickness of the sound pieces of 3, 4, and 7.8 is 2 plates, the length of the main connector will be 1.75+tm, which is too short by 1.5 tm.

Therefore, if we select 12-=, /, λ from equation (2), then l
”: 46.25mm.

In the conventional structure as described above, the main resonators 3 and 9 receive useless couple vibrational force (for example, as indicated by arrow 26) from the additional couplers 20 and 21 in a plane including the main coupler and the additional coupler. ), which has the disadvantage of inducing useless vibrations and causing spurious responses.

Furthermore, since l must be selected to be approximately 5/4λ, the overall length becomes long.

Note that the additional connectors 20 and 21 are welded to the respective sound pieces at points 22, 23, 24, and 25, but in this welding method, the effective length l of the additional connectors varies and the characteristics are not stable. There were also drawbacks such as not being able to do so.

The present invention has been made to eliminate the above drawbacks, and will be described in detail below.

2 and 3 are perspective views showing embodiments of the present invention.
2,4゜5.6,7,8,10,11,12.13...
- All 19 are the same as those with the same symbols in FIG.

A feature of the present invention is that the pole resonators 3' and 9' that couple the additional couplers 20' and 21' are made of second-mode bending transverse vibrator bars, as shown by broken lines.

Therefore, the center point 27.28 (2B is indicated by a broken line) of the two vibration primitives of the polar resonators 3' and 9' is 29°30 (30
(shown by a broken line), 27 has one side of the connector 12, 2γ
One side of connector 13 is placed on the opposite (back) side of , one side of connector 19 is placed on 29, and connector 1 is placed on the opposite (back) side of 29.
8 on one side, and additional connectors 20' on 28 and 30, respectively.
, 21' are butted and welded.

The other sides of the additional connectors 20', 21' are butt welded at points 31 and 32, respectively, which are closest to the outer edges of the folded resonator 6.

With this structure, each resonator vibrates as shown by the broken lines in the low-frequency attenuation range, so 28, 31, and 3
0 and 32 both vibrate in the same phase.

Therefore, the distance between the welds of the additional resonators 20' and 2m', ie, the effective length l, may be λ/2<7<λ (3).

Therefore, if A = 43/4λ, then according to the previous example #
= 27.75mm, which is 60mm compared to the conventional 46.25mm.
The length φ is sufficient, and the size can be reduced.

Furthermore, since both the pole resonators 3' and 9' receive the vibration force at the center of the original line of vibration, no useless coupled vibration force acts on them, so that harmful spurious responses are less likely to occur.

Furthermore, since both ends of the additional connectors 20' and 21' are butt welded, there is little variation in their respective effective lengths l, so there is a practical effect such as less variation in characteristics.

The difference between Figures 2 and 3 is that, as is clear from the figures, the direction of the vibration planes of the pole resonators 3' and 9' is perpendicular to or in the same direction as the vibration plane of the main resonator. That's the difference.

In addition, FIG. 4 shows that if the conversion resonators 1°10 are too close together in FIG. 3, electrostatic coupling will occur between the piezoelectric ceramic plates 2 and 11, which will have an adverse effect. This is an embodiment in which the main connectors 12 and 19 are butted and welded to the centers 33 and 34 of the outer primitive lines, and the interval between the conversion resonators 1°10 is widened.

Of course, this can be done similarly for FIG.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a conventional folded polar mechanical filter, FIG. 2 is a perspective view showing an embodiment of the present invention, and FIGS. 3 and 4 are other embodiments of the present invention. FIG. 1j10...conversion resonator 31,9/,...
...Pole resonator, 6...Folding resonator, 12
~19... Main connector, 20', 21'...
...Additive connector.

Claims (1)

[Claims] 1 Using the second-mode bent transverse vibration resonator as a resonator for folding, the bent transverse vibration resonator and the longitudinal vibration thin bar main coupler are connected in cascade in two rows, and the resonator for folding and the adjacent resonator are skipped. In a polarized mechanical filter in which the folding resonator is connected to another resonator by an additional coupler, the vibration mode of the polar resonator connected to the folding resonator and the additional coupler is a second mode bending. Transverse vibration, the vibration mode of the other main resonators is the first mode bending transverse vibration, the main coupler is at the center of the origin of vibration of the main resonator, pole resonator, and folding resonator, and the additional coupler is A polarized mechanical filter characterized in that the center of the layer wire of a polar resonator and the near outer edge of a folded resonator are butt-welded to each other.