JPS5926659Y2 - Sound wave shielding cover for mechanical filter - Google Patents

Description

[Detailed description of the invention] This invention prevents acoustic coupling between the resonators due to sound waves generated by the mechanical resonators in a mechanical filter constructed by connecting multiple mechanical resonators in a chain with a mechanical coupler. Regarding sound wave shielding.

Mechanical filters used in communication devices and measuring instruments sometimes generate sound waves by vibrating the medium around the resonators as the mechanical resonators vibrate, but these sound waves serve as acoustic coupling between the resonators. It is well known that this causes deterioration of mechanical filter transmission characteristics.

Conventionally, to prevent this acoustic coupling, for example, a sound absorbing material or a sound wave reflection plate was used, and if there was the necessary space within the mechanical filter case, a sound absorbing material etc. was used to obtain the practically necessary sound wave attenuation effect. However, as space becomes more constrained due to the miniaturization of components, it becomes difficult to effectively insert sound absorbing materials and diffused reflectors, creating a new problem.

Another method is to create a vacuum or reduce the pressure inside the case of a mechanical filter to eliminate the effects of air or sealed gas that propagate sound waves.

In this case, there are no restrictions on sound-absorbing materials or miniaturization, and acoustic coupling can be effectively prevented, but the case and electrical terminals are required to be airtight, and a depressurization or vacuuming device is required.

For this reason, there are problems in manufacturing costs and in guaranteeing long-term reliability of airtightness.

The present invention was developed to eliminate the drawbacks or problems of the conventional methods described above.Acoustic coupling between resonators caused by sound waves generated by mechanical resonators is effectively suppressed sufficiently by a sound wave shielding cover, and the acoustic coupling is effectively suppressed. Deterioration of the transmission characteristics of mechanical filters, such as humps in the transmission band
The present invention is characterized in that it prevents disturbances in the flow rate and decrease in attenuation, is inexpensive, and is suitable for miniaturization.The present invention will be explained in detail below with reference to the drawings.

First, let us explain the sound waves generated from mechanical resonators.
In a bending resonator 1 such as the tuning fork shape shown in FIG. 1A or the sound piece shape shown in FIG.

This sound wave jumps and acoustically couples to adjacent resonators or to resonators located further away.

FIG. 2 is a perspective view of a sound wave shielding cover according to the present invention for preventing this acoustic coupling.

Of these, a has a structure that shields five sides, but in reality b
It has been experimentally confirmed that the required sound wave shielding effect can be obtained by using a structure that covers (shields) three sides including vibration displacement and the sound wave generation direction as shown in FIG.

In FIG. 2, the shielding cover 4 is manufactured by punching and bending a thin metal plate or by molding synthetic resin, which can be mass-produced at low cost.

Mechanical couplers (called couplers) are installed on both sides of this cover 4.
A slit 5 is provided for passing the wire.

After the shielding cover 4 is fixed to a substrate (for example, 10 in FIG. 3), the slit 5 through which the coupler 8 passes is notched circumferentially as shown in the figure to provide a dimensional margin.

Reference numeral 6 in the figure denotes a protrusion for fixing the shielding cover 4 to a printed circuit board or a metal board, and the cover is fixed to the board by passing it through the board and bending or soldering.

FIG. 3 is a perspective view of an example of a tuning fork-shaped multi-stage mechanical filter in which the shielding cover of the present invention is applied, and the cover of the mechanical filter is not shown below.

In the example shown in this figure, a sound wave shielding cover 4a is attached to every other tuning fork-shaped resonator 1.

Note that 8 in the figure is a coupler that mechanically couples the tuning fork resonator 1.

Further, 9 is a resonator for electromechanical conversion (transducer) to which the piezoelectric ceramic 7 is bonded.

FIGS. 4 and 5 are perspective views of one example of a vibrating piece type multi-stage mechanical filter in which the present invention is implemented.

There is strong coupling between adjacent mechanical resonators 1 due to the coupler 8, and there are cases where the acoustic coupling between adjacent resonators is significantly weaker than this and can be ignored.

However, in this case, adjacent resonators vibrate out of phase with each other, but 1
Since alternating resonators vibrate in the same mode, acoustic coupling across adjacent resonators often becomes a problem.

4 and 5 are examples of the use of a sound wave shielding cover suitable for such a case. Instead of a cover 4a that shields only one resonator 1, a cover 4a that covers and shields two adjacent resonators is used. Even if the shielding cover 4b is used, the mechanical filter can achieve the required transmission characteristics without being disturbed by acoustic coupling.

The optimum frequency range for putting the sound wave shielding cover of the present invention into practical use has so far been in the range of 10 to 100 kHz, but the sound wave shielding cover of the present invention has a mechanical resonator with a mutual spacing of 1 mm or less. This structure can be implemented even when the space between the outer case and the resonator is 1 mm or less, and the necessary sound wave shielding effect can be obtained with a small size.

In addition, the structure is simple and can be mass-produced, and the practical effects are obvious, such as being inexpensive and requiring no special tools or equipment for installation.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of sound wave generation from a resonator, Figure 2 is a perspective view of the sound wave shielding cover according to the present invention, and Figures 3 to 5 are when the sound wave shielding cover of the present invention is attached to a multistage mechanical filter. FIG. 1... Resonator, 2... Vibration displacement, 3.
...Sound wave traveling direction, 4, 4 a, 4 b...
...Sound wave shielding cover 5...Slit, 6...
...Protrusion (mounting foot), 7...Piezoelectric ceramic,
8...Coupler, 9...Transducer resonator, 10...Substrate.

Claims (2)

[Scope of utility model registration request] (1) Acoustically measure the upper surface and both sides of the resonator in the direction of sound wave propagation from the resonator of a single resonator or two adjacent resonators in a mechanical filter constructed by cascading multiple mechanical resonators. A three-sided structure made by bending a thin metal plate or molding a synthetic resin with a half-section of the shield, and has a notch or slit on both opposing sides to allow a mechanical coupler to pass through. A sound wave shielding cover for a mechanical filter characterized by: (2) Utility model registration claim 1, characterized in that projections (claws) or legs for fixing the structure to the mounting board of the mechanical filter are provided at the lower ends of both opposing sides of the three-sided structure. Sound wave shielding cover for mechanical filters described in section