1. Field of the Invention
The present invention generally relates to microphone devices, and more particularly to a structure for piezoelectric contact-type microphones.
2. The Prior Arts
Microphones have been part of people's life for many years but only until recently, due to the widespread popularity of portable electronic devices such as mobile handsets and MP3 players, they have regained people's attention.
Conventional capacitive microphones receive voice signals by sensing the vibration of air caused by audio sources such as loudspeakers, people's vocal cords, etc. As the environmental noises are collected as well, capacitive microphones are not appropriate in a noisy environment. In addition, when the speaker is wearing a respirator, a gas mask, a helmet, or similar device that would block the propagation of voice, capacitive microphones are not appropriate either.
Another type of commonly seen microphones is the so-called piezoelectric contact-type microphone. This type of microphones picks up the speaker's voice by directly touching the speaker's skin and sensing the vibration of the speaker's skin, muscle, and skeleton. Since the propagation of voice is not via the noise-prone air, piezoelectric contact-type microphones are very much suitable in a noisy environment and for speakers wearing a respirator, gas mask, or helmet.
a and 1b are schematic diagrams showing the skin contacting section of two conventional piezoelectric contact-type microphones. As illustrated, the piezoelectric element 10 is usually plated on its both top and bottom sides with metallic films 12 and 14. The side with the metallic film 12 is attached to a metallic plate 11, which in turn has a conducting wire 13 attached to it as one of the piezoelectric element 10's two electrodes for signal output. Another conducting wire 15 is attached to the metallic film 14 as the other electrode. The conducting wires 13 and 15 are then connected to a circuit board containing an amplification circuit (not shown).
In the conventional piezoelectric contact-type microphones, there is usually a buffering member installed between the casing 16 and the metallic film 14. This buffering member could be a sponge 18 or object made of similar material as shown in
Experiments have discovered that, for these conventional piezoelectric contact-type microphones, high-frequency voice signals are severely attenuated as the weak, high-frequency vibrations caused by these high-frequency voice signals are absorbed by the sponge 18 or the spring 19. These conventional piezoelectric contact-type microphones therefore suffer significant high-frequency distortion.
In addition, as shown in
The major objective of the present invention is therefore to provide an improved structure for piezoelectric contact-type microphones that prevents the distortions at the high- and low-frequency ranges without sacrificing the advantages of piezoelectric contact-type microphones.
A major feature of the present invention is the omission of the sponge or spring inside the microphone so that the piezoelectric element could directly and fully pick up the vibration of skin, muscle, and skeleton, instead of indirectly through the sponge and spring. On the other hand, the empty space inside the microphone from the mission of the sponge or spring allows the piezoelectric element to have the greatest extent of structural change when picking up the vibration. The piezoelectric element therefore could accumulate the greatest amount of charge, which in turn would produce the largest signal output voltage. If further the dimension of the piezoelectric element is reduced to a certain size (for example, a round piezoelectric element has a diameter smaller than 8 mm), as experiments have discovered, the microphone would have a rather flat frequency response up to 10,000 Hz.
Another major feature of the present invention is that through openings are arranged on the body of the microphone so that the structure of the microphone does not form a low-frequency resonant structure and the microphone's low-frequency response is improved.
The performance of the present invention is vividly illustrated with reference to
The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings.
a and 1b are schematic diagrams showing the skin contacting section of two conventional piezoelectric contact-type microphones.
a is a frequency response diagram of a conventional piezoelectric contact-type microphone.
b is a frequency response diagram of a piezoelectric contact-type microphone according to the present invention.
a and 3b are schematic diagrams showing a top and side views of a piezoelectric element respectively according to a first embodiment of the present invention.
c is a schematic diagram showing a perspective view of a piezoelectric contact-type microphone according to a first embodiment of the present invention.
d is a schematic diagram showing a side view of a piezoelectric contact-type microphone according to a first embodiment of the present invention.
e is a schematic diagram showing a side view of a piezoelectric contact-type microphone according to a second embodiment of the present invention.
f is a schematic diagram showing a side view of a piezoelectric contact-type microphone according to a third embodiment of the present invention.
A piezoelectric contact-microphone according to the present invention mainly contains a piezoelectric element, and a main body.
c is a schematic diagram showing a perspective view of a piezoelectric contact-type microphone according to a first embodiment of the present invention.
Generally, the piezoelectric element 30 gets in touch with the speaker's skin only via the metallic film 34 and the main body 31. In some embodiments, the main body 31 is wrapped or covered by a piece of cloth. As the sponge or spring commonly found in conventional microphones is omitted, the piezoelectric element 30 could sense the pressure P from the skin, muscle, and skeleton directly. Please note that it is mentioned earlier that the conducting wire 36 could be replaced by an elastic conducting strip or a metallic spring. This strip or spring is not positioned between the piezoelectric element 30 and the skin, but on the other side of the piezoelectric element 30. Since the main body 31 has an appropriate length and there is only empty space but no obstacle beneath the piezoelectric element 30 and the metallic film 32, the piezoelectric element 30 could have the greatest extent of structural change under the pressure P, an largest amount of charge could be accumulated on the metallic films 32 and 34, and a greatest signal output voltage could thereby be achieved and transmitted to the amplification circuit on the circuit board (not shown).
The foregoing design, along with the reduction of the diameter (or surface area) of the piezoelectric element 30, jointly contributes to the significantly improved high-frequency response of a piezoelectric contact-type microphone according to the present invention. Further more, the omission of the sponge and spring also help to reduce the low-frequency resonance and echo.
In order to further reduce the low frequency resonance, the main body 31 could be configured to have at least a through opening 33 on its cylindrical body. There is no specific requirement either on the shape or position of the opening 33, as illustrated in
f is a schematic diagram showing a side view of a piezoelectric contact-type microphone according to a third embodiment of the present invention. The present embodiment has a structure very similar to the previous embodiments. The major differences lie in that the main body 31 is made of a non-metallic material, and a metallic plate 37 is positioned between the metallic film 34 and the inner side of the main body 31's closed end. A conducting wire 35 is soldered to the metallic plate 37 or the metallic film 34, as one of the electrodes of the piezoelectric element 30. The conducting wire 35 and the conducting wire 36 (as the other electrode) are then connected to the amplification circuit on the circuit board (not shown). The present embodiment could also have those implementation variations as mentioned above. For example, the main body 31 could have at least a through opening 33 to reduce low-frequency resonance, the seat 39 could be omitted, etc.
Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.