Physics of Ceramic Filters

[highing89]

What is the difference between a ceramic Filter and a piezoceramic filter ?

First I researched about the ceramic filter. The Murate Company offers a Pdf. Her it is described that the Filter characteristic is because of the piezoelectric effect.

I have known the piezoelectric effect from the quartz crystal filter. There we have a quartz crystal. At the bottom and at the bottom is respectively placed an electrode. If we apply a voltage at the electrodes, the quartz crystal is mechanically deformed. This results in a periodical charge transfer and an AC voltage arises at the output at the crystal.
If the applied voltage is the same like the resonance frequency of the quartz crystal, the crystal oscillates very powerful and the output voltage is very high.

Now here is my question. If we compare both pictures we can see differences in the composition of the filters.
Is it right that ceramic filters also uses the piezoelectric effect? I don’t see any electrodes. Additionally I can’t imagine that the “ceramic” shivers.

So how does a ceramic filter physically works? I read something about a standing wave of ¼ wavelength. Is that right?

I’m a little bit confused.

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here is the ceramic filter

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and the other ceramic filter

 

[FvM]

Both devices are "ceramic filters" in so far that they are built of ceramic material. Both are obviuosly different (e.g. in size), but I don't agree that the photos show much about their "composition" or if they use electrodes. I assume both devices do.

The 5.5 MHz filter is definitely a mechanical resonator utilizing the piezoelectric effect, similar to a crystal, but with three electrodes, input, output and ground.

I guess that the larger device is a dielectric bandpass filter with a high MHz or GHz passband, but that can't be clearly derived from the photo. Reading the datsheet thoroughly will surely answer your question. The mechanical resonance frequency of the ceramic cyclinders will be in a several 100 kHz up to few MHz range, so if it's a piezolectric filter, the filter frequency would be very low.

 

[jiripolivka]

Both devices are "ceramic filters" in so far that they are built of ceramic material. Both are obviuosly different (e.g. in size), but I don't agree that the photos show much about their "composition" or if they use electrodes. I assume both devices do.

The 5.5 MHz filter is definitely a mechanical resonator utilizing the piezoelectric effect, similar to a crystal, but with three electrodes, input, output and ground.

I guess that the larger device is a dielectric bandpass filter with a high MHz or GHz passband, but that can't be clearly derived from the photo. Reading the datsheet thoroughly will surely answer your question. The mechanical resonance frequency of the ceramic cyclinders will be in a several 100 kHz up to few MHz range, so if it's a piezolectric filter, the filter frequency would be very low.

Please try not to confuse different devices utilizing ceramic materials.

One device used to make resonators and filters for VHF up to microwaves is a dielectric resonator. Dielectric resonator uses a block of a dielectric material as a resonant cavity instead of hollow metal cavity. Various dielectrics are used. Ceramic materials have recently been developed that offer a high permittivity (to reduce resonator dimensions) and their composition is designed to reduce thermal expansion, so their resonant frequency is stable over temperature.

Ceramic resonators are used in microwave and VHF/UHF oscillators and filters.

Another effect is the "piezo-electric" effect. Originally known in quartz and tourmaline, recently ceramic materials having this capability have been developed. Piezo means that by mechanical stress such devices generate a voltage, and their dimensions determine a resonant frequency. Usually such piezo resonators are used from low to high frequencies, have very sharp resonance response and can be thermally compensated.
Some quartz and ceramic resonators are made for up to 1 GHz, and oscillate mechanically.
A similar ceramic device can be found in piezo-lighters, where a small mechanical stress generates a high-voltage pulse that can ignite gas or gasoline vapor.

The third effect is called SAW , surface acoustic wave, and the devices using it are mostly band-pass filters, from ~1 MHz up to ~500 MHz. It is a thin-layer structure allowing one frequency or a band to propagate between a pair of transducers. These transducers and sometimes the complete structure may utilize a ceramic material as a substrate, as a piezo-device, etc.

The fourth interesting use of ceramic material is LTCC, low-temperature cofired ceramic. A multi-layer structure is composed of metal conductors and ceramic insulators, then fired together at a low temperature (under 1000 deg.C) to make a hermetic block. Some examples can be seen at "www.minicircuits.com".

Ceramic insulators have been known for more than a century, now we can see a wide range of new varieties and functions of ceramics.