SAW es el acrónimo de Surface Acoustic Wave o Onda Acústica Superficial que se traduce al español. Este tipo de onda acústica o mecánica que se propaga a través de la superficie de un material da lugar a un tipo de filtro que encuentra una amplia aplicación en la electrónica. El filtro SAW o SAW Filter.

Este componente consiste en una base piezoeléctrica en la que se graban tiras metálicas entrelazadas que consisten en los electrodos de entrada y salida de las señales. Cuando se aplica una señal al dispositivo, genera ondas acústicas que se propagan a través del dispositivo induciendo una señal en la salida, como se muestra en la figura 1.

 

Figura 1 - Principio de funcionamiento
Figura 1 - Principio de funcionamiento

 

   

Cuando se aplica una señal de RF, hace que los electrodos actúen sobre la base del material digital para crear una onda de superficie (SAW) que se propaga hacia los otros electrodos.

   Cuando estas ondas alcanzan el otro electrodo, formado por tiras conductoras, se genera una señal eléctrica de la misma frecuencia.

   Dado que la velocidad de propagación de una señal acústica es mucho más lenta que la velocidad de una señal eléctrica, incluso con el pequeño tamaño del chip piezoeléctrico se puede lograr un retraso de señal considerable que se puede utilizar en aplicaciones electrónicas, especialmente en RF.

   Los componentes principales son filtros que se fabrican para aplicaciones en el rango de RF que generalmente van desde unas pocas docenas de kHz a 3 GHz.

   En la figura 2 tenemos el aspecto de un chip típico de un filtro SAW.

 

 

Figura 2 - El chip de filtro SAW
Figura 2 - El chip de filtro SAW

 

   En la figura 3 tenemos un circuito típico de un filtro SAW. Este circuito pasa señales de una frecuencia única determinada por el filtro.

 

Figura 3 - Un circuito de aplicación
Figura 3 - Un circuito de aplicación

 

   Una aplicación importante para este tipo de filtro son los controles remotos del tipo utilizado en las puertas de garaje donde la señal recibida pasa a dicho filtro, como se muestra en el ejemplo de la Figura 4.

 

Figura 4 - Receptor de filtro SAW de 433 MHz para control remoto
Figura 4 - Receptor de filtro SAW de 433 MHz para control remoto

 

   En la figura tenemos un pequeño módulo que tiene en su parte de sintonía este tipo de filtro, capaz de proporcionar una buena selectividad suficiente para cumplir con la aplicación que es menos crítica y así recibir las señales codificadas emitidas.

   Una característica que debe tenerse en cuenta al usar estos filtros es su sensibilidad a las variaciones de temperatura. A medida que disminuye la frecuencia de resonancia térmica, lo que debería anticiparse en algunas aplicaciones con la adición de componentes externos.

   Este tipo de filtro también tiene su selectividad disminuida a frecuencias superiores a 1,5 GHz.

   

 

 

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