超声波传感器spm0404ud5

　　超声波传感器spm0404ud5

　　诺尔斯MEMS技术使一个独特的宽带商业超声波传感器元件。本文解释了产品的性能优势和实用可能性。

　　超声波被定义为高于人体听觉频率极限的循环声压，大约为20千赫。这是超声波最明显的特点，但不一定是最重要的。根据应用程序的要求，用户也可能关心：

　　衍射和包装的影响

　　对于许多音频设备来说，设备的大小和形状对音频性能影响不大。当物理物体的波长大约为1/4波长或更大时，衍射开始变得重要。在20千赫，1/4波长约4毫米，在100千赫，1/4波长小于1毫米。

　　由于这个原因，超声波麦克风是定向的，尽管它只有一个声学端口。方向图取决于麦克风是如何包装和测量的。极性响应测量需要确定特定频率下的精确方向图。

　　传播损耗和吸收

　　随着点光源距离的加倍，声强降低了6分贝。

　　超声波由于吸收作用而迅速丧失能量，吸收率随频率和湿度的增加而增加。对于较高的湿度，损失可以达到3分贝/米的频率为80千赫。

　　Measurement and calibration

　　When performing measurements， the following guidelines should be considered：

　　Ultrasonic sound source

　　The acoustic bandwidth requirement determines what type of speaker may be used.

　　An ordinary tweeter component may be adequate for measurements up to 50 kHz. Check the component specification.

　　For measurements up to 100 kHz， a specialized speaker is required. One example is the Murata ES-105A （discontinued）。

　　Ultrasonic reference microphone

　　For measurements up to 50 kHz， a 1/4 inch reference microphone is recommended. Check with Bruel and Kjaer or GRAS for available types and required equipment.

　　For measurements up to 100 kHz， a 1/8 inch reference microphone is recommended. Check with Bruel and Kjaer or GRAS for available types and required equipment.

　　Calibration measurement

　　Place the test microphone and reference microphone with the sound ports at 90 degree incidence to the speaker at a distance of 1 m. Microphone ports should be placed as close as possible without touching.

　　Sweep the sound source through the frequency range of interest， and compare the reference microphone output to test the microphone output. Calculate the response of the test microphone for the given sound pressure. An audio analyzer may be used to facilitate the measurement.