Signal amplitude peak - peak vs frequency
Sensitivity in dB vs frequency
We chose to use a piezo sensor as our results showed it was much more sensitive than electret, capacitor or piezo-tweeter. We used a SN35610 piezo receiver which gave the following results.
Experimental procedure: a Motorola piezo ceramic tweeter with a response from 20 - 70kHz was set up facing the piezo receiver, at a distance of 120mm from it. A signal of 1V at various frequencies was applied to the tweeter, and the size of the signal at the receiver was recorded, peaking at nearly 100 mV. By comparison an electret microphone gave a signal of less than 1 mV at all frequencies above 20kHz.
When loaded with only a 100k resistor the sensor showed a narrow peak response at 42kHz with a 6dB bandwidth of about 1kHz. the results below show the effect of adding a 10mH inductor in parallel across the sensor.
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Signal amplitude peak - peak vs frequency |
Sensitivity in dB vs frequency |
The SN35610 sensor is available from Farnell EC, CPC, and MAPLIN in the UK.
Larger sensors are even more sensitive.