Hello smart people,
I have a client that requires the detection of 20-40Khz signals at ranges of 20 meters or more. I designed and tested a prototype circuit that employs a MEMS microphone receiver, a high gain op amp, a multiple feedback band pass filter, a comparator and a phase locked loop to detect a 25kHz signal at a distance of about 14 meters. I'm generating the signal with a microcontroller, a MOSFET and a 25kHz COTS ceramic transducer from PROWAVE.
This circuit is so sensitive (80dB gain) that it readily amplifies unwanted audio that swamps the 25kHz signal. It seems likely that a COTS ceramic transducer would be less sensitive to out of resonance sound pressure levels however I have not seen reasonable range out of these devices. I am intrigued by TI application report SLDA053 and its logarithmic amplifier approach to detect weak signals and I'm wondering if such an AFE would work at lower frequencies and at what range. I'd love to hear your comments. Maybe some of you have relative experience in this area. A reference design would of course be greatly appreciated if one exists.
Thanks in advance,
Regards,
JD
