Using ultrasonic sensors in noisy environments can cause the sensor to detect false ultrasonic signals created by whistles, brakes, animals, machinery and other sources. One method to minimize this problem is to use a multifrequency ultrasonic transmission chirp. SensComp’s 600 series electrostatic transducers can be used for this application. Unlike piezo transducers that operate at one frequency, SensComp’s electrostatic ultrasonic transducer has a flat, low-resonate range between 20-100KHz. Just like a loudspeaker, the unit can operate in this wide dynamic range.
Example: Multi-Frequency Chirp Transmission
Using a microprocessor or DSP, a sensor can transmit a short sequence of multiple ultrasonic frequencies to create a unique signal signature.
For example:
- Transmit 5 cycles at 45 kHz
- Then 5 cycles at 50 kHz
- Then 5 cycles at 55 kHz
- This produces a 15-cycle composite chirp with a distinctive pattern
When the transducer switches to receive mode:
- The processor listens specifically for this same multi-frequency signature in the returning echo
- Only echoes matching the transmitted pattern are accepted as valid
- Unrelated ultrasonic noise is ignored
In summary, electrostatic transducers can operate at many frequencies between 20-100KHz. Creative signal processing can produce a sensor that is highly resistive to unwanted ultrasonic noise.