TDC1000: Object sensing in the container with air or water

Hello,

1. This is technically possible, but it will be very challenging. There will be significant attenuation in air over this distance. In order to counteract this, a lower frequency is recommended (maybe even down to 40kHz). However, using such a low frequency in water, where the speed of sound is much greater will result in a significant loss of resolution. For example, at 40kHz the resolution in air is about 8mm, while in water it is 3.7cm. Overall, the greatest challenge will be in the attenuation of the signal through air. The TDC1000GASEVM has a daughtercard (TDC1000BSTEVM) that is made to increase the transducer drive voltage to 30V, which will help produce the acoustic power needed for this application.

2. Is the goal to measure the distance, or just to do detect whether the object is there or not? If it is the latter, this simplifies things, as there should be no concern for resolution, and you can use the lowest frequency transducer possible to achieve the least amount of attenuation through air. As mentioned above, the greatest challenge is in the difference in speed of sound between water and air and the far greater attenuation you will see through air.

3. The TOF will of course change with the medium. As long as you have a general idea of the expected TOF in both air and water, then you should be able to determine if the object is there or not regardless of whether or not the container is filled with water. However to determine the real world use case, it would of course be ideal to measure every case (water, air, object, no object, and all combinations) to establish a baseline.

4. The bandpass filter is entirely determined by the user. If you are using one of the EVMs, you will need to modify the bandpass filter to match whatever frequency transducer you end up using. The filter on the TDC1000-TDC7200EVM is made with a 1Mhz transducer in mind. One disadvantage of using a low frequency transducer like 40kHz is that it will require larger and more expensive components to construct the bandpass filter, so that is another consideration.

There are many app notes available for further reading on the TDC1000 product page. Additionally you can find all of the EVMs (the user's guides contain the full layout and schematic) and reference designs on the TDC1000 Tools and Software tab

Regards,