It just occurred to me that it may be possible to “jam” an ultrasonic sensor just like you could jam a radio frequency. Just get a speaker at the same frequency of the sonar sensors and point it at the opposing alliance carefully and BAM! instant autonomous win! Now I know this is illegal and I’ve never seen it done or encourage anyone to do this but would It even be possible? I’m concerned people will do this and it would be really hard to know. I feel like if it is possible it should be specifically addressed in the rules and result in immediate disqualification or even worse. What if your ultrasonic sensor could jam another ultrasonic sensor? That’s why I think it would be hard because ultrasonic sensors are probably like cheap fm rc cars and operate at different frequencies so you could only be able to jam one at a time unless two happened to be operating at the same frequencies. Anyways just a thought I had let me know what you think.
You could build a bot covered in ultrasonic sensors that does nothing but jam all the other ultrasonic sensors at the competition even the ones on the other fields! 
yes, this is possible
i dont know if the cortex’s ADC can produce 40Khz for the vex speaker though
In terms of building a robot with a lot of sensors to block people. In general most ultrasonic sensor libraries do not ever pull more than 1 sensor at a time because of interference. I haven’t looked into how ROBOTC does it but seeing as how no one has talked about problems I would assume sensors poll in a round robin fashion.
First of all, it is illegal.
But really, why bother to do that?
Getting the frequency right is one thing, but you will need to know exactly where do your opponents mount their sensor, and point it exactly there.
And after all these trouble (and of course, I presume you will be too busy to do any scoring yourself), most teams that I am aware of do not use ultrasonic sensor.