Found in a 90's EDN this circuit can be used as a shield. The transistor is a general-purpose type and the frequency of the emitted sound is determined by R1 / C1.
We found this circuit in an old publication. The circuit can be implemented with modern equivalent...
Operational amplifiers used in this 80's circuit is not very common today, but the setting can be...
No information is given about the transformers in this circuit suggested by Motorola in a 1968...