@misc{indiciae120d03e6d78b,
  title = {Resonant difference-frequency atomic force ultrasonic microscope},
  author = {Cantrell, John H. and Cantrell, Sean A.},
  year = {2010},
  url = {https://ntrs.nasa.gov/citations/20110000824},
  note = {Source identifier: 20110000824}
}