@misc{1150511, author = {David A Hill}, title = {Gradiometer antennas for tunnel detection:}, year = {1992}, month = {1992-01-01 05:01:00}, publisher = {, National Institute of Standards and Technology, Gaithersburg, MD}, doi = {https://doi.org/10.6028/NIST.IR.3990}, language = {en}, }