University System of Maryland

United States of America as Represented by the Secretary of the Air Force

National Security Agency

John Matthews

Frederick Charles Wellstood

Kosta P Vlahacos

Su-Young Lee

Soun Pil Kwon

Claudio Felipe Busko

A scanning SQUID microscope is set forth to provide improved output imaging. The SQUID microscope includes a vertically adjustable housing adapted to securely retain a SQUID loop or sensor. A scanning stage of the SQUID microscope is adapted to support a sample while moving the sample along a predetermined path to selectively position predetermined portions of the sample in close proximity to the SQUID loop or sensor to permit the loop or sensor to detect predetermined magnetic field information provided by the predetermined portions of the sample. A position control processor coupled to the scanning stage is operative to receive and process the predetermined magnetic field information to provide corresponding position noise information. Criteria are also presented for determining the expected level of position noise under given experimental conditions.

Scanning SQUID microscope having position noise compensation

A scanning SQUID microscope capable of high frequency magnetic field measurements uses a hysteretic SQUID detector and a pulsed sampling technique which permits to extend the bandwidth of the SQUID microscope to above GHz region. The system can be readily incorporated into a 4.2scanning SQUID microscope for imaging chips at room temperature. By biasing the hysteretic SQUID with pulses of a predetermined amplitude, and adjusting a modulation flux applied to the hysteretic SQUID at a plurality of time delays between the activation of the sample under study and the bias pulse, the hysteretic SQUID can be switched on, and the modulation flux value corresponding to such a switching event as a function of time is considered as representation of the magnetic field emanating from the sample under study.

High frequency scanning SQUID microscope and method of measuring high frequency magnetic fields

A technique for eliminating edge artifacts in magnetic microscopy includes the steps of scanning a SQUID over an object under study to acquire values of magnetic fields produced by currents running in the object to create a first data set having N data points. At the end of the first data set, N zero data points are added to create a second data set having 2N data points. Fast Fourier Transform (FFT) is further applied to the 2N data set to obtain k-space having b(k) values. The b(k) values of the k-space are averaged, and the averaged b(k) values corresponding to k exceeding a predetermined k value are filtered off. A set of current density representations i(k) in the k-space are obtained to which inverse FFT is applied to obtain a map of current densities I(x,y) of the object. A system for performing the method of the present invention includes a software designed to suppress (or eliminate) edge artifacts present in the obtained images.

Method for suppressing edge artifacts in magnetic microscopy

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Greenbelt, MD, United States of America

John Matthews