Electrocardiography (ECG) records the heart's electrical activity using electrodes attached to the skin. ECG readings depend on differences in the electrical conductivity of body tissues. Magnetocardiography (MCG) detects the magnetic fields generated by cardiac activity: it does not require skin contact, and tissue conductivity has little impact on measurement accuracy. However, recording such signals requires extremely sensitive instruments. In the past, MCG required expensive and complex technologies such as superconducting quantum interference devices and optically pumped magnetometers. Until now, these methods have outperformed diamond sensors in sensitivity and the ability to distinguish signals from background noise.
Scientists from Gutenberg University Mainz have undertaken to explore the practical application of diamonds in medical magnetic measurements. They have developed a sensor with a diamond shaped like a truncated pyramid and a volume of less than 0.5 mm³. This small size makes it easier to use and allows for more detailed mapping of magnetic signals at room temperature. Furthermore, the device operates without a bias magnetic field—an external magnetic field used in other systems to filter out ambient magnetic interference.
The results of the measurements demonstrated the potential for medical applications and also made it possible to determine what improvements are needed for the practical implementation of these systems, writes Scitech Daily.
"NV-based magnetometers are characterized by fast initialization, excellent biocompatibility, and stable operation over a wide temperature range. This makes them particularly attractive for biomedical applications," said Arne Wickenbrock, project coordinator.
NV stands for "nitrogen-vacancy," a specific defect in the diamond crystal structure. In an NV center, a nitrogen atom takes the place of a carbon atom, leaving an empty position next to it. Researchers can study the energy levels of these centers to make precise measurements of magnetic and electric fields, temperature, and mechanical stress.
Two spatially separated sensors can form a gradiometer, recording the difference in magnetic field values at their locations. This approach is used in oncological surgery and allows for monitoring nerve activity during operations in the absence of magnetic shielding. Sensitivity to spatial field variations can also help distinguish the fetal heart signal from the maternal signal without invasive procedures.
One way to improve the device's performance is to concentrate a stronger magnetic field in a tiny diamond: structures called flux concentrators concentrate the magnetic flux in the sensor area, amplifying the signal. The small volume of the sensors allows for signal amplification by more than 100 times, and combining detectors with such structures could eventually provide image quality comparable to ECG.
"Adapting magnetic structures to optimally concentrate magnetic field lines from a source inside a diamond is the path to practical implementation of these quantum technologies," said Muhiba Omar, the detector's creator.
Modern science can detect gravitational waves, or disturbances in the fabric of spacetime, at high and ultra-low frequencies, but the mid-frequency range remains a "blind spot." A new detector concept, proposed a year ago, uses advanced optical resonator and atomic clock technologies to detect gravitational waves in the elusive millihertz range.
