VLF Magnetic Field-Based Quantum Receiver
Abstract
Communication and positioning technologies are based primarily on the generation, transmission and reception of electromagnetic signals. In certain cases, the environment can distort, attenuate or even completely prevent signals from propagating between transmitter and receiver (RF-, GPS-denied environments associated with medium conductivity). Many other applications face the problem of relatively poor signal-to-noise, and to reach the intrinsic receiver noise floor, the measurements are often performed in heavily-shielded environment. The successful use of low-frequency magnetic signals thusfaces the common problems of low signal-to-noise ratio and is limited to specialized laboratories.The traditional low-frequency receivers are based on loop coil antennas, with detection based on theMaxwell s equations even in the case of Superconducting Quantum Interference Devices (SQUIDs). Receivers based on optically-pumped magnetometers (OPMs) are successfully competing with the traditional receivers in terms of performance metrics, but it is often overlooked that they rely on atomic spin precession based on the Schr~dinger s equation. The different physics of signal detection allows the quantum receivers to offer several unique features unavailable to the traditional ones.We propose to develop a very-low-frequency magnetic field-based quantum receiver system that can operate in an unshielded environment. The receiver system will consist of (1) an RF atomic magnetometer array for magnetic signal detection, (2) a bias magnetic field scheme for channel multiplexing/bandwidthincrease, (3) an ambient noise suppression scheme, and (4) a communication protocol. The main application of the receiver is for low-frequency (3 kHz - 30 kHz, extendable to 100 kHz) magnetic signal communication in the case of strong signal absorption and ambient magnetic field noise. The receiver willoffer unique advantages over conventional antennas based on electromagnetic induction:~ improved sensitivity/bandwidth with smaller size and non-cryogenic operation~ intrinsic noise rejection schemes relying on angular momentum conservationThe noise rejection schemes, combined with the low noise floor of the sensor, will significantly reduce thepower requirements for the signal transmitters. For a factor of 10 decrease of the measurement amplitude noise floor, the transmitted power required to maintain the same signal-to-noise ratio will be decreased by two orders of magnitude. Correspondingly, the communications range will be increased by a factor of two, due to the cubic dependence on the range of the typically used magnetic dipole-type signals. We have demonstrated more than 30 decibels of suppression between linearly- and circularlypolarized signals and intend to rely on this suppression mechanism to combat the ambient magnetic noise to either increase the communications range or relax the requirements imposed on the transmitter. The channel capacity, used to characterize a communications link, is proportional to the channel bandwidth and depends logarithmically on the signal-to-noise. The most efficient way to increase the channel capacity is to increase the receiver s bandwidth. It has been demonstrated that the opticallypumpedatomic magnetometers relying on Larmor precession have noise floors below 1 femto-Tesla at frequencies up to 1 MHz - essentially covering the range where their size is competitive to that of resonant loop systems.The goal of the project is to develop an RF atomic magnetometer-based sensor that demonstrates the advantages outlined above in an unshielded environment. Upon success, the project will enhance the communication capabilities in harsh environments and could potentially lead to improvements in existing and new applications.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 25, 2019
- Source ID
- N000141912269
Entities
People
- Vladislav Gerginov
Organizations
- Office of Naval Research
- Regents of the University of Colorado
- United States Navy