Electromagnetic sensors play a crucial role in various applications, ranging from communication systems and radar technology to medical imaging and security systems. In recent times, the Department of Defense (DoD) has shown a keen interest in pushing the boundaries of electromagnetic sensing capabilities, specifically in the high-frequency (HF) regime and below. To meet these ambitious goals, the Defense Advanced Research Projects Agency (DARPA) issued a Request for Information (RFI) in March 2023, inviting insights into the fundamental sensitivity limits of HF electromagnetic sensors without size, weight, and power (SWaP) constraints. Additionally, DARPA seeks information on innovative technologies, signal processing approaches, and decluttering algorithms that can enhance sensor performance even in the presence of background electromagnetic clutter.
In this article, we delve into the significance of electromagnetic sensors, explore the HF regime’s applications, and discuss the RFI’s key focus areas.
Electromagnetic Sensors and Their Applications:
Electromagnetic sensors are devices designed to detect and measure electromagnetic fields across various segments of the electromagnetic spectrum. They find application in communication systems, radar technology, navigation systems, security, medical imaging, and industrial processes. Some examples of electromagnetic sensors include:
Magnetic sensors: Used in compasses, proximity sensors, and magnetic speed sensors, these devices detect magnetic fields.
Radio frequency (RF) sensors: Employed in radar systems and wireless communication systems, these sensors detect radio waves.
Infrared sensors: Detecting infrared radiation, they are used in temperature sensors, motion detectors, and night vision cameras.
The Department of Defense (DoD) has a long history of pursuing research in the fundamental limits of electromagnetic sensing. Recent advances in quantum sensors, materials science, electromagnetic shielding, cryogenic systems, and vacuum components have pushed the state-of-the-art in sensing technologies. As the enabling technology improves, a wider variety of protocols and methodologies become possible and previous notions of the performance limits require validation.
High-Frequency (HF) Electromagnetic Sensors:
It can detect and measure different types of electromagnetic radiation, including radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays. Electromagnetic sensors that operate in the HF regime are often referred to as HF sensors.
The high-frequency (HF) regime of the electromagnetic spectrum, spanning from 3 MHz to 30 MHz, has significant applications in communication, radar, and navigation systems. Noteworthy examples of HF sensors include:
High-Frequency Radio (HF Radio): Utilized in aviation, maritime communication, and military applications, HF radio systems transmit and receive radio signals over long distances.
HF Radar: Designed for long-range surveillance and detection of objects, HF radar systems are employed in monitoring ships, aircraft, and other targets.
For deeper understanding on HF radio technology and applications please visit: Mastering HF Radio: A Comprehensive Guide to Communication, DXing, Military Applications, and Beyond
DARPA’s RFI Focus Areas:
March 2023, RFI from DARPA/MTO seeks information on the fundamental sensitivity limits of electromagnetic sensing in the high frequency (HF) regime and below without size, weight, and power (SWaP) constraints.
The DARPA RFI emphasizes exploring the fundamental sensitivity limits of electromagnetic sensors in the HF regime and below, particularly in environments without background electromagnetic clutter.
Various definitions are needed when trying to discuss the electromagnetic sensitivity of a given sensor. For example, magnetic sensitivity is defined by 𝜂 = 𝛿B√𝑇, where 𝛿 is the minimum detectable magnetic field and 𝑇 is the measurement time. Both magnetometers and electric field sensors are of interest. In some communities, the volume normalized sensitivity is defined to account for the square root volume scaling of ensemble sub-sensors (such as an ensemble of atoms). When discussing the sensitivity limits, fundamental (shot-noise, projection noise, thermal noise) and technical (electronic, background clutter, environmental perturbations) limits need to be evaluated.
In the lab, the fundamental limits can be pursued through system engineering, operation in shielded environments, and improved isolation. In these table-top systems, the fundamental physics are understood and pushing experimental performance towards the fundamental limits is a vibrant research community.
The two main focus areas are as follows:
Fundamental Sensitivity and Bandwidth Limits of Electromagnetic Sensors:
a. Operating Modality: This includes a comprehensive description of the sensor type, its receiving technique for electromagnetic radiation, operational specifics, and whether it operates in a broadband or narrowband manner with tunability options.
b. Current Performance and Bridging the Gap: A thorough evaluation of the present sensor performance, along with proposed pathways to close the gap between current capabilities and fundamental sensitivity limits.
Innovative Technologies and Signal Processing Approaches:
a. Innovative Technologies: Comparison of novel technologies against both fundamental sensitivity limits and the current state-of-the-art in electromagnetic sensing.
b. Signal Processing and Decluttering Algorithms: Insights into techniques that enhance sensor performance and reduce noise in cluttered environments, thereby allowing efficient sensor operation even in the presence of background clutter.
DARPA’s pursuit of ultrasensitive high-frequency electromagnetic sensors presents exciting opportunities for advancing sensing technologies, benefiting defense applications and beyond. By exploring the fundamental sensitivity limits, leveraging innovative technologies, and developing efficient signal processing and decluttering algorithms, the DoD aims to achieve groundbreaking capabilities in the field of electromagnetic sensing. Collaborative efforts from researchers and technologists in this vibrant research community will be crucial in pushing the boundaries of electromagnetic sensing and unlocking new possibilities for future applications.