Device that can remotely monitor your breathing: as tested on cane toads

Constant monitoring of vital health signs is needed in a variety of clinical environments such as intensive care units, for patients with critical health conditions, health monitoring in aged care facilities and prisons, or in safety monitoring situations where drowsiness can cause accidents.

This is now mostly achieved via wired or invasive contact systems. However, these are either inconvenient or, for patients with burns or for infants with insufficient skin area, are unsuitable.

Scientists at the University of Sydney Nano Institute and the NSW Smart Sensing Network have now developed a photonic radar system that allows for highly precise, non-invasive monitoring.

The research is published today in Nature Photonics.

Using their newly developed and patented radar system, the researchers monitored cane toads and were able accurately to detect pauses in breathing patterns remotely. The system was also used on devices that simulate human breathing.

The scientists say this demonstrates a proof of principle for using photonic radar that could enable the vital-sign monitoring of multiple patients from a single, centralised station.

The University of Sydney Pro-Vice-Chancellor (Research) and lead for this research Professor Ben Eggleton said: “Our guiding principle here is to overcome comfort and privacy issues, while delivering highly accurate vital sign monitoring.”

An advantage to this approach is the ability to detect vital signs from a distance, eliminating the need for physical contact with patients. This not only enhances patient comfort but reduces the risk of cross-contamination, making it valuable in settings where infection control is crucial.

“Photonic radar uses a light-based, photonics system – rather than traditional electronics – to generate, collect and process the radar signals. This approach allows for very wideband generation of radio frequency (RF) signals, offering highly precise and simultaneous, multiple tracking of subjects,” said lead author Ziqian Zhang, a PhD student in the School of Physics.

“Our system combined this approach with LiDAR – light detection and ranging. This hybrid approach delivered a vital sign detection system with a resolution down to six millimetres with micrometre-level accuracy. This is suitable for clinical environments.”

Alternate approaches to non-contact monitoring have typically relied on optical sensors, using infrared and visible wavelength cameras.

“Camera-based systems have two problems. One is high sensitivity to variations in lighting conditions and skin colour. The other is with patient privacy, with high-resolution images of patients being recorded and stored in cloud computing infrastructure,” said Professor Eggleton who is also the co-Director of the NSW Smart Sensing Network.

Radio frequency (RF) detection technology can remotely monitor vital signs without the need for visual recording, providing built-in privacy protection. Signal analysis, including identification of health signatures, can be performed with no requirement for cloud storage of information.

Co-author Dr Yang Liu, a former PhD student in Professor Eggleton’s team, now based at EPFL in Switzerland, said: “A real innovation in our approach is complementarity: our demonstrated system has the capability to simultaneously enable radar and LiDAR detection. This has inbuilt redundancy; if either system encounters a fault, the other continues to function.”

Conventional RF radar systems, which rely entirely on electronics, have narrow RF bandwidth and therefore have lower-range resolution. This means they cannot separate closely located targets or distinguish them in a cluttered environment.

Relying solely on LiDAR, which uses much shorter light wavelengths, provides improved range and resolution, but has limited penetration abilities through objects such as clothes.

“Our proposed system maximises the utility of both approaches through integrating the photonic and radio frequency technologies,” Mr Zhang said.

Working with collaborators and partners in the NSW Smart Sensing Network, the researchers hope this research provides a platform to develop a cost-effective, high-resolution and rapid-response vital sign monitoring system with application in hospitals and corrective services.

“A next step is to miniaturise the system and integrate it into photonic chips that could be used in handheld devices,” Mr Zhang said.

Q&A with Ziqian Zhang

1.     What is photonic radar? 

Photonic radars, also known as microwave photonic radars or photonics-assisted radars, are radar systems that use photonic technologies to enhance the performance of traditional electronic radar systems. This means its systems use photons – light energy at high frequency – rather than electrons and electricity to generate the radio waves. It is crucial to recognise that despite incorporating photonics techniques, these systems still rely on radio waves or microwaves for the sensing.

2.     How it works

Traditional electronic radar systems process and transmit radar signals within the electrical domain, utilising electronic components. In contrast, photonic radar systems employ technologies that enable the conversion between electronic and optical signals. This allows them to harness the power of modern photonics for processing RF (radio frequency) signals within the optical domain. Additionally, photonic radar systems can distribute these signals over long distances with minimal loss and distortion, thanks to the properties of optical fibres.

3.     What are the advantages?

Optical signals can carry more information than conventional electronic signals. When we use optical signals for radar signal generation, processing, and distribution (photonic radar), the system tends to have a wider radar bandwidth and better signal quality. This delivers exceptional range resolution and sensing precision. The range resolution refers to the minimum distance between targets that the radar system can separate apart. Our photonic system has a millimetre-level range resolution, thus can separate closely located subjects and extract their vital signs without interference with each other. Meanwhile, the high sensing precision, thanks to the high-quality signal generation, ensures vital sign detection accuracy.

4.     Differences with conventional electronic radar systems

The photonic radar system enables distributed, multi-band sensing with expanded signal coverage. This results in superior radar performance from a centralised system, facilitating improved coordination and lower costs without the need to employ multiple independent systems and synchronise them together.

5.     Hybrid Radar-LiDAR System

A noteworthy innovation in our demonstrated system is its capability to simultaneously enable both radar and LiDAR detection as a sensor fusion system, combining different sensor modalities. Here are the key advantages:

- Redundancy: If either the radar or LiDAR system encounters a fault, the other continues to function, ensuring uninterrupted performance.

- Complementarity: Information garnered from the radar and LiDAR systems can supplement each other.

6.     What comes next?

We could continue investigating the use of on-chip components to shrink the device's footprint or test its performance with human subjects, possibly those with identified lung diseases or heart conditions. Another prospect is delving into advanced algorithms to boost the system's performance for moving subjects in real-world application scenarios, such as in aged-care facilities.

7.     Potential application scenarios

Our photonic radar sensor boasts a broad array of applications spanning the corrective services sector, national security, MedTech, aged care, home care, livestock and veterinary uses, and healthcare.

Declaration

The research was in part supported by grants from the Australian Research Council, the US Air Force and the US Office of Naval Research.