Øyvind Lund Aardal

• Eide, Sigurd; Casademont, Titus; Aardal, Øyvind Lund & Hamran, Svein-Erik (2022). Modeling FMCW Radar for Subsurface Analysis. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. ISSN 1939-1404. doi: 10.1109/JSTARS.2022.3165135. Full text in Research Archive Show summary

  Determining subsurface properties through ground penetrating radar sounding can be challenging, especially in planetary exploration, where little is known about the terrain and additional observations are limited. Analysis and interpretation of data acquired with the Radar Imager for Mars’ Subsurface Experiment (RIMFAX) could therefore be improved by in-detail comparison with forward modeling. RIMFAX transmits a frequency modulated continuous waveform and utilizes a stretch processing receiver, and we demonstrate how accurate modeling can be achieved through finite-difference time-domain simulations. As the simulation scheme do not allow for direct implementation of such radar system, this study presents the necessary steps in order to replicate the same transmitter and receiver characteristics. In particular, we investigate how the method holds for modeling sounding in a realistic subsurface medium with attenuating and dispersive properties, by comparing the results with analytical estimates. The modeling approach is also assessed through comparison with RIMFAX field test measurements.

• Aardal, Øyvind; Brovoll, Sverre; Berger, Tor; Balasingham, Ilangko & Hamran, Svein-Erik (2017). Phase distortions in radar respiration monitoring, 2017 First IEEE MTT-S International Microwave Bio Conference (IMBIOC). IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781538617137. doi: 10.1109/IMBIOC.2017.7965778. Full text in Research Archive
• García-Pardo, Concepción; Chavez-Santiago, Raul; Fornes-Leal, Alejandro; Brovoll, Sverre; Aardal, Øyvind & Bergsland, Jacob [Show all 10 contributors for this article] (2016). Experimental Ultra Wideband Path Loss Models for Implant Communications, 2016 IEEE 27th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), 4-8 September 2016. IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781509032549. doi: 10.1109/PIMRC.2016.7794780. Full text in Research Archive
• Solberg, Lars Erik; Aardal, Øyvind; Berger, Tor; Balasingham, Ilangko; Fosse, Erik & Hamran, Svein-Erik (2015). Experimental investigation into radar-based central blood pressure estimation. IET Radar, Sonar & Navigation. ISSN 1751-8784. 9(2). doi: 10.1049/iet-rsn.2014.0206. Full text in Research Archive Show summary

  To assess whether radar technology can be used for monitoring blood pressure via information from the aorta, two experiments were performed: (i) measurements on a phantom model and (ii) acquisitions on a human subject for in vivo experiments. A linear dependency of phase on radius in the radar echoes in the phantom model showed that the information regarding the radius of a circular, cylindrical object depended on the clutter environment: in a low-clutter case two distinct reflections were identified, whereas in the high-clutter case it was possible to extract a proxy. Radar echoes from antennas strapped to the back of a human subject showed a clear signature from a discernible, distinct reflector believed to be the aorta. However, as for the high-clutter case, only a proxy for aortic radius is available as basis for estimation, which is most likely coupled with aortic displacements.

• Aardal, Øyvind; Brovoll, Sverre; Paichard, Yoann; Berger, Tor; Lande, Tor Sverre & Hamran, Svein-Erik (2015). Radar sensitivity to human heartbeats and respiration. Proceedings of SPIE, the International Society for Optical Engineering. ISSN 0277-786X. doi: 10.1117/12.2180924. Full text in Research Archive Show summary

  Human heartbeats and respiration can be detected from a distance using radar. This can be used for medical applications and human being detection. It is useful to have a system independent measure of how detectable the vital signs are. In radar applications, the Radar Cross Section (RCS) is normally used to characterize the detectability of an object. Since the human vital signs are seen by the radar as movements of the torso, the modulations in the person RCS can be used as a system independent measure of the vital signs detectability. In this paper, measurements of persons seated in an anechoic chamber are presented. The measurements were calibrated using empty room and a metallic calibration sphere. A narrowband radar operating at frequencies from 500 MHz to 18 GHz in discrete steps was used. A turntable provided measurements at precise aspect angles all around the person under test. In an I & Q receiver, the heartbeat and respiration modulation is a combination of amplitude and phase mod- modulations. The measurements were filtered, leaving the modulations from the vital signs in the radar recordings. The procedure for RCS computation was applied to these filtered data, capturing the complex signatures. It was found that both the heartbeat and respiration detectability increase with increasing frequency. The heartbeat signatures are almost equal from the front and the back, while being almost undetectable from the sides of the person. The respiration signatures are slightly higher from the front than from the back, and smaller from the sides. The signature measurements presented in this paper provide an objective system independent measure of the detectability of human vital signs as a function of frequency and aspect angle. These measures are useful for example in system design and in assessing real measurement scenarios. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

• Floor, Pål Anders; Chavez-Santiago, Raul; Brovoll, Sverre; Aardal, Øyvind; Bergsland, Jacob & Grymyr, Ole-Johannes [Show all 12 contributors for this article] (2015). In-Body to On-Body Ultrawideband Propagation Model Derived from Measurements in Living Animals. IEEE Journal of Biomedical and Health Informatics. ISSN 2168-2194. 19(3). doi: 10.1109/JBHI.2015.2417805. Full text in Research Archive Show summary

  Ultra wideband (UWB) radio technology for wireless implants has gained significant attention. UWB enables the fabrication of faster and smaller transceivers with ultra low power consumption, which may be integrated into more sophisticated implantable biomedical sensors and actuators. Nevertheless, the large path loss suffered by UWB signals propagating through inhomogeneous layers of biological tissues is a major hindering factor. For the optimal design of implantable transceivers, the accurate characterization of the UWB radio propagation in living biological tissues is indispensable. Channel measurements in phantoms and numerical simulations with digital anatomical models provide good initial insight into the expected path loss in complex propagation media like the human body, but they often fail to capture the effects of blood circulation, respiration, and temperature gradients of a living subject. Therefore, we performed UWB channel measurements within 1-6 GHz on two living porcine subjects because of the anatomical resemblance with an average human torso. We present for the first time a path loss model derived from these invivo measurements, which includes the frequency-dependent attenuation. The use of multiple on-body receiving antennas to combat the high propagation losses in implant radio channels was also investigated.

• Brovoll, Sverre; Berger, Tor; Paichard, Yoann; Aardal, Øyvind; Lande, Tor Sverre & Hamran, Svein-Erik (2014). Time-lapse imaging of human heart motion with switched array UWB radar. IEEE Transactions on Biomedical Circuits and Systems. ISSN 1932-4545. doi: 10.1109/TBCAS.2014.2359995. Full text in Research Archive Show summary

  Radar systems for detection of human heartbeats have mostly been single-channel systems with limited spatial resolution. In this paper, a radar system for ultra-wideband (UWB) imaging of the human heart is presented. To make the radar waves penetrate the human tissue the antenna is placed very close to the body. The antenna is an array with eight elements, and an antenna switch system connects the radar to the individual elements in sequence to form an image. Successive images are used to build up time-lapse movies of the beating heart. Measurements on a human test subject are presented and the heart motion is estimated at different locations inside the body. The movies show rhythmic motion consistent with the beating heart, and the location and shape of the reflections correspond well with the expected response form the heart wall. The spatial dependent heart motion is compared to ECG recordings, and it is confirmed that heartbeat modulations are seen in the radar data. This work shows that radar imaging of the human heart may provide valuable information on the mechanical movement of the heart.

• Aardal, Øyvind; Paichard, Yoann; Brovoll, Sverre; Berger, Tor; Lande, Tor Sverre & Hamran, Svein-Erik (2013). Physical Working Principles of Medical Radar. IEEE Transactions on Biomedical Engineering. ISSN 0018-9294. doi: 10.1109/TBME.2012.2228263. Full text in Research Archive Show summary

  There has been research interest in using radar for contactless measurements of the human heartbeat for several years. While many systems have been demonstrated, not much attention have been given to the actual physical causes of why this work. The consensus seems to be that the radar senses small body movements correlated with heartbeats, but whether only the movements of the body surface or reflections from internal organs are also monitored have not been answered definitely. There has recently been proposed another theory that blood perfusion in the skin could be the main reason radars are able to detect heartbeats. In this paper, an experimental approach is given to determine the physical causes. The measurement results show that it is the body surface reflections that dominate radar measurements of human heartbeats.

• Aardal, Øyvind; Hamran, Svein-Erik; Berger, Tor; Paichard, Yoann & Lande, Tor Sverre (2011). Chest movement estimation from radar modulation caused by heartbeats. In Cauwenberghs, G. (Eds.), IEEE Biomedical Circuits and Systems Conference 2011. IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781457714696. p. 422–425. doi: 10.1109/biocas.2011.6107825. Full text in Research Archive
• Aardal, Øyvind; Hamran, Svein-Erik; Berger, Tor; Hammerstad, Jan & Lande, Tor Sverre (2011). Radar cross section of the human heartbeat and respiration in the 500MHz to 3GHz band. In Ponchak, George E. (Eds.), Radio and Wireless Symposium (RWS), 2011 IEEE. IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781424476879. p. 422–425. doi: 10.1109/rws.2011.5725466. Full text in Research Archive
• Aardal, Øyvind; Hamran, Svein-Erik; Berger, Tor; Hammerstad, Jan & Lande, Tor Sverre (2010). Radar Cross Section of the Human Heartbeat and Respiration. In Georgiou, Julius (Eds.), Proceedings of BioCAS 2010. IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781424472680. Full text in Research Archive

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• Aardal, Øyvind (2017). Remote life sign detection and medical radar imaging. Full text in Research Archive
• Aardal, Øyvind; Brovoll, Sverre; Berger, Tor; Balasingham, Ilangko & Hamran, Svein-Erik (2017). Phase distortions in radar respiration monitoring. Full text in Research Archive
• Brovoll, Sverre; Berger, Tor; Aardal, Øyvind; Lande, Tor Sverre & Hamran, Svein-Erik (2014). Distortion effects in a switch array UWB radar for time-lapse imaging of human heartbeats. Full text in Research Archive
• Brovoll, Sverre; Aardal, Øyvind; Paichard, Yoann; Berger, Tor; Lande, Tor Sverre & Hamran, Svein-Erik (2013). Optimal frequency range for medical radar measurements of human heartbeats using body-contact radar. Full text in Research Archive
• Brovoll, Sverre; Berger, Tor; Paichard, Yoann; Aardal, Øyvind; Lande, Tor Sverre & Hamran, Svein-Erik (2013). Time-lapse imaging of human heartbeats using UWB radar. Full text in Research Archive
• Aardal, Øyvind; Brovoll, Sverre; Paichard, Yoann; Berger, Tor; Lande, Tor Sverre & Hamran, Svein-Erik (2013). Detecting changes in the human heartbeat with on-body radar. Full text in Research Archive
• Aardal, Øyvind; Hamran, Svein-Erik; Lande, Tor Sverre & Berger, Tor (2013). Radar monitoring of heartbeats and respiration. Universitetet i Oslo. Full text in Research Archive Show summary

  This thesis addresses the use of radar for heartbeat and respiration monitoring. Medical radar can be used for detecting vital signs at distances up to several meters. A medical radar works by transmitting electromagnetic waves towards a person, and receiving echoes reflected off the person. Vital signs appear as modulations in the radar data in period with the heartbeats and respiration. We have measured and analyzed these modulations.<br> The ability to detect human heartbeats from a distance can be used for monitoring patients’ heartbeats without the need of attaching the measurement equipment to the patient. A radar system can be placed over a bed, integrated in a mattress or chair or used for non-intrusive home monitoring. It could also be used as an alternative to the diagnostic monitoring tools of today. In this thesis, the understanding of radar heartbeat detection is explored.<br> Although heartbeats and respiration monitoring using radar have been reported many times before, the optimal frequencies, waveforms and aspect angle of detection were not known. We have described the vital signs modulations as functions of frequency and aspect angle, and found both narrowband and ultra wideband radar to be suited for the task. In addition to quantizing the modulations, an experimental approach to understanding why heartbeat and respiration detection with radar is possible was made. We found that small body surface movements are the cause of the observed heartbeat modulations in radar data, discarding the theory that reflections from internal body organs are seen. On-body radar have been used as well, and a closer connection between the actual movements of the heart and the radar recordings were found than what is achievable using remote radar. With on-body radar and the processing presented in this thesis, details of the heart mechanics can be identified using radar. It is also possible to see changes in the measured waveform when the pulse and blood pressure of the person changes.

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