| 1. |
- Fhager, Andreas, 1976, et al.
(författare)
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Clinical Diagnostics and Treatment with Electromagnetic Fields
- 2010
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Ingår i: 4th European Conference on Antennas and Propagation, EuCAP 2010; Barcelona; Spain; 12 April 2010 through 16 April 2010. - 9788476534724 ; , s. C15P2-1
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Konferensbidrag (refereegranskat)abstract
- There is a need for novel diagnostic and treatment systems to overcome the limitations with todays modalities. Microwave and THz based system has the potential to become both sensitive and specific in several applications. In this paper we discuss several applications that are currently being developed at the Chalmers University of Technology.
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| 2. |
- Fhager, Andreas, 1976, et al.
(författare)
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Microwave Technology in Medical Diagnostics and Treatment
- 2015
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Ingår i: 2015 Ieee Mtt-S International Microwave Workshop Series on Rf and Wireless Technologies for Biomedical and Healthcare Applications. - New York : Ieee. - 9781479985432 ; , s. 133-134
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- There is a great need for novel diagnostics and treatment tools in today's healthcare. In this paper we describe our development and progress in novel microwave based diagnostics and treatment applications. The target applications are stroke diagnostics, breast cancer detection and microwave hyperthermia.
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| 3. |
- Fhager, Andreas, 1976, et al.
(författare)
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Progress in clinical diagnostics and treatment with electromagnetic fields
- 2011
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Ingår i: Proceedings of the 5th European Conference on Antennas and Propagation, EUCAP 2011. Rome, 11-15 April 2011. - 9788882020743 ; , s. 1936-1937
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Konferensbidrag (refereegranskat)abstract
- There is a need for novel diagnostic and treatment systems to overcome the limitations with todays modalities. Microwave and THz based system has the potential to become both sensitive and specific in several applications. In this paper we discuss several applications that are currently being developed at the Chalmers University of Technology.
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| 4. |
- Persson, Mikael, 1959, et al.
(författare)
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Broadband microwave based diagnostics and treatment
- 2009
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Ingår i: 3rd European Conference on Antennas and Propagation, EuCAP 2009; Berlin; Germany; 23 March 2009 through 27 March 2009. - 9781424447534 ; , s. 1873-1876
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Konferensbidrag (refereegranskat)abstract
- An efficient 3D microwave tomography system based on wide band antennas and detailed modelling using the finite difference time domain methods is presented together with a microwave system design study and a novel microwave hyperthermia cancer treatment system based on a time reversal algorithms.
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| 5. |
- Persson, Mikael, 1959, et al.
(författare)
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Microwave based diagnostics and treatment in practice
- 2013
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Ingår i: 2013 IEEE MTT-S International Microwave Workshop Series on RF and Wireless Technologies for Biomedical and Healthcare Applications, IMWS-BIO 2013 - Proceedings.
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Konferensbidrag (refereegranskat)abstract
- Globally, around 15 million people each year suffer a stroke. Only a small fraction of stroke patients who could benefit from thrombolytic treatment reach diagnosis and treatment in time. To increase this low figure we have developed microwave technology aiming to differentiate hemorrhagic from ischemic stroke patients. The standard method for breast cancer diagnosis today is X-ray mammography. Despite its recognized ability to detect tumors it suffers from some limitations. Neither the false positive nor the false negative detection rates are negligible. An interesting alternative being researched extensively today is microwave tomography. In our current strive to develop a clinical prototype we have found that the most suitable design consists of an antenna array placed in a full 3D pattern. During the last decade clinical studies have demonstrated the ability of microwave hyperthermia to dramatically enhance cancer patient survival. The fundamental challenge is to adequately heat deep-seated tumors while preventing surrounding healthy tissue from undesired heating and damage. We are specifically addressing the challenge to deliver power levels with spatial control, patient treatment planning, and noninvasive temperature measurements. © 2013 IEEE.
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| 6. |
- Persson, Mikael, 1959, et al.
(författare)
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Microwave imaging for medical applications
- 2011
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Ingår i: Proceedings of the 5th European Conference on Antennas and Propagation, EUCAP 2011. Rome, 11-15 April 2011. - 9788882020743 ; , s. 3070-3072
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Konferensbidrag (refereegranskat)abstract
- Microwave tomography is currently being researched for breast cancer detection. Our research has shown that clinical imaging preferably has to be made in a full 3D setting. In this paper we show results in order to evaluate the performance of a clinical system under construction.
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| 7. |
- Pishnamaz, Seyed Moein, 1995, et al.
(författare)
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Asymmetry Detection in a Noisy Microwave-Based Biomedical Diagnosis
- 2024
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Ingår i: 2024 IEEE MTT-S International Microwave Biomedical Conference, IMBioC 2024. ; , s. 12-14
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Konferensbidrag (refereegranskat)abstract
- This paper explores the conditions for detecting asymmetries in a noisy microwave-based diagnosis scenario with the potential to be used in biomedical applications. The asymmetry is caused by changing the real and imaginary part of the permittivity in one-third of the diagnosis domain where 3 antennas that form 2 symmetric channels are used. It is shown that with a simple diagnosis algorithm, the diagnosis rate can be improved by using the information from both channels.
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| 8. |
- Pishnamaz, Seyed Moein, 1995, et al.
(författare)
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Reducing Waves on the Body Surface in Near-Field Medical Diagnostics by a Dielectric Rod Antenna
- 2023
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 71:10, s. 7958-7969
-
Tidskriftsartikel (refereegranskat)abstract
- The multipath interference caused by the waves traveling on the body surface is a factor that limits the detection accuracy of microwave-based biomedical diagnostic systems. The waves traveling along these paths do not carry information of the area of interest, which is inside the body and are more sensitive to the changes in the space close to the antennas. In this paper for the first time, by placing a dielectric rod between the radiating element of the antenna and the body, the waves on the body surface are largely reduced while the antenna remains matched to the body. We design a Dielectric Rod Antenna (DRA) by deriving a 2-dimensional analytical solution of the wave propagation in a 2-layers cylindrical structure. The design is extended to 3D and further optimized using numerical simulations. It was shown that the addition of the dielectric rod enhances the field confinement by a factor of 2. The performance of the antenna, as verified by phantom measurements, shows that using the DRA increases the ratio of the transmission coefficient to power on the body surface to up to 24 dB and the antenna bandwidth is increased by 71% compared with the antenna without the dielectric rod.
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| 9. |
- Sidén, Johan, et al.
(författare)
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Remote Moisture Sensing utilizing Ordinary RFID Tags
- 2007
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Ingår i: Proceedings of IEEE Sensors. - New York : IEEE conference proceedings. - 9781424412617 ; , s. 308-311
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Konferensbidrag (refereegranskat)abstract
- The paper presents a concept where pairs of ordinary RFID tags are exploited for use as remotely read moisture sensors. The pair of tags is incorporated into one label where one of the tags is embedded in a moisture absorbent material and the other is left open. In a humid environment the moisture concentration is higher in the absorbent material than the surrounding environment which causes degradation to the embedded tag’s antenna in terms of dielectric losses and change of input impedance. The level of relative humidity or the amount of water in the absorbent material is determined for a passive RFID system by comparing the difference in RFID reader output power required to power up respectively the open and embedded tag. It is similarly shown how the backscattered signal strength of a semi-active RFID system is proportional to the relative humidity and amount of water in the absorbent material. Typical applications include moisture detection in buildings, especially from leaking water pipe connections hidden beyond walls. Presented solution has a cost comparable to ordinary RFID tags, and the passive system also has infinite life time since no internal power supply is needed. The concept is characterized for two commercial RFID systems, one passive operating at 868 MHz and one semi-active operating at 2.45 GHz.
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| 10. |
- Takook, Pegah, 1982, et al.
(författare)
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A computational study using time reversal focusing for hyperthermia treatment planning
- 2017
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Ingår i: Progress in Electromagnetics Research B. - 1937-6472. ; 73:1, s. 117-130
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Tidskriftsartikel (refereegranskat)abstract
- In hyperthermia treatment planning (HTP) the goal is to find the amplitudes and phases of antennas in the applicator to efficiently heat the tumor. To do this prior information regarding tumor characteristics such as the size, position and geometry, in addition to an exact model of the hyperthermia applicator is needed. Based on this information, the optimal frequency of operation can be determined. In this paper the optimum frequency for hyperthermia treatment based on the tumor and applicator characteristics, using time reversal as the focusing technique, is studied. As prior information, we consider tumor size and position, the number of the antennas in the applicator and the frequency characteristics. The obtained optimal frequency range is found using hyperthermia quality indicator values calculated from simulations. We also determine the optimum position of the virtual source in the initial step of the time reversal method to increase the quality of the treatment.
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| 11. |
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| 12. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Accuracy evaluation of time domain measurement systems for microwave tomography
- 2009
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Ingår i: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. - 9781424428045 ; , s. 1441-1444
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Konferensbidrag (refereegranskat)abstract
- The measurement accuracy of time domain systemsfor microwave tomography are evaluated through system levelsimulations and compared with that of a network analyzerbased frequency domain system. In the analysis, both a timedomain ultra-wideband (UWB) impulse and multiband systemarchitectures are considered. It is shown that the measurementerror of the time domain systems mainly comes from analogto digital (A/D) conversion. For a simple comparison case, therelative measurement error involved in an estimated objectresponse signal from the time domain UWB impulse system andUWB multiband system measurements are around three timesand ten times higher than that from frequency domain system.
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| 13. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Accuracy Evaluation of Ultrawideband Time Domain Systems for Microwave Imaging
- 2011
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 59:11, s. 4279-4285
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Tidskriftsartikel (refereegranskat)abstract
- We perform a theoretical analysis of the measurement accuracy of ultrawideband time domain systems. The theory is tested on a specific ultrawideband system and the analytical estimates of measurement uncertainty are in good agreements with those obtained by means of simulations. The influence of the antennas and propagation effects on the measurement accuracy of time domain near field microwave imaging systems is discussed. As an interesting application, the required measurement accuracy for a breast cancer detection system is estimated by studying the effect of noise on the image reconstructions. The results suggest that the effects of measurement errors on the reconstructed images are small when the amplitude uncertainty and phase uncertainty of measured data are less than 1.5 dB and 15 degrees, respectively.
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| 14. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Accuracy investigation of an ultra-wideband time domain microwave imaging system
- 2011
-
Ingår i: Proceedings of the 5th European Conference on Antennas and Propagation, EUCAP 2011. Rome, 11-15 April 2011. - 9788882020743 ; , s. 1928-1932
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Konferensbidrag (refereegranskat)abstract
- We investigate the measurement accuracy of an ultra-wideband time domain microwave tomography system. A phantom is imaged by means of the system and the reconstructed images are compared to those obtained with an ultra-wideband frequency domain system. The results suggest that the permittivity reconstructions obtained by means of the time domain and the frequency domain systems are very similar to each other, but the conductivity profile reconstructed from time domain measurements presents worse quality than that obtained from frequency domain measurements.
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| 15. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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An ultrawideband microwave medical diagnostic system: Design considerations and system performance
- 2012
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Ingår i: Proceedings of 6th European Conference on Antennas and Propagation, EuCAP 2012. Prague, 26-30 March 2012. - 9781457709180 ; , s. 3664-3668
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Konferensbidrag (refereegranskat)abstract
- We discuss several issues in the design of an ultra-wideband microwave system dedicated to medical diagnostics. Based on the discussion, a FPGA-based time domain microwave diagnostic system is proposed. The noise sources of the system are identified and the system noise performance is analyzed. As an example, a 2-D antenna system is considered and the measurement signal to noise ratios are evaluated.
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| 16. |
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| 17. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Design and Performance Evaluation of a Time Domain Microwave Imaging System
- 2013
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Ingår i: International Journal of Microwave Science and Technology. - : Hindawi Limited. - 1687-5826 .- 1687-5834. ; 2013, s. Art. no. 735692-
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Tidskriftsartikel (refereegranskat)abstract
- We design a time domain microwave system dedicated to medical imaging. The measurement accuracy of the system, that is, signal-to-noise ratio, due to voltage noise and timing noise, is evaluated. Particularly, the effect of coupling media on the measurement accuracy is investigated both numerically and experimentally. The results suggest that the use of suitable coupling media betters the measurement accuracy in the frequency range of interest. A signal-to-noise ratio higher than 30 dB is achievable in the range of 500 MHz to 3 GHz when the effective sampling rate is 50 Gsa/s. It is also indicated that the effect of the timing jitter on the strongest received signal is comparable to that of the voltage noise.
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| 18. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Development of a Time Domain Microwave System for Medical Diagnostics
- 2014
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Ingår i: IEEE Transactions on Instrumentation and Measurement. - 1557-9662 .- 0018-9456. ; 63:12, s. 2931-2939
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a time-domain system dedicated to medical diagnostics has been designed, a prototype has been built and its performance has been evaluated. Measurements show that the system has a 3-dB bandwith of about 3.5 GHz and a signal to noise ratio over 40 dB in the frequency range about 800 MHz to 3.8 GHz. The system has been used to perform a microwave tomographic image reconstruction test. The same target was reconstructed based on data measured with a network analyzer. A comparison between the images shows very small differences, and proves the functionality of the time domain system.
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| 19. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Effects of noise on tomographic breast imaging
- 2011
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Ingår i: 30th URSI General Assembly and Scientific Symposium, URSIGASS 2011, Istanbul, 13-20 August 2011. - 9781424451173
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Konferensbidrag (refereegranskat)abstract
- We study the effect of noise on microwave breast imaging by numerical simulations. A high contrast breast model is considered and the image reconstructions are carried out in time domain using a nonlinear inversion algorithm. A relative reconstruction error is defined in order to quantitatively evaluate the image distortion due to noise. The relative reconstruction errors of noisy reconstructions are obtained when different levels of amplitude and phase errors are taken into account.
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| 20. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Experimental Investigation of the Accuracy of an Ultrawideband Time-Domain Microwave-Tomographic System
- 2011
-
Ingår i: IEEE Transactions on Instrumentation and Measurement. - 1557-9662 .- 0018-9456. ; 60:12, s. 3939-3949
-
Tidskriftsartikel (refereegranskat)abstract
- The measurement accuracy of an ultrawideband (UWB) time-domain microwave-tomographic system is investigated. In order to make an assessment of the random variation of the measurements, the measurement repeatability of the system is evaluated by comparison with an UWB frequency-domain system. A phantom is imaged with the time-domain microwave-tomographic system, and the reconstructed images are compared with those obtained by using the frequency-domain system. The results suggest that with the averaging tens of measurements, the time-domain system can achieve the same level of measurement repeatability as that of the frequency-domain system in the interesting frequency range of microwave tomography. The imaging results, however, indicate that the phantom reconstruction does not require such high measurement accuracy. The permittivity profile of the phantom reconstructed from the nonaveraging time-domain measurements is very similar with that obtained by means of the frequency-domain system.
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| 21. |
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| 22. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Investigation of a Time Domain Microwave System for Biomedical Applications
- 2018
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Ingår i: 2018 48th European Microwave Conference, EuMC 2018. - 9782874870514 ; , s. 503-506
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Konferensbidrag (refereegranskat)abstract
- A time domain microwave system completely based on off-the-shelf components is developed for biomedical applications. This work is the investigation of this system for two different type of applications: medical diagnosis and vital sign detection. The results show that the system is accurate enough for most of the measurement scenarios. Both the respiration rate and heartbeat rate are detectable with the system and the success rate of respiration detection is 100% for seventeen tests we have performed.
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| 23. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Investigation of an ultra wideband noise sensor for health monitoring
- 2020
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Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 20:4
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Tidskriftsartikel (refereegranskat)abstract
- Quick on-scene assessment and early intervention is the key to reduce the mortality of stroke and trauma patients, and it is highly desirable to develop ambulance-based diagnostic and monitoring devices in order to provide additional support to the medical personnel. We developed a compact and low cost ultra wideband noise sensor for medical diagnostics and vital sign monitoring in pre-hospital settings. In this work, we demonstrated the functionality of the sensor for respiration and heartbeat monitoring. In the test, metronome was used to manipulate the breathing pattern and the heartbeat rate reference was obtained with a commercial electrocardiogram (ECG) device. With seventeen tests performed for respiration rate detection, sixteen of them were successfully detected. The results also show that it is possible to detect the heartbeat rate accurately with the developed sensor.
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| 24. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Investigation of stimulus signals for a time domain microwave imaging system
- 2017
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Ingår i: IET Microwaves, Antennas and Propagation. - : Institution of Engineering and Technology (IET). - 1751-8725 .- 1751-8733. ; 11:11, s. 1636 - 1643
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Tidskriftsartikel (refereegranskat)abstract
- Two different types of time domain signals, pulse and pseudo random noise (PN) sequence, were investigated for a time domain microwave imaging system in order to study the effect of stimulus signals on the system performance. The system's measurement accuracy was investigated when the two different stimulus signals were used, respectively. An imaging test was performed in order to show the effect of transmitted waveforms on the imaging quality. The results suggest that the PN sequence in general gives higher measurement accuracy than the pulse. Better imaging results, although not significant, were also obtained when the pseudo random sequence was employed.
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| 25. |
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| 26. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Measurement quality of a software defined radio system for medical diagnostics
- 2022
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Ingår i: JOURNAL OF ENGINEERING-JOE. - : Institution of Engineering and Technology (IET). - 2051-3305. ; 2022:12, s. 1162-1172
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Tidskriftsartikel (refereegranskat)abstract
- The measurement quality of a software defined radio system was investigated and discussed for medical diagnostics in the frequency band of interest 500 MHz-2 GHz. A calibration approach was proposed in order to deal with the random phase problem, and the obtained performance was evaluated and benchmarked against a vector network analyser. The results suggest that the measurement quality of the software defined radio system is mainly limited by the signal leakage from the transmitter to the receiver. Good agreement between the measurement data obtained with the software defined ratio system and the network analyser was achieved when the transmission loss is less than 70 dB. With some a priori knowledge of the measured object, the software defined radio system is able to perform accurate measurement when the transmission loss is even higher.
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| 27. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Microwave System Development for Medical Diagnostics
- 2015
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Ingår i: International Federation for Medical and Biological Engineering Proceedings. - Cham : Springer International Publishing. - 1680-0737. - 9783319129662 ; 48, s. 117-119
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Konferensbidrag (refereegranskat)abstract
- This paper presents a time domain microwave system developed for medical diagnostics. An imaging test was carried out with the developed prototype and reconstructed images were compared with those obtained by using a network analyzer. Results show small difference between reconstructions, which validates the imaging functionality of the prototype.
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| 28. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Noise performance comparison between two different types of time-domain systems for microwave detection
- 2017
-
Ingår i: International Journal of Microwave and Wireless Technologies. - 1759-0787 .- 1759-0795. ; 9:3, s. 535-542
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Tidskriftsartikel (refereegranskat)abstract
- This paper compares the noise performance of two different types of time-domain microwave detection systems: a pulsed system and a pseudo-random noise sequence system. System-level simulations and laboratory-based measurements are carried out in the study. Results show that the effect of timing jitter is more significant on the measurement accuracy of the pseudo-random noise sequence system than that of the pulsed system. Although the signal power density of the pseudo-random sequence system is tens of dBs higher than that of the pulsed system over the frequency band of interest, the signal-to-noise ratio difference between these two systems can be just a few dBs or even smaller depending on the jitter level.
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| 29. |
- Zeng, Xuezhi, 1980
(författare)
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Performance Evaluation of a Time Domain Microwave System for Medical Diagnostics
- 2019
-
Ingår i: IEEE Transactions on Instrumentation and Measurement. - 1557-9662 .- 0018-9456. ; 68:8, s. 2880-2889
-
Tidskriftsartikel (refereegranskat)abstract
- A time-domain microwave system for medical diagnostics was developed using off-the-shelf components. The system's performance was evaluated for realistic measurement scenarios when two different measurement strategies: with and without variable gain controls (VGCs) were employed. The results showed that without the employment of the VGC strategy, the system was able to measure loss up to 80 dB in the frequency range of 500 MHz-3 GHz. A 20 dB higher dynamic range was obtained when the VGC strategy was used. This measurement accuracy was obtained with settings which results in the measurement speed of 20 μs per trace.
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| 30. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Phase calibration of a software defined radio system for medical applications
- 2019
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Ingår i: Asia-Pacific Microwave Conference Proceedings, APMC. ; 2019-December, s. 1414-1416
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Konferensbidrag (refereegranskat)abstract
- Accurate phase measurement is crucial for many medical applications. We presented the challenge of using a software defined radio system for phase measurement and proposed two different calibration strategies to address this problem. Both strategies were implemented and evaluated. The results show that the first strategy gives better measurement repeatability than the second one. With this strategy, the random phase offset between the transmitter and receiver can be effectively compensated and the obtained phase measurement uncertainty is in the order of sub-degrees.
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| 31. |
- Zeng, Xuezhi, et al.
(författare)
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Silver Ink Patch Antenna for Passive RFID
- 2007
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Ingår i: Proceedings of ISAP2007, Niigata, Japan. - : IEEE conference proceedings. - 9784885522239 ; , s. 612-615
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Konferensbidrag (refereegranskat)
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| 32. |
- Zeng, Xuezhi, et al.
(författare)
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Slots in Metallic Label as RFID Tag Antenna
- 2007
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Ingår i: IEEE Antennas and Propagation Society, AP-S International Symposium (Digest). - New York : IEEE conference proceedings. - 9781424408771 ; , s. 1600-1603
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Konferensbidrag (refereegranskat)
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| 33. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Study on the sensitivity of image reconstruction to the measurement uncertainty in microwave tomography
- 2010
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Ingår i: EuCAP 2010 - The 4th European Conference on Antennas and Propagation. - 9788476534724
-
Konferensbidrag (refereegranskat)abstract
- We investigated the effects of measurement uncertainty on the image reconstructions for different breast models. Three different contrast levels between the background tissue and tumor were chosen. It was shown that the reconstruction of lower contrast breast model was more sensitive to the measurement uncertainty. For a breast model with contrast as low as 1.1 : 1, an amplitude uncertainty of 0.2 dB or a phase uncertainty of 2 degrees would result in an unsuccessful reconstruction.
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| 34. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Time domain microwave imaging system for biomedical applications
- 2017
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Ingår i: European Microwave Week 2016: "Microwaves Everywhere", EuMW 2016 - Conference Proceedings; 46th European Microwave Conference, EuMC 2016. - 9782874870439 ; , s. 679-682
-
Konferensbidrag (refereegranskat)abstract
- A time domain microwave imaging system for biomedical applications was developed using off-the-shelf components. Two different types of signals: a pulse and a pseudo random sequence, were employed as stimulus signal. The system's measurement accuracy and imaging functionality were investigated when these two different stimulus signals were used respectively. The results show that the system has a higher dynamic range when the pseudo random sequence was used. An imaging test also indicates the advantage, although not significant, to using the pseudo random sequence than the pulse.
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| 35. |
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| 36. |
- Zeng, Xuezhi, 1980
(författare)
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Time Domain Systems for Microwave Imaging: Accuracy Evaluations and Prototype Design
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on microwave hardware development for medical applications. In this thesis, we have evaluated the accuracy of time domain systems for medical imaging, and a time domain system dedicated to medical imaging has been designed, developed and tested.As a potential imaging modality for biomedical applications, microwave medical imaging has attracted a lot of attention in recent years. Most of the ultra wideband microwave imaging systems reported so far are based on commercial instruments, which are only appropriate for experimental purpose due to the high cost and big size. In order to speed up clinical trials, it is highly desirable to have a custom designed system with low cost, small size, high speed and enough accuracy.With the development of solid state technology, time domain measurement technology has become more and more attractive for ultra-wideband applications. This is due to the low cost, high speed and simple structure.The accuracy of time domain systems is the main concern for the use in medical applications. In the first part of the thesis, we studied the accuracy issueof time domain systems. Theoretical analysis was performed to estimate the measurement accuracy and the results were verified by simulations and experiments. An imaging study was performed in order to compare the image reconstructions obtained by using a time domain experimental systemand an ultra wideband frequency domain system respectively, with comparable results in the permittivity reconstructions. The study of a high contrast breast model showed that when the amplitude uncertainty and phase uncertainty of measurements were less than 1.5 dB and 15 degrees, the effects of noise on reconstructed images were small.Based on the investigations and current technology limitations, we proposed a time domain system design dedicated to microwave medical imaging. A prototype was developed and its measurement accuracy was evaluated. An imaging test was also performed with the prototype and the results were compared with those obtained using our experimental system. The imaging results demonstrated the capability of the developed system for imaging.
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| 37. |
- Zeng, Xuezhi, 1980
(författare)
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Towards in-Home Quantitative Gait Assessment Using Millimeter-wave Radar
- 2023
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Ingår i: 2023 IEEE MTT-S International Microwave Biomedical Conference, IMBioC 2023. ; , s. 88-90
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Konferensbidrag (refereegranskat)abstract
- Recent findings suggest that gait assessment is a useful tool for the early detection and prediction of neurode-generative diseases (such as Alzheimer's and Parkinson's) and fall risk in the elderly. This work proposed a method based on millimeter-wave radar for in-home quantitative gait assessment. The results obtained from experimental studies demonstrated the high capability of the millimeter wave radar for capturing instantaneous gait change in real-life environments. Particularly, the developed method gives high accuracy in the measurement of step time, which is a key gait parameter for predicting fall risk and neurodegenerative diseases in the elderly.
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| 38. |
- Zeng, Xuezhi, 1980
(författare)
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Ultra-Wideband Time Domain Measurement Systems for Microwave Tomography
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As a potential imaging modality for biomedical applications, microwave tomography has attracted a lot of interests in recent years. With microwave tomography, microwave signals are transmitted into the biological tissues and the scattered fields are recorded. By making use of the received information, the dielectric property profiles of the tissues are quantitatively reconstructed. Based on the difference in dielectric properties, tissues are differentiated andconsequentially can be imaged.It has been shown that the reconstructions from wideband data present very good quality with high spatial resolution and high accuracy. In our previous work, the wideband data were obtained in frequency domain with a vector network analyzer, which was time consuming and expensive. Anultra-wideband time domain measurement system has the advantage of fast measurement of wideband data, which is preferable for the clinical applications.A time domain measurement system is either based on equivalent time sampling or real time sampling. In this thesis, the system architectures and work principles of ultra-wideband time domain measurement systems basedon these two different sampling strategies are described.In comparison with a frequency domain measurement system, a time domain system, especially that with real time sampling, has lower measurement accuracy due to the poor signal to noise ratio. In this thesis, the accuracy analysis of time domain measurement systems are carried out, which includesthe identification of the error sources, the modeling of different types of errors and the terminologies of interest for evaluating the measurementaccuracy. The effects of measurement error on the image reconstruction isalso investigated by taking a 2-D breast model as an example.Last, an ultra-wideband time domain experimental system for microwave tomography is presented. Its measurement repeatability is evaluated and phantom reconstructions made from the time domain measurements are compared with those obtained by using a wideband frequency domain system
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| 39. |
- Zeng, Xuezhi, 1980, et al.
(författare)
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Walking Step Monitoring with a Millimeter-Wave Radar in Real-Life Environment for Disease and Fall Prevention for the Elderly
- 2022
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Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 22:24
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Tidskriftsartikel (refereegranskat)abstract
- We studied the use of a millimeter-wave frequency-modulated continuous wave radar for gait analysis in a real-life environment, with a focus on the measurement of the step time. A method was developed for the successful extraction of gait patterns for different test cases. The quantitative investigation carried out in a lab corridor showed the excellent reliability of the proposed method for the step time measurement, with an average accuracy of 96%. In addition, a comparison test between the millimeter-wave radar and a continuous-wave radar working at 2.45 GHz was performed, and the results suggest that the millimeter-wave radar is more capable of capturing instantaneous gait features, which enables the timely detection of small gait changes appearing at the early stage of cognitive disorders.
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| 40. |
- Zhang, Zhuo, et al.
(författare)
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Demonstration of three‐dimensional indoor visible light positioning with multiple photodiodes and reinforcement learning
- 2020
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Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 20:22, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- To provide high‐quality location‐based services in the era of the Internet of Things, visible light positioning (VLP) is considered a promising technology for indoor positioning. In this paper, we study a multi‐photodiodes (multi‐PDs) three‐dimensional (3D) indoor VLP system enhanced by reinforcement learning (RL), which can realize accurate positioning in the 3D space without any off-line training. The basic 3D positioning model is introduced, where without height information of the receiver, the initial height value is first estimated by exploring its relationship with the received signal strength (RSS), and then, the coordinates of the other two dimensions (i.e., X and Y in the horizontal plane) are calculated via trilateration based on the RSS. Two different RL processes, namely RL1 and RL2, are devised to form two methods that further improve horizontal and vertical positioning accuracy, respectively. A combination of RL1 and RL2 as the third proposed method enhances the overall 3D positioning accuracy. The positioning performance of the four presented 3D positioning methods, including the basic model without RL (i.e., Benchmark) and three RL based methods that run on top of the basic model, is evaluated experimentally. Experimental results verify that obviously higher 3D positioning accuracy is achieved by implementing any proposed RL based methods compared with the benchmark. The best performance is obtained when using the third RL based method that runs RL2 and RL1 sequentially. For the testbed that emulates a typical office environment with a height difference between the receiver and the transmitter ranging from 140 cm to 200 cm, an average 3D positioning error of 2.6 cm is reached by the best RL method, demonstrating at least 20% improvement compared to the basic model without performing RL.
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