Yi LiAssociate Professor
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Paper
- Fast Array Ground Penetrating Radar Localization by CNN-based Optimization Method
Changyu Zhou; Xu Bai; Li Yi; Munawar Shah; Motoyuki Sato; Xiaohua Tong, This article presents an optimization-based approach to overcome redundancy arising from the multivariables enumeration process in multiple signal classification (MUSIC). By incorporating Broyden-Fletcher-Goldfarb-Shanno (BFGS) optimization, the computational speed of the MUSIC algorithm is significantly improved while maintaining mathematical accuracy. The optimization techniques require reasonable initial values to start the iteration, while for single target imaging purposes, the initial values can be acquired by the boundary between the near field and the far field. To generate suitable initial values for the optimization, we employ a modified convolutional neural network (CNN) to approximate the boundaries between the near and far fields, which vary with array system properties. Besides, the proposed method introduces a method for the Hessian matrix and gradient initialization for the BFGS method. Using simulation results as training samples, the modified CNN successfully establishes boundary approximations. Simulation and experimentation confirm the feasibility of our proposed method, showing its advantages in both accuracy and computation speed compared to existing techniques., Institute of Electrical and Electronics Engineers (IEEE)
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2024 - Photonic Radar for 3D Imaging: From Millimeter to Terahertz Waves
Li Yi; Yihan Li; Tadao Nagatsuma, With the development of 5G and other technologies, radar imaging techniques in high-frequency bands up to the terahertz (THz) range have attracted considerable attention. In particular, the photonic radar technique benefits from the unique advantages of optical devices, including an ultrawide and flexible bandwidth of more than 100 GHz, leading to submm-order range resolution, reduced phase noise, and flexible optical links. This article reviews recent progress in photonic radar systems from the millimeter wave to THz bands, including the hardware components, imaging technology, and radar imaging applications, and discusses the potential high-resolution imaging techniques enabled by photonic radar systems.
IEEE Journal of Selected Topics in Quantum Electronics, Sep. 2023, [Reviewed], [Invited] - Ultrawide-band Millimeter-wave Photonic Radar Mounted on Drone
Yosuke Koyabu; Haruka Tokunaga; Yaheng Wang; Li Yi; Takahiro Ohtsuka; Yasuyuki Tagami; Tadao Nagatsuma, To expand the use of millimeter-wave (MMW) radars in nondestructive testing applications, a drone-mounted radar system using photonics technologies for signal generation and transmission was developed. Stable measurement was realized not only by decreasing the data acquisition time but also by downsizing the drone with a light-weight radar frontend. Visualization of defects was successfully demonstrated for test objects simulating defects in building walls.
Asia-Pacific Microwave Conference Proceedings, APMC, 2023 - High-Speed 600 GHz-Band Terahertz Imaging Scanner System with Enhanced Focal Depth
Yaheng Wang; Li Yi; Masayoshi Tonouchi; Tadao Nagatsuma, Lenses/mirrors with fast data acquisition speeds and extended focal depths have practical importance in terahertz (THz) imaging systems. Thus, a high-speed 600 GHz-band THz imaging scanner system with enhanced focal depth is presented in this work. A polygon mirror with a 250 Hz scanning frequency and an integrated off-axis parabolic (OAP) mirror with an ~170 mm focal depth were employed for 2D imaging. The simulation and experimental results show that a spatial resolution of ~2 mm can be achieved as the imaging distance varies from ~85 to 255 mm. The proposed system was applied to image a hidden metal object as a potential security application, demonstrating that this system can image targets with an enhanced focal depth., MDPI AG
Photonics, 28 Nov. 2022, [Reviewed] - THz Imaging System with a Single Resonant Tunneling Diode Transceiver in 300-GHz Band
Ryoko Mizuno; Ryohei Kaname; Yosuke Nishida; Li Yi; Masayuki Fujita; Tadao Nagatsuma, To reduce the cost of terahertz (THz) imaging systems, we propose an active THz imaging system in which both transmitting and receiving are performed using a single resonant tunneling diode (RTD) transceiver. The self-mixing phenomenon of the RTD was used for 2D imaging with a spatial resolution of 0.8 mm. To increase imaging speed, fast 2D imaging was demonstrated using the beam scanning. The data acquisition time was shortened from 188 to 6 seconds for the imaging area of 60 × 90 mm2. Phase-averaged imaging by controlling the bias voltage of the RTD was proposed to reduce imaging artifacts caused by the interference effect., IEEE
2022 47th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), 28 Aug. 2022, [Reviewed] - Ultra-Low-Loss and Broadband All-Silicon Dielectric Waveguides for WR-1 Band (0.75–1.1 THz) Modules
Ratmalgre Koala; Ryoma Maru; Kei Iyoda; Li Yi; Masayuki Fujita; Tadao Nagatsuma, This study presents ultra-low-loss and broadband all-silicon dielectric waveguides for the WR-1 band (0.75–1.1 THz). The waveguides are built in high-resistivity silicon (10 kΩ-cm) and integrated with supportive frames fabricated from the same silicon wafer in a single etch process to achieve a compact design. We pursued low-loss, broadband, substrateless, unclad and effective medium waveguides. Smaller propagation losses of 0.3 dB/cm and 0.1 dB/cm were achieved for the unclad and effective medium waveguides, respectively. The 3 dB bandwidth was not encountered in the frequency range of interest and was as broad as 350 GHz. An unclad waveguide was employed to devise a Y-junction to demonstrate its practical applications in terahertz imaging. An integrated circuit card was successfully scanned. In addition, we developed unclad waveguide, effective medium waveguide, and Y-junction modules. The modules incorporated an input/output interface compatible with a standard WR-1 flange (254 μm × 127 μm). Unlike the conventional hollow waveguide modules, the unclad waveguide and effective medium waveguide modules reported total loss improvements of 6 dB and 8 dB, respectively, across the operation band. Our results provided a systematic way of achieving low-loss, compact, and versatile modules in the WR-1 band based on all-dielectric-waveguide platforms., MDPI AG
Photonics, 24 Jul. 2022, [Reviewed] - Silicon Dielectric Diplexer Module for 600-GHz-Band Frequency-Division Multiplexing Wireless Communication
Norihiko Shibata; Yuta Uemura; Yuma Kawamoto; Li Yi; Masayuki Fujita; Tadao Nagatsuma, We developed a silicon (Si) dielectric diplexer module for 600-GHz-band frequency-division multiplexing wireless communication. This diplexer was developed based on Si dielectric waveguide technology, which provides low-loss transmission characteristics compared with the conventional metallic terahertz-transmission platform, such as metallic hollow waveguides. It includes straight waveguides based on an effective medium composed of Si and air, and a coupler comprising of two adjacent unclad Si waveguides. Furthermore, for the communication system integration, we developed a practical and low-insertion loss module with WR1.5 metallic hollow waveguide input-output interfaces and modularized the diplexer. We performed transmission measurement experiments with the fabricated diplexer module and achieved 3-dB bandwidths of 101 and 37 GHz, and crosstalk of $-$34 dB at 680 GHz and $-$41 dB at 618 GHz in the cross and bar directions, respectively. Finally, we performed a two-channel wireless communication experiment using the developed diplexer module in the 600-GHz band. We achieved error-free communication at 10 and 6 Gbit/s on the cross and bar channels, respectively. In addition, we achieved a data rate of up to 12.5 Gbit/s at the forward error correction limits for both channels., IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
IEEE Transactions on Terahertz Science and Technology, 01 Jul. 2022, [Reviewed] - Photonic Generation of Highly-Linear Ultra-Wideband Stepped-Frequency Microwave Signals With Up to 6·106 Time-Bandwidth Product
Yujie Lyu; Yihan Li; Chunlong Yu; Li Yi; Tadao Nagatsuma; Zheng Zheng, A photonic-based technique for the generation of highly-linear ultra-wideband stepped-frequency microwave signals with large time-bandwidth product is proposed and experimentally demonstrated. The double-gated recirculating frequency-shifting optical fiber loop enables the frequency of the generated microwave signal to hop step-wisely at exact increment. The generation of signals with up to 20 GHz bandwidth and ∼300 μs temporal duration, corresponding to a time-bandwidth product of 6·106, is achieved by the proof-of-concept system with electronics of only up to 80 MHz bandwidth. Nonlinearity of less than 10-7 and high intra- and inter-period coherence are also experimentally validated. This work provides applications such as high resolution radar with a promising low-cost solution for generating large time-bandwidth product waveforms with frequency scalability and extreme linearity., Institute of Electrical and Electronics Engineers ({IEEE})
Journal of Lightwave Technology, 15 Feb. 2022, [Reviewed] - Generation of broadband highly-linear frequency-modulated signals for optical sensing
Yujie Lyu; Yihan Li; Chunlong Yu; Li Yi; Zheng Zheng, We demonstrate a generation method based on a recirculating frequency shifting fiber loop for frequency-modulated optical signals with up to 48 GHz tuning range and 10-7 linearity for fast and high resolution optical sensing.
2022 Conference on Lasers and Electro-Optics, CLEO 2022 - Proceedings, 2022 - Water Content Estimation in Thermal Insulation Layer Using Millimeter-Wave Optical Coherence Tomography
Yushi Tamenori; Haruka Tokunaga; Li Yi; Tadao Nagatsuma, The demand for non-destructive inspection of the thermal insulation layer of Japanese houses has been increasing. Surface temperature measurement is commonly used for estimating the condition of the thermal insulation layer that is located inside the walls. However, the accuracy needs to be improved because this approach only considers the surface information. To evaluate the thermal insulation layer inside the walls, a millimeter-wave tomography system is proposed for measuring the water content. The system can provide ∼10 mm range resolution to differentiate the reflections from the thermal insulation layer behind the external wall. The Lichtenecker-Rother model is applied for the quantitative evaluation of the water content using the reflected signal. The proposed model is consistent with the experimental data, confirming that a maximum error of 16.0% is obtained. It is also demonstrated that the water content distribution can be visualized with a range resolution of 10.6 mm.
IEICE Transactions on Electronics, Jan. 2022 - Ultra-Wideband Frequency Modulated Continuous Wave Photonic Radar System for Three-Dimensional Terahertz Synthetic Aperture Radar Imaging
Li Yi; Ryohei Kaname; Ryoko Mizuno; Yihan Li; Masayuki Fujita; Hiroshi Ito; Tadao Nagatsuma, Lead, Three-dimensional (3D) imaging remains an expensive and challenging task in the THz band. In this study, a frequency-modulated continuous-wave photonic radar system was presented in the 300-GHz band, instead of using electronic-based devices. The proposed system can obtain a 6-dB bandwidth of 120 GHz to achieve a range resolution of ∼1.1 mm. The frequency sweep linearity of a laser source was calibrated with respect to the imaging distance and range resolution, through which a maximum detectable distance of ∼800 mm was achieved with the collimated beam. To obtain the desired 3D information, the synthetic aperture radar (SAR) technique was introduced to the proposed system to achieve 3D imaging, which was not bounded by the fixed focal distance of a focus lens. It can provide a spatial resolution of ∼1.5 mm within a 3D imaging range up to ∼300 mm. The potential and limitations of SAR imaging schemes are discussed based on the theoretical and experimental results.
Journal of Lightwave Technology, 2022, [Reviewed] - Towards Practical Terahertz Imaging System With Compact Continuous Wave Transceiver
Li Yi; Yosuke Nishida; Tomoki Sagisaka; Ryohei Kaname; Ryoko Mizuno; Masayuki Fujita; Tadao Nagatsuma, Lead, Terahertz (THz) imaging techniques have attracted significant attention and have developed rapidly in recent years. However, despite several advances, these techniques are still not mature, and their high cost and system complexity continue to limit their applications. In this article, the techniques for achieving a practical imaging system with a compact THz transceiver are addressed, while considering the limitations of the current technique. The aim is to provide a brief review of related topics, while also covering our recent progress, which can provide some general perspectives and contrasting approaches for realizing a practical THz imaging system. The continuous wave devices are mainly focused for their flexibility of balancing the imaging resolution and data acquisition time. The importance of transceiver integration is also discussed and illustrated by introducing a 600-GHz band micro-photonic interface for integrating a THz source and detector, with a single resonant tunneling diode as a transceiver. With regard to system issues, spatial sampling with mechanical beam-scanning is discussed as an intermediate approach for moving stage and array technology. The potential and limitations of this approach are evaluated, along with an elliptical reflector as an alternative to an f-theta lens owing to its low cost and simplicity. The combination of integrated devices, along with the mechanical beam-scanning, is also discussed for demonstrating our current concept of realizing a practical THz imaging system., IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
JOURNAL OF LIGHTWAVE TECHNOLOGY, Dec. 2021, [Reviewed] - Millimeter-wave and Terahertz Photonics for Communications and Sensors
Tadao Nagatsuma; Masayuki Fujita; Li Yi, This paper presents an efficient use of telecom-based photonics technologies in millimeter-wave and terahertz systems, which include high-speed wireless communications in the 300-GHz and 600-GHz bands, and ultra-broadband millimeter-wave radars equipped on the drone.
2021 Optical Fiber Communications Conference and Exhibition, OFC 2021 - Proceedings, Jun. 2021 - Subsurface velocity change estimation of pavement with multistatic GPR system
Kazutaka Kikuta; Li Yi; Lilong Zou; Motoyuki Sato, In this paper, we propose a cross-correlation method applied to multistatic ground penetrating radar (GPR) data sets to detect road pavement damage. Pavement cracks and delamination cause variations in electromagnetic wave propagation. The proposed method can detect velocity change using cross-correlation of data traces at different times. An artificially damaged airport taxiway model was measured, and the method captures the positions of damaged parts.
IEICE Transactions on Electronics, Apr. 2021, [Reviewed] - Fast Three-dimensional Terahertz Imaging with Continuous-wave Photomixing
Ryohei Kaname; Li Yi; Tadao Nagatsuma, A high-speed frequency modulated continuous wave (FMCW) radar system is proposed for three-dimensional (3D) terahertz imaging. In order to obtain a high range resolution of mm-order together with fast data acquisition speed, the photonics-based approach is adopted. Thanks to the high-speed frequency sweep of a tunable laser device, the wide bandwidth ranged from 200 GHz to 420 GHz, which corresponds to a range resolution of ~1.3 mm, can be achieved within 35 msec. Furthermore, the 3D imaging of a multi-layer model was demonstrated with quasi-optical imaging system, both range and spatial resolution can achieve to ~1.3 mm without using complicated signal processing.
International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz, 2021 - Drone-mounted Optical Fiber-fed Millimeter-wave Radar
Haruka Tokunaga; Yushi Tamenori; Li Yi; Tadao Nagatsuma, In order to expand the use of millimeter-wave (MMW) radars in non-destructive inspection applications, a drone-mounted radar system has been developed by using the photonic techniques. The radar unit mounted on the drone weights less than 500 g, and is connected to the optical signal generator placed on the ground via an optical fiber cable. The system provides fast data acquisition speed of 0.4 msec for a single sweep over 26-GHz bandwidth, which corresponds to 10-mm spatial resolution for the range detection. The developed radar system has successfully been applied to the wall of a real chimney to measure the thickness of refractory materials.
International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz, 2021 - Millimeter-wave and Terahertz Photonics for Communications and Sensors
Tadao Nagatsuma; Masayuki Fujita; Li Yi, This paper presents an efficient use of telecom-based photonics technologies in millimeter-wave and terahertz systems, which include high-speed wireless communications in the 300-GHz and 600-GHz bands, and ultra-broadband millimeter-wave radars equipped on the drone. (C) 2021 The Author(s), IEEE
2021 OPTICAL FIBER COMMUNICATIONS CONFERENCE AND EXPOSITION (OFC), 2021 - Enabling Device Technologies for Photonics-assisted Millimeter and Terahertz Wave Applications
Tadao Nagatsuma; Masayuki Fujita; Li Yi, This paper presents device technologies for practical combination of telecom-based photonics and electronic devices in millimeter-wave and terahertz systems, which include high-speed wireless communications and sensing applications. Enabling semiconductor devices and their integrated modules are also highlighted., IEEE
2021 IEEE INTERNATIONAL ELECTRON DEVICES MEETING (IEDM), 2021 - 600-GHz-Band Frequency-Division Multiplexing Communication with Silicon Unclad Diplexer
Norihiko Shibata; Yuta Uemura; Yuma Kawamoto; Li Yi; Masayuki Fujita; Tadao Nagatsuma, This paper presents a 600-GHz-band frequency-division multiplexing wireless communication using a silicon unclad diplexer. The designed diplexer has the advantages of lower loss and cost than the conventional metallic hollow waveguide in the 600-GHz and higher bands. It includes straight waveguides based on the effective medium approximation and a coupler comprised of unclad silicon wires, which provide a 3-dB bandwidth of 37 and 101 GHz and a crosstalk of -41 and -34 dB in the bar and cross directions, respectively. The parameters of the diplexer were optimized using 3-D full-wave simulation and validated with experimental results. Finally, we used the designed diplexer for frequency-division multiplexing in the 600-GHz band. The two channels operate simultaneously with carrier frequencies of 618 and 680 GHz. Both channels achieve a data-rate of 6 Gbit/s under error-free conditions and 12.5 Gbit/s at the forward error correction limit., IEEE
2021 IEEE ASIA-PACIFIC MICROWAVE CONFERENCE (APMC), 2021, [Reviewed] - 600-GHz-band Silicon Dielectric Waveguide Module
Norihiko Shibata; Yuta Uemura; Yuma Kawamoto; Li Yi; Masayuki Fujita; Tadao Nagatsuma, We propose a novel 600-GHz-band silicon dielectric waveguide module for terahertz-band applications. The I/O interface of the proposed module is compatible with a standard waveguide flange, WR-1.5, which is intended for use with other conventional hollow-wave guide-packaged components. The design and fabrication of the module is evaluated based on both simulation and experimental results. Using this module, an insertion loss as low as 0.2 dB was achieved, thereby indicating its superiority over the conventional metallic hollow waveguide in the 600 GHz band., IEEE
2021 46TH INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER AND TERAHERTZ WAVES (IRMMW-THZ), 2021 - Integrated Terahertz Optics with Effective Medium for 600-GHz-band Imaging
Tomoki Sagisaka; Ryohei Kaname; Masato Kikuchi; Naoya Kukutsu; Daniel Headland; Li Yi; Masayuki Fujita; Tadao Nagatsuma, Terahertz waves hold potential in industrial imaging applications, to detect sub-millimeter defects and undesired foreign materials. However, terahertz imaging systems are generally bulky due to the need for optical components, and this is a key issue that has limited the scope of practical applications. In this work, we address this limitation by integrating terahertz optics in micro-structured intrinsic silicon. Four half-Maxwell fisheye lenses and a beam splitter are directly integrated together, and fabricated from a single silicon wafer, to realize a terahertz imaging system for the 600-GHz band. The device is evaluated with both full-wave simulation and experimental techniques. It is found to exhibit ultra-wide bandwidth as a spatial mixer, which is beneficial for low-coherence imaging using a terahertz noise source. The proposed method demonstrates a promising new approach for imaging and sensing applications using compact terahertz devices.
2020 International Topical Meeting on Microwave Photonics, MWP 2020 - Proceedings, 24 Nov. 2020 - 600-GHz-Band Terahertz Imaging System Using Frequency-Independent Concave Mirror
Ryohei Kaname; Tomoki Sagisaka; Li Yi; Tadao Nagatsuma, An ultra-wide band scanner using a concave mirror is proposed for 600-GHz-band imaging systems. A frequency-independent mirror was designed to focus beams from different angles which were steered with a galvanometer mirror. Such systems enable three-dimensional imaging as well as two-dimensional spectroscopic imaging with high spatial resolution. The fundamental performance of the concave mirror was described with both the numerical simulation and experimental evaluation. We experimentally confirmed that the area of 100 × 80 mm2 can be imaged in 1 second with a spatial resolution of ~2.5 mm. Finally, we applied the system to a tag reader and a thickness measurement with a resolution of ~1 mm by sweeping the frequency from 450 to 750 GHz.
2020 International Topical Meeting on Microwave Photonics, MWP 2020 - Proceedings, 24 Nov. 2020, [Reviewed] - Imaging Applications with a Single Resonant Tunneling Diode Transceiver in 300-GHz Band
Li Yi; Ryohei Kaname; Yosuke Nishida; Xiongbin Yu; Masayuki Fujita; Tadao Nagatsuma, A resonant tunneling diode (RTD) is a promising device for future terahertz (THz) applications owing to its capacity to operate as both a transmitter and a receiver of THz waves. It is noteworthy that the RTD can simultaneously detect incoming terahertz signals while operating as an oscillator. In this study, we investigated the possibility of employing a single RTD transceiver module as both a source and a detector in THz sensing applications. Such a configuration can greatly simplify THz imaging systems while maintaining excellent phase stability owing to the injection locking phenomenon. The developed imaging system identifies small deformation with a dimension of approximately 0.1 mm from a distance of ~70 cm. Finally, two-dimensional imaging of 0.3-mm-thick tape was successfully demonstrated.
2020 International Topical Meeting on Microwave Photonics, MWP 2020 - Proceedings, 24 Nov. 2020, [Reviewed] - Activation and inactivation of seismicity: The terminations of two injection tests in Okuaizu Geothermal Field, Japan
Kyosuke Okamoto; Li Yi; Hiroshi Asanuma; Takashi Okabe; Yasuyuki Abe; Masatoshi Tsuzuki, The injection of water into geothermal systems is an important procedure required to recover subsurface water resources and enhance permeability for increasing the reservoir volume. The injected water often leads to microseismic events during migration, which can be used to directly track the location of the injected water. However, in rare cases, unexpectedly large induced seismicity occurs after the injection termination. For risk control, understanding the differences between cases that cause post-termination seismicity and those that do not is necessary. For this purpose, we used microseismic monitoring to examine the behavior of water during two injection tests, including their post-termination periods, in Okuaizu geothermal field, Japan. In this field, a new remote microseismic cluster, apart from the injection well, was created in the post-termination period of the first injection test. However, this cluster was not well activated in the second injection test. As a result, we revealed that this microseismic cluster was created on a structure that was different from the target fracture of the injection, possibly owing to pore-pressure migration in the post-termination period of the first injection. Its inactivation in the second post-termination period may be attributable to the lower magnitude of pore-pressure migration derived from the smaller amount of injected volume compared with that of the first injection test. The lower pore-pressure migration was insufficient to reactivate the seismicity. We concluded that the occurrence of seismicity after injection termination may depend on the magnitude of pressure in the injection well at the shut-in time. The Kaiser effect (i.e., a fault is not reactivated by stress that is less than the maximum stress loaded previously) could explain the observed phenomena.
Seismological Research Letters, Sep. 2020, [Reviewed] - Wireless communication using fermi-level-managed barrier diode receiver with J-band waveguide-input port
Tadao Nagatsuma; Fumiya Ayano; Keita Toichi; Li Yi; Masamichi Fujiwara; Noriko Iiyama; Junichi Kani; Hiroshi Ito, Fermi-level managed barrier diodes (FMBDs) are packaged with WR-3 rectangular metallic waveguides to ensure J-band (220-325 GHz) operation. A broadband amplifier is integrated in the packaged module to be used as a receiver for high-speed communications applications. Wireless transmission experiments at around 300 GHz with data rates up to 32 Gbit/s have been conducted for both direct and coherent detection schemes by using photonically generated RF and LO signals., Institute of Electrical and Electronics Engineers Inc.
IEEE MTT-S International Microwave Symposium Digest, 01 Aug. 2020 - On the Use of Lateral Wave for the Interlayer Debonding Detecting in an Asphalt Airport Pavement Using a Multistatic GPR System
Lilong Zou; Li Yi; Motoyuki Sato, In this article, we focus on the detection of the interlayer debonding of the asphalt airport pavement by the ground-penetrating radar (GPR) system. Since the interlayer debonding usually occurs in the shallow region of the asphalt airport pavement (several centimeters), it is difficult to interpret the anomalies or the defects from the GPR signals composed of many waves under the boundary conditions. Moreover, the wavelength of the ordinary GPR system is over several centimeters. Therefore, the spatial resolution of the system is not accurate enough to consider the millimeter thickness of the debonding layer. To overcome these problems, we propose a new method based on evaluating the lateral wave behavior of common midpoint (CMP) gathers collected by a multiple static GPR system. The multistatic GPR system is a stepped frequency continuous wave (SFCW) radar system, which consists of eight transmitting and eight receiving bowtie antennas. The system operates in the frequency range from 50 MHz to 1.5 GHz. After the validation of the simulation, the results of the interlayer debonding detection were evaluated by a field experiment obtained at Tokyo International Airport. The proposed method can detect the debonding layers which are less than 1 mm. Also, it is shown that our proposed method has a high consistency with the conventional acoustic finding method in the field measurement. It provides an innovative and effective method for the interlayer debonding detection of a partially damaged airport asphalt pavement, which is difficult to be observed by the ordinary GPR signals.
IEEE Transactions on Geoscience and Remote Sensing, Jun. 2020, [Reviewed] - 300-GHz-band wireless communication using a low phase noise photonic source
Yi, L.; Iwamoto, K.; Yamamoto, T.; Ayano, F.; Rolland, A.; Kuse, N.; Fermann, M.; Li, Y.; Nagatsuma, T.,Abstract The implementation of advanced multi-level modulation schemes such as quadrature phase-shift keying (QPSK) in contrast to the conventional on–off keying is crucial to further boost the terahertz (THz) communications speed. Thereby, carrier phase noise reduction in the THz range is one of the key goals that need to be urgently achieved. In this paper, the photonic-based THz sources and the phase noise problem are briefly summarized. Then, a low phase-noise photonic source based on the stimulated Brillouin scattering (SBS) optical fiber cavity is first applied for a 300-GHz-band QPSK wireless communication link. The highest data rate at forward-error-correction limited condition was 15 Gbaud utilizing the SBS-based photonic source with a small transmit power of ~ −36 dBm. Its transmission characteristics are evaluated and compared with the conventional optical frequency comb generator (OFCG)-based source at 5 Gbaud. The proposed SBS-based photonic source has been proven to offer better performances than the OFCG-based source with respect to the phase noise, optical carrier to noise ratio, and bit error rate in communications., Cambridge University Press (CUP)
International Journal of Microwave and Wireless Technologies, 2020, [Reviewed] - Photonic-based Wireless Communication Link at 600-GHz Band
YI Li; 園田理人; 木村亮; 東本大樹; 永妻忠夫, Lead
電子情報通信学会論文誌 C(Web), 2020, [Reviewed], [Invited] - Filtering out Antenna Effects From GPR Data by an RBF Neural Network
Jing Wei Zhang; Sheng Bo Ye; Hai Liu; Li Yi; Guang You Fang, Institute of Electrical and Electronics Engineers (IEEE)
IEEE Geoscience and Remote Sensing Letters, Sep. 2019 - Robust subsurface velocity change detection method with Yakumo multistatic GPR system
Kazutaka Kikuta; Li Yi; Lilong Zou; Motoyuki Sato, To detect pavement damage of airport taxiway caused by cracks inside layer, we applied a novel method to common midpoint (CMP) dataset obtained by multistatic ground penetrating radar (GPR) system YAKUMO. Thin cracks within asphalt layers cause slight variation to the electromagnetic (EM) signal propagation velocity. The proposed method can show higher-resolution images of velocity changes of two different time set data with a small number of CMP traces. YAKUMO can acquire several parallel distributed CMP datasets at each position while moving the system linearly in real time, which makes it possible to apply this method to large-scale inspections. In this research, we acquired datasets at an airport taxi-way model with artificial damages at several times over a year. The datasets are analyzed with the proposed method to find out how the conditions of pavement changes by pressurization and time course. The results show that the method can detect not only overall change but also local area changes., Institute of Electrical and Electronics Engineers Inc.
International Geoscience and Remote Sensing Symposium (IGARSS), 2019 - A Hybrid Method Applied to Improve the Efficiency of Full-Waveform Inversion for Pavement Characterization
Jingwei Zhang; Shengbo Ye; Li Yi; Yuquan Lin; Hai Liu; Guangyou Fang
Sensors, Sep. 2018, [Reviewed] - A simplified velocity estimation method for monitoring the damaged pavement by a multistatic GPR system YAKUMO
Li Yi; Lilong Zou; Motoyuki Sato, To identify the slight spatial variability in the electromagnetic(EM) signal propagation velocity and thickness of an asphalt layer caused by the presence of thin cracks within the layer, a practical interferometric approach using the multistatic ground-penetrating radar system YAKUMO was introduced in this study. It was demonstrated that several parallel distributed common midpoint (CMP) datasets can be acquired at each position while moving the system in real time, which makes it possible to apply this method to large-scale inspections. the proposed method can provide much higher-resolution estimations of slight deviations in the velocity and thickness from their corresponding reference values in the undamaged asphalt through the comparison of two CMP datasets, and these deviations can be obtained analytically instead of graphically extracted from the velocity spectrum. In this work, a short-term monitoring dataset is acquired at an airport taxi-way model during it was damaged artificially. This dataset is analyzed with proposed method in order to recognize the conditions of damaged pavement at different stages. The results show that the performed method can indicate the damaged part at different stages. This method provides a novel way to inspect partially damaged pavement when the damage is difficult to observe using the reflected signal only., Institute of Electrical and Electronics Engineers Inc.
2018 17th International Conference on Ground Penetrating Radar, GPR 2018, 20 Aug. 2018 - Practical Approach for High-Resolution Airport Pavement Inspection with the Yakumo Multistatic Array Ground-Penetrating Radar System
Li Yi
Sensors, Aug. 2018, [Reviewed] - High-resolution microseismic monitoring for water injection in Okuaizu Geothermal Field, Japan
Kyosuke Okamoto; Li Yi; Hiroshi Asanuma; Takashi Okabe; Yasuyuki Abe; Masatoshi Tsuzuki, © 22nd International Symposium on Recent Advances in Exploration Geophysics, RAEG 2018. All rights reserved. A continuous water injection test was conducted to halt the reduction of steam production in the Okuaizu Geothermal Field, Japan. Understanding the spatiotemporal behavior of water flow within the reservoir associated with the water injection is essential to ensuring effective steam production. We conducted a high-resolution hypocenter determination using the double-difference method. In this method, relative hypocenter locations are corrected by using time difference in P-wave onsets of seismic event pairs. We found three characteristic seismic clusters associated with the water injection using this method. The creation of microseismic clusters seems to have a qualitative relationship with the distribution of well head pressures in this field, suggesting that microseismic monitoring could be a method for understanding fluid behavior in the reservoir.
22nd International Symposium on Recent Advances in Exploration Geophysics, RAEG 2018, 24 May 2018, [Reviewed] - Near range radar imaging based on block sparsity and cross-correlation fusion algorithm
Feng, W.; Yi, L.; Sato, M.
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2018, [Reviewed] - High-Resolution Velocity Analysis Method Using the ℓ-1 Norm Regularized Least-Squares Method for Pavement Inspection
Yi, L.; Zou, L.; Takahashi, K.; Sato, M., We propose a high-resolution velocity analysis method to estimate the electromagnetic wave propagation velocity in subsurface medium. The estimation is achieved by applying the ℓ-1 norm regularized least-squares method to the conventional common-midpoint (CMP) velocity analysis algorithm. The proposed method can provide not only higher resolution than the conventional velocity analysis method, but can also be applied with a coarse sampling array system, such as our array ground penetrating radar YAKUMO, which returns eight CMP traces within a two meter width. The main purpose of this approach is for precise pavement inspection at shallow depths. We applied this method to both a simulated dataset and real data acquired by YAKUMO at a model airport taxiway to detect the slight velocity changes caused by millimeter-thin cracks filled with air or water within the 15 cm-thick asphalt pavement. In both cases slight velocity changes of about 0.005 m/ns can be detected, and the difference between air- and water-filled cracks can be distinguished. Also, this method is applied to a data acquired at airport taxi-way, the damaged parts are detected successfully and shows good agreement with the corning results. The results indicate that the proposed method is effective for pavement inspection, especially in the presence of thin cracks that cannot be seen directly with the reflected signal., Institute of Electrical and Electronics Engineers
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2018, [Reviewed] - Triggering processes of microseismic events associated with water injection in Okuaizu Geothermal Field, Japan
Okamoto, K.; Yi, L.; Asanuma, H.; Okabe, T.; Abe, Y.; Tsuzuki, M., A continuous water injection test was conducted to halt the reduction in steam production in the Okuaizu Geothermal Field, Japan. Understanding the factors triggering microseismicity associated with water injection is essential to ensuring effective steam production. We identified possible triggering processes by applying methods based on microseismic monitoring, including a new method to determine the presence of water in local fractures using scattered P-waves. We found that the evolving microseismicity near the injection point could be explained by a diffusion process and/or water migration. We also found that local microseismicity on a remote fault was likely activated by stress fluctuations resulting from changes in the injection rate. A mediator of this fluctuation might be water remaining in the fracture zone. After the injection was terminated, microseismicity possibly associated with the phase transition of the liquid was found. We conclude that a variety of triggering processes associated with water injection may exist.[Figure not available: see fulltext.]., Springer Berlin Heidelberg
Earth, Planets and Space, 2018, [Reviewed] - Near range radar imaging by SFCW linear sparse array based on block sparsity
Weike Feng; Li Yi; Motoyuki Sato, A novel compressive sensing (CS) based imaging method for SFCW radar near range targets is proposed. Different from existing CS based methods, the azimuth-dependency of the target reflection coefficient is considered. Based on the block sparsity property of the received signal in the proposed sparsifying dictionary, the 2D image of targets can be obtained at each spatial sampling point. Cross-correlation method is then employed to fuse these 2D images to get the final result. Compared to the classical back projection (BP) method, the proposed method can obtain higher resolution with fewer artifacts via fewer frequencies. Compared to the conventional CS based method, artifacts can be significantly reduced. Experiment results of a SFCW linear sparse array radar system demonstrate that, with only 1/8 data, the proposed method can achieve accurate high-resolution 2D image of targets in the near range. In 30dB dynamic range, no artifact was produced on the imaging result., Institute of Electrical and Electronics Engineers Inc.
International Geoscience and Remote Sensing Symposium (IGARSS), 01 Dec. 2017, [Reviewed] - Enhancement of the migrated results with the deblurring filter
Li Yi; Kazunori Takahashi; Motoyuki Sato
European Geosciences Union General Assembly 2016 (EGU2016), 20 Apr. 2016, [Reviewed] - Optimization of Antenna Polarization of the Multistatic GPR System "Yakumo"
Sato, M.; Yi, L.; Iitsuka, Y.; Zou, L.; Takahashi, K.; IEEE, We have developed 8Ch array GPR system "Yakumo" and have demonstrated the performance of the multistatic radar. At first, the effect of the antenna polarization and the antenna spacing to GPR signal in the multistatic GPR system was evaluated by a laboratory experiment. Using this multistatic GPR system, we can estimate the vertical profile of the electromagnetic wave velocity by CMP method at every position while operating the system along a survey line. However, in order to improve the quality of the CMP data, antenna polarization should be perpendicular to the direction of the survey line, which is 90 degree rotated from conventional GPR measurements. We found that this arrangement may decrease the quality of B-scan of GPR data. We then rotated the antenna polarization, so that the antenna polarization can be set perpendicular to the direction of survey. The B-scan quality was improved, but CMP data quality was decreased. Meanwhile, we have not observed much difference in C-scan images., IEEE
Proceedings of 2016 16th International Conference on Ground Penetrating Radar (Gpr), 2016, [Reviewed] - Application of L1 norm approach to data acquired by the array GPR "Yakumo"
Yi, Li; Takahashi, Kazunori; Sato, Motoyuki; IEEE, We apply the L1 norm approaches on sparsely acquired data of the array ground penetrating radar (GPR) system YAKUMO. Due to the limitation of the antenna size of YAKUMO system, the antenna offsets between each element are much larger than the wavelength. Such sparsely acquired data may introduce strong artifacts to the imaging results such as synthetic aperture radar (SAR) processing and the velocity analysis. In order to use these sparsely acquired data properly, we improved these algorithms by applying the sparsely promoted L1 norm regularization. The results shows that the proposed method can provide high resolution results with sparsely acquired dataset., IEEE
2016 10th European Conference on Antennas and Propagation (Eucap), 2016, [Reviewed] - A Fast Iterative Interpolation Method in f-k Domain for 3-D Irregularly Sampled GPR Data
Yi, Li; Takahashi, Kazunori; Sato, Motoyuki, We propose a new iterative interpolation method for ground penetrating radar (GPR) data based on projection onto convex sets (POCS) and frequency-wavenumber (f-k) zone-pass filtering. The main purpose of this method is to simplify the three-dimensional (3-D) GPR data acquisition; it can also be used for conventional GPR data that include some missing traces. This approach allows the reconstruction of the image from sparsely sampled data that violate the Nyquist criterion. The method can fully use 3-D information and works well with irregularly sampled data. Compared to other iterative interpolation methods, the proposed method needs many fewer iterations and can avoid aliasing. The algorithm is demonstrated with both synthetic data and real GPR measurements from a sand pit experiment. In the latter, the target could still be well reconstructed after 80% of the traces were randomly removed. The average spatial interval of the resampled data was 12 cm, which is much larger than the necessary interval as calculated using the Nyquist criterion. Detailed discussions on the large gap recovery issue and aliasing issue are also provided. The results indicate that it should be possible to reduce the data acquisition density in many GPR applications., IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Ieee Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2016, [Reviewed] - ESTIMATION OF VERTICAL VELOCITY PROFILE BY MULTISTATIC GPR YAKUMO
Yi, Li; Takahashi, Kazunori; Sato, Motoyuki; IEEE, We investigated a velocity analysis algorithm for the new array Ground Penetrating Radar (GPR) system "Yakumo". The common mid-point (CMP) data, which is used to estimate the vertical profile of subsurface velocity can be acquired easily with this system. However, each CMP data set acquired by Yakumo includes only 8 GPR traces with more than 20 cm trace interval. In order to estimate the velocity with this sparse GPR data, we proposed a reversible normal move-out (NMO) processing to remove aliasing and to interpolate the data with a new iterative f-k domain interpolation method to reconstruct the dense data before the velocity analysis. The proposed processing algorithm is applied to both the simulated and the measured data. With the CMP data acquired by 100 MHz antennas, the re-sampled data with more than 0.5 m gaps can still be well interpolated. And the artifacts in the velocity spectrum caused by the noise were well suppressed. We also applied the process to Yakumo CMP data and the estimated the velocity profile in a sandpit. Comparing to the velocity measured by Time Domain reflectometer (TDR), the error was less than 10%. With Yakumo system, we can obtain the CMP data together with the three dimensional GPR data, which greatly benefit the data acquisition., IEEE
2015 Ieee International Geoscience and Remote Sensing Symposium (Igarss), 2015, [Reviewed] - Optimization of data sampling and imaging reconstruction by GPR
Li Yi; Motoyuki Sato; Kazunori Takahashi, Brussels, Belgium
GPR2014, 01 Jul. 2014, [Reviewed] - Optimization of Data Sampling and Image Reconstruction by GPR
Sato, Motoyuki; Takahashi, Kazunori; Yi, Li, This paper focuses on 3-dimensional (3D) image reconstruction by ground penetrating radar (GPR) data. Conventionally, we acquired a GPR gridded dataset with a fine interval, which satisfies the Nyquist spatial sampling criterion for an antenna. However, it takes long time for data acquisition. In this study, we tried two different approaches to reconstruct the image with sparse data that violated the Nyquist spatial sampling criterion: A non-gridded 3D migration method and a new interpolation method based on Projection onto convex sets (POCS) and frequency-wave number (f-k) filtering. Both methods are demonstrated with sand pit experiment datasets and a field experiment data that is acquired by our 3DGPR system. The results shows that both the non-gridded 3D migration method and the interpolation method can reconstruct the main target (a metal pipe at 0.8 m depth) well with the average spatial interval that equals to half wave length. But the non-gridded migration results (especially in shallow depth) suffer from the migration artifacts. The migrated result after interpolation is also demonstrated, and the migration artifacts can be reduced. These results indicate that it is possible to reduce the data density., IEEE
Proceedings of the 2014 15th International Conference on Ground Penetrating Radar (Gpr 2014), 2014, [Reviewed] - Archaeological Survey of Dangoyama Kofun by 3DGPR
Yi, L; Takahashi, K; Sato, M
Proceedings of the 11th SEGJ International Symposium,, 18 Nov. 2013, [Reviewed]
MISC
- 「 Beyond 5G/6G ジダイ ノ マクアケ ニ ムケタ 5G オ ササエル フォトニクス ギジュツ 」 トクシュウゴウ
永妻 忠夫; 冨士田 誠之; 易 利; ウェバー ジュリアン; 胡間 遼; 五十嵐 稜; 原 一貴; 可児 淳一
レーザー研究 = The review of laser engineering : レーザー学会誌 / レーザー学会 編, May 2022 - Design and evaluation of 600-GHz-band silicon dielectric waveguide module
柴田紀彦; 上村悠太; 川本勇真; YI Li; 冨士田誠之; 永妻忠夫
電子情報通信学会大会講演論文集(CD-ROM), 2021 - Two-dimensional Imaging System using a Single Resonant Tunneling Diode Transceiver
水野遼子; YI Li; 要遼平; 大城敦司; 岩松秀弥; 西田陽亮; 冨士田誠之; 永妻忠夫
電子情報通信学会大会講演論文集(CD-ROM), 2021 - Broad band FMCW radar using photonics-based approach in 300-GHz-band
要遼平; YI Li; 永妻忠夫
電子情報通信学会大会講演論文集(CD-ROM), 2021 - Ultrafast frequency-swept radar for drone applications
徳永遥; 為則勇志; YI Li; 永妻忠夫
電子情報通信学会大会講演論文集(CD-ROM), 2021 - Demonstration of AND Operation Using Homodyne Detection in 300-GHz-band
綾野史也; 十市敬太; YI Li; 伊藤弘; 加藤和利; 永妻忠夫
電子情報通信学会大会講演論文集(CD-ROM), 2020 - Recent Trend and Future Prospect of Integrated Systems for Terahertz Sensing and Imaging
永妻忠夫; YI Li; 冨士田誠之; 匂坂知貴; 要遼平
電子情報通信学会大会講演論文集(CD-ROM), 2020 - 600-GHz-band Heterodyne Receiver System using Photonic Techniques
上村悠太; 東本大樹; YI Li; 永妻忠夫
電子情報通信学会大会講演論文集(CD-ROM), 2020 - 600-GHz-band Diplexer Using Photonic Crystals and Its Application to Wireless Communications
柴田紀彦; 上村悠太; 東本大樹; YI Li; 冨士田誠之; 永妻忠夫
電子情報通信学会大会講演論文集(CD-ROM), 2020 - 300-GHz-band Wireless Communication Using Fermi-level Managed Barrier Diode Receiver
十市敬太; 綾野史也; YI Li; 藤原正満; 飯山法子; 可児淳一; 伊藤弘; 永妻忠夫
電子情報通信学会大会講演論文集(CD-ROM), 2020 - 12.5-Gbit/s Wireless Link at 720 GHz Based on Photonics
Tadao Nagatsuma; Masato Sonoda; Taiki Higashimoto; Li Yi; Jeffrey Hesler
International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz, 01 Sep. 2019 - Terahertz Information Tag System with Over-100-bit/s Reading Speed
Tadao Nagatsuma; Yusuke Kujime; Masayuki Fujita; Tomoki Sagisaka; Li Yi
International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz, Sep. 2019 - 300-GHz-band Wireless Communication Using Fermi-level Managed Barrier Diode Receiver
Tadao Nagatsuma; Masato Sonoda; Taiki Higashimoto; Ryo Kimura; Li Yi; Hiroshi Ito
IEEE MTT-S International Microwave Symposium Digest, 01 Jun. 2019 - A game of geothermal resources exploration in FREA open house 2017
村田 泰章; 浅沼 宏; ウィディアトモジョ アリフ; 石川 慧; 石原 武志; 易 利; 石橋 琢也; 内田 洋平; 大月 文恵; 岡本 京祐; 片山 泰樹; 桑名 栄司; 最首 花恵; 柴田 由美子; シュレスタ ガウラブ; 土屋 由美子; 牧野 雅彦; 柳澤 教雄; 山谷 祐介; 渡邉 教弘
GSJ地質ニュース = GSJ chishitsu news, Feb. 2018 - A Practical Approach for High-resolution Pavement Inspection with Multistatic Array GPR YAKUMO (宇宙・航行エレクトロニクス) -- (地下電磁計測ワークショップ)
易 利; 鄒 立龍; 佐藤 源之
電子情報通信学会技術研究報告 = IEICE technical report : 信学技報, 04 Oct. 2017 - Investigation on passive imaging methods of geothermal reservoirs by using the microearthquake event
易 利; 岡本 京祐; 浅沼 宏
公益社団法人物理探査学会学術講演会講演論文集 = Proceedings of the SEGJ Conference, 2017 - Study on factors of microseismic events following injection into a geothermal field using analyses of hypocenter clusters and seismic scattering waves
岡本 京祐; 易 利; 浅沼 宏
公益社団法人物理探査学会学術講演会講演論文集 = Proceedings of the SEGJ Conference, 2017 - Simultaneous Estimation of Velocity and Thickness of Stratified Material with Array GPR System YAKUMO (宇宙・航行エレクトロニクス) -- (地下電磁計測ワークショップ)
易 利; 高橋 一徳; 佐藤 源之
電子情報通信学会技術研究報告 = IEICE technical report : 信学技報, 26 Nov. 2015 - Large scale subsurface velocity estimation with array GPR system "YAKUMO"
L. Yi; K. Takahashi; M. Sato
URSI Radio Science Bulletin, 25 Aug. 2015, [Reviewed]
Lead - Investigation on 3D migration of non-gridded GPR data
Yi Li; Takahashi Kazunori; Sato Motoyuki
Technical report of IEICE. SANE, 22 Nov. 2013
Research Themes
- Investigation of a practical sparse array terahertz imaging sysytem for real-time 3-dimensional imaging applications
Grant-in-Aid for Early-Career Scientists
Osaka University
01 Apr. 2019 - 31 Mar. 2022
