Microwave & Radio Frequency

Microwave & Radio Frequency

Microwaves and radio-frequency (RF) are at the heart of many electronic applications such as cellular phones, WiFi, RFID, GPS, Radar and satellites etc.. The research efforts of the Microwave & RF faculty staff embrace both hardware implementations and theoretical studies in electromagnetic theory, antennas and RF, microwave and millimeter-wave circuits and systems for various government, industry and defense related applications, e.g. wireless communications, biomedical and healthcare applications, and satellite and space thrusts. Further details on their research can be found by clicking on the Center for Microwave & Radio Frequency link.

The laboratories in the microwave & RF area own the major measurement instruments for microwave circuits, MMICs and antennas, including antenna anechoic chamber (Fig.1), probe station and pulse based DCIV system up to 50 GHz (Fig.2), and VNA (up to 110 GHz) and spectrum analyzer (50 GHz) and signal generator (40 GHz). The laboratories in the microwave & RF area also have various commercial RF circuit and EM simulation tools, e.g. ADS, Microwave Office, HFSS, CST, etc. for RF circuit and antenna designs.

Fig.1 Antenna anechoic chamber

Fig.2 Probe station and pulse-based DCIV system

Technical expertise of Microwave & RF area colleagues mainly covers

  • Development of cube-/micro-satellites and payloads and satellite communication/navigation;
  • Microwave remote sensing (SAR, ISAR, InSAR, InISAR, BiISAR, MIMO SAR);
  • Vehicular/unmanned vehicular and other radar systems;
  • Electromagnetic inverse problems and optimization methods;
  • Engineering and applications of super materials, metamaterials and metasurfaces;
  • RF, microwave and millimeter-wave circuits, subsystems, RFICs and MMICs;
  • Phased array antennas and digital beam forming techniques;
  • Radio-frequency coils and MRI systems;
  • RF wireless power and ambient electromagnetic-wave energy harvesting;
  • Antenna bandwidth enhancement and miniaturization techniques;
  • Antennas for biomedical implants and on-body communications;
  • Multiple antennas, and super-absorbers for the next-generation mobile communications (from microwave to sub-millimeter wave bands);
  • Microwave and acoustic imaging and nondestructive evaluation/test (NDE or NDT);
  • Optics microscope and microwave impedance microscope;
  • Optical encryption/decryption;
  • Optical force, micromanipulation and bio-application;
  • Diffraction, nano-optics, and color display;

Research Highlights

Highlights of recent research progress and achievements made by the Microwave & RF area colleagues are listed below.

Fig.3 Layout of nano-satellite under development

1. More youths have been inspired to consider satellite and space-related technologies after the successful launch of Singapore’s first satellite (X-SAT). More recently, nano-satellites have changed the communication philosophy from long-range point-to-point propagation to a multi-hop network of small orbiting nodes. One of the exciting projects being undertaken by NUS undergraduates is to develop a nano-satellite with only a size of 10cm x 10cm x 20cm. Fig. 3 shows the layout of the nano-satellite with all its subsystems assembled by NUS students for launch in late 2015. This project is led by Dr Luo Sha.

(a) Concept of the through-wall radar

(b) The reconstructed image (on the right) agrees well with the exact object (on the left).

Fig.4 Through-wall radar under development

2. The electromagnetic modeling activities also cover radiation, scattering and inverse imaging which find applications in radar, stealth cloaking, bio-electromagnetics and nano-electromagnetics. For instance, through-wall imaging (TWI) as illustrated in Fig.4 is required for a range of applications including police, defence and fire rescue applications. The goal of TWI is to provide vision into otherwise obscured areas. Accurate sensing and imaging can allow the police to obtain an accurate description of a building interior during a hostage crisis or allow firefighters to locate people trapped inside a burning building. The problem of reconstructing objects behind a wall is basically an inverse electromagnetic scattering problem. In a Through-Wall-Imaging (TWI) system, transmitting and receiving antennas are placed on one side of the wall, and the shapes and compositions of objects on the other side of the wall are reconstructed based on data of how objects scatter electromagnetic waves. This work is led by Prof Chen Xudong.

Fig.5 (a) Optical tractor beam: negative pulling force; (b) Metasurface hologram: Dispersionless, high-quality, broadband, subwavelegnth-pixel holography; (c) A reproduction of Monet’s painting in micrometer scale, using plasmonic nano-structures; (d) A device that can transform the perception of a perfectly conducting (or metallic) object into three apparent objects.

3. The scattering force, for the first time, is found to be negative, namely, pulling an actual object in space or underwater physically becomes reasonable and plausible as shown in Fig. 5(a). Prof Qiu Chengwei’s 2011 PRL work is amongst the first three papers reporting the optical tractor beam, and was widely featured by various technical press including Science. His pioneering work paves an unprecedented avenue to many unforeseen future endeavors in biomolecular engineering (driving and separating cells), underwater towing, optical pulling, and outer space junk cleaning. Prof Qiu Also in 2012 pioneered the ultrathin flat metasurface which empowers uniquely dual functions in one device, as well as performs exactly as its counterpart (i.e., bulky and curved optical lensing devices), ashown in Fig.5(b). Beyond that, this new device provides greater flexibility in designing and adding new functionalities to optical systems since the focusing properties of the same lens can be altered between a convex lens and a concave lens at one’s will. Furthermore, the compact size, and the planar nature of the lens could also have an impact on photonic integrated devices. It leads to drastic down-scaling and integration of all optical devices. Conventional optics suffers from the diffraction limit, while plasmonics can address such a limit, via guiding and manipulating light to the deep sub-wavelength scale. It was also featured by IET (The Institution of Engineering and Technology), UK. He developed plasmonic mixed palatte using nano-patterned Al pillars to recreate Monet’s famous painting over micron –meter scale with high resolution as shown in Fig.5(c). His Adv Funct Mater paper demonstrated a device that can transform the perception of a perfectly conducting (or metallic) object into three apparent objects as shown in Fig.5(d). It will pave the way for future applications of advanced optical illusions, camouflage, and cloaking in an interesting new sense. The work has enormous potential to enhance our ability to mold, harness, and perceive waves at will. In future work he will explore the use of optical frequencies, which can also make the real object or person ‘disappear’ or ‘appear’ in a controllable form This work was also widely featured by Daily Mail (UK), Wired (UK), Le Monde (France), LiveScience (US), Science Daily, MIT Technological Review (US), Phys. Org, 联合早报, SPIE Newsroom (US), Nanowerk News, etc.

4. The development on novel metamaterials-based antenna technologies headed by Prof Chen Zhi Ning has led to win IES Prestigious Engineering Awards in 2013 and 2014 as in Fig. 6.

Fig. 6 The ceremony of IES Prestigious Engineering Award in 2014. The back screen shows the large metamaterials-based antenna array.

(a) RF wireless power

(b) SiP based temperature sensor capsule platform for implantable biomedical applications

(c) 60-GHz CMOS power amplifier

(d) 60-GHz LTCC integrated antenna array

Fig.7 Innovative RF/Microwave circuits and antennas

5. At the component and subsystem level, various RF/Microwave planar integrated circuits, MMICs and antennas have been proposed by RF/Microwave colleagues for a diversity of applications such as next generation wireless communications, biomedical and healthcare applications and satellite and space thrusts. For instance, Prof Guo Yongxin and his team proposed an adaptive RF energy harvesting approach by improving the input dynamic range by 20 dB and more. This innovative technique has been filed for a PCT patent and can be applied in many applications such as RFIDs, near field communications (NFCs), wireless power and internet of things (IoTs) with a prototype as shown in Fig. 7(a). Prof Guo’s PhD student won the Second Prize for this work in the 2013 IEEE International Workshop on Electromagnetics 2013 (iWEM2013), Hong Kong. Fig.7(b) shows the system-in-package (SiP) based temperature sensor capsule platform for implantable biomedical applications by Prof Guo’s team with medical colleagues. Prof Guo’s miniaturized implantable antenna presentation won the best poster award in 2014 International Conference on Wearable & Implantable Body Sensor Networks (BSN 2014), Zurich, Switzerland. Millimeter-wave wireless technologies are very promising for multi-gigabit communication systems, high resolution imaging, sensing and detection. In fact, the world-wide opening of a massive amount of unlicensed spectrum at around 60 GHz has triggered great interest in developing affordable 60-GHz radios; novel CMOS power amplifiers and high-performance antenna arrays for 60 GHz radios have been developed by Prof Guo and his team as shown in Fig. 7(c) and (d). Prof Guo’s PhD student won the Best Student Paper Award on his 60-GHz CMOS power amplifier in 2010 International conference on microwave and millimeter wave technology (ICMMT2010), Chengdu, China.

6. Prof TS Yeo, who has been working on the development of SAR, ISAR, BiISAR, InISAR, and MIMO SAR and ISAR algorithms for almost 20 years. His pioneering work in the imaging of moving targets with rotating parts, and nonlinear chirp scaling and phase error estimations, have been well-received and were cited by fellow researchers for over 90 (the first work) and 80s (the second and third work) times respectively. His current work on MIMO 3-D imaging, Bi-ISAR imaging, and the application of compressed sensing in MIMO ISAR are being published in high-quality journals such as IEEE Transactions on Geoscience and Remote Sensing, Image Processing, Signal Processing, and Antennas and Propagation.

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