Prof. Dr. Changjun LIU
School of Electronics and Information Engineering, Sichuan University, Chengdu, Sichuan, China
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Academic Career Length
27Years (2000-Present)
(Calculated once Scilit publication data is synced: current year − year of first publication + 1)
Representative Publications
View All Publications29 November 2016 in IEEE Transactions on Microwave Theory and Techniques
Journal Article
A single-diode compact microwave rectifier with a series band-stop structure is presented in this paper. The bandstop structure is connected to the diode in series to block the harmonics produced during rectifying. It replaces the cascading bandpass or low-pass filter between the input and the diode in a conventional microwave rectifier. A microwave rectifier at 2.45 GHz with an HSMS 282 Schottky diode is realized based on the proposed design method. A short-ended eighthwavelength microstrip transmission line is applied to the rectifier in series with the diode as a band-stop structure. The short-ended microstrip transmission line presents an inductive impedance to compensate the diode capacitive impedance at fundamental frequency and turns to an open circuit to block the second harmonic for power recycling. The proposed circuit shows a novel schematic for compact microwave rectifiers. The fabricated rectifier is compact with a dimension of 0.15λg × 0.2λg. A microwave-to-dc conversion efficiency of 80.9% is achieved at 20 dBm input power with a 580-Ω dc load.
23 March 2020 in IEEE Microwave and Wireless Components Letters
Journal Article
ZHZhongqi He
Zhongqi HeChangjun LIUIn this letter, a compact high-efficiency broadband microwave rectifier with an extended range of input power is proposed for energy harvesting. In the proposed structure, a novel broadband impedance-matching network is employed to reach high radio frequency (RF) to dc conversion efficiency. The reduction in mismatching loss over a wide bandwidth and input power range is achieved by impedance transformation from three segments of microstrip lines, which leads to a compact design to realize broadband impedance matching. A theoretical analysis and simulations of the proposed rectifier are presented. For validation, a broadband rectifier operating between 2.1 and 3.3 GHz is implemented and tested. The proposed rectifier shows a bandwidth of 44.4% for efficiency over 70% at an input power of 14 dBm. The measured efficiency remains above 50% from 2 to 3.3 GHz with an input power from 4 to 16 dBm. Moreover, the proposed rectifier has a compact size of 31 mm x 18 mm.
2 October 2015 in IEEE Microwave and Wireless Components Letters
Journal Article
Changjun LIUFTFan Tong
Fan Tong
This letter presents a novel substrate integrated waveguide (SIW) resonator sensor that is specifically designed to measure the complex permittivity of liquids. The resonant characteristics of the sensor are influenced by liquids through a slot opened on the top plane. The inverse problem of obtaining permittivity is solved with artificial neural network. Experiments were performed with an SIW resonator sensor designed at C band. Experimental data were reported and they agreed well to the reference values. The sensor is simple and low cost, which may be applied to permittivity measurements in applications at the industrial, scientific and medical (ISM) frequencies.
16 March 2022 in IEEE Transactions on Microwave Theory and Techniques
Journal Article
Changjun LIUHLHang Lin
Hang LinZHZhongqi He
Zhongqi HeZCZhizhang (David) Chen
Zhizhang (David) ChenIn microwave wireless power receivers, impedance matching networks can maximize power transmission from RF to dc. However, they require circuit components and physical space to implement. To circumvent the problem, we present two compact patch rectennas that do not require matching networks. They comprise a patch antenna and rectifying Schottky diodes which are mounted on the ground plane and connected to the patch antenna through metallic vias. The positions of the vias are chosen in such a way that the input impedance of the antenna and that of the rectifying units are conjugately matched. The two rectenna types are all fabricated and tested: one with one rectifying unit and the other with double rectifying units, respectively. Measurements show that the rectenna with the single rectifying unit has the peak RF-dc conversion efficiency of 77% at 2.45 GHz and the dynamic power range (>60%) is 10 dB. The rectenna with the double rectifying units has the peak conversion efficiency of 74.14% at 2.45 GHz and the dynamic power range (>60%) is 10 dB. Both rectennas are good candidates for integrated microwave wireless power receivers due to the removal of the impedance matching networks and the suppression of harmonic components.
6 November 2018 in IEEE Microwave and Wireless Components Letters
Journal Article
PWPengde Wu
Pengde WuSHShao Ying Huang
Shao Ying HuangWZWenshen Zhou
Wenshen ZhouZRZhi Hua Ren
Zhi Hua RenZLZhenlong Liu
Zhenlong LiuChangjun LIU +1
In this letter, a microwave rectifier with a wide input power range is presented by proposing a self-tuning impedance matching (STIM). The STIM consists of a varactor reversely biased by the output voltage of the rectifier to compensate the variation of the input impedance caused by the input power, so that impedance matching is obtained over a wider input power range. For validation, the proposed rectifier at 2.4 GHz was designed and implemented. The experimental results show that the RF-dc power conversion efficiency maintains over 50% and 70% within the input power ranges of 2.5-25.5 dBm and 11-24.5 dBm, respectively. Compared with the counterpart without the STIM, an improvement of 7.2 dB in terms of the input power range when the reflection coefficient is less than -10 dB was successfully demonstrated.
Journal Article
Changjun LIUCLChongwei Liao
Chongwei LiaoYPYujie Peng
Yujie PengWZWeixin Zhang
Weixin ZhangBWBo Wu
Bo WuPYPeixiang Yang
Peixiang YangThis paper reviews microwave sensors and their applications in permittivity measurement. The detection, diagnosis, classification, and monitoring without contact and invasion have been the subject of numerous studies based on permittivity characteristics tracking. This review illustrates many new types of research in recent years. Firstly, the application background is briefly introduced, and several main measurement methods are presented. An overview of measurement technology in various applications is compiled and summarized based on numerous typical examples. Exciting applications are compared and presented separately, combining resonator sensors with strong electric fields. Furthermore, differential signals represent trends for future applications with strong environmental immunity, an alternative option to expensive measuring equipment. With the alternation of metamaterials, microfluidics technologies, cross-technology, algorithms, and so on, sensors play an exceptionally prominent role in practical and low-cost applications.
About Me
Changjun Liu (Senior Member, IEEE) received his BS degree in applied physics from Hebei University, Baoding, China, in 1994, and his MS degree in radio physics and PhD degree in biomedical engineering from Sichuan University, China, in 1997 and 2000, respectively.
From 2000 to 2001, he was a post-doctoral researcher with Seoul National University, Seoul, South Korea. From 2006 to 2007, he was a visiting scholar with Ulm University, Ulm, Germany. Since 1997, he has been with the Department of Radio Electronics, Sichuan University, where he has been a professor since 2004. He has authored one book and more than 100 articles. He holds more than 10 patents. His current research interests include microwave power combining of large-power vacuum components, microwave wireless power transmission (WPT), and microwave power industrial applications.
Dr. Liu has been a recipient of several honors, such as the outstanding reviewer for the IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES from 2006 to 2010; a recipient of support from the MOE under the Program for New Century Excellent Talents in University, China, from 2012 to 2014; a recipient of the Sichuan Province Outstanding Youth Fund from 2009 to 2012; and was named by Sichuan Province as an Expert with Outstanding Contribution. He is the Associate Editor of the Chinese Journal of Applied Science.
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