Xiaoping Liao

Bio: Xiaoping Liao is an academic researcher from Southeast University. The author has contributed to research in topics: Monolithic microwave integrated circuit & Phase detector. The author has an hindex of 17, co-authored 171 publications receiving 1089 citations.

Review of Micro Thermoelectric Generator

Abstract: Used for thermal energy harvesting, thermoelectric generator (TEG) can convert heat into electricity directly. Structurally, the main part of TEG is the thermopile, which consists of thermocouples connected in series electrically and in parallel thermally. Benefiting from massive progress achieved in a microelectromechanical systems technology, micro TEG ( $\mu$ -TEG) with advantages of small volume and high output voltage has obtained attention in recent 20 years. The review gives a comprehensive survey of the development and current status of $\mu$ -TEG. First, the principle of operation is introduced and some key parameters used for characterizing the performance of $\mu$ -TEG are highlighted. Next, $\mu$ -TEGs are classified from the perspectives of structure, material, and fabrication technology. Then, almost all the relevant works are summarized for the convenience of comparison and reference. Summarized information includes the structure, material property, fabrication technology, output performance, and so on. This will provide readers with an overall evaluation of different studies and guide them in choosing the suitable $\mu$ -TEGs for their applications. In addition, the existing and potential applications of $\mu$ -TEG are shown, especially the applications in the Internet of things. Finally, we summarize the challenges encountered in improving the output power of $\mu$ -TEG and predicted that more researchers would focus their efforts on the flexible structure $\mu$ -TEG, and combination of $\mu$ -TEG and other energy harvestings. With the emergence of more low-power devices and the gradual improvement of ZT value of the thermoelectric material, $\mu$ -TEG is promising for applications in various fields. [2017-0610]

A Micromachined Inline-Type Wideband Microwave Power Sensor Based on GaAs MMIC Technology

Abstract: Wideband 8-12-GHz inline-type microwave power sensors that are based on measuring the microwave power coupled from the coplanar waveguide line by a microelectromechanical systems membrane are presented. In this method, the signal is available during the power detection. In order to obtain the low reflection losses and insertion losses, as well as the wideband response of the power sensor, an impedance match structure and a compensating capacitance are proposed. The fabrication of the power sensor is compatible with the GaAs monolithic microwave integrated circuit (MMIC) process. The experimental results show that the sensor has reflection losses better than 20 dB and insertion losses less than 0.45 dB up to 12 GHz. A sensitivity of more than 30 muV/mW and a resolution of 0.2 mW are obtained at the 10-GHz frequency.

RF MEMS membrane switches on GaAs substrates for X-band applications

Abstract: Micromechanical switches have demonstrated great potential at microwave frequencies. For low-loss applications at microwave frequencies, it is important to use high-resistivity substrates. This paper presents the design and fabrication of the shunt-capacitive MEMS switch on GaAs substrates. Analytical mechanical and impedance models of the membrane switch are given, and the results are confirmed by using the ANSYS and HFSS software, respectively. A surface micromachining process, which is compatible with the conventional millimeter-wave integrated circuits (MMICs) fabrication technology, was adopted to fabricate the RF switch on GaAs substrates. Its S-parameter was taken using a HP8510C vector network analyzer and a Cascade Probe station. The measured insertion loss of the switch and its associated transmission line is less than 0.25 dB from 1 to 25.6 GHz, and the isolation may reach -42 dB at its self-resonate frequency of 24.5 GHz. The actuation voltage is about 17 V. The switch has demonstrated lifetimes as long as 5/spl times/10/sup 6/ cycles. The wideband high performance in isolation and insertion loss offers the monolithic integration capability with GaAs MMICs.

A terminating-type MEMS microwave power sensor and its amplification system

Abstract: A terminating-type MEMS microwave power sensor and its amplification system are presented in this paper. A SPICE model is introduced to simulate temperature distribution of this power sensor, and the model has a reference value to estimate the sensitivity of the power sensor. This power sensor is designed and fabricated using MEMS technology and the GaAs MMIC process. It is measured in the frequency range up to 20 GHz with an input power in the 0 to 50 mW range. Over the 50 mW dynamic range, the sensitivity is about 0.29, 0.24 and 0.22 mV mW−1 at 5, 10 and 15 GHz, respectively. The output voltage of the power sensor ranges from 0.64 to 15.2 mV at 5 GHz. After amplification, the output voltage ranges from 0.19 to 6.56 V. The amplification gain is about 437.5, and the sensitivity is increased to 1274 mV mW−1. At 15 GHz, the output voltage of the power sensor ranges from 0.57 to 11.69 mV. After amplification, the output voltage ranges from 0.146 to 5.02 V. The amplification gain is about 438, and the sensitivity is increased to 974.8 mV mW−1. The measurement results show that the amplification system can amplify the output weak signal of the power sensor well and have good linearity.

Optimization of Indirectly-Heated Type Microwave Power Sensors Based on GaAs Micromachining

Abstract: In this paper, the indirectly-heated type microwave power sensors based on GaAs micromachining are optimized to obtain a reasonable microstructure dimension and achieve the compatibility of miniaturization with high performance. The thermal properties and the microwave properties of microwave power sensors are researched. The fabrication is divided into a front side and a back side processing of GaAs. The matching characteristics and the sensitivity characteristics of microwave power sensors are measured. With a tradeoff consideration between the miniaturization and the high performance, a reasonable microstructure dimension of the microwave power sensor is obtained. This optimized power sensor has very good RF-dc linearity, and the response time is about 6 ms.

Micropower energy harvesting

Abstract: More than a decade of research in the field of thermal, motion, vibration and electromagnetic radiation energy harvesting has yielded increasing power output and smaller embodiments. Power management circuits for rectification and DC-DC conversion are becoming able to efficiently convert the power from these energy harvesters. This paper summarizes recent energy harvesting results and their power management circuits.

Development Trends and Perspectives of Future Sensors and MEMS/NEMS.

Abstract: With the fast development of the fifth-generation cellular network technology (5G), the future sensors and microelectromechanical systems (MEMS)/nanoelectromechanical systems (NEMS) are presenting a more and more critical role to provide information in our daily life. This review paper introduces the development trends and perspectives of the future sensors and MEMS/NEMS. Starting from the issues of the MEMS fabrication, we introduced typical MEMS sensors for their applications in the Internet of Things (IoTs), such as MEMS physical sensor, MEMS acoustic sensor, and MEMS gas sensor. Toward the trends in intelligence and less power consumption, MEMS components including MEMS/NEMS switch, piezoelectric micromachined ultrasonic transducer (PMUT), and MEMS energy harvesting were investigated to assist the future sensors, such as event-based or almost zero-power. Furthermore, MEMS rigid substrate toward NEMS flexible-based for flexibility and interface was discussed as another important development trend for next-generation wearable or multi-functional sensors. Around the issues about the big data and human-machine realization for human beings’ manipulation, artificial intelligence (AI) and virtual reality (VR) technologies were finally realized using sensor nodes and its wave identification as future trends for various scenarios.

Wearable Thermoelectric Materials and Devices for Self-Powered Electronic Systems.

Abstract: The emergence of artificial intelligence and the Internet of Things has led to a growing demand for wearable and maintenance-free power sources. The continual push toward lower operating voltages and power consumption in modern integrated circuits has made the development of devices powered by body heat finally feasible. In this context, thermoelectric (TE) materials have emerged as promising candidates for the effective conversion of body heat into electricity to power wearable devices without being limited by environmental conditions. Driven by rapid advances in processing technology and the performance of TE materials over the past two decades, wearable thermoelectric generators (WTEGs) have gradually become more flexible and stretchable so that they can be used on complex and dynamic surfaces. In this review, the functional materials, processing techniques, and strategies for the device design of different types of WTEGs are comprehensively covered. Wearable self-powered systems based on WTEGs are summarized, including multi-function TE modules, hybrid energy harvesting, and all-in-one energy devices. Challenges in organic TE materials, interfacial engineering, and assessments of device performance are discussed, and suggestions for future developments in the area are provided. This review will promote the rapid implementation of wearable TE materials and devices in self-powered electronic systems.