Shuai-Min Chen

Improvement on magnetic power loss of MnZn-ferrite materials by V2O5 and Nb2O5 co-doping

Abstract Simultaneous incorporation of V2O5 and Nb2O5 dopants into low loss MnZn-ferrites markedly improves the power loss characteristics of the materials, provided no abnormal grain growth phenomenon was induced. The finer the grain size is, the smaller the power loss. The beneficial effect of V2O5 and Nb2O5 co-doping is presumed to be the reduction on the eddy current loss for the MnZn-ferrite materials. However, the prime factor reducing the power loss in high frequency regime (3 MHz) is the suppression on residual power loss of the materials. The mechanism for the decrease in the residual power loss, in addition to the reduction on grain size (GS 70 Ω), is probably the increase in the uniformity of grain size distribution.

The influence of grain boundary internal stress on permeability: temperature curve for Mn–Zn ferrites

Abstract The oxygen partial pressure (PO2) utilized in homogenization or cooling stage of sintering process has been observed to significantly influence the initial permeability-temperature (μi–T) characteristics of the materials. Higher oxygen partial pressure (PO2) during homogenization period lowers the μi-value without shifting the secondary maximum peak (Tsmp). However, higher PO2 (0.1%) during cooling period shifts the Tsmp toward lower-temperature regime. This phenomenon is accounted for by the induction of compressive stress onto the ferrite grains, which in turn, is due to preferential oxidation along grain boundaries.

Secure and Efficient Handover Schemes for Heterogeneous Networks

With the rapid development of wireless communication, mobile users are able to manually switch their network interfaces to different types of networks. The IEEE 802.21 Draft Standard was proposed to integrate the Media Independent Handover (MIHs) between the wireless network interfaces, such as WiFi, WiMAX, 3 GPP, and 3GPP2. However, it may not hold the seamless roaming character and does not provide the security mechanism.In this paper, we propose an efficient handover mechanism among WiFi and WiMAX networks to meet the seamless roaming character by reducing the authentication processes. In addition, the proposed scheme involves security mechanisms that guarantee the handover messages to be secure and maintain the authenticity for the reduced steps.

CRFID: An RFID system with a cloud database as a back-end server

Radio-frequency identification (RFID) systems can benefit from cloud databases since information on thousands of tags is queried at the same time. If all RFID readers in a system query a cloud database, data consistency can easily be maintained by cloud computing. Privacy-preserving authentication (PPA) has been proposed to protect RFID security. The time complexity for searching a cloud database in an RFID system is O(N), which is obviously inefficient. Fortunately, PPA uses tree structures to manage tags, which can reduce the complexity from a linear search to a logarithmic search. Hence, tree-based PPA provides RFID scalability. However, in tree-based mechanisms, compromise of a tag may cause other tags in the system to be vulnerable to tracking attacks. Here we propose a secure and efficient privacy-preserving RFID authentication protocol that uses a cloud database as an RFID server. The proposed protocol not only withstands desynchronizing and tracking attacks, but also provides scalability with O(logN) search complexity.

A Secure RFID Authentication Protocol Adopting Error Correction Code

RFID technology has become popular in many applications; however, most of the RFID products lack security related functionality due to the hardware limitation of the low-cost RFID tags. In this paper, we propose a lightweight mutual authentication protocol adopting error correction code for RFID. Besides, we also propose an advanced version of our protocol to provide key updating. Based on the secrecy of shared keys, the reader and the tag can establish a mutual authenticity relationship. Further analysis of the protocol showed that it also satisfies integrity, forward secrecy, anonymity, and untraceability. Compared with other lightweight protocols, the proposed protocol provides stronger resistance to tracing attacks, compromising attacks and replay attacks. We also compare our protocol with previous works in terms of performance.

Zinc loss of Mn-Zn ferrite sintered under alumina plate

Cover plate materials and the core-to-plate spacing were observed to significantly lower the initial permeability (/spl mu/i) of the sintered Mn-Zn ferrite samples. The degradation of the /spl mu/i-value correlates very well with the Zn loss from the samples. The serious Zn loss was enhanced when using Al/sub 2/O/sub 3/ materials as cover plate. The Al/sub 2/O/sub 3/ plate act as Zn-sink and the transportation in gas phase is the controlling process for Zn loss.

An Efficient Rekeying Scheme for Multicast and Broadcast (M&B) in Mobile WiMAX

Mobile WiMAX (IEEE 802.16e) is an emerging technology for wireless broadband access network. It provides wider converge and higher bandwidth than conventional wireless technologies. Multicast and Broadcast (M&B) in WiMAX are suitable for multimedia applications such as Pay-TV system because multimedia providers can efficiently distribute the same contents to the users within the same M&B group. Although IEEE 802.16e has defined Multicast/Broadcast Rekeying Algorithm (MBRA) to secure M&B, recent research indicates that MBRA is insecure. In this paper, we propose an efficient rekeying scheme which depends on Linear Ordering of Receivers (LORE) to protect M&B group communication. Our scheme requires O(1) messages for rekeying and addresses the security problem of MBRA. Therefore, our rekeying scheme is suitable for protecting large dynamic groups such as M&B groups.