Initial Resonant Frequency Research Articles

A NOVEL COMPACT ARCHIMEDEAN SPIRAL ANTENNA WITH GAP-LOADING

A novel compact Archimedean spiral antenna with gap- loading is investigated in this paper. A circular frame sharing the same centre with the spiral elements introduces a capacitive gap. By adjusting the width of the gap and the width of the circular frame, the initial resonant frequency of the proposed antenna is shifted from 2.79 to 1.93 GHz. Compared with the traditional Archimedean spiral antenna with the same lowest operation frequency, the area of the proposed antenna can be reduced by more than 30simulated radiation pattern results.

A Newly Designed Resonance Frequency Analysis Device for Dental Implant Stability Detection

Resonance frequency (RF) analysis technology was used to design a new dental implant stability detector. To calibrate and test the performance of this novel apparatus, in vitro and in vivo models, respectively, were used. The RF values of the test implants detected using our new device and a commercially available analogous device (Osstell) were compared. Further, implant stability status was also detected clinically using our device at 2, 4, 8, and 12 weeks after surgery. A high correlation was demonstrated between the values measured with the two devices (y = 0.31x-12.45; R2 = 0.98, p < 0.05). In our clinical tests, an initial RF value above 10.0 kHz indicated that the implant was ready to accept functional loading, while values in the 4.0-10.0 kHz range reflected the need for further osseointegration. In conclusion, these results indicated that our new device might be useful in a clinical setting for evaluating the healing status of a placed implant.

Effects of different sintering temperature and Nb 2O 5 content on structural and magnetic properties of Z-type hexaferrites

Nb-doped Z-type hexaferrites (Ba 3(Co 0.4Zn 0.6) 2Fe 24O 41) with composition of Ba 3(Co 0.4Zn 0.6) 2Fe 24O 41+ x Nb 2O 5 (where x=0.0, 0.1, 0.2, 0.4, 0.6, 0.8, 1.2, 1.6 and 2.0 wt%) were prepared by a solid-state reaction method. The effects of different sintering temperature ( T s) and Nb 2O 5 content on the sintering behaviors, phase composing, microstructure, and magnetic properties of the samples were investigated. The results from X-ray diffraction and scanning electron microscopy show that as the amount of Nb 2O 5 additive increases, the major phase changes to Z-phase, Simultaneously, M-phase and a small amount of niobate phase appear. The Nb 2O 5 additive promotes the grain growth as reaction center at lower sintering temperature (1220 °C), but at higher temperature (1260 °C), niobate phase separated out in grain boundaries as secondary phase will restrain abnormal grain growth, so closed pores in grains are not formed. The Nb 2O 5 additive can enhance densification, improve initial permeability of hexaferrites by increasing the grain growth of hexaferrite and the displacement of ions in the sintering process due to the aberration and activation of crystal lattice, which is accompanied by the solubility of Nb 5+ in the hexaferrites. A relative density of 96%, maximum initial permeability (32–33), minimum coercivity (454–455 A/m) and resonance frequency above 400 MHz were obtained for the sample with 0.8 wt% Nb 2O 5 sintered at 1260 °C for 6 h.

Design of a stability-detecting device for dental implants

Resonance frequency (RF) analysis technology was used to design a dental implant stability detector. The device uses a miniature-sized electromagnetic triggering rod to elicit vibration in a dental implant. Vibrational signals were recorded via an acoustic receiver. To assess the in vivo performance of the test apparatus, animal models were used. Implants were placed in the left tibia of 12 rabbits using a conventional surgical procedure. Standard 3.2 mm x 8 mm implants were placed in each test tibia with pre-tapping cavities of 3.2 mm and 3.7 mm diameters to simulate either a 'well-fitting' or a 'loosely fitting' situation. The RF values of the test implants were detected by the newly developed device which was directly mounted on the healing abutments of the implants. The results showed that the RF values of the implants under well-fitting conditions significantly increased (p < 0.01) 3 weeks after surgery and reached a plateau at around 6-7 weeks. Meanwhile implants with higher initial RF values had shorter healing times and higher final RF values at the plateau. Based on these findings, it was concluded that the idea of using the current designed device for detecting the degree of bone healing during the osseointegration process seems feasible.

A frequency-reduction scheme for spiral slot antenna

We present a new technique to reduce the initial resonant frequency, enhance the bandwidth, and miniaturize the antenna size for microstrip-feeding spiral slot antennas. Two spiral slot antennas were fabricated and measured to demonstrate the capability of lowering the initial resonant frequency by adding a circular capacitive stub at the end of the feedline. According to results, the initial resonant frequency of the proposed antenna has been shifted from 1.58 to 1.28 GHz; in other words, the antenna size can be reduced by 20%, approximately. The radiation patterns are simulated and measured at 1.3 GHz and 3 GHz to examine the excitation mode. The variations of the initial resonant frequency versus the radius of the circular stub are also shown to find the optimum radius of the stub.

傾斜機能材料 高周波用異方性傾斜Ｎｉ‐Ｚｎフェライト

Ni-Zn ferrites with graded magnetic anisotropy for high frequency of megahertz order were prepared by the addition of CoO. When the CoO content increased, resonance frequency was expanded. However, initial permeability was decreased and anisotropy field was increased. Therefore we tried to prepare Ni-Zn ferrite with high initial permeability and high resonance frequency by the addition of graded CoO content. Troidal core samples were made to layer Ni-Zn ferrite with different CoO content. As the result, the sample which had large CoO content with inner layer, steep gradation and little Ni-Zn ferrite with outer layer showed excellent high frequency characteristics. The Ni-Zn ferrite added CoO with graded CoO content 0, 5, 0 wt.% had initial permeability of 80 for 20-60 MHz.

Electrophotographic and microwave photodielectric studies (I) effect of various transition metal dopants on titanium dioxide pigments in the solid state

Several titanium dioxide pigments in the rutile crystalline form have been doped with Ni, Co, Fe, Pb, Cu, V and Mo ions by co-precipitation in aqueous alkaline solution with titanium (IV) chloride. The photoconductivities in thin poly (vinyl carbazole) films and photodielectric microwave responses of the various transition-metal-doped titanium dioxide pigments have been measured and are discussed in terms of their photoactivities. The results suggest that different dopants affect the photoconductive and photodielectric responses of the titanium dioxide pigments to different extents. Photoconductive responses of the rutile pigments measured electrophotographically are enhanced on doping with the metal ions, and these responses increase with increasing concentration. Using microwave spectroscopy, the initial resonant frequency return loss decreases with a magnitude which is dependent upon the type and concentration of the cation. On steady-state illumination, the half-life of the photodielectric shift of the resonant frequency return loss is reduced, i.e., is more facile after doping, with the same order as that observed electrophotographically. The results are discussed in terms of the dopants occupying interstitial Ti(IV) sites in the crystal lattice and behaving as traps for photogenerated holes, thus reducing the photoactivity of the pigment.

Kinetics and spectroscopy of near-resonant optical pumping in intense fields

The resonant Raman scattering in a three level system produces an optical pumping of molecules from the initial to the final states which are radiatively coupled to the intermediate resonant state. We consider the pumping that is produced by an intense, pulsed, monochromatic radiation field that is near-resonant with the initial resonance frequency. The Heitler–Ma damping theory is solved exactly for the case when the resonance fluorescence is weak compared to the Raman scattering, or any other processes which might cause irreversible decay of the resonant state. In particular, we examine the usefulness of dressed states to describe the intense field limit. The spectral line shape for the Raman scattering is obtained. The transient behavior following the onset of the laser pulse is examined and a careful analysis of the pumping rate and its relationship to both weak and strong field theories is presented.