ABSTRACT
In this work, the frequency doubling effect of thermoacoustic speakers is studied, and a method is analyzed to suppress the frequency doubling effect. Three cases were analyzed by superimposing the DC bias on the AC excitation: (1) DC is less than AC; (2) DC is equal to AC; (3) DC is greater than AC. We found that the frequency doubling effect can be well suppressed by superimposing a larger DC excitation on the AC excitation. The laser scribing technology was used to prepare graphene film in only one step, and the screen printing technology was used to prepare conductive electrodes. The microphone and B&K system was used to record the sound pressure level and study the suppression of frequency doubling effect. Finally, the sound pressure levels with the three different kinds of excitations were measured. The measured results show that they have a good agreement with the theoretical results. The suppression effect will be better when DC amplitude is greater than AC amplitude. Therefore, this work has certain reference significance for the further study and application of thermoacoustic speakers.
Subject(s)
Graphite , Sound , Electric Conductivity , Electrodes , LasersABSTRACT
At present, the proposed microwave power detection systems cannot provide a high dynamic detection range and measurement sensitivity at the same time. Additionally, the frequency band of these detection systems cannot cover the 5G-communication frequency band. In this work, a novel microwave power detection system is proposed to measure the power of the 5G-communication frequency band. The detection system is composed of a signal receiving module, a power detection module and a data processing module. Experiments show that the detection frequency band of this system ranges from 1.4 GHz to 5.3 GHz, the dynamic measurement range is 70 dB, the minimum detection power is -68 dBm, and the sensitivity is 22.3 mV/dBm. Compared with other detection systems, the performance of this detection system in the 5G-communication frequency band is significantly improved. Therefore, this microwave power detection system has certain reference significance and application value in the microwave signal detection of 5G communication systems.
ABSTRACT
An enhanced quarter-spherical acoustic energy harvester (AEH) with dual Helmholtz resonators was designed in this work. Compared with the previous research, this AEH can harvest multi-directional acoustic energy, has a widened resonance frequency band, and has an improved energy conversion efficiency. When the length of resonator's neck is changed, the acoustic resonant frequency of the two resonators is different. The theoretical models of output voltage and output power were studied, and the relationship of output performance with frequency was obtained. The results showed that this AEH can operate efficiently in a frequency band of about 470 Hz. Its output voltage was found to be about 28 mV, and its output power was found to be about 0.05 µW. The power density of this AEH was found to be about 12.7 µW/cm2. Therefore, this AEH could be widely used in implantable medical devices such as implantable cardiac pacemakers, cochlear implants, and retinal prosthesis.
ABSTRACT
In oxide glasses, the microscopic hidden flow and the structural origin of the glass-to-liquid transition (GLT) are unclear due to the lack of detailed structural information. Herein, we investigate the evolution of the microscopic localized flow during GLT in a V2O5-P2O5 bulk oxide glass (BOG) by combining differential scanning calorimetry, temperature- and frequency-dependent bending experiments and stress relaxation spectra. The characteristic changes, their intrinsic correlations with the GLT process and the complete relaxation process are discussed in detail. We have observed three relaxation stages in the V2O5-P2O5 bulk oxide glass. Stage (I) corresponds to the nano-scale liquid-like movement with reversible activation of flow units. Stage (II) refers to the cooperative interaction of α and ß relaxation, whereas stage (III) represents the glass transition process. In the frequency spectra, we have obtained a different result with metallic glasses by using a quasi-point defect model. When T < 480 K (Tß), the correlation factor χ related to the quasi-point defect concentration is low and nearly constant, whereas, for T > 480 K (Tß), χ shows a linear relationship with temperature. The present study provides useful insights to describe the relationship between the architecture of local atomic arrangements and mechanical properties of oxide glass.
