The photoacoustic signals denoising of glucose is one of most important steps in the quality identification of the fruit because the real-time photoacoustic singals of glucose are easily interfered by all kinds of noises. To remove the noises and some useless information, an improved wavelet threshld function were proposed. Compared with the traditional wavelet hard and soft threshold functions, the improved wavelet threshold function can overcome the pseudo-oscillation effect of the denoised photoacoustic signals due to the continuity of the improved wavelet threshold function, and the error between the denoised signals and the original signals can be decreased. To validate the feasibility of the improved wavelet threshold function denoising, the denoising simulation experiments based on MATLAB programmimg were performed. In the simulation experiments, the standard test signal was used, and three different denoising methods were used and compared with the improved wavelet threshold function. The signal-to-noise ratio (SNR) and the root-mean-square error (RMSE) values were used to evaluate the performance of the improved wavelet threshold function denoising. The experimental results demonstrate that the SNR value of the improved wavelet threshold function is largest and the RMSE value is lest, which fully verifies that the improved wavelet threshold function denoising is feasible. Finally, the improved wavelet threshold function denoising was used to remove the noises of the photoacoustic signals of the glucose solutions. The denoising effect is also very good. Therefore, the improved wavelet threshold function denoising proposed by this paper, has a potential value in the field of denoising for the photoacoustic singals.
In this study, a kind of glucose measurement system based on pulsed-induced ultrasonic technique was established. In this system, the lateral detection mode was used, the Nd: YAG pumped optical parametric oscillator (OPO) pulsed laser was used as the excitation source, the high sensitivity ultrasonic transducer was used as the signal detector to capture the photoacoustic signals of the glucose. In the experiments, the real-time photoacoustic signals of glucose aqueous solutions with different concentrations were captured by ultrasonic transducer and digital oscilloscope. Moreover, the photoacoustic peak-to-peak values were gotten in the wavelength range from 1300nm to 2300nm. The characteristic absorption wavelengths of glucose were determined via the difference spectral method and second derivative method. In addition, the prediction models of predicting glucose concentrations were established via the multivariable linear regression algorithm and the optimal prediction model of corresponding optimal wavelengths. Results showed that the performance of the glucose system based on the pulsed-induced ultrasonic detection method was feasible. Therefore, the measurement scheme and prediction model have some potential value in the fields of non-invasive monitoring the concentration of the glucose gradient, especially in the food safety and biomedical fields.
With the development of holography technique and nano-superfinishing technique, holography grating has being used into the spectrometer. To overcome some drawbacks of optical system for traditional plane and concave grating typed spectrometer, a splitting-light optical system for spectrometer based on volume phase holographic transmission (VPHT) grating is designed and developed in this paper. Meanwhile, the principle of VPHT grating is introduced by using the coupled-wave theory, and the relationship between the diffraction efficiency of the VPHT and the grating depth and the irradiation wavelength are simulated by means of MATLAB numerical computing method. In order to validate this splitting-light optical system, the experiment of measuring spectral resolution is performed and the spectral resolution reached 2nm, a calibration equation between the diffraction wavelengths and the shift of the corresponding wavelengths is obtained by using polynomial fitting algorithm. The experimental results demonstrate that the design of the splitting-light optical system for spectrometer based on VPHT grating is feasible.
Photoacoustic spectroscopy (PAS) is a hybrid, well-established and promising detection technique that has widely applied into a lot of fields such as bio-medical, material and environment monitoring etc. PAS has high contrast and resolution because of combining the advantages of the pure-optical and the pure-acoustic. In this paper, a photoacoustic experiment of glucose solution induced by 532nm pumped Nd:YAG tunable pulsed laser with repetition rate of 20Hz and pulse width of 10ns is performed. The time-resolved photoacoustic signals of glucose solution induced by pulsed laser in the average time of 512 are obtained. And the photoacoustic experiments of different concentrations of glucose solutions and different wavelengths of pulsed laser are carried out in this paper. Experimental results demonstrate that the bipolar sine-wave profiles for the time-resolved photoacoustic signal of glucose solution are in good agreement with the past reported literatures. And the different absorbing coefficients of glucose solution can be gotten according to the slope of the first part of the time-resolved photoacoustic signals. In addition, the different acoustic velocities of glucose solution can also be gotten according to the shift change of the time-resolved photoacoustic peak values. Research results illustrate that the characteristic wavelengths, different optical and acoustic properties of glucose solution can be interpreted by the time-resolved and peak-to-peak photoacoustic signals induced by the pulsed laser.
To overcome some drawbacks of optical system for plane and concave grating typed spectrometer, including serious
aberration, worse spectral fatness and low diffraction efficiency etc, a novel optical system based on volume phase
holographic transmission (VPHT) grating was designed in this paper. For this grating, its manufacture and theories were
investigated, and its diffraction efficiency was numerically simulated. In order to validate this designed optical system,
the spectral scaling experiment was performed and the spectral resolution reached 2nm, the calibration equation between
the scaling wavelength and corresponding pixels was gotten via linear least square fitting algorithm. It was proved that
the wavelength absolute value reach 1.7nm on the wavelength of 635nm, the root-mean-square error (RMSE) of full
scaling wavelengths was 0.3nm. These experimental results illustrated that the design of the optical system for
spectrometer based on VPHT grating is good.
ZnO has a significant advantage for applications in optical devices. Especially ZnO doped with the rare earths (RE)
shows great electronic and optical properties. Based on the density functional theory, using the first-principles
calculations method, the crystal structure, electronic structure and optical properties of ZnO doped with various
concentrations of Er were investigated. The calculated results show that with the increase of concentrations of Er, the
volume of ZnO system is expanded. Simultaneously, the band gap of ZnO with dopant system becomes broad. However, the conductivity of system is enhanced with the decrease of Er concentration. On the other hand, imaginary part of the dielectric function of ZnO doped with Er also changes certainly. A new peak is observed in the low energy region. The results are helpful to gain a systematic understanding of geometrical structures, electrical structures and optical properties of Er-doped ZnO.
The first-principles with pseudopotentials method based on the density functional theory was applied to calculate the
electronic structure of ZnO doped with carbon. It optimized the wurtzite structure of ZnO when carbon was on the
substitutional O site (CO), the substitutional Zn site (CZn) or in the interstitial site (Ci) respectively. The calculated conclusions show that the CZn and Ci behave as donor. However, CO results in acceptor. It is illuminated that CO is helpful to achieve p-type ZnO.
We have investigated the geometrical structures, the electronic properties, and the formation energies of nN-Mg codoped
ZnO in neutral state by adopting the first-principles calculations based on the density function theory (DFT). The
calculated results indicate that N atoms prefer to occupy the substitution O site and Mg substitutes the Zn site of the
nearest site of N, which act as an acceptor. Compared with the formation energies of various configurations in neutral
state, it is found that 4N-Mg complex has the lowest formation energy using NO as dopant resource under Zn-rich
condition, indicating that 4N-Mg codoping can enhance the N dopant solubility under this condition. Meanwhile, the Znrich
condition is better for p-type doping than the O-rich condition. It demonstrates that 4N-Mg complex is in favor of
achieving p-type conduction in ZnO. Simultaneously, analysis of density of states (DOS) of nN-Mg complex find that
the valence band maximum (VBM) has a little raise near the Fermi energy level, indicating that the complexes are the
typical p-type characteristic. However, for 4N-Mg complex, the Fermi level is located near the top of valence band.
Furthermore, from the band structure and PDOS of 4N-Mg complex, it is observed that the complex produces an
additional impurity band at the top of the valence band. Meanwhile, the PDOS value of 4N-Mg complex at the Fermi
level is relatively large. In addition, 4N-Mg complex has much lower ionization energy of 0.167eV than that of other
complexes. Therefore, better quality p-type conductivity is achieved by codoping 4N-Mg in ZnO.
Ag monodoped, N monodoped and (nN, Ag) codoped ZnO have been investigated by the first-principles calculations,
where the formation energies and ionization energies of various complexes and the electronic structure for 3N-Ag
complex are studied. The calculated results are that N prefers to substitute O site, and Ag substitutes Zn site under the
most growth condition, which indicate NO and AgZn all act as acceptors. Meanwhile, it's shown that N-Ag, 2N-Ag
complex contribute little to p-type conduction because of the relatively higher ionization energy. However, 3N-Ag
complex may have the lowest ionization energy among various complexes, while the formation energy of 3N-Ag is
lower than that of N monodoped, Ag monodoped, N-Ag and 2N-Ag complex under the Zn-rich condition, which
indicates that 3N-Ag complex is energetically favorable for the formation of p-type ZnO. Furthermore, by studying the
electronic structure of 3N-Ag complex, it may generate an additional impurity band above the valence band maximum of
ZnO. It is found that NO generated holes around the top of the valence band, and at the same time, N 2p states hybridized
with 4d states of AgZn at the Fermi energy, and the hybridization lowered the repulsive interaction between the two dual
acceptors, which enhance the concentration of impurities and the stability of the system, indicating that the dual
acceptors evidently improve p-type conductivity of ZnO. Thus, it is found that 3N-Ag complex is the better dopant
configuration. That can gain a better quality p-type ZnO under the Zn-rich condition. Our theoretical results are
consistent with the experiment results.
The geometry, electronic structures and conduction properties of V-doped anatase TiO2 with O vacancy were
investigated by using the plane-wave ultrasoft pseudopotential method based on the density functional theory(DFT). The
calculated results show that the 3d state of V plays an important role in red-shift and the band gap will narrow after V
doping in TiO2. Furthermore, it was also found that a certain concentration of O vacancy in V-doped TiO2 shows better
electronic conductivity due to the increase of electronic concentration in the band gap. Our theoretical results are in good
agreement with the experiment results.
We perform density functional theory within the generalized gradient approximation to investigate infinitely wurtzite
bare GaN nanowires in the [0001] direction. We report atomic and electronic structure of GaN nanowires with diameters
of 10 and 16 Å. We find that relaxations on the facets are very similar to the ones in nonpolar (10-10) surfaces and play
an important role in stabilizing the wires, and the average Ga-N bond length of the GaN nanowires decreases compared
with bulk GaN. Both wires are found to be semiconducting and have a direct gap, with band gaps slightly smaller than
that in bulk GaN. The shape of the band edge remains unaltered as the size of the nanowire increases. It is also found, for
Ga and N atoms at the edge of the nanowires, the Ga 3p predominantly contribute to the edge states near the conduction
band minimum, while the N 2p contribute mainly to the edge states near the valence band maximum. The present
calculated results are helpful to gain a systematic understanding of structure, electrical properties of wurtzite GaN
nanowires.
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