Ultra-low noise front-end design for smart optical sensors with high sensitivity and wide dynamic range.

Ultra-low noise is a critical component in the design of high-precision sensor front-ends. We introduced differential phase-sensitive detection (d-PSD) to mitigate both multiplicative and additive noise in optical sensors, aiming for an enhanced performance and cost-effectiveness. The d-PSD combines a capacitive transimpedance amplifier (C-TIA), a delta-sigma analog-to-digital converter (ΔΣ-ADC), and a software-based lock-in amplifier (s-LIA). The first two components utilize the DDC112 (a dual current input 20-bit ADC) for a minimal analog channel length, thus reducing noise efficiently, while the latter employs a cost-effective 32-bit microcontroller unit (MCU), the HC32F460. This approach was successfully implemented as the front-end for a smart optical sensor. Testing indicated that the sensor achieved an equivalent current noise level of 0.6 nA/√Hz, primarily attributed to the light source driver rather than the sensor's front-end circuit. The sensor exhibited an exceptional performance, with a 3σ measurement precision of 5.4 × 10-4 over a 1-second integration time and a dynamic range of 100 dB, leveraging the proposed method and design. Furthermore, the front-end of the sensor boasts a compact size, low power consumption, and affordability, making it an ideal, versatile solution for ultra-high precision, smart optical sensors.

Self-corrected frequency modulation spectroscopy immune to phase random and light intensity fluctuation.

Light intensity fluctuations and phase randomness in quadrature demodulation disturb the accuracy of frequency modulation spectroscopy. The proposed self-corrected method eliminated these effects: the profile of correctly demodulated signals identified whether a demodulation was phase matched and corrected a phase-mismatched demodulated signal; we extracted the measured signal's direct current component and corrected the light intensity fluctuation. We conducted theoretical analysis and experimental verification to reduce light-intensity errors by 16.8% under different intensity conditions and obtained spectral features by phase difference corrections under the same measurement conditions. We reduced the effect of light intensity fluctuation and demodulated signals were freed from phase stability limitations.

Membership Function-Weighted Non-Linear Fitting Method for Optical-Sensing Modeling and Reconstruction.

Imprecise measurements present universally due to variability in the measurement error. We devised a very simple membership function to evaluate fuzzily the quality of optical sensing with a small dataset, where a normal distribution cannot be assumed. The proposed membership function was further used as a weighting function for non-linear curve fitting under expected mathematical model constraints, namely the membership function-weighted Levenberg⁻Marquardt (MFW-LM) algorithm. The robustness and effectiveness of the MFW-LM algorithm were demonstrated by an optical-sensing simulation and two practical applications. (1) In laser-absorption spectroscopy, molecular spectral line modeling was greatly improved by the method. The measurement uncertainty of temperature and pressure were reduced dramatically, by 53.3% and 43.5%, respectively, compared with the original method. (2) In imaging, a laser beam-profile reconstruction from heavy distorted observations was improved by the method. As the dynamic range of the infrared camera increased from 256 to 415, the detailed resolution of the laser-beam profiles increased by an amazing 360%, achieving high dynamic-range imaging to capture optical signal details. Therefore, the MFW-LM algorithm provides a robust and effective tool for fitting a proper physical model and precision parameters from low-quality data.

Measurement of Atmospheric Dimethyl Sulfide with a Distributed Feedback Interband Cascade Laser.

This paper presents a mid-infrared dimethyl sulfide (CH3SCH3, DMS) sensor based on tunable laser absorption spectroscopy with a distributed feedback interband cascade laser to measure DMS in the atmosphere. Different from previous work, in which only DMS was tested and under pure nitrogen conditions, we measured DMS mixed by common air to establish the actual atmospheric measurement environment. Moreover, we used tunable laser absorption spectroscopy with spectral fitting to enable multi-species (i.e., DMS, CH4, and H2O) measurement simultaneously. Meanwhile, we used empirical mode decomposition and greatly reduced the interference of optical fringes and noise. The sensor performances were evaluated with atmospheric mixture in laboratory conditions. The sensor's measurement uncertainties of DMS, CH4, and H2O were as low as 80 ppb, 20 ppb, and 0.01% with an integration time 1 s, respectively. The sensor possessed a very low detection limit of 9.6 ppb with an integration time of 164 s for DMS, corresponding to an absorbance of 7.4 × 10-6, which showed a good anti-interference ability and stable performance after optical interference removal. We demonstrated that the sensor can be used for DMS measurement, as well as multi-species atmospheric measurements of DMS, H2O, and CH4 simultaneously.

Antagonist of thromboxane A2 receptor by SQ29548 lowers DOCA-induced hypertension in diabetic rats.

Diabetes is one of high risk factors for cardiovascular diseases, including atherosclerosis and hypertension. This study was conducted to elucidate whether and how thromboxane receptor (TPr) activation contributes to hypertension in diabetes. Human umbilical vein endothelial cells (HUVECs) were cultured. The phosphorylated levels of endothelial nitric oxide synthase (eNOS) and Akt were monitored by western blot. Endothelial function was determined by organ bath. High glucose (HG) or thromboxane A2 mimetic U46619 significantly reduced the levels of p-eNOS and p-Akt in cultured HUVECs, which were reversed by inhibition of TPr. HG/U46619-induced reductions of p-eNOS and p-Akt were accompanied with increases of total and phosphorylated tumor suppressor phosphatase and tensin homolog on chromosome 10 (PTEN). PTEN siRNA restored Akt-eNOS signaling in cells treated with HG. In rats, streptozotocin-induced hyperglycemia was associated with aortic PTEN upregulation and reductions of p-Akt and p-eNOS. TPr antagonist SQ29548 ablated these alterations and reduced blood pressure in rats with DOCA-induced hypertensive. In conclusion, hyperglycemia activates thromboxane A2 receptor to augment DOCA-induced high blood pressure in rats via the PTEN-Akt-eNOS signaling.

Pathologic Progression, Possible Origin, and Management of Multiple Primary Intracranial Neuroendocrine Carcinomas.

BACKGROUND: Primary intracranial neuroendocrine carcinomas (NECs) are extremely rare malignant tumors with no previous reports of multiple ones in the literatures. CASE DESCRIPTION: The clinical presentation, preoperative and reexamined magnetic resonance imaging findings, as well as histopathologic studies of a 56-year-old female subject with multiple intracranial NECs mimicking multiple intracranial meningiomas, who underwent 3 operations with left parietal craniotomy, right occipital parietal craniotomy, and left frontal craniotomy, separately and chronologically, are presented in this article. Noteworthy, the first and second tumors were confirmed as NECs exhibiting histologic characteristics of typical anaplastic meningiomas with features of whorl formation, while the third tumor was a typical NEC with features of organoid cancer nests. In other words, the first 2 lesions were diagnosed as meningioma as opposed to NEC. It was only after the third surgery that the pathology for the first 2 cases was reviewed and had a revised diagnosis. After the third surgical resection, the patient further received whole brain radiotherapy and systemic chemotherapy (temozolomide combined with YH-16). At her 10-month follow-up, the patient achieved a good outcome. CONCLUSIONS: Multiple primary intracranial NECs are extremely rare. The tumor might be of arachnoidal or leptomeningeal origin, with histologic patterns that might lead to transformation and/or progression. Maximal surgical resection is warranted for symptomatic mass effect. Postoperative adjuvant treatments including radiotherapy and chemotherapy should be a recommended therapeutic modality.

Combined Hyperactive Dysfunction Syndrome of the Cranial Nerves: A Retrospective Systematic Study of Clinical Characteristics in 44 Patients.

BACKGROUND: Combined hyperactive dysfunction syndrome (HDS) is defined as the combination symptoms arising from overactivity in cranial nerves, specifically, trigeminal neuralgia (TN), hemifacial spasm (HFS), and glossopharyngeal neuralgia (GPN), without an obvious explanatory structural lesion. This study retrospectively analyzes the clinical characteristics of combined HDS treated with microvascular decompression (MVD) in a single institution. METHODS: A total of 1450 patients with HDS were treated with MVD in our department during a 10-year period, among which 44 cases of combined HDS were identified. Clinical records and follow-ups were reviewed. RESULTS: Combined HDS comprised 3.03% (44/1450) of all HDS in our series, with female predominance compared with single HDS (P = 0.002), including combined TN-HFS (14 cases), combined TN-GPN (26 cases), bilateral TN (2 cases), and combined TN-HFS-GPN (2 cases). The average age at diagnosis of patients with combined HDS (60.9 years) was significantly older than that of patients with single HDS (53.5 years) (P = 0.035). Hypertension was closely associated with the prevalence of combined HDS compared with single HDS (P = 0.009). The curative rate was 97.7% (43/44) after MVD, and the recurrence rate was 3.33%. The incidence rates of postoperative cardiac, pulmonary, thromboembolic, and delirium complications were higher in combined HDS than in single HDS (P < 0.05). CONCLUSIONS: Combined HDS is a rarely occurring syndrome usually observed in older females, and the most common types are combined TN-GPN and combined TN-HFS. Age and gender seemed to be causes for developing combined HDS, and MVD shows potential as a favorable treatment choice.

Detection of Atmospheric Methyl Mercaptan Using Wavelength Modulation Spectroscopy with Multicomponent Spectral Fitting.

Detection of methyl mercaptan (CH3SH) is essential for environmental atmosphere assessment and exhaled-breath analysis. This paper presents a sensitive CH3SH sensor based on wavelength modulation spectroscopy (WMS) with a mid-infrared distributed feedback interband cascade laser (DFB-ICL). Multicomponent spectral fitting was used not only to enhance the sensitivity of the sensor but also to determine the concentration of interferents (atmospheric water and methane). The results showed that the uncertainties in the measurement of CH3SH, H2O, and CH4 were less than 1.2%, 1.7% and 2.0%, respectively, with an integration time of 10 s. The CH3SH detection limit was as low as 7.1 ppb with an integration time of 295 s. Overall, the reported sensor, boasting the merits of high sensitivity, can be used for atmospheric methyl mercaptan detection, as well as multiple components detection of methyl mercaptan, water, and methane, simultaneously.

[The Development of Ammonia Sensor Based on Tunable Diode Laser Absorption Spectroscopy with Hollow Waveguide].

Hollow waveguides(HWG)have recently emerged as a novel concept serving as an efficient optical waveguide and a highly miniaturized gas cell. Compared with conventional multi-pass gas cells, HWG gas cell has the advantages of facilitating gas exchanging because of its small size and fast responding speed. In this paper, we poposed an ammonia sensor based on tunable diode laser absorption spectroscopy(TDLAS) using HWG as the gas cell. The sensor employs wavelength modulation spectrum(WMS) with simultaneous detection of the second harmonic(2f) signal and the first hamonic(1f) signal. Normalization of the 2f signal by the 1f signal enables the sensor for calibration free measurement. The sensor performance is tested with gas standards and the result shows good linearity with correlation coefficient of 0.999 8, and the detection limit is 26 ppb with an integration time of 18 s. The sensor based on HWG gas cell is suitable for sensative and real-time monitoring ammonia in the air.

Modulation index optimization for optical fringe suppression in wavelength modulation spectroscopy.

Optical fringes constitute one of the major obstacles in the gas detection based on wavelength modulation spectroscopy (WMS). In order to suppress optical fringes, a convenient method of modulation index optimization was presented, using the signal-fringe ratio as a criterion. In addition to suppressing optical fringes, the optimized modulation index enables the detection of gas absorption. This method was demonstrated in a WMS based oxygen sensor. By comparing the sensor performances with and without the use of the optimized modulation index, we showed that the optical fringes are reduced by using the optimized modulation index; furthermore, the system stability and detection limit are improved. More specifically, the long-term fluctuation of the sensor measurement is dramatically reduced by a factor of 8, and a detection limit of as low as 120 ppm (with effective optical path length of 32 cm and integral time of 2.6 s), characterized by the Allan variance, was derived. This method can be applied in other existing WMS systems without the need for additional devices or complex algorithms and has the potential to be used in both laboratory and industrial settings.

[Absorption spectrum of Quasi-continuous laser modulation demodulation method].

A software phase-locked amplifier demodulation method is proposed in order to demodulate the second harmonic (2f) signal of quasi-continuous laser wavelength modulation spectroscopy (WMS) properly, based on the analysis of its signal characteristics. By judging the effectiveness of the measurement data, filter, phase-sensitive detection, digital filtering and other processing, the method can achieve the sensitive detection of quasi-continuous signal The method was verified by using carbon dioxide detection experiments. The WMS-2f signal obtained by the software phase-locked amplifier and the high-performance phase-locked amplifier (SR844) were compared simultaneously. The results show that the Allan variance of WMS-2f signal demodulated by the software phase-locked amplifier is one order of magnitude smaller than that demodulated by SR844, corresponding two order of magnitude lower of detection limit. And it is able to solve the unlocked problem caused by the small duty cycle of quasi-continuous modulation signal, with a small signal waveform distortion.

[Selection of digital filtering in the escaping ammonia monitoring with TDLAS].

Tunable diode laser absorption spectroscopy technology (TDLAS), with its advantages of high selectivity and accuracy, provides a reliable approach to the on-line detection of escaping ammonia. Firstly, the present paper introduces the TDLAS principle, experimental system and the analyses of system noise. Then with the concentration of 90 x 10(-6) and 30 x 10(-6) NH3 for example, we used TDLAS system to collect their second harmonic original spectrum with all kinds of noise interference. To improve the signal spectrum, five types of digital filtering methods were respectively used to filter the original spectrum. Finally we did the NH3 experiments of concentration gradient and the long time monitoring: NH3 experiment of 20 x 10(-6). The analysis indicated that the averaging-wavelet filtering is validated to be more accurate than the other filtering methods in the noise reduction, which can improve the precision of the monitoring system from 10 x 10(-6) to 1.25 x 10(-6) and the SNR also increases by 14 times. It provides an effective pretreatment during the monitoring of escaping ammonia of extremely low concentration.

[Comparison of quasi-continuous and continuous tunable diode laser absorption spectroscopy for gas detection].

The theoretical analysis of the direct absorption spectroscopy, the continuous modulation spectroscopy and the quasi-continuous modulation spectroscopy was shown and the corresponding experiments were carried out in order to choose the adequate scheme of the laser modulation spectroscopy to satisfy different requirements of the detection. CO2 gas with different concentrations was detected under the same experimental conditions by using the three different modulation techniques with the same laser. Technical characteristics, signal features and detection limits were compared respectively. Results showed that the detection limit of the quasi-continuous modulation spectroscopy was approaching to that of the continuous modulation spectroscopy. However the linear distortion of the detection signal was obvious, because of the effects of laser energy intermittent and parasitic amplitude modulation on the line shape. Therefore the quasi-continuous modulation spectroscopy is not suitable for the pressure and flow measurements, which closely depend on the line shape. This work has provided reference for selections of the laser modulation spectroscopy.

[Research on the analytical line auto-selection for quantitative analysis of materials with laser-induced breakdown spectroscopy].

To realize auto-selection of analytical lines for quantitative analysis of materials with laser-induced breakdown spectroscopy, two parameters, i. e. the relative detected-to-theory intensity ratio (RDTIR) and wavelength difference of detected and theory (WDDT) were defined. The spectral lines seriously disturbed by self-absorption and spectral interference were excluded automatically by setting reasonable thresholds of RDTIR and WDDT. By analyzing the experimental data of high-alloy steel (GBW01605), the analytical lines of iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn) and copper (Cu) were selected, and the results were in line with the principle of lines selection.

[Multi-harmonic analysis of quasi-continuous-wave laser modulation absorption spectroscopy].

Numerous harmonic components such as multiple frequency, sum frequency and difference frequency of multiple modulation signals were found in quasi-continuous-wave (QCW) diode laser modulation absorption spectroscopy. Then, the authors analyzed these harmonic components' existence in terms of non-linear interactions of laser and gas absorption line. And the signals' characteristics were studied experimentally. The results shows that there are some sum frequency and difference frequency components that have larger amplitudes compared to the second harmonic wavelength modulation spectroscopy signal (2f-WMS) commonly used in tunable diode laser spectroscopy (TDLAS), and it may improve the detection sensitivity of QCW modulation spectroscopy.

[System parameters selection and optimization of tunable diode laser absorption spectroscopy].

The system performance of tunable diode laser absorption spectroscopy (TDLAS) is affected by the modulation parameters such as modulation index, modulation frequency, scanning amplitude and scanning frequency. There is a lack of definite parameters selection basis in practical measurement. Aiming at this problem, the influence of modulation parameters on second harmonic signals was observed by experiment based on a certain theory in the present paper, and the basis and method of modulation parameters optimization for various system functions and demands were summarized by analyzing the signal characteristic including amplitude, signal to noise ratio, symmetry and peak width. For the system of concentration or temperature detection the amplitude and signal to noise ratio will be taken into prior consideration which require optimum modulation index, lower modulation frequency and lower scanning frequency. In condition of pressure detection deduced by lineshape the signal symmetry and peak width are more important to ascertain the modulation parameters according to practical demands. Scanning amplitude will be adjusted to obtain complete signal waveforms, then scanning frequency can be adjusted according to system speed and accuracy requirement. The result of the experiment provided a definite basis for conforming the working state of such system.

[Techniques of on-line monitoring volatile organic compounds in ambient air with optical spectroscopy].

Volatile organic compounds (VOCs) are harmful gaseous pollutants in the ambient air. The techniques of on-line monitoring VOCs are very significant for environment protection. Until now, there is no single technology that can meet all the needs of monitoring various VOCs. The characteristics and present situation of several optical methods, which can be applied to on-line monitoring VOCs, including non dispersive infrared (NDIR), Fourier transform infrared (FTIR) spectroscopy, differential optical absorption spectroscopy (DOAS), and laser spectroscopy were reviewed. Comparison was completed between the national standard methods and spectroscopic method for measuring VOCs. The main analysis was focused on the status and trends of tuning diode laser absorption spectroscopy (TDLAS) technology.

[Research on shortwave NIR spectroscopy and its application to in situ flammable liquid detection].

Fast, accurate and highly effective detection in situ was important to the control of illegal transportation and the use of liquid state dangerous goods. The present article used the strong penetrability of the shortwave near-infrared ray to the packing material and liquid and measured the absorption spectra of some flammable liquids such as the absolute ethyl alcohol, absolute methanol, ammonia, turpentine, gasoline, diesel oil, petroleum etc and the partial liquors in the short wavelength region of NIR (667-1000 nm). The primitive spectral data were standardized and compressed, and then, the characteristic wavelength of the absorption spectra was analyzed using the SPSS statistics software. A math model for flammable liquid distinction was established based on the designated characteristic wavelength and can correctly detect flammable liquid using the absorbency of 3 wavelengths (881, 935 and 981 nm). According to the above the authors may construct the inexpensive spectrum instrument to check the flammable liquid non-destructively in situ.

[Theoretical analysis of the single optical path spectrum detection in biological tissue].

The technology of spectrum detection with high sensitivity is of significance in clinic diagnosis and tissue optical parameter measurement. A new method of difference-modulated laser spectrum detection was developed in the present paper. The measuring light and the reference light are separated from the lasing light source in this method. After passing through the tissue, the measuring light interferes with the reference light, and the frequency character of spectrum includes the information of the difference of optical path-length between the measuring light and reference light. By using the phase sensitive detector, the spectrum signal with different frequency can be separated, and consequently the measuring light passed through the tissue with different optical length will be apart. The mechanism of difference-modulated laser spectrum was analyzed and the value of dominant frequency of spectrum was deduced. Based on the theory of the optical path distribution in biological tissue, the spectrum signature of measuring light was discussed also. The distribution of dominant frequency component is decided by the difference of optical path-length between measuring light and reference light when the modulation parameters are invariable, and the magnitude of tissue' s modulus decay will effect the energy distribution of spectrum frequencies component. Theoretical analysis showed that the method of difference modulation can be used to separate lights according to the optical path-length and realize the single optical path measurement in biological tissue.

[Application of NIR spectroscopy to multiple gas components identification].

Multiple gas components monitoring in situ by near infrared (NIR) spectroscopy is of great significance in the environmental monitoring. In the present paper, the apectral characteristics of the three types of the volatile organic compounds (VOCs)-propane, propylene and methylbenzene were analyzed, the linear relationship of propylene between concentration and absorbance was considered, and the NIR spectra from 1620 to 1750 nm including the characteristic absorption of the three VOCs were acquired, A linear regression model of chemical metrology was created by partial least-squares method and it predicted the concentration of propane and isobutene in the validation set. The results of the experiment indicated that NIR spectroscopy could easily, accurately and quantitatively determine the content of the multiple gas components, and can be used for monitoring the multiple components of the VOCs in situ.