Frequency-domain Sensor Research Articles

Design of Nanosecond-Level Transient Electric Field Sensor and Its Application in HVDC Converter Station

In this paper, a nanosecond-level transient electric field (E-field) sensor based on a monopole electrically small rod antenna is proposed. The working principle and design process of the sensor are analyzed in detail while a finite element simulation is carried out to verify the response characteristics of the sensor both in time and frequency domain, whose upper cut-off frequency can reach 680 MHz. For the purpose of assessing the actual detection capability of the sensor in HVDC converter stations, the sensor designed in this paper was used to detect the transient radiation E-field in the valve hall during the artificial short-circuit test in the Zhoushan 1200 kV five-terminal flexible DC transmission project. The measurement results of the transient E-field indicates that the sensor is able to respond instantaneously to the radiated E-field generated by the operation of the key power electronic equipment in the valve hall. It demonstrates that the designed sensor can be effectively applied in the scenario of the measurement of transient electromagnetic environment and non-invasive situational awareness technology for high-voltage devices in HVDC systems.

Research on the Development Path of Manufacturing Industry and Its Economic Effect Based on Computational Visualization

In order to improve the analysis effect of the manufacturing development path and improve the economic benefits of the manufacturing industry, this paper combines the computer visualization technology to analyze the manufacturing development path and its economic effect. Moreover, this paper introduces the minimum ill-posedness criterion in the optimal placement criteria of time-domain sensors and the modal guarantee criterion in the optimal placement criteria for frequency-domain sensors. In addition, in this paper, the optimal arrangement of sensors is carried out based on the above two criteria, and the improved monkey swarm algorithm is applied to the optimization problem of the sensor of the visual system, and an intelligent computer visualization system is constructed. The experimental research results show that the research model of the manufacturing development path and its economic effects based on computational visualization proposed in this paper has certain practical effects.

Temperature compensated differential acoustic sensor for CO2 sensing

Temperature must be accounted for in order to provide accurate measurements in acoustic wave resonator based gas sensors. We present a flexible printed flexural plate wave (FPW) sensor for CO2 monitoring employing temperature compensation. The FPW sensor is based on a differential interdigitated transducers (IDTs) structure consisting of an input IDT and two identical output IDTs with same distance from the input IDT. Among the two outputs of the differential structure, one is sensitive to the target gas CO2 and the other one is insensitive to the target gas. The difference between the two output signals’ resonant frequencies is considered as the sensor’s differential response. Experiments at 25 ∘C and 45 ∘C show that the sensor’s differential response changes linearly with CO2 concentration over 20–3000 ppm range. The differential responses at both temperatures are very similar showing the ability of the sensor’s structure to compensate for the temperature change. Sensitivity and limit of detection for CO2 sensing are measured to be 543 Hz ppm−1 and 5.6 ppm, respectively. Further, the sensor shows good repeatability and low hysteresis. Sensor’s responses are mostly measured by measuring the scattering parameter, forward transmission (S21) between each output IDT and input IDT of the sensor in frequency domain. In the last section, a prototype time domain measurement system is demonstrated to show the feasibility of the time domain measurements with the sensors. The sensor with the potential to be printed with roll-to-roll printing can be a good candidate for CO2 monitoring where temperature varies.

In-situ and non-invasive measurement of stem water content of trees using an innovative interdigitated-electrodes dielectric sensor less susceptible to stem diameter variation

Stem water content (StWC) of plants is an important parameter for assessing plant response to drought stress in arid and semi-arid areas and for irrigation scheduling. The measurement accuracies of in-situ non-invasive approaches are degraded by plant growth and by diurnal changes in stem diameter associated with water content. Here we develop a frequency-domain (FD) dielectric sensor operating at 100 MHz with an innovative interdigitated-electrodes (IE) probe design for measuring StWC. We characterize the performance of the IE sensor and compare it with a previously described pair-strap-ring-electrodes (2RE) FD sensor. Simulations and experimental measurements were conducted to assess the electric field distribution and volume of sensitivity (VOS) of each probe, the sensitivity of each probe to stem diameter and the accuracy of each sensor for determining StWC of three apple trees in a greenhouse environment. The simulation analysis and the measurement showed that the IE probe has a smaller but denser VOS than the 2RE probe. The sensitivity test showed that the new IE probe (0.85 mV mm−1, R2 = 0.7108) was less susceptible to stem diameter variation in comparison with the 2RE probe (32.83 mV mm−1, R2 = 0.9977). The observations in the greenhouse showed that the three apple trees (AT-1, AT-2 and AT-3) experienced a daily dehydration-rehydration cycle and the averaged midnight-to-predawn StWC gradually decreased without irrigation. According to the reference values of the maximum daily trunk shrinkage (MDS) reported by a previous study, both AT-2 and AT-3 may experience water deficit before the irrigation. Besides, the stem diameter variation decreased the measurement accuracy of 2RE sensor to be ~0.0410 cm3 cm−3 mm−1. The stronger electric field intensity of the IE probe and its less susceptible to stem diameter variation make the new IE dielectric sensor an improved method for accurate in-situ measurement of diurnal stem water content.

Performance Analysis of Parameter Estimation in Electromagnetic Induction Data

We derive the Cramer–Rao lower bound (CRB) for target tensor amplitudes and target location parameters that can be estimated from electromagnetic induction (EMI) measurements of a target. In deriving the bound, no restrictions are placed on the target type, target orientation, quantity, or location of the measurement positions, nor the geometry of the EMI sensor or sensor array. The analysis is applicable to both a scanned sensor and a stationary array, as well as both time- and frequency-domain sensors. We show how the bound varies as a function of target type, orientation, depth, and signal-to-noise ratio. In addition, we illustrate the ways to use the CRB and the Fisher information matrix to analyze the relationships between the tensor amplitudes and location parameters. We show results of the CRB analysis applied to an experimental frequency-domain Georgia Tech sensor for a few target types for a nominal 2-D scan geometry as well as the Time-domain Electromagnetic Multi-sensor Towed Array Detection System. We also provide an algorithm for estimating the target location and tensor that achieves the CRB.

Experimental investigation of D dot sensor performance in frequency domain

Isotropic field probes are used to characterize the electric field in radiated susceptibility testing of electronic systems. These probes are required to be periodically calibrated by the original equipment manufacturer, which is essential as per test requirements. Getting a probe calibration done is a time consuming process for an EMC laboratory. If the probe calibration is not done periodically, than the validity of test results are questionable. In this paper, we have demonstrated to use the ACD type D dot sensor in frequency domain in place of isotropic probes, in radiated susceptibility testing. The D dot sensors do not have active electronic circuitry and therefore are not required to be calibrated periodically.

In situ measurement of stem water content and diurnal storage of an apricot tree with a high frequency inner fringing dielectric sensor

Stem water content (StWC) is a key parameter characterizing plant water relations. However, a reliable yet non-invasive method of determining StWC in trees has not been developed. Here we examined an inner fringing frequency domain (FD) sensor in a 12-year old apricot tree. Two strap rings operating at 100 MHz accurately measured StWC in stems 4–12 cm in diameter. Effective sensing depth (ESD) inside the stems, and the allowable maximum stem diameter (AMStD) were systematically evaluated. To determine ESD, a novel experimental method, stepwise stem core removal (SStCR), was developed, and combined with numerical simulation using a High Frequency Structure Simulator (HFSS). The experimental and analytical approaches were in good agreement, demonstrating that the ESD must include substantial sapwood. In apricot, with ring-porous distribution of xylem vessels, performance was excellent up to AMStD ≤ 8 cm following temperature correction. In the current study, we characterize diurnal patterns of water loss and recharge in stems of varying diameter, demonstrate hysteresis in water content between stems of different sizes and heights in the canopy, and evaluate potential interactions with ambient temperature fluctuations. The inner fringing FD sensor can be easily constructed at low cost, suggesting the potential for routine measurement of StWC in diverse woody plants.

Beat Frequency Characterization and Stabilization for Short-Cavity DBR Fiber Grating Laser Based Sensor

In this paper, we propose our observation, analysis, and alleviation method of the beat frequency fluctuation in short-cavity dual-polarization distributed Bragg reflector (DBR) fiber grating laser sensor in time and frequency domain. According to our observation, beat frequency fluctuation varies from 8 to 800 kHz under different pump power. Research shows frequency domain beat signal linewidth broadening aggravates beat frequency fluctuation due to time domain irregular self-pulsation effect. By introducing self-injection into laser cavity as an auxiliary pump laser with a circulator, self-pulsation effect in DBR fiber laser sensor can be greatly suppressed, resulting in the compression of frequency domain beat signal linewidth as well as the stabilization of beat frequency fluctuation. Experimental results demonstrate that beat frequency fluctuation can be greatly reduced from 800 to 8 kHz within 1 h through self-injection, which is significant for high-accurate sensing.

Monitoring soil moisture from middle to high elevation in Switzerland: set-up and first results from the SOMOMOUNT network

Abstract. Besides its important role in the energy and water balance at the soil–atmosphere interface, soil moisture can be a particular important factor in mountain environments since it influences the amount of freezing and thawing in the subsurface and can affect the stability of slopes. In spite of its importance, the technical challenges and its strong spatial variability usually prevents soil moisture from being measured operationally at high and/or middle altitudes. This study describes the new Swiss soil moisture monitoring network SOMOMOUNT (soil moisture in mountainous terrain) launched in 2013. It consists of six entirely automated soil moisture stations distributed along an altitudinal gradient between the Jura Mountains and the Swiss Alps, ranging from 1205 to 3410 m a.s.l. in elevation. In addition to the standard instrumentation comprising frequency domain sensor and time domain reflectometry (TDR) sensors along vertical profiles, soil probes and meteorological data are available at each station. In this contribution we present a detailed description of the SOMOMOUNT instrumentation and calibration procedures. Additionally, the liquid soil moisture (LSM) data collected during the first 3 years of the project are discussed with regard to their soil type and climate dependency as well as their altitudinal distribution. The observed elevation dependency of LSM is found to be non-linear, with an increase of the mean annual values up to ∼ 2000 m a.s.l. followed by a decreasing trend towards higher elevations. This altitude threshold marks the change between precipitation-/evaporation-controlled and frost-affected LSM regimes. The former is characterized by high LSM throughout the year and minimum values in summer, whereas the latter typically exhibits long-lasting winter minimum LSM values and high variability during the summer.

A New Approach to Measurement of Frequency Shifts Using the Principle of Rational Approximations

Abstract When a frequency domain sensor is under the effect of an input stimulus, there is a frequency shift at its output. One of the most important advantages of such sensors is their converting a physical input parameter into time variations. In consequence, changes of an input stimulus can be quantified very precisely, provided that a proper frequency counter/meter is used. Unfortunately, it is well known in the time-frequency metrology that if a higher accuracy in measurements is needed, a longer time for measuring is required. The principle of rational approximations is a method to measure a signal frequency. One of its main properties is that the time required for measuring decreases when the order of an unknown frequency increases. In particular, this work shows a new measurement technique, which is devoted to measuring the frequency shifts that occur in frequency domain sensors. The presented research result is a modification of the principle of rational approximations. In this work a mathematical analysis is presented, and the theory of this new measurement method is analysed in detail. As a result, a new formalism for frequency measurement is proposed, which improves resolution and reduces the measurement time.

Error Analysis of Clay-Rock Water Content Estimation with Broadband High-Frequency Electromagnetic Sensors--Air Gap Effect.

Broadband electromagnetic frequency or time domain sensor techniques present high potential for quantitative water content monitoring in porous media. Prior to in situ application, the impact of the relationship between the broadband electromagnetic properties of the porous material (clay-rock) and the water content on the frequency or time domain sensor response is required. For this purpose, dielectric properties of intact clay rock samples experimental determined in the frequency range from 1 MHz to 10 GHz were used as input data in 3-D numerical frequency domain finite element field calculations to model the one port broadband frequency or time domain transfer function for a three rods based sensor embedded in the clay-rock. The sensor response in terms of the reflection factor was analyzed in time domain with classical travel time analysis in combination with an empirical model according to Topp equation, as well as the theoretical Lichtenecker and Rother model (LRM) to estimate the volumetric water content. The mixture equation considering the appropriate porosity of the investigated material provide a practical and efficient approach for water content estimation based on classical travel time analysis with the onset-method. The inflection method is not recommended for water content estimation in electrical dispersive and absorptive material. Moreover, the results clearly indicate that effects due to coupling of the sensor to the material cannot be neglected. Coupling problems caused by an air gap lead to dramatic effects on water content estimation, even for submillimeter gaps. Thus, the quantitative determination of the in situ water content requires careful sensor installation in order to reach a perfect probe clay rock coupling.

Quantitative Study of Music Listening Behavior in a Smartphone Context

Context-based services have attracted increasing attention because of the prevalence of sensor-rich mobile devices such as smartphones. The idea is to recommend information that a user would be interested in according to the user’s surrounding context. Although remarkable progress has been made to contextualize music playback, relatively little research has been made using a large collection of real-life listening records collected in situ . In light of this fact, we present in this article a quantitative study of the personal, situational, and musical factors of musical preference in a smartphone context, using a new dataset comprising the listening records and self-report context annotation of 48 participants collected over 3wk via an Android app. Although the number of participants is limited and the population is biased towards students, the dataset is unique in that it is collected in a daily context, with sensor data and music listening profiles recorded at the same time. We investigate 3 core research questions evaluating the strength of a rich set of low-level and high-level audio features for music usage auto-tagging (i.e., music preference in different user activities), the strength of time-domain and frequency-domain sensor features for user activity classification, and how user factors such as personality traits are correlated with the predictability of music usage and user activity, using a closed set of 8 activity classes. We provide an in-depth discussion of the main findings of this study and their implications for the development of context-based music services for smartphones.

Frequency Domain Sensors and Frequency Measurement Techniques

Getting fast and accurate information is of paramount importance for most monitoring, data acquisition, and monitoring systems; there are sensors that transform their input into a frequency domain output, this kind of sensors are known as Frequency Domain Sensors (FDS); when the value of the output frequency is measured in a FDS, the value of the sensor’s input (measurand) can be calculated, that is why the frequency measurement in the output of FDS is critical for using such sensors. In this work different kinds of resonant sensors (FDS) are reviewed; also frequency measurement techniques are explored; finally a novel frequency measurement method is proposed and analyzed for resolution improvement in frequency domain sensors.

Mathematical Modelling of molecular adsorption in zeolite coated frequency domain sensors

Fast and accurate information is important for most monitoring, data acquisition, and monitoring systems; sensors are transducers that allow to accomplish such task. In this work different kinds of resonant sensors known as frequency domain sensors are reviewed; also frequency measurement techniques are explored; finally resolution improvement is proposed and analyzed for using frequency domain sensors by mathematical modelling.

New technique to measure particle size using electrostatic sensor

Abstract A new technique is proposed to measure the particle mean size using an electrostatic sensor in frequency domain. This paper starts with a finite-element modeling simulator to model the induced electric charge of a ring electrode and to find the electrode sensitivity. The mathematical modeling was used to extract particle size information from the simulated signal in frequency domain. The method is applied in an experimental test where a low-noise signal conditioning was designed with a ring electrode as the electrostatic sensor. The method can be used to establish a cost effective size measurement system using electrostatic sensor.

Investigating xylem embolism formation, refilling and water storage in tree trunks using frequency domain reflectometry

Trunks of large trees play an important role in whole-plant water balance but technical difficulties have limited most hydraulic research to small stems, leaves, and roots. To investigate the dynamics of water-related processes in tree trunks, such as winter embolism refilling, xylem hydraulic vulnerability, and water storage, volumetric water content (VWC) in the main stem was monitored continuously using frequency domain moisture sensors in adult Betula papyrifera trees from early spring through the beginning of winter. An air injection technique was developed to estimate hydraulic vulnerability of the trunk xylem. Trunk VWC increased in early spring and again in autumn, concurrently with root pressure during both seasons. Diurnal fluctuations and a gradual decrease in trunk VWC through the growing season were observed, which, in combination with VWC increase after significant rainfall events and depletion during periods of high water demand, indicate the importance of stem water storage in both short- and long-term water balance. Comparisons between the trunk air injection results and conventional branch hydraulic vulnerability curves showed no evidence of ‘vulnerability segmentation’ between the main stem and small branches in B. papyrifera. Measurements of VWC following air injection, together with evidence from air injection and xylem dye perfusion, indicate that embolized vessels can be refilled by active root pressure but not in the absence of root pressure. The precise, continuous, and non-destructive measurement of wood water content using frequency domain sensors provides an ideal way to probe many hydraulic processes in large tree trunks that are otherwise difficult to investigate.

Moisture Content Measurements of Green Roof Substrates Using Two Dielectric Sensors

Little is known about the accuracy of soil moisture dielectric sensors in coarse-textured root zones and green roof substrates. In the present study, the accuracy of two dielectric sensors of different technologies (frequency domain and time domain dielectric sensor) in measuring moisture content was investigated in six coarse-textured green roof substrates. Calibration equations were developed for both sensors, and the effect of electrical conductivity (EC) on substrate moisture content calculation was determined. It was found that for frequency domain sensor the relationship between dielectric permittivity square root () and actual substrate moisture content (θm) was strongly linear for all tested substrates. However, for each substrate a distinct specific calibration equation of was required. The correlation between substrate permittivity and EC was linear for frequency domain sensor for all moisture levels (0% to 35%). In the case of time domain sensor, each green roof substrate was also described from a different calibration curve between actual substrate moisture content and period of time that was recorded by the device. It was found that their relationship was quadratic for all substrates. In addition, time domain sensor output responded in a quadratic manner to increasing levels of EC. This response was found to interact with actual substrate moisture content as well. It was concluded that the most reliable results for moisture content determination of the coarse-textured green roof substrates were obtained by substrate-specific calibration curves for both dielectric sensors.

Automotive FDS Resolution Improvement by Using the Principle of Rational Approximation

In this paper, a novel method of frequency counting of signals coming from automotive sensors is presented. The present method helps to improve fast resolution of output parameters of typical automotive frequency-domain sensors (FDS). Controlling the electromechanical systems in today's cars is a task that requires a high processing speed. The method proposed here has been tested under computer experiments, and theoretical results have shown that it meets the requirements of speed of response and offset error of the parameters under measurement. Here, both a principle of rational approximation and its application to fast registration of frequency changes in the signal that is proportional to the physical parameter under measurement are shown. Finally, some experimental results are shown as well.

Analysis of jitter influence in fast frequency measurements

This paper presents a theoretical analysis of possible jitter impact in application of numeric criterion for fast measurement of frequency by coincidence principle. The primary goal is the generation of a signal containing a known amount of each jitter components. This signal was used for testing signals with regular pulse trains. Initially, jitter components are analyzed and modeled individually. Next, sequences for combining different kinds of jitter are modeled, simulated and evaluated. Jitter model simulation in Matlab is utilized to show the independence of frequency measurement results on the total jitter present in the reference and desired pulse trains independently. A good agreement between previously introduced theory of fast measurement of frequency and simulation in jitter presence is verified; these results allows to engineers use the numeric criterion for fast measurement of frequency in spite to interactions among jitter components in various applications for frequency domain sensors.

Water wave frequency detection by optical fiber sensor

An optical fiber sensor has been developed and applied to measure frequency of water waves based on wave induced polarization change of the light. The fiber sensor can accurately detect water wave frequency for regular and irregular waves. The optimum sag of sensing fiber to the sensor output’s linearity has been studied. The agreement of the fiber sensor and wave gauge in frequency and time domain suggests that the fiber sensor has great potential for passive acoustic sensing and wave monitoring.