Ground penetrating radar (GPR) is a non-destructive and continuous electromagnetic (EM) detection technique for civil and environmental parameter measurement applications such as pavement condition and soil property characterization. This technique is based on the measurement of the travel time and reflection amplitude of a short EM pulse, which are functions of medium properties. Most GPR measurements of sub-layer thickness are conducted based on the priori knowledge of dielectric constants of the pavement materials. And actually, the dielectric constant is an unknown but important parameter in the applications. For some applications, the dielectric constants are estimated based on manuals or tables that can only provide rough results not the real changes of pavement materials. In some other cases, the dielectric constants are estimated by using the surface reflectivity information. However, such method is not applicable for rough surface and ground-coupled GPR applications.
Compared to the air-launching GPR mode, the ground-coupled mode is more complicated because of the coupling effect between the antennas and ground. In this paper, numerical simulations about the wave propagation paths of the ground-coupled GPR are conducted. The simulation results reveal some interesting ray paths of GPRs in the ground-coupled mode. And based on the simulation results, new methods are introduced for calculating the pavement dielectric constant and thickness directly from the ground-coupled GPR data. Finally, applications and field test results for pavement evaluation are presented.
Thermo-plastic tape (TPT) provides delineation on highways around the world. The thickness of TPT on pavement is a very important parameter to control the quality of TPT, calculate durability of TPT, and provide information for the maintenance and replacement of TPT. Traditionally, the thickness measurement is conducted by using pre-embedded plates and measuring the thickness of TPT after spraying of the TPT marking materials. This method is labor intensive and cannot obtain a continuous-thickness profile. Developing an automatic thickness measurement system for TPT marking materials is critical to pavement management and public safety.
The measurement system developed in this paper uses laser triangulation technique to detect the thickness of TPT. A dedicated digital laser signal processing circuit is developed to restore thickness information. The thickness measurement system provides continuous real-time thickness measurement of TPT. Lab and field tests under various conditions with TPT marking materials on real pavement surfaces were conducted. The test results showed that the measurement system is capable of reaching the resolution of 5 mils on pavement. The developed system for thickness measurement of TPT has a 267 KHz working frequency, which is the highest among similar devices. The high speed allows the system to provide higher accuracy and more flexibility in various applications.
Accurate measurements of soil water content are important to land activities, especially those involving agriculture, forestry, hydrology, and engineering. In this paper, a theoretical and experimental study of the microwave moisture measurement sensors is conducted.
A phase-based moisture sensor system using a transmission line sensor is designed. The amplitude of the transmission measurement is a strong function of the conductivity (loss of the media) and the imaginary part of the dielectric constant, and the phase is mainly a strong function of the real part of the dielectric constant. One can obtain the soil moisture information from measuring the phase shift of the transmitted waves. Microstrip resonator sensors are also studied and fabricated. The effective permittivity will change if a dielectric material is present near the substrate of the resonator, which causes the shift of the resonant frequency. The measured data show that both sensors are sensitive and accurate.
Pavement marking materials provide delineation on highways around the world. The condition of the marking materials is very important for the driver's safety as well as the comfort and the driving expenses. Currently thermoplastic pavement marking materials (TPMM) are widely used in states. Measuring the thickness of TPMM on pavement is an essential index to monitor the contractors, calculate durability of marking materials, and provide better information for the pavement marking evaluation.
In recent years to measure the thickness of TPMM, a procedure involving pre-embedded plates sprayed with the marking materials has been widely accepted. This method is labor intensive, and cannot obtain a continuous-thickness profile. Therefore there are demands to develop a high-speed automatic measuring system for determining the thickness and uniformity of marking materials.
In this paper, a laser range sensor based on auto-synchronized laser scanning is proposed for the thermoplastic pavement marking material thickness measurement. Compare to classical triangulation method, this approach doesn't scarify the system resolution for large field of view and it is more suitable for highway speed measurement. To achieve high speed measurement, PSD (Position Sensitive Detector) is used in the prototype system instead of CCD (Charge Couple Device) in traditional auto-synchronized system. The standoff distance and transverse scan range of the prototype system both are 1 foot. The lab test results show that the prototype system can measure the thermoplastic type thickness with error in 5mil at laser scanning rate up to 50Hz.
In weigh-in-motion (WIM) system, the gross weight or the axle weight of the passing vehicle can be measured dynamically by the sensors installed in or on the pavement. One of the WIM sensors is piezoelectric sensor. Although piezoelectric sensor has limited measurement accuracy, it is widely deployed for its low cost and easy installation. To use the piezoelectric sensor, several factors have to be considered for the WIM site itself to ensure the vehicle passing over the sensor with a relative stable state. In addition, the piezoelectric sensor is seldom used for low speed measurement because of the piezoelectric material's performance. Traditional measurement method just uses the interactions between the sensor and the vehicle's tires that make the measurement inaccurate because the sensor cannot cover the whole tire patch along the driving direction. In this paper, the pavement deflection by the vehicle under measurement is introduced. New weighing method is developed for embedded piezoelectric sensors. Field tests are performed and the measurement errors are calculated based on the static weights measured from a static scale. Comparing to the traditional method, the proposed method is proved to have a higher accuracy and require less from installation site and vehicles under measurement. Furthermore, the method shows a better performance at low vehicle speed.
Pavement life span is often affected by the amount of voids in the base and subgrade soils, especially moisture content in pavement. Most available moisture sensors are based on the capacitive sensing using planar blades. Since the planar sensor blades are fabricated on the same surface to reduce the overall size of the sensor, such structure cannot provide very high accuracy for moisture content measurement. As a consequence, a typical capacitive moisture sensor has an error in the range of 30%. A more accurate measurement is based on the time domain refelctometer (TDR) measurement. However, typical TDR system is fairly expensive equipment, very large in size, and difficult to operate, the moisture content measurement is limited.
In this paper, a novel microstrip transmission line based moisture sensor is presented. This sensor uses the phase shift measurement of RF signal going through a transmission line buried in the soil to be measured. Since the amplitude of the transmission measurement is a strong function of the conductivity (loss of the media) and the imaginary part of dielectric constant, and the phase is mainly a strong function of the real part of the dielectric constant, measuring phase shift in transmission mode can directly obtain the soil moisture information. This sensor was designed and implemented. Sensor networking was devised. Both lab and field data show that this sensor is sensitive and accurate.
A highway crack monitoring system (HCMS) has been successfully developed to measure the pavement crack and its coverage of the road. A road-image processing algorithm is presented in this paper. Recurring thresholding (RT) segmentation is developed to extract crack objects from a complicated background on an estimation-verification process. A connect component object identification (CCOI) identifies the binary image object according to its connectivity with other objects. A boundary contour convolution (BCC) is applied in the binary-image object analysis to achieve fast processing and reduce computational complexity. The experiment results are provided to illustrate the performance of the system scheme.
A high-speed measurement system has been successfully developed to measure the pavement surface texture. This device is based on the laser triangulation measurement using a position sensitive device (PSD) as detector. In this paper we will discuss the basic design and implementation of the system. This system has a sampling rate of 175kHz, which greatly increases the ability of texture profiling and provides more quantitative information for the pavement measurement. The proper accuracy of dynamic measurement (0.02mm) guarantees correct detection in the particular applications on the pavement surface quality inspection. The flexible-hardware design enhances the system's performance under various practical situations, especially the high-response frequency, which makes the system control more prompt in handling the suddenly changed slopes and colors. The resolution in both static and dynamic measurement, the temperature shifting, the noise level, and the good repeatability indicates that the system has a good functionality at a very low cost. The experiment results illustrate that the system not only facilitates the high-speed macro/micro texture profiling, but also provides great potential to the wide industrial applications that need fast measurement.
Many theoretical studies have been reported on applications of ground penetrating radar (GPR) system to detect the permittivity and thickness of subsurface layers. However, to develop a GPR system that can accurately measure the thickness and the permittivity simultaneously is not a straightforward task. The main difficulty of quantitative thickness measurement is that the reflected wave from the subsurface interface is very weak compared to the directly coupled waves. The reflected signal may be completely submerged into the strong direct waves. Secondly, the inversion computation from measured data is very noise sensitive. In this paper, we present the development of a frequency-modulated-continuous-wave (FMCW) radar for quantitative layer thickness measurement. A new mathematical model for the calculation of depth and permittivity from the measured electromagnetic data is presented. The new model is based on the time delay between the direct wave and the reflected wave recorded by a bistatic radar. The data inversion algorithm considers the influences from air-ground interface. It is found that neglecting the air layer effects as the case applied in seismic analysis, the inversion will not be correct. This is because the electromagnetic rays from the GPR take different propagation path from straight or curved ray in seismic-like analysis. Ray path searching must be included in the calculation algorithm. With the consideration of wave path, the experimental results agree well with the actual values either in field test of in laboratory test.
(Mn, Sb) doped-PZT (PMSZT) thin films have been grown on La<SUB>0.5</SUB>Sr<SUB>0.5</SUB>CoO<SUB>3-(delta</SUB> )/Si and La<SUB>0.5</SUB>Sr<SUB>0.5</SUB>CoO<SUB>3- (delta</SUB> )/LaAlO<SUB>3</SUB> substrates for pyroelectric detector arrays. The La<SUB>0.5</SUB>Sr<SUB>0.5</SUB>CoO<SUB>3(delta</SUB> ) thin films, acting as a bottom electrode and as an atomic template for epitaxial growth of PMSZT, were deposited below 550 degrees Celsius thus allowing for integration with silicon technology. The epitaxial PMSZT thin films was designed to achieve high infrared responsivity using (100) oriented LSCO electrodes. The Ni-Cr/PMSZT/LSCO/Si capacitor-like structures show good ferroelectric properties with a large remnant polarization P<SUB>r</SUB> of 40 (mu) C/cm<SUP>2</SUP>, a spontaneous polarization P<SUB>s</SUB> of 74 (mu) C/cm<SUP>2</SUP>, and a coercive field E<SUB>c</SUB> of 115 kV/cm under an electric field of 650 kV/cm. The PMSZT films have an electrical field breakdown strength in excess of 467 kV/cm, which is much higher than the coercive field. Voltage responsivity R<SUB>v</SUB> of 4062 V/W at 2 Hz and current responsivity R<SUB>i</SUB> of 281 (mu) A/W at 25 Hz was achieved under black body illumination. With CO<SUB>2</SUB> laser illumination at a wavelength equals 10.6 micrometer, an R<SUB>v</SUB> of 4140 V/W at 2 Hz and an R<SUB>i</SUB> of 441 (mu) A/W at 25 Hz was achieved.
A digital, multi-frequency EM image system is developed based on the induction principle for subsurface imaging near a sewage pipe. This system, which features a broadband operation, can transmit sinusoidal in a frequency range of 1.25 KHz to 10 KHz. A micro controller is used for all controls and computations for both the transmitter and receiver circuits. Synchronous sampling is used for digitization in order to compute the phase as well as the amplitude of the receiving signal. The system operates in the frequency domain and both the phase and amplitude information can be computed through a DSP algorithm. Test results indicate that the multi-frequency EM sensor is superior in both the missing manhole detection and general subsurface conductivity imaging to the conventional single- frequency sensors. For loop antennas with a spacing of 0.5 m, the system has phase resolution about 1 degree(s) and amplitude resolution about 0.5 percent.