Probe In Direct Contact Research Articles

A Correction of Measurement for Complex Magnetic Permeability by Direct Contact Probe

A Correction of Measurement for Complex Magnetic Permeability by Direct Contact Probe

Determining soil organic carbon concentration in agricultural fields using a handheld spectroradiometer: Implication for soil fertility measurement

The soil organic carbon (SOC) plays a vital role in plant growth and development, and therefore is considered as one of the most important indicators of soil quality. This study was carried out in the central region of Saudi Arabia to explore the potential of spectroscopy in determining the SOC concentration in low-fertility soils. Spectral reflectance data were collected, under the controlled laboratory conditions on 39 air-dried 2.0 mm sieved soil samples, using a handheld spectroradiometer of a wavelength range between 350 nm and 2500 nm in the direct contact probe mode. The concentration of the SOC was determined using the Walkley and Black (W&B) and the UV-VIS spectrophotometric methods. The increase in the concentration of SOC was associated with a decrease in the corresponding spectral reflectance. Regression analysis showed linear relationships with high significant correlation between the spectral reflectance and the SOC measured by both the UV-VIS (Model-1: R2=0.46, p=0.00015 and RMSE=6.6 g/kg) and the W&B (Model-2: R2=0.48, p=8.92E-05 and RMSE= 2.8 g/kg) methods. For these models, two wavebands with wavelengths of 2167 nm (Model-1) and 1359 nm (Model-2) were identified as the most sensitive bands to the SOC concentration. The cross-validation confirmed the validity of Model-1 with R2, p and RMSE values of 0.50, 0.0099 and 6.6 g/kg, respectively. The validation results of the Model-2 showed values of R2, p and RMSE of 0.72, 0.00023 and 4.0 g/kg, respectively. Results of this study revealed the possibility and the potential of using the spectral reflectance technique in predicting the concentration of SOC. Keywords: soil fertility, organic carbon, modeling, spectroscopy, reflectance DOI: 10.25165/j.ijabe.20181106.4061 Citation: Tola E, Al-Gaadi K A, Madugundu R, Kayad A G, Alameen A A, Edrees H F, et al. Determining soil organic carbon concentration in agricultural fields using a handheld spectroradiometer: Implication for soil fertility measurement. Int J Agric & Biol Eng, 2018; 11(6): 13–19.

Photoacoustic imaging of a human vertebra: implications for guiding spinal fusion surgeries

It is well known that there are structural differences between cortical and cancellous bone. However, spinal surgeons currently have no reliable method to non-invasively determine these differences in real-time when choosing the optimal starting point and trajectory to insert pedicle screws and avoid surgical complications associated with breached or weakened bone. This paper explores 3D photoacoustic imaging of a human vertebra to noninvasively differentiate cortical from cancellous bone for this surgical task. We observed that signals from the cortical bone tend to appear as compact, high-amplitude signals, while signals from the cancellous bone have lower amplitudes and are more diffuse. In addition, we discovered that the location of the light source for photoacoustic imaging is a critical parameter that can be adjusted to non-invasively determine the optimal entry point into the pedicle. Once inside the pedicle, statistically significant differences in the contrast and SNR of signals originating from the cancellous core of the pedicle (when compared to signals originating from the surrounding cortical bone) were obtained with laser energies of 0.23–2.08 mJ (p < 0.05). Similar quantitative differences were observed with an energy of 1.57 mJ at distances ⩾6 mm from the cortical bone of the pedicle. These quantifiable differences between cortical and cancellous bone (when imaging with an ultrasound probe in direct contact with each bone type) can potentially be used to ensure an optimal trajectory during surgery. Our results are promising for the introduction and development of photoacoustic imaging systems to overcome a wide range of longstanding challenges with spinal surgeries, including challenges with the occurrence of bone breaches due to misplaced pedicle screws.

Determining soil organic carbon concentration in agricultural fields using a handheld spectroradiometer: Implication for soil fertility measurement

The soil organic carbon (SOC) plays a vital role in plant growth and development, and therefore is considered as one of the most important indicators of soil quality. This study was carried out in the central region of Saudi Arabia to explore the potential of spectroscopy in determining the SOC concentration in low-fertility soils. Spectral reflectance data were collected, under the controlled laboratory conditions on 39 air-dried 2.0 mm sieved soil samples, using a handheld spectroradiometer of a wavelength range between 350 nm and 2500 nm in the direct contact probe mode. The concentration of the SOC was determined using the Walkley and Black (W&B) and the UV-VIS spectrophotometric methods. The increase in the concentration of SOC was associated with a decrease in the corresponding spectral reflectance. Regression analysis showed linear relationships with high significant correlation between the spectral reflectance and the SOC measured by both the UV-VIS (Model-1: R2=0.46, p=0.00015 and RMSE=6.6 g/kg) and the W&B (Model-2: R2=0.48, p=8.92E-05 and RMSE= 2.8 g/kg) methods. For these models, two wavebands with wavelengths of 2167 nm (Model-1) and 1359 nm (Model-2) were identified as the most sensitive bands to the SOC concentration. The cross-validation confirmed the validity of Model-1 with R2, p and RMSE values of 0.50, 0.0099 and 6.6 g/kg, respectively. The validation results of the Model-2 showed values of R2, p and RMSE of 0.72, 0.00023 and 4.0 g/kg, respectively. Results of this study revealed the possibility and the potential of using the spectral reflectance technique in predicting the concentration of SOC. Keywords: soil fertility, organic carbon, modeling, spectroscopy, reflectance DOI: 10.25165/j.ijabe.20181106.4061 Citation: Tola E, Al-Gaadi K A, Madugundu R, Kayad A G, Alameen A A, Edrees H F, et al. Determining soil organic carbon concentration in agricultural fields using a handheld spectroradiometer: Implication for soil fertility measurement. Int J Agric & Biol Eng, 2018; 11(6): 13–19.

Non-contact Raman spectroscopy for in-line monitoring of glucose and ethanol during yeast fermentations.

The monitoring of microbiological processes using Raman spectroscopy has gained in importance over the past few years. Commercial Raman spectroscopic equipment consists of a laser, spectrometer, and fiberoptic immersion probe in direct contact with the fermentation medium. To avoid possible sterilization problems and biofilm formation on the probe tip, a large-aperture Raman probe was developed. The design of the probe enables non-contact in-line measurements through glass vessels or inspection glasses of bioreactors and chemical reactors. The practical applicability of the probe was tested during yeast fermentations by monitoring the consumption of substrate glucose and the formation of ethanol as the product. Multiple linear regression models were applied to evaluate the Raman spectra. Reference values were determined by high-performance liquid chromatography. The relative errors of prediction for glucose and ethanol were 5 and 3%, respectively. The presented Raman probe allows simple adaption to a wide range of processes in the chemical, pharmaceutical, and biotechnological industries.

Terahertz Diode Arrays and Differential Probes based on Heterogeneous Integration and Silicon Micromachining

Due to the technological needs of the radio astronomy and remote sensing scientific communities, as well as emerging applications in the areas of imaging, security, and broadband communications, terahertz and submillimeter-wave electronics continues to be an area of growth and increasing interest for academic researchers, government laboratories, and industry. The recent establishment of a commercial infrastructure for test and measurement instrumentation in this spectral region has fueled this growth and the emergence of CMOS as a submillimeter-wave technology has greatly expanded access to this spectral region by providing circuit designers with a platform for realizing terahertz circuits without need for specialized fabrication facilities or processes. The continued emergence of new terahertz devices has created a need for improved approaches to packaging, integration, and measurement tools for diagnostics and characterization in this portion of the spectrum. This paper focuses on progress in two parallel efforts aimed at addressing these needs: (1) the development of a direct-contact probe technology for on-wafer measurement of differential scattering-parameters in the WR-5.1 (140—220 GHz) and WR-3.4 (220—330 GHz) frequency bands, and (2) the development of processing technologies for realizing highly-integrated submillimeter-wave diode-based quasi-optical arrays, including phase modulators and sideband generators, that are based on heterogeneous integration of III-V semiconductors onto thin silicon membranes as a support substrate. The foundation for these efforts is micromachining and processing of silicon, allowing the fabrication of mechanically-robust and low-loss membrane carriers that can support and interconnect terahertz devices as well as directly interface them to surrounding circuitry. Examples of heterogeneous integration onto silicon as an approach to packaging and interfacing terahertz components that are detailed in this paper include development of differential micromachined wafer probes for in situ measurements of devices and circuits in the 140—330 GHz region. The probe design concept includes an integrated on-chip balun and matching network for terminating common-mode signals that may be generated by the DUT. The design methodology and initial measurement results for this probe will be presented. In addition, an example of heterogeneous integration/packaging of a submillimeter-wave frequency sideband generator array for phase modulation at 1.6 THz will be discussed. The sideband generator design incorporates 100 planar varactor diodes integrated into an array of bowtie antennas on a common substrate. Performance of the array as a phase shifter is described and the application of a new quasi-vertical diode fabrication process that consists of transfer of GaAs epitaxy to thin silicon support substrates will be discussed as an approach for implementing optimized arrays in the terahertz frequency range.

Heterogeneous Integration and Micromachining Technologies for Terahertz Devices and Components

Terahertz electronics has been a topic of research and development for many years, motivated largely by the technological needs of the radio astronomy and remote sensing scientific communities. Over the past decade, however, this field has experienced dramatic growth and intense, renewed interest from academic researchers and federal agencies, as well as from industry. This interest has arisen, in part, from recent funding initiatives from the federal government (such as DARPA's Terahertz Electronics Program), but is also largely due to the establishment of a commercial infrastructure that has made test and measurement instrumentation available to the engineers and scientists working at these frequencies. Moreover, the emergence of CMOS as a potential submillimeter-wave device technology has greatly expanded access to this spectral region by providing circuit designers with a platform for realizing terahertz circuits without need for specialized fabrication facilities or processes. The recent and rapid progress in terahertz electronics has created a demand for improved approaches to packaging and integration, as well as a need for new measurement instrumentation for characterizing emerging terahertz devices. This paper focuses on two recent research developments aimed at addressing these needs and broadening the technology base for both terahertz system implementation and terahertz metrology. These developments include (1) the development of a direct-contact probe technology that permits on-wafer scattering-parameter characterization and measurement of planar integrated devices at frequencies to 1 THz and beyond, and (2) the establishment of processing technologies that permit fabrication of highly-integrated submillimeter-wave diode-based circuits, such as heterodyne receivers and frequency multipliers, that are based on heterogeneous integration of III-V semiconductor devices with thin silicon membranes as a support and integration substrate. The technical foundation for each of these efforts is micromachining of silicon that allow the formation of mechanically-robust and low-loss membrane carriers to support terahertz devices and circuitry. Two examples of heterogeneous integration with silicon as an approach to packaging terahertz components are detailed in this paper. These include development of micromachined probes for on-wafer measurements of devices and circuits in the WR-1.0 waveguide band (0.75 – 1.1 THz). The probe design concept will be presented and methods for characterizing the probe described. Measurements demonstrate that the probes exhibit an insertion loss of less than 7 dB and return loss of greater than 15 dB over 750—1100 GHz band, yielding the first demonstration of on-wafer probe operating above 1 THz. In addition, an example of heterogeneous integration/packaging of a submillimeter-wave frequency quadrupler operating at 160 GHz with efficiency of 30% and corresponding output power of 70 mW will be discussed. The quadrupler design includes two frequency doubler stages in cascade and is based on a balanced circuit architecture that addresses degradation issues often arising from impedance mismatches between multiplier stages. A unique quasi-vertical diode fabrication process consisting of transfer of GaAs epitaxy to the thin silicon support substrate is used to implement the quadrupler, resulting in an integrated drop-in chip module that incorporates 18 varactors, matching networks and beamleads for mounting.

Detection of hotspots and rapid determination of methane emissions from landfills via a ground-surface method.

We present a method for the rapid determination of methane emissions from landfills based on atmospheric dispersion theory, which suggests that the methane concentration, at a small distance from the soil/atmosphere interface, is proportional to its flux. Thus, after suitable calibration, the determination of methane concentrations close to the ground allows for flux determination in a shorter time than with standard enclosure techniques. This concept was tested using a surface probe in direct contact with the ground. The probe extracts a continuous sample of the air at the probe/ground interface and transports it to a portable methane analyzer. It was observed that stable methane concentrations were measured 30s after the probe was positioned at the measurement point. These concentrations correlated well with the fluxes measured by standard static chambers. The method was used to determine the fluxes at 217 points within a 90,000m(2) landfill. These measurements facilitated mapping of the CH4 emissions and the localization of hotspots. We conclude that the method is simple, effective, and relatively quick, compared to existing standard methods.

Deconvoluting the Mechanism of Microwave Annealing of Block Copolymer Thin Films

The self-assembly of block copolymer (BCP) thin films is a versatile method for producing periodic nanoscale patterns with a variety of shapes. The key to attaining a desired pattern or structure is the annealing step undertaken to facilitate the reorganization of nanoscale phase-segregated domains of the BCP on a surface. Annealing BCPs on silicon substrates using a microwave oven has been shown to be very fast (seconds to minutes), both with and without contributions from solvent vapor. The mechanism of the microwave annealing process remains, however, unclear. This work endeavors to uncover the key steps that take place during microwave annealing, which enable the self-assembly process to proceed. Through the use of in situ temperature monitoring with a fiber optic temperature probe in direct contact with the sample, we have demonstrated that the silicon substrate on which the BCP film is cast is the dominant source of heating if the doping of the silicon wafer is sufficiently low. Surface temperatures as high as 240 °C are reached in under 1 min for lightly doped, high resistivity silicon wafers (n- or p-type). The influence of doping, sample size, and BCP composition was analyzed to rule out other possible mechanisms. In situ temperature monitoring of various polymer samples (PS, P2VP, PMMA, and the BCPs used here) showed that the polymers do not heat to any significant extent on their own with microwave irradiation of this frequency (2.45 GHz) and power (∼600 W). It was demonstrated that BCP annealing can be effectively carried out in 60 s on non-microwave-responsive substrates, such as highly doped silicon, indium tin oxide (ITO)-coated glass, glass, and Kapton, by placing a piece of high resistivity silicon wafer in contact with the sample-in this configuration, the silicon wafer is termed the heating element. Annealing and self-assembly of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) and polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) BCPs into horizontal cylinder structures were shown to take place in under 1 min, using a silicon wafer heating element, in a household microwave oven. Defect densities were calculated and were shown to decrease with higher maximum obtained temperatures. Conflicting results in the literature regarding BCP annealing with microwave are explained in light of the results obtained in this study.

Endoscopic ultrasonographic evaluation of the esophagus in healthy dogs

To characterize the ultrasonographic appearance of the canine esophagus. 14 healthy Beagles. Endoscopic ultrasonography (EUS) examinations were performed with a radial ultrasonographic gastrovideoscope in anesthetized dogs. Images were obtained at 3-cm intervals along the esophageal length to allow evaluation of the esophageal wall. Images were obtained with the probe in direct contact with the esophageal wall and with a water-filled balloon as a standoff. Images were obtained with (12 dogs) and without (10) the water-filled balloon. Median thickness of the esophageal wall was 2.19 mm (range, 1.03 to 5.62 mm) in the proximal third of the esophagus, 2.15 mm (range, 1.10 to 4.45 mm) in the middle third, and 2.84 mm (range, 1.35 to 5.92 mm) in the distal third. Wall thickness differed significantly between proximal and distal thirds. Results were similar when the water-filled balloon was used. Esophageal wall layers appeared as 5 alternating hyperechoic and hypoechoic bands that could not be consistently identified in all dogs. All layers could be identified in 26 of 198 (13%) images, 3 layers could be identified in 67 of 198 (34%) images, and 105 of 198 (53%) images had no layers. Visual identification of layers in images obtained with and without the balloon did not differ significantly. EUS appeared to be a useful technique for assessing esophageal wall integrity in dogs; however, complete evaluation of all layers could not be accomplished in all instances. Further studies with this technique in dogs are needed.

In vivo intravital endoscopic confocal fluorescence microscopy of normal and acutely injured rat lungs

We present a new lung imaging technique based on endoscopic confocal fluorescence microscopy (ECFM), which is a new method that is able to provide cellular and structural assessment of living tissue using a small confocal probe in direct contact with the visceral pleura. To observe distal airspace structure and cellular condition in normal and injured lungs (hyperoxic and bleomycin challenged), we used fluorescent-specific marker contrast and ECFM. Alveolar space ECFM with spectral analyses were performed at 488-nm excitation using FITC-labeled markers or naturally fluorescent dyes. The normal lung was compared with the sick lung, where our in vivo imaging experiments correlated well with results obtained with corresponding ex vivo conventional assays. Four main elements pertaining to the acute lung injury/acute respiratory distress syndrome (ALI/ARDS) pathophysiology and established early key events were specifically studied: alveolar epithelial membrane phenotype, lung cell apoptosis, neutrophil recruitment, and edema. ECFM allowed visualization of (i) fine-tuned ultrastructural lectin (RCA-1) and sialoglycoprotein (RTI40) epithelial cell membrane expression, (ii) YO-PRO-1-related DNA linking of lung cell apoptosis, (iii) PKH2 green fluorescent cell linker-labeled neutrophil tracking in lung microcirculatory network and airspaces, (iv) FITC-dextran plasma contrast and extravasation with edema formation. ECFM provides reliable results to corresponding ex vivo fluorescent methods. ECFM, using the minimally invasive Five-1® optical instrument and specific fluorescent markers, is able to provide real-time potentially useful imaging of live unfixed normal and injured lung tissue with promising developments for improving bedside diagnostic and decision-making therapeutic strategy in patients with ALI.

An ultrasonic measurement model to predict the response from flat bottom hole for dual crystal contact probe

Dual crystal contact probes play an important role in many practical ultrasonic inspections, so it is essential to develop an ultrasonic measurement model in order to get a thorough understanding of the characteristics of this kind of transducers. By combining the multi-Gaussian beam model and the Kirchhoff approximation scattering model, a complete ultrasonic measurement model is provided to predict testing signals of a flat bottom hole for a dual crystal focused direct contact probe. By comparing with experimental results, the accuracy of predicted signals using this model has been verified.

Monitoring of neuronal and glial calcium activity using a novel direct‐contact probe

In vivo neuronal and glial calcium activity was monitored using a novel direct-contact probe that was designed for fluorescence detection deep within biological tissue. A small diameter fibre bundle direct-contact probe was employed with a laser scanning confocal microscope to detect evoked neuronal and glial activity in the posteromedial barrel subfield of the rat somatosensory cortex in vivo. Resolution of the probe allowed discrimination of single cells, and calcium dynamics spanning milliseconds to several seconds were observed. Initial results indicate that the probe has useful practical applications in the imaging of individual cells and monitoring rapid calcium fluctuations within their cell body and large processes.

Pilot Study of a Prototype Endoscopic Doppler Ultrasound (DOP-US) Device in Measuring Changes in Variceal Blood Flow After Band Ligation

Background: Endoscopic band ligation (EBL) is commonly used to treat acute esophageal variceal hemorrhage (EVH). However, there is no objective marker of adequacy of EBL and, in some cases, recurrent varices or EVH may be secondary to ineffective or incomplete EBL. The utility of DOP-US in assessing persistent blood flow (BF) in arteries after endoscopic therapy for acute peptic ulcer bleeding has been well-documented. Data on DOP-US for varices are limited. Aims: To assess the utility of the VTI Flowmeter, a prototype DOP-US device, in examining esophageal varices. The Flowmeter provides both an audible Doppler signal and quantitative values of relative BF velocity and signal intensity based on vessel size and reflectance from blood cells. The second aim was to determine whether quantitative changes in variceal BF occur after EBL. Methods: Pts presenting to our institution with suspected EVH or for elective follow-up EBL were recruited for the study. A total of 5 Flowmeter studies in 4 pts were conducted in this pilot study. During initial EGD, variceal BF was measured 5 cm above the GE junction by placing the DOP-US probe in direct contact with the varix at an oblique angle. The angle was varied until the most consistent audible Doppler signal was obtained. After BF measurement, EBL was performed by standard technique. Repeat DOP-US exam was then performed. BF measurements following EBL were made by placing the probe 1 cm above the variceal band. If no signal was detected, the incident angle was varied to ensure that no signal was present. Means of quantitative DOP-US signals were compared by ANOVA. Results: In 5 studies, a total of 8 columns of Grade I, 8 Grade II, and 4 Grade III varices were examined. The pre-EBL signal intensity of Grade I varices (15.8) was lower than the signal intensity of Grade II (81.4) and Grade III (84.3) varices (p < 0.01). Relative BF velocity pre-EBL did not correlate with vessel size. 70% of examined varices had a positive (+) audible Doppler signal pre-EBL. Only 1 varix had a persistently (+) signal post-EBL. In this varix signal intensity decreased by 33% and relative BF velocity decreased by 23% post-EBL. Conclusions: In our preliminary experience, the Flowmeter is able to detect and quantify blood flow in pts with esophageal varices pre- and post-EBL. Varix size correlated with signal intensity. The absence of a detectable signal in all but 1 varix post-EBL suggests that EBL is highly effective at arresting BF. Additional studies with long term follow-up are needed to determine whether such a device can predict variceal recurrence or rebleeding in pts with a persistently (+) Doppler signal post-EBL.

SHELL EGG ALBUMEN HEIGHT ASSESSMENT BY FT-NIR SPECTROSCOPY

Fourier transform near-infrared (FT-NIR) spectroscopy was used for quantitative measurements of thick albumenheight. By means of a fiber optic probe in direct contact with the shell, non-destructive acquisitions by diffuse reflectancewere carried out to establish a model to predict this egg quality index. After breaking the egg and measuring the referenceparameter albumen height, transmission acquisitions of the thick portion of the albumen were also performed. The predictivemodels obtained from the two experiments showed a good correlation in terms of coefficient of determination (R2 = 0.819for non-destructive analysis, and R2 = 0.764 for transmission measurements) between the spectral data and the thick albumenheight. In both cases, about 80% of the eggs that were not used for model development were predicted with a maximum errorof 1 mm.

Near-infrared spectroscopy for soil water determination in small soil volumes

Critical soil water levels for soil microscale processes are difficult to determine because of variability in large soil volumes and lack of techniques for logging soil water contents in small soil volumes. This study tested nearinfrared (NIR) spectroscopy for soil water content determination. Five soil horizons with a range in soil texture, soil organic carbon, carbonates, pH and horizon depth, were tested at air-dry, field capacity and 0.1 MPa tension water content. Volumetric soil water content, determined using the standard method of oven-drying and soil bulk density, was compared to NIR absorbance in various combinations and wavelengths. The NIR spectra obtained with the probe in direct contact with the soil gave better results than when the probe was separated from the soil with a glass slide. The most reliable validation results were obtained using a multivariate partial least squares regression of the full spectrum with an r2 of 0.95 and RMSE of prediction of 6.4%. Smoothing and derivatives of the spectra did not improve the validation results. The relationships for absorbance at single wavelength segments, ratios, differences and area under the curve around the 1940 nm peak were good (r2 values near 0.85 ) but poorer than the results using the full spectra. The high correlation coefficients obtained with the wide variety of soils utilized in this study suggest that NIR absorbance is a practical method for determining volumetric soil water content for small soil volumes. Key words: Near-infrared spectroscopy, soil water, Near-infrared absorbance

Direct identification of key intermediates in containers using Fourier-transform near-infrared spectroscopy through the protective polyethylene primary packaging

A fast and non-destructive Fourier-transform near-infrared (NIR) spectroscopy method with corresponding chemomet- ric calibrations was developed for the identification of key intermediates of pharmaceutical active substances through the pro- tective polyethylene (PE) primary packaging in containers. The samples were measured with a laboratory spectrometer. NIR spec- tra of incoming containers samples were also recorded for calibration with a spectrometer installed in the warehouse. The spect ra of the different samples were recorded by diffuse reflectance with a 2 m long glass fiber optics probe in direct contact with th e PE-protected surface of the material. The NIR spectra of the same products were stored in files and principal component analy- sis combined with cluster analysis were used to refine the identification criteria. To achieve validation of the resulting math e- matical models, the samples were split into a calibration set and a validation set. The latter was used for external and indepe n- dent tests. The resulting NIR application can be transferred to any spectrometer of the same type.

FDTD analysis of the radiometric temperature measurement of a bilayered biological tissue using a body-contacting waveguide probe

Radiometric signal received by an open-ended rectangular waveguide probe in direct contact with a bilayered biological tissue is analyzed by the FDTD method. A two-layer tissue model consists of an outer thin skin layer over a semi-infinite fat layer is analyzed for a X-band total power radiometer. A spherical tumor with same permittivity as, but slightly higher temperature than, the surrounding normal fat tissue is assumed to exist inside the fat tissue. Active probe characteristics are analyzed first using the FDTD method for a propagating, sinusoidally time-varying, TE/sub 10/ type of excitation source. For the same waveguide probe operated as the radiometer antenna, radiometric weighting factors associated with individual tissue cells are then derived from the FDTD calculated field values. Near field radiating characteristics of the probe and radiometric signals determined for tumors of various size and depth are discussed. The presence of the skin is found to result in a lower power transmission coefficient across the probe aperture and significantly lower absorbed powers by fat; both of these contribute to the much lower radiometric signals observed. >