Kevin G. Rhoads

Bio: Kevin G. Rhoads is an academic researcher from Massachusetts Institute of Technology. The author has contributed to research in topics: Space charge & Electric field. The author has an hindex of 9, co-authored 17 publications receiving 274 citations. Previous affiliations of Kevin G. Rhoads include Varian Semiconductor.

A high-accuracy, calibration-free technique for measuring the electrical conductivity of liquids

Abstract: A high-accuracy, calibration-free technique to measure the electrical conductivity of liquids has been developed — the coaxial cylinders technique. Because the liquid under investigation comes in contact only with metal and not with anything dielectric, this technique enables the measurement of the electrical properties of liquids inaccessible by classical high-accuracy techniques. Two coaxial cylindrical electrodes are immersed in the liquid to an arbitrary initial depth, and ac impedance is measured over a wide range of frequency. This process is repeated at many immersions. The electrical conductivity is calculated from the change in measured conductance with immersion. This technique was validated in 1.0, 0.1, and 0.01 D KCl(aq) solutions at room temperature. Measured electrical conductivities were within ±0.5% of the standard reference values.

Method for characterizing coating and substrates

Abstract: A system for characterizing coatings and substrates of a material under test. A sensor is positioned against a coated sample which is to be measured to obtain phase and magnitude measurements. Penetration depth of the magnetic waves of the sensor is a function of frequency. Measurements are made at each of a plurality of signal frequencies. The measured phase and magnitude data is applied with respect to a frequency independent parameter, such as conductivity, using a grid method. The conductivities of the coating and the substrate are determined by the limits of conductivity with respect to frequency. With the assumed conductivities of the coating and substrate, the sensor is once again placed over the material, and coating thickness and lift-off are determined. By examining the coating thickness versus frequency the accuracy of the measurement can be determined, since actual coating thickness does not vary with frequency in the material. Through iterative approximations, conductivity can then be accurately determined.

Electro-Optic Charge Injection and Tramsport Measurements in Highly Purified Water and Water/Ethylene Glycol Mixtures

Abstract: Extensive Kerr electro-optic field mapping and voltage/ current measurements have been taken with highly purified water over the temperature range of T= 0 to 30°C using parallel plane electrodes with average field strengths up to 160 kV/cm. The Kerr constant of water B was measured to be B ?, 3.4 to 3.6x1O-14 M/V2 for free-space light wavelength 590 nm and varies only slightly with temperature over the measurement range. Photomultiplier tube measurements at 633 nm at ?10°C found water to have a Kerr constant B ? 2.7 to 2.9x10-14 m/V2 while ethylene glycol had a negative Kerr constant B ? -(.8 to .9)x1O-14 m/V2. Water/ethylene glycol mixtures had an essentially linear variation of Kerr constant between these limits as a function of weight fractions, having a zero Kerr constant at about 79% glycol/21% water by weight . With pure water, a HV step has no volume charge at t=0. For times greater than 500 ?s, stainless steel and copper electrodes generally inject positive charge although under some conditions with mixed electrodes they injected negative charge, aluminum electrodes only inject negative charge, while brass electrodes can inject either positive or negative charge. Thus, by appropriate choice of electrode material combinations and voltage polarity, it is possible to have uncharged water, unipolar charged negative or positive, or bipolar charged water. Generally, the bipolar case allows a higher applied voltage without breakdown, presumably due to the lower electric field strengths at the electrodes due to the space charge shielding.

Surface deactivateable tag

Abstract: A security tag used with an electronic security system comprises a dielectric substrate having first and second opposite principal surfaces and a resonant circuit capable of resonating at a frequency within a detection frequency range. The resonant circuit is formed, in part, by a first conductive area on the first substrate surface and a second conductive area on the second substrate surface, the two conductive areas being generally aligned with one another to establish a capacitor with the substrate therebetween forming the capacitor dielectric. A third conductive area is provided on one of the principal substrate surfaces proximate to but not electrically connected to one of the two capacitor plates. The third conductive area is electrically connected to the other capacitor plate. A portion of the third conductive area is spaced from a portion of the one capacitor plate by a predetermined minimum distance whereby upon the application of electromagnetic energy to the tag at a frequency generally corresponding to the resonant frequency of the resonant circuit and at or above a predetermined minimum energy level, an electric arc extends between the spaced portions of the third conductive area and the one capacitor plate creating a persistent conductive bridge which connects the two plates of the capacitor in a short circuit.

Transference number measurements of TiO2-BaO melts by stepped-potential chronoamperometry

Abstract: TiO2–BaO melts have been under investigation as candidate electrolytes for the electrolytic production of titanium. Transference number measurements have been made by stepped-potential chronoamperometry at two compositions: 67 mol% TiO2 (1328

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Object tracking system with non-contact object detection and identification

Abstract: An object tracking system is provided for tracking the removal of objects from a location and the replacement of the objects at the location. The system includes a radio frequency identification (RFID) tag attached to each of the objects to be tracked and each tag has an antenna. When activated, the RFID tag of an object transmits a unique code identifying the object. A storage unit is provided at the location and the storage unit has a plurality of receptacles configured to receive objects replaced at the location. Each receptacle has an associated antenna for activating the RFID tag of an object in the receptacle and receiving the radio frequency transmitted code of the object. The antennae of the system can be capacitive plates for conveying the radio frequency transmissions through capacitive coupling or inductive loops for conveying the transmissions through inductive coupling. A computer-based controller is coupled to the antenna of the receptacles for receiving transmitted codes and determining based thereon the absence or presence and location of objects within the storage unit.

Object tracking method and system with object identification and verification

Abstract: A system and method for tracking and controlling access to objects such as keys includes a lockable storage cabinet adapted to receive, store, and dispense objects within transparent security containers. A control computer is operably coupled to the cabinet. Information about objects, such as their weight, an image, or magnetic characteristics, is extracted by sensors when the objects within their containers are dispensed to a user or checked in by a user. This information is compared to a data base of the same information previously extracted for these objects. From the comparison, the connected control computer verifies that the objects present in the security container are the objects expected to be in the security container. If they are not, then theft or tampering is indicated and the computer takes remedial actions such as setting alarms or notifying security personnel.

Object control and tracking system with zonal transition detection

Abstract: An object tracking and control system is provided and is particularly suited to implementation at an automobile dealership. The system includes a Key Track system (21) adapted to control access to and log the check out and check in of keys to vehicles on the lot. RFID tags (26 and 27) are provided on the vehicles and tag readers (32, 42, 47, 52) are embedded at selected locations within the dealership parking lot to detect movement of vehicles. In one embodiment, the lot is subdivided into zones (1-4) and the readers are located at transitions regions between the zones. Information about the check out and check in of keys from the Key Track system is combined and integrated with information about the movement of vehicles about the lot to reach conclusions regarding authorized movement to provide useful information to dealership management.

Information storage and identification tag

Abstract: An information and storage identification tag (20) includes a substrate (12), an input mechanism (24) disposed on the substrate and configured to receive a query signal, an output mechanism (24) disposed on the substrate and a response circuit (22) disposed on the substrate The response circuit is disposed in operative communication with the input mechanism and the output mechanism and is configured to output via the output mechanism at least one selectable response code in response to receipt of a query signal by the input mechanism