Maciej A. Noras

Surface Charge Density Measurements

This paper is devoted to the Kelvin probe technique which is noncontacting method for the quantitative evaluation of an electric field, surface potential, and surface charge distribution. It does not change the physical state of the object under test. Lack of contact with the measured object assures that there is no charge transfer between the meter and the tested surface. This article investigates the uses and limitations of Kelvin probe-based instruments for surface charge density measurements of dielectric materials.

Ion imbalances on an ionizer-controlled work surface

This paper presents results of investigations carried out to test the influence of charged objects introduced into the vicinity of an ionizer-controlled work surface. The qualitative and quantitative distribution of ions on the surface was the main focus of the experiment. Experiments were conducted using ionizers with a feedback signal taken from a sensor at the output of the ionizer (factory installed internal feedback).

Electric Field Sensor Based on a Varactor Diode/MIS/MOS Structure

In this paper a voltage controlled variable capacitance is being proposed as a method for non-contacting measurement of electric fields. There are several microelectronic devices that can be utilized for that purpose: a varactor (a.k.a. varicap), a MOS (metal-oxide-semiconductor) or a MIS (metal-insulator-semiconductor) structure. The construction that has been tested and presented in this paper is based on a varactor diode. Although numerous non-contacting instrument designs are widely available, they either lack precision (meters utilizing Kerr or Pockel effect, rotating vane fieldmeters, fieldmeters with mechanically vibrating sensors) or are relatively expensive and complicated (electrostatic voltmeters). Other types of electric field meters such as capacitive coupling or induction instruments rely on variation of the electric quantity that is being measured, therefore they are not useful for detection and quantification of static (DC) electric charges and fields. The sensor used in the experiment described in this manuscript can be used for the DC and AC electric field measurements. The construction is very simple, therefore inexpensive, and it can be easily miniaturized.

An evaluation of electric-field sensors for projectile detection

The U.S. Army Research Laboratory (ARL) conducted an experiment at Aberdeen Proving Ground (APG), MD, to collect bullet signature data using three different types of electric-field sensors. The first type is a free-space electric potential sensor; we used Remote Voltage Sensors (RVSs) manufactured by Quasar Federal Systems (QFS). The second type of sensor measures the electric field; we used QFS potential gradiometers and a varactor-based E-field sensor prototype designed by the University of North Carolina - Charlotte (UNCC). The third type of sensor is a “D-dot” charge induction probe designed and built by ARL. We analyzed the performance of each sensor type with regard to bullet detection capability. Mathematical models and signatures were developed for each sensor type, and actual signatures were measured and compared to these models.

Hysteresis characterization using charge feedback control for a LIPCA device

In this paper, we study the no-load behavior of a lightweight piezo-composite curved actuator (LIPCA) subjected to voltage and charge control. First, we examine the effect of hysteresis and creep when the actuator is voltage controlled at a slow scan speed. The experimental results show that creep increases the displacement hysteresis by over 25% when scanning at 1/60 Hz. Afterwards, we discuss the design and implementation of a charge-feedback circuit to control the displacement of the actuator. The hysteresis curves between voltage- and charge-control modes are compared for the scan frequencies of 1 and 5 Hz. The results show that charge control (compared to voltage control) of a LIPCA device exhibits significantly less hysteresis, over 80% less.

Monitoring of flowing charges with an electrostatic voltmeter

This paper describes a simple method of monitoring the net electric charge of powders transported pneumatically through a dielectric pipe. An electrostatic voltmeter (ESVM) is used to measure the voltage induced on an isolated ring electrode placed on the outside surface of the pipe. An equivalent circuit model of the measurement system was constructed and experimentally verified using an electrophotographic toner and an aluminum oxide powder (Al/sub 2/O/sub 3/). Knowledge of the voltage induced by flowing charged particles on the electrode allows for the calculation of the total charge that flew through the pipe. However, in order to obtain an accurate voltage measurement, the input impedance of the instrument used for that purpose must be very high. The high impedance of an ESVM makes it uniquely suited for this application.

An apparatus for the charge-to-mass and charge-to-diameter measurements on powders

This paper presents design and evaluation of a simple tool for assessing of electric charge levels on powders. The testing device uses a stackable Faraday cup arrangement for measurement of charges on size fractions of the powder under investigation. The powder is pneumatically transported through the Faraday cups column. The cups utilize specially designed sieves for separation of the powder particles by size. Additionally, the sieving membrane in the topmost cup is acoustically vibrated to help with the powder separation process

Evaluation of Surface Charge Density with Electrostatic Voltmeter - Measurement Geometry Considerations

Use and limitations of Kelvin probe based instruments for surface charge density measurements of dielectric materials are discussed. Three different devices are evaluated: a DC feedback electrostatic voltmeter (ESVM), an AC feedback ESVM and a fieldmeter. Special attention is paid to influence of geometry of the measured object. The effect of viewing angle of the probe, thickness of the sample as well as of stray capacitances are shown theoretically and verified experimentally.

Application of novel quasi-electrostatic sensor arrays for time based data collection and processing of supersonic, subsonic, and transonic revolving projectiles

Sensors capable of measuring the quasi-electrostatic field of traveling projectiles have been developed to detect the passage of a bullet in flight. These sensors provide an alternative to existing optical chronograph technologies, which are sensitive to variations in environmental lighting, and magnetic chronographs, which require close proximity to the bullet’s path. In contrast, electric field sensors are insensitive to lighting changes and prior testing has demonstrated the ability to reliably detect bullets at distances of at least three meters. A linear array of these sensors has been used to measure the time of flight between the sensors, which with the known distance between the sensors can be used to calculate the projectile’s velocity. These velocity measurements are compared to established chronograph technology as a measurement validation. By extending this array of sensors along the projected path of the projectile, a profile of the projectile’s position and velocity through flight can be calculated. This expected utility of this data is in refining the calculations that are performed to determine a ballistic solution, particularly in long range engagements, where there has been limited availability of accurate projectile velocity measurements. This robust sensor array that can easily be deployed represents an inexpensive way to experimentally investigate numerous phenomena related to ballistics modeling.

Use of a piezo-driven cantilever beam as a sensor for electrostatic voltmeter

In this paper authors examine the design and implementation of a cantilever beam-style probe for non-contacting electrostatic voltmeter. The beam is driven by a piezoelectric actuator with a feedback loop controlling amplitude of the electrostatic sensor displacement. Choice of the vibration mode and placement of the actuator and sensor are discussed. A simple model for the first three natural frequencies of the beam is constructed and compared with the experimental results.