Two-dimensional dielectric spectroscopy: Implementation and validation of a scanning open-ended coaxial probe

Abstract

Dielectric spectroscopy is a powerful tool for characterizing and classifying materials based on their electrical properties. In order to perform dielectric measurements on a sample with spatially varying properties, the measuring probe typically is repositioned manually on the surface of the sample for each measurement. In this paper, we present a novel technique, based on a reconfigurable multielectrode array, which facilitates the recording of measurements at various different spatial locations without physically moving the measuring electrodes. By electronically selecting one of the electrodes as the inner line and connecting the remainder of the electrodes together to form the outer line, an open-ended coaxial probe is created, which can be repositioned by simply selecting different electrode combinations; hence the name of a "traveling" coaxial probe. The geometric factor, or the cell constant, of each coaxial probe in the array was estimated from measurements on saline solutions with known electrical characteristics. In order to validate the setup for measurement of dielectric properties of biological cells, the plasma membrane capacitance and cytoplasm conductivity of yeast cells suspended in aqueous solutions were measured and compared to results from published reports. Dielectric spectroscopy imaging was carried out on tissue phantoms made of an agar gel with inclusions consisting of concentrated yeast cell suspensions. Measurements were performed on the phantoms, and the dielectric data were spatially mapped with respect to electrode location. The spatial electrical data correlated precisely with locations of yeast cell inclusions within the phantoms.

Two‐dimensional dielectric imaging for dermatologic screening: a feasibility study

“…To obtain the advantages of coaxial probing without the disadvantages associated with the need for manual positioning, the design and implementation of a new electronic device has been recently introduced, termed a ‘scanning open‐ended coaxial probe’ , which uses an electronically configurable two‐dimensional electrode measurement array. As shown in Fig.…”

“…A proof‐of‐concept design has been realized in the form of a 4 × 4 array of square electrodes, connected to a switching network implemented with high‐speed monolithic CMOS video switches (AD1234, Analog Devices, Norwood, MA, USA) as described in detail elsewhere . In this design, the video switches are used to configure the array by connecting one of sixteen electrodes to the high‐current/high‐potential ports of an impedance analyzer, while the remaining electrodes – as well as a surrounding shield electrode – are connected to the low‐current/low‐potential ports of the impedance analyzer which serve as a virtual ground.…”

“…Recently, we have introduced a new method and instrumentation capable of determining the dielectric properties of solid objects from surface measurements . We have further modified the instrumentation to make it suitable for noninvasive imaging of the skin, based on the spatially dependent dielectric properties of the skin; this instrumentation eliminates the need for physical movement of the electrodes in generation of a two‐dimensional image.…”

“…Preliminary proof‐of‐principle results are given below; the intent is to demonstrate feasibility of the technique, to motivate a more complete clinical study to follow. Tissue phantoms which incorporate living cells were initially used in the testing, as reported in a previous article . In this work, we describe follow‐on testing of a select group of normal healthy subjects as well as a subject with diagnosed squamous cell carcinoma.…”

Millimeter-Wave Tissue Diagnosis: The Most Promising Fields for Medical Applications

“…As an alternative to mechanically scanning over the sample, probe arrays have been developed [46], [49], [50].…”