In this paper we examine the SIGMA-Eye hyperthermia applicator (BSD Medical Corp., Salt Lake City, Utah 84119) with respect to the control of electric field distributions. This applicator is equipped with 12 pairs of antennas fed by 12 amplifiers, allowing the individual adjustment of phase and power for each of them. Measurements were conducted using phantoms with well-defined electrical properties. Specific electro-optical sensors, capable of measuring both electric field amplitudes and phases, have been developed, and a system for data acquisition and analysis has been set up. In its initial state the applicator appeared not to be satisfactorily matched at 100 MHz for the phantom used, with return losses up to 20% in power. By tuner readjustments we achieved values below 5%. For various settings of the amplifiers’ control parameters we measured field distributions, both in the phantom and in the surrounding water bolus. The experimental results were compared with numerical simulations based on finite difference and finite element methods. Measured and calculated electric fields exhibit deviations of 10% on average, allowing, in principle, a satisfactory prediction of fields by numerical simulations or as well by on-line measurements at selected locations of the applicator at antenna proximity. However, to obtain this satisfactory agreement a modification of the control parameters in the calculations (phases and amplitudes in the feed points of the antennas) was necessary. The origin of these problems is mainly attributed to cross-talk phenomena and other characteristics of the transforming network, which need to be scrutinized further for a full understanding.

Electric field distributions in a phased-array applicator with 12 channels: measurements and numerical simulations.

The measurement of intense E-fields is a fundamental need in various research areas. Integrated optical E-field sensors (IOESs) have important advantages and are potentially suitable for intense E-field detection. This paper comprehensively reviews the development and applications of several types of IOESs over the last 30 years, including the Mach-Zehnder interferometer (MZI), coupler interferometer (CI) and common path interferometer (CPI). The features of the different types of IOESs are compared, showing that the MZI has higher sensitivity, the CI has a controllable optical bias, and the CPI has better temperature stability. More specifically, the improvement work of applying IOESs to intense E-field measurement is illustrated. Finally, typical uses of IOESs in the measurement of intense E-fields are demonstrated, including application areas such as E-fields with different frequency ranges in high-voltage engineering, simulated nuclear electromagnetic pulse in high-power electromagnetic pulses, and ion-accelerating field in high-energy physics.

https://www.mdpi.com/1424-8220/12/8/11406/pdf

Development and Application of Integrated Optical Sensors for Intense E-Field Measurement

Thermoacoustic signal excitation is a function of intrinsic tissue properties and illuminating electric field. De-ionized (DI) water is a preferred acoustic coupling medium for thermoacoustics because acoustic and electromagnetic waves propagate in DI water with very little loss. We have designed a water-filled testbed propagating a controlled electric field with respect to pulse shape, power, and polarization. Directional coupler line sections permit measurement of incident, reflected, and transmitted powers. Both S-parameters and E(y) measurement show that the electric-field distribution is relatively uniform in testbed. Comparing baseline power measurements to those taken with a test object in place yields power loss in the object, which should correlate to thermoacoustic signal strength. Moreover, power loss--and therefore thermoacoustic computerized tomography signal strength--is sensitive to the orientation of the object to the polarization of the electric field. This testbed will enable quantitative characterization of the thermoacoustic contrast mechanism in ex vivo tissue specimens.

RF testbed for thermoacoustic tomography.

A new E-field probe with small outer dimensions of 5/spl times/5/spl times/5 mm/sup 3/ is presented. It has all-optical interconnections to achieve minimum field disturbance and employs a vertical cavity surface emitting laser (VCSEL) for transmitting the signal to the remote unit. In aqueous media the probe has a sensitivity of /spl sim/50 /spl mu/V/spl middot/m/sup -1//spl middot/Hz/sup -1/2/ and a dynamic range of 130 dB (1 Hz measurement bandwidth).

VCSEL-based miniaturised E-field probe with high sensitivity and optical power supply

E-field measurements are an important task for the investigation of newly developed hyperthermia applicators as well as for online control of hyperthermia treatments. Compact and non-perturbing integrated optical E-field sensors based on LiNbO3 as well as optical E-field sensors based on infrared emitting diodes and light bulbs are suitable for nearfield measurements of hyperthermia antennas. In order to investigate their properties a calibration cell with transverse electromagnetic (TEM) waves has been constructed. By using this cell, calibration curves and directional patterns for all sensors have been measured. Due to the threshold behaviour of the IRED and light bulb sensor, only the LiNbO3 sensor is capable of measuring weak fields inside an applicator or a homogeneous phantom.

Calibrated electro-optic E-field sensors for hyperthermia applications.

Compact and nonperturbing E-field sensors are used for antenna near field measurements. For application in the research area of hyperthermia these sensors are used in a water environment. Owing to the high dielectric constant of water in the frequency range from DC to /spl sim/1 GHz the sensitivity is changed. To perform a calibration of E-field sensors, a water-filled TEM-cell has been developed. The technique employs a transverse electromagnetic (TEM) transmission cell that operates as a 50 W impedance matched system. A uniform TEM-field is established inside the cell.

D. Pouhe

Papers

Calibration cell for E-field sensors in water environment