Sophie Kohler

Simultaneous High Intensity Ultrashort Pulsed Electric Field and Temperature Measurements Using a Unique Electro-Optic Probe

High intensity nanosecond pulsed electric fields and temperature were simultaneously measured using a unique electro-optic (EO) probe. The measurements were performed in an electroporation cuvette with 4 mm electrode gap and filled with a buffered salt solution. High voltage generators delivering 2.6 and 10 ns duration pulses with different pulses shape and intensity were investigated. The EO probe linearity was characterized up to 2 MV/m. The temperature measurement uncertainty was found to be less than 22 mK. Excellent measurement abilities were achieved with this EO probe showing its suitability for bioelectromagnetic experiments and particularly for wideband high intensity field applications.

Experimental Microdosimetry Techniques for Biological Cells Exposed to Nanosecond Pulsed Electric Fields Using Microfluorimetry

In the last decade, high-intensity pulsed electric fields with nanosecond durations (3–300 ns) have found breakthrough biomedical applications, e.g., in cancer treatment and gene therapy; however, the physical mechanisms underlying the interaction between nanosecond pulsed electric fields (nsPEFs) and cells, tissues, or organs are not yet fully elucidated. The precise knowledge of the electromagnetic dose received by the exposed sample at the macroscopic, and better still at the microscopic scale, is essential to complete our understanding of the phenomena involved and for adequate interpretation and reproducibility of the results. In this paper, we report a dosimetric and microdosimetric study of an in vitro exposure setup based on a transverse electromagnetic (TEM) cell that allows the exposure of cells in a Petri dish to nsPEFs. The rectangular and bipolar pulses delivered to the cells had a total duration of 1.2 ns and an amplitude of 2 kV. The electric field in situ was characterized experimentally with a nonmetallic probe and numerically using a finite-difference time-domain algorithm. Results of real-time monitoring of temperature were obtained at the subcellular level by using microfluorimetry, which is a method of imaging temperature by using a fluorescent molecular probe with thermosensitive properties.

Electrooptic Probe Adapted for Bioelectromagnetic Experimental Investigations

In this paper, we present radio-frequency electro-magnetic field characterization of an electrooptic (EO) probe. This probe is able to simultaneously measure temperature and one component of the electric field (e-field) in a continuous wave (CW) or in a pulsed regime. For this purpose, linearity, selectivity, and sensitivity measurements are performed in air and in a cuvette filled with a water solution. The media are exposed to 1800-MHz CW electromagnetic wave through a transverse electromagnetic cell. Numerical characterization is also performed using finite-difference time-domain simulations. The EO probe presents a dynamic range exceeding 70 dB. Selectivity up to 25 dB is measured, demonstrating the ability of the EO probe to measure one unique component of the e-field. The EO probe sensitivity is equal to 0.77 and to 0.18 V · m-1Hz-½, in the air and in the water solution, respectively. This millimeter-sized EO probe is particularly suited for the measurement of ultrawide bandwidth and high-voltage e-fields up to a few megavolts per meter.

Specific Absorption Rate Assessment Using Simultaneous Electric Field and Temperature Measurements

In this letter, the temperature measurement ability of an electrooptic probe as well as specific absorption rate (SAR) assessments via simultaneous in situ temperature and electric field characterization are reported. The measurements are carried out at 1800 MHz in a Petri dish filled with a water solution and placed in a transverse electromagnetic (TEM) cell. From the temperature sensitivity measurements, a standard deviation of 27 mK is obtained. The SAR values obtained both via temperature and electric field are also compared to finite-difference time-domain (FDTD) simulated numerical results. A difference of 5% is obtained between the two experimental SAR values. These measured SAR values are consistent with those obtained by the numerical simulations.

A versatile high voltage nano- and sub-nanosecond pulse generator

High-voltage (HV) ultrashort pulse technologies have found many applications in areas such as medicine, biology, food processing, environmental science and defense. Some applications are dependent on the pulse parameters such as duration, amplitude, shape, as well as the number of pulses applied and the frequency rate. Generators that can produce powerful electrical pulses with adjustable duration, amplitude and shape are convenient but still unusual. In this paper, we present and characterize a robust and versatile generator built on the frozen wave generator concept using photoconductive semiconductor switches. The results show that the generator can produce pulses of various shapes, peak-to-peak amplitudes up to 13.1 kV, maximum amplitudes of 6.9 kV and with durations in the nanosecond and subnanosecond range. Intense subnanosecond pulses have recently gained attention due to their potential ability to reach cells interior.

Electromagnetic Analysis of an Aperture Modified TEM Cell Including an ITO Layer for Real-Time Observation of Biological Cells Exposed to Microwaves

We propose to analyze the aperture and ITO layer presence of a modified transverse electromagnetic (TEM) cell. This TEM cell can be used to study the potential effects of microwave electromagnetic fields on biological cells. This modified delivery device allows real-time observation of biological cells during exposure. Microscopic observation is achieved through an aperture in the lower wall of the TEM cell that is sealed with a 700-nm film of the transparent conducting material Indium tin oxide (ITO). To determine the device efficiency, numerical and experimental electromagnetic dosimetry was conducted. For assessing the effect of the aperture on the specific absorption rate (SAR) in the exposed sample, a plastic Petri dish containing cell culture medium, full-wave 3-D electromagnetic simulations and temperature measurements were performed. For 1-W input power, the SAR values obtained at 1.8 GHz in the sample exposed in the TEM cell with the sealed or non-sealed aperture of 20-mm diameter were 1.1 W/kg and 23.6 W/kg, respectively. An excellent homogeneity of the SAR distribution was achieved when the aperture was sealed with the ITO layer. The performance of the delivery system was confirmed by microwave exposure and simultaneous observation of living cells.

Characterization of a TEM cell-based setup for the exposure of biological cell suspensions to high-intensity nanosecond pulsed electric fields (nsPEFs)

In this paper, we propose and characterize a setup based on a Transverse ElectroMagnetic (TEM) cell to expose a Petri dish filled with a biological suspension to nanosecond high-voltage pulsed electric fields. Monopolar and bipolar pulses of 1.2 ns duration and 1.6 kV amplitude are delivered to the TEM cell. Time domain measurements and numerical results show that the system is well suited to deliver high-intensity pulsed electric fields with 1.2 ns duration and amplitudes of at least 100 kV/m.

Setup for Simultaneous Microwave Heating and Real-Time Spectrofluorometric Measurements in Biological Systems

In this paper, a delivery system allowing simultaneous microwave heating and real-time spectro∞uorometric measurements in biological systems is proposed and characterized. This system is used to investigate the phase behavior of lipid bilayers from about 15 - C to 45 - C. The delivery system is based on an open transverse electromagnetic (TEM) cell combined with a spectro∞uorometer via an optical cable system. A numerical and experimental dosimetry of the delivery system is conducted. The Speciflc Absorption Rate (SAR) e-ciency of the system is 26:1§2:1W/kg/W. Spectro∞uorometric measurements on Laurdan labeled small unilamellar vesicles (SUVs) are carried out. Generalized polarization (GP) of the SUVs membrane is obtained from the ∞uorescence intensities measured at two emission wavelengths.

Electrical Analysis of Cell Membrane Poration by an Intense Nanosecond Pulsed Electric Field Using an Atomistic-to-Continuum Method

Pulsed electric fields of sufficient magnitude and duration trigger functional responses and modifications in biological cells. Transient nanometer-sized pores are believed to form within nanoseconds in cell membranes exposed to high-intensity (MV/m) nanosecond pulsed electric fields (nsPEFs), and while it is clear that polar water molecules play a key role in electroporation, no signature for pore initiation has yet been identified. To address this, we combine molecular dynamics simulations and quasi-static 3-D finite-difference analysis to investigate the electrostatic interactions that drive pore formation in homogenous lipid bilayers exposed to intense nsPEFs. The developed methodology uniquely enables the extraction of 3-D spatiotemporal profiles of electric potentials, electric fields, and electric field gradients in biological membranes with atomistic detail and sub-nanosecond resolution. As a result, this study captures and elucidates several dynamic phenomena observed experimentally and provides a fundamental framework for further development.

Electrical Measurements for Nanosecond Repetitive Pulsed Discharges

In this paper, a device for accurate electrical measurements for nanosecond repetitive pulsed discharges (NRPDs) is presented. The experimental setup developed is based on an interelectrode system integrated in a transverse electromagnetic cell. This setup allows synchronizing the voltage and current measurements with a 4-GHz frequency bandwidth, corresponding to 250-ps pulse duration. A coaxial-shaped sharp metallic needle serves as a probe for current measurements. The needle probe is also the point electrode of a point-to-plane system used to generate discharges. The experimental setup was used to electrically characterize NRP corona and diffuse discharges, in negative polarity. Discharge current pulses with rise times less than 1 ns and amplitudes up to 120 mA were measured. The energy deposited by discharges was also determined.