Changyul Cheon

A Wideband Spiral Antenna for Ingestible Capsule Endoscope Systems: Experimental Results in a Human Phantom and a Pig

This paper presents the design of a wideband spiral antenna for ingestible capsule endoscope systems and a comparison between the experimental results in a human phantom and a pig under general anesthesia. As wireless capsule endoscope systems transmit real-time internal biological image data at a high resolution to external receivers and because they operate in the human body, a small wideband antenna is required. To incorporate these properties, a thick-arm spiral structure is applied to the designed antenna. To make practical and efficient use of antennas inside the human body, which is composed of a high dielectric and lossy material, the resonance characteristics and radiation patterns were evaluated through a measurement setup using a liquid human phantom. The total height of the designed antenna is 5 mm and the diameter is 10 mm. The fractional bandwidth of the fabricated antenna is about 21% with a voltage standing-wave ratio of less than 2, and it has an isotropic radiation pattern. These characteristics are suitable for wideband capsule endoscope systems. Moreover, the received power level was measured using the proposed antenna, a circular polarized receiver antenna, and a pig under general anesthesia. Finally, endoscopic capsule images in the stomach and large intestine were captured using an on-off keying transceiver system.

A V-band micromachined 2-D beam-steering antenna driven by magnetic force with polymer-based hinges

This paper presents a new type of antenna fabricated by micromachining technology for mechanical beam steering with two degrees of freedom of motion. A V-band two-dimensional mechanical beam-steering antenna was designed and fabricated on a single high-resistivity silicon substrate using microelectromechanical systems technologies. A fabricated antenna is driven by magnetic force to overcome the limit of electrostatic actuation, and a polymer-based hinge structure is used to increase the maximum scanning angle to as much as 40/spl deg/. Simulation result for validating the mechanical beam-steering concept is presented. In addition, mechanical properties such as static actuation angles are investigated together with microwave properties such as the return loss and radiation pattern at the V-band.

Optimal shape design of microwave device using FDTD and design sensitivity analysis

In this paper, a novel optimal shape design method is proposed using the finite-difference time-domain (FDTD) method and the design sensitivity analysis to obtain broad-band characteristics of microwave devices. In shape design problem, the nodes that describe the shape of geometry to be optimized are taken as design variables. The design sensitivity is evaluated using the adjoint variable equation that is obtained from a terminal-value problem. The adjoint equation can be solved by the FDTD technique with the backward time scheme. With this method, a Ka-band unilateral fin line is tested to show validity.

Microwave detection of metastasized breast cancer cells in the lymph node; potential application for sentinel lymphadenectomy.

Metastasis is the leading cause of death in breast cancer patients and an appropriate detection of metastasis can provide better prognosis and quality treatments. Microwaves can reveal the unique electromagnetic properties of materials, and this study aims to unleash the electromagnetic properties of breast cancer cells, especially, metastasized cancer cells in the lymph nodes, using broad-band microwaves in attempts to detect metastases. To distinguish the cancer-specific patterns of cancer tissues, three primary microwave parameters were assessed, i.e., permittivity in mid-band frequency (3–5 GHz), conductivity in high-band frequencies (25–30 GHz) and slope changes of permittivity at high-band frequencies (15–30 GHz). An additional parameter, Cancer Metastasis Index (CMI), was developed to effectively represent all parameters. Broadband microwave scanning can reveal cancer specific electromagnetic behaviors in all three parameters, and these were reliably reflected by CMI. CMI effectively magnified the difference of the electromagnetic properties between normal nodal tissues and cancer tissues. immunohistochemistries were performed to verify the origin of electromagnetic changes represented by CMI values.

Novel low-cost planar probes with broadside apertures for nondestructive dielectric measurement of biological materials at microwave frequencies

Novel planar-type probes were developed to demonstrate the possibility of replacing the existing high-cost open-ended coaxial probes. The planar probes of this study define an aperture on the broadside of the probe body. In this way, the contact area can be maximized and/or customized according to specific medical needs. The probes with various aperture sizes and shapes can also be fabricated simultaneously in a single batch process. Three probes are developed in this paper: a probe combining two laminates, a microelectromechanical systems (MEMS)-based probe with a single benzocyclobutene (BCB) layer on a quartz substrate, and another MEMS probe with two BCB layers defined on a silicon substrate. The third probe was specifically designed for monolithic integration with driving circuits on a single substrate. Limitations in the high-frequency performance of the planar probes were carefully studied, and higher order modes and incomplete shielding were found to be the main causes. The measurement results of each probe showed excellent compatibility with those of the open-ended coaxial probe up to almost 40 GHz. The proposed planar-type probes have great potentials for practical medical applications in view of low cost, disposability, and monolithic integration capability with the driving circuits.

Nondestructive measurement of complex permittivity and permeability using multilayered coplanar waveguide structures

A method for simultaneous measurement of both complex permeability and permittivity is presented using a multilayered conductor-backed coplanar waveguide (MCBCPW) structure to evaluate the possibility of MCBCPW as a sensor for nondestructive electromagnetic measurement. Formulae and methods are developed to extract the electromagnetic parameters of material under test (MUT) placed on the topside of CPW. The measurement results for magnetic powder on MCBCPW sensor showed good agreement with those using coaxial sensors. The method allows both permittivity and permeability to be measured in a single-step measurement without modifying or reshaping the material, making this method particularly attractive for inhomogeneous materials such as biological materials.

A Design of a High-Speed and High-Efficiency Capsule Endoscopy System

This paper presents a high-speed and high-efficiency capsule endoscopy system. Both a transmitter and a receiver were optimized for its application through an analysis of the human body channel. ON-OFF keying modulation is utilized to achieve low power consumption of the in-body transmitter. A low drop output regulator is adopted to prevent performance degradation in the event of a voltage drop in the battery. The receiver adopts superheterodyne structure to obtain high sensitivity, considering the link budget from the previous analysis. The receiver and transmitter were fabricated using the CMOS 0.13-μm process. The output power of the transmitter is -1.6 dB·m and its efficiency is 27.7%. The minimum sensitivity of the receiver is -80 dB·m at a bit error ratio (BER) of 3 × 10 . An outer wall loop antenna is adopted for the capsule system to ensure a small size. The integrated system is evaluated using a liquid human phantom and a living pig, resulting in clean captured images.

110 GHz broadband measurement of permittivity on human epidermis using 1 mm coaxial probe

In this work, we have characterized the permittivity of human epidermis (outer skin layer) using microwave up to 110 GHz. A one mm-diameter coaxial probe was adopted to increase measuring bandwidth as well as to enhance the spatial resolution. Pork was used to discriminate the permittivities between muscle tissues and fat tissues. The influence of the sample thickness was also. studied. Considering several factors, the permittivity was measured on epidermis of the human palm and the wrist. In addition, a relaxation phenomenon observed in the wrist skin, revealed by Cole-Cole parameters, suggested that it originated from high water content beneath the thin epidermis of the wrist skin. A relaxation phenomenon revealed by Cole-Cole parameters was observed in the wrist skin. This explains that high water content cells exist beneath the thin epidermis of the wrist skin.

High-frequency microwave ablation method for enhanced cancer treatment with minimized collateral damage

To overcome the limits of conventional microwave ablation, a new frequency spectrum above 6 GHz has been explored for low‐power and low collateral damage ablation procedure. A planar coaxial probe‐based applicator, suitable for easy insertion into the human body, was developed for our study to cover a wideband frequency up to 30 GHz. Thermal ablations with small input power (1–3 W) at various microwave frequencies were performed on nude mice xenografted with human breast cancer. Comparative study of ablation efficiencies revealed that 18‐GHz microwave results in the largest difference in the temperature rise between cancer and normal tissues as well as the highest ablation efficiency, reaching 20 times that of 2 GHz. Thermal profile study on the composite region of cancer and fat also showed significantly reduced collateral damage using 18 GHz. Application of low‐power (1 W) 18‐GHz microwave on the nude mice xenografted with human breast cancer cells resulted in recurrence‐free treatment. The proposed microwave ablation method can be a very effective process to treat small‐sized tumor with minimized invasiveness and collateral damages.

Permittivity measurements up to 30 GHz using micromachined probe

We implemented a micromachined probe for the measurement of biological properties using MEMS technology, and experimentally showed the suitability of the micromachined probe in biological applications. The micromachined probe was fabricated on a silicon substrate, and to remove wave transmission through the silicon substrate, we etched the silicon substrate from beneath a lower ground and made the etched silicon surface conducting by using thermal evaporation of Cr/Au and a coating of conductive epoxy. The micromachined probe consists of a CPW and strip line between benzo cyclo butene (BCB) layers, which is known to be a material with high resistivity, low loss tangent, and low permittivity at high frequency. We measured the permittivity of a number of well-known liquids—0.5%, 0.9% and 1.3% saline, acetone, ethanol, and muscle and fat of pork—as biological samples using the micromachined probe after liquid calibration. The measured permittivity of 0.9% saline agreed well with the expected value of the Cole–Cole equation. In this paper, we first demonstrate that the micromachined probe can provide broadband measurement of measurable solid materials, such as biological samples, and also of well-known liquids at microwave frequencies. The size of the micromachined probe is 2000 µm (width) × 580 µm (thickness) × 30 000 µm (length), and the aperture size of the micromachined probe is only 650 µm × 70 µm. Therefore, we can extract the biological information from very small biological tissues and reduce radiation effects. Thus we show the feasibility of low-cost, small and portable permittivity measurement systems using a micromachined open-ended coaxial RF MEMS probe.