Fritzi Töpfer

Micromachined 100GHz near-field measurement probe for high-resolution microwave skin-cancer diagnosis

This paper reports for the first time on a novel micromachined millimeter-wave near-field measurement probe for skin-cancer diagnosis, which is designed for high lateral resolution for resolving small skin cancer speckles as well as for vertically discriminating shallow tissue-layer anomalies. A tip size as small as 0.18 mm2, which is 18times smaller than conventional measurement tips for the design frequency of 100 GHz, could be achieved by micromachining a silicon-core tapered dielectric-rod waveguide. This metallized dielectric probe is positioned centrally into a standard WR-10 waveguide by a micromachined holder which allows for easily exchanging the probes at high reproducibility. The dielectric-wedge transition between the waveguide and the probe is optimized for 100–105 GHz. Furthermore, this paper presents a unique concept of micromachined test samples with tailor-made permittivity ranging from 1.7 to 7.1, which enables emulation of the different water content of tissue anomalies. This test method results in highly reproducible test measurements for evaluating and comparing different prototype probe designs. The paper presents successful measurement results of fabricated probes and test samples. Different single test samples as well as sample stacks with emulated tissue anomalies could clearly be distinguished.

Millimeter-Wave Near-Field Probe Designed for High-Resolution Skin Cancer Diagnosis

This paper presents a detailed technical characterization of a micromachined millimeter-wave near-field probe developed for skin cancer diagnosis. The broadband probe is optimized for frequencies from 90 to 104 GHz and consists of a dielectric-rod waveguide, which is metallized and tapered towards the tip to achieve high resolution by concentrating the electric field in a small sample area. Several probes with different tip sizes were fabricated from high-resistivity silicon by micromachining and were successfully characterized using silicon test samples with geometry-defined tailor-made permittivity. The probes show a high responsivity for samples with permittivities in the range of healthy and cancerous skin tissue at 100 GHz (from 3.2-j2.3 to 7.2-j8.0, loss tangent of approximately 1.26). The sensing depth was determined by simulations and measurements from 0.3 to 0.4 mm, which is adapted for detecting early-stage skin tumors before they metastasize. The lateral resolution was determined to 0.2 mm for a tip size of 0.6 × 0.3 mm, which allows for resolving small skin tumors and inhomogeneities within a tumor.

Dermatological verification of micromachined millimeter-wave skin-cancer probe

This paper presents for the first time measurement data on in-vivo dermatological experiments verifying the performance of a millimeter-wave medical probe designed for skin-cancer diagnosis. The probe consists of a micromachined silicon-core dielectric-rod waveguide, which is metallized and tapered at its tip as a compromise for high field concentration at the probe-to-skin interface, high sensitivity, high resolution, and an interaction volume depth adapted to diagnosing early-stage melanoma. The in-vivo dermatological tests on humans comprise: (1) measurement at different skin sites; (2) measurements of skin burns; (3) scanning the profile of benign skin neoplasma; (4) standardized dermatological tests with skin-irritant in 5 concentrations on 5 test persons, including monitoring of the healing process and reference measurements using a commercial transepidermal water loss instrument. All tests were successfully completed and show that millimeter-wave sensors are well capable of detecting physiologic changes of the skin and experimental skin reactions.

2-Dimensional near-field millimeter-wave scanning with micromachined probe for skin cancer diagnosis

This paper reports for the first time on the 2-dimensional scanning performance of a micromachined millimeter-wave (100 GHz) near-field probe with a substantially reduced tip size which is designed for skin cancer diagnosis. Furthermore, it introduces a novel concept of creating inhomogeneous test samples with tailor-made and locally altered permittivity which mimick skin tissue with small anomalies and are used for characterizing the probe. A probe prototype with a tip size of 300 × 600 μm2 and test samples with permittivity in the range of cancerous and healthy skin tissue were fabricated by micromachining and used for evaluating the sensitivity and resolution of the probe. This paper reports for the first time on 2-dimensional scanning performance, resolution, repeatability, long-term stability, and sensitivity, which are important for qualifying such measurement probes for medical applications. The resolution of the prototype, which is important for early detection of small tumor speckles, was found to be better than 200 μm, i.e. 1/6 of the medium-normalized wavelength. The reproducibility of the probe setup including operator uncertainty is 1.36% (1σ) and the long term stability of reference measurements is 0.59% (1σ) over 8 hours.

Millimeter wave silicon micromachined waveguide probe as an aid for skin diagnosis – results of measurements on phantom material with varied water content

More than 2 million cases of skin cancer are diagnosed annually in the United States, which makes it the most common form of cancer in that country. Early detection of cancer usually results in less extensive treatment and better outcome for the patient. Millimeter wave silicon micromachined waveguide probe is foreseen as an aid for skin diagnosis, which is currently based on visual inspection followed by biopsy, in cases where the macroscopical picture raises suspicion of malignancy.

Micromachined-silicon W-band planar-lens antenna with metamaterial free-space matching

In this work, we present for the first time a miniaturized planar W-band dielectric-lens antenna which is micromachined in a 300 µm silicon wafer. The antenna edge comprises a metamaterial anti-reflection geometry in order to reduce parasitic reflections at the free-space to high-permittivity dielectric interface. Furthermore, the dielectric lens is matched to a standard WR-10 metal waveguide by an optimized tapered dielectric-wedge transition. Prototype lens-antennas were fabricated in a single-mask micromachining process. The radiation pattern for the design frequency of 100 GHz was measured to 13° half-power beam-width in E-plane, a directivity of 14 dB, −15 dB side-lobe level, −15 dB reflected power for almost the whole W-band, for a lens diameter of 10 mm and an operating frequency of 100 GHz.

OPTIMIZATION OF MICROMACHINED MILLIMETER-WAVE PLANAR SILICON LENS ANTENNAS WITH CONCENTRIC AND SHIFTED MATCHING REGIONS

This paper presents a study of planar extended hemispherical lens antennas, fabricated from a high-resistivity silicon substrate. The high-permittivity lenses are matched to free-space using up to ...

Microwave cancer diagnosis

For many malignant tumors a different microwave signature as compared to the surrounding tissue has been observed. Thus microwave measurements and imaging can potentially aid the diagnosis of malignant tumors, and a multitude of techniques and systems have been developed during the past decades. Active techniques include, e.g., the evaluation of the complex permittivity of a sample by free-space quasi-optical techniques and near-field probes, as well as imaging by microwave tomography and ultra-wideband radar. Furthermore, passive microwave imaging systems and hybrid techniques have been suggested. The most advanced systems exist for breast cancer imaging, of which several have reached the stage of clinical trials. Other application areas for microwave cancer diagnosis are tumors of the skin as well as brain tumors.