Barry Friedman

Microwave dielectric resonator biosensor for aqueous glucose solution

We report a near-field microwave biosensor based on a dielectric resonator to detect glucose concentration. A microwave biosensor with a high Q dielectric resonator allows observation of the small variation of the glucose concentration by measuring the shift of the resonance frequency and the microwave reflection coefficient S(11). We observed the concentration of glucose with a detectable resolution up to 5 mgml at an operating frequency of about f=1.68 GHz. The change in the glucose concentration is directly related to the change in the reflection coefficient due to the electromagnetic interaction between the dielectric resonator and the glucose solution.

Development of a near-field scanning microwave microscope using a tunable resonance cavity for high resolution

We report on the operational principles and the practical implementation of a near-field scanning microwave microscope system consisting of a λ/4 coaxial resonator with a tunable resonance cavity coupled to a sharp probe tip. The changes of sensitivity and spatial resolution as a function of cavity length are clearly modulated by tuning the resonance cavity. By tuning the resonance cavity, we demonstrate improved sensitivity and spatial resolution better than 4 µm of the near-field images of a YBa2Cu3Oy thin film on a MgO substrate at an operating frequency of f = 1–1.5 GHz. We modelled the λ/4 coaxial resonator by a LCR circuit and the principles of operation can be explained by using perturbation theory, considering the radius of the probe tip, the quality factor, impedance matching, and the sample–tip distance.

Near-field scanning microwave microscope using a dielectric resonator

We describe a near-field scanning microwave microscope which uses a high-quality dielectric resonator with a tunable screw. The operating frequency is f=4.5 GHz. The probe tip is mounted in a cylindrical resonant cavity coupled to a dielectric resonator for the TE011 mode. We tuned the resonance cavity to match the impedance of 50 Ω by using a tunable screw and could improve sensitivity and spatial resolution to better than 1 μm. To demonstrate the ability of local microwave characterization, the surface resistance dependence of the metallic thin films on film thickness has been mapped.

Distance control for a near-field scanning microwave microscope in liquid using a quartz tuning fork

We demonstrate a scanning near-field microwave microscope (NSMM) in the liquid environment using a tuning fork shear-force feedback method to control the distance between tip and sample. Only the probe tip for the NSMM is immersed in water. The dry part of the probe is attached to one prong of a quartz tuning fork and directly coupled to a high-quality dielectric resonator at an operating frequency f=4.5–5.5GHz. This distance control method is independent of the local microwave characteristics. The amplitude of the tuning fork was used as a set point of the distance control parameter in the liquid. To demonstrate the distance regulation system, we present the NSMM images of a copper film in air and liquid without and with readjustment of the distance set point, as well as an image of a DNA film in buffer solution. Imaging under buffer environments is of particular interest for future studies of biomolecular association reactions on solid supports.

Sodium chloride sensing by using a near-field microwave microprobe

The authors observed the NaCl concentration of solutions using a near-field microwave microprobe (NFMM). Instead of the usual technique, they take advantage of the noncontact evaluation capabilities of a NFMM. A NFMM with a high Q dielectric resonator allows observation of small variations of the permittivity due to changes in the NaCl concentration. By measuring the reflection coefficient S11, they could observe the concentration of NaCl. The measured signal-to-noise was about 53dB and the minimum detectible signal was about 0.005dB∕(mg∕ml). In order to determine the probe selectivity, they measured a mixture solution of NaCl and glucose.

Tip–sample distance control for near-field scanning microwave microscopes

We demonstrate a near-field scanning microwave microscope (NSMM) which uses a tuning fork shear-force feedback method to control the distance between tip and sample. This distance control method is independent of local microwave characteristics. The probe tip for the NSMM is attached to one prong of a quartz tuning fork and directly coupled to a high-quality microstrip resonator with a dielectric resonator at an operating frequency of f=4.5–5.5 GHz. The amplitude of the tuning fork was used as a distance control parameter in the feedback system. To demonstrate the ability of the distance regulation system, we present topographic images of an uneven conducting metal sample and compare the height response and the NSMM image.

Spin-polarized quasiparticle tunnel injection in a YBa2Cu3Oy/Au/Co junction

We report the strong suppression of YBa2Cu3Oy (YBCO) supercurrent by injection of spin-polarized quasiparticles (QP) using a cobalt ferromagnetic injector. The injection of spin-polarized QP generates a substantially larger nonequilibrium population as compared with that of an unpolarized injection current. The observed current gain depends on the thickness of Au interlayer (dAu) and is directly related to the nonequilibrium magnetization due to spin relaxation effects. For dAu=15 nm, the tunnel characteristic a YBCO/Au/Co junction exhibited a zero bias conductance peak, which may be interpreted by spin scattering processes at a ferromagnetic/d-wave superconductor junction.

Noninvasive in vitro measurement of pig-blood D-glucose by using a microwave cavity sensor

We have developed an electromagnetic microwave cavity sensor based on the resonant frequency shift for real time measurement of the glycemia in pig blood. We could determine the concentration of d-glucose in pig blood in the range of 150-550mg/dl at the resonance frequency near 4.75GHz with a bandwidth of 300MHz. The change in the d-glucose concentration in blood brings microwave reflection coefficient S(11) changes of about 6.26dB and resonance frequency shifts of about 11.25MHz due to the electromagnetic interaction between the cavity resonator and the blood filled plastic tube inserted into the cavity. This proposed system provides a unique approach for real time noninvasive and contactless glucose monitoring.

Improving images from a near-field scanning microwave microscope using a hybrid probe

We fabricated a near-field scanning microwave microscope (NSMM) using a hybrid tip combining a reduced length of the tapered part with a small apex. In order to understand the function of the probe, we fabricated three different tips using a conventional chemical etching technique and observed three different NSMM images for patterned Cr films on glass substrates. These probe tips were coupled to a high-quality dielectric resonator at an operating frequency f=4.46 GHz. By using the hybrid tip, we demonstrated an improved, high-contrast NSMM image of lambda phage DNA on a glass substrate.

Real-Time Noninvasive Measurement of Glucose Concentration Using a Microwave Biosensor

We measured the glucose concentration by using the real-time electromagnetic interaction between probe-tip and glucose solution using a microwave biosensor. The microwave biosensor, consisting of a dielectric resonator coupled to the probe-tip, allows observation of the small variation of the glucose concentration changes in the ranges of 0–300 mg/ml by measuring the microwave reflection coefficient . We could observe the concentration of glucose with a detectable resolution up to 1 mg/ml at an operating frequency of about GHz. The change of the glucose concentration is directly related to the change of the reflection coefficient due to the electromagnetic interaction between the microwave resonator and the glucose solution. The operational principal is explained by the plane-wave solution model. The measured signal-to-noise ratio was about 37 dB, and the minimum detectible signal was about 0.003 dB/(mg/ml). A glucose biosensor using a microwave resonator with probe provides a unique approach for glucose real-time monitoring.