Small Sensor Elements Research Articles

Near-field metasurface sensor for an early-stage breast cancer detection

In this paper, a novel and highly sensitive metasurface sensor for microwave breast tumor detection is proposed. The proposed sensor array comprises 8 × 8 small-size sensor elements that are capable of reacting to changes in both electric and magnetic fields. This allows the sensor to detect even minor variations in the surrounding medium, resulting in improved sensitivity. Additionally, designing a sensor array improves sensitivity by covering all areas of the breast tissues with multiple small sensor elements. Numerical studies have been conducted to assess the sensor sensitivity using realistic healthy and non-healthy breast models with diagnosed tumors placed at different locations within healthy breast models in the CST simulation environment at varying stand-off distances. An experiment was conducted to validate the sensor’s concept. It involved testing a metasurface sensor with phantoms resembling both healthy female breast tissues and those with a 10 mm tumor. The results from simulations and experiments demonstrate that the metasurface sensor is capable of detecting breast tumors at different distances. For safety compliance, specific absorption rate (SAR) values were obtained through both simulation and experimentation. The simulated SAR values were calculated to be 0.357 W/kg and 0.216 W/kg at 1 g and 10 g, respectively, using 17 dBm for safety. The measured SAR values were 0.101 W/kg and 0.1 W/kg at 1 g and 10 g, respectively.

MTF and DQE enhancement using an apodized-aperture x-ray detector design.

Acquisition of high-quality x-ray images using low patient exposures requires detectors with high detective quantum efficiency (DQE). We describe a novel apodized-aperture pixel (AAP) design that increases high-frequency modulation transfer function (MTF) and DQE values. The AAP design makes a separation of physical sensor elements from image pixels by using very small sensor elements (e.g., 0.010-0.025 mm) to synthesize desired larger image pixels (e.g., 0.1-0.2 mm). A cascaded systems model of signal and noise propagation is developed to describe the benefits of the AAP approach in terms of the MTF, Wiener noise power spectrum (NPS), and DQE. The theoretical model was validated experimentally using a CMOS/CsI detector with 0.05 mm sensor elements to synthesize 0.20 mm image pixels and a clinical Se detector with 0.07 mm sensor elements to synthesize 0.28 mm pixels. A Monte Carlo study and x-ray images of a star-pattern and rat leg are used to visually compare AAP images. When used with a high-resolution converter layer and sensor elements one quarter the size of image pixels, the MTF is increased by 53% and the DQE by a factor of 2.3× at the image sampling cut-off frequency. Both simulated and demonstration images show improved detectability of high-frequency content and removal of aliasing artifacts. Evidence of Gibbs ringing is sometimes seen near high-contrast edges. It is shown that the AAP approach preserves the MTF of the small sensor elements and attenuates frequencies above the image sampling cut-off frequency. This has the double benefit of improving the MTF while reducing both signal and noise aliasing, resulting in an increase of the DQE at high spatial frequencies. For optimal implementation, the converter layer must have very high spatial resolution and the detector must have low readout noise.

1112 ロボット指用分布型触覚センサのための小型センサ素子の開発とその特性評価(制御用センサ・アクチュエータ)

1112 ロボット指用分布型触覚センサのための小型センサ素子の開発とその特性評価(制御用センサ・アクチュエータ)

Magnetostrictive LC Circuit Sensors

Highly sensitive sensors for strain or stress measurements are of increasing interest for industrial applications in areas like automotive, aerospace, process control, automation and biotechnology. In comparison to classical metallic or piezoresistive strain gauges, magnetostrictive thin film sensors show a higher sensitivity, almost no substrate limitations, and allow the fabrication of small sensor elements. Furthermore, the LC circuit sensor design allows wireless operation using either radar reflectivity or inductive coupling. Inverse magnetostriction (Villari effect) is a powerful transducer mechanism for strain sensors. As a result of the inverse magnetostriction the orientation of the magnetic domains changes in response to an applied strain. An illustration of this mechanism is given in Fig. 1. The figure shows domain rotation of small FeCoBSi discs on a Si substrate. The stress was applied perpendicular to the initial domain orientation and increased from left to right. The sense of the rotation is determined by the sign of both the magnetostriction and the strain and by the initial magnetic domain pattern. In materials with positive magnetostriction the saturation domain orientation will be preferably parallel or antiparallel to the direction of the tensile strain, while compressive strains will induce a perpendicular domain pattern. This relationship is reversed for materials with negative magnetostriction. In combination with other effects this change of the domain pattern can be transferred into an electrical signal. The rotation of the domains influences e.g. the magnetic permeability of the magnetostrictive material as shown in a VSM measurement in Fig. 2. This change in permeability can also be detected by impedance- 1,2) or inductivity measurements. 3)

Field distributions in rotational single sheet testers

This paper concerns rotational single sheet testers (RSST) as applied for investigations of laminated soft magnetic materials. Most RSSTs use a square 64 cm 2 sample with rather small sensor elements. They yield effective average loss values for fine-grained SiFe rotationally magnetized up to 1,2 T. For highly grain oriented (h.g.o.) SiFe sheets, characterized by large grain size and high crystallographic order, we have developed a 3-phase exited RSST which uses a hexagonal sample of 166 cm 2 area. It allows for increased induction values and for the application of large, well averaging sensors, the degree of flux homogeneity however being questionable. The aim of this study was a numerical estimation of the actual conditions of homogeneity for the two set-ups. Calculation was performed for the whole apparatuses by means of 2-dimensional FEM. The material was assumed to show uniaxial anisotropy with orthogonal principal directions for the permeability tensor. For both RSSTs, the results indicate good homogeneity of the induction vector B for the entire sample area. Effects of air gaps between sample and yokes prove to be less critical in the hexagonal case. In a second step, a heterogeneous model was used to simulate the magnetically hardest 55°-direction of Goss-textured material. With respect to the areally averaged vector interdependence between B and H, a comparison with measured results shows good qualitative agreement.

A study on impulsive pressure of a collapsing cavitation bubble. (Evaluation of the effect of a water microjet)

The motion of a spark-induced cavitation bubble is examined near a solid boundary by high-speed photography and the impulsive pressure generated at its collapse-reexpansion stage is detected by a local pressure sensor with four small sensor elements. As a result, the impulsive pressures of a shock wave and of a water microjet are separately measured by the local pressure sensor. The result is ascertained by high-speed photographs of the cavitation bubble, which indicate that a microjet is generated at the top surface of the collapsing bubble and collides against one of the pressure sensor elements through the interior of the bubble at its collapsing stage. Moreover, the diameter of the generated microjet tip and its travelling velocity through the interior of the bubble are evaluated to be about 0.5mm and 100110 m/s, respectively.

A study on impulsive pressure of a collapsing cavitation bubble. (Evaluation of the effect of a water microjet)

The motion of a spark-induced cavitation bubble was examined near a solid boundary by high-speed photography and the impulsive pressure generated at its collapsing stage was detected by a local pressure sensor, which was manufactured for trial with four small sensor elements. As a result the impulsive pressures of a shock wave and of a water microjet were separately measured by the local pressure sensor, and the results was ascertained by high-speed photographs of the cavitation bubble, which indicated a microjet was generated at the top surface of the collapsing bubble, impacting one of the pressure sensor elements through the bubble inside at its collapsing stage. Moreover, the diameter of the generated microjet tip and its travelling velocity through the bubble inside were evaluated to be about 0.5 mm and 100110 m/s, respectively.