L. Fu

Rapid microwave phase detection based on a solid state spintronic device

A technique for rapidly detecting microwave magnitude and phase has been developed using a spintronic device as a microwave sensor, which allows a lock-in amplifier to perform real-time microwave measurement. To demonstrate the feasibility and reliability of the proposed approach, the resonance including the amplitude and phase in a complementary electric inductive-capacitive resonator has been characterized. The results are in agreement with measurement preformed by a vector network. This sensor approach is not limited for use only with spintronic devices, but can also be used with semiconductor devices and hence offers a useful alternative to existing microwave imaging and characterization technologies.A technique for rapidly detecting microwave phase has been developed which uses a spintronic device that can directly rectify microwave fields into a dc voltage signal. Use of a voltage-controlled phase shifter enables the development of a spintronic device that can simultaneously ”read” the magnitude and phase of incident continuous-wave (CW) microwaves when combined with a lock-in amplifier. As an example of many possible practical applications of this device, the resonance phase in a complementary electric inductive-capacitive (CELC) resonator has been characterized using a spintronic sensor based on a magnetic tunnel junction (MTJ). This sensor device is not limited for use only with spintronic devices such as MTJs, but can also be used with semiconductor devices such as microwave detectors, and hence offers a useful alternative to existing microwave imaging and characterization technologies.

Nondestructive two-dimensional phase imaging of embedded defects via on-chip spintronic sensor

A microwave near field phase imaging technique has been achieved by an on-chip spintronic sensor. The sensor directly rectifies a microwave field into a dc voltage signal by employing the spintronic principle, in which the relative phase between microwave electric and magnetic fields plays an important role. By manipulating the relative phase, the sensor can nondestructively detect embedded defects of subwavelength size.

Microwave reflection imaging using a magnetic tunnel junction based spintronic microwave sensor

A far-field microwave imaging technique has been developed using a spintronic sensor based on a magnetic tunnel junction (MTJ). Such a sensor can directly rectify a microwave field into a dc voltage signal using the Seebeck effect. Thanks to the high conversion efficiency of the microwave rectification in MTJs, the microwave power sensitivity of the spintronic sensor is on the order of 1–10 mV/mW. This high sensitivity allows the sensor to directly measure the coherent spatial scattered microwave field distribution, which gives it the ability to non-destructively detect hidden objects down to a few wavelengths in size.

Microwave holography using a magnetic tunnel junction based spintronic microwave sensor

In this work, a spintronic sensor based microwave holographic imaging system is developed, demonstrating the feasibility of microwave holographic imaging applications using a spintronic microwave sensor. The high sensitivity of the microwave phase measurement allows the coherent imaging of the target reconstructed in noise environments. Adapting the broadband measurement, not only the shape but also the distance of target can be determined, which implies that a three-dimensional imaging is achievable using a spintronic device.

Life signal detection using an on-chip split-ring based solid state microwave sensor

A technique for measuring the amplitude and frequency of breathing and heartbeat has been developed using an on-chip solid state sensor integrating a semiconductor microwave sensor and a split ring operating at a resonance frequency of 4.2 GHz. This technique allows the lock-in amplifier to make real-time measurements, analogous to measurements taken by a vector network analyser through an antenna, but with the advantage of being portable and having a user friendly DC output. The effectiveness of this approach is shown by performing several experiments to determine the breathing and heartbeat frequency with and without the presence of an obstacle between the test subject and the microwave sensor and transducer. The experimental results demonstrate the high sensitivity and large dynamic range over which the proposed system can be used for practical applications.

Ground penetrating detection using miniaturized radar system based on solid state microwave sensor

We propose a solid-state-sensor-based miniaturized microwave radar technique, which allows a rapid microwave phase detection for continuous wave operation using a lock-in amplifier rather than using expensive and complicated instruments such as vector network analyzers. To demonstrate the capability of this sensor-based imaging technique, the miniaturized system has been used to detect embedded targets in sand by measuring the reflection for broadband microwaves. Using the reconstruction algorithm, the imaging of the embedded target with a diameter less than 5 cm buried in the sands with a depth of 5 cm or greater is clearly detected. Therefore, the sensor-based approach emerges as an innovative and cost-effective way for ground penetrating detection.

Experimental feasibility of multistatic holography for breast microwave radar image reconstruction.

PURPOSE The goal of this study was to assess the experimental feasibility of circular multistatic holography, a novel breast microwave radar reconstruction approach, using experimental datasets recorded using a preclinical experimental setup. The performance of this approach was quantitatively evaluated by calculating the signal to clutter ratio (SCR), contrast to clutter ratio (CCR), tumor to fibroglandular response ratio (TFRR), spatial accuracy, and reconstruction time. METHODS Five datasets were recorded using synthetic phantoms with the dielectric properties of breast tissue in the 1-6 GHz range using a custom radar system developed by the authors. The datasets contained synthetic structures that mimic the dielectric properties of fibroglandular breast tissues. Four of these datasets the authors covered an 8 mm inclusion that emulated a tumor. A custom microwave radar system developed at the University of Manitoba was used to record the radar responses from the phantoms. The datasets were reconstructed using the proposed multistatic approach as well as with a monostatic holography approach that has been previously shown to yield the images with the highest contrast and focal quality. RESULTS For all reconstructions, the location of the synthetic tumors in the experimental setup was consistent with the position in the both the monostatic and multistatic reconstructed images. The average spatial error was less than 4 mm, which is half the spatial resolution of the data acquisition system. The average SCR, CCR, and TFRR of the images reconstructed with the multistatic approach were 15.0, 9.4, and 10.0 dB, respectively. In comparison, monostatic images obtained using the datasets from the same experimental setups yielded average SCR, CCR, and TFRR values of 12.8, 4.9, and 5.9 dB. No artifacts, defined as responses generated by the reconstruction method of at least half the energy of the tumor signatures, were noted in the multistatic reconstructions. The average execution time of the images formed using the proposed approach was 4 s, which is one order of magnitude faster than the current state-of-the-art time-domain multistatic breast microwave radar reconstruction algorithms. CONCLUSIONS The images generated by the proposed method show that multistatic holography is capable of forming spatially accurate images in real-time with signal to clutter levels and contrast values higher than other published monostatic and multistatic cylindrical radar reconstruction approaches. In comparison to the monostatic holographic approach, the images generated by the proposed multistatic approach had SCR values that were at least 50% higher. The multistatic images had CCR and TFRR values at least 200% greater than those formed using a monostatic approach.

Electromagnetic Field Enhancement and Its Application in Spin Rectification

A subwavelength antenna, which has the capability to enhance both the microwave electric and magnetic fields, is proposed for use in spintronic devices. The geometric resonance of the microwave electric and magnetic fields in the antenna are determined by spintronic techniques, and are in remarkable agreement with measurements taken using a vector network analyzer and simulations based on the finite-difference time-domain method. Our simulations predict that the performance of a spin dynamo may be improved by three orders of magnitude if properly integrated with this antenna on-chip.

Through-wall bio-radio location and characterization of human activities

In this paper, a through-the-wall life detection system has been developed by using a broadband microwave technique. This system can not only determine and characterize human movement behind an obstacle but also determine the persons position by employing the Fourier transform technique. The effectiveness of this system is shown by the experimental results where the presence of stationary and moving person behind an obstacle can be identified upto a distance of 17 and 30 m respectively. Since the movement of a human body is continuous, an averaged background subtraction technique has been developed which allows real time detection of human activities without requiring any prior knowledge of the environment, thus making the system suitable for practical applications.

Detection of concealed targets using spintronic microwave sensor

In this paper, we demonstrate the feasibility of microwave holographic imaging application based on spintronic microwave sensors. By adapting the rapid phase detection technique, a magnetic tunnel junction can achieve a real-time measurement of both the amplitude and phase of the scattered microwave using a lock-in amplifier. The built system has a capability to detect not only the existence of the concealed objects but also their shapes, allowing the concealed threat to be distinguished along with other hidden objects. The system is also able to estimate the distance of target by a broadband measurement. Anticipating the phase-detection of the dielectric function of the targets, we have also carried out extensive density functional theory calculations for a number of condensed phase energetic materials to determine their dielectric response in the microwave range.