Zheng Yuanjin

Photoacoustic-Based-Close-Loop Temperature Control for Nanoparticle Hyperthermia.

Goal: Hyperthermia therapy requires tight temperature control to achieve selective killing of cancerous tissue with minimal damage on surrounding healthy tissues. Methods: To this end, accurate temperature monitoring and subsequent heating control are critical. However, an economic, portable, and real-time temperature control solution is currently lacking. To bridge this gap, we present a novel portable close-loop system for hyperthermia temperature control, in which photoacoustic technique is proposed for noninvasive real-time temperature measurement. Exploiting the high sensitivity of photoacoustics, the temperature is monitored with an accuracy of around 0.18 °C and then fed back to a controller implemented on field programmable gate array (FPGA) for temperature control. Dubbed as portable hyperthermia feedback controller (pHFC), it stabilizes the temperature at preset values by regulating the hyperthermia power with a proportional-integral-derivative (PID) algorithm; and to facilitate digital implementation, the pHFC further converts the PID output into switching values (0 and 1) with the pulse width modulation (PWM) algorithm. Results: Proof-of-concept hyperthermia experiments demonstrate that the pHFC system is able to bring the temperature from baseline to predetermined value with an accuracy of 0.3° and a negligible temperature overshoot. Conclusion: The pHFC can potentially be translated to clinical applications with customized hyperthermia system design. Significance: This paper can facilitate future efforts in seamless integration of close-loop temperature control solution and various clinical hyperthermia systems.

A novel channel estimation and tracking method for wireless OFDM systems based on pilots and Kalman filtering

In this paper, a new on-line channel estimation and tracking method for wireless OFDM systems based on comb-type pilots is developed. Long training sequences are used to estimate the channel response in frequency domain, and a scalar Kalman filtering scheme is designed to refine the channel estimation. To track the channel variations during a long burst packet, estimated pilots via a vector Kalman filtering are used to linearly interpolate and modify the estimated channel response. Both channel AWGN and state variable noise variance are adaptively estimated. Furthermore, to overcome the phase changes across the symbols owing to frequency offset estimation error, pilot based phase compensation scheme is incorporated. The complete algorithm can be processed in real time with much better performance than training sequence based or pilots based channel estimation methods. Simulation results based on 802.11a wireless LAN standard are presented.

Self tuned fully integrated high image rejection low IF receivers: architecture and performance

Two new architectures of fully integrated low inter-mediate frequency (IF) receiver with high image rejection ratio (IRR) are proposed in this paper. Image rejection is realized by following an in-phase and a quadrature (I/Q) mixers with a complex filter which is tuned to the desired IF signal passband. To eliminate the phase mismatch of I/Q local oscillators and the gain mismatch of I/Q mixers, two new compensation techniques are developed. One is with a feedback loop and two variable gain amplifiers (VGA). The gains of two VGAs are self tuned through a feedback loop so that both the I/Q amplitude and phase mismatches in the forward receiver can be eliminated. The other employs two tuning loops, which are designed to automatically compensate the I/Q amplitude and phase mismatches separately. After the compensation, the IRRs of these two architectures both can be significantly improved (to /spl sim/70 dB). The proposed low IF receivers are self tuned image rejection systems with very fast settling time and high adjusting precision. They can be fully integrated and applied in most of wireless receiver systems including GSM, DECT, WCDMA, Bluetooth and wireless LAN etc. Simulation results for a Bluetooth receiver as well as a GSM receiver are presented.

A Low-Voltage Low-Power High Linear and Wide-Band Mixer

This paper describes a low-voltage low-power high linear wideband down conversion mixer based on chartered 0.18 mum RF CMOS technology. By introducing cross coupled NMOS transistors in the transconductance stage as well as an IIP2 intermodulation current path to the folded cascode Gilbert cell structure, this design can achieve a voltage conversion gain of 5.8 dB, power conversion gain of 5.6 dB, IIP3 of -1.3 dBm and IIP2 of +70.7 dBm at a 1 V supply voltage. The design consumes 4 mA current consumption and gives a good noise performance of 9.3 dB. This mixer is designed to operate at a frequency bandwidth of 3-5 GHz.

A cognitive radio receiver front-end IC based on spread spectrum sensing technique

Spectrum sensing in cognitive radio is an important part to detect unknown signal(s). This paper introduces a spread spectrum technique for spectrum sensing in cognitive radio in order to detect the availability of input spectrum within 800MHz to 3.5GHz frequency band. The designed receiver front-end IC can achieve the simulated gain of 30dB, QVCO phase noise of -117dBc/Hz at 1MHz offset at 2.4GHz carrier, noise figure of 5.3dB, IIP3 of -21dBm and total power dissipation of 90mW, including VCO and Mixer buffer.

Magnetically mediated thermoacoustic imaging and technical considerations on its coil design

Magnetically mediated thermoacoustic imaging exploits the electromagnetic spectrum of radio frequency magnetic field under 20 MHz to perform thermoacoustic imaging, which can provide deeper penetration than microwave or light irradiation. To achieve effective imaging, current implementation relies on magnetic resonance of the coil to deliver sufficiently strong magnetic field into conductive objects, including tissues. Different kind of coils can be utilized, which affects both the magnetic field distribution and the design of the resonance circuits. We investigated here those various coils and their implications for the imaging system. Preliminary thermoacoustic signal generation and imaging results are also presented.

Design and experimental investigation of UWB microwave imaging via MIMO beamforming

Multiple-input multiple-output (MIMO) beamforming, a new technique for ultra-wideband microwave imaging is being investigated. An experimental model is being constructed to test the approach. Using a UWB pulse of 4 GHz central frequency and 0.4 ns pulse width, differential UWB antennas and a pseudo-breast model, the proposed MIMO approach was adopted and yielded excellent results. The results are compared to a monostatic and a bistatic delay-and-sum beamformer and it was proven that the MIMO approach was far more superior. This suggests that UWB pulse technology is indeed feasible for real tumour detection and MIMO beamforming has the potential to produce accurate tumour images with acceptable resolution.

FEM modelling of a SAW microfluidic sensor based on the photoacoustic effect

Surface acoustic wave (SAW) integrated with microfluidics has been used for various acoustofluidic applications including sensing mechanical properties of fluids such as viscosity and density of fluids. We have recently demonstrated the excitation of a surface acoustic wave using the photoacoustic (PA) effect in a microfluidic channel. The opto-mechanical properties of the liquids in the microchannel can be detected using the mode-converted SAW. In this work, we investigated the response mechanism of the sensor using detailed numerical FEM simulation. The simulation study has shown that the microfluidic channel on the substrate acts as an acoustic resonator with multiple eigen modes. PA signals generated inside the microfluidic channel resonates at these modes. The displacement profile on the piezoelectric surface confirmed that the pressure mode propagating parallel to the piezoelectric substrate has the highest mode conversion efficiency (longitudinal wave to SAW). This mode is sensitive to the microchannel dimensions. The study has shown that a SAW device matched to this mode-frequency could be used for improving the sensitivity of the sensor. Experimental observation confirmed the theory.

A non-invasive magnetic resonance biomedical system

This paper proposes a pair of coils coupled by magnetic resonance coupling, which effectively induced a current at the biological medium for potential biomedical applications. Calculations and field estimation was done using finite element modeling software. Ferrite cores were added to the setup which showed larger induced current density in the tissue (more than 2 times) due to eddy current generation, as compared to the coils without core. Further, experiments were conducted with an animal tissue placed between two resonating coils, which showed similar results with an induced current of 0.07 mA using 1NI coil. Also, 1.6 times larger current was induced in the tissue when ferrite cores were used as compared to air core.

MIMO ultra-wideband system for breast cancer detection

In this paper, we study the use of ultra-wideband (UWB) system for early breast cancer detection. Images are formed using a number of advanced imaging algorithms, and the effectiveness of the different algorithms are presented and compared. In addition, the use of multiple input multiple output (MIMO) systems are studied and the experiments results are presented.