Novel Piezoelectric Composite Systems for Biomedical and Industry Applications

Open Access
Author:
Mei, Lei
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
November 19, 2015
Committee Members:
  • Qiming Zhang, Dissertation Advisor
  • Qiming Zhang, Committee Chair
  • Qing X Yang, Committee Member
  • Zhiwen Liu, Committee Member
  • Mehdi Kiani, Committee Member
  • Michael T Lanagan, Committee Member
Keywords:
  • piezoelectric
  • magnetostrictive
  • magnetic sensor
  • transducer
  • iron detection
  • logging while drilling
Abstract:
In the past decades, piezoelectric sensors and transducers are widely used in various areas of modern technologies, such as medical technology, mechanical and automotive engineering, aerospace industry, etc. This dissertation investigates the two novel piezoelectric sensor and transducer configurations for applications in (i) biomagnetic signal detection; (ii) industry acoustic logging. One general approach through the entire dissertation is to theoretically analyze these novel piezoelectric composite systems, optimize composite structure design and develop fabrication/measurement strategies for real biomedical/industry applications. Two types of piezoelectric composite systems will be discussed in this dissertation: (i) magnetoelectric (ME) sensors and ME sensor based 1st order gradiometer system for biomagnetic liver susceptometry (BLS); and (ii) ceramic/polymer piezocomposite acoustic transducer system for logging while dilling (LWD). The ultra high sensitivity of piezoelectric sensors makes them good candidates for medical ultrasonic image and diagnostics. However, lacking of efficiently coupling between the magnetic and electric signals prevent them from being used for biomagnetic detection. ME sensors open up the opportunities for non-invasive room temperature magnetic diagnostic imaging. In this dissertation, we will first study sensor configurations to meet the requirements of biomedical applications, such as possible detection of neutron signal brain image and tissue iron detection. Very sensitive magnetometers are highly desired for neutron signal brain image. Besides longitudinal or transverse type ME composites, shear mode resonance operation could provide magnetic sensors with ultra high sensitivity. Equivalent circuit analysis of shear piezomagnetic/shear piezoelectric (S-S) mode resonance sensor is carried out in this dissertation. The modeling results reveal the potential of such a S-S high Q-factor ME sensor to achieve an exceptional high ME coefficient and signal-to-noise ratio (SNR), e.g., the sensors at resonance of RF frequency (> MHz) exhibits a ME coefficient of 175,000 V/ cm・Oe and SNR of 4.4×1011 √Hz/Oe. For iron detection in tissue, strong DC bias magnetic field (0.5 T or higher) exists while the AC biomagnetic signal is very weak ( 10nT or lower). Hence ultra sensitive ME sensor with high dynamic range is required. An ME sensor based 1st order gradiometer structure with an equivalent magnetic noise of 0.45 nT/Hz1/2 at 1 Hz is then presented. In addition to this, a prototype ME gradiometer based magnetoelectric liver susceptometry was built and tested with liver phantoms. The preliminary measurement shows a linear response in the iron concentrations from normal iron dose(0.05mg/g-liver) to 5mg/g-liver -iron over load (100×overdose). The demonstration of ME gradiometer based magnetometer opens the possibility for compact size, portable, economical room temperature systems for quantitative tissue iron determination. Besides ME sensors and ME sensor based biomagnetic diagnostic systems, piezoelectric composite systems are also studied for industrial acoustic logging, such as LWD, in this dissertation. The working conditions for the LWD piezoelectric composite transducers are rather harsh: (i) High working pressure; (ii) High working temperature; (iii) Strong vibrations between 2 Hz and 1 kHz from drilling practice; (iv) Corrosive gas and drilling fluids. In this case, a well packaged transducer system is required and there are two research objectives in developing piezoelectric composite transducer system. The first research objective is to optimize piezoelectric receiver design with finite element analysis (FEA). Improving fabrication techniques and establishing characterization protocols suitable for LWD applications are also part of the research objectives. A composite configuration to increase the sensitivity is proposed and then electric serial/parallel connections to further improve the signal to noise ratio (SNR) and impedance matching to the receiving electronics is discussed. In addition to the design optimization, fabrication process of receiver transducer under extreme conditions is also very challenging compared with the conventional piezoelectric transducer fabrication methods. Fabrication details on high strength vacuum epoxy bonding is given after piezocomposite receiver design strategies and optimization. Finally an anticorrosion high pressure thermal cycle characterization protocol simulating the real working conditions is provided. The design optimization and fabrication process provide some guidelines for the novel piezoelectric composite logging system design.