Implantable medical devices touch virtually every major function in the human body. Cardiac pacemakers and defibrillators, neural recording and stimulation devices, cochlear and retinal implants, etc. Wireless telemetry for these devices is necessary to monitor battery level and device health, upload reprogramming for device function, and download data for patient monitoring. Antennas are inevitably one of the largest if not the largest component of the telemetry communication system and are generally mounted on or in the implanted battery pack, usually in a body cavity. This limited real estate significantly constrains the performance of implantable antennas and results in substantial power loss in the body. Lost power means lost transmit distance and lost battery life.

The proposed research will fundamentally change the design of implantable antennas by tattooing (nearly invisible) conductive nanoparticles in the skin and adjacent fat layer at the body surface, coupling passively to the implant. The antenna will be able to use as much surface area as needed, and dramatically reduce the transmission lost in the body tissues. 

Objective : Enable THz imaging capabilities in a continuous wave (CW) terahertz spectroscopy setup.

Methodology : (i) Develop a spatial light modulator via photo-excitation of carriers in semiconductor materials as the platform for THz imaging (i.e. spatially control the amplitude of the THz beam). (ii) Integrate this with an existing CW THz spectrometer in order to perform THz imaging in reflection and transmission mode. (iii) Implement coded aperture algorithms to enable image compression at the moment of acquisition. (iv) Study the tradeoff between speed, spatial resolution, and noise of the system. 

1) We use deep level transient spectroscopy (DLTS), a time domain technique, and admittance spectroscopy, a frequency domain technique to measure traps in solar cells. Our current setup only allows one cell to be measured at a time but our samples typically have 6-7 cells. Keithley instruments is interested in helping us parallelize the measurement by loaning a switch matrix for testing and demonstration. Duties would include adding wiring to our cryostat for multiple samples then integrating using MyDAQ and Labview a LCR meter and the switch matrix for admittance spectroscopy and the switch matrix, a lockin amplifier, and a programmable DC voltage source for DLTS as well as developing a data analysis program in Matlab. 1-3 students

2) Develop a genetic algorithm approach for the inverse problem of constructing and fitting the parameters of an equivalent RLC circuit having multiple parallel and series RC and RL sections to model the complex impedance response of an unknown circuit (in this case a solar cell). 1-2 students.

3) Simulate drive level capacitance profiling (DLCP) from devices using Matlab. This involves calculating the capacitance response of a pn junction containing trap states with varying AC bias. Different depths in the junction are probed by adding a DC voltage offset. This technique has been shown to separate traditional dopant states from trap states with larger activation energy as well as trapped charge at interfaces from spatially distributed states. Neither of these can be done with traditional CV profiling. The methodology of calculation exists but a modern code does not. Developing such a code would assist those working in semiconductor characterization around the world as well and be of interest to instrument companies such as Agilent and Keithley. 1-2 students.

4) Implement thermal capacitance and total integrated current using Labview and MyDAQ. In both techniques the sample is held at cryogenic temperature and exposed to light and then the temperature is raised slowly. In the first measurement the capacitance is measured using a capacitance bridge to yield the characteristic energies of the trap states measured and in the 2nd a current-integrating circuit would be built and the total charge stored in the trap states measured for absolute calibration of their number. 1 student per technique.

5) Implement modulated photocurrent using modulated LEDs. The in- and out-of phase current of the sample is measured in response to the light from LEDs of various colors driven with a DC plus small AC modulation. The different color LEDs probe different physical depths in the sample while the frequency of the AC modulation and temperature probes the defects’ energy levels. The LEDs are driven by a function generator, the temperature is controlled by a cryogenic temperature controller, and the sample response is measured with a lock-in amplifier. LABVIEW and MyDAQ will be used to integrate the measurement and Matlab for data analysis. 1-3 students.

6) Implement photoacoustic absorption spectroscopy using Labview and data analysis using Matlab. Photoacoustic detection allows the measurement of very weak light absorption in a sample from sub-bandgap states and also allows this measurement on samples with metal contacts such as thin film solar cells. This will require testing and possibly repairing the electronics on an existing photoacoustic detector, modifying labview code to gather the data, and then analyzing the data in Matlab.

7) Design and improve our solar cell fabrication process. Participate in thin film deposition and annealing processes, contact deposition, and solar cell testing. Use the results to improve the process to make more efficient solar cells. 1-3 students.

8) Simulate the effects of laser annealing on semiconductors using COMSOL finite element software. We need to add phase field modelling to our existing EM and heat flow simulations in order to simulate processes such as melting and solidification of semiconductors and the phase transformation from insulating to conductive states in VO2 devices used by Prof. Sensale-Rodriguez for THz modulation. 1-2 students.

9) Implement using MATLAB a model of point defect equilibrium in semiconductors which requires simultaneously solving a system of exponential and integral equations self-consistently given constraints. 1 student.
 

My research group in MSE and ECE works on depositing thin films of semiconductors for use in solar cells and understanding and improving their properties in order to improve the solar cell technology. We have developed a method for chemically depositing thin films of CdTe and CZTS but need to automate the process for improved properties and uniformity.

This is where you come in: designing a deposition system which can repeatedly dip and withdraw the samples in a succession of chemical solutions at programmed velocities and hold them for certain times. The different solutions would be held at different temperatures. In an advanced implementation, the solutions could be topped-off from individual syringes or pumped reservoirs as a function of time or even based on liquid level measurement or weight of the beakers as they are used. Minimally, it will have one vertical actuator and either a linear or rotary axis in the horizontal plane to switch solutions. The system will be automated with Labview or another programmable interface to execute arbitrary user-defined recipes.
 

My research group in MSE and ECE works on depositing thin films of semiconductors for use in solar cells and understanding and improving their properties in order to improve the solar cell technology. One of our thrusts involves irradiating semiconductor layers with high powered lasers in order to anneal and change their properties.

This is where you come in: We have some existing 2D and 3D simulations of the interaction of lasers with materials (COMSOL or Matlab optical simulation) and the resulting heat flow (COMSOL heat diffusion equation). We need to add the capability to simulate phase changes induced by the heating – for example if the sample melts the properties of the liquid are different than those of the solid and thus the optical and heat flow problems are dynamically coupled. The best implementations use phase fields – a scalar field with associated PDEs which can change continuously between the different possible phases. The COMSOL package has this capability but implementing and verifying the fully coupled optical/thermal/phase model will be challenging but feasible.
 

TBD

In this project we will expand the efficiency benefits of the switched-capacitor PA (SCPA) by improving the linearity and spectral performance of the SCPA. To do so we will implement signal processing techniques in an SCPA (e.g., digital filtering, dynamic element