Human tissue is relatively transparent to light between 700 and 1000 nm in the near infrared (NIR). NIR spectroscopy is a technique that can measure non-invasively and safely, the optical properties of tissue. Several different types of spectroscopic instrumentation have currently been developed, ranging from simple continuous intensity systems, through to complex time and frequency resolved techniques. This thesis describes the development of a near infra-red time-resolved system, using an inexpensive avalanche photodiode (APD) detector and a microwave step recovery diode (SRD) in a novel way to implement a totally electronic crosscorrelator, with no moving parts. The aim of the work was to develop a simple instrument to monitor scattering changes in tissue during laser induced thermal therapy. The APD was gain-modulated by rapidly varying the bias voltage using electrical pulses generated by the SRD (120 ps full width half maximum (FWHM) and 8 V in amplitude). The resulting cross-correlator had a temporal resolution of 275 ps FWHM - significantly faster than the 750 ps FWHM of the APD when operating with a conventional fixed bias voltage. Spurious responses caused by the SRD were observed, which were removed by the addition of Schottky diodes on the SRD’s output, although this slightly degraded the system temporal resolution from 275 to 380 ps FWHM. The ability of the system to monitor scattering changes was tested using an IntralipidTM phantom containing infra-red absorbing dye. An 800 nm fibre coupled mode-locked (2 ps pulse width) laser source was used with the cross-correlator measuring the temporal point spread function (TPSF) at 5 to 30 mm away from the source fibre. Five different numerical algorithms to derive the scattering coefficient from the measured TPSF were compared. The optimum choice of algorithm was found to depend on whether absolute accuracy or minimum computation time is the most important consideration.

Despite the fact ultra-wideband (UWB) technology has been around for over 30 years, there is a newfound excitement about its potential for communications. With the advantageous qualities of multipath immunity and low power spectral density, researchers are examining fundamental questions about UWB communication systems. In this work, we examine UWB communication systems paying particular attention to transmitter and receiver design. This thesis is specifically focused on a software radio transceiver design for impulse-based UWB with the ability to transmit a raw data rate of 100 Mbps yet encompasses the adaptability of a reconfigurable digital receiver. A 500 ps wide Gaussian pulse is generated at the transmitter utilizing the fast-switching characteristics of a step recovery diode. Pulse modulation is accomplished via several stages of RF switches, filters, and amplifiers on a fully designed printed circuit board specifically manufactured for this project. Critical hardware components at the receiver consist of a bank of ADCs performing parallel sampling and an FPGA employed for data processing. Using a software radio design, various modulation schemes and digital receiver topologies are accommodated along with a vast number of algorithms for acquisition, synchronization, and data demodulation methods. Verification for the design is accomplished through transmitter hardware testing and receiver design simulation. The latter includes bit error rate testing for a variety of modulation schemes and wireless channels using a pilot-based matched filter estimation technique. Ultimately, the transceiver design demonstrates the advantages and challenges of UWB technology while boasting high data rate communication capability and providing the flexibility of a research testbed. / Master of Science