Effects of parasitic electrical components on an ultrasound system: measurements and simulations using SPICE models

Abstract

When driver and receiver electronics for an ultrasound measurement system are physically implemented, parasitic components are introduced in the system. These may arise from bond wires, circuit board paths or cabling. The parasitic components will influence the excitation pulse behavior as well as amplitude and time of arrival for received pulses. In the system investigated, a coaxial cable is used to connect the transducer with the electronics. The inductance and capacitance of the cable are dominating parasitic components in the system. This paper investigates the effects of these components for varying cable lengths and compares measurements with system simulations using SPICE models. The simulations give highly accurate temporal behavior of the excitation pulse. The peak to peak amplitude and the perceived time of flight of the received echo in a pulse echo system is measured. Amplitude variations of 60% are recorded for cable lengths varied between 0.07 m and 2.3 m., with simulations predicting the same variations. The time of flight is measured using the excitation pulse as time trigger. Variations are up to 40 ns for a total travel time of about 8 μs. The simulations predict this variation within a few ns.