<title>Behavioral modeling and simulation of a MEMS-based ultrasonic pulse-echo system</title>

Abstract

This paper describes the design, modeling and simulation of an acoustic microsystem in a pulse-echo ultrasonic application. The microsystem, used as emitter and receiver of ultrasonic signals, consists of a bulk micromachined suspended membrane. During emission, the membrane is placed in an oscillator loop and is thermally actuated at its resonance frequency (approximately equals 40 kHz). This frequency is slightly dependent on the membrane average temperature. The electronic interface circuit monitors this temperature. The membrane oscillations generate an ultrasonic signal (pulse) that propagates in the air and interacts with a solid body. As a result of this interaction, the ultrasonic signal is reflected on the solid surface and is received by the microsystem (echo). During reception, a piezoresistive bridge placed on the membrane is used for monitoring the membrane deflections. The resonance frequency of the membrane is tuned to the emitted frequency by keeping the membrane at the same temperature, achieving then maximum sensitivity. This paper presents in detail the behavioral modeling and simulation of the complete system. Some MEMS parts and the acoustic waves propagation are modeled using an Analogue Hardware Description Language (Verilog-A). The associated electronics are implemented in CMOS and the overall system is simulated with the SpectreHDL simulator in the CADENCE environment.