Fundamental Noise Limit of an IEPE Accelerometer

Abstract

One of the important advantages of IEPE accelerometers is their small noise permitting them to measure small vibration signals at frequency range from about 0.001 Hz to 20 kHz. Specifically, some modern ultra-low-noise IEPE accelerometers feature a noise floor (equivalent input noise acceleration spectral density) estimated at a few dozen $\mathrm{ng}/\sqrt{\mathrm{Hz}}$ at frequency 1 Hz and a few $\mathrm{ng}/\sqrt{\mathrm{Hz}}$ at frequency 100 Hz [1–4]. Designers of IEPE sensors try to decrease their noise more and more. In this matter, the question about the fundamental noise limit of an IEPE accelerometer becomes vital. This chapter describes noise of the PE transducer as the fundamental noise limit of the IEPE accelerometer [5]. Most literature sources on noise of vibration and acoustic sensors describe the mechanical-thermal noise of a damped harmonic oscillator as the only noise source determining the sensor’s noise limit [6–10]. A few other literature sources present the electrical-thermal noise of a piezoelectric (PE) element (crystal) caused by its loss factor as the only noise limit for a PE transducer [11, 12]. But a few, if any, literature sources describe the complete noise analysis of the PE transducer. In this chapter, both noise sources of the PE transducer mentioned above are considered for determination of the fundamental noise limit of the IEPE sensor. The chapter content is based on the author’s work [5].