Closed-loop Electronics Research Articles

Piezoelectric microresonant pressure sensor using aluminum nitride

This paper presents the design and fabrication of a silicon island supported resonating beam-based micropressure sensor with piezoelectric excitation and detection. The sensor consists of a silicon frame with silicon islands supporting a silicon nitride (SIN) resonating beam placed diagonally on the island in a square diaphragm made of silicon. Aluminum nitride (AlN) thin films deposited at the extreme ends of the SIN beam is used for resonant actuation and sensing. Customized process steps are followed with seven masks to fabricate the sensor, which is first of its kind in the fabrication of microresonant pressure sensors with AlN as piezoelectric material for sensing and actuating the resonating beam. Basic mechanical and electrical characterization is carried out on the unit devices individually to identify the resonance characteristics of the sensor. The results obtained from numerical simulations and experimentation are in close agreement and in the same dimensional range. Closed loop electronics are also designed and tested to vibrate the resonating beam of the unit device at its resonant frequency under no pressure load conditions, which is found to be close to the measured resonance frequency from the mechanical characterization.

A novel resonance based magnetic field sensor using a magneto-rheological fluid

A new technique to measure the magnetic flux density based on the resonance principle using magneto-rheological (MR) fluid is proposed in this paper. The magnetic field sensor is designed using MR fluid placed between two piezo laminated circular disc resonators. The resonant frequency of the disc is changed by the magnetic field dependent viscosity of the MR fluid. The key enabling concept in this work is stiffening the circular metal disc using the rheological effect of MR fluid i.e., resonant frequency varies with respect to magnetic field strength. The change in resonant frequency is measured using simple closed loop electronics connected between the two piezo crystals. The analytical model of the vibrating circular discs with MR fluid placed at the center is derived and the results are validated with experimentation. The proposed magnetic flux density measurement concept is novel and it is found to have good sensitivity and also the input output characteristic is piecewise linear.

Resonance based DC current sensor

The paper presents design, development and testing of a resonant proximity DC current sensor to measure current in the range of 0–20mA. The sensor is built using cantilever structure with piezoelectric excitation, sensing and closed loop electronics. The sensor measures the DC current by measuring the shift in resonance frequency of the cantilever beam. The proposed measurement system is novel, simple and accuracy is found to be 1.1% of full scale deflection.

Piezoelectric based resonant mass sensor using phase measurement

The paper presents design, development and testing of a resonant sensor to measure mass in the range of 0–12 g. The sensor is built using cantilever structure with piezoelectric excitation, sensing and microcontroller based closed loop electronics. The sensor measures the unknown mass by measuring the shift in resonance frequency of the cantilever beam. The shift in resonance frequency for a change in mass is detected by measuring the phase difference between the piezoelectric sensor output and actuator input using microcontroller. The proposed measurement system is simple and accuracy is found to be ±1.2% of full scale deflection.

Microcontroller based split mass resonant sensor for absolute and differential sensing

Two degrees of freedom resonant systems are employed to improve the resonant property of resonant sensor, as compared to a single degree of freedom resonant system. This paper presents design, development and testing of two degrees of freedom resonant sensor. To measure absolute mass, cantilever shaped two different masses (smaller/absorber mass and bigger/drive mass) with identical resonant frequency are mechanically linked to form 2 - Degree-of-Freedom (DOF) resonator which exhibits higher amplitude of displacement at the smaller mass. The same concept is extended for measuring differential quantity, by having two bigger mass and one smaller mass. The main features of this work are the 3 - DOF resonator for differential detection and the microcontroller based closed loop electronics for resonant sensor with piezoelectric sensing and excitation. The advantage of using microcontroller is that the method can be easily extended for any range of measurand.

Design of Microcontroller Based Resonant Sensor with Piezoelectric Excitation and Detection

This paper presents design, development, and testing of a resonant sensor to measure mass in the range of 0–10 grams. The main feature of the proposed sensor is the microcontroller based closed loop electronics. The advantage of using the microcontroller is that the method can be easily extended for any range of measurand.