Projects:2015s1-28 Wireless Rotation Detector

Supervisors

• Prof Christophe Fumeaux
• Dr Ali Karami Horestani

Honours students

• 2015: Guowei Deng and Shuopeng Wang, see Wireless Rotation Detector

Project objects

Scope

• Design and construct a portable wireless device which can accurately measure the speed of rotating object.

Specific Aims

The aim of the project is to design and construct a portable wireless device which can be used for rotation speed measurement. The device is supposed to consist of antennas, absorbers, Arduino UNO Board with software, etc. The outcomes of the project will be as follows:

• A metamaterial absorber with resonant frequency of 2.4GHz
• A planar dual-antennas with capability of transmitting and receiving signals
• A software system for rotation speed calculation

The device should be able to measure the rotational speed of various objects such as sport equipment, car tyres, turbines, fans, etc. The system shall be operational under a set of circumstances and able to achieve reliable results.

Background & Significance

• Motivation

The rotation speed measurement devices have already ubiquitously used in industries. They are embedded on turbines, wheels or fans to extract the rotation speed of objects. However, most of commonly used angular speed measurement devices, such as laser tachometer, use visible light. One of the constraints in such devices is that the line of sight cannot be impaired [1]. Hence, the optical devices cannot be used if there is an obstacle between rotating objects and the test devices or under sophisticated circumstances such as fog or smoke.

In order to improve the performance of the measurement device, the 2.4GHz electromagnetic waves will be used instead of visible light due to its good ability of propagation. Accordingly, the devices can be used under more complicated situations, even if the line of sight has been impaired, once delivered.

• Technical Background

1. Polarization of Antennas

The polarization of antenna is defined as “the polarization of the wave transmitted (radiated) by the antenna” [2]. There are 3 different types of polarization including linear polarization, circular polarization and elliptical polarization [2]. All of them are defined as “time-varying direction and magnitude of the electric field vector” [2].

2. Polarization Loss Factor

Polarization loss is defined as the power loss due to polarization mismatch. For example, if a horizontally polarized antenna communicates with a vertically polarized antenna, the vertically polarized antenna will transmit vertically polarized waves, while the horizontally polarized antenna can only receive horizontally polarized wave. Thus, there is no power transfer between a horizontally polarized antenna and vertically antenna according to the reciprocity principle. In contrast, if 2 vertically polarized antennas communicate with each other, the power transfer will be maximum. Hence, if two linearly polarized antennas are rotated from each other by an angle θ, the polarization loss factor base on power loss for polarization mismatch is defined as

                                                𝑃𝐿𝐹 = 𝑐𝑜𝑠2θ

3. Metamaterial Absorber

Metamaterials are man-made materials with the unique characteristics, such as negative permittivity and permeability, which cannot be found in natural materials [3]. The metamaterial absorber has been one of the most important applications due to its astonishing properties [4]. A single metallic metamaterial absorber typically consists of a LC resonant circuit and a ground plane, separated by a substrate in between [5]. For example, as shown in Figure 1, the capacitor-like structure can provide capacitance and is connected with two loops in parallel, which can be considered as two inductors in the resonant circuit [6]. The resonator can strongly respond to a properly oriented electric field due to the capacitor-like structure when the circuit is driven by EM field at resonant frequency.

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The metamaterial absorber is expected to have the ability of dissipating the incident waves inside of the structure with limited energy reflected back from it [8]. As shown in Figure 2, the incident wave is transmitted into the substrate at working frequency. The surface current will be created along the ground plane when the wave reached the bottom layer. Similarly, remaining energy will be reflected back to the resonators which will also generate another surface current on the top layer. These two currents have same magnitude with opposite directions, resulting in a destructive interference [8]. Hence, the thickness of the substrate should be carefully chosen for the effective destructive interference.

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Key Requirements

From the introduction of background and related work, several key requirements have been defined as following:

• Metamaterial absorber shall absorb at least 90% (-10db) power at 2.4GHz when it has

same polarization as the transmitting antenna.

• Dual antennas shall work at 2.4GHz and crosstalk between 2 antennas shall be less

than -40dB.

• Portable system shall be operational up to 50cm from the rotating object.
• Portable system shall accurately measure the angular speed of the rotating object in

both low and high speed.

• While the mutual coupling in dual antennas is reduced, the dimensions of dual antenna

should remain small, and specifically the antenna system should be planar.

Proposed Approaches

• Method exploited - ‘Divide-And-Conquer’.

• The entire project can be decomposed into several aspects.

• Hardware (design required)

1. Metamaterial Absorber
2. Dual-Antennas

• Software

1. Calculation Algorithm for rotating speed
2. GUI

• Other Components (from market or school)

1. VCO
2. Arduino UNO Board
3. Power Detector

Hardware Design

• Understand the requirements and specifications of the hardware
• Design the hardware in software such as HFSS
• Fabricate the designed hardware
• Measure the prototype and compare the measured results with simulation results
• Redesign if the prototype does not meet requirements

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Software Design

• Software design will start after antenna and absorber design has been finished.
• Software – in C language, based on the Fourier Transform
• Combine software, hardware and other components together and measure the rotating speed.
• Redesign if the measured speed and real speed are not identical.

Entire System

• The entire system is the integration of all several aspects.
• Use ‘Waterfall’ model for the system design.

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Schedule and Milestone

• Milestone in Semester 1

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• Milestone in Semester 2

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Reference

[1] C.A Balanis, “Antenna Theory Analysis and Design”, 3rd ed., New York: Wiley, 2005.

[2] “Arduino FFT Library”, openmusiclabs, Available: http://wiki.openmusiclabs.com/wiki/ArduinoFFT.

[3] D. Schurig, J.J. Mock, and D. R. Smith, “Electric-filed-coupled resonators for negative permittivity metamaterials”, Appl. Phys. Lett. 88, art. no. 041109(2006).

[4] Y. Chen, “Wireless Rotation Detector for Sport Equipment”, 2014.

[5] T. Mark, “System Overview,” Wireless Rotation Detector for Sport Equipment, 2014, pp 6-8.

[6] H. M. Lee, “Absorption Bandwidth-Enhanced Metamaterial absorber Using In-planed ELC resonator and Cut-Wire,” available: http://ournal.sapub.org/eee [Accessed: 22 March 2015]

[7] A. Grasso, Notes of Project Management for Electrical Engineering & Sustainable Energy, 2014. [Online]. Available: https://myuni.adelaide.edu.au/bbcswebdav/pid-5997024-dt-content-rid-6342045_1/courses/3420_ELEC_ENG_COMBINED_0001/Project%20Management%20%283024%20%26%203029%29%20Lecture%20Notes_2014.pdf