Chipless RFID ph Sensor for Food Spoilage Monitoring

Transcription

1 Chipless RFID ph Sensor for Food Spoilage Monitoring ECE 4600 Group Design Project Proposal Group #5 John Baldwin Marvin Bataller Christian Espino Project Supervisor: Dr. G. Bridges Date of Submittal: October 1, 2012

2 1. INTRODUCTION Food quality is an important manufacturing requirement for consumer health and safety. Current methods to monitor the quality of food during the transit and storage process are to use temperature sensors, enzyme sensors, or gas sensors. Such sensors, however, have significant drawbacks, which include low sensing accuracy in moist environments, high operating temperatures, complicated fabrication processes, and several design constraints which prohibit a wireless integration [1]. These factors reduce the cost-effectiveness and feasibility of their use in commercial applications. An alternative technique used to manage food quality is to monitor the change of ph levels of the product. ph is essentially the measurement of the hydrogen ion concentration and is usually expressed in the logarithmic scale [2]. A ph sensor commonly consists of two electrodes which provide a linear potential response over a wide range of ph values [3]. During the food spoilage process, the ph profile changes due to the growth and metabolic actions of microbes [1]. The ph level can therefore provide an accurate indication of the freshness of the product. The objective of this project is to design and fabricate a ph sensing device which can be embedded into packaged material. The device will have three main components, which will include the ph detector, two resonator circuits, and the transceiver. Furthermore, the device will also be magnetically coupled to an external source, where the resonant frequency of one of the resonator circuits will be proportional to the ph of the material. The change of ph will vary the potential across a set of electrodes integrated into the resonator circuit. The response of the device will be measured by a network analyzer. Furthermore, existing Radio Frequency Identification (RFID) concepts will be incorporated into the design for a wireless passive device approach. This passive wireless design will be an efficient method of measuring food quality as it can be embedded directly into packaged materials. 1

3 2. SPECIFICATIONS The ph sensing device will operate in a 4-7 ph range environment and have a ± 0.3 ph accuracy. To determine the accuracy, the output of the sensor will be compared to a commercial ph sensor. The device will also operate in a high moisture environment in an ambient temperature between 2 30 C. Since this device will be designed to be embedded into packaged materials such as 2L carton of milk, the maximum length, width, and thickness will be 15.0cm, 10.0cm, and 0.250cm respectively. The device will be comprised of a ph detector, two resonator circuits, and a transceiver as shown in figure 1. The ph detector will use an iridium oxide electrode in tandem with a silver chloride reference electrode. The hydrogen ion concentration will induce a change in voltage across the electrodes of approximately 60mV/pH [3]. The induced voltage will be used to bias a variable capacitor, also known as a varactor, which will be integrated into the resonator component. The resonator component will consist of a reference and sensing circuit, and will each be modelled as an RLC circuit shown in figure 2. The resonant frequency of an RLC circuit can be calculated by where is the resonant frequency in Radians/Second, L is the inductance in Henrys, and C is the capacitance in Farads. Both the reference and sensing circuits will be designed to resonate at a frequency of approximately 2.4 GHz. The sensing resonator, however, will have a varactor integrated into the circuit which will vary the resonant frequency by approximately ± 0.1 GHz. To achieve the highest sensitivity in the change of reverse bias voltage across the varactor, a characteristic capacitance curve slope that is greatest between 100 to 500 mv will be selected. The transceiver will be comprised of two antennas which will be required to handle the reception and transmission of a frequency sweep in the 2 to 3 GHz range. The antenna will be designed to be cross-polarized to minimize the interference between the input and output signals. Circular disk monopole antennas will be used in the design due to large bandwidth requirements and its simplistic design [4]. The transmitted signal of the ph sensor will be designed to be distinguishable at a distance of at least 5cm. The specifications of the device are summarized in Table 1 on the following page.. 2

4 Table 1: Specifications ph Operating Range ph Sensing Accuracy Operating Environment SPECIFICATIONS 4 7 ph ± 0.3 ph High Moisture Operating Temperature 2 30 C Maximum Device Dimensions: Length Width Thickness Reference Resonator Sensing Resonator Voltage Sensitivity Range Antennas Minimum Interrogation Distance Fluid Proximity Distance to Tag 15.0 cm 10.0 cm cm Fixed Frequency at 2.4 GHz Variable Frequency at 2.4 ± GHz 100 to 500 mv 2 UWB Circular Cross Polarized 5.0 cm 0.2 cm Rx E-field T x Resonator Circuit Network Analyzer RLC Model Tx E-field R x Electrodes Figure 1: Operating Principle of the Chipless RFID System Figure 2: RLC Model of the Resonator with Variable Capacitor and Electrodes 3

5 3. TASKS AND MILESTONES Table 2 shows the milestones and the tasks to complete this project, as well as how the work will be distributed among each group member. The timeline for each task is indicated in the Gantt chart on the following page. Table 2. Milestones, Tasks, and Division of Work MILESTONES AND TASKS 1. Preliminary Work Research Chipless RFID Research ph Sensing Ansoft Programming Review 2. Materials Gather Materials List and Pricing Order Materials 3. Replicate Existing Chipless RFID Systems Simulate System in Ansoft Build Chipless RFID System Test Chipless RFID System 4. Simulate and Design Chipless ph Sensor ph Sensing Circuit Transceiver Resonators Build Chipless ph Sensor 5. Testing and Optimization Monitor ph of Milk Optimize Design 6. Administrative Work Project Proposal Informal Oral Progress Report Formal Written Progress Report Formal Oral Progress Report Project Title Final Report Project Presentation ASSIGNED INDIVIDUAL(S) Christian, John Marvin John, Marvin Christian, John Christian Marvin John Christian, Marvin John, Marvin 4

6 4. GANTT CHART 5

7 5. BUDGET The materials and cost required for this project is shown in Table 2. The total cost of the project is estimated to be $ Table 2: Budget ITEM UNIT UNIT COST TOTAL COST 1. Varactor BB NXP $ Rogers RT/Duroid 5880 Glass Microfiber Reinforced 1 $ $ PTFE Composite Material (.062 x12 x18 ) 3. Iridium Oxide Wire % Metal Basis 1 $ $ (5cm length x 0.5mm dia.) 4. Silver Oxide Wire 99.9% Metal Basis 1 $60.00 $60.00 (1m length x 1.0mm dia.) 5. SMA Jack Flange Mount to PCB 2 $22.41 $ % Milk (2L) 1 $2.57 $ ADSV 2.2 Software 1 1 $0.00 $ HFSS Software 1 1 $0.00 $ Network Analyzer - HP 8753E 1 1 $0.00 $ Impedance Analyzer - HP Agilent 4290A 1 1 $0.00 $ Commercial ph Sensor Exstik II 1 1 $0.00 $ Estimated Shipping and Brokerage Fees - - $ Provided by the Electrical and Computer Engineering Department GRAND TOTAL: $

8 6. REFERENCES [1] W. Huang, S. Deb, Y. Seo, S. Rao, M. Chiao, J.C. Chiao. A Passive Radio-Frequency ph- Sensing Tag for Wireless Food-Quality Monitoring. IEEE Sensors Journal. Vol. 12, pp March [2] R. Petrucci, W. Hardwood, F. Herring, J. Madura. General Chemistry. Upper Saddle River, New Jersey: Pearson Prentice Hall, 2007, pp [3] S. Bhadra. Electrode Potential-Based Coupled Coil Sensor for Remote ph Monitoring, IEEE Sensors Journal. Vol. 11, pp November [4] S. Preradovic and N. Karmakar. Chipless Millimeter Wave Identification (MMID) Tag at 30 GHz, in Microwave Conference (EuMC), 2011, pp