Development of a Wireless Temperature Sensor Using Polymer-Derived Ceramics

Development of a Wireless Temperature Sensor Using Polymer-Derived Ceramics


A temperature sensor has been developed using an embedded system and a sensor head made of polymer-derived SiAlCN ceramics (PDCs). PDC is a promising material for measuring high temperature and the embedded system features low-power consumption, compact size, and wireless temperature monitor. The developed temperature sensor has been experimentally tested to demonstrate the possibility of using such sensors for real world applications.






1. Introduction


Accurate temperature measurements are crucial for many applications, such as chemical processing, power generation, and engine monitoring. As a result, development of temperature sensors has always been a focus of microsensor field. A variety of materials have been studied for temperature sensor applications, for example, semiconducting silicon and silicon carbide. Silicon based sensors are typically used at temperatures lower than 350°C due to accelerated material degradation at higher temperature [1, 2]. Silicon carbide based sensors are better than silicon based sensors in high temperature measurement and can be applied in temperatures up to 500°C [3–5].






Polymer-derived SiAlCN ceramics (PDCs) are another widely studied material that demonstrate properties such as excellent high temperature stability [6] as well as good oxidation/corrosion resistance [7]. PDCs have been considered as a promising material for measuring high temperature [8]. Our early works have showed that PDC sensor head can accurately measure high temperature up to 830°C [9] using data acquisition system from National Instruments. The cost and size of the sensor system must be significantly reduced before it can be deployed for real world applications. In this paper, we develop a temperature sensor using PDC and an embedded system. Comparing to the National Instruments data acquisition equipment used in the previous paper, the newly developed embedded sensor is much smaller (9.7?dm3 versus 0.3?dm3), lighter (5.97?kg versus 0.19?kg), and cheaper (approximately $8000 versus $170). A WiFi module is also added so the temperature measurement can be transmitted wirelessly. The embedded board and WiFi module used in this paper are commercially available. The experiments in this paper demonstrate the possibility of deploying PDC based sensors for real world applications.






2. Fabrication of the PDC Sensor Head


In this study, the PDC sensor head is fabricated by following the procedure reported previously [9]. In brief, 8.8?g of commercially available liquid-phased polysilazane (HTT1800, Kion) and 1.0?g of aluminum-tri-sec-butoxide (ASB, Sigma-Aldrich) are first reacted together at 120°C for 24 hours under constant magnetic stirring to form the liquid precursor for SiAlCN. The precursor is then cooled down to room temperature, followed by adding 0.2?g of dicumyl peroxide (DP) into the liquid under sonication for 30 minutes. DP is the thermal initiator which can lower the solidification temperature and tailor the electrical properties [10]. The resultant liquid mixture is solidified by heat-treatment at 150°C for 24 hours. The disk-shaped green bodies are then prepared by ball-milling the solid into fine powder of ~1?μm and subsequently uniaxially pressing. A rectangular-shaped sample is cut from the discs and pyrolyzed at 1000°C for 4 hours. The entire fabrication is carried out in high-purity nitrogen to avoid any possible contamination.






Pt wires are attached to the sensor head by two ceramic fasteners on the two mounting holes on the diagonal of the sensor head. To improve the conductivity, both mounting holes are coated with Pt plasma; see Figure 1.






To measure temperature using the PDC sensor, the processor needs to perform the following tasks: () supply voltage  to the circuit through DAC7724; () sample the circuit output  using AD7656 and convert the output to temperature measurement; and () transmit data to readers from the RS232 port.






The input signal  to the conversion circuit is a sinusoidal signal of ±10?V. The sinusoidal signal can bypass the parasitic capacitor in series to the PDC probe. The noise from the furnace coil can also be greatly subdued. The sensor output voltage  is approximately sinusoidal as well and its magnitude can be computed using Fast Fourier Transformation (FFT) or curve fitting using recursive least square method (RLSM) [11]. Comparing to FFT, RLSM is more computationally efficient but may have numerical instability because TMS320F28335 only supports IEEE 754 floating-point arithmetic. Here we prefer FFT for fast prototyping purpose because Texas Instruments provides FPU library that performs floating FFT routines on C2000 series microcontroller. Next we explain how the sensor works.






A high-priority interrupt service request (ISR1) based on a CPU timer continues reading a look-up-table and drives the DAC7724 to generate the input signal . The frequency of  is controlled by the frequency of ISR1. ISR1 also samples circuit output from AD7656 and adds the data to a 1024-point buffer if there is no FFT running. Once the buffer is filled up, ISR1 stops writing the buffer and the FFT routine starts. The FFT routine is implemented in another slower low-priority interrupt service (ISR2). Once the FFT routine is completed, ISR2 will give ISR1 the permission to clean and write the input buffer again. The magnitude from the FFT is used as the circuit output . The software flowchart is shown in Figure 4.






High temperature sensors capable of operating in harsh environments are needed in order to prevent disasters caused by structural or system functional failures due to increasing temperatures. Most existing temperature sensors do not satisfy the needs because they require either physical contact or a battery power supply for signal communication, and furthermore, neither of them can withstand high temperatures nor rotating applications. This paper presents a novel passive wireless temperature sensor, suitable for working in harsh environments for high temperature rotating component monitoring. A completely passive LC resonant telemetry scheme, relying on a frequency variation output, which has been applied successfully in pressure, humidity and chemical measurement, is integrated with a unique high-k temperature sensitive ceramic material, in order to measure the temperatures without contacts, active elements, or power supplies within the sensor. In this paper, the high temperature sensor design and performance analysis are conducted based on mechanical and electrical modeling, in order to maximize the sensing distance, the Q factor and the sensitivity. In the end, the sensor prototype is fabricated and calibrated successfully up to 235oC, so that the concept of temperature sensing through passive wireless communication is proved. 






This paper aims to develop a prototype for a web-based wireless remote temperature monitoring device for patients. This device uses a patient and coordinator set design approach involving the measurement, transmission, receipt and recording of patients’ temperatures via the MiWi wireless meter iot solution. The results of experimental tests on the proposed system indicated a wider distance coverage and reasonable temperature resolution and standard deviation. The system could display the temperature and patient information remotely via a graphical-user interface as shown in the tests on three healthy participants. By continuously monitoring participants’ temperatures, this device will likely improve the quality of the health care of the patients in normal ward as less human workload is involved.






Background


During the severe acute respiratory syndrome (SARS) outbreak in 2003, hospitals became treatment centres in most countries. Because a patient’s core body temperature is one vital parameter for monitoring the progress of the patient’s health, it is often measured manually at a frequency ranging from once every few hours to once a day [1]. However, such manual measurement of the temperature of patients requires the efforts of many staff members. In addition, when the patients suffer from conditions that result in abrupt changes of the core body temperature, e.g., due to infection at a surgical site after surgery, the staff on duty will not know such a temperature change occurred until the next temperature measurement. Such a delay may lead to patients being unnoticed while their health conditions worsen, which is dangerous because a difference of 1.5 degrees Celsius can result in adverse outcomes [2]. Furthermore, there is always a need to have a monitoring system to improve the quality of health care [3], such as temperature monitoring of elderly and challenged persons using a wireless remote temperature monitoring system.






Body temperature can be used to monitor the pain level of a patient following an operation [4] or after shoulder endoprosthesis [5]. In some cases, the tissue transient temperature was monitored during microwave liver ablation [6] for the treatment of liver metastases. Instead of using a temperature sensor, pulse-echo ultrasound [7] was used to visualize changes in the temperature of the patient’s body. In addition, a non-contact temperature-measuring device, such as a thermal imaging camera [8], was successfully used to detect human body temperature during the SARS outbreak. However, it can be quite expensive to equip each patient room with a thermal imaging camera. In addition, there are a few wireless temperature measuring solution (e.g., CADIT?, Primex?, and TempTrak?) on the market that are used to monitor and store a patient’s temperature for medical research by using body sensor networks [9]. Most of these systems consist of an electronic module and a temperature-sensing device. The systems include a stand-alone electronic module with a display screen that allows the temperature sensor data to be transmitted over a secure wireless network.






However, these systems can be difficult to reconfigure to suit the current database system used in the hospital. In addition, the current systems using short message service (SMS)-based telemedicine [10] systems with hardware equipment were developed to monitor the mobility of patients. However, proper hardware and software to manage the messages and the patient’s temperature for display on mobile phones are not widely available.






Hence, a medical device to continuously measure the body temperature of patients using a wireless temperature receiver [4,11,12] is required. With such a wireless temperature sensor system, nurses will no longer have to manually measure the temperature of patients, which will free their time for other tasks and also reduce the risk associated with coming into contact with patients with contagious diseases, such as SARS. The readings will be transmitted wirelessly to the central nurse station, where they can be monitored by the staff-on-duty. In addition, the current and past history of the body temperature measurements can be stored in an online database, which allows the medical staff to access the database when they are not in the hospital.






To the best of our knowledge, a MiWi wireless (besides using the Zigbee[11]) temperature-monitoring system using a patient and coordinator set design that provides remote internet access to the temperature database has not been reported in any publication. The objective is therefore to develop and implement a prototype temperature-monitoring system for patients using a MiWi wireless remote connection to the nurse’s station for frequent real-time monitoring. The temperature monitoring system was designed based on a proposed patient and coordinator set design approach. The proposed temperature-monitoring system for use in normal ward will likely to improve the quality of the health care of the patients as the nursing workload is reduced. In this paper, the discussion on medical regulations and policy will not be included.