The Research Of Torque Detection Based On Surface Acoustic Wave Device

In recent years, a new technology of dental restoration has been developed which is called Implant Denture. It is a kind of bone support denture technology and its transfer mode of force is closer to the natural tooth. Because of its characteristics of good stability, wide indication, beautiful and comfortable, it has been widely used in dental clinical treatment to solve the difficult cases that conventional denture repair methods can’t do.In the process of implant denture, the stability of implant is directly related to the success rate of implant denture, so it’s necessary to regularly monitor the stability of implant. At present, the resonance frequency analysis method which has been commonly used in oral clinic can only reflect the lateral force resisting ability of implant. It can not reflect the ability of the implant anti-rotational force. So, the research for the non-destructive torque detection method which can reflect the lateral force resisting ability of implant is very meaningful.The surface acoustic wave(SAW) devices are widely used in all kinds of sensors due to its unique advantages. This paper introduces the principle and structure of the SAW devices, the principle of torque detection by SAW device. A one-port SAW resonator device(the center frequency is 433.92MHz) is used sensing device of torque detection system. By using mixing method of dual-channel differential structure which contain a measurement channel and a reference channel, the SAW signal acquisition and processing circuit that includes the SAW oscillation circuit, a mixer, a low pass filter, shaping circuit and power supply circuit has been designed. The frequency hopping phenomenon of the test channel was found in circuit debugging. It is because that there is multiple phase zeros which meet the oscillation equilibrium condition on the phase- frequency characteristic curve of SAW device. In order to avoid the frequency hopping, we should adjust the parameters of oscillation circuit in detection channel and ensure that the slope of the phase- frequency characteristic curve in range of oscillation frequency is negative and there is only one phase zero near the oscillation frequency point.Using signal detection circuit of SAW device, digital oscilloscope, metal sensing shaft, portable electronic scale and wrench to build a torque detection system based on surface acoustic wave resonator. We studied the influence of two pasting methods for torque detection, which the SAW resonator paste along the axis direction or paste at 45 o against the axis direction of metal sensing shaft. The results show that the torque detection system can be used for torque detection of metal sensing shaft and the frequency of SAW resonator has a linear relationship with the applied torque, and pasting along the axis direction is superior to pasting at 45 o against the axis direction in the sensitivity.But, the experimental device made in this subject is rough. Its detection error is large and its sensitivity is low. It can’t be applied to practice and it requires a lot of continuing improvement.