| With the development of optical fiber communication technology,researchers are making rapid progress in optical fiber sensors field.A variety of fiber optic sensors have been designed to detect ultrasound,temperature,pressure,vibration and other physical parameters.So far,optical fiber sensors have been widely used in civil and military fields for their small size,high accuracy,long-term stability,self-referencing capability and immunity against electromagnetic interference(EMI).A new technique based on polarization fiber grating laser has been proposed recently.Ultrasound measurement is a general application in our daily lives such as object detection,medical testing and treatment.Dual-frequency ultrasound measurement plays an important role in medical and biological applications such as contrast enhanced ultrasound imaging and targeted therapy.A dual-frequency ultrasound measurement system(DFUS)based on Distributed Bragg Reflector(DBR)fiber laser sensor in liquid is presented in this paper.I fixed the driving frequencies of two ultrasound signals at 3MHz and 7MHz,respectively.And then I obtained four types of spectra of the DBR fiber laser corresponding to the modulation index.The experimental results were exactly consistent with the theoretical value.Two experiments were performed to compare the DBR fiber laser acoustic sensor with PZT ultrasound sensor for their dual-frequency measurement performance.By analyzing the sensitivity and signal to noise ratio(SNR)of these two acoustic sensors under different frequencies,I found that the DBR fiber laser sensor's response to wideband dual-frequency was stable,while the PZT acoustic sensor's response deteriorated sharply with the increasing of frequency spacing.The results demonstrated that the DBR fiber laser sensor could be used for dual-frequency ultrasound measurements,and the DBR fiber laser sensor performed much better in wide bandwidth dual-frequency ultrasound measurements. |
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