基于频域相位信息的声表面波谐振器回波频率估计

提出一种基于频域相位信息的频率估计算法,利用正弦信号傅里叶变换相位谱中相位与频率的关系实现对声表面波谐振器回波频率的估计,并采用自相关运算消除回波信号初相位对估计结果的影响。通过无线测试系统和仿真回波信号对该算法进行了验证,表明算法的频率估计精度不受激励信号频率变化的影响,并且在整个声表面波谐振器的谐振频率变化范围内都具有较高的精度和稳定性。     

基于声表面波技术的室内定位系统

针对现有采用接收信号强度RSSI原理的室内定位系统存在的问题,鉴于声表面波技术的无源、受多径效应影响小等优势,搭建了由声表面波定位标签和阅读器构成的室内定位系统.阅读器分时读取3个阅读器天线接收到的定位标签回波信号,与常规的室内定位硬件系统采用3个信号接收机相比,大幅度降低了成本.标定了系统的信号强度与距离之间的关系,采用基于RSSI原理的三边定位算法测试了系统的定位性能,其有效定位范围为1.6 m×1.6 m,定位精度为13 cm.     

声表面波标签的相参阅读器设计

现有与声表面波标签匹配的阅读器通常采用非相参的超外差结构,并通过开关截断以产生激励脉冲信号。由于开关闭合时刻和本振信号初相位的随机性,该方案所测回波相位为一个不确定的值,无法与距离等待测量建立函数关系。本文设计了一种相参阅读器,在发射链路使用功分器将信号源产生的信号分为两路同相信号,并把其中一路引入接收链路的下混频器作为本振信号,由此可使回波相位为一确定值。实际制作了阅读器电路,测试了发射、接收链路,并结合声表面波标签进行了实验,通过与矢量网络分析仪测量结果对比,表明了该阅读器的有效性。     

硅酸镓镧单晶材料的声表面波标签研究

声表面波射频识别标签在射频标签领域获得广泛关注,其中对标签基底材料的研究也成了研究热点。文章旨在研究使用硅酸镓镧单晶材料为压电基底的声表面波标签的标签特性。对使用硅酸镓镧单晶材料为压电基底的声表面波标签进行频域和时域分析,并结合有限元分析方法,对标签的特征频率、叉指换能器(Interdigital Transducer, IDT)的反射系数、叉指电极金属化比、金属电极厚度以及标签回波特性进行研究分析,提取了耦合模COM(Coupled-mode)模型参数。分析结果表明了压电效应是声表面波的谐振与反谐振频率存在的根源,验证了脉冲幅度编码方式,并为使用硅酸镓镧材料作为压电基底的声表面波标签的制作提供了仿真实验依据。     

用于包装物管理的无源声表面波标签设计

目的针对声表面波相位编码标签中不同位置反射栅的回波能量不一致,易受噪声干扰、误解调等问题,设计一种回波脉冲能量一致性高的声表面波标签模型,以降低误码率。方法基于耦合模理论并利用COMSOL有限元仿真软件建立反射栅膜厚、膜宽与反射栅反射率之间的关系;根据最优原则优化设计反射栅的结构参数,降低插入损耗,提高声表面波回波信号能量的一致性。结果通过仿真分析得出,当反射栅的厚度为530 nm、宽度为0.23λ时,反射栅的反射率达到最大值;优化反射栅结构得到回波一致性较好的标签,其4条反射栅的厚度均为640 nm;当宽度分别为0.245p、0.27p、0.32p、0.46p时,回波的最大幅值误差为2.02%。通过数字正交解调方法提取了回波脉冲幅值一致性调整前后的标签相位信息,结果证明经过回波脉冲幅值一致性调整后,可以正确地恢复标签的相位信息。结论设计的SAW标签模型可提高标签的抗干扰性和编码容量。     

激光超声探测铝板表面微缺陷深度的数值研究

采用平面应变有限元法模拟了脉冲激光线源在含有表面微缺陷的铝板表面激发声表面波的物理过程,计算结果给出了激光线源逐渐靠近表面微缺陷时接收点得到的位移信号波形特征的显著变化规律;比较了不同深度的表面微缺陷对声表面波时域位移信号特征的定量影响;并在此基础上分析了紧随双极性R ay le igh波之后出现的振荡位移信号的时间间隔随表面缺陷深度增加而呈线性单调递增的趋势;同时证明不同的线光源半宽只会改变振荡信号的相对强度,而不会影响振荡信号的时间间隔;文中结果为利用声表面波位移信号中振荡成分的时间间隔来定量检测材料表面微缺陷深度提供了理论依据.     

声表面波温度传感器抗干扰技术研究

目的设计一种声表面波(SAW)温度传感器抗干扰技术,以提高温度测量的稳定性。方法分析SAW谐振器(SAWR)回波特性,建立SAWR回波信号熵能量模型,发现SAWR回波信号的衰减过程与熵能量的上升过程对应。当回波信号达到噪声水平时,熵能量的单调上升过程消失。为了抑制正弦干扰设计一种改进型自相关算法,利用该算法对信号进行去噪的同时使谐振器回波信号的衰减特性和正弦干扰的等幅特性得到保持。结果根据模拟仿真结果设置了SAWR回波信号的检测阈值(V_(thre)=1),并对该阈值进行了蒙特卡罗仿真实验。仿真结果表明,当信号信噪比大于4dB时,SAWR回波信号的检测率达到86%,而正弦干扰误检率小于0.5%。最后应用该算法对实际的正弦信号和SAWR回波信号进行了检测,得到的误检率接近于0。结论实验结果显示,所设计的算法可以用作声表面波温度传感器的抗干扰技术。     

采用双本振源激励的声表面波谐振器无线测量系统

在声表面波无线传感的实际应用中,针对以差动形式同时出现的两个声表面波谐振器设计了一种采用双本振源激励的阅读器,每次产生包括两个载波频率的激励信号,使两个谐振器同时响应。实际搭建了无线测量系统,对阅读器的发射和接收链路进行了测试,并通过上位机实时显示谐振频率,测量结果表明了系统的可靠性。最后,实验分析了系统在不同载波频率激励信号下的差动频率测量结果和最远测量距离。     

基于MATLAB的激光测高仪回波信号分析

利用MATLAB实现了激光测高仪回波信号分析。在激光测高仪回波信号是由多个高斯函数叠加的理论前提下,基于MATLAB平台,从回波数据中分解出每个有效的高斯分量,获取各个高斯分量的特征参数(中心位置、半宽和幅度)。在信号分析过程中,采用了平面曲线离散点集拐点的快速查找算法和Levenberg-marquardt拟合方法。文章通过实例证明,该算法对激光测高回波信号进行分析可以准确获得高斯函数的特性参数。     

应用于雷达系统的双路高速数据采集存储系统设计

介绍了一种用于对雷达回波I/Q信号进行双路高速采集与数据存储的系统,采样速率为200MHz,分辨率为12位,存储深度为4GB.该系统采用FPGA作为主控制器,ADS62P29作为高速数据转换器,K9K8G08U0M作为大容量数据存储器,通过USB实现系统与计算机之间的通信.利用Cadence软件和VHDL语言完成了系统设计、软件仿真及关键信号的完整性仿真.测试结果表明,ADC的有效位数可达10.69,输入信号为80 MHz的正弦信号时,两路ADC信号之间的相干系数达到0.998 4,可满足雷达系统对回波信号进行高精度相位测量的要求.     

Z-path SAW RFID tag

Surface acoustic wave (SAW) radio-frequency identification (RFID) tags are soon expected to be produced in very high volumes. The size and cost of a SAW RFID tag will be key parameters for many applications. Therefore, it is of primary importance to reduce the chip size. In this work, we describe the design principles of a 2.4-GHz SAW RFID tag that is significantly smaller than earlier reported tags. We also present simulated and experimental results. The coded signal should arrive at the reader with a certain delay (typically about 1 micros), i.e., after the reception of environmental echoes. If the tag uses a bidirectional interdigital transducer (IDT), space for the initial delay is needed on both sides of the IDT. In this work, we replace the bidirectional IDT by a unidirectional one. This halves the space required by the initial delay because all the code reflectors must now be placed on the same side of the IDT. We reduce tag size even further by using a Z-path geometry in which the same space in x-direction is used for both the initial delay and the code reflectors. Chip length is thus determined only by the space required by the code reflectors.     

Inline SAW RFID tag using time position and phase encoding

Surface acoustic wave (SAW) radio-frequency identification (RFID) tags are encoded according to partial reflections of an interrogation signal by short metal reflectors. The standard encryption method involves time position encoding that uses time delays of response signals. However, the data capacity of a SAW RFID tag can be significantly enhanced by extracting additional phase information from the tag responses. In this work, we have designed, using FEM-BEM simulations, and fabricated, on 128 degrees -LiNbO3, inline 2.44-GHz SAW RFID tag samples that combine time position and phase encoding. Each reflective echo has 4 possible time positions and a phase of 0 degrees , -90 degrees , -180 degrees , or -270 degrees. This corresponds to 16 different states, i.e., 4 bits of data, per code reflector. In addition to the enhanced data capacity, our samples also exhibit a low loss level of -38 dB for code reflections.     

Pseudo-orthogonal frequency coded wireless SAW RFID temperature sensor tags

SAW sensors are ideal for various wireless, passive multi-sensor applications because they are small, rugged, radiation hard, and offer a wide range of material choices for operation over broad temperature ranges. The readable distance of a tag in a multi-sensor environment is dependent on the insertion loss of the device and the processing gain of the system. Single-frequency code division multiple access (CDMA) tags that are used in high-volume commercial applications must have universal coding schemes and large numbers of codes. The use of a large number of bits at the common center frequency to achieve sufficient code diversity in CDMA tags necessitates reflector banks with >30 dB loss. Orthogonal frequency coding is a spread-spectrum approach that employs frequency and time diversity to achieve enhanced tag properties. The use of orthogonal frequency coded (OFC) SAW tags reduces adjacent reflector interactions for low insertion loss, increased range, complex coding, and system processing gain. This work describes a SAW tag-sensor platform that reduces device loss by implementing long reflector banks with optimized spectral coding. This new pseudo-OFC (POFC) coding is defined and contrasted with the previously defined OFC coding scheme. Auto- and cross-correlation properties of the chips and their relation to reflectivity per strip and reflector length are discussed. Results at 250 MHz of 8-chip OFC and POFC SAW tags will be compared. The key parameters of insertion loss, cross-correlation, and autocorrelation of the two types of frequency-coded tags will be analyzed, contrasted, and discussed. It is shown that coded reflector banks can be achieved with near-zero loss and still maintain good coding properties. Experimental results and results predicted by the coupling of modes model are presented for varying reflector designs and codes. A prototype 915-MHz POFC sensor tag is used as a wireless temperature sensor and the results are shown.     

Feasibility of ultra-wideband SAW RFID tags meeting FCC rules

We discuss the feasibility of surface acoustic wave (SAW) radio-frequency identification (RFID) tags that rely on ultra-wideband (UWB) technology. We propose a design of a UWB SAW tag, carry out numerical experiments on the device performance, and study signal processing in the system. We also present experimental results for the proposed device and estimate the potentially achievable reading distance. UWB SAW tags will have an extremely small chip size (<0.5 times 1 mm²) and a low cost. They also can provide a large number of different codes. The estimated read range for UWB SAW tags is about 2 m with a reader radiating as low as <0.1 mW power levels with an extremely low duty factor.     

Diffraction in the reflective SAW tags

A specific feature of the acoustoelectric scattering of the nonuniform surface acoustic wave (SAW) beams by the straight metal strips placed on the piezoelectric substrates is discussed. A closed-form solution is obtained to describe the influence of diffraction on the reflective delay line with finite aperture. The found results allow us to develop the fast simulation and synthesis tool that can be applied to evaluate and compensate for the diffraction effect in SAW tags of arbitrary architectures. Efficiency of the proposed approach is illustrated by example of SAW tag synthesized on 128°-LiNbO₃.     

声表面波压力传感器信号采集与处理

声表面波 (SAW)传感器能将被测量转换成容易检测的频率信号 ,即一种准数字信号的输出。针对 SAW压力传感器 (以 CSF- 1 0型 SAW压力传感器为对象 )的输出特点 ,利用等精度频率测量法测量输出频率 ,并用 Dallas的单线数字温度传感器 DS1 8B2 0测出现场温度 ,采用 BP神经网络对所得数据进行温度补偿后得到精确的被测压力值     

A review of wireless SAW sensors

Wireless measurement systems with passive surface acoustic wave (SAW) sensors offer new and exciting perspectives for remote monitoring and control of moving parts, even in harsh environments. This review paper gives a comprehensive survey of the present state of the measurement systems and should help a designer to find the parameters required to achieve a specified accuracy or uncertainty of measurement. Delay lines and resonators have been used, and two principles have been employed: SAW one-port devices that are directly affected by the measurand and SAW two-port devices that are electrically loaded by a conventional sensor and, therefore, indirectly affected by the measurand. For radio frequency (RF) interrogation, time domain sampling (TDS) and frequency domain sampling (FDS) have been investigated theoretically and experimentally; the methods of measurement are described. For an evaluation of the effects caused by the radio interrogation, we discuss the errors caused by noise, interference, bandwidth, manufacturing, and hardware tuning. The system parameters, distance range, and measurement uncertainty are given numerically for actual applications. Combinations of SAW sensors and special signal processing techniques to enhance accuracy, dynamic range, read out distance, and measurement repetition rate (measurement bandwidth) are presented. In conclusion, an overview of SAW sensor applications is given.     

主动声呐阵元信号监测仪系统的开发

介绍了一种基于信号处理机的主动声呐阵元信号监测仪系统,该系统具有基阵阵元测试、声学谱级测量、指向性测量、幅相一致性测量和混响级测量等功能。首先介绍了该系统的硬件平台、软件平台及主要功能,之后详细介绍各主要模块的设计流程及实现,最后给出实录信号分析结果,应用情况表明该系统稳定可靠,使用便捷,功能全面,可明显提高主动声呐设备的研发速度和试验的效率。     

An interrogation unit for passive wireless SAW sensors based on fourier transform

The application of surface acoustic wave (SAW) resonators as sensor elements for different physical parameters such as temperature, pressure, and force has been well-known for several years. The energy storage in the SAW and the direct conversion from physical parameter to a parameter of the wave, such as frequency or phase, enables the construction of a passive sensor that can be interrogated wireless. This paper presents a temperature-measurement system based on passive wireless SAW sensors. The principle of SAW sensors and SAW sensor interrogation is discussed briefly. A new measurement device developed for analyzing the sensor signals is introduced. Compared to former interrogation units that detect resonance frequency of the SAW resonator by comparing amplitudes of sensor response signals related to different stimulating frequencies, the new equipment is able to measure the resonance frequency directly by calculating a Fourier transformation of the resonator response signal. Measurement results of an experimental setup and field tests are presented and discussed.