广西乐器用材研究初报

木材作为乐器音板,主要决定于声辐射品质常数和声阻抗。优良的乐器板用材必须具有较高的声辐射品质常数和较低的声阻抗,这两种因素都与材料的密度和传声速度有密切关系。声辐射品质常数用声速与密度之比,声阻抗用密度与声速的乘积表示。不同的材料,其声辐射品质常数和声阻抗差异较大。如木材的密度小于铜、铁、铅、玻璃等3倍至10倍左右,因     

果汁和饮料中糖组分的超声检测研究

为研究果汁、饮料生产中糖浓度的在线快速测定技术,采用基于超声传播特性的液态食品质量检测装置,测定了纯果糖、葡萄糖、蔗糖溶液及葡萄糖—蔗糖混合溶液的糖组分浓度与声速的关系。结果表明：纯糖溶液中声速与浓度用二次方程回归呈极显著正相关(R²>0.9970);声速与混合溶液糖组分浓度关系密切,可用二元二次多项式拟合(P<0.0001);采用声速与浓度的经验公式和与理论结合的半经验公式组成方程组,对果汁饮料中的还原糖、蔗糖和总糖含量进行分析,与传统检测方法和高效液相色谱法(HPLC)的检测结果一致,其差异不显著(P≤0.05)。该研究表明超声检测技术有可能应用于果汁、饮料中糖组分浓度的检测。     

基于声振响应法的香梨硬度无损检测

为了探索香梨硬度无损检测的方法,该研究搭建了由压电梁式传感器进行信号激励和感测的检测装置,分析了装置信号检测的稳定性,提取了香梨共振频率和声速并进行香梨硬度评估,然后将这两响应参数的评估硬度与香梨硬度的M-T穿刺法(Magness-Taylor)测量结果进行线性回归分析,以构建香梨硬度的检测模型。结果表明,检测装置的共振频率和声速信号检测稳定可靠,并且在香梨赤道部不同位置激励感测均无显著差异(P0.05);基于共振频率法和声速法的硬度评估指标可以构建3种香梨硬度检测模型,相关系数分别为0.841、0.877和0.938,其中由共振频率检测硬度和声速检测硬度联合构建的检测模型硬度检测敏感度为67.30%,最接近M-T穿刺法检测敏感度,该模型对香梨正常果和粗皮果的检测准确率较高,达到86.7%。研究结果可为声振法无损检测香梨硬度提供参考。     

用超声谐振法确定牛奶凝固时间的试验研究

在奶酪的生产过程中,确定牛奶的凝固时间是极为关键的一步,它直接关系到奶酪的品质和产量。文中提出一种非破坏性测定凝固时间的新方法一超声谐振检测法。即利用超声的衰减特性测定牛奶在凝固过程中的物理性能变化,以确定牛奶凝固点和凝块切割的最佳时间。试验研究结果表明:超声信号的衰减与牛奶在凝固过程中的物理性能变化密切相关。超声谐振法可显著地提高检测的精确度。     

超声波土壤含水量检测装置的模型建立与验证

为探究利用超声波脉冲速度检测土壤体积含水量的可行性,以广东省红壤、赤红壤、水稻土为研究对象,设计了一种超声波土壤含水量检测装置,并利用ZBL-U510型非金属超声波检测仪在3种不同温度环境下(10、20、30℃)对不同含水量的土壤样本进行声速测定,构建了土壤体积含水量与超声波差值声速的温度效应数学模型。结果表明:超声波在水稻土中的传播速度比红壤、赤红壤快,且温度对超声波声速随土壤体积含水量变化节律的影响不同。20℃环境下超声波在土壤中的传播速度最快,10℃其次,30℃最慢。采用Richards模型表征土壤体积含水量与超声波差值声速关系的预测误差在3%左右,采用分段结构温度效应模型的预测误差在5%以内,证明该文提出的超声波脉冲速度-土壤体积含水量的温度效应模型可用于动态温度条件下的土壤含水量预测。该研究可为超声波技术在土壤水分检测领域的应用研究提供参考。     

含水果颗粒液态食品物料通电加热温度场研究

利用自行设计研制的测试系统对含水果颗粒液态食品物料通电加热中颗粒中心与液态物料的温度及电导率变化进行测试,研究得出不同固液混合食品物料通电加热中温度和固液两相电导率的变化规律;固液两相的电导率及其加热中的变化不同是物料加热中非均匀温度场产生的主要原因,加热装置的管壁和入料口散热及电极板附近局部过热对物料在装置加热中的温度分布也一定影响。研究结果对进一步研究含颗粒食品电加热特性、研制实用的通电加热装置及开发高品质的含颗粒食品有参考价值。     

利用敲击声音信号进行禽蛋破损检测和模糊识别

为了在蛋品加工中能够快速检测并剔除异常蛋(钢壳蛋、尖嘴蛋)和破损蛋，利用一个微型话筒和声卡采集蛋在敲击时的声脉冲信号，将采集到的声脉冲信号送计算机处理和分析。研究结果表明：正常蛋、破损蛋、钢壳蛋、尖嘴蛋的敲击声音信号在衰竭时间、最小共振峰频率和四点最大频率差等参数上存在差异，且差异的边界是模糊的。利用最大隶属度原则进行模糊识别，破损蛋的识别准确率达95%。     

含颗粒液态食品通电加热研究动态

通过对国内外含颗粒液态食品通电加热研究分析,介绍了含颗粒液态食品通电加热的原理和加工特性,总结出影响通电加热食品品质的因素,概述了通电加热技术在含颗粒食品中的研究动态,阐述了含颗粒食品通电加热中数学模型的应用现状,指出含颗粒液态食品通电加热研究中存在的问题,为今后研究及发展趋势提出了建议.对进一步深入研究含颗粒液态食品通电加热的加工特性、影响因子及其应用具有参考价值和指导意义.     

低频超声雾化栽培喷头阻抗特性的数值模拟

为了加速低频超声雾化栽培喷头的设计制造进程、降低研发成本,该文提出了其阻抗的测试原理电路图,建立了阻抗分析的有限元模型,在大型通用有限元分析软件ANSYS中进行了静态分析、模态分析和谐响应分析。应用静态分析、模态分析以及谐响应分析分别确定了静态电容、谐振频率和反谐振频率以及动态电阻、半功率点频率、动态电感、机械品质因数。利用阻抗分析仪PVC 70A对该喷头的阻抗特性进行了测量,并与有限元模拟结果进行了比较,结果表明各个参数可以作为设计超声波发生器的计算依据。     

基于超声多重反射法测量高衰减流体媒质声阻抗及浓度

利用超声波在固(钢)液界面处声阻抗差异导致的多重反射回波,该文建立了测量被测流体媒质声阻抗及浓度的测量系统.用该系统测量了甲醇、乙醇、蒸馏水和丙三醇4种媒质的声阻抗,与标准值相比,发现测量的误差随被测媒质阻抗增加而迅速减小;同时用系统测量了CaCl2溶液的声阻抗,结果表明溶液阻抗与浓度呈显著线性关系,最大拟合误差小于2.7 g/L.检测中,由于无需声波穿透被测媒质,此法尤其适合于工业中测定管道、容器内高衰减媒质的阻抗及浓度.     

车用两腔抗性消声器声学特性分析及结构优化

为了快速准确的研究抗性消声器的声学特性,该文提出二维解析方法研究两腔抗性消声器的传递损失特性;并基于阻抗管,采用双负载法对消声器传递损失进行了测量,以此对解析方法进行验证。进而基于解析方法,分析隔板通孔半径、隔板位置对消声器传递损失影响。最后采用遗传算法,在不增大外部总体尺寸的条件下,对消声器进行结构优化设计。研究结果表明,该文采用的理论计算方法可较准确地计算出消声器传递损失;两腔消声器比单腔消声器有更好的消声效果;隔板通孔半径及其位置对传递损失影响明显;通过对结构参数优化设计,可以使消声器在目标频带1 000~3 000 Hz的平均传递损失由17.2提升到39.5 d B,获得很好的优化效果。该文建立的二维解析模型可用于计算抗性消声器的传递损失,为快速优化设计消声器提供了参考。     

Ultrasonic Characterization of Unyeasted Bread Dough of Different Sodium Chloride Concentrations

Altering the properties of dough by reducing sodium chloride (NaCl) content affects aeration processes during mixing. The effect of NaCl concentration on the bubble size distribution (BSD) in unyeasted doughs was investigated by an ultrasonic transmission technique through analysis of frequency‐dependent ultrasonic phase velocity and attenuation coefficient. As NaCl concentration was decreased, the volume fraction of gas in the dough increased, resulting in a larger attenuation coefficient for the dough. From the peak in attenuation coefficient, estimates of the median radius and the width of the lognormal BSD in the dough were extracted, both of which were sensitive to the dough's NaCl concentration. As NaCl concentration was reduced, the bubble radius decreased and the width of the distribution increased, in accordance with expectations arising from changes in the dough's consistency. Over the course of 150 min, the radius increased (40–50%) and the width decreased (4–8%) for all dough formulations, consistent with changes in the BSD arising from disproportionation. These dynamic changes demonstrate that dough is an interesting soft material whose formulation can be manipulated to enable it to possess different BSDs; the diffusively driven evolution in these bubble sizes can be investigated noninvasively with ultrasound.     

制冷压缩机排气管消声器声学及阻力特性仿真分析

为了降低空调运行过程中制冷压缩机所产生的噪声,采用在制冷压缩机排气管设置消声器的方法。建立了消声器内部制冷剂的有限元模型,利用声学分析软件Virtual Lab Acoustics和计算流体动力学软件Fluent分别对消声器的声学性能和阻力特性进行数值模拟,分析了消声器内部的扩张腔长度、孔板位置、孔板内径等结构参数对排气管消声器传递损失和压力损失的影响。模拟结果表明:随着扩张腔长度的不断减小,消声器的传递损失曲线逐渐向高频方向移动,消声器的有效消声频率范围不断拓宽,而扩张腔长度对消声器压力损失的影响较小,合理选择扩张腔长度能够有效降低压缩机噪声;孔板位置对中高频噪声的降噪效果影响较大,随着孔板位置由扩张腔中心处向其进口端面不断移动,2 000~2 400 Hz附近频率的消声性能逐渐得到改善,并且消声器内部压力损失不断减小,且其减小幅度越来越大,因此孔板在允许的范围内应尽可能靠近消声器进口端面;随着孔板内径的不断减小,消声器的降噪效果不断增强,但消声器内部压力损失也随之逐渐增大,且增大幅度越来越大,因此孔板内径不宜太小。     

出口管过渡圆弧对抗性消声器性能的影响及应用

为了降低基于声腔模态的进出口管布置原则设计的抗性消声器的压力损失,该文以典型的扩张式消声器和回流式消声器为例,探究了出口管过渡圆弧对其压力损失及传声损失的影响规律。结果表明:出口管施加过渡圆弧对传声损失的影响很小,却能有效降低压力损失;随着过渡圆弧半径的增大,压力损失的变化率减小。最后,在不改变总体尺寸的前提下,基于声腔模态的进出口管布置原则对消声器各抗性消声结构单元的进出口管进行重新布置:进口管和出口管的偏移距离从70 mm改为63 mm,中间管的偏移距离从70 mm改为0,进出口管间的偏移角度从135°改为90°;基于出口管过渡圆弧对压力损失的影响规律对各抗性消声结构单元出口管施加10 mm的过渡圆弧。改进后的消声器不仅传声损失有所提高,且压力损失也得到降低,在750~1500 Hz频率范围内平均传声损失增加了15.3 d B,入口气流速度为60 m/s时压力损失降低了25.20%。研究结果为综合运用基于声腔模态的进出口管布置原则及出口管过渡圆弧对压力损失的影响规律设计及改进消声器提供参考。     

Comparison of ultrasonic velocities in dispersive and nondispersive food materials

Ultrasonic techniques are increasingly being used to evaluate the properties of food materials. Interpretation of the structure and dynamics on the basis of measured ultrasonic parameters requires rigorous definition of ultrasonic parameters such as velocity, especially since many food materials can display considerable dispersive behavior (changes in velocity with frequency). Agar gel (2% w/v) and agar gel (2% w/v) with a regular array of bubbles (8% volume fraction) were chosen as nondispersive and dispersive materials, respectively. Frequency and time domain techniques were used to analyze velocities. Signal, phase, and group velocities were identical in the agar gel and were indistinguishable from those of water (1500 m s(-1)), indicating the predominant effect of the bulk modulus of the water they contain on the longitudinal modulus of the gel. In contrast, the inclusion of the bubbles in the agar gel led to strongly dispersive behavior, with group velocities varying by 1000 m s(-1) above and below the 1500 m s(-1) of the agar gel without bubbles, depending on frequency. The addition of bubbles also led to strong attenuation in the agar gel with a peak occurring at a frequency associated with a band gap arising from destructive interference of sound waves. The results show that care must be taken when comparing ultrasonic parameters derived from experiments on food materials performed at different frequencies or with different ultrasonic techniques.     

Ultrasonic determination of chicken composition.

An ultrasonic technique has been developed for measuring the composition of chicken meat. The relationship between the composition and ultrasonic velocity of chicken meat was determined using chicken analogues of different composition, prepared from dried chicken powder, corn oil, and distilled water. The ultrasonic velocity of chicken analogues was measured at temperatures from 5 to 35 degrees C using an ultrasonic spectrometer. The ultrasonic velocity increased with solids-nonfat (SNF) content at all temperatures but had a more complex dependence on fat content. Around 15 degrees C the ultrasonic velocity was independent of fat content; however, at lower temperatures it increased with fat content, and at higher temperatures it decreased. Semiempirical equations were developed to describe the relationship between ultrasonic velocity and chicken composition. To determine the usefulness of these equations, the ultrasonic velocities of various chicken meats were measured. The compositions of the chicken meats predicted on the basis of ultrasonic measurements were in good agreement with those determined by using standard methods (r(2) > 0. 97). The ultrasonic technique could also be used to measure the solid fat content of chicken fat. This study shows that ultrasonic velocity measurements can be used to characterize chicken composition. This method has great potential for application in the food industry because it is simple, fast, nondestructive, and reliable.     

超声波平板冷冻提高胡萝卜冻干速率

为了探究接触式超声波辅助平板冷冻法对固体果蔬冻干过程的影响,该文研究了接触式超声波辅助胡萝卜的平板冷冻过程。首先,利用低温显微镜证实了接触式超声波能够有效促进平板冷冻固体果蔬样品成核,并且冰晶的形态与成核温度呈显著相关性(相关系数0.99),即成核温度越高,冰晶尺寸越大。其次,研究了超声波作用参数(功率,作用时间)对胡萝卜冰晶尺寸以及冻干速率的影响。结果表明,在胡萝卜样品厚度为5 mm,样品冷冻温度为?1℃时施加178.7W功率的超声波10 s能显著提高(P0.05)样品的成核温度,使冻干胡萝卜的孔隙当量直径从无超声波辅助条件下对照组样品的(66.29±3.58)μm提高到了(80.81±3.03)μm,同时干燥至实际含水率为10%时,升华干燥速率提升了29.1%。该研究为接触式超声波辅助平板冷冻用于果蔬样品的冻干过程提供了有益参考。     

Ultrasonic Investigation of the Effect of Mixing Under Reduced Pressure on the Mechanical Properties of Bread Dough

Mixing is critical to attainment of a desirable gas cell distribution in dough. By varying mixer headspace pressure, changes in the mechanical properties of dough were investigated as a function of the dough's void concentration using low frequency (50 kHz) ultrasonic techniques. For the mixer used, this allowed the volume fraction of voids (Φ) to be varied from ≈0.01 to 0.08. The ultrasonic attenuation of longitudinal waves increased linearly with increases in Φ. If, as reported, pressure reductions during mixing decrease the number density of the voids but do not affect void size, the change in attenuation is proportional to the number of voids. By contrast, the velocity of longitudinal ultrasonic waves decreased dramatically with increasing Φ in the range 0.012 < Φ < 0.03, dropping from a value near that of water to values well below the velocity of sound in air. At higher Φ, the velocity decrease was less rapid. The longitudinal elastic modulus determined from these ultrasonic results shows that the mechanical properties of the dough are sensitive to the presence of gas bubbles. At low void fractions, the elastic behavior of dough is also influenced by changes in dough matrix properties.     

循环水养殖大口黑鲈摄食颗粒饲料的声学特征

为突破智能投饲系统的技术瓶颈,近年来采用被动声学技术开展鱼虾摄食行为研究成为热点之一。该研究主要采用被动声学技术获取单体大口黑鲈（Micropterus salmoides）摄食声信号,从混合信号中提取完善的摄食信号,筛选可作为衡量大口黑鲈摄食活跃度的声学特征参数,以期对摄食活跃度进行量化。根据大口黑鲈喂食期间的同步音频与视频记录,确定信号类别并进行标记,主要提取每次吞食饲料的时域与频域特征,对比各参数与吞食次序之间的相关度。研究结果表明,摄食声信号能量主要集中于4～7 kHz,且大口黑鲈吞食间隔与吞食次序呈正相关,稳定性较强;而时域特征中的波形振幅极差与频域特征的功率积分值均与吞食次序呈负相关。吞食间隔、振幅极差及功率积分值均可以作为衡量摄食活跃度的量化指标,而共振峰与平均梅尔倒谱系数可作为摄食声识别参数,研究结果可为今后养殖鱼类被动声学智能投饲系统研发提供理论基础。     

Heat-induced changes in the ultrasonic properties of whey proteins

The physical aggregation of commercial whey protein isolate (WPI) and purified beta-lactoglobulin was studied by ultrasound spectroscopy. Protein samples were dialyzed to achieve constant ionic strength backgrounds of 0.01 and 0.1 NaCl, and gelation was induced in situ at constant temperatures (from 50 to 75 degrees C) or with a temperature ramp from 20 to 85 degrees C. Changes in the ultrasonic properties were shown in the early stages of heating, at temperatures below those reported for protein denaturation. During heating, the relative ultrasound velocity (defined as the difference between sample velocity and reference velocity) decreased continuously with temperature, indicating a rearrangement of the hydration layer of the protein and an increase in compressibility of the protein shell. At temperatures <50 degrees C the ultrasonic attenuation decreased, and <65 degrees C both velocity and attenuation differentials showed increasing values. A sharp decrease in the relative velocity and an increase in the attenuation at 70 degrees C were indications of "classical" protein denaturation and the formation of a gel network. Values of attenuation were significantly different between samples prepared with 0.01 and 0.1 M NaCl, although no difference was shown in the overall ultrasonic behavior. WPI and beta-lactoglobulin showed similar ultrasonic properties during heating, but some differences were noted in the values of attenuation of WPI solutions, which may relate to a less homogeneous distribution of aggregates caused by the presence of alpha-lactalbumin and other minor proteins in WPI.