共振吸聲

     透水混(hun)凝土路表面(mian)層若為多空(kong)(kong)腔共(gong)振吸(xi)(xi)(xi)聲(sheng)(sheng)結構，其吸(xi)(xi)(xi)聲(sheng)(sheng)原理可由單腔共(gong)振吸(xi)(xi)(xi)聲(sheng)(sheng)結構來解釋(shi)。中間(jian)封閉(bi)(bi)有一定(ding)體積的(de)(de)(de)空(kong)(kong)腔，通過一定(ding)深度的(de)(de)(de)小孔(kong)(kong)(kong)和(he)(he)外界聲(sheng)(sheng)場空(kong)(kong)間(jian)相連形成(cheng)一個(ge)單腔共(gong)振吸(xi)(xi)(xi)聲(sheng)(sheng)結構。當孔(kong)(kong)(kong)的(de)(de)(de)深度t和(he)(he)孔(kong)(kong)(kong)徑d遠遠小于(yu)聲(sheng)(sheng)波波長，孔(kong)(kong)(kong)中的(de)(de)(de)空(kong)(kong)氣(qi)柱彈(dan)性變形很小，可視為無形變的(de)(de)(de)質量塊(質點)，而封閉(bi)(bi)空(kong)(kong)腔V的(de)(de)(de)體積比孔(kong)(kong)(kong)頸大得(de)多，隨聲(sheng)(sheng)波作彈(dan)性振動(dong)，起著(zhu)空(kong)(kong)氣(qi)彈(dan)簧的(de)(de)(de)作用(yong)。整個(ge)系統(tong)類似彈(dan)簧振子，稱(cheng)為亥姆霍茲共(gong)振器。當外界入射聲(sheng)(sheng)波頻(pin)率(lv)和(he)(he)系統(tong)的(de)(de)(de)固有頻(pin)率(lv)相等時，孔(kong)(kong)(kong)頸中的(de)(de)(de)空(kong)(kong)氣(qi)柱就由于(yu)共(gong)振而產生劇烈(lie)的(de)(de)(de)振動(dong)。在振動(dong)中，空(kong)(kong)氣(qi)柱和(he)(he)孔(kong)(kong)(kong)頸側(ce)壁摩擦而消(xiao)耗(hao)聲(sheng)(sheng)能吸(xi)(xi)(xi)聲(sheng)(sheng)。

多孔吸聲

    聲(sheng)(sheng)(sheng)波(bo)(bo)在空(kong)(kong)(kong)(kong)氣(qi)(qi)中(zhong)(zhong)的(de)(de)(de)(de)傳(chuan)播(bo)滿足惠更斯(si)原理，即聲(sheng)(sheng)(sheng)源的(de)(de)(de)(de)振(zhen)(zhen)動(dong)(dong)(dong)(dong)引(yin)起(qi)波(bo)(bo)動(dong)(dong)(dong)(dong)，波(bo)(bo)動(dong)(dong)(dong)(dong)的(de)(de)(de)(de)傳(chuan)播(bo)是由(you)于介質中(zhong)(zhong)質點(dian)間的(de)(de)(de)(de)相(xiang)互作用。在連續介質中(zhong)(zhong)，任何一點(dian)的(de)(de)(de)(de)振(zhen)(zhen)動(dong)(dong)(dong)(dong)都將直接引(yin)起(qi)鄰近質點(dian)的(de)(de)(de)(de)振(zhen)(zhen)動(dong)(dong)(dong)(dong)。多孔(kong)(kong)(kong)吸(xi)聲(sheng)(sheng)(sheng)材(cai)(cai)(cai)(cai)料(liao)(liao)具(ju)(ju)有許多微小(xiao)的(de)(de)(de)(de)間隙(xi)和(he)連續的(de)(de)(de)(de)氣(qi)(qi)泡，孔(kong)(kong)(kong)隙(xi)間彼(bi)此貫(guan)通，且通過(guo)表(biao)面(mian)(mian)(mian)與外界相(xiang)通。當聲(sheng)(sheng)(sheng)波(bo)(bo)入射(she)到材(cai)(cai)(cai)(cai)料(liao)(liao)表(biao)面(mian)(mian)(mian)時，一部分在材(cai)(cai)(cai)(cai)料(liao)(liao)表(biao)面(mian)(mian)(mian)上(shang)反射(she)，另(ling)一部分則透(tou)入到材(cai)(cai)(cai)(cai)料(liao)(liao)內(nei)部向前傳(chuan)播(bo)。先(xian)，由(you)于聲(sheng)(sheng)(sheng)波(bo)(bo)產(chan)生的(de)(de)(de)(de)振(zhen)(zhen)動(dong)(dong)(dong)(dong)引(yin)起(qi)小(xiao)孔(kong)(kong)(kong)或間隙(xi)內(nei)的(de)(de)(de)(de)空(kong)(kong)(kong)(kong)氣(qi)(qi)運動(dong)(dong)(dong)(dong)，造成和(he)孔(kong)(kong)(kong)壁(bi)的(de)(de)(de)(de)摩(mo)擦，緊靠(kao)孔(kong)(kong)(kong)壁(bi)表(biao)面(mian)(mian)(mian)的(de)(de)(de)(de)空(kong)(kong)(kong)(kong)氣(qi)(qi)受孔(kong)(kong)(kong)壁(bi)的(de)(de)(de)(de)影響不易(yi)動(dong)(dong)(dong)(dong)起(qi)來(lai)，因摩(mo)擦和(he)粘滯(zhi)力的(de)(de)(de)(de)作用，使(shi)相(xiang)當一部分聲(sheng)(sheng)(sheng)能(neng)轉化為熱(re)能(neng)，從而(er)使(shi)聲(sheng)(sheng)(sheng)波(bo)(bo)衰減，反射(she)聲(sheng)(sheng)(sheng)減弱達到吸(xi)聲(sheng)(sheng)(sheng)的(de)(de)(de)(de)目的(de)(de)(de)(de)；其次，小(xiao)孔(kong)(kong)(kong)中(zhong)(zhong)的(de)(de)(de)(de)空(kong)(kong)(kong)(kong)氣(qi)(qi)和(he)孔(kong)(kong)(kong)壁(bi)之間的(de)(de)(de)(de)熱(re)交換引(yin)起(qi)的(de)(de)(de)(de)熱(re)損(sun)失，也使(shi)聲(sheng)(sheng)(sheng)能(neng)衰減。另(ling)外，高頻聲(sheng)(sheng)(sheng)波(bo)(bo)可使(shi)空(kong)(kong)(kong)(kong)隙(xi)間空(kong)(kong)(kong)(kong)氣(qi)(qi)質點(dian)的(de)(de)(de)(de)振(zhen)(zhen)動(dong)(dong)(dong)(dong)速度加(jia)快，空(kong)(kong)(kong)(kong)氣(qi)(qi)與孔(kong)(kong)(kong)壁(bi)的(de)(de)(de)(de)熱(re)交換也加(jia)快，使(shi)多孔(kong)(kong)(kong)材(cai)(cai)(cai)(cai)料(liao)(liao)具(ju)(ju)有良好(hao)的(de)(de)(de)(de)高頻吸(xi)聲(sheng)(sheng)(sheng)性能(neng)。若路面(mian)(mian)(mian)存在許多連通的(de)(de)(de)(de)小(xiao)孔(kong)(kong)(kong)，當輪胎滾動(dong)(dong)(dong)(dong)時被壓縮的(de)(de)(de)(de)空(kong)(kong)(kong)(kong)氣(qi)(qi)能(neng)夠通暢地鉆入路面(mian)(mian)(mian)內(nei)，而(er)不是向周圍(wei)排射(she)，在聲(sheng)(sheng)(sheng)學(xue)上(shang)可以將這種路面(mian)(mian)(mian)看成是具(ju)(ju)有剛性骨架的(de)(de)(de)(de)多孔(kong)(kong)(kong)吸(xi)聲(sheng)(sheng)(sheng)材(cai)(cai)(cai)(cai)料(liao)(liao)，具(ju)(ju)有相(xiang)當好(hao)的(de)(de)(de)(de)吸(xi)聲(sheng)(sheng)(sheng)性能(neng)。