本論文研究提出創新之變頻式超音波測距法，以改良超音波測距法的準確性。此一新法是由雙頻式測距法改良而來。將原本為兩次分別獨立發送之雙頻超音波，改為串接式發射。我們透過系統模擬之實驗驗證新方法的可行性及其特性之探討，如此可以得到與雙頻法相近之量測精準度，進而有效地提升量測速度，同時也得到更好的雜訊免疫力。 經由模擬實驗之結果，變頻式量測法應採用的最佳聲波頻率範圍為39~41kHz，最佳之第二頻發送延遲時間應與前後兩頻之波群延遲時間差相等。若使用最佳化參數進行模擬，在最大4.5m之量測範圍內，最大之量測誤差在0.03um以下。藉由選擇適當的第二頻發送延遲時間，可以降低變頻時系統瞬態響應之影響，並且不需經由線性迴歸修正，就可以使理論量測誤差降低到微米等級。 本論文研究亦根據新量測法之計算結構進行了軟硬體實體測試系統之規劃與設計。然而其功能的實踐尚待後繼者之努力。 A frequency switching method was proposed to improve, further than the dual frequencies method, the accuracy of the distance measurement by ultrasound. By the latter, wave packet of two different frequencies were transmitted separately and were compared at the receiver to identify the delay time for compensation, while the new method switches the ultrasound from one frequency to the other in sequence with a predetermined gap time and thus fixed correlations. The feasibility of the new method was verified through system simulation that both methods yielded similar accuracy, yet the new method required shorter measurement time and had better noise immunity. Optimal parameters for the new methods were also found through simulation studies that the frequency should range from 39 to 41 KHz, the gap time between of the frequency switch should equal to the difference of the group delays at the two frequencies. With total distance under 4.5m the maximum measurement error was below 0.03um. Properly adjusting the gap time of frequency switch, transient effects of the frequency switch could be minimized such that the theoretical measurement error could be reduced to nanometers. The hardware and software system architectural design was carried out in an attempt to realize a physical prototype of the new measurement technology. The physical implementation awaits to be done by successors.