Method and device for ultrasonic measurements

1. An ultrasonic measurement method comprising:

(a) acoustically coupling an ultrasonic transducer to an object to be measured by means of a resilient material contact layer;

(b) transmitting, by using said transducer, a plurality of consecutive ultrasonic transmit signals into said object being measured, so that the signals travel from the transducer to an end of the object where the transmit signal is reflected and where a transmit frequency of each of said plurality of transmit signals is distinct from the frequency of the other transmit signals of said plurality of transmit signals;

(c) selecting, based on received signal echoes, at least one transmit frequency to be used for ultrasonic measurement of said object; and

(d) transmitting, during measurement, signals into said object using the selected transmit frequency and receiving signal echoes of said transmit signals, wherein said signal echoes are detected by demodulation in two orthogonal channels, so as to allow determination of a phase of a signal echo with respect to the selected transmit signal.

2. The method according to claim 1 ,

wherein step (b) further comprises:

selecting a first transmit frequency,

using said transducer,

transmitting a first ultrasonic transmit signal having said first transmit frequency, and

transmitting a second ultrasonic transmit signal having a second transmit frequency; and

wherein step (c) further comprises:

determining at least one of a signal power and an amplitude of a received signal echo of said first transmit signal,

determining at least one of a signal power and an amplitude of a received signal echo of said second transmit signal,

comparing at least one of the determined signal powers and the determined amplitudes of said received signal echoes, and

selecting the transmit frequency resulting in at least one of a highest signal power and a highest amplitude.

3. The method according to claim 1 , further comprising repeating said steps (b)-(d) until a transmit frequency having at least one of a signal power and an amplitude exceeding a first threshold is detected, and selecting a transmit frequency exceeding said first threshold for measurement.

4. The method according to claim 1 , further comprising repeating said steps (b)-(d) until a transmit frequency having at least one of a peak signal power and a peak amplitude is detected, and selecting a transmit frequency substantially resulting in said at least one of said peak signal power and said peak amplitude for measurement.

5. The method according to claim 1 , wherein said transmit signals each have a distinct and fixed frequency.

6. The method according to claim 1 , wherein execution of said steps (a)-(d) is performed under control of a microprocessor in a fastener tightening tool.

7. The method according to claim 6 , further comprising:

prior to tightening of a fastener, determining said transmit frequency, and

performing real-time ultrasonic measurement during said tightening of said fastener using said fastener tightening tool.

8. The method according to claim 1 , wherein said contact layer has a thickness of 0.1-5 mm.

9. The method according to claim 1 , wherein said transmit frequencies are in at least a subrange of 2-50 MHz.

10. An ultrasonic measurement device comprising:

an ultrasonic transducer for coupling to an object to be measured and for transmitting ultrasonic transmit gnals through said object;

receiving means for receiving ultrasonic signal echoes resulting from the ultrasonic transmit signals transmitted by said ultrasonic transducer; and

a resilient material contact layer for acoustically coupling said transducer and receiver to the object to be measured,

wherein the ultrasonic measurement device is adapted to perform functions comprising:

transmitting, by using said transducer, a plurality of consecutive ultrasonic transmit signals into said object being measured, so that the signals travel from the transducer to an end of the object where the transmit signal is reflected and where a transmit frequency of each of said plurality of transmit signals is distinct from the frequency of the other transmit signals of said plurality of transmit signals;

selecting, based on received signal echoes, at least one transmit frequency to be used for ultrasonic measurement of said object; and

transmitting, during measurement, signals into said object using the selected transmit frequency and receiving signal echoes of said transmit signals, wherein said signal echoes are detected by demodulation in two orthogonal channels, so as to allow determination of a phase of a signal echo with respect to the selected transmit signal.

11. The device according to claim 10 , wherein said receiving means comprises said transducer.

12. The device according to claim 10 , wherein said device comprises a fastener tightening tool.

13. The device according to claim 12 , wherein said fastener tightening tool is arranged to measure elongation of a fastener being tightened thereby.