Structural analyzer, in particular for medical implants

A dental analyzer for analyzing dental implants includes a dental probe having a probe tip for contacting a patient's dental implant. An accelerometer is coupled to the probe tip. A hammer fired by an actuator against the accelerometer impacts the probe tip against the dental implant which vibrates the dental implant. The accelerometer measures the acceleration time history of the vibrating dental implant. A processor converts the measured acceleration time history of the dental implant into a frequency spectrum from which a diagnosis can then be made regarding the condition of the dental implant.

BACKGROUND 
When a dental implant is implanted into the jaw bone of a patient, it is 
often difficult to determine whether sufficient bonding has occurred 
between the dental implant and the jaw bone. Currently, taking an x-ray of 
a patient's jaw and inspecting the x-ray for structural integrity between 
the dental implant and the jaw bone is a common method for determining 
whether a dental implant is properly bonded to the jaw bone. However, in 
cases where the progress of a dental implant must be followed over a 
period of time, the use of x-rays is undesirable due to medical 
considerations caused by the cumulative effect of multiple exposures to 
x-rays. 
A number of attempts have been made to provide an apparatus for determining 
the mobility of a dental implant or tooth which does not require x-rays to 
be taken. One such attempt is found in U.S. Pat. No. 3,094,115, which 
discloses a tooth mobility indicator. In use, the patient sits in a dental 
chair with his head resting upon an oscillating element which vibrates the 
patient's teeth. A hand-held probe containing an accelerometer is placed 
upon a tooth to measure the amplitude of the vibrating tooth. The probe 
registers the departure of the amplitude and frequency of the signal 
received by the accelerometer from the input signal of the oscillating 
element. This method of measurement is subject to error due to variability 
in the placement of the oscillating element as well as distortion of the 
data measured through the patient's head and by the probe resonances 
themselves. 
Another attempt is found in U.S. Pat. No. 4,470,810 which discloses a hand 
held probe for applying a motion to a tooth and measuring the displacement 
of the tooth from which the displacement rate of the tooth can be found. 
Since the displacement of a tooth is usually less than 1 millimeter, an 
instrument measuring such small displacements must be extremely accurate. 
However, displacement measurements measured with this probe use the probe 
itself as a reference point. As a result, the displacement measurements 
are subject to a high degree of error caused by variations in the angle at 
which the probe is held as well as the force at which the probe is pressed 
against the tooth. 
A similar attempt is found in U.S. Pat. No. 4,881,552 which discloses a 
tooth stability monitor having a hand-held probe for assessing the 
rigidity of a tooth. The probe measures the displacement of the tooth and 
the resulting force applied to the tooth. This instrument is subject to 
the same errors experienced by the probe in U.S. Pat. No. 4,470,810. 
Still another attempt is found in U.S. Pat. No. 4,482,324 which discloses a 
hand-held probe for determining the degree of looseness of a tooth. The 
instrument includes a ram which is disposed at a right angle with respect 
to the handle of the instrument. The ram is accelerated to a specific 
velocity and after impact against a tooth, the ram is repelled in a 
direction towards the initial position. The time required for the ram to 
return is a direct indicator of the degree of tooth mobility. This method 
is also subject to error due to variations in the manner which the probe 
is held relative to the tooth. 
SUMMARY OF THE INVENTION 
These attempts for determining the mobility of a tooth or dental implant 
through the use of a mechanical probe have not proven to be accurate or 
repeatable due to the parameter being measured, the method of measurement 
or the probe design. In order to accurately follow the progress of a 
dental implant over a period to time, the measuring instrument must be 
accurate enough to detect small changes in the condition of the dental 
implant. Accordingly, there is a continuing need for a mechanical 
instrument accurate enough to detect small changes in the condition of a 
dental implant such that the progress of a dental implant can be followed 
over a period of time. 
The present invention provides a probe having a probe tip for contacting a 
structure. An accelerometer is coupled to the probe tip for measuring an 
acceleration time history of the structure. The probe includes an actuator 
for firing a hammer in order to impact the probe tip against the 
structure. 
In preferred embodiments, a probe body comprising a hollow tube houses the 
actuator and the hammer. A membrane secured to the probe body supports the 
accelerometer and isolates motion of the accelerometer from motion of the 
probe body. The actuator includes an electromagnetic coil for positioning 
the hammer into firing position and a spring positioned against the hammer 
for firing the hammer. A sensor prevents the actuator from firing the 
hammer until the probe tip is pressed against the structure at a 
predetermined force. A processor converts the measured acceleration time 
history of the structure into a frequency spectrum through a Fourier 
transform function. Characteristics of the generated frequency spectrum 
are compared with a database of frequency spectrums enabling a diagnosis 
to be made. 
The present invention probe is capable of analyzing a dental implant in a 
manner which is extremely accurate such that small changes in the 
condition of the dental implant can be detected. As a result, progress of 
a dental implant can be accurately followed over a period of time. The 
present invention, by measuring the acceleration time history of a dental 
implant, acquires enough data to provide information such as stiffness, 
mobility, damping, resonant modes/frequencies and osseointegration of a 
dental implant. Additionally, the present invention probe is capable of 
accurately analyzing the condition of any other medical implant, teeth, 
bones or mechanical structures used in industry.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, dental analyzer 10 includes a dental probe 20, an 
electronics box 16 and a computer or processor 12. Dental probe 20 impacts 
crown 76 of dental implant 28 (FIG. 2) and measures the acceleration time 
history of the dental implant as the dental implant vibrates from the 
impact. Dental probe 20 has a probe body 24 for housing an actuator 44, a 
hammer 42 extending from actuator 44 and an accelerometer 56. The 
accelerometer 56 is secured to a rigid, light weight probe tip 26 which in 
use is positioned against the crown 76 of dental implant 28. Probe tip 26 
and accelerometer 56 are supported by a flexible diaphragm or membrane 58 
(FIG. 11) stretched over the distal end of probe body 24. The diaphragm 58 
serves to press probe tip 26 against crown 76 of dental implant 28 and 
isolates motion of the probe tip 26 and accelerometer 56 from motion of 
probe body 24. Actuator 44 includes an electromagnetic coil 45 and a 
spring 40. A firing button 34 activates actuator 44 which brings hammer 42 
into spring 40 which returns the hammer against the accelerometer 56. This 
causes probe tip 26 to transfer the impact energy into the dental implant 
28 causing the dental implant to vibrate. Accelerometer 56 can then 
measure the acceleration time history of the vibrating dental implant 28. 
Dental probe 20 is electrically connected to electronics box 16 by 
electrical connector 22 and line 18. The electronics box 16 includes a 
capacitive storage power source 16a for providing power to actuator 44. As 
presented in greater detail below with regard to FIG. 5, electronics box 
16 also includes signal conditioning filters for conditioning or filtering 
the acceleration time histories measured with dental probe 20 to remove 
unwanted signals. Electronics box 16 and dental probe 20 also contain 
amplifiers for amplifying the accelerating time history signal. 
Electronics box 16 is connected to computer 12 by line 14. Computer 12 
converts the conditioned acceleration time histories provided to it by 
electronics box 16 into a frequency spectrum through a Fourier transform 
function. A diagnosis of the condition of the dental implant 28 can then 
be made from the frequency spectrum. 
Opto-isolation buffers within electronics box 16 isolate the 110 volt 
electronics of computer 12 from dental probe 20 for patient safety. The 
computer can be of the portable type which uses harmless low voltage (less 
than 5 v) causing no danger to the patient. Furthermore, the electronics 
box can operate with similar harmless voltage precluding the use of 
opto-isolators. 
In operation, referring to FIG. 2, dental probe 20 is held in the hand of a 
dentist or dental technician and the end 27 of probe tip 26 is pressed 
against crown 76 of dental implant 28 stretching diaphragm 58 (FIG. 11). 
Dental implant 28 consists of a crown 76 secured to the jaw bone 70 by 
implant post 74. The end 27 of probe tip 26 is positioned against the 
crown 76 of dental implant 28 above gum tissue 72. Glue or wax can be used 
to prevent the end 27 of probe tip 26 from moving or losing contact with 
crown 
The firing button 34 is then depressed in order to provide power to 
actuator 44 which activates the hammer 42. However, power will not be 
provided to actuator 44 until force sensor 30 (FIG. 11) detects that probe 
tip 26 is pressed against dental implant 28 with a 
predetermined/presetable force. Alternatively, force sensor 30 can be 
substituted with a position sensor which allows power to be delivered to 
actuator 44 when diaphragm 58 has deflected enough so that accelerometer 
56 is in a predetermined position relative to probe body 24. Once this 
predetermined force is attained, a pulse of power from the capacitive 
storage power source 16a in electronics box 16 is released to momentarily 
energize electromagnetic coil 45 of actuator 44. This draws hammer 42 into 
firing position toward the electromagnetic coil 45 and away from 
accelerometer 56, compressing spring 40. 
After the energy in the capacitor has dissipated in the actuator, the 
electromagnetic coil 45 releases the potential energy of the compressed 
spring 40. Hammer 42 then strikes accelerometer 45 to provide a calibrated 
flat frequency response impact (FIG. 3). Since accelerometer 56 is rigidly 
secured to probe tip 26, probe tip 26 impacts against crown 76 to deflect 
implant post 74. By only firing hammer 42 when probe tip 26 is pressed 
against crown 76 of dental implant 28 with a predetermined force, dental 
probe 20 consistently delivers a constant impact. Indicator light 32 
illuminates to provide an indication that an impact has occurred. 
Once dental implant 28 has been impacted by probe tip 26, dental implant 28 
oscillates back and forth as indicated by arrows 78a (FIG. 4). Hammer 42 
provides a Dirac-Delta input function to dental implant 28 causing dental 
implant 28 to vibrate at a range of frequencies. Probe tip 26 remains 
pressed against crown 76 such that the end 27 of probe tip 26 remains in 
contact with crown 76. Diaphragm 58 allows probe tip 26 and accelerometer 
56 to oscillate independently of probe body 24 while probe tip 26 remains 
pressed against crown 76. As a result, the probe tip 26 and accelerometer 
56 vibrate in unison with dental implant 28 as shown by arrows 78b. This 
vibration is the complex dynamic resonance of the structure under test 
(the dental implant in this case) which when transformed to the frequency 
domain provides a spectral signature which is unique to the structure 
under test. It is also an extremely sensitive measurement because a 
measurement of frequency is the most accurate and resolute measurement 
that can be made in the field of electronics. 
The accelerometer 56 measures accelerations of motion of the dental implant 
28 to provide an acceleration time history of the dental implant 28 
recorded in volts over time. The acceleration of dental implant 28 is 
measured by accelerometer 56 at 100 microsecond intervals which results in 
a total of about 1000 samples of data taken for an acceleration time 
history. 
The electronics box 16 (FIG. 1) conditions the measured acceleration time 
history by rejecting non-useable data from the acceleration time history. 
FIG. 5 depicts a preferred electrical circuit for electronics box 16. A 
time delay 96 is connected to accelerometer 56 via opto-isolator 90b and 
line 92. Firing button 34 is connected to the adjustable time delay 96a of 
time delay 96 by opto-isolator 90a and line 94. Opto-isolators 90a and 90b 
electrically isolate dental probe 20 from electronics within electronics 
box 16. Firing button 34 is also connected to capacitor storage power 
source 16a via opto-isolator 90a, lines 94 and 110 and sequential pulse 
generator 112. High pass filter 16b is connected to time delay 96 by line 
98. Low pass filter 16c is connected to high pass filter 16b by line 100. 
Notch filter 104 is connected to low pass filter 16c by line 102. Notch 
filter 104 is connected to computer 12 via line 106, opto-isolator 108 and 
line 104. 
When firing button 34 is depressed, sequential pulse generator 112 produces 
a series of pulses which discharges capacitive storage power source 16a 
into actuator 44. The pulses are spaced to allow a full time history 
measurement after each, and the multiple measurements may be averaged for 
improved signal to noise ratio. Once the crown 76 of dental implant 28 has 
been impacted, time delay 96 opens momentarily to reject the data 
generated by the initial impact of the probe tip 26 which is typically the 
first 1/2 cycle after impact against dental implant 28 so that only the 
data associated with the resulting vibration of dental implant 28 is 
recorded. Once the time delay 96 closes, the acceleration time history 
signal passes through high pass filter 16b where low frequency signals or 
noise (approximately 0 to 10 Hz) is filtered out. These low frequency 
signals are unusable, contain noise, and when rejected, increase the 
signal to noise ratio of the desired signal. The signal then passes 
through low pass filter 16c which rejects high frequency noise above the 
Nyquist sampling rate of the data acquisition system (5 kHz), thereby 
increasing again the signal to noise ratio of the desired signal. Notch 
filter 104 then rejects unwanted resonances. An optional sinx/x filter can 
be located after notch filter 104 to increase resolution through curve 
fitting extrapolation. The signal to noise ratio is further increased 
through data averaging of 3 or more successive samples of data taken 
within a 5 second period. The data from these successive samples is 
statistically averaged or route-summ-squared to provide a resultant signal 
with increase signal to noise ratio. FIG. 6 is a graph depicting the 
conditional acceleration time history of dental implant 28. 
The conditioned acceleration time history is then transferred from 
electronics box 16 to the computer 12 for processing. Computer 12 employs 
a standard commercially available software program to perform a frequency 
domain fast Fourier transform on the conditioned acceleration time history 
of dental implant 28 which converts the acceleration time history into a 
frequency spectrum recorded in volts versus frequency (FIG. 7). For each 
dental implant 28 which is measured, the corresponding frequency spectrum 
has a unique spectral signature similar to a fingerprint. As a result, 
each dental implant can be identified by its corresponding frequency 
spectrum. Additionally, information regarding the condition of the dental 
implant 28 can be mathematically extracted from the acceleration time 
history and the generated frequency spectrum. 
For example, the double integration of the conditioned acceleration time 
history of dental implant 28 provides the mobility or position of the 
dental implant 28 over time. This mobility or position of dental implant 
28 can be plotted on a graph over time. Such a plot records the movement 
of dental implant 28 along a single dimension over time as seen in FIG. 8. 
An example of two dimensional mobility over time is seen in the 
position/displacement time history graph of FIG. 9 where the displacement 
of dental implant 28 is plotted in the x and y directions. The 
two-dimensional feature of the graph is preferably provided by securing a 
second accelerometer to the probe tip 26 orientated in a direction 
orthogonal to accelerometer 56. As a result, two acceleration time 
histories of dental implant 28 are measured in directions perpendicular to 
each other forming x and y components. A preferred configuration for 
measuring acceleration time histories in two directions is depicted in 
FIG. 10 where two accelerometers 29a and 29b are mounted in orientations 
perpendicular to each other near the end 27 of probe tip 26. A third 
accelerometer can be added for measuring acceleration time histories in a 
third direction in order to acquire three dimensional data. Alternatively, 
multiple accelerometers can be bonded directly to dental implant 28. 
The velocity of the dental implant 28 can be determined by performing a 
single integration of the acceleration time history. This also can be 
plotted on a graph as a function of time. 
The frequency spectrum also provides information regarding the condition of 
dental implant 28. For example, the damping of the dental implant 28 is 
mathematically determined by the rate at which the amplitude of a 
particular frequency of the frequency spectrum dies out over time. 
After impact, the implant 28, probe tip 26 and accelerometer 56 vibrate 
together as a damped single degree of freedom oscillator that satisfies 
the following differential equation: 
EQU mx+cx+kx=0 Equation 1 
where: 
m=mass 
c=damping coefficient 
k=spring rate 
x=tooth displacement 
The homogenous solution of Equation 1 may be expressed for damping as: 
EQU x=e.sup.-.xi.wt {A sin wt +B cos wt} Equation 2 
where: 
w=natural frequency of the oscillator (rad/sec) 
t=time (secs) 
A,B=coefficients that depend on the boundary conditions 
.xi.=percent critical damping (c/Cc) 
Applying the known boundary conditions at t=0 where x=0 and tooth velocity 
V.sub.o =0 yields: 
B=0 
A=Vo/w 
Hence, the tooth vibration after impact is given by the expression: 
EQU x=Vo/w e.sup.-.xi.wt sin wt Equation 3 
EQU x=f(t) 
Equation 3 expresses the response displacement x as a function of time t. 
Note that x approaches zero as t approaches infinity due to the presence 
of the damping term: 
EQU e.sup.-.xi.wt 
The presence of damping results in a decaying sinusoid. 
The resonant frequencies of the dental implant 28 are indicated by the 
peaks in the frequency spectrum. Once the resonant frequencies are known, 
the mode shapes of dental implant 28 can be determined. By treating the 
dental implant 28 as a cantilever beam, the various known mode shapes of a 
vibrating cantilever beam can be correlated to each resonant frequency of 
dental implant 28. 
The stiffness of dental implant 28 is determined by the equation: 
EQU k=w.sup.2 m Equation 4 
The Fourier transform function which transforms the acceleration time 
history from the time domain to the frequency domain is given by: 
##EQU1## 
Other information such as osseointegration and/or bond characteristics of 
the dental implant 28 and spectral discrimination are determined through 
spectral analysis in which the frequency spectrum of dental implant 28 is 
compared with a database of previously recorded frequency spectrums. The 
data base includes software identifying certain characteristics regarding 
dental implants with corresponding specific characteristics of the 
frequency spectrum. 
Once the computer 12 matches features of the generated frequency spectrum 
with features found in frequency spectrums stored in the database, a 
diagnosis can be made regarding the condition of the dental implant 28. 
Information regarding the patient's age, sex and medical history can be 
entered into the computer 12 to aid in the diagnosis. In applications 
where a simple answer is desired, the diagnosis can be signalled by a red 
or green indicator light. In such a case, a green light would indicate 
that certain characteristics of the frequency spectrum are within an 
acceptable range and would designate that the implant is good. A red light 
would indicate that certain characteristics of the frequency spectrum are 
outside of an acceptable range and would designate that the implant is 
bad. In applications where more information is desired, the results of the 
diagnosis can be provided on the screen of computer 12 or printed out on a 
printer. 
When following the osseointegration and/or bond characteristics of a 
particular dental implant 28 over time, the measured frequencies of the 
dental implant will shift to higher frequencies over a period of time if 
the bond between the dental implant and the bone improves over time. 
Conversely, a shift to lower frequencies will occur over time if the bond 
deteriorates. 
FIG. 11 provides a more detailed depiction of dental probe 20. Probe body 
24 consists of a main tube 24a and an extension tube 48. Extension tube 48 
is secured to main tube 24a by a nut 38. The two piece probe body 24 
allows longitudinal adjustment between the accelerometer 56 and the 
actuator 44. 
Actuator 44 is secured to the distal end of main tube 24a by a "G" clip 36 
which is preferably made of corrosion resistant spring steel. The "G" clip 
exerts an expansion force on the inner diameter of main tube 24a and 
allows the location of actuator 44 to be adjusted along the longitudinal 
axis of main tube 24a to calibrate dental probe 20. Alternatively, 
actuator 44 can be secured to main tube 24a by other suitable means such 
as by threading the interior of main tube 24a and securing actuator 44 
with a threaded adapter. 
Firing button 34 is electrically connected to electrical connector 22 by 
lines 34a and 34b. Actuator 44 is electrically connected to electrical 
connector 22 by lines 44a and 44b. 
The head of hammer 42 is preferably made from a molded highly damped epoxy 
with an inner densaloy weight 42a for an ideal impact force. Hammer 42 has 
a ferromagnetic stem 46 which slides within bore 45a of electromagnetic 
coil 45. This ensures linear motion of hammer 42 along the longitudinal 
axis of probe body 24 when fired. Spring 40 is positioned about stem 46 
and is positioned against both hammer 42 and electromagnetic coil 45. 
The accelerometer 56 is small with a low mass such that accelerometer 56 
does not substantially distort or alter the vibration of dental implant 
28. Accelerometer 56 is electrically connected to electrical connector 22 
by lines 56a and 56b. Two "O"-rings 54 are mounted around accelerometer 56 
to keep the motion of accelerometer 56 along the longitudinal axis of 
probe body 24. A low friction sleeve 50 preferably made of 
polytetrafluoroethylene (PTFE) is positioned on the interior surface of 
extension tube 48 surrounding accelerometer 56. This ensures smooth 
undisturbed motion of accelerometer 56 such that the acceleration of 
accelerometer 56 is not significantly altered if the "O"-rings 54 contact 
low friction sleeve 50. 
Diaphragm or membrane 58 is stretched over the distal end of extension tube 
48 and is secured by a force ring 52. Diaphragm 58 is preferably made from 
surgical rubber 0.007 inches thick but alternately can be of other 
suitable thicknesses and elastic materials. Threaded neck 57 extends 
through diaphragm 58 and is threaded into adapter 60 which sandwiches 
diaphragm 58 between the adapter 60 and the accelerometer 56, thereby 
securing accelerometer 56 to diaphragm 58. Diaphragm 58 isolates motion of 
the probe tip 26, adapter 60 and accelerometer 56 from the motions of the 
probe body 24 so that only the motions of dental implant 28 are measured 
by accelerometer 56. 
Probe tip 26 has a female threaded portion 26b which mounts onto the male 
threaded portion 60a of adapter 60. Probe tip 26 is hollow having a cavity 
26a to reduce the mass of probe tip 26. The end 27 of probe tip 26 has a 
non-slip flat surface for positioning against dental implant 28. The 
diameter of end 27 is typically small which can be, for example, 0.1 
inches in diameter. A long tip of about 2.5 inches is preferable for 
measuring deep within a patient's mouth while a shorter pointed tip is 
preferable for testing bone structure through layers of skin. Probe tip 26 
is typically disposable for health considerations. Adapter 60 and probe 
tip 26 have wrench flats which allow probe tip to be tightened on to 
adapter 60 with a wrench. It is preferable that probe tip 26 have a 
transfer function of unity or 1 over the bandwidth analyzed so that the 
collected data is not distorted. 
In the preferred embodiment, dental probe 20 is about 6 inches long and 0.5 
inches wide which makes it suitable for hand held use. The probe body 24, 
probe tip 26, adapter 60 and nut 38 are preferably made of titanium for 
reduced weight. However, alternatively, other suitable materials such as 
stainless steel, aluminum or plastic can be used. 
In other applications, the present invention can be used for analyzing 
other medical implants such as hip implants, knee implants, elbow 
implants, shoulder implants, wrist implants or any other medical 
orthopedic implant. Structures covered by skin, cartilage or hair can be 
analyzed by employing a pointed probe tip which penetrates the covering 
material and becomes in intimate contact with the structure below. 
Additionally, the present invention can be used to analyze organic 
structures of a patient such as teeth or bones, for example, vertebrae, 
ribs or limb bones. 
When analyzing a medical implant, the medical implant can be analyzed 
during installation before the surgical wound is closed. FIG. 12 depicts 
an example of a hip implant 126 being analyzed prior to closure of the 
surgical wound. The femur bone 122 and the newly installed hip implant 126 
are exposed by the open surgical wound 124 in patient 120. A probe 20a 
which is similar probe 20, has a probe tip 26 positioned against hip 
implant 126. The acceleration time history of the hip implant 126 is 
measured by probe 20a and converted into a frequency spectrum in the same 
manner as described above with respect to dental implant 28. The frequency 
spectrum of hip implant 126 is compared to a clinical data base containing 
previously stored frequency spectrums for hip implants. Characteristics of 
the frequency spectrum for hip implant 126 are compared with 
characteristics of the stored frequency spectrums. The clinical data base 
includes acceptable ranges for certain characteristics of frequency 
spectrums which correlate to acceptable clinical standards for a hip 
implant. If the frequency spectrum of hip implant 126 correlates to lower 
than acceptable clinical standards, hip implant 126 is likely to be poorly 
attached due to inadequate cementation, cartilage or soft tissue inclusion 
in the receptor site, or a crack in the receptor site, etc. This condition 
alerts the surgeon of the need for correcting the problem before the wound 
124 is closed which eliminates the need for a second procedure when the 
hip implant fails. 
Referring to FIG. 13, hip implant 126 can be analyzed after the wound 124 
is closed through arthroscopic techniques. In such a procedure, probe 20a 
is incorporated into the tip of an endoscope 128. The endoscope 128 is 
inserted into the patient 120 through an incision 130 and probe 20a is 
positioned against hip implant 126, thereby allowing probe 20a to analyze 
hip implant 126. This allows measurements of hip implant 126 to be 
conducted over a long period of time. The frequency spectrums of hip 
implant 126 taken over a period of time can be compared against each other 
to determine whether hip implant 126 is becoming more stable or 
deteriorating. By detecting small changes before they become major 
problems, interceptive therapy may be instituted in an attempt to avoid 
prosthesis replacement. 
The present invention apparatus can also be used in the industry for 
determining the structural characteristics of mechanical structures such 
as airplane wings, machinery, or structural buildings using vibration 
signature analysis for predictive maintenance. In such a case, the probe 
would be employed to impact and measure the acceleration time history of 
the structure at a desired location on the structure. The frequency 
spectrum would then be generated from the acceleration time history. In 
many engineering applications, only the frequency spectrum is needed. 
However, alternatively, previously measured acceleration time histories 
and their corresponding frequency spectrums can be stored in a database 
for comparison with measured acceleration time histories and corresponding 
frequency spectrums. 
FIG. 14 depicts a system suitable for industrial maintenance or other 
applications where a portable unit is desirable. The system includes a 
probe 20 which is coupled to a portable computer 13. Portable computer 13 
is small enough to be hand-held or worn on a belt and includes a screen 
13a for viewing acceleration time histories and frequency spectrums. A 
keypad 13b allows the user to input information. The electronics for 
conditioning the acceleration time history are included within portable 
computer 13. 
EQUIVALENTS 
Those skilled in the art will recognize, or be able to ascertain using no 
more than routine experimentation, many equivalents to specific 
embodiments of the invention described specifically herein. Such 
equivalents are intended to be encompassed in the scope of the following 
claims. For example, although actuator 44 is described to be 
electromechanically operated, alternatively, actuator 44 can be 
pneumatically or mechanically operated. Additionally, the accelerometer 
can be substituted with a velocity or a position sensor for measuring the 
velocity or position of probe tip 26. Furthermore, the electronics of 
electrical box 16 can be incorporated into computer 12. Also, the open 
wound and arthroscopic analyzing techniques depicted in FIGS. 12 and 13 
can be used to analyze any type of medical implant as well as to analyze a 
patient's bones.